Without any nucleation sites, liquids can be cooled without setting solid.
|
|
Bono's team now presents evidence that nucleation began after 565 million years ago.
|
|
Those particles then serve as nucleation points, allowing moisture to condense and form droplets.
|
|
These particles serve as nucleation points to form clouds and eventually lead to more rainfall.
|
|
When these ice crystals encounter still-liquid supercooled droplets, they act as nucleation points triggering further crystallization.
|
|
"People have tried to understand how [the bacteria] control ice nucleation and they've done theoretical and computational studies," says Weidner.
|
|
This thinning could be theoretically accomplished by seeding cirrus clouds with particles that disrupt ice crystal formation (nucleation), leading to reduced cirrus cloud cover.
|
|
Seeding works best in clouds which have a pre-existing mixture of water droplets and ice, as this type of nucleation requires ice-crystals to form.
|
|
He thought that once the initial core norms were established, eventually everyone would come together as a society all at once—a social network nucleation event.
|
|
What the team does is entirely encapsulate the liquid metal in a smooth shell that contains no imperfections known as nucleation sites, which are required for solidification to occur.
|
|
The fact that the field got stronger after this time instead of collapsing suggests that nucleation began and gave Earth's dynamo the juice it needed to beef up the field.
|
|
Now, theorists at Lawrence Livermore National Laboratories have demonstrated how water transitions to ice VII, a process known as "nucleation," which helps explain how this exotic phase of ice forms on alien ocean planets.
|
|
The timeline proposed by Bono and his colleagues suggests that nucleation occurred just before the Cambrian explosion, a period of enormous evolutionary progress 541 million years ago that resulted in the rapid emergence of animal life.
|
|
Without the impurities found in tap water, there is nothing to start the nucleation process that causes water to freeze, delivering a supercooled liquid that, once jostled or disturbed, will instantly turn to a slushy ice.
|
|
Scientists led by Richard Bono, a palaeomagnetism researcher at the University of Rochester, used ancient crystals from a site near the city of Sept-Îles, Québec, to reconstruct this timeline of Earth's inner core "nucleation," or solidification.
|
|
"Recent research from the CLOUD experiment as a whole stands in contrast to Svensmark's results, and found that, given the present day atmosphere and all of its particles, "cosmic ray intensity cannot meaningfully affect climate via nucleation.
|
|
The reason that some experiments showed ice VII nucleation starting at the boundary between the container and water, while others showed it happening throughout the sample has to do with the pressure levels inflicted on the water, as well as the temperature of the sample.
|
|
The machines use a fan to accelerate a finely-tuned mix of water and air at high speeds, evaporating some of the water, which cools the remainder, causing a few tiny rain drops to freeze into ice particles, giving nucleation sites for the rest of the water to turn to snow.
|
|
The incentives are aligned for China to aggressively pursue thorium molten-salt reactors, but experts say this isn't the case in the US. "The nuclear industry is conservative, and there's a lot of momentum behind uranium," says Leslie Dewan, a nuclear engineer and a founding principal at Nucleation Capital, which invests in advanced nuclear energy companies.
|
|
SATURN&aposS ICY MOON ENCELADUS, A POSSIBLE HOME FOR LIFE "The data constrain the macromolecular structure of organics detected in the ice grains and suggest the presence of a thin organic-rich film on top of the oceanic water table, where organic nucleation cores generated by the bursting of bubbles allow the probing of Enceladus' organic inventory in enhanced concentrations," the study reads.
|
|
Schulson went on, "Even though it seems that with this region"—he pointed to the nucleus—"the energy should be lower than in the randomly organized water molecules around it," that is not the case until the array reaches a certain size, at which point, because "the surface-energy barrier to nucleation is no longer important," the liquid becomes solid.
|
|
"With the caveat that there are still significant uncertainties associated with ice nucleation in cirrus clouds and its representation in climate models, cirrus seeding appears to represent a powerful [climate engineering model] with reduced side effects," concluded a team led by Trude Storelvmo, a climate scientist at Yale University, in a 2013 Philosophical Transactions of the Royal Society study that modeled the impact of cirrus cloud seeding.
|
|
Heterogeneous nucleation occurs at nucleation sites on surfaces in the system. Homogeneous nucleation occurs away from a surface.
|
|
Nucleation is the formation and growth of a new phase with or without the presence of external surface. The presence of this surface results in heterogeneous nucleation whereas in its absence homogeneous nucleation occurs. Heterogeneous nucleation occurs in cases where there are pre-existing nuclei present, such as tiny dust particles suspended in a liquid or gas or reacting with a glass surface containing . For the process of Hoffman nucleation and its progression to Lauritzen–Hoffman growth theory, homogeneous nucleation is the main focus.
|
|
This is because the nucleation barrier for heterogeneous nucleation is much lower than for homogeneous nucleation. To see this, note that the nucleation barrier is determined by the positive term in the free energy \Delta G, which is proportional to the total exposed surface area of a nucleus. For homogeneous nucleation the surface area is simply that of a sphere. For heterogeneous nucleation, however, the surface area is smaller since part of the nucleus boundary is accommodated by the surface or impurity onto which it is nucleating.
|
|
However, the CNT fails in describing experimental results of vapour to liquid nucleation even for model substances like argon by several orders of magnitude.A. Fladerer, R. Strey: „Homogeneous nucleation and droplet growth in supersaturated argon vapor: The cryogenic nucleation pulse chamber.“ in: The Journal of Chemical Physics 124(16), 164710 (2006). (Online) For nucleation of a new thermodynamic phase, such as the formation of ice in water below 0°C, if the system is not evolving with time and nucleation occurs in one step, then the probability that nucleation has not occurred should undergo exponential decay. This is seen for example in the nucleation of ice in supercooled small water droplets.
|
|
Three droplets on a surface, illustrating decreasing contact angles. The contact angle the droplet surface makes with the solid horizontal surface decreases from left to right. A diagram featuring all of the factors that affect heterogeneous nucleation Unlike homogeneous nucleation, heterogeneous nucleation occurs on a surface or impurity. It is much more common than homogeneous nucleation.
|
|
In contrast, new phases at continuous phase transitions start to form immediately. Nucleation is often found to be very sensitive to impurities in the system. These impurities may be too small to be seen by the naked eye, but still can control the rate of nucleation. Because of this, it is often important to distinguish between heterogeneous nucleation and homogeneous nucleation.
|
|
Nucleation in Microcellular plastic is an important stage which decides the final cell size, cell density and cell morphology of the foam. In the recent past, numerous researchers have put their efforts in studying the cell nucleation phenomenon in microcellular polymers. Studies were performed with the ultrasound induced nucleation during microcellular foaming of Acrylonitrile butadiene styrene polymers. M.C.Guo studied nucleation under the shear action.
|
|
The decay rate of the exponential gives the nucleation rate. Classical nucleation theory is a widely used approximate theory for estimating these rates, and how they vary with variables such as temperature. It correctly predicts that the time you have to wait for nucleation decreases extremely rapidly when supersaturated. It is not just new phases such as liquids and crystals that form via nucleation followed by growth.
|
|
In these small volumes, the time until the first crystal appears is usually defined to be the nucleation time. In larger volumes many nucleation events will occur. A simple model for crystallisation in that case, that combines nucleation and growth is the KJMA or Avrami model.
|
|
Crystal formation requires two steps: nucleation and growth. Nucleation is the initiation step for crystallization. At the nucleation phase, protein molecules in solution come together as aggregates to form a stable solid nucleus. As the nucleus forms, the crystal grows bigger and bigger by molecules attaching to this stable nucleus.
|
|
An interesting condition occurs when nucleation occurs on specific sites (such as grain boundaries or impurities) that rapidly saturate soon after the transformation begins. Initially, nucleation may be random, and growth unhindered, leading to high values for n (3 or 4). Once the nucleation sites are consumed, the formation of new particles will cease. Furthermore, if the distribution of nucleation sites is non-random, then the growth may be restricted to 1 or 2 dimensions.
|
|
It is very high for bubbles that form in the liquid itself (homogeneous nucleation), and much lower if bubble growth occurs within tiny bubbles trapped in some other surface (heterogeneous nucleation). Bubble nucleation and growth in carbonated beverages almost always occurs by heterogeneous nucleation: diffusion of carbon dioxide into pre-existing bubbles within the beverage. When dissolved gas diffuses into bubbles that already exist in a liquid, it is called Type IV bubble nucleation. When the pressure is released from a soda bottle upon opening it, dissolved carbon dioxide can escape into any tiny bubble located within the beverage.
|
|
The former might be considered analogous to a homogeneous nucleation event—whereas the latter would clearly be considered a heterogeneous nucleation event, being catalyzed by the surface of the glass tube.
|
|
It is important to note that σms is dependent on parameters such as temperature and the number of nucleation sites for phase nucleation. Interfaces and inclusions will provide general sites for the transformation to begin, and if these are great in number, it will increase the driving force for nucleation. A smaller σms will be needed than for homogeneous nucleation. Likewise, increasing temperature will reduce the driving force for the phase transformation, so a larger σms will be necessary.
|
|
During this time it is possible to have a large density fluctuation in a very small volume. This fluctuation of density results in the nucleation of a bubble. The bubble nucleation process occurs homogeneously everywhere in the substance. The rate of bubble nucleation and vapor sphere growth rate increases exponentially closer to the critical temperature.
|
|
Nucleation at a surface (black) in the 2D Ising model. Up spins (particles in lattice-gas terminology) shown in red, down spins shown in white. Nucleation is usually a stochastic (random) process, so even in two identical systems nucleation will occur at different times. A common mechanism is illustrated in the animation to the right.
|
|
At these conditions, nucleation of ice is either slow or does not occur at all. However, at lower temperatures ice crystals appear after little or no delay. At these conditions ice nucleation is fast. Nucleation is commonly how first-order phase transitions start, and then it is the start of the process of forming a new thermodynamic phase.
|
|
The remaining droplets freeze in a stochastic way, at rates 0.02/s if they have one impurity particle, 0.04/s if they have two, and so on. These data are just one example, but they illustrate common features of the nucleation of crystals in that there is clear evidence for heterogeneous nucleation, and that nucleation is clearly stochastic.
|
|
Chemical oxidative polymerization is a traditional and commonly used method for the polymerization of aniline in large quantities. When aniline is mixed with an oxidant in an acidic solution, polymerization will occur. The most important parameter to be controlled in this method for the synthesis of polyaniline nanofibers is the domination of homogeneous nucleation over heterogeneous nucleation. Homogeneous nucleation describes when the nuclei are formed spontaneously in solution while heterogeneous nucleation describes when the nuclei are grown on other species.
|
|
The self-assembly process that forms objects like the amyloid aggregates associated with Alzheimer's disease also starts with nucleation. Energy consuming self-organising systems such as the microtubules in cells also show nucleation and growth.
|
|
Nucleation is the initiation of a phase change in a small region, such as the formation of a solid crystal from a liquid solution. It is a consequence of rapid local fluctuations on a molecular scale in a homogeneous phase that is in a state of metastable equilibrium. Total nucleation is the sum effect of two categories of nucleation – primary and secondary.
|
|
It is typically difficult to experimentally study the nucleation of crystals. The nucleus is microscopic, and thus too small to be directly observed. In large liquid volumes there are typically multiple nucleation events, and it is difficult to disentangle the effects of nucleation from those of growth of the nucleated phase. These problems can be overcome by working with small droplets.
|
|
In addition to the nucleation and growth of crystals e.g. in non-crystalline glasses, the nucleation and growth of impurity precipitates in crystals at, and between, grain boundaries is quite important industrially. For example in metals solid-state nucleation and precipitate growth plays an important role e.g. in modifying mechanical properties like ductility, while in semiconductors it plays an important role e.g.
|
|
Though the γ-TuRC is the primary protein cells turn to when faced with the task of nucleating microtubules, it is not the only protein postulated to act as a nucleation factor. Several other MAPs assist the γ-TuRC with the nucleation process, while others nucleate microtubules independently of γ-TuRC. In the branching nucleation described above, the addition of TPX2 to the egg extracts led to a dramatic increase in nucleation events—while in other studies, the protein XMAP215, in vitro, nucleated microtubule asters with its depletion in vivo reducing nucleation potential of centrosomes. The microtubule-binding protein doublecortin, in vitro, nucleates microtubules—acting by binding to the side rather than the end of growing microtubules.
|
|
Actin nucleation is an initial step in the formation of an actin filament. The nucleation core activity of Arp2/3 is activated by members of the Wiskott-Aldrich syndrome family protein (WASP, N-WASP, WAVE, and WASH proteins). The V domain of a WASP protein interacts with actin monomers while the CA region associates with the Arp2/3 complex to create a nucleation core. However, de novo nucleation followed by polymerization is not sufficient to form integrated actin networks, since these newly synthesized polymers would not be associated with pre-existing filaments.
|
|
In the early stages of this polymerization, only nanofibers are formed since there are no heteronuclei available for heterogeneous nucleation. However, if the reaction is left uncontrolled, heterogeneous nucleation will begin to dominate as the polyaniline will preferentially grow on existing particles, leading to irreversible agglomeration. The reaction can be made to favor homogeneous nucleation throughout by increasing reaction speed, temperature of the reaction, and allowing the reaction to proceed without stirring. Route I shows the heterogeneous nucleation route, where the nanofibers are formed, followed by secondary growth on the wires which cause agglomeration.
|
|
Bubble nucleation happens when the a volatile becomes saturated. Actually the bubbles are composed of molecules that tend to aggregate spontaneously in a process called homogeneous nucleation. The surface tension acts on the bubbles shrinking the surface and forces them back to the liquid. The nucleation process is greater when the space to fit is irregular and the volatile molecules can ease the effect of surface tension.
|
|
Thus, adding Mentos candies to a carbonated beverage introduces millions of nucleation sites into the drink, which allows for degassing that is rapid enough to support a jet of foam out of a bottle. Pre-existing bubbles provide a way for the reaction to occur without requiring bubbles to form within the liquid itself (homogeneous nucleation). Because Type IV nucleation sites (such as found on Mentos) allow the reaction to proceed with a substantially lower activation energy, Mentos candies can appropriately be considered a catalyst of the process. As another example, dropping grains of salt or sand into the solution provides Type IV nucleation sites, lowers the activation energy compared to that of homogeneous nucleation, and increases the rate of carbon dioxide precipitation.
|
|
Silver crystal growing on a ceramic substrate. Nucleation can be either homogeneous, without the influence of foreign particles, or heterogeneous, with the influence of foreign particles. Generally, heterogeneous nucleation takes place more quickly since the foreign particles act as a scaffold for the crystal to grow on, thus eliminating the necessity of creating a new surface and the incipient surface energy requirements. Heterogeneous nucleation can take place by several methods.
|
|
4.15, 4.19 The size of spherulites varies in a wide range, from micrometers up to 1 centimeter and is controlled by the nucleation. Strong supercooling or intentional addition of crystallization seeds results in relatively large number of nucleation sites; then spherulites are numerous and small and interact with each other upon growth. In case of fewer nucleation sites and slow cooling, a few larger spherulites are created.Ehrenstein and Theriault pp.
|
|
Experiments show that "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than .
|
|
The time until the appearance of the first crystal is also called primary nucleation time, to distinguish it from secondary nucleation times. Primary here refers to the first nucleus to form, while secondary nuclei are crystal nuclei produced from a preexisting crystal. Primary nucleation describes the transition to a new phase that does not rely on the new phase already being present, either because it is the very first nucleus of that phase to form, or because the nucleus forms far from any pre- existing piece of the new phase. Particularly in the study of crystallisation, secondary nucleation can be important.
|
|
Thin films, for example, may be effectively two-dimensional, in which case if nucleation is again uniform the exponent n = 3. In general, for uniform nucleation and growth, n = D + 1, wgere D is the dimensionality of space in which crystallization occurs.
|
|
An actin nucleation core is a protein trimer with three actin monomers. It is called a nucleation core because it leads to the energetically favorable elongation reaction once a tetramer is formed from a trimer. Actin protein dimers and trimers are energetically unfavorable.
|
|
The magnetization can also change by addition or subtraction of domains (called nucleation and denucleation).
|
|
The creation of a dislocation by homogeneous nucleation is a result of the rupture of the atomic bonds along a line in the lattice. A plane in the lattice is sheared, resulting in 2 oppositely faced half planes or dislocations. These dislocations move away from each other through the lattice. Since homogeneous nucleation forms dislocations from perfect crystals and requires the simultaneous breaking of many bonds, the energy required for homogeneous nucleation is high.
|
|
The nucleation can occur thanks to the presence of solid crystals, which are stored in the magma chamber. They are perfect potential nucleation sites for bubbles. If there is no nucleation in the magma the bubbles formation might appear really late and magma becomes significantly supersaturated. The balance between supersaturation pressure and bubble's radii expressed by this equation: ∆P=2σ/r, where ∆P is 100 MPa and σ is the surface tension.
|
|
In scientific experiments this removes contamination and nucleation issues associated with physical contact with a container.
|
|
Retrieved on 2007-12-16. The specific physical process by which this occurs is called nucleation.
|
|
ABPs regulate the organization and dynamics of the actin cytoskeleton. As stated previously, actin filaments are continuously synthesized from the apical membrane. This indicates the presence of membrane-anchored actin nucleation factors. Through experimentation, it has been theorized that formins are representative of such actin nucleation factors.
|
|
In reinforced polymers, crack initiation usually occurs at the interface of polymer fiber and the matrix. Fatigue performances in polymers caused by cyclical loading usually go through two stages: crack initiation/nucleation and crack growth. Hence, a lot of researcher design experiments to study the fatigue behaviors of polymers according to these two phases, especially for rubber fatigue. Crack Nucleation Approach The crack nucleation approach considers that polymers will eventually crack under a history of stress and strains.
|
|
There are two stages in the crystallization process: nucleation and growth. In the first nucleation stage, a small nucleus containing the newly forming crystal is created. Nucleation occurs relatively slowly as the initial crystal components must impinge on each other in the correct orientation and placement for them to adhere and form the crystal. After successful formation of a stable nucleus, a growth stage ensues in which free particles (atoms or molecules) adsorb onto the nucleus and propagate its crystalline structure outwards from the nucleating site.
|
|
This different mechanism is called nucleation and growth, and there, in contrast to spinodal decomposition, there is a nucleation barrier which typically takes a time to overcome before the new phase appears. As there is no barrier (by definition) to spinodal decomposition, at least some fluctuations start growing instantly. These fluctuations start growing throughout the volume, whereas nucleation typically involves the formation of a small number of nuclei of a new phase, at random points in the volume. Spinodal decomposition occurs for phases that are thermodynamically unstable.
|
|
In precipitation models, nucleation is generally a prelude to models of the crystal growth process. Sometimes precipitation is rate-limited by the nucleation process. An example would be when someone takes a cup of superheated water from a microwave and, when jiggling it with a spoon or against the wall of the cup, heterogeneous nucleation occurs and most of water particles convert into steam. If the change in phase forms a crystalline solid in a liquid matrix, the atoms might then form a dendrite.
|
|
The red curve is a fit of a function of the Gompertz form to these data. To the right is shown an example set of nucleation data. It is for the nucleation at constant temperature and hence supersaturation of the crystal phase in small droplets of supercooled liquid tin; this is the work of Pound and La Mer. Nucleation occurs in different droplets at different times, hence the fraction is not a simple step function that drops sharply from one to zero at one particular time.
|
|
The fit values are that the nucleation rate due to a single impurity particle is 0.02/s, and the average number of impurity particles per droplet is 1.2. Note that about 30% of the tin droplets never freeze; the data plateau at a fraction of about 0.3. Within the model this is assumed to be because, by chance, these droplets do not have even one impurity particle and so there is no heterogeneous nucleation. Homogeneous nucleation is assumed to be negligible on the timescale of this experiment.
|
|
713–721, 1978. At temperatures above Msσ, yielding and plastic deformation occur before transformation, and nucleation of martensite occurs at the intersection of shear bands created from the strain of the plastic deformation.OLSON, G. B., AND COHEN, M., “Kinetics of strain-induced martensitic nucleation,” Metallurgical and Materials Transactions A, vol. 6, no.
|
|
Casting is a solidification process, which means the solidification phenomenon controls most of the properties of the casting. Moreover, most of the casting defects occur during solidification, such as gas porosity and solidification shrinkage. Solidification occurs in two steps: nucleation and crystal growth. In the nucleation stage solid particles form within the liquid.
|
|
While both intramolecular and intermolecular aurophilic interactions have been observed, only intramolecular aggregation has been observed at such nucleation sites.
|
|
Having other NPFs bind to the Arp2/3 complex at the same time as cortactin may enhance nucleation site stability.
|
|
The nucleation stage of seed-mediated growth consists of the reduction of metal ions in a precursor to metal atoms. In order to control the size distribution of the seeds, the period of nucleation should be made short for monodispersity. The LaMer model illustrates this concept. Seeds typically consist small nanoparticles, stabilized by a ligand.
|
|
In physical chemistry terms, the AFPs adsorbed onto the exposed ice crystal force the growth of the ice crystal in a convex fashion as the temperature drops, which elevates the ice vapour pressure at the nucleation sites. Ice vapour pressure continues to increase until it reaches equilibrium with the surrounding solution (water), at which point the growth of the ice crystal stops. The aforementioned effect of AFPs on ice crystal nucleation is lost at the thermal hysteresis point. At a certain low temperature, the maximum convexity of the ice nucleation site is reached.
|
|
Georg Menges, Edmund Haberstroh, Walter Michaeli, Ernst Schmachtenberg: Plastics Materials Science Hanser Verlag, 2002, Apart from the thermal mechanism, nucleation is strongly affected by impurities, dyes, plasticizers, fillers and other additives in the polymer. This is also referred to as heterogeneous nucleation. This effect is poorly understood and irregular, so that the same additive can promote nucleation in one polymer, but not in another. Many of the good nucleating agents are metal salts of organic acids, which themselves are crystalline at the solidification temperature of the polymer solidification.
|
|
Nucleation factors are enhancers of actin polymerization and contribute to the formation of the trimeric polymerization nucleus. This is a structure required to initiate the process of actin filament polymerization in a stable and efficient way. Nucleation factors such as WASP (Wiskott-Aldrich syndrome protein) help to form the seven-protein Arp2/3 nucleation complex, which resembles two actin monomers and therefore allows for easier formation of the polymerization nucleus. Arp2/3 is able to cap the trailing ("minus") end of the actin filament, allowing for faster polymerization at the "plus" end.
|
|
In addition, work from the Kaverina group at Vanderbilt, as well as others, suggests that the Golgi apparatus can serve as an important platform for the nucleation of microtubules. Because nucleation from the centrosome is inherently symmetrical, Golgi-associated microtubule nucleation may allow the cell to establish asymmetry in the microtubule network. In recent studies, the Vale group at UCSF identified the protein complex augmin as a critical factor for centrosome-dependent, spindle-based microtubule generation. It that has been shown to interact with γ-TuRC and increase microtubule density around the mitotic spindle origin.
|
|
Most of the microtubules that form the mitotic spindle originate from the centrosome. Originally it was thought that all of these microtubules originated from the centrosome via a method called search and capture, described in more detail in a section above, however new research has shown that there are addition means of microtubule nucleation during mitosis. One of the most important of these additional means of microtubule nucleation is the RAN-GTP pathway. RAN-GTP associates with chromatin during mitosis to create a gradient that allows for local nucleation of microtubules near the chromosomes.
|
|
Hoffman nucleation theory is a theory developed by John D. Hoffman and coworkers in the 1970s and 80s that attempts to describe the crystallization of a polymer in terms of the kinetics and thermodynamics of polymer surface nucleation. The theory introduces a model where a surface of completely crystalline polymer is created and introduces surface energy parameters to describe the process. Hoffman nucleation theory is more of a starting point for polymer crystallization theory and is better known for its fundamental roles in the Hoffman–Weeks lamellar thickening and Lauritzen–Hoffman growth theory.
|
|
This shows nucleation of a new phase (shown in red) in an existing phase (white). In the existing phase microscopic fluctuations of the red phase appear and decay continuously, until an unusually large fluctuation of the new red phase is so large it is more favourable for it to grow than to shrink back to nothing. This nucleus of the red phase then grows and converts the system to this phase. The standard theory that describes this behaviour for the nucleation of a new thermodynamic phase is called classical nucleation theory.
|
|
The unbound SAFs then promote microtubule nucleation and stabilization around mitotic chromatin, and spindle bipolarity is organized by microtubule motor proteins.
|
|
In such materials, the coercivity is controlled by nucleation. To obtain much coercivity, impurity control is critical in the fabrication process.
|
|
In GeSbTe, the nucleation process of crystallization is long with many small crystalline nuclei being formed before a short growth process where the numerous small crystals are joined together. In AgInSbTe, there are only a few nuclei formed in the nucleation stage and these nuclei grow bigger in the longer growth stage such that they eventually form one crystal.
|
|
Kinks are steps in a dislocation line parallel to glide planes. Unlike jogs, they facilitate glide by acting as a nucleation point for dislocation movement. The lateral spreading of a kink from the nucleation point allows for forward propagation of the dislocation while only moving a few atoms at a time, reducing the overall energy barrier to slip.
|
|
Centrosome reduction is the gradual loss of centrosomal components that takes place after mitosis and during differentiation In cycling cells, after mitosis the centrosome has lost most of its pericentriolar material (PCM) and its microtubule nucleation capacity. In sperm, centriole structure is also changed in addition to the loss of PCM and its microtubule nucleation capacity.
|
|
Figure 1. Snapshot images taken from a video showing the nucleation and growth of a TEM in an endothelial cell intoxicated with C3 exoenzyme from Clostridium botulinum for 24 hours, Bar = 10 μm. For the dynamics see Video. Cellular dewetting refers to the process of nucleation and enlargement of transendothelial cell macroaperture (TEM) tunnels in endothelial cells (Figure 1).
|
|
Here, low nucleation rates due to superfluidity prevent nucleation until the liquid is well below the mineral growth curve. Growth then occurs at extreme rates, favoring slender, long crystals. Additionally, at crystal vertices and terminations, spikes and skeletal shapes may form because growth is favoured at crystal edges. Spinifex or dendritic texture is an example of this result.
|
|
Homogeneous nucleation occurs where no such contaminants are present and is less commonly seen. Homogeneous nucleation begins with small clusters of molecules forming from one phase to the next. As the clusters grow, they aggregate through the condensation of other molecules. The size continues to increase and ultimately form macroscopic droplets (or bubbles depending on the system).
|
|
Gases preferentially condense onto surfaces of pre- existing aerosol particles, known as heterogeneous nucleation. This process causes the diameter at the mode of particle-size distribution to increase with constant number concentration.Hinds, 1999, p.288 With sufficiently high supersaturation and no suitable surfaces, particles may condense in the absence of a pre-existing surface, known as homogeneous nucleation.
|
|
Result from the nucleation of narrow shear bands, which propagate discontinuously or do not propagate due to the adjacent nucleation sites, and thus oscillate about the general level of the flow curve. It occurs at higher temperature or lower strain rates than type A. It may also be developed from type A when it comes to higher strain.
|
|
The method of self-assembly tries to reproduce not only the properties, but also the processing of bioceramics. In this process, raw materials readily available in nature are used to achieve stringent control of nucleation and growth. This nucleation occurs on a synthetic surface with some success. The technique occurs at low temperature and in an aqueous environment.
|
|
Large the Ge(II) reduction rate may lead to the increase in particle nucleation rate, resulting in the reduction of particle diameter.
|
|
The nucleation of calcium carbonate is dependent on four major factors: 1. Calcium concentration, 2. DIC concentration, 3. pH level, and 4.
|
|
More specifically, AtFH3 uses the actin/profilin complex in order to interact with the end of actin filaments, thereby initiating actin filament nucleation.
|
|
The condition that the number of droplets should be much larger than the number of ice crystals depends on the fraction of cloud condensation nuclei that would later (higher in the cloud) act as ice nuclei. Alternatively, an adiabatic updraft has to be sufficiently fast so that high supersaturation causes spontaneous nucleation of many more droplets than cloud condensation nuclei are present. In either case, this should happen not far below the freezing point as this would cause direct nucleation of ice. The growth of the droplets would prevent the temperature from soon reaching the point of fast nucleation of ice crystals.
|
|
When ammi visnaga extract is taken daily, as a tea or as a pill, calcium oxalate kidney stone formation is inhibited, making it a good treatment for hyperoxaluria (a condition in which there is excessive oxalate excretion in the urine, causing kidney stones). Khellin was thought to slow or prevent calcium oxalate nucleation, preventing stones from forming. However, studies have shown that khellin is not the active ingredient in Ammi Visnaga extract. Upon studying calcium oxalate nucleation, ammi visnaga extract as a whole was shown to prolong nucleation time as well as change stone conformation, while khellin alone had no effect.
|
|
However, these two motifs are not the only essential ones in microtubule branching nucleation; the FKARP motifs of α5 and α6 are also essential for stimulating this process. Furthermore, the α-helical region stretch of domain α7 and the C-terminal residues that interact with Eg5 are critical for microtubule branching nucleation as well. While α5-7 domains are important in this process, none of them have intrinsic microtubule nucleation activity. In terms of binding to and bundling microtubules, at least any of the three domains α3-7 of TPX2 are necessary for significant binding and bundling in vitro.
|
|
Classical nucleation theory (CNT) is the most common theoretical model used to quantitatively study the kinetics of nucleation.H. R. Pruppacher and J. D. Klett, Microphysics of Clouds and Precipitation, Kluwer (1997)P.G. Debenedetti, Metastable Liquids: Concepts and Principles, Princeton University Press (1997) Nucleation is the first step in the spontaneous formation of a new thermodynamic phase or a new structure, starting from a state of metastability. The kinetics of formation of the new phase is frequently dominated by nucleation, such that the time to nucleate determines how long it will take for the new phase to appear.
|
|
Undercooling, or supercooling, is the cooling of a liquid below its equilibrium freezing temperature while it remains a liquid. This can occur wherever crystal nucleation is suppressed. In levitated samples, heterogeneous nucleation is suppressed due to lack of contact with a solid surface. Levitation techniques typically allow samples to be cooled several hundred degrees Celsius below their equilibrium freezing temperatures.
|
|
Geoffrey W. Hoffmann has argued that a complex nucleation event as the origin of life involving both polypeptides and nucleic acid is compatible with the time and space available in the primitive oceans of Earth Hoffmann suggests that volcanic ash may provide the many random shapes needed in the postulated complex nucleation event. This aspect of the theory can be tested experimentally.
|
|
The rate of branched formation is also enhanced in the presence of both components compared to Ran alone. The TPX2 region necessary for branching microtubule nucleation resides in its carboxy-terminal half (amino acids 319-716), with TPX2 domains α5-7 as the minimal necessary requirement and domains α3-4 serving as contributors to nucleation efficiency by enabling earlier induction at faster rates.
|
|
As nucleation is stochastic, many droplets are needed so that statistics for the nucleation events can be obtained. The black triangles are the fraction of a large set of small supercooled liquid tin droplets that are still liquid, i.e., where the crystal state has not nucleated, as a function of time. The data are from Pound and La Mer (1952).
|
|
This criticism has been responded to in a review as follows. The most important feature of Kerner’s theory is the explanation of the empirical nucleation nature of traffic breakdown at a road bottleneck by the F → S transition. The empirical nucleation nature of traffic breakdown cannot be explained with earlier traffic flow theories including two-phase traffic flow models studied in.
|
|
This can result in spontaneous boiling (nucleation) which may be violent enough to eject the boiling liquid from the container and cause severe scalding.
|
|
Bubbles form, and coalesce, into globular shapes, because those shapes are at a lower energy state. For the physics and chemistry behind it, see nucleation.
|
|
The unusual properties of AFPs are attributed to their selective affinity for specific crystalline ice forms and the resulting blockade of the ice-nucleation process.
|
|
This Cobl-actin tetramer is forming a nucleus to facilitate further G-actin addition. Cobl-mediated actin nucleation is very efficient. In fact already low nanomolar concentrations of Cobl can generate unbranched filaments with similar characteristics as WASp–Arp2/3-complex-mediated actin nucleation. Like Spire-1, The expression of Cobl is mainly restricted to the brain; much weaker expression was detected in other tissues.
|
|
The two Arp subunits form the first subunits of each branch and the two branches continue to grow by addition of G-actin to each Arp Many actin-related molecules create a free barbed end for polymerization by uncapping or severing pre-existing filaments and using these as actin nucleation cores. However, the Arp2/3 complex stimulates actin polymerization by creating a new nucleation core.
|
|
MVC proceeds in three stages: nucleation, growth, and coalescence of microvoids. The nucleation of microvoids can be caused by particle cracking or interfacial failure between precipitate particles and the matrix. Additionally, microvoids often form at grain boundaries or inclusions within the material. Microvoids grow during plastic flow of the matrix, and microvoids coalesce when adjacent microvoids link together or the material between microvoids experiences necking.
|
|
The crystallization of ice from supercooled water is generally initiated by a process called nucleation. Because of the speed and size of nucleation, which occurs within nanoseconds and nanometers. The surface environment does not play a decisive role in the formation of ice and snow. The density fluctuations inside drops result in that the possible freezing regions cover the middle and the surface regions.
|
|
Thiel's research group pioneered studies of nucleation and growth of metal films on quasicrystal surfaces, demonstrating that local pseudomorphic growth, including starfish- shaped formations, can occur at very specific nucleation sites. Focusing on metallic, aluminum-rich quasicrystals, Thiel and her collaborators extensively explored how quasicrystal atomic-scale surface structures were related to their unusual surface properties, including low friction, low adhesion, and good oxidation resistance.
|
|
A tectonic earthquake begins by an initial rupture at a point on the fault surface, a process known as nucleation. The scale of the nucleation zone is uncertain, with some evidence, such as the rupture dimensions of the smallest earthquakes, suggesting that it is smaller than 100 m while other evidence, such as a slow component revealed by low-frequency spectra of some earthquakes, suggest that it is larger. The possibility that the nucleation involves some sort of preparation process is supported by the observation that about 40% of earthquakes are preceded by foreshocks. However, some large earthquakes, such as the M8.6 1950 India - China earthquake.
|
|
During potential variant experiments common to go through a redox couple in which the major species is transformed from a species that is soluble in the solution to one that is insoluble. This results in nucleation process in which a new species plates out on the working electrode. If a species has been deposited on the electrode during a potential sweep then on the return sweep a stripping wave is usually observed. :[MLn]+(solvated) \+ e− → [MLn]0(solid) nucleation :[MLn]0(solid) → e− \+ [MLn]+(solvated) stripping While the nucleation wave may be pronounced or difficult the detect the stripping wave is usually very distinct.
|
|
Any further cooling will actually result in a "spreading" of the nucleation site away from this convex region, causing rapid, uncontrollable nucleation of the ice crystal. The temperature at which this phenomenon occurs is the thermal hysteresis point. The adsorption-inhibition hypothesis is further supported by the observation that antifreeze activity increases with increasing AFP concentration – the more AFPs adsorb onto the forming ice crystal, the more 'crowded' these proteins become, making ice crystal nucleation less favourable. In the R. inquisitor beetle, AFPs are found in the haemolymph, a fluid that bathes all the cells of the beetle and fills a cavity called the haemocoel.
|
|
A tectonic earthquake begins by an initial rupture at a point on the fault surface, a process known as nucleation. The scale of the nucleation zone is uncertain, with some evidence, such as the rupture dimensions of the smallest earthquakes, suggesting that it is smaller than while other evidence, such as a slow component revealed by low-frequency spectra of some earthquakes, suggest that it is larger. The possibility that the nucleation involves some sort of preparation process is supported by the observation that about 40% of earthquakes are preceded by foreshocks. Once the rupture has initiated, it begins to propagate along the fault surface.
|
|
Classical nucleation theory makes a number of assumptions, for example it treats a microscopic nucleus as if it is a macroscopic droplet with a well-defined surface whose free energy is estimated using an equilibrium property: the interfacial tension σ. For a nucleus that may be only of order ten molecules across it is not always clear that we can treat something so small as a volume plus a surface. Also nucleation is an inherently out of thermodynamic equilibrium phenomenon so it is not always obvious that its rate can be estimated using equilibrium properties. However, modern computers are powerful enough to calculate essentially exact nucleation rates for simple models.
|
|
In vivo, cells get around this kinetic barrier by using various proteins to aid microtubule nucleation. The primary pathway by which microtubule nucleation is assisted requires the action of a third type of tubulin, γ-tubulin, which is distinct from the α and β subunits that compose the microtubules themselves. The γ-tubulin combines with several other associated proteins to form a conical structure known as the γ-tubulin ring complex (γ-TuRC). This complex, with its 13-fold symmetry, acts as a scaffold or template for α/β tubulin dimers during the nucleation process—speeding up the assembly of the ring of 13 protofilaments that make up the growing microtubule.
|
|
However a small crystal in the supercooled water or a nucleation cell on the surface may act as a seed for ice crystals and block the generator.
|
|
The location of micronuclei or where bubbles initially form is not known. Heterogeneous nucleation and tribonucleation are considered the most likely mechanism for bubble formation. Homogeneous nucleation requires much greater pressure differences than experienced in decompression. The spontaneous formation of nanobubbles on hydrophobic surfaces is a possible source of micronuclei, but it is not yet clear if these can grow to symptomatic dimensions as they are very stable.
|
|
The production of microcellular plastics is dependent on temperature and pressure. Dissolving gas under high temperature and pressure creates a driving force that activates nucleation sites when the pressure drops, which increases exponentially with amount of dissolved gas. Homogeneous nucleation is the primary mechanism for producing the bubbles in the cellular matrix. The dissolved gas molecules have a preference to diffuse to activation sites that have nucleated first.
|
|
For simple model systems, modern computers are powerful enough to calculate numerically exact nucleation rates. One such example is the nucleation of the crystal phase in the model of hard spheres. This is a simple model of some colloids consisting of perfectly hard spheres in thermal motion. The agreement of CNT with the calculated rates for this system confirms that the classical theory is a very reasonable approximate theory.
|
|
INF2 accelerates actin nucleation and elongation by interacting with barbed ends (fast-growing ends) of actin filaments, but also accelerates disassembly of actin through encircling and severing filaments.
|
|
While x-ray diffraction reveals the isotropic nature of q-glass, a nucleation barrier exists implying an interfacial discontinuity (or internal surface) between the glass and melt phases.
|
|
Bubbles from rosé Champagne An initial burst of effervescence occurs when the Champagne contacts the dry glass on pouring. These bubbles form on imperfections in the glass that facilitate nucleation or, to a minimal extent, on cellulose fibres left over from the wiping/drying process as shown with a high-speed video camera. However, after the initial rush, these naturally occurring imperfections are typically too small to consistently act as nucleation points as the surface tension of the liquid smooths out these minute irregularities. The nucleation sites that act as a source for the ongoing effervescence are not natural imperfections in the glass, but actually occur where the glass has been etched by the manufacturer or the customer.
|
|
Typical pulses are of tens of nanoseconds in duration and are therefore capable of resolving the first nucleation sites of domain reversal and then observing how these sites evolve.
|
|
After a period of time the mother liquor is drained and the crystals removed. Nucleation and size of crystals are difficult to control. Typically, labor costs are very high.
|
|
As a result, the hypothesis predicts that growth will be directed into regions containing more presynaptic elements. This morphology can be stabilized by creating microtubule nucleation at the microtubules.
|
|
Seed-mediated growth is a synthetic method in which small, stable nuclei are grown in a separate chemical environment to a desired size and shape. Seed-mediated methods consist of two different stages: nucleation and growth. Variation of certain factors in the synthesis (e.g. ligand, nucleation time, reducing agent, etc.), can control the final size and shape of nanoparticles, making seed-mediated growth a popular synthetic approach to controlling morphology of nanoparticles.
|
|
Dubrovskii main areas are currently in modeling and shaping of sophisticated nanowire nanoheterostructures, nucleation theory in the nanoscale, physical chemistry of alloys and compounds, and analytic size distributions. He is working with experimentalists on design and functionalization of optoelectronic nanoheterostructures. ;Lecture courses and PhD students Dubrovskii is lecturing in nucleation theory, epitaxy of nanostructures and growth modeling of nanowires. He has supervised 10 PhD students, 2 of them under European Marie Curie Initial Training Networks.
|
|
The lower initial temperatures increase the driving force of nucleation. More driving force means more nucleation sites, and more sites means more places for dislocations to be disrupted while the finished part is in use. Many alloy systems allow the ageing temperature to be adjusted. For instance, some aluminium alloys used to make rivets for aircraft construction are kept in dry ice from their initial heat treatment until they are installed in the structure.
|
|
Manganese – Cleans impurities in steels (most commonly used to tie up sulfur) and also forms oxides that are necessary for the nucleation of acicular ferrite. Acicular ferrite is desirable in HY-80 steels because it promotes excellent yield strength and toughness. Silicon – Oxide former that serves to clean and provide nucleation points for acicular ferrite. Chromium – Is a ferrite stabilizer and can combine with carbon to form chromium carbides for increased strength of the material.
|
|
Fine emulsions of pure water have been cooled to −38 degrees Celsius without nucleation to form ice. Nucleation occurs due to fluctuations in the properties of the material. If the material is kept still there is often nothing (such as physical vibration) to trigger this change, and supercooling (or superheating) may occur. Thermodynamically, the supercooled liquid is in the metastable state with respect to the crystalline phase, and it is likely to crystallize suddenly.
|
|
US EPA (2009) commented on research by Duplissy et al. (2009): > The CLOUD experiments at CERN are interesting research but do not provide > conclusive evidence that cosmic rays can serve as a major source of cloud > seeding. Preliminary results from the experiment (Duplissy et al., 2009) > suggest that though there was some evidence of ion mediated nucleation, for > most of the nucleation events observed the contribution of ion processes > appeared to be minor.
|
|
The Lauritzen–Hoffman growth theory breaks the kinetics of polymer crystallization into ultimately two rates. The model breaks down into the addition of monomers onto a growing surface. This initial step is generally associated with the nucleation of the polymer. From there, the kinetics become the rate which the polymer grows on the surface, or the lateral growth rate, in comparison with the growth rate onto the polymer extending the chain, the secondary nucleation rate.
|
|
The red curve is a fit of a Gompertz function to the data. This is a simplified version of the model Pound and La Mer used to model their data. The model assumes that nucleation occurs due to impurity particles in the liquid tin droplets, and it makes the simplifying assumption that all impurity particles produce nucleation at the same rate. It also assumes that these particles are Poisson distributed among the liquid tin droplets.
|
|
Thus a family of proteins acting as nucleation factors may be present in cells, lowering, through various mechanisms, the energetic cost of nucleating microtubules. Several proteins are involved in formatting the γ-TuRC and temporal and spatial control of microtubule nucleation. These include, for example, coiled-coil proteins with structural functions and regulatory proteins, such as components of the Ran cycle. NEDD1 recruits the γ-TuRC to the centrosome by binding to γ-tubulin.
|
|
The CAD, like other aerosol detectors (e.g., evaporative light scattering detectors (ELSD) and condensation nucleation light scattering detectors (CNLSD)), falls under the category of destructive general-purpose detectors (see Chromatography Detectors).
|
|
The diffraction pattern shows it to be an isotropic glassy phase. Yet there is a nucleation barrier, which implies an interfacial discontinuity (or internal surface) between the glass and the melt.
|
|
At high temperatures, equilibrium thermodynamic models appear to be satisfactory for the description of kaolinite dissolution and nucleation, because the thermal energy suffices to overcome the energy barriers involved in the nucleation process. The importance of syntheses at ambient temperature and atmospheric pressure towards the understanding of the mechanism involved in the nucleation of clay minerals lies in overcoming these energy barriers. As indicated by Caillère and Hénin (1960) the processes involved will have to be studied in well- defined experiments, because it is virtually impossible to isolate the factors involved by mere deduction from complex natural physico-chemical systems such as the soil environment. Fripiat and Herbillon (1971), in a review on the formation of kaolinite, raised the fundamental question how a disordered material (i.e.
|
|
When the urine becomes supersaturated (when the urine solvent contains more solutes than it can hold in solution) with one or more calculogenic (crystal-forming) substances, a seed crystal may form through the process of nucleation. Heterogeneous nucleation (where there is a solid surface present on which a crystal can grow) proceeds more rapidly than homogeneous nucleation (where a crystal must grow in a liquid medium with no such surface), because it requires less energy. Adhering to cells on the surface of a renal papilla, a seed crystal can grow and aggregate into an organized mass. Depending on the chemical composition of the crystal, the stone-forming process may proceed more rapidly when the urine pH is unusually high or low.
|
|
Critical radius is the minimum particle size from which an aggregate is thermodynamically stable. In other words, it is the lowest radius formed by atoms or molecules clustering together (in a gas, liquid or solid matrix) before a new phase inclusion (a bubble, a droplet or a solid particle) is viable and begins to grow. Formation of such stable nuclei is called nucleation. At the beginning of the nucleation process, the system finds itself in an initial phase.
|
|
Certain intracellular pathogens such as the bacterial species Listeria monocytogenes and Shigella flexneri can manipulate host cell actin polymerization to move through the cytosol and spread to neighboring cells (see below). Studies of these bacteria, especially of Listeria Actin assembly-inducing protein (ActA), have resulted in further understanding of the actions of WASP. ActA is a nucleation promoting factor that mimics WASP. It is expressed polarized to the posterior end of the bacterium, allowing Arp2/3-mediated actin nucleation.
|
|
Such situations arise when many adatoms are required to reach a critical nucleus size on the surface and at nucleation the resulting adsorbed layer constitutes a significant fraction of a monolayer. After nucleation, metastable adatoms on the surface are incorporated into the nuclei, causing the Auger signal to fall. This phenomenon is particularly evident for deposits on a molybdenum substrate. Evolution of island formation during a SK transitions have also been successfully measured using LEED and RHEED techniques.
|
|
TPX2 has been shown in several biochemical assays to behave as a microtubule-associated protein (MAP) and co- localize with spindle microtubules during M-phase. It plays a role in microtubule nucleation and is regulated by importin proteins. TPX2 serves as a complement, depleting importin α affinity in order to allow RanGTP-induced microtubule nucleation. This has been demonstrated both in vitro in Xenopus laevis egg extracts, and with the human homologue in vivo in HeLa cells.
|
|
He is remembered today for the Becker–Döring theory of nucleation of liquid droplets in solids (in condensed matter physics), and for the Zel'dovich–von Neumann–Döring detonation model (in explosives engineering).
|
|
Ice nucleation mechanisms. An ice nucleus, also known as an ice nucleating particle (INP), is a particle which acts as the nucleus for the formation of an ice crystal in the atmosphere.
|
|
Gamma-tubulin complex component 5 is a protein that in humans is encoded by the TUBGCP5 gene. It is part of the gamma tubulin complex, which required for microtubule nucleation at the centrosome.
|
|
Gamma-tubulin complex component 3 is a protein that in humans is encoded by the TUBGCP3 gene. It is part of the gamma tubulin complex, which required for microtubule nucleation at the centrosome.
|
|
Gamma-tubulin complex component 6 is a protein that in humans is encoded by the TUBGCP6 gene. It is part of the gamma tubulin complex, which required for microtubule nucleation at the centrosome.
|
|
F. Kelton of Washington University in St. Louis, USA and A. L. Greer of University of Cambridge, UK (2010) Nucleation in Condensed Matter: Applications in Materials and Biology (Elsevier Science & Technology, Amsterdam) link.
|
|
Gamma-tubulin complex component 2 is a protein that in humans is encoded by the TUBGCP2 gene. It is part of the gamma tubulin complex, which required for microtubule nucleation at the centrosome.
|
|
The degree of connectivity between nucleation sites increases with film thickness, so that thicknesses near the critical value are characterized by isolated star-shaped crack junctions and thick films show more complete networks.
|
|
772 (1958)Cahn, J.W., Theory of crystal growth and interface motion in crystalline materials, Acta Met, Vol. 8, p. 554 (1960)Cahn, J.W., Coherent fluctuations and nucleation in isotropic solids, Acta Met., Vol.
|
|
Nucleation usually begins near dislocation or at surface defects. But for nanoscale materials, the dislocation density is greatly reduced, and the surface is usually atomically smooth. Therefore, the phase transformation of nanoscale materials exhibiting superelasticity is usually found to be homogeneous, resulting in much higher critical stress. Specifically, for Zirconia, where it has three phases, the competition between phase transformation and plastic deformation has been found to be orientation dependent, indicating the orientation dependence of activation energy of dislocation and nucleation.
|
|
Distributions of this type are now widely used for modeling the growth kinetics of semiconductor nanostructures, surface islands and biological objects. ;Self-regulated nucleation and growth in nanosystems Since 2004, Dubrovskii pursued growth theories in confined systems with a limited amount of growth species in the mother phase. He developed concepts of “mononuclear” growth [22,23] whereby individual nucleation events predetermine physical properties of emerging nanomaterials. He developed methods of using different size- dependent effects for narrowing size distributions [8,24-26].
|
|
The build-up of enough ferrihydrite ions leads to nucleation, the rate of which can be altered via changing the pH at the site of nucleation. After one to two days, these ions are converted to goethite crystals.343x343pxThe unmineralized matrix consists of relatively well-ordered, densely packed arrays of chitin fibers, with only a few nanometers between adjacent fibers. The lack of space leads to the absence of pre-formed compartments within the matrix that control goethite crystal size and shape.
|
|
The nucleation step is critical for crystal formation since it is the first-order phase transition of samples moving from having a high degree of freedom to obtaining an ordered state (aqueous to solid). For the nucleation step to succeed, the manipulation of crystallization parameters is essential. The approach behind getting a protein to crystallize is to yield a lower solubility of the targeted protein in solution. Once the solubility limit is exceeded and crystals are present, crystallization is accomplished.
|
|
Nucleation is often described mathematically through the change in Gibbs free energy of n moles of vapor at vapor pressure P that condenses into a drop. Also the nucleation barrier, in polymer crystallization, consists of both enthalpic and entropic components that must be over come. This barrier consists of selection processes taking place in different length and time scales which relates to the multiple regimes later on. This barrier is the free energy required to overcome in order to form nuclei.
|
|
In 1992 Ross started her academic career as a staff scientist inn the University of California, Berkeley National Center for Electron Microscopy. She moved to the Thomas J. Watson Research Center in 1997 where she worked as a research staff member. Here she developed various microscopic techniques, including in situ environmental transmission electron microscopy (TEM). By monitoring the growth of materials in situ it is possible to understand the nucleation and growth of materials, including observing individual nucleation events and transient intermediate states.
|
|
This is the formation of nuclei of a new crystal directly caused by pre-existing crystals. For example, if the crystals are in a solution and the system is subject to shearing forces, small crystal nuclei could be sheared off a growing crystal, thus increasing the number of crystals in the system. So both primary and secondary nucleation increase the number of crystals in the system but their mechanisms are very different, and secondary nucleation relies on crystals already being present.
|
|
The works of 2016 brought up the new size distributions describing length statistics in nanowire ensembles [9,10]. In 2015-2016, he developed the first theory for the compositional control of ternary III-V nanowires [11], sharpening their axial heterointerfaces [12] and, more generally, nucleation theory of ternary solids from ternary and quaternary liquid alloys. He contributed into understanding the VLS versus selective area growth of nanowires [13] and self-induced nucleation of GaN nanowires on silicon substrates [14]. ;Classical nucleation theory In 2009, Dubrovskii discovered fluctuation-induced broadening (the Dubrovskii broadening) of the size distributions described by a Fokker-Planck type kinetic equation in terms of the Kuni invariant variables [15], and presented a map of the power exponents for the spectrum spreading in 2D and 3D systems.
|
|
Tubulin, gamma complex associated protein 4 is a protein in humans that is encoded by the TUBGCP4 gene. It is part of the gamma tubulin complex, which required for microtubule nucleation at the centrosome.
|
|
This prevents overgrowth onto the existing wires, allowing for homogeneous nucleation to continue occurring. Conditions in the interfacial synthesis can be tuned, such as the type of acid used as well as the oxidant used.
|
|
As a common phenomenon, static fatigue is manifested in many kinds of embrittlement, of which the mechanisms are closely related to the nucleation and growth of cracks. Two typical situations are listed here for reference.
|
|
Heterogeneous freezing may already be common in cirrus, which could limit the cooling potential of the technique. There are significant uncertainties associated with not only ice nucleation processes in cirrus clouds and the fraction of nucleation that occurs via heterogeneous and homogeneous freezing, but also its representation in climate models. “Over- seeding” might lead to warming, as opposed to the desired cooling. Several studies assess the potential and viability of cirrus cloud thinning and the effectiveness of the technique remains a subject of debate.
|
|
Using a single body-centered cubic colloidal crystal, the occurrence of Kossel lines in diffraction patterns were used to monitor the initial nucleation and subsequent motion caused distortion of the crystal. Continuous or homogeneous deformations occurring beyond the elastic limit produce a 'flowing crystal', where the nucleation site density increases significantly with increasing particle concentration. Lattice dynamics have been investigated for longitudinal as well as transverse modes. The same technique was used to evaluate the crystallization process near the edge of a glass tube.
|
|
There is a fundamental difference between traditional emulsion polymerisation and a miniemulsion polymerisation. Particle formation in the former is a mixture of micellar and homogeneous nucleation, particles formed via miniemulsion however are mainly formed by droplet nucleation. In the pharmaceutical industry, oil droplets act as tiny containers that carry water-insoluble drugs, and the water provides a mild environment that is compatible with the human body. Moreover, miniemulsions that carry drugs allow the drugs to crystallize in a controlled size with a good dissolution rate.
|
|
The association of the Vps35-Vps29-Vps26 complex to the cytosolic domains of cargo molecules endosomal membranes initiates the activation of retrograde trafficking and cargo capture. The nucleation complex was formed through the interaction of VPS complex with GTP-activated Rab7 with clathrin, clathrin-adaptors and various binding proteins. The SNX-BAR dimer enters the nucleation complex via direct binding or lateral movement on endosomal surface. The increased level of Retromer SNX-BARs causes a conformational switch to a curvature-inducing mode which initiates membrane tubule formation.
|
|
However, when a large enough disturbance occurs at the bottleneck, an F → S phase transition does occur. Such a disturbance that initiates the F → S phase transition in metastable free flow at the bottleneck can be called a nucleus for traffic breakdown. In other words, real traffic breakdown (F → S phase transition) at a highway bottleneck exhibits the nucleation nature. Kerner considers the empirical nucleation nature of traffic breakdown (F → S phase transition) at a road bottleneck as the empirical fundamental of traffic and transportation science.
|
|
Igneous microstructure is a combination of cooling rate, nucleation rate, eruption (if a lava), magma composition and its relationships to what minerals will nucleate, as well as physical effects of wall rocks, contamination and especially vapor.
|
|
For the simple models CNT works quite well, however it is unclear if it describes complex (e.g. molecular) systems equally well. Jones et al. computationally explored the nucleation of small Water cluster using classical water model.
|
|
Schematic diagram of Water concentration profile across a pumice-obsidian sample. The shape of the profile can be translate into a diffusion timescale. Vesiculation, i.e. the nucleation and growth of bubbles commonly initiates eruptions in volcanic domes.
|
|
At very high temperatures, the high rates of recovery relieve the stress at inclusion and suppress the nucleation of internal voids. Therefore, with no other fracture mechanism intervenes, deformation continues until the cross- section area becomes zero.
|
|
Weinberg has worked on various branches in theoretical high energy physics, including the theory of spontaneous symmetry breaking, inflation, the theory of supersymmetric solitons, and the theory of vacuum decay via the nucleation of quantum/thermal bubbles.
|
|
Otherwise, the growth solution will form new nucleation sites instead of growing on preexisting ones (seeds). Growth is the result of the competition between surface energy (which increases unfavorably with growth) and bulk energy (which decreases favorably with growth). The balance between the energetics of growth and dissolution is the reason for uniform growth only on preexisting seeds (and no new nucleation). Growth occurs by the addition of metal atoms from the growth solution to the seeds, and ligand exchange between the growth ligands (which have a higher bonding affinity) and the seed ligands.
|
|
Microstructural evolution under the Cahn–Hilliard equation, demonstrating distinctive coarsening and phase separation.Spinodal decomposition is one thermodynamic phase decomposing into two phases, when there is no nucleation barrier to this decomposition. Thus at least some fluctuations in the system spontaneously grow as they reduce the free energy, and so there is no waiting, as there typically is when there is a nucleation barrier. Spinodal decomposition can occur, for example, when mixtures of polymers are unstable as a mixture and separate into two coexisting phases, each one rich in one polymer, and poor in the other.
|
|
Two of its subunits, the Actin-Related Proteins ARP2 and ARP3, closely resemble the structure of monomeric actin and serve as nucleation sites for new actin filaments. The complex binds to the sides of existing ("mother") filaments and initiates growth of a new ("daughter") filament at a distinctive 70 degree angle from the mother. Branched actin networks are created as a result of this nucleation of new filaments. The regulation of rearrangements of the actin cytoskeleton is important for processes like cell locomotion, phagocytosis, and intracellular motility of lipid vesicles.
|
|
Time- lapse of growth of a citric acid crystal. The video covers an area of 2.0 by 1.5 mm and was captured over 7.2 min. The crystallization process consists of two major events, nucleation and crystal growth which are driven by thermodynamic properties as well as chemical properties. In crystallization Nucleation is the step where the solute molecules or atoms dispersed in the solvent start to gather into clusters, on the microscopic scale (elevating solute concentration in a small region), that become stable under the current operating conditions.
|
|
She also found MIT a more positive environment for black students in science and engineering; though the proportion of African American students at MIT was small, it was still higher than at other colleges in the country. Patrick enjoyed the tough and challenging atmosphere, and was a very dedicated student, working seven days a week. She studied thermodynamics, homogeneous nucleation, heat and mass transfer, and worked as a research assistant. Her advisor was Robert C. Reid, a world-renowned thermodynamicist, and her thesis topic dealt with nucleation phenomena.
|
|
Like most Atg proteins, Atg8 is localized in the cytoplasm and at the PAS under nutrient-rich conditions, but becomes membrane-associated in case of autophagy induction. It then localizes to the site of autophagosome nucleation, the phagophore-assembly site (PAS). Nucleation of the phagophore requires the accumulation of a set of Atg proteins and of class III phosphoinositide 3-kinase complexes on the PAS. The subsequent recruitment of Atg8 and other autophagy-related proteins is believed to trigger vesicle expansion in a concerted manner, presumably by providing the driving force for membrane curvature.
|
|
Inactive cortactin diffuses throughout the cytoplasm, but upon phosphorylation, the protein begins to target certain areas in the cell. Cortactin-assisted Arp2/3-nucleated actin branches are most prominent in the actin cortex, around the periphery of the cell. A phosphorylated cortactin monomer binds to, activates, and stabilizes an Arp2/3 complex on preexisting F-actin, which provides a nucleation site for a new actin branch to form from the “mother” filament. Branches formed from cortactin-assisted nucleation sites are very stable; cortactin has been shown to inhibit debranching.
|
|
In some alloys, the effect is reduced by adding elements such as tungsten that interfere with cementite nucleation, but more often than not, the nucleation is allowed to proceed to relieve stresses. Since quenching can be difficult to control, many steels are quenched to produce an overabundance of martensite, then tempered to gradually reduce its concentration until the preferred structure for the intended application is achieved. The needle-like microstructure of martensite leads to brittle behavior of the material. Too much martensite leaves steel brittle; too little leaves it soft.
|
|
Current evidence suggests that the vacuum permeating the observable Universe is not a Minkowski space, but rather a de Sitter space with a positive cosmological constant.Mukhanov, V., Physical Foundations of Cosmology (Cambridge: Cambridge University Press, 2005), p. 30. In a de Sitter vacuum (but not in a Minkowski vacuum), a Boltzmann brain can form via nucleation of non-virtual particles gradually assembled by chance from the Hawking radiation emitted from the de Sitter space's bounded cosmological horizon. One estimate for the average time required until nucleation is around 10^{10^{69}} years.
|
|
Wynne has authored over 90 published scientific papers. His work is focused on the structure and dynamics of liquids and solutions as well as peptides, proteins, and other biomolecules treated as amorphous objects behaving much like liquids. He described the Mayonnaise Effect, which explains the anomalous increase of the viscosity of solutions with concentration in terms of a jamming transition. He is particularly interested in phase behaviour such as "supercooling of liquids, folding transitions in peptides, phase separation and nucleation using laser-tweezing, nucleation of crystals from solution", and liquid-liquid and liquid-crystalline transitions.
|
|
These have been compared with the classical theory, for example for the case of nucleation of the crystal phase in the model of hard spheres. This is a model of perfectly hard spheres in thermal motion, and is a simple model of some colloids. For the crystallization of hard spheres the classical theory is a very reasonable approximate theory. So for the simple models we can study, classical nucleation theory works quite well, but we do not know if it works equally well for (say) complex molecules crystallising out of solution.
|
|
In many cases, liquids and solutions can be cooled down or concentrated up to conditions where the liquid or solution is significantly less thermodynamically stable than the crystal, but where no crystals will form for minutes, hours, weeks or longer. Nucleation of the crystal is then being prevented by a substantial barrier. This has consequences, for example cold high altitude clouds may contain large numbers of small liquid water droplets that are far below 0°C. In small volumes, such as in small droplets, only one nucleation event may be needed for crystallisation.
|
|
There are a number of mechanisms of ice nucleation in the atmosphere through which ice nuclei can catalyse the formation of ice particles. In the upper troposphere, water vapor can deposit directly onto solid particle. In clouds warmer than about −37 °C where liquid water can persist in a supercooled state, ice nuclei can trigger droplets to freeze. Contact nucleation can occur if an ice nucleus collides with a supercooled droplet, but the more important mechanism of freezing is when an ice nucleus becomes immersed in a supercooled water droplet and then triggers freezing.
|
|
In cell biology, microtubule nucleation is the event that initiates de novo formation of microtubules (MTs). These filaments of the cytoskeleton typically form through polymerization of α- and β-tubulin dimers, the basic building blocks of the microtubule, which initially interact to nucleate a seed from which the filament elongates. Microtubule nucleation occurs spontaneously in vitro, with solutions of purified tubulin giving rise to full-length polymers. The tubulin dimers that make up the polymers have an intrinsic capacity to self-aggregate and assemble into cylindrical tubes, provided there is an adequate supply of GTP.
|
|
To reach this goal, in congested traffic a new traffic phase called synchronized flow has been introduced. The basic feature of the synchronized flow traffic phase formulated in the three-phase traffic theory leads to the nucleation nature of the F → S transition. In this sense, Kerner’s synchronized flow traffic phase that ensures the nucleation nature of the F → S transition at a highway bottleneck and Kerner’s three-phase traffic theory can be considered synonyms. Initially developed for highway traffic, Kerner expanded the three phase theory for the description of city traffic in 2011–2014.
|
|
Synthetic ikaite was discovered in the nineteenth century in a study by Pelouze. Ikaite is only thermodynamically stable at moderate pressures, so when found near the Earth's surface is always metastable. Nevertheless, as it appears to be at least moderately common in Nature, it is clear that the conditions for metastable nucleation and growth cannot be too restrictive. Cold water is certainly required for formation, and nucleation inhibitors like phosphate ions for the growth of anhydrous calcium carbonate phases, such as calcite, aragonite, and vaterite probably aid its formation and preservation.
|
|
The time to nucleate can vary by orders of magnitude, from negligible to exceedingly large, far beyond reach of experimental timescales. One of the key achievements of classical nucleation theory is to explain and quantify this immense variation.
|
|
Micrograph showing the viral cytopathic effect of herpes simplex virus (multi- nucleation, ground glass chromatin). Pap test. Pap stain. Cytopathic effect or cytopathogenic effect (abbreviated CPE) refers to structural changes in host cells that are caused by viral invasion.
|
|
David Turnbull. Harvard Gasette (November 4, 2010 ) In 1946, he joined the General Electric research laboratory, performing research into nucleation of structural transformations occurring during the solidification of liquid metals, demonstrating that such complex processes could be quantitatively understood.
|
|
This is then warmed towards room temperature, producing solvated metal atoms or (over time) larger clusters. Sometimes, catalysts supports (such as SiO2 or Al2O3) are added to improve nucleation, as it can more readily take place on surface OH groups.
|
|
This pushes the bacterium in the anterior direction, leaving a trailing "comet tail" of actin. In the case of Shigella, which also moves using an actin comet tail, the bacterial factor recruits host cell WASPs in order to promote actin nucleation.
|
|
Furthermore, a second pathway known as the augmin/HAUS complex (some organisms use the more studied augmin complex, while others such as humans use an analogous complex called HAUS) acts an additional means of microtubule nucleation in the mitotic spindle.
|
|
Aaronson has published more than 300 scientific papers for teaching and supporting his young colleagues, and has organized conferences that influenced with the field. His well-known major contributions are about diffusional nucleation and growth, and the mechanisms of phase transformations.
|
|
The average timescale required for formation of a Boltzmann brain is vastly greater than the current age of the Universe. In modern physics, Boltzmann brains can be formed either by quantum fluctuation, or by a thermal fluctuation generally involving nucleation.
|
|
The most common methods for nanoparticle synthesis fall under the category of wet chemistry, or the nucleation of particles within a solution. This nucleation occurs when a silver ion complex, usually AgNO3 or AgClO4, is reduced to colloidal silver in the presence of a reducing agent. When the concentration increases enough, dissolved metallic silver ions bind together to form a stable surface. The surface is energetically unfavorable when the cluster is small, because the energy gained by decreasing the concentration of dissolved particles is not as high as the energy lost from creating a new surface.
|
|
The Arp2/3 complex is composed of seven subunits: Arp2/ACTR2, Arp3/ACTR3, p41/ARPC1A&B;, p34/ARPC2, p21/ARPC3, p20/ARPC4, p16/ARPC5. The subunits Arp2 and Arp3 closely resemble monomeric actin allowing for a thermodynamically stable actin-like dimer. p41 has been proposed to interact with nucleation promoting factors (NPFs) because it is only known to have minor contacts with the mother filament and there is a major loss of nucleation efficiency in the absence of p41. p34 and p20 dimerize to form a structural backbone that mediates the interaction with the mother filament.
|
|
For example, formin AtFH5 has been identified as a major regulator of actin filament nucleation, specifically for actin filaments synthesized from the apical membrane of the pollen tube. Genetic knockouts of AtFH5 resulted in a decreased abundance of actin filaments in both apical and subapical regions of the pollen tube, thereby providing more evidence to support the theory that AtFH5 nucleates actin filament assembly in apical and subapical regions of the pollen tube. Class I formin AtFH3 is another actin nucleation factor. AtFH3 nucleates actin filament assembly of the longitudinal actin cables located in the shank region of the pollen tube.
|
|
When these particles form their internal energy is lower than the surrounded liquid, which creates an energy interface between the two. The formation of the surface at this interface requires energy, so as nucleation occurs the material actually undercools, that is it cools below its solidification temperature, because of the extra energy required to form the interface surfaces. It then recalescences, or heats back up to its solidification temperature, for the crystal growth stage. Nucleation occurs on a pre-existing solid surface, because not as much energy is required for a partial interface surface, as is for a complete spherical interface surface.
|
|
The amino-terminal half of TPX2 also increases the efficiency of the reaction. TPX2 α5-7 is different from the remainder of the protein in that it contains conserved regions in its amino acid sequence that share sequence similarity with two known γ-TuRC nucleation activator motifs: SPM and γ-TuRC. The SPM-like motif is found within the α5 domain, while the γTuNA-like motif is found to start in the α5 domain and stretch into the SPM-like motif. Without these two motifs, no microtubule nucleation was observed in vitro, though microtubule binding ability was maintained.
|
|
C: Microdialysis Protein crystals are almost always grown in solution. The most common approach is to lower the solubility of its component molecules very gradually; if this is done too quickly, the molecules will precipitate from solution, forming a useless dust or amorphous gel on the bottom of the container. Crystal growth in solution is characterized by two steps: nucleation of a microscopic crystallite (possibly having only 100 molecules), followed by growth of that crystallite, ideally to a diffraction-quality crystal. The solution conditions that favor the first step (nucleation) are not always the same conditions that favor the second step (subsequent growth).
|
|
Studies using Xenopus egg extracts have identified a novel form of microtubule nucleation that generates fan-like branching arrays, in which new microtubules grow at an angle off of older microtubules. Researchers suspect that this process involves non-centrosomal γ-TuRCs that bind to the sides of existing microtubules through the augmin complex. This method of microtubule-dependent microtubule nucleation leads to rapid amplification in microtubule number, and creates daughter microtubules with the same polarity as the mother microtubules they branch from. It has been postulated that such a method could be important in the generation of the mitotic spindle.
|
|
To explain this phenomenon Kerner developed a microscopic theory of the S → F instability. None of the classical traffic flow theories and models incorporate the S → F instability of the three-phase theory. The basic result of the three-phase theory about the nucleation nature of traffic breakdown (F → S transition) shows that the three-phase theory is incommensurable with all earlier traffic flow theories and models (see explanations below). As mentioned, the main reason of Kerner’s three-phase traffic theory is the explanation of the empirical nucleation nature of traffic breakdown (F → S transition) at the bottleneck.
|
|
Due to the lack of realistic representation of ice crystal nucleation in Earth system models, some studies have used a simplified representation of cirrus cloud thinning by increasing the terminal velocity of ice crystals below the homogeneous freezing threshold of about -38 °C.
|
|
Whether this happens depends on the saturation of the air. The composition of the ice is currently an active topic of study. The main mechanism for ice formation is homogeneous nucleation. The ice crystals are mostly small spheroidal and irregular-shaped particles.
|
|
This aggregation result in a reduced rate of virus inactivation promptly showing that viral particles that do not aggregate are more easily destroyed. It has also been proven that aggregation may form spontaneously or may result by nucleation on particles of water.
|
|
Unlike pearlite, whose formation involves the diffusion of all atoms, bainite grows by a displacive transformation mechanism. The transformation of pearlite to austenite takes place at lower critical temperature of 723C. At this temperature pearlite changes to austenite because of nucleation process.
|
|
In certain ADPs, such as Gerstmann-Straussler or fatal familial insomnia, individuals naturally encode a form of the PrP protein that shifts the equilibrium slightly to make the beta form more favorable, thus increasing the likelihood of additional nucleation and extended polymerization.
|
|
Particia Martin Dove is an American mineralogist. She is the University Distinguished Professor and C.P. Miles Professor of Science at Virginia Tech. She works on crystal nucleation and growth, in particular biomineralization. She was elected a member the National Academy of Sciences (NAS) in 2012.
|
|
Its low-temperature (around ) formation is known to require alternations between precipitation and dissolution intervals.Deelman, J.C. (1999): "Low-temperature nucleation of magnesite and dolomite", Neues Jahrbuch für Mineralogie, Monatshefte, pp. 289–302.Alves dos Anjos et al. (2011): Synthesis of magnesite at low temperature.
|
|
With a high affinity for oxygen, titanium alloy can absorb oxygen easily. Oxygen can promote the formation of α2 phase. These coherent α2 particles lead to easy crack nucleation and fast crack propagation within the planar slip bands. Therefore, toughness of titanium alloy is decreased.
|
|
Spc72p associates with Nud1p and to components of the γ-tubulin complex. The half-bridge is the site of new SPB assembly, and it also plays a role in cytoplasmic microtubule nucleation during G1 and karyogamy. Both sides of the half-bridge are not equivalent.
|
|
However it is possible for particles smaller than the MPPS to not have filtering efficiency greater than that of the MPPS. This is due to the fact that these particles can act as nucleation sites for mostly condensation and form particles near the MPPS.
|
|
This metal will form the core. The pre-formed nanoparticle acts as the seed required for the nucleation of the second metal around it. These structures can be characterized using TEM imaging. The shape and size can be manipulated by varying the different parameters.
|
|
Hence, the organic component of mineralized tissues increases their toughness. Moreover, many proteins are regulators in the mineralization process. They act in the nucleation or inhibition of hydroxyapatite formation. For example, the organic component in nacre is known to restrict the growth of aragonite.
|
|
Using a functional S105-GFP fusion, it was demonstrated that the protein accumulates uniformly in the membrane, and then within 1 minute, it forms aggregates at the time of lethality. Thus, like bacteriorhodopsin, the protein accumulates until it reaches a critical concentration for nucleation.
|
|
In conventional covalent polymerization, two models based on step-growth and chain-growth mechanisms are operative. Nowadays, a similar subdivision is acceptable for supramolecular polymerization; isodesmic also known as equal-K model (step-growth mechanism) and cooperative or nucleation-elongation model (chain-growth mechanism).
|
|
The location of micronuclei or where bubbles initially form is not known. The most likely mechanisms for bubble formation are tribonucleation, when two surfaces make and break contact (such as in joints), and heterogeneous nucleation, where bubbles are created at a site based on a surface in contact with the liquid. Homogeneous nucleation, where bubbles form within the liquid itself is less likely because it requires much greater pressure differences than experienced in decompression. The spontaneous formation of nanobubbles on hydrophobic surfaces is a possible source of micronuclei, but it is not yet clear if these can grow large enough to cause symptoms as they are very stable.
|
|
Recent results favour the side branching model, in which the Arp2/3 complex binds to the side of a pre-existing ("mother") filament at a point different from the nucleation site. Although the field lacks a high-resolution crystal structure, data from electron microscopy, together with biochemical data on the filament nucleation and capping mechanisms of the Arp2/3 complex, favour side branching. In the alternative barbed end branching model, Arp2/3 only associates at the barbed end of growing filaments, allowing for the elongation of the original filament and the formation of a branched filament., a model based on kinetic analysis and optical microscopy.
|
|
While this equation provides a better description of the process it still assumes that the grains are spherical, the nucleation and growth rates are constant, the nuclei are randomly distributed and the nucleation time t0 is small. In practice few of these are actually valid and alternate models need to be used. It is generally acknowledged that any useful model must not only account for the initial condition of the material but also the constantly changing relationship between the growing grains, the deformed matrix and any second phases or other microstructural factors. The situation is further complicated in dynamic systems where deformation and recrystallization occur simultaneously.
|
|
Rapid formation of ice crystals in supercool water (home freezer experiment) In spite of the second law of thermodynamics, crystallization of pure liquids usually begins at a lower temperature than the melting point, due to high activation energy of homogeneous nucleation. The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is expended to form this interface, based on the surface energy of each phase. If a hypothetical nucleus is too small, the energy that would be released by forming its volume is not enough to create its surface, and nucleation does not proceed.
|
|
It was found that as the temperature of the cladding increased the rate of heat transfer from the surface of the cladding increased at first as the water boiled at nucleation sites. When the heat flux is greater than the critical heat flux a boiling crisis occurs. This occurs as the temperature of the fuel cladding surface increases so that the surface of the metal was too hot (surface dries out) for nucleation boiling. When the surface dries out the rate of heat transfer decreases, after a further increase in the temperature of the metal surface the boiling resumes but it is now film boiling.
|
|
The crystallographer's goal is to identify solution conditions that favor the development of a single, large crystal, since larger crystals offer improved resolution of the molecule. Consequently, the solution conditions should disfavor the first step (nucleation) but favor the second (growth), so that only one large crystal forms per droplet. If nucleation is favored too much, a shower of small crystallites will form in the droplet, rather than one large crystal; if favored too little, no crystal will form whatsoever. Other approaches involves, crystallizing proteins under oil, where aqueous protein solutions are dispensed under liquid oil, and water evaporates through the layer of oil.
|
|
The protein encoded by this gene is expressed in the cytoplasm and centrosome throughout the cell cycle, and to a lesser extent, in the nucleus. It is an integral component of the PCM, which is a centrosome scaffold that anchors microtubule nucleating complexes and other centrosomal proteins. In one model, PCNT complexes with CEP215 and is phosphorylated by PLK1, leading to PCM component recruitment and organization, centrosome maturation, and spindle formation. The protein controls the nucleation of microtubules by interacting with the microtubule nucleation component γ-tubulin, thus anchoring the γ-tubulin ring complex to the centrosome, which is essential for bipolar spindle formation and chromosome assembly in early mitosis.
|
|
This process is significantly faster than nucleation. The reason for such rapid growth is that real crystals contain dislocations and other defects, which act as a catalyst for the addition of particles to the existing crystalline structure. By contrast, perfect crystals (lacking defects) would grow exceedingly slowly.
|
|
In an alternative self assembly model, microtubules undergo acentrosomal nucleation among the condensed chromosomes. Constrained by cellular dimensions, lateral associations with antiparallel microtubules via motor proteins, and end-on attachments to kinetochores, microtubules naturally adopt a spindle-like structure with chromosomes aligned along the cell equator.
|
|
These various techniques have also been used to uncover the kinetic pathway of pre-nucleation transient oligomerization events and associated structures involving the protein encoded by huntingtin exon-1, which may provide a potential avenue for therapeutic intervention in Huntington's disease, a fatal autosomal dominant, neurodegenerative condition.
|
|
In Kerner's three phase traffic theory, in addition to the free flow traffic phase (F), there are two traffic phases in congested traffic: the synchronized flow traffic phase (S) and the wide moving jam phase (J). One of the main results of Kerner's theory is that traffic breakdown at a highway bottleneck is a random (probabilistic) phase transition from free flow to synchronized flow (F → S transition) that occurs in a metastable state of free flow at a highway bottleneck. This means that traffic breakdown (F → S transition) exhibits the nucleation nature. The main reason for the Kerner’s three-phase theory is the explanation of the empirical nucleation nature of traffic breakdown (F → S transition) at highway bottlenecks observed in real field traffic data. The prediction of the Kerner’s three-phase theory is that this metastability of free flow with respect to the F → S phase transition is governed by the nucleation nature of an instability of synchronized flow with respect to the growth of a large enough local increase in speed in synchronized flow (called a S → F instability).
|
|
Since crystal nucleation is suppressed by levitation, and since it is not limited by sample conductivity (unlike electromagnetic levitation), aerodynamic levitation can be used to make glassy materials, from high temperature melts that cannot be made by standard methods. Several silica-free, aluminium oxide based glasses have been made.
|
|
Therefore, a quantitative study of deformation twinning in TWIP steels is critical to understand their strain- hardening mechanisms and mechanical properties. Deformation twinning can be considered as a nucleation and growth process. Twin growth is assumed to proceed by co-operative movement of Shockley partials on subsequent {111} planes.
|
|
Foturan can be structured via UV-exposure, tempering and etching: Crystal nucleation grow in Foturan when exposed to UV and heat treated afterwards. The crystalized areas react much faster to hydrofluoric acid than the surrounding vitreous material, resulting in very fine microstructures, tight tolerance and high aspect ratio.
|
|
At sufficiently low temperature, cleavage usually dominates the fracture for most crystalline solids because the temperature limits the plasticity of the material and makes it brittle. Generally, cleavage is controlled by nucleation and propagation of cracks either of which can determine the stress at which the specimen fails.
|
|
It is the formation of the nuclei from the bulk to a surface that is the interfacial free energy. The interfacial free energy is always a positive term and acts to destabilize the nucleus allowing the continuation of the growing polymer chain. The nucleation continues as a favorable reaction.
|
|
At the end of 1990's Kerner introduced a new traffic phase, called synchronized flow whose basic feature leads to the nucleation nature of the F → S transition at a highway bottleneck. Therefore, Kerner's synchronized flow traffic phase can be used synonymously with the term three-phase traffic theory.
|
|
If the concentration of ice nuclei is seeded such that the resulting cloud particle density is less than that for the natural case, the cloud particles should grow larger due to less water vapor competition and attain higher settling velocities. By seeding with aerosols, ice crystals could grow rapidly and deplete water vapor, suppress nucleation and any growth of ice crystals by homogeneous nucleation. The net effect would be a reduced optical thickness and a reduced cloud lifetime, allowing more infrared radiation to be emitted at the top of the atmosphere, as the ice particles sediment out. Less upper tropospheric water vapor and infrared radiation in the atmosphere would consequently cool the climate.
|
|
A distinguishable feature of histone-like or heat-stable nucleoid structuring protein (H-NS) from other NAPs is the ability to switch from the homodimeric form at relatively low concentrations (<1 x 10−5 M) to an oligomeric state at higher levels. Because of oligomerization properties, H-NS spreads laterally along AT-rich DNA in a nucleation reaction, where high-affinity sites function as nucleation centers. The spreading of H-NS on DNA results in two opposite outcomes depending on the magnesium concentration in the reaction. At low magnesium concentration (< 2 mM), H-NS forms rigid nucleoprotein filaments whereas it forms inter- and intra-molecular bridges at higher magnesium concentrations (> 5 mM).
|
|
Devitrification occurs in glass art during the firing process of fused glass whereby the surface of the glass develops a whitish scum, crazing, or wrinkles instead of a smooth glossy shine, as the molecules in the glass change their structure into that of crystalline solids. While this condition is normally undesired, in glass art it is possible to use devitrification as a deliberate artistic technique. Causes of devitrification, commonly referred to as "devit", can include holding a high temperature for too long, which causes the nucleation of crystals. The presence of foreign residue such as dust on the surface of the glass or inside the kiln prior to firing can provide nucleation points where crystals can propagate easily.
|
|
Another similar material is AgInSbTe. It offers higher linear density, but has lower overwrite cycles by 1-2 orders of magnitude. It is used in groove-only recording formats, often in rewritable CDs. AgInSbTe is known as a growth-dominated material while GeSbTe is known as a nucleation- dominated material.
|
|
Physica 7, 284–304 (1940). It is unlikely, however, that new phases often arise by this fluctuation mechanism and the resultant spontaneous nucleation. Calculations show that the chance, e−ΔS/k, is usually too small. It is more likely that tiny dust particles act as nuclei in supersaturated vapours or solutions.
|
|
Linde, A. (2007). Sinks in the landscape, Boltzmann brains and the cosmological constant problem. Journal of Cosmology and Astroparticle Physics, 2007(01), 022. If no cosmological constant exists, and if the presently observed vacuum energy is from quintessence that will eventually completely dissipate, then infinite Boltzmann nucleation is also avoided.
|
|
The microscopic process of evaporation and condensation at the liquid surface. If vapor pressure exceeds the thermodynamic equilibrium value, condensation occurs in presence of nucleation sites. This principle is indigenous in cloud chambers, where ionized particles form condensation tracks when passing through. alcohol and is closed with a piece of cork.
|
|
A significant part of the activity of Sornette's group has also been devoted to the statistical physics modelling as well as properties of fractures and faults at different scales. Those features are important as they may control various transport properties of the crust as well as represent the loci of earthquake nucleation.
|
|
Stephan W. Koch studied physics at the University of Frankfurt, obtained his doctorate 1979 about the theory of electron–hole droplet nucleation in strongly excited semiconductorsKoch, S. W. (1979). Zur Theorie der Elektron- Loch-Tropfennukleation in stark angeregten Halbleitern (PhD). Johann Wolfgang Goethe-Universität Frankfurt am Main (Germany). under the supervision of Prof.
|
|
A high-strength glass-ceramic cooktop with negligible thermal expansion. Glass- ceramic materials contain both non-crystalline glass and crystalline ceramic phases. They are formed by controlled nucleation and partial crystallisation of a base glass by heat treatment. Crystalline grains are often embedded within a non-crystalline intergranular phase of grain boundaries.
|
|
In contrast, another study reported JADE1 localization to the cilia and centrosome. The study did not communicate on JADE1 isoform specificity. Centrosomes are the cytoskeleton nucleation centers. Centrosome signaling contributes to the definition of cell shape, motility, orientation, polarity, division plane and to the fidelity of sister chromosome separation during mitosis and cytokinesis.
|
|
In February 2005 the documentary series Horizon commissioned two leading sonoluminescence researchers, Seth Putterman, Seth Putterman personal page. and Kenneth S. Suslick, to reproduce Taleyarkhan's work. Using similar acoustic parameters, deuterated acetone, similar bubble nucleation, and a much more sophisticated neutron detection device, the researchers could find no evidence of a fusion reaction.
|
|
Part I Full-field solution and asymptotics. Journal of the Mechanics and Physics of Solids, 2008, 56, 815–838.D. Bigoni, F. Dal Corso and M. Gei, The stress concentration near a rigid line inclusion in a prestressed, elastic material. Part II Implications on shear band nucleation, growth and energy release rate.
|
|
When the Gibbs free energy change is positive, the nucleation process will not be prosperous. The nanoparticle radius is small, the superficial term prevails the volum term \Delta G_S > \Delta G_V. Contrary, if the variation rate is negative, it will be thermodynamically stable. The size of the cluster surpasses the critical radius.
|
|
Cdc42, Rac) via G-proteins. Rho GTPases are able to activate WASp which in turn activate Arp2/3 complex which serve as nucleation sites for actin polymerization. The actin polymers then push the membrane as they grow, forming the pseudopod. The pseudopodium can then adhere to a surface via its adhesion proteins (e.g.
|
|
Instead, they are released for transport into dendrites and axons after their nucleation in the centrosome. Therefore, both ends of the neurotubules terminates in the cytoplasm instead. Neurotubules are crucial in various cellular processes in neurons. Together with neurofilaments, they help to maintain the shape of a neuron and provide mechanical support.
|
|
The deformation fields around large (over 1 μm) non-deformable particles are characterised by high dislocation densities and large orientation gradients and so are ideal sites for the development of recrystallization nuclei. This phenomenon, called particle stimulated nucleation (PSN), is notable as it provides one of the few ways to control recrystallization by controlling the particle distribution. The effect of particle size and volume fraction on the recrystallized grain size (left) and the PSN regime (right) The size and misorientation of the deformed zone is related to the particle size and so there is a minimum particle size required to initiate nucleation. Increasing the extent of deformation will reduce the minimum particle size, leading to a PSN regime in size-deformation space.
|
|
Further studies revealed the influence of kinetic fluctuations on the size distributions of islands and droplets in the stages of their nucleation, growth, and Ostwald ripening [16,17]. He also contributed into binary nucleation theory with a saddle point of the formation energy, with applications in growth theory of strain-induced islands [18] and ternary VLS nanowires. ;Statistical size distributions and scaling properties In 1996, he published exact solution for the infinite set of rate equations for heterogeneous growth with size-linear rate constants [19], reduced to one-parametric Polya distribution. Further investigation of the growth systems with size-linear capture rates led to a two-parametric modified beta-distribution (2015) [20] which acquires the Vicsek-Family scaling form [21] in the continuum limit.
|
|
In thermodynamics, explosive boiling or phase explosion is a method whereby a superheated metastable liquid undergoes an explosive liquid-vapor phase transition into a stable two-phase state because of a massive homogeneous nucleation of vapor bubbles. This concept was pioneered by M. M. Martynyuk in 1976 and then later advanced by Fucke and Seydel.
|
|
Phosvitin is one of the egg (commonly hen’s egg) yolk phosphoproteins known for being the most phosphorylated protein found in nature. Phosvitin isolation was first described by Mecham and Olcott in the year 1949. Recently it has been shown that disordered secondary structure of phosvitin orchestrates nucleation and growth of biomimetic bone like apatite.
|
|
Carbonated sodas contain elevated levels of carbon dioxide under pressure. The solution becomes supersaturated with carbon dioxide when the bottle is opened, and the pressure is released. Under these conditions, carbon dioxide begins to precipitate from solution, forming gas bubbles. The activation energy for bubble nucleation (formation of bubbles) depends on where the bubble forms.
|
|
In statistical mechanics, the Zimm–Bragg model is a helix-coil transition model that describes helix-coil transitions of macromolecules, usually polymer chains. Most models provide a reasonable approximation of the fractional helicity of a given polypeptide; the Zimm–Bragg model differs by incorporating the ease of propagation (self-replication) with respect to nucleation.
|
|
Usually, this represents the protolith chemistry, which forms distinct mineral assemblages. However, compositional banding can be the result of nucleation processes which cause chemical and mineralogical differentiation into bands. This typically follows the same principle as mica growth, perpendicular to the principal stress. Metamorphic differentiation can be present at angles to protolith compositional banding.
|
|
J[ohn] Turkevich, P. C. Stevenson, J. Hillier, "A Study of the Nucleation and Growth Processes in the Synthesis of Colloidal Gold", Discuss. Faraday. Soc., 1951, 11, pp. 55–75, explains how to suspend gold nanoparticles in liquid. It owes its awakening to medicine, which now employs gold nanoparticles to detect tumors and deliver drugs.
|
|
Changing the solvent will change the intermolecular interactions and possibly lead to cocrystal formation. Also, by changing the solvent, phase considerations may be utilized. The role of a solvent in nucleation of cocrystals remains poorly understood but critical in order to obtain a cocrystal from solution. Cooling molten mixture of cocrystal formers often affords cocrystals.
|
|
Glass-ceramics are mostly produced in two steps: First, a glass is formed by a glass-manufacturing process. The glass is cooled down and is then reheated in a second step. In this heat treatment the glass partly crystallizes. In most cases nucleation agents are added to the base composition of the glass-ceramic.
|
|
These nucleation agents aid and control the crystallization process. Because there is usually no pressing and sintering, glass-ceramics have, unlike sintered ceramics, no pores. A wide variety of glass-ceramic systems exists, e.g., the Li2O × Al2O3 × nSiO2 system (LAS system), the MgO × Al2O3 × nSiO2 system (MAS system), the ZnO × Al2O3 × nSiO2 system (ZAS system).
|
|
Hydrohalite is a mineral that occurs in saturated halite brines at cold temperatures (below 0.1 °C). It was first described in 1847 in Dürrnberg, Austria. It exists in cold weather. Phase diagram of water–NaCl mixture Hydrohalite has a high nucleation energy, and solutions will normally need to be supercooled for crystals to form.
|
|
The gas will not necessarily form bubbles in the solvent at this stage, but supersaturation is necessary for bubble growth. A supersaturated solution of gases in a tissue may form bubbles if suitable nucleation sites exist. Supersaturation may be defined as a sum of all gas partial pressures in the liquid which exceeds the ambient pressure in the liquid.
|
|
Bubble formation occurs in the blood or other tissues. One of the hypothetical loci of bubble nucleation is in crevices in macromolecules. A solvent can carry a supersaturated load of gas in solution. Whether it will come out of solution in the bulk of the solvent to form bubbles will depend on a number of factors.
|
|
The evolution of vesiculation can be summarized in these steps: # The magma becomes progressively saturated with volatiles when water and carbon dioxide dissolves in it. Nucleation of bubbles start when then magma is supersaturated with these volatiles. # Bubbles continue to grow by diffusive transfer of water gases from the magma. Stresses buildup inside the volcanic dome.
|
|
In order to reach a stable state, cell nucleation takes place. During this step, the cells created would be much smaller than that of traditional foams. After this, cell growth, or matrix relaxation would initiate. The novelty of this method was the ability to control the mechanical properties of the product by varying the temperature and pressure inputs.
|
|
Moche history may be broadly divided into three periods – the emergence of the Moche culture in Early Moche (CE 100–300), its expansion and florescence during Middle Moche (CE 300–600), and the urban nucleation and subsequent collapse in Late Moche (CE 500–750).Bawden, G. 2004. "The Art of Moche Politics", in Andean Archaeology. (ed. H. Silverman).
|
|
She studied the chemistry of hot vents on the sea floor, which De Leeuw proposed could produce the organic molecules essential for life. She has also investigated biomaterials, such as the carbonated hydroxyapatite present in bone and teeth. She investigated the nucleation of calcium carbonate. De Leeuw was awarded a Royal Society Wolfson Research Merit Award in 2010.
|
|
Nevertheless, it can be prepared due to the relative ease of crystal nucleation and growth.T. L. Aselage J. Mater. Research, 13 (1998) pp. 1786–1794. Both SiB4 - x and SiB6 become superficially oxidized when heated in air or oxygen and each is attacked by boiling sulfuric acid and by fluorine, chlorine, and bromine at high temperatures.
|
|
It was suggested that the Cassie–Wenzel transition occurs via a nucleation mechanism starting from the drop center.C. Ishino, K. Okumura, Europhys. Lett., 2006, 76(3), 464–470. On the other hand, recent experiments showed that the Cassie–Wenzel transition is more likely to be due to the displacement of a triple line under an external stimulus.
|
|
While teaching, he earned a further degree, a D.Sc. in biological chemistry, from Nottingham in 1973. At Case Western, Walton served as Professor of Macromolecular Science. Walton's early research at Case involved the formation of crystals, or nucleation. In 1966, he was promoted to associate professor and granted tenure; he became a full professor in 1971.
|
|
This causes the water at that wall to become supercooled, create a counter- clockwise flow, and initially overpower the warm current. This plume is caused by a delay in the nucleation of the ice. Once ice begins to form, the flow returns to a similar pattern as before and the solidification propagates gradually until the flow is redeveloped.
|
|
This technique brings together protein and precipitation solutions without premixing them, but instead, injecting them through either sides of a channel, allowing equilibrium through diffusion. The two solutions come into contact in a reagent chamber, both at their maximum concentrations, initiating spontaneous nucleation. As the system comes into equilibrium, the level of supersaturation decreases, favouring crystal growth.
|
|
Stages in the intracellular lifecycle of L. monocytogenes: (Center) Cartoon depicting entry, escape from a vacuole, actin nucleation, actin-based motility, and cell-to-cell spread. (Outside) Representative electron micrographs from which the cartoon was derived. LLO, PLCs, and ActA are all described in the text. The cartoon and micrographs were adapted from Tilney and Portnoy (1989).
|
|
Schematic of actin comet tail formation by Listeria using ActA. The nucleation complex Arp2/3 is recruited to ActA, a WASP mimic. Actin filament polymerization then takes place at the posterior end of the bacterium, propelling it through the host cell cytoplasm in the anterior direction. Actin is one of the main cytoskeletal proteins in eukaryotic cells.
|
|
Stages in the intracellular life-cycle of Listeria monocytogenes. (Center) Cartoon depicting entry, escape from a vacuole, actin nucleation, actin-based motility, and cell-to-cell spread. (Outside) Representative electron micrographs from which the cartoon was derived. The two main examples of paracytophagy are the modes of cell-cell transmission of Listeria monocytogenes and Shigella flexneri.
|
|
Spherulitic texture is the result of cooling and nucleation of material in a magma which has achieved supersaturation in the crystal component. Thus it is often a subsolidus process in supercooler felsic rocks. Often, two minerals will grow together in the spherulite. Axiolitic texture results from spherulitic growth along fractures in volcanic glass, often from invasion of water.
|
|
In this two step method the oxide is ball-milled for longer periods of time to ensure a homogeneous solid solution of the oxide in the metal matrix. Then the powder is annealed at higher temperatures to begin a controlled nucleation of the nano-oxide clusters. Finally the powder is again compressed and sintered to yield the final material.
|
|
The water is sometimes mixed with ina (ice nucleation-active) proteins from the bacterium Pseudomonas syringae. These proteins serve as effective nuclei to initiate the formation of ice crystals at relatively high temperatures, so that the droplets will turn into ice before falling to the ground. The bacterium itself uses these ina proteins in order to injure plants.
|
|
This can happen for three reasons: # Lowering the temperature of the system lowers the vapor pressure. # Chemical reactions may increase the partial pressure of a gas or lower its vapor pressure. # The addition of additional vapor to the system may lower the equilibrium vapor pressure according to Raoult's law. There are two types of nucleation processes.
|
|
Arising from the repeated nucleation of shear bands and the continuous propagation of Lüders bands, this type consists of periodic locking serrations with abrupt increase in flow stress followed by drop of stress below the general level of the stress-strain curve. It is usually seen in the low temperature (high strain rate) part of the DS regime.
|
|
The basic result of Kerner's three-phase traffic theory about the nucleation nature of traffic breakdown (F → S transition) at a bottleneck shows the incommensurability of three-phase traffic theory with all earlier (standard) traffic flow theories. The term "incommensurability" has been introduced by Kuhn in his classical bookT.S. Kuhn, "The structure of scientific revolutions". Fourth edition.
|
|
The continuous phase consists of a concentrated, unfrozen liquid of sugars. The final average diameter of ice crystals depends on the rate of freezing. The faster this is, the more nucleation is promoted and the greater the number of small ice crystals. Usually, after a cooling treatment ice crystal dimensions in the freezer are about 35–80 µm.
|
|
This solution is capable of cooling to room temperature without forming crystals. By pressing on a metal disc within the heating pad, a nucleation center is formed, causing the solution to crystallize back into solid sodium acetate trihydrate. The bond-forming process of crystallization is exothermic. The latent heat of fusion is about 264–289 kJ/kg.
|
|
The chronology of nucleated villages is much debated and not yet clear. Yet there is strong evidence to support the view that nucleation occurred in the tenth century or perhaps the ninth, and was a development parallel to the growth of towns.Hamerow, Helena, David A. Hinton, and Sally Crawford, eds. The Oxford Handbook of Anglo-Saxon Archaeology.
|
|
Difficulties are encountered when trying to explain kaolinite formation under atmospheric conditions by extrapolation of thermodynamic data from the more successful high-temperature syntheses (as for example Meijer and Van der Plas, 1980 have pointed out). La Iglesia and Van Oosterwijk-Gastuche (1978) thought that the conditions under which kaolinite will nucleate can be deduced from stability diagrams, based as they are on dissolution data. Because of a lack of convincing results in their own experiments, La Iglesia and Van Oosterwijk-Gastuche (1978) had to conclude, however, that there were other, still unknown, factors involved in the low- temperature nucleation of kaolinite. Because of the observed very slow crystallization rates of kaolinite from solution at room temperature Fripiat and Herbillon (1971) postulated the existence of high activation energies in the low-temperature nucleation of kaolinite.
|
|
210, no. 6, 19 May 2000, pp. 277–288. Springer Nature , . Iwasa's work with Savage focused on identifying regulatory genes engaged in the formation of segment patterns in annelids, investigating a gene in leeches called Leech Zinc Finger II (LZF2), considered to be an orthologue of the hunchback (hb) gene in Drosophila. Iwasa, Savage, and Suver concluded that LZF2 likely plays an important part in the morphological progressions of gastrulation and the specification of the central nervous system in leeches but does not contribute to the formation of anteroposterior patterns. In 2007, she published an article on her research at the University of California with Mullins, "Spatial and temporal relationships between actin-filament nucleation, capping, and disassembly."Iwasa JH, Mullins RD. Spatial and temporal relationships between actin-filament nucleation, capping, and disassembly.
|
|
Growing graphene in an industrial resistive-heating cold wall CVD system was claimed to produce graphene 100 times faster than conventional CVD systems, cuts costs by 99 percent and produce material with enhanced electronic qualities. Cold wall CVD technique can be used to study the underlying surface science involved in graphene nucleation and growth as it allows unprecedented control of process parameters like gas flow rates, temperature and pressure as demonstrated in a recent study. The study was carried out in a home-built vertical cold wall system utilizing resistive heating by passing direct current through the substrate. It provided conclusive insight into a typical surface-mediated nucleation and growth mechanism involved in two-dimensional materials grown using catalytic CVD under conditions sought out in the semiconductor industry.
|
|
Rather, it is the physical structure of candies that contributes to the fountain effect. The structure of the Mentos is the most significant cause of the eruption due to nucleation. MythBusters reported that when fruit-flavored Mentos with a smooth waxy coating were tested in carbonated drink there was hardly a reaction, whereas mint-flavored Mentos (with no such coating) added to carbonated drink formed an energetic eruption, supporting the nucleation-site theory. According to MythBusters, the surface of the mint Mentos is covered with many small holes that increase the surface area available for reaction (and thus the quantity of reagents exposed to each other at any given time), thereby allowing CO2 bubbles to form with the rapidity and quantity necessary for the "jet"-, "geyser"-, or "eruption"-like nature of the effusion.
|
|
WRC recruitment to the sites of actin nucleation events at the cell periphery is mediated by the binding of a number of ligands containing a conserved WRC interacting receptor sequence (WIRS) which binds to a conserved location shared across the surfaces of Abi2 and CYFIP1. The WRC is activated by interaction with the Rac1 (via the CYFIP1 component of the complex) and Arf small GTPases (such as ARF1, ARF5, and ARF6 ) or the similar protein ARL1, which causes dissociation of the CYFIP1-Nap1-Abi2 heterotrimer at the membrane periphery. This allows the V domain of the WAVE1 component to interact with the actin monomers while its CA domain interacts with the Arp2/3 complex, allowing the Arp2/3 complex to act as a nucleation core for the branching and extension of actin filaments.
|
|
The empirical nucleation nature of traffic breakdown at highway bottlenecks cannot be explained by classical traffic theories and models. The search for explanation of the empirical nucleation nature of traffic breakdown (F → S phase transition) at a highway bottleneck has been the reason for the development of Kerner’s three-phase theory. In particular, in two-phase traffic flow models in which traffic breakdown is associated with free flow instability, this model instability leads to the F → J phase transition, i.e. in these traffic flow models traffic breakdown is governed by spontaneous emergence of a wide moving jam(s) in an initial free flow (see Kerner’s criticism on such two- phase models as well as on other classical traffic flow models and theories in Chapter 10 of the book as well as in critical reviews,).
|
|
The mechanism by which TPX2 promotes microtubule nucleation has yet to be determined. One proposed mechanism has been based on TPX2's role in directly suppressing tubulin subunit off-rates at the microtubule tip during microtubule assembly and disassembly, verified by fluorescence microscopy. This is made possible partially by TPX2's role in sequestering free tubulin subunits and nucleating small multi-subunit tubulin complexes, which inadvertently also slows the rate of growth by decreasing the effective free tubulin concentration. TPX2's stabilization of the microtubule in its polymer form therefore contributes to microtubule nucleation. Computational simulations speculate that TPX2 suppresses tubulin subunit kinetics at the microtubule tip by randomly increasing the bond stability between adjacent tubulin subunits. In addition, TPX2 has been shown to be important in chromatin-dependent spindle assembly. Even with duplicated centrosomes, TPX2 has been demonstrated to be required for formation of a stable bipolar spindle with overlapping antiparallel microtubule arrays. More specifically, TPX2 contributes to microtubule branching during spindle assembly by cooperating with augmin in order to amplify microtubule mass and preserve its polarity. Branching nucleation by TPX2 is observed without RanGTP, though more fan-shaped microtubule structures are formed when both RanGTP and TPX2 are present.
|
|
Also see the movie corresponding to this figure. Preprophase is an additional phase during mitosis in plant cells that does not occur in other eukaryotes such as animals or fungi. It precedes prophase and is characterized by two distinct events: #The formation of the preprophase band, a dense microtubule ring underneath the plasma membrane. #The initiation of microtubule nucleation at the nuclear envelope.
|
|
His interest in nanoparticles includes his master's thesis entitled, "Step Dynamics for Modeling of Crystal Surfaces." A focus on crystal structures and growth behavior continued with a focus on the nucleation, growth and design of nanoporous materials including zeolites and MOFs. His research on nanoparticle synthesis was frequently combined in the impact on applications including catalysis, adsorption, and separation via membranes.
|
|
Studies on induced seismicity have been ongoing since the 1970s. Focus on the cause of induced seismicity has shifted from activities related to conventional resources like mining to unconventional resource exploration and production. Barriers to understanding induced seismicity processes include lack of access to subsurface hydrogeological and geomechanical data, insufficient stress state data, and limited records of seismicity at the nucleation process scale.
|
|
15 The HiPCO process helps in producing high purity single walled carbon nanotubes in higher quantity. The HiPCO reactor operates at high temperature 900-1100 °C and high pressure ~30-50 bar. It uses carbon monoxide as the carbon source and Iron pentacarbonyl or Nickel tetracarbonyl as a catalyst. These catalyst acts as the nucleation site for the nanotubes to grow.
|
|
Plant cells lack centrioles or spindle pole bodies except in their flagellate male gametes, and they are entirely absent in the conifers and flowering plants.Marshall, W.F. (2009) Centriole Evolution. Current Opinion in Cell Biology 21(1), 14–19. Instead, the nuclear envelope itself appears to function as the main MTOC for microtubule nucleation and spindle organization during plant cell mitosis.
|
|
Retrieved 10 December 2017. In 2007, Iwasa gained teaching experience at Harvard Medical School with a course named "Visualizing Molecular Processes with Maya." In this course, she worked as a teaching assistant, writing tutorials and supervising projects. She also worked with another software platform at Harvard called Massive, adapting a program designed for video game animation to depict the process of nucleation elongation.
|
|
The association of PIP2 with villin inhibits the actin capping and severing action and increases actin binding at the headpiece region, possibly through structural changes in the protein. PIP2 increases actin bundling not only by decreasing the severing action of villin but also through dissociating capping proteins, releasing actin monomers from sequestering proteins and stimulating actin nucleation and cross linking.
|
|
In the cloud chamber, it is the clusters of ions caused by a passing high-energy particle that acts as nucleation centers. Actually, vapours seem to be much less finicky than solutions about the sort of nuclei required. This is because a liquid will condense on almost any surface, but crystallization requires the presence of crystal faces of the proper kind.
|
|
S. Parveen, R. J. Davey, G. Dent and R. G. Pritchard, Linking solution chemistry to crystal nucleation: the case of tetrolic acid, Chem. Commun. 2005, 1531–1533. The second type of approach take into account all the relevant crystal structures of a given compound and this constitutes a structural landscape.G. R. Desiraju, Crystal Engineering: From Molecule to Crystal, J. Am. Chem. Soc.
|
|
Lamellae form during crystallization from the melt. The arrow shows the direction of temperature gradient. Nucleation starts with small, nanometer-sized areas where as a result of heat motion some chains or their segments occur parallel. Those seeds can either dissociate, if thermal motion destroys the molecular order, or grow further, if the grain size exceeds a certain critical value.
|
|
The most used substrate is indium phosphide (InP). Other substrates like glass or ceramic can be applied for special applications. To facilitate nucleation, and to avoid tension in the grown layer the thermal expansion coefficient of substrate and grown layer should be similar. Centrifugal liquid-phase epitaxy is used commercially to make thin layers of silicon, germanium, and gallium arsenide.
|
|
After a surface is initially affected by cavitation, it tends to erode at an accelerating pace. The cavitation pits increase the turbulence of the fluid flow and create crevices that act as nucleation sites for additional cavitation bubbles. The pits also increase the components' surface area and leave behind residual stresses. This makes the surface more prone to stress corrosion.
|
|
The PCM is essential for nucleation and organization of microtubules. The centrosome cycle is important to ensure that daughter cells receive a centrosome after cell division. As the cell cycle progresses, the centrosome undergoes a series of morphological and functional changes. Initiation of the centrosome cycle occurs early in the cell cycle in order to have two centrosomes by the time mitosis occurs.
|
|
In a water-rich ouzo mixture the droplet coalescence is dramatically slowed without mechanical agitation, dispersing agents, or surfactants. It forms a stable homogeneous fluid dispersion by liquid-liquid nucleation. The size of the droplets has been measured by small-angle neutron scattering to be on the order of a micron. Smaller droplets, in order of 100 nanometers, were found in Limoncello.
|
|
Porphyritic structure is caused by the nucleation of crystal sites and the growth of crystals in a liquid magma. Often a magma can only grow one mineral at a time especially if it is cooling slowly. This is why most igneous rocks have only one type of phenocryst mineral. Rhythmic cumulate layers in ultramafic intrusions are a result of uninterrupted slow cooling.
|
|
During her undergraduate degree she decided she would pursue studying, and chose to for academics who were becoming increasingly interested in air quality and environmental issues. She moved to California Institute of Technology for her graduate studies, earning a Master's degree in 1985 and a doctorate in 1989. She was supervised by John H. Seinfeld and worked on binary nucleation.
|
|
The grain macrostructure in ingots and most castings have three distinct regions or zones: the chill zone, columnar zone, and equiaxed zone. The image below depicts these zones. 500px The chill zone is named so because it occurs at the walls of the mold where the wall chills the material. Here is where the nucleation phase of the solidification process takes place.
|
|
DMS, a product of DMSOR, is a component of the sulfur cycle. DMS is oxidized to Methanesulfonates, which nucleate cloud condensation over open oceans, where the alternative source of nucleation, dust, is absent. Cloud formation is a key component in increasing earth's albedo and regulating atmospheric temperature, thus this enzyme and the reaction it catalyzes could prove helpful on the climate control frontier.
|
|
The area religious institutions are Christian. Within the foreignry of St Ishmael to the west, a nucleation around Llansaint Church - which occupies a distinct, central location within the village - lies at the focus of a number of roads within a discrete area of former field strips. The Medieval All Saints Church, Llansaint, with a landmark tower, is Grade B listed.
|
|
Therefore, minerals in soil such as anorthite or wollastonite have no time for nucleation-crystal growth. This results in the color of celadon being closer to the gray side. In Goryeo celadon, quartz, black particles, bubbles, cracks can be observed too. The technical contribution of the celadon is that it has a white, black, or gray inlay to emphasize the grayish green color.
|
|
Liquid–vapor equilibrium If the vapor pressure exceeds the equilibrium value, it becomes supersaturated and condenses on any available nucleation sites e. g. particles of dust. This principle is used in cloud chambers, where particles of radiation are visualized because they nucleate formation of water droplets. The vapor pressure is the equilibrium pressure from a liquid or a solid at a specific temperature.
|
|
The commercially most important system is the Li2O × Al2O3 × nSiO2 system (LAS system). The LAS system mainly refers to a mix of lithium, silicon, and aluminum oxides with additional components, e.g., glass-phase-forming agents such as Na2O, K2O and CaO and refining agents. As nucleation agents most commonly zirconium(IV) oxide in combination with titanium(IV) oxide is used.
|
|
The increasing nucleation prevents the system from going to the spinodal. When the bubble radius reaches the critical size it continues to expand and eventually explodes resulting a mixture of gas and droplets which is termed as explosive boiling or phase explosion. At the beginning, explosive boiling was used by Martynyuk to calculate the critical temperature of metals. He used electric resistance to heat up metal wire.
|
|
Although pGSN is capable of initiating the polymerization of actin through nucleation, its primary relationship with it in blood is depolymerization through filament severing. Actin severing occurs rapidly in the presence of pGSN and Ca2+. pGSN wraps around filaments, non-enzymatically cleaving them. It remains attached, "capping" the barbed/plus end of the severed filament and inducing a torsional twist that is cooperative through its length.
|
|
Discovery of multiple binding sites in GAB proteins has led to the N-terminal folding nucleation (NFN) hypothesis for the structure of the disordered region. This theory suggests that the disordered domain is looped back to connect to the N-terminal, structured region several times to make the protein more compact. This would assist in promoting interactions between molecules bound to GAB and resisting degradation.
|
|
Hillert, M., A Theory of Nucleation for Solid Metallic Solutions, Sc. D. Thesis (MIT, 1955) Building on Hillert's work, a more flexible continuum model was subsequently developed by John W. Cahn and John Hilliard, who included the effects of coherency strains as well as the gradient energy term. The strains are significant in that they dictate the ultimate morphology of the decomposition in anisotropic materials.
|
|
Tubulin, gamma 1 is a protein in humans that is encoded by the TUBG1 gene. This gene encodes a member of the tubulin superfamily. The encoded protein localizes to the centrosome where it binds to microtubules as part of a complex referred to as the gamma-tubulin ring complex. The protein mediates microtubule nucleation and is required for microtubule formation and progression of the cell cycle.
|
|
Outcrop of orbicular granite near Caldera, Chile. Close-up of orbicular granite near Caldera, Chile. Orbicular granite (also known as orbicular rock or orbiculite) is an uncommon plutonic rock type which is usually granitic in composition. These rocks have a unique appearance due to orbicules - concentrically layered, spheroidal structures, probably formed through nucleation around a grain in a cooling magma chamber due to rapid physical changes.
|
|
Solute atoms, both deliberate additions and impurities, have a profound influence on the recrystallization kinetics. Even minor concentrations may have a substantial influence e.g. 0.004% Fe increases the recrystallization temperature by around 100 °C (Humphreys and Hatherly 2004). It is currently unknown whether this effect is primarily due to the retardation of nucleation or the reduction in the mobility of grain boundaries i.e. growth.
|
|
Another failure mode that may occur without any tearing is ductile fracture after plastic deformation (ductility). This may occur as a result of bending or shear deformation (inplane or through the thickness). The failure mechanism may be due to void nucleation and expansion on a microscopic level. Microcracks and subsequent macrocracks may appear when deformation of the material between the voids has exceeded the limit.
|
|
Isolated pools of liquid form inside solidified metal, which are called hot spots. The shrinkage defect usually forms at the top of the hot spots. They require a nucleation point, so impurities and dissolved gas can induce closed shrinkage defects. The defects are broken up into macroporosity and microporosity (or micro shrinkage), where macroporosity can be seen by the naked eye and microporosity cannot.
|
|
Such nuclei should immediately re- evaporate, and the emergence of a new phase at the equilibrium pressure, or even moderately above it should be impossible. Hence, the over-saturation must be several times higher than the normal saturation value for spontaneous nucleation to occur. There are two ways of resolving this paradox. In the first place, we know the statistical basis of the second law of thermodynamics.
|
|
Afterwards, the formation of aggregates or clusters from the new phase occurs gradually and randomly at the nanoscale. Subsequently, if the process is feasible, the nucleus is formed. Notice that the formation of aggregates is conceivable under specific conditions. When these conditions are not satisfied, a rapid creation-annihilation of aggregates takes place and the nucleation and posterior crystal growth process does not happen.
|
|
Using etching techniques such as focused ion beam milling, micro- or nano- sized pillars can be formed in magnetic materials. However, repeated bending of crystal pillars can cause defect formation and fatigue damage. This damage comes from the nucleation of cracks on the pillars surface, even in the elastic regime, due to localized plasticity. Crack propagation during successive compression and tension cycles can lead to pillar fracture.
|
|
During the intermediate period the transformation is rapid as the nuclei grow into particles and consume the old phase while nuclei continue to form in the remaining parent phase. Once the transformation approaches completion, there remains little untransformed material for further nucleation, and the production of new particles begins to slow. Additionally, the previously formed particles begin to touch one another, forming a boundary where growth stops.
|
|
There is about 300 times more gas than dust observed in the circumstellar material around S stars. It is believed to be made up of metallic iron, FeSi, silicon carbide, and forsterite. Without silicates and carbon, it is believed that nucleation is triggered by TiC, ZrC, and TiO2. Detached dust shells are seen around a number of carbon stars, but not S-type stars.
|
|
Nucleation is the step wherein the molecules start to gather into clusters, on the nanometer scale, arranging in a defined and periodic manner that defines the crystal structure. The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. The thermodynamics of freezing and melting is a classical discipline within physical chemistry, which nowadays develops in conjunction with computer simulations.
|
|
Solid GeTe can transform between amorphous and crystalline states. The crystalline state has a low resistivity (semiconducting at room temperature) and the amorphous state has a high resistivity. The difference in resistivity can be up to six orders of magnitude depending on the film quality, GeTe compositions, and nucleation site formation. The drastic changes in the properties of the material have been exploited in data storage applications.
|
|
As mentioned, microvilli are formed as cell extensions from the plasma membrane surface. Actin filaments, present in the cytosol, are most abundant near the cell surface. These filaments are thought to determine the shape and movement of the plasma membrane. The nucleation of actin fibers occurs as a response to external stimuli, allowing a cell to alter its shape to suit a particular situation.
|
|
The nucleation of bubbles causes a rapid expansion and cooling of the surrounding melt, producing glassy shards that may erupt explosively as tephra (also called pyroclastics). Fine-grained tephra is commonly referred to as volcanic ash. Whether a volcano erupts explosively or effusively as fluid lava depends on the composition of the melt. Felsic magmas of andesitic and rhyolitic composition tend to erupt explosively.
|
|
For this application, epitaxial growth on copper is a promising method. The carbon's solubility into copper is extremely low and therefore mainly surface diffusion and nucleation of carbon atoms are involved. Because of this and the growth kinetics, the graphene thickness is limited to predominantly a monolayer. The big advantage is that the graphene can be grown on Cu foil and subsequently transferred to for example SiO2.
|
|
Seth Lloyd has stated "they fail the Monty Python test: Stop that! That's too silly!" A New Scientist journalist summarizes that "the starting point for our understanding of the universe and its behavior is that humans, not disembodied brains, are typical observers." Some argue that brains produced via quantum fluctuation, and maybe even brains produced via nucleation in the de Sitter vacuum, don't count as observers.
|
|
The folding of the transition state is shown to be rate-determining, and even though it exists in a higher energy state than the native fold, it greatly resembles the native structure. Within the transition state, there exists a nucleus around which the protein is able to fold, formed by a process referred to as "nucleation condensation" where the structure begins to collapse onto the nucleus.
|
|
The protein encoded by this gene, a member of the Wiskott–Aldrich syndrome protein (WASP) family, plays a critical role downstream of Rac, a Rho-family small GTPase, through its involvement in the WAVE regulatory complex in regulating the actin cytoskeleton required for membrane ruffling. It has been shown to associate with an actin nucleation core Arp2/3 complex while enhancing actin polymerization in vitro.
|
|
Already studied by Bischoff (1968), magnesium ion is a long known inhibitor of calcite nucleation and crystal growth. The cation is the second-most abundant cation present in seawater after , as is the second anion after . Although closely resembling , the ionic radius of the naked cation is smaller. Some paradoxical consequences arise between its contrasted electrostatic behavior in the mineral solid phase and in aqueous solution.
|
|
Self-assembling films form templates that effect the nucleation of ceramic phases. The downside with this technique is its inability to form a segmented layered microstructure. Segmentation is an important property of nacre used for crack deflection of the ceramic phase without fracturing it. As a consequence, this technique does not mimic microstructural characteristics of nacre beyond the layered organic/inorganic layered structure and requires further investigation.
|
|
The ANTH domain is a membrane binding domain that shows weak specificity for PtdIns(4,5)P2. It was found in AP180 (homologous to CALM) endocytotic accessory protein that has been implicated in the formation of clathrin-coated pits. The domain is involved in phosphatidylinositol 4,5-bisphosphate binding and is a universal adaptor for nucleation of clathrin coats. Its structure is a solenoid of 9 helices.
|
|
J. Mech. Phys. Solids 52, 2683-2724. Moreover, great progresses have been made on numerical simulations, so that shear band nucleation and propagation in relatively complex situations can be traced numerically with finite element models, although still at the cost of a great computational effort. Of further interest are simulations that reveal the crystallographic orientation dependence of shear banding in single crystal and polycrystals.
|
|
In the processing of glass-ceramics, molten glass is cooled down gradually before reheating and annealing. In this heat treatment the glass partly crystallizes. In many cases, so-called 'nucleation agents' are added in order to regulate and control the crystallization process. Because there is usually no pressing and sintering, glass-ceramics do not contain the volume fraction of porosity typically present in sintered ceramics.
|
|
In a single de Sitter Universe with a cosmological constant, and starting from any finite spatial slice, the number of "normal" observers is finite and bounded by the heat death of the Universe. If the Universe lasts forever, the number of nucleated Boltzmann brains is, in most models, infinite; cosmologists such as Alan Guth worry that this would make it seem "infinitely unlikely for us to be normal brains". One caveat is that if the Universe is a false vacuum that locally decays into a Minkowski or a Big Crunch-bound anti- de Sitter space in less than 20 billion years, then infinite Boltzmann nucleation is avoided. (If the average local false vacuum decay rate is over 20 billion years, Boltzmann brain nucleation is still infinite, as the Universe increases in size faster than local vacuum collapses destroy the portions of the Universe within the collapses' future light cones).
|
|
A process of precipitation known as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle is known by the geologic community as a probable mechanism for Liesegang ring formation in sedimentary rocks. In this process the "...diffusion of reactants leads to supersaturation and nucleation; this precipitation results in localized band formation and depletion of reactants in adjacent zones." As Ostwald suggests, there is a localized formation of crystal seeds that occurs when the right level of supersaturation is reached, and once the crystal seeds form, the growth of the crystals is believed to lower the supersaturation level of fluids in pore spaces surrounding the crystals, thus mineralization that occurs after the initial crystal growth in the surrounding areas develops in bands or rings. One classic example based on the Ostwald-Liesegang hypothesis is observed in water and rock interactions where iron hydroxide precipitates in sandstone through pore space.
|
|
Several actin nucleators are present in mammalian cells. Cobl, Spire and Leiomodin form one group of such proteins because of their molecular mechanisms of actin nucleation all critically require their WH2 - a common motif found in all of these nucleators. Other protein containing WH2 domain have other functions. And other nucleators, such as formins, nucleate actin filaments using a different actin-binding motif, e.g. the FH2 (formin homology 2) domain.
|
|
Often phase separation will occur via nucleation during this transition, and spinodal decomposition will not be observed. To observe spinodal decomposition, a very fast transition, often called a quench, is required to move from the stable to the spinodally unstable region of the phase diagram. In some systems, ordering of the material leads to a compositional instability and this is known as a conditional spinodal, e.g. in the feldspars.
|
|
In this method, flow of methane and hydrogen gas is maintained in such a way that pressure inside the chamber is maintained at 40Torr. CH4 and H2 are dissociated at elevated temperature of 2100 °C with the help of Ta filament. Nucleation sites are created on the tip of the cantilever. Once CVD is complete, CH4 flow is stopped and the chamber is cooled under flow of H2.
|
|
Many halophilic bacteria and archaea are easy to maintain, and their high cellular osmotic pressure has been exploited in recombinant protein production. The cellular environments of halophiles can be fine-tuned to accommodate folding of protein of interest by adjusting the concentration of osmolytes in the culture medium. Successful expression and folding of Ice nucleation protein, GFP, α-amylase, nucleotide diphosphate kinase, and serine racemase have been reported in halophiles.
|
|
Pyrite takes the place of phyllosilicates in some BST deposits. Labile tissues are associated with framboids, as they produced many nucleation sites due to the rapid production of sulfides (perhaps by sulfur-reducing bacteria); recalcitrant tissues are associated with euhedra. It's not entirely clear whether pyrite is involved in the preservation of the anatomy, or whether they simply replace carbon films later in diagenesis (in the same fashion as phyllosilicates).
|
|
The hydroxyl moiety of the T residues fits well, when spaced as they are in the internal repeats, with the hydroxyl moieties of externally facing water molecules in the forming ice lattice. This mimics the formation of the growth cone at a nucleation site in the absence of AFPs. Thus, the binding of RiAFP inhibits the growth of the crystal in the basal and prism planes of the ice.
|
|
67,83 The seeds can be induced by impurities, plasticizers, fillers, dyes and other substances added to improve other properties of the polymer. This effect is poorly understood and irregular, so that the same additive can promote nucleation in one polymer, but not in another. Many of the good nucleating agents are metal salts of organic acids, which themselves are crystalline at the solidification temperature of the polymer solidification.
|
|
The methods used to determine the degree of crystallinity can be incorporated over time to measure the kinetics of crystallization. The most basic model for polymer crystallization kinetics comes from Hoffman nucleation theory. The crystallization process of polymers does not always obey simple chemical rate equations. Polymers can crystallize through a variety of different regimes and unlike simple molecules, the polymer crystal lamellae have two very different surfaces.
|
|
The characteristic features of tungsten deposition from the WF6/SiH4 are high speed, good adhesion and layer smoothness. The drawbacks are explosion hazard and high sensitivity of the deposition rate and morphology to the process parameters, such as mixing ratio, substrate temperature, etc. Therefore, silane is commonly used to create a thin tungsten nucleation layer. It is then switched to hydrogen, that slows down the deposition and cleans up the layer.
|
|
The protein encoded by this gene contains a formin homology 2 domain and has high sequence identity to the mouse Wbp3 protein. Two alternative transcripts encoding different isoforms have been described. The C-terminus has been shown to accelerate actin polymerization activity of this protein through its WH2-like motif. FMNL3 has been crystallized in complex with actin providing insight into the mechanism of formin-mediated actin nucleation.
|
|
The name was approved in the United States by the Advisory Committee on Antarctic Names (US-ACAN) in 1962. East Antarctica is generally higher than West Antarctica, and is considered the coldest place on Earth. The subglacial Gamburtsev Mountain Range, about the size of the European Alps, in the center of East Antarctica, are believed to have been the nucleation site for the East Antarctic Ice Sheet, just underneath Dome A.
|
|
Generally, if the melt is cooled slowly, nucleation of new crystals will be less than at large undercooling. The dendritic growth will result in dendrites of a large size. Conversely, a rapid cooling cycle with a large undercooling will increase the number of nuclei and thus reduce the size of the resulting dendrites (and often lead to small grains). Smaller dendrites generally lead to higher ductility of the product.
|
|
Millerite is a common metamorphic mineral replacing pentlandite within serpentinite ultramafics. It is formed in this way by removal of sulfur from pentlandite or other nickeliferous sulfide minerals during metamorphism or metasomatism. Millerite is also formed from sulfur poor olivine cumulates by nucleation. Millerite is thought to form from sulfur and nickel which exist in pristine olivine in trace amounts, and which are driven out of the olivine during metamorphic processes.
|
|
Low viscosity permits rapid nucleation and ion migration, necessary for crystal formation. The high silica content of rhyolitic lavas gives them much higher viscosities. Such lavas tend to form glass (obsidian) when they cool rapidly from a fully melted liquid state; though many obsidians also contain microlites. Low viscosity mafic magmas must be quenched very rapidly from a high temperature to form glass that is free of any crystalline content.
|
|
Born in 1902 in the city of Ústí nad Labem, Czech Republic, Bohemia, then in Austria-Hungary. He received a PhD from the University of Bern. In 1926, he became head of the department of Metallography X-ray Spectrography at the Technische Hochschule in Karlsruhe in Germany. His activities included work on crystal nucleation and on refrigeration technology, and experiments on the prevention of super cooling of water.
|
|
This combination of roles makes microtubules important for organizing and moving intracellular constituents. The organization of microtubules in the cell is cell-type specific. In epithelia, the minus-ends of the microtubule polymer are anchored near the site of cell-cell contact and organized along the apical-basal axis. After nucleation, the minus-ends are released and then re- anchored in the periphery by factors such as ninein and PLEKHA7.
|
|
Some cell types, such as plant cells, do not contain well defined MTOCs. In these cells, microtubules are nucleated from discrete sites in the cytoplasm. Other cell types, such as trypanosomatid parasites, have a MTOC but it is permanently found at the base of a flagellum. Here, nucleation of microtubules for structural roles and for generation of the mitotic spindle is not from a canonical centriole-like MTOC.
|
|
Generally, HY-80 is welded with an AWS ER100S-1 welding wire. The ER100S-1 has a lower Carbon and Nickel content to assist in the dilutive effect during welding discussed previously. An important function of the filler metal is to nucleate acicular ferrite. Acicular ferrite is formed with the presence of oxides and the composition of the filler metal can increase the formation of these critical nucleation sites.
|
|
Generally, polycrystals cannot be superheated; they will melt promptly once they are brought to a high enough temperature. This is because grain boundaries are amorphous, and serve as nucleation points for the liquid phase. By contrast, if no solid nucleus is present as a liquid cools, it tends to become supercooled. Since this is undesirable for mechanical materials, alloy designers often take steps against it (by grain refinement).
|
|
The liquid shell nucleation model (LSN) predicts that a surface layer of atoms melts prior to the bulk of the particle. The melting temperature of a nanoparticle is a function of its radius of curvature according to the LSN. Large nanoparticles melt at greater temperatures as a result of their larger radius of curvature. The model calculates melting conditions as a function of two competing order parameters using Landau potentials.
|
|
A study in 2008 provided further evidence of cyclin A/CDK2 complex's role in mitosis. Cells were modified so their CDK2 was inhibited and their cyclin A2 gene was knocked out. These mutants entered mitosis late due to a delayed activation of the cyclin B/CDK1 complex. Coupling of microtubule nucleation in the centrosome with mitotic events in the nucleus was lost in the cyclin A knockout/CDK2 inhibited mutant cells.
|
|
Assortment of Alnico magnets in 1956. Alnico 5, developed during World War 2, led to a new generation of compact permanent magnet motors and loudspeakers.Alnico's anisotropy is oriented along the desired magnetic axis by applying an external magnetic field to it during the precipitate particle nucleation, which occurs when cooling from to , near the Curie point. Without an external field there are local anisotropies of different orientations due to spontaneous magnetization.
|
|
As catalysis is carried out on the nanoparticle surface, the atoms at the center are wasted. This becomes more important when expensive metals are used as catalysts. To reduce the cost of the catalysts an inexpensive metal is made the core and the catalytically active metal is taken as the shell. This is achieved by first reducing the core metal followed by nucleation of the shell metal around it.
|
|
The ferroelectric memristor is based on a thin ferroelectric barrier sandwiched between two metallic electrodes. Switching the polarization of the ferroelectric material by applying a positive or negative voltage across the junction can lead to a two order of magnitude resistance variation: (an effect called Tunnel Electro-Resistance). In general, the polarization does not switch abruptly. The reversal occurs gradually through the nucleation and growth of ferroelectric domains with opposite polarization.
|
|
Monohydrocalcite forms via a Mg-rich amorphous calcium carbonate (ACC) precursor. This Mg-rich ACC forms rapidly (seconds) and then transforms to monohydrocalcite via dissolution and reprecipitation, with monohydrocalcite forming via a nucleation-controlled reaction like spherulitic growth. Recent studies have highlighted the importance of Mg in the formation process of monohydrocalcite. The presence of Mg in solution is known to inhibit the formation of vaterite and calcite.
|
|
A significant quantity of fibrils resulting from primary nucleation and fibril elongation may be formed during the lag phase and secondary steps, rather than only fibril elongation, can be the dominant processes contributing to fibril growth during the exponential phase. With this new model, any perturbing agents of amyloid fibril formation, such as putative drugs, metabolites, mutations, chaperones, etc., can be assigned to a specific step of fibril formation.
|
|
Further experiments by Svensmark and collaborators published in 2013Svensmark, Enghoff, Pedersen, Response of cloud condensation nuclei (>50 nm) to changes in ion-nucleation, Physics Letters A, Volume 377, Issue 37, 8 November 2013, Pages 2343–2347 that showed that aerosols with diameter larger than 50 nm are produced by ultraviolet light (from trace amounts of ozone, sulfur dioxide, and water vapor), large enough to serve as cloud condensation nuclei.
|
|
The company works with WatchWater water filters using a German-made media that works differently to traditional ion-exchange media for water hardness treatment. These new products include a technology known as Nucleation Assisted Crystallization (NAC) to break down hard limescale into nano particles that do not attach to coffee machine or boiler elements, nor do they produce a potentially harmful change in water pH to being mildly acidic.
|
|
Temperature also affects the rate of crystallization, with the fastest growth occurring between . Crystal nuclei (seeds) tend to form more readily if the honey is disturbed, by stirring, shaking, or agitating, rather than if left at rest. However, the nucleation of microscopic seed-crystals is greatest between . Therefore, larger but fewer crystals tend to form at higher temperatures, while smaller but more-numerous crystals usually form at lower temperatures.
|
|
On the basis of results from vibrational spectroscopy and modeling with density functional theory-optimized water clusters, they suggest that the reason might lie in the vast diversity and peculiar occurrence of different hydrogen bonds. Their key argument is that the number of strong hydrogen bonds increases as temperature is elevated. The existence of the small strongly- bonded clusters facilitates in turn the nucleation of hexagonal ice when warm water is rapidly cooled down.
|
|
Common pre-seeding methods include in-situ thermal decomposition of zinc acetate crystallites, spincoating of ZnO nanoparticles and the use of physical vapor deposition methods to deposit ZnO thin films. Pre-seeding can be performed in conjunction with top down patterning methods such as electron beam lithography and nanosphere lithography to designate nucleation sites prior to growth. Aligned ZnO nanowires can be used in dye-sensitized solar cells and field emission devices.
|
|
Small-angle laser light scattering has provided information about spatial density fluctuations or the shape of growing crystal grains. In addition, confocal laser scanning microscopy has been used to observe crystal growth near a glass surface. Electro-optic shear waves have been induced by an ac pulse, and monitored by reflection spectroscopy as well as light scattering. Kinetics of colloidal crystallization have been measured quantitatively, with nucleation rates being depending on the suspension concentration.
|
|
Streak seeding is a method first described during ICCBM-3 by Enrico Stura to induce crystallization in a straight line into a sitting or hanging drop for protein crystallization by introducing microseeds. The purpose is to control nucleation and understand the parameters that make crystals grow. It is also used to test any particular set of conditions to check if crystals could grow under such conditions. Result from streak seeding of protein crystals.
|
|
Pseudomonas syringae has ina (ice nucleation-active) genes that make INA proteins which translocate to the outer bacterial membrane on the surface of the bacteria, where the proteins act as nuclei for ice formation. Artificial strains of P. syringae known as ice-minus bacteria have been created to reduce frost damage. Pseudomonas syringae has been found in the center of hailstones, suggesting the bacterium may play a role in Earth's hydrological cycle.
|
|
Nucleation can be intentionally induced, for example to create a bubblegram in a solid. In medical ultrasound imaging, small encapsulated bubbles called contrast agent are used to enhance the contrast. In thermal inkjet printing, vapor bubbles are used as actuators. They are occasionally used in other microfluidics applications as actuators.R. J. Dijkink, J. P. van der Dennen, C. D. Ohl, A. Prosperetti,The ‘acoustic scallop’: a bubble-powered actuator, J. Micromech. Microeng.
|
|
Next, proteins undergo a nucleation phase, where submicroscopic sized protein aggregates, or particles, are generated. Growth of these particles is under Brownian diffusion control. Once the particles reach a critical size (0.1 µm to 10 µm for high and low shear fields, respectively), by diffusive addition of individual protein molecules to it, they continue to grow by colliding into each other and sticking or flocculating. This phase occurs at a slower rate.
|
|
Although immunogold labeling is typically used for transmission electron microscopy, when the gold is 'silver-enhanced' it can be seen using brightfield microscopy. The silver enhancement increases the particle size, also making scanning electron microscopy possible. In order to produce the silver-enhanced gold particles, colloidal gold particles are placed in an acidic enhancing solution containing silver ions. Gold particles then act as a nucleation site and silver is deposited onto the particle.
|
|
She is studying the ageing of aerosols using computational chemistry, mathematical modelling and spectroscopy. She gave a talk at 2014 TEDx Laurier University, To Dream and To Act. In 2015 she published a study showing that aqueous phases reactions of guaiacol and catechol with iron leads to the formation of secondary colored particles. This study highlighted additional pathways for particle growth in the atmosphere in addition to particle nucleation and growth from gas phase precursors.
|
|
The primary site of infection is the intestinal epithelium, where the bacteria invade nonphagocytic cells via the "zipper" mechanism. Uptake is stimulated by the binding of listerial internalins (Inl) to E-cadherin, a host cell adhesion factor, or Met (c-Met), hepatocyte growth factor. This binding activates certain Rho-GTPases, which subsequently bind and stabilize Wiskott Aldrich syndrome protein (WAsp). WAsp can then bind the Arp2/3 complex and serve as an actin nucleation point.
|
|
Surface modification of materials has often led to new and improved properties. Corrosion inhibition, polymer adhesion and nucleation, preparation of organic superconductor/insulator/high-Tc superconductor trilayer structures, and the fabrication of metal/insulator/superconductor tunnel junctions have been developed using surface-modified YBCO. These molecular layered materials are synthesized using cyclic voltammetry. Thus far, YBCO layered with alkylamines, arylamines, and thiols have been produced with varying stability of the molecular layer.
|
|
The SPB diameter depends on DNA content. A larger SPB diameter increases microtubule nucleation capacity of the SPB, which is important for chromosome segregation. All SPB proteins can be divided into three groups: core components, half-bridge components and components needed for connection with NE. There is no known motif or structure, that makes a protein belong to SPB, but analysis of known SPB proteins and their genes shows several common features.
|
|
This initiates adhesion forces between the particles. The next step, nucleation, is the process by which the native particles come together and are held with liquid bridges and capillary forces. Then, through coalescence or the growth phase, these small groups of particles come together to create larger particles until the particles are the desired size. Consolidation occurs as the agglomerates increase in density and strength through drying and collisions with other particles.
|
|
Studies demonstrated that FH2 domains protect the rapidly elongating barbed ends of filaments from the vast molar excesses of actin capping proteins. The precise mechanisms of actin filament nucleation remains an area of active investigation. The rate of FH2 movement while elongation on an actin filament matches the rate of actin subunit addition, which can exceed 100 subunits per second. Profilin as a ubiquitous actin-binding protein is associated with most actin monomers in cells.
|
|
The general principle governing the course of this irreversible geochemical reaction has been coined "breaking Ostwald's step rule".Deelman, J.C. (1999): "Low-temperature nucleation of magnesite and dolomite" , Neues Jahrbuch für Mineralogie, Monatshefte, pp. 289–302. There is some evidence for a biogenic occurrence of dolomite. One example is that of the formation of dolomite in the urinary bladder of a Dalmatian dog, possibly as the result of an illness or infection.
|
|
Nucleate boiling of water over a kitchen stove burner Nucleate boiling is characterized by the growth of bubbles or pops on a heated surface, which rises from discrete points on a surface, whose temperature is only slightly above the temperature of the liquid. In general, the number of nucleation sites is increased by an increasing surface temperature. An irregular surface of the boiling vessel (i.e., increased surface roughness) or additives to the fluid (i.e.
|
|
It is suggested that the predominant mechanism of cytochalasin B is the inhibition of actin filament polymerization through binding to the fast-growing (barbed) end of F-actin filaments. An alternative could involve capping proteins. By doing so, CB not only inhibits actin polymerization but also consecutive processes such as filament network build-up. This inhibition can affect all three major steps of actin polymerization # Nucleation: A core of minimal 3 actin monomers is formed.
|
|
Champagne is usually served in a Champagne flute, whose characteristics include a long stem with a tall, narrow bowl, thin sides and an etched bottom. The intended purpose of the shape of the flute is to reduce surface area, therefore preserving carbonation, as well as maximizing nucleation (the visible bubbles and lines of bubbles).Ames, D. L., Garrison, J. R., Gitlin, J., Herrmann, G., Isenstadt, S., Jenkins, M., ... & Winn, L. (2014). Shopping: Material Culture Perspectives.
|
|
If the nucleation starts later when the magma is very supersaturated, the distance between bubbles becomes smaller. Essentially if the magma rises rapidly to the surface, the system will be more out of equilibrium and supersaturated. When the magma rises there is competition between adding new molecules to the existing ones and creating new ones. The distance between molecules characterizes the efficiency of volatiles to aggregate to the new or existing site.
|
|
Whereas mantle dentin forms from the preexisting ground substance of the dental papilla, primary dentin forms through a different process. Odontoblasts increase in size, eliminating the availability of any extracellular resources to contribute to an organic matrix for mineralization. Additionally, the larger odontoblasts cause collagen to be secreted in smaller amounts, which results in more tightly arranged, heterogeneous nucleation that is used for mineralization. Other materials (such as lipids, phosphoproteins, and phospholipids) are also secreted.
|
|
Condensation and evaporation Aerosol partitioning theory governs condensation on and evaporation from an aerosol surface, respectively. Condensation of mass causes the mode of the particle-size distributions of the aerosol to increase; conversely, evaporation causes the mode to decrease. Nucleation is the process of forming aerosol mass from the condensation of a gaseous precursor, specifically a vapor. Net condensation of the vapor requires supersaturation, a partial pressure greater than its vapor pressure.
|
|
It is suggested that if a framework does not possess this property then it cannot be feasibly synthesised. # As zeolites are metastable, certain frameworks may be inaccessible as nucleation cannot occur because more stable and energetically favourable zeolites will form. Post-synthetic modification has been used to combat this issue with the ADOR method, whereby frameworks can be cut apart into layers and bonded back together by either removing silica bonds or including them.
|
|
Ice-minus bacteria is a common name given to a variant of the common bacterium Pseudomonas syringae (P. syringae). This strain of P. syringae lacks the ability to produce a certain surface protein, usually found on wild-type P. syringae. The "ice-plus" protein (INA protein, "Ice nucleation-active" protein) found on the outer bacterial cell wall acts as the nucleating centers for ice crystals. This facilitates ice formation, hence the designation "ice- plus".
|
|
Different oils have different evaporation permeabilities, therefore yielding changes in concentration rates from different percipient/protein mixture. It is extremely difficult to predict good conditions for nucleation or growth of well-ordered crystals. In practice, favorable conditions are identified by screening; a very large batch of the molecules is prepared, and a wide variety of crystallization solutions are tested. Hundreds, even thousands, of solution conditions are generally tried before finding the successful one.
|
|
In liquid- assisted grinding, or kneading, a small or substoichiometric amount of liquid (solvent) is added to the grinding mixture. This method was developed in order to increase the rate of cocrystal formation, but has advantages over neat grinding such as increased yield, ability to control polymorph production, better product crystallinity, and applies to a significantly larger scope of cocrystal formers. and nucleation through seeding. Supercritical fluids (SCFs) serve as a medium for growing cocrystals.
|
|
In this method, the metastable form acts as an unstable intermediate on the nucleation pathway to a cocrystal. As always, a clear connection between pairwise components of the cocrystal is needed in addition to the thermodynamic requirements in order to form these compounds. Importantly, the phase that is obtained is independent of the synthetic methodology used. It may seem facile to synthesize these materials, but on the contrary the synthesis is far from routine.
|
|
She has focussed on ink-jet printed two- dimensional materials as well as nanotubes for sensors, photodetectors and solar cells. Casiraghi was awarded a European Research Council (ERC) consolidator grant to study the Nucleation of Organic Crystals on 2D Templates. She has also demonstrated diamond-like carbon can be to increase storage density of data storage. Outside of academia, Casiraghi has contributed to popular science segments for BBC Radio 4 and The Guardian.
|
|
Boiling chips A boiling chip, boiling stone, porous bit or anti-bumping granule is a tiny, unevenly shaped piece of substance added to liquids to make them boil more calmly. Boiling chips are frequently employed in distillation and heating. When a liquid becomes superheated, a speck of dust or a stirring rod can cause violent flash boiling. Boiling chips provide nucleation sites so the liquid boils smoothly without becoming superheated or bumping.
|
|
Frogs, mice, or small fish were killed after one to two minutes of exposure, replicating Langevin's earlier observation. Wood and Loomis also investigated the formation of emulsions and fogs, crystallization and nucleation, chemical reactions, interference patterns, and standing waves in solids and liquids under high-intensity ultrasound. After completing this broad array of experiments, Wood returned to optics and did not return to ultrasonic work. Loomis would go on to advance the science further with other collaborators.
|
|
In addition to the three C-terminal WH2 domains, also the presence of the linker region L2 between the second and third WH2 domain was of importance for Cobl-mediated actin nucleation. Cobl assembles non-bundled, unbranched actin filaments. In contrast to other actin nucleators, which are directly or indirectly via their activators controlled by Rho type GTPases, Cobl hereby is controlled by calcium/calmodulin signalling and by arginine methylation brought about by the arginine methyltransferase 2 PRMT2.
|
|
Some of the most typical are small inclusions, or cuts, in the container the crystal is being grown on. This includes scratches on the sides and bottom of glassware. A common practice in crystal growing is to add a foreign substance, such as a string or a rock, to the solution, thereby providing nucleation sites for facilitating crystal growth and reducing the time to fully crystallize. The number of nucleating sites can also be controlled in this manner.
|
|
PiezoMEMS still face many difficulties that impede its ability to be successfully commercialized. For instance, the success of depositing uniform films of piezoelectrics still depend heavily on the use of appropriate layers of proper nucleation and film growth. As a result, extensive device-specific development efforts are needed to create a proper sensor structure. In addition, researchers continue to search for ways to reduce and control the material and sensor drift and aging characteristics of thin film piezoelectric materials.
|
|
The primary provoking agent in decompression sickness is bubble formation from excess dissolved gases. Various hypotheses have been put forward for the nucleation and growth of bubbles in tissues, and for the level of supersaturation which will support bubble growth. The earliest bubble formation detected is subclinical intravascular bubbles detectable by doppler ultrasound in the venous systemic circulation. The presence of these "silent" bubbles is no guarantee that they will persist and grow to be symptomatic.
|
|
Bubble formation can occur in the blood or other tissues. A solvent can carry a supersaturated load of gas in solution. Whether it will come out of solution in the bulk of the solvent to form bubbles will depend on a number of factors. Something which reduces surface tension, or adsorbs gas molecules, or locally reduces solubility of the gas, or causes a local reduction in static pressure in a fluid may result in a bubble nucleation or growth.
|
|
The microtubule-organizing center (MTOC) is a structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division. The MTOC is a major site of microtubule nucleation and can be visualized in cells by immunohistochemical detection of γ-tubulin. The morphological characteristics of MTOCs vary between the different phyla and kingdoms.
|
|
She was awarded a National Science Foundation CAREER Award to develop an interdisciplinary framework for the fundamental understanding and prediction of earthquake processes. The unique computational framework developed by Lapusta and collaborators have provided transformative insights into the nature of earthquake processes and fault slip across scales. The model can predict the seismic (fast) and aseismic (slow) behaviour. She used this model to simulate various fault behaviours, including earthquake nucleation, post- seismic slip and inter-seismic deformation.
|
|
As the subgrain boundaries absorb dislocations, the subgrains transform into grains by rotation, instead of growth. This process generally occurs at elevated temperatures, which allows dislocations to both glide and climb; at low temperatures, dislocation movement is more difficult and the grains are less mobile. By contrast, discontinuous dynamic recrystallization involves nucleation and growth of new grains, where due to increased temperature and/or pressure, new grains grow at high angles compared to the surrounding grains.
|
|
In order to decrease the value of the critical radius r_c and promote nucleation, a supercooling or superheating process may be used. Supercooling is a phenomenon in which the system's temperature is lowered under the phase transition temperature without the creation of the new phase. Let \Delta T = T_f - T be the temperature difference, where T_f is the phase transition temperature. Let \Delta g_v = \Delta h_v - T \Delta s_v be the volume Gibbs free energy, enthalpy and entropy respectively.
|
|
It builds a 3-D bio- matrix with binding sites for Calcium-ions serving as nucleation point for hydroxyapatite (tooth mineral) formation. The high affinity to tooth mineral is based on matching distances of Ca-ion binding sites on P11-4 and Ca spacing in the crystal lattice of hydroxyapatite. The matrix formation is pH controlled and thus allows control matrix activity and place of formation. Self assembling properties of P11-4 are used to regenerate early caries lesions.
|
|
To accommodate such constraints while maintaining sinusoidal geometry, less competent layers would need to be subjected to extensive flow. Kinked, yielding and highly localized hinges with straight limbs greatly reduce the geometrical need for deformation. Chevron folds are energetically preferred to conventional sinusoidal folds as they minimize ductile flow to the expense of localized bending. Four stages mark development of chevron folds: sinusoidal nucleation, concentric folding, straightening of limbs/sharpening of hinges, and tightening of the chevron fold.
|
|
Centrosomal protein of 192 kDa, also known as Cep192, is a protein that in humans is encoded by the CEP192 gene. It is the homolog of the C. elegans and D. melanogaster gene SPD-2. Cep192 is a major regulator of pericentriolar material recruitment, centrosome maturation, and centriole duplication in mammalian cells. It stimulates the formation of the scaffolding upon which gamma tubulin ring complexes and other proteins involved in microtubule nucleation and spindle assembly become functional during mitosis.
|
|
Nucleation is the event that initiates the formation of microtubules from the tubulin dimer. Microtubules are typically nucleated and organized by organelles called microtubule-organizing centres (MTOCs). Contained within the MTOC is another type of tubulin, γ-tubulin, which is distinct from the α- and β-subunits of the microtubules themselves. The γ-tubulin combines with several other associated proteins to form a lock washer-like structure known as the "γ-tubulin ring complex" (γ-TuRC).
|
|
Statue of Aryabhata on the grounds of IUCAA, Pune The Inter-University Centre for Astronomy and Astrophysics (IUCAA) is an autonomous institution set up by the University Grants Commission to promote nucleation and growth of active groups in astronomy and astrophysics in Indian universities. IUCAA is located in the University of Pune campus next to the National Centre for Radio Astrophysics, which operates the Giant Metrewave Radio Telescope. IUCAA has a campus designed by Indian architect Charles Correa.
|
|
This can be advantageous because fine-grained castings possess better properties than coarse-grained castings. A fine grain structure can be induced by grain refinement or inoculation, which is the process of adding impurities to induce nucleation. All of the nucleations represent a crystal, which grows as the heat of fusion is extracted from the liquid until there is no liquid left. The direction, rate, and type of growth can be controlled to maximize the properties of the casting.
|
|
In a sense, the RRE acts as a scaffolding platform onto which a specific and co-operative complex of Revs (and eventually cellular export machinery) assembles. This cooperativity that is dictated by RRE structure and sequence is required for the formation of a high affinity, export-competent complex. Current models of Rev assembly on the RRE suggest an initial Rev nucleation event at stem IIB followed by progressive addition of Rev molecules to form the full complex.
|
|
Microtubules of the eukaryotic cytoskeleton perform essential and diverse functions and are composed of a heterodimer of alpha and beta tubulins. The genes encoding these microtubule constituents belong to the tubulin superfamily, which is composed of six distinct families. Genes from the alpha, beta and gamma tubulin families are found in all eukaryotes. The alpha and beta tubulins represent the major components of microtubules, while gamma tubulin plays a critical role in the nucleation of microtubule assembly.
|
|
The resulting displacement of calcium for water destabilizes the lipid-water interface and promotes intimate interbilayer contact. A recently proposed alternative hypothesis is that the binding of calcium induces a destabilizing lateral tension. Whatever the mechanism of calcium-induced fusion, the initial interaction is clearly electrostatic, since zwitterionic lipids are not susceptible to this effect. In the fusion process, the lipid head group is not only involved in charge density, but can affect dehydration and defect nucleation.
|
|
Recovery is related to the similar process of recrystallization and grain growth, each of them being stages of annealing. Recovery competes with recrystallization, as both are driven by the stored energy, but is also thought to be a necessary prerequisite for the nucleation of recrystallized grains. It is so called because there is a recovery of the electrical conductivity due to a reduction in dislocations. This creates defect-free channels, giving electrons an increased mean-free path.
|
|
In 1954, Cahn joined the chemical metallurgy research effort at the General Electric laboratory in Schenectady, New York, led by David Turnbull. Turnbull had done pioneering work on the kinetics of nucleation, and there was a focus in the group on understanding the thermodynamics and kinetics of phase transformations in solids. In 1964, Cahn became a professor in the Department of Metallurgy (now Materials Science) at the Massachusetts Institute of Technology. He left MIT in 1978.
|
|
Microtubules of the eukaryotic cytoskeleton perform essential and diverse functions and are composed of a heterodimer of alpha and beta tubulin. The genes encoding these microtubule constituents are part of the tubulin superfamily, which is composed of six distinct families. Genes from the alpha, beta and gamma tubulin families are found in all eukaryotes. The alpha and beta tubulins represent the major components of microtubules, while gamma tubulin plays a critical role in the nucleation of microtubule assembly.
|
|
Chaperone-usher fimbriae (CU) are linear, unbranching, outer-membrane pili secreted by gram-negative bacteria through the chaperone-usher system rather than through type IV secretion or extracellular nucleation systems. These fimbriae are built up out of modular pilus subunits, which are transported into the periplasm in a Sec dependent manner. Chaperone-usher secreted fimbriae are important pathogenicity factors facilitating host colonisation, localisation and biofilm formation in clinically important species such as uropathogenic Escherichia coli and Pseudomonas aeruginosa.
|
|
Microtubules of the eukaryotic cytoskeleton perform essential and diverse functions and are composed of a heterodimer of alpha and beta tubulin. The genes encoding these microtubule constituents are part of the tubulin superfamily, which is composed of six distinct families. Genes from the alpha, beta and gamma tubulin families are found in all eukaryotes. The alpha and beta tubulins represent the major components of microtubules, while gamma tubulin plays a critical role in the nucleation of microtubule assembly.
|
|
Researchers determined that this particular point marks the position where the suspension is in an equilibrium state (i.e. freezing temperature and suspension temperature are equal). We can say then that the size of the initial and transition zones are controlled by the extent of supercooling beyond the already low freezing temperature. If the freeze-casting setup is controlled so that nucleation is favored at only small supercooling, then the TZ will give way to the SSZ sooner.
|
|
Lagrangian sedimentation is calculated by following individual nitric acid trihydrate (NAT) particles that may grow or shrink by the uptake or release of HNO3 from/to the gas phase. These particle parcels are simulated independently from the Lagrangian air parcels. Their trajectories are determined using the horizontal winds and their vertical settling velocity that depends on the size of the individual particles. NAT particles are nucleated assuming a constant nucleation rate and they evaporate where temperatures grow too high.
|
|
Schematic of directional solidification Directional solidification uses a thermal gradient to promote nucleation of metal grains on a low temperature surface, as well as to promote their growth along the temperature gradient. This leads to grains elongated along the temperature gradient, and significantly greater creep resistance parallel to the long grain direction. In polycrystalline turbine blades, directional solidification is used to orient the grains parallel to the centripetal force. It is also known as dendritic solidification.
|
|
Chromosomes attach to the mitotic spindle through sister kinetochores, in a bipolar orientation During the synthesis phase (S phase) in the cell cycle, the centrosome starts to duplicate. Just at the beginning of mitosis, both centrioles in each centrosome reach their maximal length, centrosomes recruit additional material and their nucleation capacity for microtubules increases. As mitosis progresses, both centrosomes separate to establish the mitotic spindle. In this way, the spindle in a mitotic cell has two poles emanating microtubules.
|
|
Unlike saltwater bead nucleation, this process is not considered difficult, and technicians need only minimum training to perform the operation. The technician creates small incisions on the upper valve, and inserts the tissue piece. A small twist of the tissue upon insertion is believed to create a higher ratio of round pearls. After the maximum number of grafts have been performed, the mussel is flipped, and the procedure is performed once again on the other valve of the shell.
|
|
Snowflakes by Wilson Bentley, 1902. Snow crystals form when tiny supercooled cloud droplets (about 10 μm in diameter) freeze. These droplets are able to remain liquid at temperatures lower than , because to freeze, a few molecules in the droplet need to get together by chance to form an arrangement similar to that in an ice lattice; then the droplet freezes around this "nucleus." Experiments show that this "homogeneous" nucleation of cloud droplets only occurs at temperatures lower than .
|
|
Paul Alivisatos, from the University of California Berkeley, is also notable for his research on the fabrication and use of nanocrystals. This research has the potential to develop insight into the mechanisms of small scale particles such as the process of nucleation, cation exchange, and branching. A notable application of these crystals is the development of quantum dots. Peidong Yang, another researcher from the University of California, Berkeley, is also notable for his contributions to the development of 1-dimensional nanostructures.
|
|
She has worked on strain relaxation in lattice-mismatched semiconductor heterostructures, diffusion barriers and electrical contacts for silicon and III-V semiconductor based devices, epitaxial growth and nucleation, and electron transport through thin films and interfaces. Her work on characterization tools including electron microscopy, Rutherford backscattering, x-ray diffraction, and scanning probe microscopy. She is a Fellow of the Institute of Physics and is the author of over 130 journal papers and conference proceedings, as shown in the Web of Science.
|
|
Unlike mitotic cells, human and mouse oocytes do not have centrosomes to produce the meiotic spindle. In mice, approximately 80 MicroTubule Organizing Centers (MTOCs) form a sphere in the ooplasm and begin to nucleate microtubules that reach out towards chromosomes, attaching to the chromosomes at the kinetochore. Over time the MTOCs merge until two poles have formed, generating a barrel shaped spindle. In human oocytes spindle microtubule nucleation begins on the chromosomes, forming an aster that eventually expands to surround the chromosomes.
|
|
Working model of Cobl-induced actin nucleation. Cobl is responsible for the actin polymerization of filaments with fast- growing barbed ends. Cobl stabilizes a longitudinal actin-GTP dimer by two consecutive WH2 domains and it can interact laterally with another actin monomer to form an actin trimer. Rearrangements of the actin–actin contacts have to occur within this trimer to make a helical nucleus; the third WH2 domain of Cobl has been proposed to interact with the third actin subunit of this trimer.
|
|
If a brand- new piece of glassware or a plastic container is used, crystals may not form because the container surface is too smooth to allow heterogeneous nucleation. On the other hand, a badly scratched container will result in many lines of small crystals. To achieve a moderate number of medium-sized crystals, a container which has a few scratches works best. Likewise, adding small previously made crystals, or seed crystals, to a crystal growing project will provide nucleating sites to the solution.
|
|
Thus, the Arp2/3 complex binds to pre-existing filaments so that the new filaments can grow on the old ones and form a functional actin cytoskeleton. Capping proteins limit actin polymerization to the region activated by the Arp2/3 complex, and the elongated filament ends are recapped to prevent depolymerization and thus conserve the actin filament. The Arp2/3 complex simultaneously controls nucleation of actin polymerization and branching of filaments. Moreover, autocatalysis is observed during Arp2/3-mediated actin polymerization.
|
|
Nucleation is endoepithelial in Neopilina and Nautilus, but exoepithelial in the bivalves and gastropods. The formation of the shell involves a number of genes and transcription factors. On the whole, the transcription factors and signalling genes are deeply conserved, but the proteins in the secretome are highly derived and rapidly evolving. engrailed serves to demark the edge of the shell field; dpp controls the shape of the shell, and Hox1 and Hox4 have been implicated in the onset of mineralization.
|
|
This protein can interact with the ssDNA- binding protein RPA, BRCA2, PALB2 and RAD52. The structural basis for Rad51 filament formation and its functional mechanism still remain poorly understood. However, recent studies using fluorescent labeled Rad51 have indicated that Rad51 fragments elongate via multiple nucleation events followed by growth, with the total fragment terminating when it reaches about 2 μm in length. Disassociation of Rad51 from dsDNA, however, is slow and incomplete, suggesting that there is a separate mechanism that accomplishes this.
|
|
Dr. Lindow, now a plant pathologist at the University of California-Berkeley, found that when this particular bacterium was introduced to plants where it is originally absent, the plants became very vulnerable to frost damage. He went on to identify the bacterium as P. syringae, investigate the role of P. syringae in ice nucleation and in 1977, discover the mutant ice-minus strain. He was later successful at developing the ice-minus strain of P. syringae through recombinant DNA technology, as well.
|
|
The crystal growth is the subsequent size increase of the nuclei that succeed in achieving the critical cluster size. Crystal growth is a dynamic process occurring in equilibrium where solute molecules or atoms precipitate out of solution, and dissolve back into solution. Supersaturation is one of the driving forces of crystallization, as the solubility of a species is an equilibrium process quantified by Ksp. Depending upon the conditions, either nucleation or growth may be predominant over the other, dictating crystal size.
|
|
When cloud seeding, increased snowfall takes place when temperatures within the clouds are between . Introduction of a substance such as silver iodide, which has a crystalline structure similar to that of ice, will induce freezing nucleation. In mid-altitude clouds, the usual seeding strategy has been based on the fact that the equilibrium vapor pressure is lower over ice than over water. The formation of ice particles in supercooled clouds allows those particles to grow at the expense of liquid droplets.
|
|
A few of his lab's notable scientific contributions include the structural and molecular mechanism of DNA end resection by RecBCD (E. coli) and DNA2-Sgs1-RPA and regulatory stimulation by Top3-Rmi1 and Mre11-Rad50-Xrs2 (S. cerevisiae), the kinetics of RecA filament nucleation and growth and regulation by RecFOR (E. coli), the purification and molecular mechanism of the human breast cancer susceptibility gene BRCA2 (humans), the mechanism of the Holliday junction dissolution by the Bloom's Syndrome helicase (BLM) homologue, Sgs1 (S.
|
|
The BiFC system has been applied to record ribosome biogenesis events in E.coli. The process of ribosomes assembly involves nucleation of ribosomal proteins in proper order and orientation. Perturbations in assembly can lead to structural defects in ribosomal subunits which as a result cannot join in the correct orientation to form fully functional ribosomes. Thus, the events of subunit joining signaled by the appearance of BiFC is an easy way to monitor ribosome biogenesis in contrast to laborious polysome profiling methods.
|
|
More ammonia and air is added for oxidation. The solution is removed from the autoclave and sulfuric acid added to remove nickel as nickel(II) sulfate-ammonium sulfate hexahydrate ((NiSO4)•((NH4)2SO4)•6H2O) which is then sent to have its nickel recovered. The solution is then further reduced with more sulfuric acid and cobalt metal powder is added to aid in the nucleation of precipitants (seeding). Addition of hydrogen gas to saturation precipitates cobalt powder with a purity of approximately 99.6%.
|
|
Thermal creep in irradiated materials is negligible, by comparison to the irradiation creep, which can exceed 10−6sec−1. The mechanism is not enhanced diffusivities, as would be intuitive from the elevated temperature, but rather interaction between the stress and the developing microstructure. Stress induces the nucleation of loops, and causes preferential absorption of interstitials at dislocations, which results in swelling. Swelling, in combination with the embrittlement and hardening, can have disastrous effects on any nuclear material under substantial pressure.
|
|
Centrosomes are composed of two centrioles arranged at right-angles to each other, and surrounded by a dense, highly structured mass of protein termed the pericentriolar material (PCM). The PCM contains proteins responsible for microtubule nucleation and anchoring including γ-tubulin, pericentrin and ninein. In general, each centriole of the centrosome is based on a nine triplet microtubule assembled in a cartwheel structure, and contains centrin, cenexin and tektin. In many cell types the centrosome is replaced by a cilium during cellular differentiation.
|
|
In 2015, researchers in the George Washington University discovered a new pathway to synthesize MWCNTs by electrolysis of molten carbonates. The mechanism is similar to CVD. Some metal ions were reduced to a metal form and attached on the cathode as the nucleation point for the growing of CNTs. The reaction on the cathode is :Li2CO3 -> Li2O + CNTs + O2 The formed lithium oxide can in-situ absorb carbon dioxide (if present) and form lithium carbonate, as shown in the equation.
|
|
The mechanics of this process are poorly understood, partly because it is difficult to recreate the high sliding velocities in a laboratory. Also the effects of strong ground motion make it very difficult to record information close to a nucleation zone. Rupture propagation is generally modeled using a fracture mechanics approach, likening the rupture to a propagating mixed mode shear crack. The rupture velocity is a function of the fracture energy in the volume around the crack tip, increasing with decreasing fracture energy.
|
|
Cortactin (from " _cort_ ical _actin_ binding protein") is a monomeric protein located in the cytoplasm of cells that can be activated by external stimuli to promote polymerization and rearrangement of the actin cytoskeleton, especially the actin cortex around the cellular periphery. It is present in all cell types. When activated, it will recruit Arp2/3 complex proteins to existing actin microfilaments, facilitating and stabilizing nucleation sites for actin branching. Cortactin is important in promoting lamellipodia formation, invadopodia formation, cell migration, and endocytosis.
|
|
A novel application for dual-polarization interferometry emerged in 2008, where the intensity of light passing through the waveguide is extinguished in the presence of crystal growth. This has allowed the very earliest stages in protein crystal nucleation to be monitored. Later versions of dual- polarization interferometers also have the capability to quantify the order and disruption in birefringent thin films. This has been used, for example, to study the formation of lipid bilayers and their interaction with membrane proteins.
|
|
The liquid nucleation and growth model (LNG) treats nanoparticle melting as a surface initiated process. The surface melts initially, and the liquid-solid interface quickly advances through the entire nanoparticle. The LNG defines melting conditions through the Gibbs-Duhem relations, yielding a melting temperature function dependent on the interfacial energies between the solid and liquid phases, volumes and surface areas of each phase, and size of the nanoparticle. The model calculations show that the liquid phase forms at lower temperatures for smaller nanoparticles.
|
|
A formin dimer remains constantly bound to the plus end of an actin filament despite ongoing polymerization. One formin of a dimer dissociates from the barbed end to take the next step while the second formin of the dimer remains bound. Thus the formin dimer processively adds actin monomers to the barbed end and are constantly present at the barbed end of an actin filament (processive capping). The FH1 domain recruits actin monomers through profilin binding, but it does not promote nucleation.
|
|
In order to mimic a mature bone matrix, self-assembled fibrils can be used to align a given mineral matrix. This is accomplished using a self- assembling molecule with a hydrophobic alkyl tail and a hydrophilic oligopeptide head. These molecules form micellar structures in situ, and disulfide bridges at low pH, leading to the formation and crystallization of 200 kDa polymeric nanofibrils. The mineral matrix ultimately interacts with the synthetic fibril via a phosphoserine residue which results in mineral nucleation and growth.
|
|
In vitro studies showed that a concentration of 30 μM of cytochalasin B significantly reduces the relative viscosity of a 20 μM normal actin filament solution as well as it has decreased in a 20 μMm gluthathionyl- actin filament solution. In vivo the effective concentration is even lower. It seemed that a 2 μM concentration is sufficient in living cells to accomplish a measurable influence on the actin polymerization. The nucleation phase took 2-4 times as long as in the control groups.
|
|
Finally, he was professor of materials science and engineering at Johns Hopkins University. He was awarded the Department of Commerce Gold Medal in 1965, the Samuel Wesley Stratton Award of the National Bureau of Standards in 1967, and the Presidential Rank Award of Meritorious Executive. He published over 60 scientific papers, but is best remembered for his 1961 work with John I. Lauritzen on Hoffman nucleation theory. Hoffman died from congestive heart failure at George Washington University Hospital on February 21, 2004.
|
|
Slip in the material is localized at these PSBs, and the exaggerated slip can now serve as a stress concentrator for a crack to form. Nucleation and growth of a crack to a detectable size accounts for most of the cracking process. It is for this reason that cyclic fatigue failures seem to occur so suddenly where the bulk of the changes in the material are not visible without destructive testing. Even in normally ductile materials, fatigue failures will resemble sudden brittle failures.
|
|
1998, 114. The copper content must be greater than the lime content in order to create a blue frit.Tite et al. 1998, 112-113. Ultimately the frit consists of cuprorivaite (CaCuSi4O10) crystals and “partially reacted quartz particles bonded together” by interstitial glass.Hatton, Shortland, and Tite 2008, 1591. Despite an argument to the contrary, scientists have found that, regardless of alkali content, the cuprorivaite crystals develop by “nucleation or growth within a liquid or glass phase.”Pradell et al. 2006, 1430-1431.
|
|
Crystallization is triggered by flexing a small flat disc of notched ferrous metal embedded in the liquid. Pressing the disc releases very tiny adhered crystals of sodium acetate into the solution which then act as nucleation sites for the crystallization of the sodium acetate into the hydrated salt (sodium acetate trihydrate, CH3COONa·3H2O). Because the liquid is supersaturated, this makes the solution crystallize suddenly, thereby releasing the energy of the crystal lattice. The use of the metal disc was invented in 1978.
|
|
She and her team worked on the nucleation of iron sulphides, which regulate and control geochemical iron and sulphur in the environment. In 2014 Liane G. Benning was appointed Head of Interface Geochemistry at the GFZ German Research Centre for Geosciences and became a professor at the Free University of Berlin in April 2016. At the GFZ she leads the Potsdam Imaging and Spectral Analysis Facility (PISA). In 2016 she was awarded the Mineralogical Society Schlumberger Medal and the Geological Society Bigsby Medal.
|
|
Normal urine contains chelating agents, such as citrate, that inhibit the nucleation, growth, and aggregation of calcium-containing crystals. Other endogenous inhibitors include calgranulin (an S-100 calcium-binding protein), Tamm–Horsfall protein, glycosaminoglycans, uropontin (a form of osteopontin), nephrocalcin (an acidic glycoprotein), prothrombin F1 peptide, and bikunin (uronic acid-rich protein). The biochemical mechanisms of action of these substances have not yet been thoroughly elucidated. However, when these substances fall below their normal proportions, stones can form from an aggregation of crystals.
|
|
Similar ZnO multipod- shaped templates, having various diameters and network density and topology, are used for deposition of aerographite. Common aspects of synthesis: With the aerographite's Chemical Vapor Deposition (CVD) process metal oxides had been shown in 2012 to be a suitable template for deposition of graphitic structures. The templates can be in situ removed. Basic mechanism is the reduction of metal oxide to a metallic constituent, the nucleation of carbon in and on top of metal and the simultaneous evaporation of metal component.
|
|
Furthermore, subduction is likely to have spontaneously initiated at some point in Earth's history, as induced subduction nucleation requires existing plate motions, though an unorthodox proposal by A. Yin suggests that meteorite impacts may have contributed to subduction initiation on early Earth. Geophysicist Don L. Anderson has hypothesized that plate tectonics could not happen without the calcium carbonate laid down by bioforms at the edges of subduction zones. The massive weight of these sediments could be softening the underlying rocks, making them pliable enough to plunge.
|
|
Another process in common use is to rub a rod on the side of a glass vessel containing the solution to release microscopic glass particles which can act as nucleation centres. In industry, centrifugation is used to separate the crystals from the supernatant liquid. Some compounds and mixtures of compounds can form long-living supersaturated solutions. Carbohydrates are a class of such compounds; The thermodynamic barrier to formation of crystals is rather high because of extensive and irregular hydrogen bonding with the solvent, water.
|
|
Therefore, it competes with the irreversible plastic deformation by dislocation motion. At nanoscale, the dislocation density and possible Frank–Read source sites are greatly reduced, so the yield stress is increased with reduced size. Therefore, for materials exhibiting superelasticity behavior in nanoscale, it has been found that they can operate in long-term cycling with little detrimental evolution. On the other hand, the critical stress for martensitic phase transformation to occur is also increased because of the reduced possible sites for nucleation to begin.
|
|
Following nucleation, the rupture propagates away from the hypocentre in all directions along the fault surface. The propagation will continue as long as there is sufficient stored strain energy to create new rupture surface. Although the rupture starts to propagate in all directions, it often becomes unidirectional, with most of the propagation in a mainly horizontal direction. Depending on the depth of the hypocentre, the size of the earthquake and whether the fault extends that far, the rupture may reach the ground surface, forming a surface rupture.
|
|
Nucleation in a champagne glass helps form the wine's bubbles; too much surface area allows carbonation to fizzle out quickly. More bubbles create greater texture in the taster's mouth, and a flute's deep bowl allows for greater visual effect of bubbles rising to the top. The flute's narrow cross- section also minimizes the oxygen-to-wine ratio, which enhances both the wine's aroma and taste. While most commonly used for sparkling wines, flutes are also used for certain beers, especially fruit beers and Belgian lambics and gueuzes.
|
|
The production of amorphous ice hinges on the fast rate of cooling. Liquid water must be cooled to its glass transition temperature (about 136 K or −137 °C) in milliseconds to prevent the spontaneous nucleation of crystals. This is analogous to the production of ice cream from heterogeneous ingredients, which must also be frozen quickly to prevent the growth of crystals in the mixture. Pressure is another important factor in the formation of amorphous ice, and changes in pressure may cause one form to convert into another.
|
|
Laboratory experiments with formamide, a liquid resembling water, have shown how no such dehydration barrier can be involved. The fundamental difficulty to nucleate anhydrous magnesium carbonate remains when using this non-aqueous solution. Not cation dehydration, but rather the spatial configuration of carbonate anions creates the barrier in the low-temperature nucleation of magnesite.Xu, J; Yan, C.; Zhang, F.; Konishi, H., Xu, H. & Teng, H. H. (2013): Testing the cation- hydration effect on the crystallization of Ca – Mg- CO3 systems. Proc. Natl. Acad. Sci.
|
|
These ready-made bubbles (which are nucleation sites) exist in things such as tiny fibers or non-wettable crevices on the sides of the bottle. Because there usually are very few of such pre-existing bubbles, the degassing process is slow. Mentos candies contain millions of cavities, roughly 2-7 μm in size, that remain unwetted when added to a soda. Because of this, addition of Mentos candies to a carbonated beverage provides enormous numbers of pre-existing bubbles into which dissolved carbon dioxide can escape.
|
|
Nucleated base of a pint glass It is increasingly common to find pint glasses which contain markings on the base; very often these glasses are branded to one particular beer. The markings themselves are formed from small pits, which aid in nucleation, allowing the gas within it to be released more easily, thus preserving the head. Without the aid of these pits a regular pint glass will keep a head for only 3 or 4 minutes before appearing "flat".Top tips for beer quality. .
|
|
This type of hand warmer can be recharged by immersing the hand-warmer in very hot water until the contents are uniform and then allowing it to cool. The release of heat is triggered by flexing a small metal disk in the hand warmer, which generates nucleation centers that initiate crystallisation. Heat is required to dissolve the salt in its own water of crystallisation and it is this heat that is released when crystallisation is initiated. The latent heat of fusion is about 264–289 kJ/kg.
|
|
The boundary between the two formed a squall line stretching from Devon, along the England–Wales border and up across Northern England to the River Tees. Thick clouds, darkened by the Sahara dust, rose to , plunging areas along the squall line into total darkness. In some areas, the lightning continued for 24 hours, and ball lightning was seen at RAF Chivenor in Devon. The dust particles served as seeds for nucleation, causing water to rapidly precipitate out and form especially large raindrops and hailstones.
|
|
The freezing from the surface or from within may be random. However, in the strange world of water, tiny amounts of liquid water theoretically still are present, even as temperatures go below minus 48 C (minus 55 F) and almost all the water has turned solid, either into crystalline ice or amorphous water. Below minus 48 C (minus 55 F), ice is crystallizing too fast for any property of the remaining liquid to be measured. The freezing speed directly influences the nucleation process and ice crystal size.
|
|
P11-4 is an α-peptide that self-assembles into β-sheet amyloids with a hydrogel appearance at low pH. It builds a 3-D bio-matrix with binding sites for calcium ions serving as nucleation point for hydroxyapatite (tooth mineral) formation. The high affinity to tooth mineral is based on matching distances of Ca-ion binding sites on P11-4 and Ca spacing in the crystal lattice of hydroxyapatite. The matrix formation is pH controlled and thus allows control matrix activity and place of formation.
|
|
They are all good carbide and nitride former , where the precipitates formed can prevent grain growth by pinning grain boundary. They are also all ferrite former, which increase the transition temperature of austenite-ferrite two phase region and reduce the non-recrystallization region . The reduction in non-recrystallization region induces the formation of deformation bands and activated grain boundaries, which are alternative ferrite nucleation site other than grain boundaries . Other alloying elements are mainly for solid solution strengthening including Silicon, Manganese, Chromium, Copper, and Nickel .
|
|
First, RhoA stimulates nucleation of unbranched actin filaments by activation of Diaphanous-related formins. This local generation of new actin filaments is important for the contractile ring formation. This actin filament formation process also requires a protein called profilin, which binds to actin monomers and helps load them onto the filament end. Second, RhoA promotes myosin II activation by the kinase ROCK, which activates myosin II directly by phosphorylation of the myosin light chain and also inhibits myosin phosphatase by phosphorylation of the phosphatase-targeting subunit MYPT.
|
|
It is also used as the fluid in Christmas lights that have the colored bubbling tube above a lamp as a source of heat and a small amount of rock salt to provide thermal mass and a nucleation site for the phase changing solvent. DCM chemically welds certain plastics. For example, it is used to seal the casing of electric meters. Often sold as a main component of plastic welding adhesives, it is also used extensively by model building hobbyists for joining plastic components together.
|
|
Traditional brown rock sugar White rock sugar Rock candy or sugar candy, also called rock sugar, or crystal sugar, is a type of confection composed of relatively large sugar crystals. This candy is formed by allowing a supersaturated solution of sugar and water to crystallize onto a surface suitable for crystal nucleation, such as a string, stick, or plain granulated sugar. Heating the water before adding the sugar allows more sugar to dissolve thus producing larger crystals. Crystals form after 6 to 7 days.
|
|
As with natural bone, the primary issue with bone scaffolds is brittle failure. They typically follow linear elastic behavior, and under compressive forces experiences a plateau and recovery reminiscent of cellular solids as well as trabecular bone. The elastic modulus of natural bone ranges from 10 to 20 GPa; it requires a high stiffness to withstand constant mechanical load. Bone scaffolds must therefore be as stiff as natural bone, or the scaffold will fail through crack nucleation and propagation before the host tissue can regenerate.
|
|
Cracks on Goryeo celadon Glaze of Goryeo celadon had a definite composition starting from the 11th century to the 15th century. It contained a lot of calcium in composition, with 0.5% of manganese oxide, which was more concentrated than glaze used in Chinese celadon. Also in the case of Chinese ceramics, there is enough time for nucleation-crystal growth, so it takes jade color. But the kilns in Goryeo were smaller than that in China, so the firing and cooling process took place quickly.
|
|
The binding of these drugs at the high affinity sites results in strong kinetic suppression of tubulin exchange even at low drug concentration while their binding to the low affinity sites in relatively high drug concentration depolymerizes microtubules. In contrast to colchicine and vinca alkaloids, paclitaxel enhances microtubule polymerization promoting both the nucleation and elongation phases of the polymerization reaction, and it reduces the critical tubulin sub-unit concentration (i.e., soluble tubulin concentration at steady- state). Microtubules polymerized in presence of paclitaxel are extremely stable.
|
|
The reasons why amyloid cause diseases are unclear. In some cases, the deposits physically disrupt tissue architecture, suggesting disruption of function by some bulk process. An emerging consensus implicates prefibrillar intermediates, rather than mature amyloid fibers, in causing cell death, particularly in neurodegenerative diseases. The fibrils are, however, far from innocuous, as they keep the protein homeostasis network engaged, release oligomers, cause the formation of toxic oligomers via secondary nucleation, grow indefinitely spreading from district to district and, in some cases, may be toxic themselves.
|
|
Turner and I. S. Servi developed homogeneous nucleation theory for a solid-solid transformation, providing the technologically important basis for strengthening metallic alloys through precipitation hardening. With Morrel Cohen, he developed the free volume theory for fluid flow. In 1950, Turnbull formulated a criterion for the ease of glass formation from supeercooled melts with a high viscosity by rapid solidification. Independently and simultaneously to Cohen, he predicted the formation of metallic glass phases from sufficiently fast cooling of an alloy melt with a deep eutectic.
|
|
Many different types of atmospheric particulate matter can act as ice nuclei, both natural and anthropogenic, including those composed of desert dust, soot, organic matter, bacteria (e.g. Pseudomonas syringae), pollen, fungal spores and volcanic ash amongst others. However, the exact nucleation potential of each type varies greatly, depending on the exact atmospheric conditions. Very little is known about the spatial distribution of these particles, their overall importance for global climate through ice cloud formation, and whether human activity has played a major role in changing these effects.
|
|
MARMOT is a finite element-based phase field code for modeling irradiation-induced microstructure evolution. MARMOT predicts the effect of radiation damage on microstructure evolution, including void nucleation and growth, bubble growth, grain boundary migration, and gas diffusion and segregation. The phase field equations can be coupled with heat conduction and solid mechanics from ELK to consider the effect of temperature and stress gradients on the evolution. In addition, MARMOT calculates the effect of the microstructure evolution on various bulk material properties, including thermal conductivity and porosity.
|
|
Poured fondant is formed by supersaturating water with sucrose. More than twice as much sugar dissolves in water at the boiling point than at room temperature. After the sucrose dissolves, if the solution is left to cool undisturbed, the sugar remains dissolved in a supersaturated solution until nucleation occurs. While the solution is supersaturated, if a cook puts a seed crystal (undissolved sucrose) into the mix, or agitates the solution, the dissolved sucrose crystallizes to form large, crunchy crystals (which is how rock candy is made).
|
|
Thus the scientists whose ideas led to these classical fundamentals and methodologies of traffic and transportation theory could not know the nucleation nature of real traffic breakdown. Many of the diverse driver behavioral characteristics related to real traffic as well as some of the mathematical approaches to traffic flow modeling, which have been discovered in classical approaches to traffic flow theory, are also used in three-phase traffic theory and associated microscopic traffic flow models (for more details, see Sec. 11 of a review).
|
|
Functional groups (amide, amino and carboxyl) act as ionic pumps capturing calcium ions from the test fluids; then calcium cations bind with phosphate anions to generate calcium-phosphate mineral nuclei on the dendrimer surface. SPRM is expected to be sensitive enough to provide important quantitative information on mineralization's occurrence and kinetics. This detection of the mineralization is based on the specific mass change induced by the mineral nuclei formation and growth. Nucleation and progress in mineralization can be monitored by SPRM as shown in Figure 20.
|
|
Through a process called secondary nucleation, the crystals quickly increase in number, and because of its supercooled surrounding, the crystals will continue to grow. Sometimes, the concentration is estimated to reach one million ice crystals per cubic meter. As the crystals grow in number and size, the frazil ice will begin to adhere to objects in the water, especially if the objects themselves are at a temperature below water's freezing point. The accumulation of frazil ice often causes flooding or damage to objects such as trash racks.
|
|
These were originally thought to be scattered only around the centrosomes, but further studies proved that PCM1 was also found throughout the cytoplasm. PCM1 was shown to be essential for cell division because PCM1 antibodies cause cell-cycle arrest when microinjected into fertilized murine eggs. Targeting of centrin, pericentrin and ninein was also dramatically reduced after PCM1 depletion using siRNA, overexpression of PCM1 deletion mutants and PCM1 antibody microinjection. As a result of this depletion, the radial organization of the microtubules was found to be disrupted, but did not appear to effect microtubule nucleation.
|
|
Solanezumab binds the amyloid-β peptides that aggregate and form plaques in the brain that are an early pathological feature of Alzheimer's disease. Solanezumab binds the central epitope of monomeric amyloid-β, KLVFFAED, (PDB ID 4XXD) with picomolar affinity. This epitope is known as the nucleation site for Aβ oligomerization, and it is these oligomers of Aβ that are thought to be toxic to neurons. Solanezumab is thought to act as an “amyloid beta sink” that is “facilitating flux of amyloid beta from a central to peripheral compartment”.
|
|
In dropwise condensation the condensate liquid collects in the form of countless droplets of varying diameters on the condensing surface, instead of forming a continuous film, and does not wet the solid cooling surface. The droplets develop at points of surface imperfections (pit, scratch), called nucleation sites, and grow in size as more vapour condenses on its exposed surface. When the size of droplets is large there comes a time the droplet breakaway from the surface and knock off other droplets and carries it downstream. The moving droplet devours the droplets of smaller size.
|
|
In the biomineralization of the mollusc shell, specialized proteins are responsible for directing crystal nucleation, phase, morphology, and growths dynamics and ultimately give the shell its remarkable mechanical strength. The application of biomimetic principles elucidated from mollusc shell assembly and structure may help in fabricating new composite materials with enhanced optical, electronic, or structural properties. The most described arrangement in mollusc shells is the nacre - prismatic shells, known in large shells as Pinna or the pearl oyster (Pinctada). Not only the structure of the layers differ, but their mineralogy and chemical composition also differ.
|
|
Fungi are a diverse group of organisms that belong to the eukaryotic domain. Studies of their significant roles in geological processes, "geomycology", has shown that fungi are involved with biomineralization, biodegradation, and metal-fungal interactions. In studying fungi's roles in biomineralization, it has been found that fungi deposit minerals with the help of an organic matrix, such as a protein, that provides a nucleation site for the growth of biominerals. Fungal growth may produce a copper-containing mineral precipitate, such as copper carbonate produced from a mixture of (NH4)2CO3 and CuCl2.
|
|
Something which reduces surface tension, or adsorbs gas molecules, or locally reduces solubility of the gas, or causes a local reduction in static pressure in a fluid may result in a bubble nucleation or growth. This may include velocity changes and turbulence in fluids and local tensile loads in solids and semi-solids. Lipids and other hydrophobic surfaces may reduce surface tension (blood vessel walls may have this effect). Dehydration may reduce gas solubility in a tissue due to higher concentration of other solutes, and less solvent to hold the gas.
|
|
Large bubbles in cooling passages will be self-sustaining or grow larger, with a virtually complete loss of cooling in the area. With pure MEG (mono-ethylene glycol) the hot spot will reach . Cooling by other effects such as air draft from fans (not considered in pure nucleation analysis) will assist in preventing large-bubble formation. The mixture of ethylene glycol with water provides additional benefits to coolant and antifreeze solutions, such as preventing corrosion and acid degradation, as well as inhibiting the growth of most microbes and fungi.
|
|
Bubbles in a rosé sparkling wine An initial burst of effervescence occurs when the sparkling wine contacts the dry glass on pouring. These bubbles form on imperfections in the glass that facilitate nucleation. Nucleations are needed to stimulate the formation of bubbles because carbon dioxide has to first diffuse from the wine solution before it can rise out of the glass and into the air. A poured glass of sparkling wine will lose its bubbliness and carbon dioxide gas much more quickly than an open bottle alone would.
|
|
High temperature conditions during the initial stages of implantation will increase the impurity diffusion in the substrate and as a result limit the impinging ion saturation, which is required for nanoparticle nucleation. Both the implant temperature and ion beam current density are crucial to control in order to obtain a monodisperse nanoparticle size and depth distribution. A low current density may be used to counter the thermal agitation from the ion beam and a buildup of surface charge. After implantation on the surface, the beam currents may be raised as the surface conductivity will increase.
|
|
Cofilin is a ubiquitous actin-binding factor required for the reorganization of actin filaments. ADF/Cofilin family members bind G-actin monomers and depolymerize actin filaments through two mechanisms: severing and increasing the off-rate for actin monomers from the pointed end. "Older" ADP/ADP-Pi actin filaments free of tropomyosin and proper pH are required for cofilin to function effectively. In the presence of readily available ATP-G-actin cofilin speeds up actin polymerization via its actin-severing activity (providing free barbed ends for further polymerization and nucleation by the Arp2/3 complex).
|
|
Germanium dioxide (GeO2, Germania), in many respects a structural analogue of silica, fluoride, aluminate, phosphate, borate, and chalcogenide glasses) have physico-chemical properties useful for their application in fibre-optic waveguides in communication networks and other specialized technological applications. Silica-free glasses may often have poor glass forming tendencies. Novel techniques, including containerless processing by aerodynamic levitation (cooling the melt whilst it floats on a gas stream) or splat quenching (pressing the melt between two metal anvils or rollers), may be used increase cooling rate, or reduce crystal nucleation triggers.
|
|
Rap1 contains a Sir3-binding domain that recruits SIR3 to the silencers. Once at the silencers, Sir3 recruits Sir4-Sir2 dimers to the chromatin nucleation site. Sir2 then deacetylates histone H3 and H4 tails, and free Sir3 binds the now-deacetylated lysine residues H4K16,79, and recruits additional Sir4-Sir2 dimers to promote the further spreading of the heterochromatin domain. Once it has spread to cover a genomic locus, the SIR2,3,4 effectively prevents transcription from the region it occupies, in a process that is thought to depend on the physical occlusion of DNA by SIR proteins.
|
|
An unstable phase lies at a maximum in free energy. In contrast, nucleation and growth occurs in a metastable phase, which is a phase that lies at a local but not global minimum in free energy, and is resistant to small fluctuations. J. Willard Gibbs described two criteria for a metastable phase: that it must remain stable against a small change over a large area, and that it must remain stable against a large change over a small area.Gibbs, J.W., Scientific Papers of J Willard Gibbs, 2 vols.
|
|
Oxalate solubility for metals decreases in the order Mg > Ca > Cd > Zn > {Mn, Ni, Fe, Cu} > {As, Sb, Pb} > Hg. The highly insoluble iron(II) oxalate appears to play a major role in gout, in the nucleation and growth of the otherwise extremely soluble sodium urate. This explains why gout usually appears after age 40 , when ferritin levels in blood exceed 1 μg/L . Foods high in oxalate should be avoided by people suffering from, or at risk of gout. Cadmium catalyzes the transformation of vitamin C into oxalic acid.
|
|
Foaming is an intricate, yet essential component that can be used to assess the overall quality of a cider and distinguish between natural and sparkling ciders. Chemically, hydrophobic polypeptides contribute to the initial foam, bubble size, the extent to which it persists, number of nucleation sites, and the froth of the foam (foam collar). These chemical compositions and parameters are quantitatively measured through metrics such as foam height, foam stability height, and stability time.Blanco-Gomis, D., Mangas-Alonso, J. J., Expósito- Cimadevilla, Y., & Gutiérrez-Álvarez, M. D. (2010).
|
|
A parameter, Da, was defined to measure the variations of temperature, species concentration and potentials.Y. Wang and S. C. Cho, Analysis of Air Cathode Performance for Lithium–air Batteries, Journal of the Electrochemical Society, 160 (10) A1-A9 (2013).Y. Wang, Z. Wang, H. Yuan and T. Li, Discharge Oxide Storage Capacity And Voltage Loss In Li–air Battery, Electrochimica Acta, 180 (2015) 382–393 The effects of pore size and pore size distribution remain poorly understood. Catalysts have shown promise in creating preferential nucleation of over , which is irreversible with respect to lithium.
|
|
The lamellipodium (plural lamellipodia) (from Latin ', "thin sheet"; pod, "foot") is a cytoskeletal protein actin projection on the leading edge of the cell. It contains a quasi-two-dimensional actin mesh; the whole structure propels the cell across a substrate. Within the lamellipodia are ribs of actin called microspikes, which, when they spread beyond the lamellipodium frontier, are called filopodia. The lamellipodium is born of actin nucleation in the plasma membrane of the cell and is the primary area of actin incorporation or microfilament formation of the cell.
|
|
Most viruses have an outer capsule 20 to 300 nm in diameter. Virus capsules are remarkably robust and capable of withstanding temperatures as high as 60 °C; they are stable across the pH range 2-10. Viral capsules can be used to create nano device components such as nanowires, nanotubes, and quantum dots. Tubular virus particles such as the tobacco mosaic virus (TMV) can be used as templates to create nanofibers and nanotubes, since both the inner and outer layers of the virus are charged surfaces which can induce nucleation of crystal growth.
|
|
Route II shows the homogeneous nucleation route, where only nanofibers are formed. The diameter of the polyaniline nanofibers can be controlled with this method through choice of acid. Hydrochloric acid produces nanofibers with a diameter of about 30 nm, while camphorsulfonic acid and perchloric acid produce a diameter of 50 nm and 120 nm respectively. Under normal synthetic methods polyaniline derivatives, such as ones that are alkyl and fluoro substituted, do not exhibit a well-defined fibrous shape, however, in the presence of an aniline oligomer nanofibers of certain derivatives can be synthesized.
|
|
The protein product of WAS is known as WASp. It contains 502 amino acids and is mainly expressed in hematopoietic cells (the cells in the bone marrow that develop into blood cells). The main function of WASp is to activate actin polymerization by serving as a nucleation-promoting factor (NPF) for the Arp2/3 complex, which generates branched actin filaments. Several proteins can serve as NPFs, and it has been observed that in WAS platelets the Arp2/3 complex functions normally, indicating that WASp is not required for its activation in platelets.
|
|
At the anodic surface, dissolution of the metallic lithium occurs, with the production of electrons and lithium ions during the discharge and electrodeposition during the charge. The half-reaction is expressed as: Li <=> Li+ + e- In analogy with lithium batteries, the dissolution / electrodeposition reaction causes over time problems of unstable growth of the solid-electrolyte interface (SEI), generating active sites for the nucleation and dendritic growth of lithium. Dendritic growth is responsible for the internal short circuit in lithium batteries and leads to the death of the battery itself.
|
|
If the nuclei were larger than some critical radius then it would be thermodynamically stable and could start to grow. The main problem with this theory is that the stored energy due to dislocations is very low (0.1-1 Jm−3) while the energy of a grain boundary is quite high (~0.5Jm−2). Calculations based on these values found that the observed nucleation rate was greater than the calculated one by some impossibly large factor (~1050). As a result, the alternate theory proposed by Cahn in 1949 is now universally accepted.
|
|
Villin is believed to function in the bundling, nucleation, capping and severing of actin filaments. In vertebrates, the villin proteins help to support the microfilaments of the microvilli of the brush border. However, knockout mice appear to show ultra-structurally normal microvilli reminding us that the function of villin is not definitively known; it may play a role in cell plasticity through F-actin severing. The six-repeat villin core is responsible for Ca2+ actin severing while the headpiece is responsible for actin crosslinking and bundling (Ca independent).
|
|
In polymer physics, spherulites (from Greek sphaira = ball and lithos = stone) are spherical semicrystalline regions inside non-branched linear polymers. Their formation is associated with crystallization of polymers from the melt and is controlled by several parameters such as the number of nucleation sites, structure of the polymer molecules, cooling rate, etc. Depending on those parameters, spherulite diameter may vary in a wide range from a few micrometers to millimeters. Spherulites are composed of highly ordered lamellae, which result in higher density, hardness, but also brittleness when compared to disordered regions in a polymer.
|
|
"This new political system led, among other things, to cities and towns that centered around these leaders, also known as territorial nucleation. In this context, the oppidum or fortified Iberian town became the centre of reference in the landscape and the political space." The settlement of Castellet de Banyoles in Tivissa was one of the most important ancient Iberian settlements in the north eastern part of the Iberian peninsula that was discovered in 1912. Also, the 'Treasure of Tivissa', a unique collection of silver Iberian votive offerings was found here in 1927.
|
|
This means that a greater proportion of aragonite will dissolve in water, producing calcium (Ca2+) and carbonate (CO32−) ions. The amount of magnesium (Mg) incorporated into the mineral matrix during calcium carbonate deposition can also alter the properties of the shell, because magnesium inhibits calcium deposition by inhibiting nucleation of calcite and aragonite. Skeletons with significant amounts of magnesium incorporated into the matrix (greater than 12%) are more soluble, so the presence of this mineral can negatively impact shell durability, which is why some organisms remove magnesium from the water during the calcification process.
|
|
The first is nucleation, the appearance of a crystalline phase from either a supercooled liquid or a supersaturated solvent. The second step is known as crystal growth, which is the increase in the size of particles and leads to a crystal state. An important feature of this step is that loose particles form layers at the crystal's surface and lodge themselves into open inconsistencies such as pores, cracks, etc. The majority of minerals and organic molecules crystallize easily, and the resulting crystals are generally of good quality, i.e.
|
|
Second, the icephobicity implies the ability to prevent ice formation on the surface. Such ability is characterized by whether a droplet of supercooled water (below the normal freezing temperature of 0 C) freezes at the interface. The process of freezing can be characterized by time delay of heterogeneous ice nucleation. The mechanisms of droplet freezing are quite complex and can depend on the temperature level, on whether cooling down of the droplet is performed from the side of the solid substrate or from vapor and by other factors.
|
|
The biomineralisation of magnetite () requires regulating mechanisms to control the concentration of iron, the crystal nucleation, the redox potential and the acidity (pH). This is achieved by means of compartmentalisation in structures known as magnetosomes that allow the biochemical control of the above-mentioned processes. After the genome of several MTB species had been sequenced, a comparative analysis of the proteins involved in the formation of the BMP became possible. Sequence homology with proteins belonging to the ubiquitous cation diffusion facilitator (CDF) family and the "Htr-like" serine proteases has been found.
|
|
This is distinct from the use of the term superheating to refer to water at atmospheric pressure above its normal boiling point, which has not boiled due to a lack of nucleation sites (sometimes experienced by heating liquids in a microwave). Many of water's anomalous properties are due to very strong hydrogen bonding. Over the superheated temperature range the hydrogen bonds break, changing the properties more than usually expected by increasing temperature alone. Water becomes less polar and behaves more like an organic solvent such as methanol or ethanol.
|
|
Crystal formation can begin by spontaneous nucleation or may be encouraged by the use of a seed. As material precipitates out of the solution, the amount of solute in the flux decreases and the temperature at which the solution is saturated lowers. This process repeats itself as the furnace continues to cool until the solution reaches its melting point or the reaction is stopped artificially. One advantage of this method is that the crystals grown often display natural facets, which often makes preparing crystals for measurement significantly easier.
|
|
Originally, n was held to have an integer value between 1 and 4, which reflected the nature of the transformation in question. In the derivation above, for example, the value of 4 can be said to have contributions from three dimensions of growth and one representing a constant nucleation rate. Alternative derivations exist, where n has a different value. If the nuclei are preformed, and so all present from the beginning, the transformation is only due to the 3-dimensional growth of the nuclei, and n has a value of 3.
|
|
FogQuest - Fog Collection / Water Harvesting Projects - Welcome It is also a crucial process in forming particle tracks in a cloud chamber. In this case, ions produced by an incident particle act as nucleation centers for the condensation of the vapor producing the visible "cloud" trails. Commercial applications of condensation, by consumers as well as industry, include power generation, water desalination, thermal management, White, F.M. ‘Heat and Mass Transfer’ © 1988 Addison-Wesley Publishing Co. pp. 602–604 refrigeration,Q&A;: Microchannel air-cooled condenser; Heatcraft Worldwide Refrigeration; April 2011; and air conditioning.
|
|
For a pure material, latent heat is released at the solid–liquid interface so that the temperature remains constant until the melt has completely solidified. The growth rate of the resultant crystalline substance will depend on how fast this latent heat can be conducted away. A dendrite growing in an undercooled melt can be approximated as a parabolic needle-like crystal that grows in a shape- preserving manner at constant velocity. Nucleation and growth determine the grain size in equiaxed solidification while the competition between adjacent dendrites decides the primary spacing in columnar growth.
|
|
Study under this proposal is first adapted by Auguest Wöhler in the 1860s, who aimed to study railroad axles. Two important parameters are involved in this conversation: maximum principal strain and strain energy density. As strain is easier to be determined by controlling displacements in actual experimental tests, it is natural to set controlled strain. The alternating and maximum values of the maximum principle strain decides the nucleation life in polymer, but there is not yet any theory to quantitatively describe the strain conditions to fatigue life in lab tests.
|
|
Formins are characterized by the presence of three formin homology (FH) domains (FH1, FH2 and FH3), although members of the formin family do not necessarily contain all three domains. In addition, other domains are usually present, such as PDZ, DAD, WH2, or FHA domains. The proline-rich FH1 domain mediates interactions with a variety of proteins, including the actin-binding protein profilin, SH3 (Src homology 3) domain proteins, and WW domain proteins. The actin nucleation- promoting activity of S. cerevisiae formins has been localized to the FH2 domain.
|
|
A specific advantage of alkaline Zn/Ni (86%/14%) involves the lack of hydrogen embrittlement by plating. It was proved that the first nucleation on steel starts with pure nickel, and that this layer is plated 2 nm thick prior to the Zn-Ni. This initial layer prevents hydrogen from penetrating deep into the steel substrate, thus avoiding the serious problems associated with hydrogen embrittlement. The value of this process and the initiation mechanism is quite useful for high strength steel, tool steels and other substrates susceptible to hydrogen embrittlement.
|
|
Instead thrust faults generally cause a thickening of the stratigraphic section. When thrusts are developed in orogens formed in previously rifted margins, inversion of the buried paleo-rifts can induce the nucleation of thrust ramps. Foreland basin thrusts also usually observe the ramp-flat geometry, with thrusts propagating within units at a very low angle "flats" (at 1–5 degrees) and then moving up- section in steeper ramps (at 5–20 degrees) where they offset stratigraphic units. Thrusts have also been detected in cratonic settings, where "far- foreland" deformation has advanced into intracontinental areas.
|
|
Conditional Dicer substrate formation via shape and sequence transduction with small conditional RNAs. scRNA A·B detects mRNA detection target X (containing subsequence 'a-b-c'), leading to production of Dicer substrate B·C targeting mRNA silencing target Y (containing independent subsequence 'w-x-y-z'). scRNAs A·B and C are stable in the absence of X. A swaps B for X (step 1) via toehold-mediated 3-way branch migration and spontaneous dissociation. B assembles with C (step 2) via loop/toehold nucleation and 3-way branch migration to form Dicer substrate B·C.
|
|
The molecular mechanisms of skeletogenesis involve several PMC-specific gene products. These include Msp30, a sulfate cell-surface glycoprotein which has been implicated in calcium uptake and deposition, and SM50, SM30, and PM27 which are three proteins of the spicule matrix. SM50 and PM27 are thought to be structurally similar, nonglycosylated, basic proteins whereas SM30 is an acidic glycoprotein. The specific roles of these matrix proteins has yet to be fully elucidated, but it is thought that they may function in the nucleation or orientation of crystal growth.
|
|
A secondary organic aerosol (SOA) is a molecule produced via oxidation over several generations of a parent organic molecule. In contrast to primary organic aerosols, which are emitted directly from the biosphere, secondary organic aerosols are either formed via homogeneous nucleation through the successive oxidation of gas-phase organic compounds, or through condensation on pre-existing particles. These gas-phase species exert high vapor pressures, meaning they are volatile and stable in the gas-phase. Upon oxidation, the increased polarity, and thus reduced volatility, of the molecules results in a reduction of vapor pressure.
|
|
In the second heating, lead in the form of lead oxide no longer reacts with tin oxide to form lead silicate, thus the recrystallised cassiterite (SnO2) remain undissolved and precipitate in the glazes. The nucleation and growth rates of the precipitation depend upon temperature and time. The particle size of the cassiterite developed is also dependent on the temperature, and smaller than that used in the very beginning. It is the smaller particle size of the recrystallised SnO2 in glazes that increases the opacity in tin-opacified glazes.
|
|
The formation of small particles of a substance with a narrow size distribution is an important process in the pharmaceutical and other industries. Supercritical fluids provide a number of ways of achieving this by rapidly exceeding the saturation point of a solute by dilution, depressurization or a combination of these. These processes occur faster in supercritical fluids than in liquids, promoting nucleation or spinodal decomposition over crystal growth and yielding very small and regularly sized particles. Recent supercritical fluids have shown the capability to reduce particles up to a range of 5-2000 nm.
|
|
Following the initial nucleation event, tubulin monomers must be added to the growing polymer. The process of adding or removing monomers depends on the concentration of αβ-tubulin dimers in solution in relation to the critical concentration, which is the steady state concentration of dimers at which there is no longer any net assembly or disassembly at the end of the microtubule. If the dimer concentration is greater than the critical concentration, the microtubule will polymerize and grow. If the concentration is less than the critical concentration, the length of the microtubule will decrease.
|
|
The guanine nucleotide exchange factor for the small GTPase Ran (Regulator of chromosome condensation 1 or RCC1) is attached to nucleosomes via core histones H2A and H2B. Thus, a gradient of GTP-bound Ran is generated around the vicinity of mitotic chromatin. Glass beads coated with RCC1 induce microtubule nucleation and bipolar spindle formation in Xenopus egg extracts, revealing that the Ran GTP gradient alone is sufficient for spindle assembly. The gradient triggers release of spindle assembly factors (SAFs) from inhibitory interactions via the transport proteins importin β/α.
|
|
Cultured saltwater pearls can also be baroque, but tend to be more teardrop-shaped due to the use of a spherical nucleation bead. The most valuable of baroque pearls are the South Sea and Tahitian pearls. These pearls are produced by Pinctada margaritifera (black-lipped oysters) and Pinctada maxima (gold-lipped and white-lipped oysters). Although these are a variety of cultured saltwater pearls, the amount of time that the pearls are cultured dramatically increases the depth of the nacre, and the likelihood of producing a baroque pearl.
|
|
Polymers such as poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide), polyvinylpyrrolidone, and poly-(diallyldimethylammonium chloride) have been found to act as crystal dispersants, imparting particle-size and morphology control. Due to their promising material properties, significant interest lies in economical large-scale production methods. Sonochemical synthesis, which allows nucleation reactions to proceed rapidly through acoustic generation of localized heat and pressure, has been explored as a way to shorten synthesis times. As with the case of zeolites, microwave-assisted synthesis has also been of interest for the rapid synthesis of ZIFs.
|
|
This phenomenon is analogous to the nucleation and growth of dry patches in viscous liquids spreading on a non-wettable substrate (Figure 2). Cellular dewetting is triggered by several protein toxins from pathogenic bacteria, notably the EDIN-like factors from Staphylococcus aureus and from Clostridium botulinum, as well as edema toxin from Bacillus anthracis. TEMs form in response to the rupture of cytoskeleton physical connections through the cytoplasm due to inhibition of the RhoA/ROCK pathway or to induction of the flux of cyclic-AMP (cAMP) broad signaling molecule.
|
|
A typical nucleated Boltzmann brain will, after it finishes its activity, cool off to absolute zero and eventually completely decay, as any isolated object would in the vacuum of space. Unlike the quantum fluctuation case, the Boltzmann brain will radiate energy out to infinity. In nucleation, the most common fluctuations are as close to thermal equilibrium overall as possible given whatever arbitrary criteria are provided for labeling a fluctuation a "Boltzmann brain". Theoretically a Boltzmann brain can also form, albeit again with a tiny probability, at any time during the matter-dominated early universe.
|
|
The self-assembly is governed by the normal processes of nucleation and growth. Small assemblies are formed because of their increased lifetime as the attractive interactions between the components lower the Gibbs free energy. As the assembly grows, the Gibbs free energy continues to decrease until the assembly becomes stable enough to last for a long period of time. The necessity of the self-assembly to be an equilibrium process is defined by the organization of the structure which requires non-ideal arrangements to be formed before the lowest energy configuration is found.
|
|
These experiments are crucial to understanding domain wall nucleation and propagation which would be necessary for the creation of complex logic circuits based on domain wall mechanics. Many properties of domain walls are still not fully understood and one particularly outstanding issue is of the magnitude and size of the resistance associated with current passing through domain walls. Both positive and negative values of domain wall resistance have been reported, leaving this an open area for future research. An example of a simple device that utilizes pinned domain walls is provided by reference.
|
|
Most materials exhibit the Hall–Petch effect at room-temperature and so display a higher yield stress when the grain size is reduced (assuming abnormal grain growth has not taken place). At high temperatures the opposite is true since the open, disordered nature of grain boundaries means that vacancies can diffuse more rapidly down boundaries leading to more rapid Coble creep. Since boundaries are regions of high energy they make excellent sites for the nucleation of precipitates and other second-phases e.g. Mg–Si–Cu phases in some aluminium alloys or martensite platlets in steel.
|
|
Other headgroups are also present to varying degrees and can include phosphatidylserine (PS) phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). These alternate headgroups often confer specific biological functionality that is highly context-dependent. For instance, PS presence on the extracellular membrane face of erythrocytes is a marker of cell apoptosis, whereas PS in growth plate vesicles is necessary for the nucleation of hydroxyapatite crystals and subsequent bone mineralization. Unlike PC, some of the other headgroups carry a net charge, which can alter the electrostatic interactions of small molecules with the bilayer.
|
|
This process occurs either after deformation or in the absence of dynamic deformation. Depending on the intensity of heat during recrystallization, the foliation will either be strengthened or weakened. If the heat is too intense, foliation will be weakened due to the nucleation and growth of new randomly oriented crystals and the rock will become a hornfels. If minimal heat is applied to a rock with a preexisting foliation and without a change in mineral assemblage, the cleavage will be strengthened by growth of micas parallel to foliation.
|
|
Both secondary events increase the number of fibril ends able to recruit new monomers or oligomers, therefore accelerating fibril formation. These events add to the well recognised steps of primary nucleation (formation of the nucleus from the mnonomers through one of models described above), fibril elongation (addition of monomers or oligomers to growing fibril ends) and dissociation (opposite process). Such a new model is described in the figure on the right and involves the utilization of a ‘master equation’ that includes all steps of amyloid fibril formation, i.e.
|
|
A German wheat beer served in the traditional glassware. The glass has a half litre fill line and is designed with extra space specifically to accommodate the head. Beer glassware is often designed to accentuate or accommodate the head. Many other properties of the glass can also influence a beer head, such as a roughened surface at the base of glass known as a widget, providing for nucleation of carbon dioxide deep in the beverage rather than at the surface, resulting in a slower release of gas to the atmosphere.
|
|
In general, the microbial abundance was found to increase with the increase in particle size. On the other hand, the fine particles may provide more favorable nucleation sites for calcium carbonate precipitation because the mineralogy of the grains could directly influence the thermodynamics of the precipitation reaction in the system. The habitable pores and traversable pore throats were found in coarse sediments and some clayey sediments at shallow depth. In clayey soil, bacteria are capable of reorienting and moving clay particles under low confining stress (at shallow depths).
|
|
In condensed matter physics, a confined liquid is a liquid that is subject to geometric constraints on a nanoscopic scale so that most molecules are close enough to an interface to sense some difference from standard bulk liquid conditions. Typical examples are liquids in porous media or liquids in solvation shells. Confinement regularly prevents crystallization, which enables liquids to be supercooled below their homeogenous nucleation temperature even if this is impossible in the bulk state. This holds in particular for water, which is by far the most studied confined liquid.
|
|
Ernst G. Bauer. Ernst G. Bauer (born 1928) is a German-American physicist known for his studies in the field of surface science. His most prominent contributions are his work on establishing thin film growth and nucleation mechanisms and his invention in 1962 of the Low Energy Electron Microscopy (LEEM), which came to fruition in 1985 in the workgroup of Ernst Bauer in Germany. In the early 90s, he extended the LEEM technique in two directions by developing Spin-Polarized Low Energy Electron Microscopy (SPLEEM) and Spectroscopic Photo Emission and Low Energy Electron Microscopy (SPELEEM).
|
|
Blue Gene/L was the first supercomputer ever to run over 100 TFLOPS sustained on a real-world application, namely a three-dimensional molecular dynamics code (ddcMD), simulating solidification (nucleation and growth processes) of molten metal under high pressure and temperature conditions. This achievement won the 2005 Gordon Bell Prize. In June 2006, NNSA and IBM announced that Blue Gene/L achieved 207.3 TFLOPS on a quantum chemical application (Qbox).hpcwire.com At Supercomputing 2006, Blue Gene/L was awarded the winning prize in all HPC Challenge Classes of awards.
|
|
In bone, mineralization starts from a heterogeneous solution having calcium and phosphate ions. The mineral nucleates, inside the hole area of the collagen fibrils, as thin layers of calcium phosphate, which then grow to occupy the maximum space available there. The mechanisms of mineral deposition within the organic portion of the bone are still under investigation. Three possible suggestions are that nucleation is either due to the precipitation of calcium phosphate solution, caused by the removal of biological inhibitors or occurs because of the interaction of calcium-binding proteins.
|
|
During this time, Boris Kerner together with V.V. Osipov developed a theory of Autosolitons - solitary intrinsic states, which form in a broad class of physical, chemical and biological dissipative systems. After emigration from Russia to Germany in 1992, Boris Kerner worked for the Daimler company in Stuttgart. His major interest since then was the understanding of vehicular traffic. The empirical nucleation nature of traffic breakdown at highway bottlenecks understood by Boris Kerner is the basis for Kerner's three phase traffic theory, which he introduced and developed in 1996–2002.
|
|
Investment casting is a metallurgical processing technique in which a wax form is fabricated and used as a template for a ceramic mold. Briefly, a ceramic mold is poured around the wax form, the wax form is melted out of the ceramic mold, and molten metal is poured into the void left by the wax. This leads to a metal form in the same shape as the original wax form. Investment casting leads to a polycrystalline final product, as nucleation and growth of crystal grains occurs at numerous locations throughout the solid matrix.
|
|
As stated above radiation produces some direct and indirect measurable changes in the glasses. In some cases, the effect is readily observable immediately upon irradiation. In other cases, thermal treatment is required to bring about the observed changes. On the whole, the result of the mentioned reactions will be atomic silvers and/or silver clusters which act as nucleant for precipitation of lithium-meta- silicate during post heat-treatment of irradiated glass and Similar to other glass-ceramic systems, the more nucleation sites leads to more reduction of crystallization temperature and finer crystalline size.
|
|
Conventional chain-growth polymerization involves at least two phases; initiation and propagation, while and in some cases termination and chain transfer phases also occur. Chain- growth supramolecular polymerization in a broad sense involves two distinct phases; a less favored nucleation and a favored propagation. In this mechanism, after the formation of a nucleus of a certain size, the association constant is increased, and further monomer addition becomes more favored, at which point the polymer growth is initiated. Long polymer chains will form only above a minimum concentration of monomer and below a certain temperature.
|
|
The chromosome plays an active role in the attachment of kinetochores to the spindle. Bound to the chromatin is a Ran guanine nucleotide exchange factor (GEF) that stimulates cytosolic Ran near the chromosome to bind GTP in place of GDP. The activated GTP-bound form of Ran releases microtubule-stabilizing proteins, such as TPX2, from protein complexes in the cytosol, which induces nucleation and polymerization of microtubules around the chromosomes. These kinetochore-derived microtubules, along with kinesin motor proteins in the outer kinetochore, facilitate interactions with the lateral surface of a spindle pole-derived microtubule.
|
|
DB propellants are composed of two monopropellant fuel components where one typically acts as a high-energy (yet unstable) monopropellant and the other acts as a lower-energy stabilizing (and gelling) monopropellant. In typical circumstances, nitroglycerin is dissolved in a nitrocellulose gel and solidified with additives. DB propellants are implemented in applications where minimal smoke is required yet medium-high performance (Isp of roughly 235 s) is required. The addition of metal fuels (such as aluminium) can increase the performance (around 250 s), though metal oxide nucleation in the exhaust can turn the smoke opaque.
|
|
Doping of the ZnO nanowires has been achieved by adding other metal nitrates to the growth solution. The morphology of the resulting nanostructures can be tuned by changing the parameters relating to the precursor composition (such as the zinc concentration and pH) or to the thermal treatment (such as the temperature and heating rate). Aligned ZnO nanowires on pre-seeded silicon, glass, and gallium nitride substrates have been grown using aqueous zinc salts such as zinc nitrate and zinc acetate in basic environments. Pre-seeding substrates with ZnO creates sites for homogeneous nucleation of ZnO crystal during the synthesis.
|
|
The glass surface influences the shape of crystals, so imperfections, scratches, or dust can modify the way ice nucleates. The patterns in window frost form a fractal with a fractal dimension greater than one but less than two. This is a consequence of the nucleation process being constrained to unfold in two dimensions, unlike a snowflake which is shaped by a similar process but forms in three dimensions and has a fractal dimension greater than two. If the indoor air is very humid, rather than moderately so, water will first condense in small droplets and then freeze into clear ice.
|
|
The presence of a nucleus is one major difference between eukaryotes and prokaryotes. Some conserved nuclear proteins between eukaryotes and prokaryotes suggest that these two types had a common ancestor. Another theory behind nucleation is that early nuclear membrane proteins caused the cell membrane to fold inwardly and form a sphere with pores like the nuclear envelope. Strictly regarding energy expenditure, endosymbiosis would save the cell more energy to develop a nuclear membrane than if the cell was to fold its cell membrane to develop this structure since the interactions between proteins are usually enabled by ATP.
|
|
Similarly, trees that grow in temperate or taiga regions have pointed leaves, presumably to prevent nucleation of ice onto the leaf surface and reduce water loss due to transpiration. Herbivory, not only by large mammals, but also small insects has been implicated as a driving force in leaf evolution, an example being plants of the genus Aciphylla, that are commonly found in New Zealand. The now-extinct moas (birds) fed upon these plants, and the spines on the leaves probably discouraged the moas from feeding on them. Other members of Aciphylla that did not co-exist with the moas were spineless.
|
|
The impact of reducing agent strength can be seen by inspecting a LaMer diagram which describes the nucleation and growth of nanoparticles. When silver nitrate (AgNO3) is reduced by a weak reducing agent like citrate, the reduction rate is lower which means that new nuclei are forming and old nuclei are growing concurrently. This is the reason that the citrate reaction has low monodispersity. Because NaBH4 is a much stronger reducing agent, the concentration of silver nitrate is reduced rapidly which shortens the time during which new nuclei form and grow concurrently yielding a monodispersed population of silver nanoparticles.
|
|
A developable photographic latent image forms when crystals of silver halide in an emulsion layer are exposed to light. The initial nucleation phase is chemically and thermodynamically unstable; it is thus temperature sensitive, and involves the production of one, or very few silver atoms as sub-latent image specks in each silver halide crystal. Once a clump of a few silver atoms has formed at one site within a crystal it is capable of triggering the development of the whole crystal. This greatly amplifies the effect of relatively few photons to produce a metallic silver image "grain".
|
|
Neural precursor cell expressed, developmentally down-regulated 1, also known as Nedd1, is a human gene and encodes the protein NEDD1. NEDD1 is localized in the centrosome and it plays a role in mitosis through its interaction with γ-tubulin. WD40 repeats are located in the amino-terminal of the protein and are responsible for NEDD1 localization in the centrosome, and the carboxy- terminal amino acids are needed for interactions with γ-tubulin. Depletion of NEDD1 causes impaired centrosome and chromatin microtubules assembly that results in the failure of microtubule nucleation and prevents proper spindle formation.
|
|
This is one of the main obstacles in brackish water membrane desalination processes, such as reverse osmosis or nanofiltration. Other forms of scaling, such as calcite scaling, depending on the water source, can also be important considerations in distillation, as well as in heat exchangers, where either the salt solubility or concentration can change rapidly. A new study has suggested that the formation of gypsum starts as tiny crystals of a mineral called bassanite (CaSO4·H2O). This process occurs via a three-stage pathway: # homogeneous nucleation of nanocrystalline bassanite; # self- assembly of bassanite into aggregates, and # transformation of bassanite into gypsum.
|
|
Crystal growth is a major stage of a crystallization process, and consists in the addition of new atoms, ions, or polymer strings into the characteristic arrangement of the crystalline lattice. The growth typically follows an initial stage of either homogeneous or heterogeneous (surface catalyzed) nucleation, unless a "seed" crystal, purposely added to start the growth, was already present. The action of crystal growth yields a crystalline solid whose atoms or molecules are close packed, with fixed positions in space relative to each other. The crystalline state of matter is characterized by a distinct structural rigidity and very high resistance to deformation (i.e.
|
|
Globular proteins seem to have two mechanisms for protein folding, either the diffusion-collision model or nucleation condensation model, although recent findings have shown globular proteins, such as PTP-BL PDZ2, that fold with characteristic features of both models. These new findings have shown that the transition states of proteins may affect the way they fold. The folding of globular proteins has also recently been connected to treatment of diseases, and anti-cancer ligands have been developed which bind to the folded but not the natural protein. These studies have shown that the folding of globular proteins affects its function.
|
|
Since acidic amino acids, such as aspartic acid and glutamic acid, are important mediators of biomineralization, shell proteins tend to be rich in these amino acids. Aspartic acid, which can make up up to 50% of shell framework proteins, is most abundant in calcitic layers, and also heavily present in aragonitic layers. Proteins with high proportions of glutamic acid are usually associated with amorphous calcium carbonate. The soluble component of the shell matrix acts to inhibit crystallization when in its soluble form, but when it attaches to an insoluble substrate, it permits the nucleation of crystals.
|
|
Shallow-focus earthquakes are the result of the sudden release of strain energy built up over time in rock by brittle fracture and frictional slip over planar surfaces. However, the physical mechanism of deep focus earthquakes is poorly understood. Subducted lithosphere subject to the pressure and temperature regime at depths greater than 300 km should not exhibit brittle behavior, but should rather respond to stress by plastic deformation. Several physical mechanisms have been proposed for the nucleation and propagation of deep-focus earthquakes; however, the exact process remains an outstanding problem in the field of deep earth seismology.
|
|
Pseudomonas syringae—more than any mineral or other organism—is responsible for the surface frost damage in plants exposed to the environment. For plants without antifreeze proteins, frost damage usually occurs between -4 and -12 °C as the water in plant tissue can remain in a supercooled liquid state. P. syringae can cause water to freeze at temperatures as high as −1.8 °C (28.8 °F), but strains causing ice nucleation at lower temperatures (down to −8 °C) are more common. The freezing causes injuries in the epithelia and makes the nutrients in the underlying plant tissues available to the bacteria.
|
|
The effect of a distribution of small particles on the grain size in a recrystallized sample. The minimum size occurs at the intersection of the growth stabilized Recrystallization is prevented or significantly slowed by a dispersion of small, closely spaced particles due to Zener pinning on both low- and high-angle grain boundaries. This pressure directly opposes the driving force arising from the dislocation density and will influence both the nucleation and growth kinetics. The effect can be rationalized with respect to the particle dispersion level F_v/r where F_v is the volume fraction of the second phase and r is the radius.
|
|
AFPs work through an interaction with small ice crystals that is similar to an enzyme-ligand binding mechanism which inhibits recrystallization of ice. This explanation of the interruption of the ice crystal structure by the AFP has come to be known as the adsorption-inhibition hypothesis. According to this hypothesis, AFPs disrupt the thermodynamically favourable growth of an ice crystal via kinetic inhibition of contact between solid ice and liquid water. In this manner, the nucleation sites of the ice crystal lattice are blocked by the AFP, inhibiting the rapid growth of the crystal that could be fatal for the organism.
|
|
This also led to the suggestion that early clusters of Nav1.2 and Nav1.6 channels are destined to later become nodes of Ranvier. Neurofascin is also reported to be one of the first proteins to accumulate at newly forming nodes of Ranvier. They are also found to provide the nucleation site for attachment of ankyrin G, Nav channels, and other proteins. The recent identification of the Schwann cell microvilli protein gliomedin as the likely binding partner of axonal neurofascin brings forward substantial evidence for the importance of this protein in recruiting Nav channels to the nodes of Ranvier.
|
|
Ed. 2007, 46, 8342–8356. It is therefore of immense importance to understand the progression from solution to the nucleus to the crystal structures, in other terms, how the entropy dominated situation in solution converts to an enthalpy driven one in the crystals through the nucleation step. As the nucleus is difficult to identify, the approaches made towards this end can be generally divided into two categories. The first type centers on the studies in solution through various spectroscopic techniques to understand the structure of the assembly in the solution and these studies give an idea about the initial stages of crystallization.
|
|
Transition path sampling (TPS) is a Rare Event Sampling method used in computer simulations of rare events: physical or chemical transitions of a system from one stable state to another that occur too rarely to be observed on a computer timescale. Examples include protein folding, chemical reactions and nucleation. Standard simulation tools such as molecular dynamics can generate the dynamical trajectories of all the atoms in the system. However, because of the gap in accessible time-scales between simulation and reality, even present supercomputers might require years of simulations to show an event that occurs once per microsecond without some kind of acceleration.
|
|
This technique exploits the phenomenon of supersaturation, and involves careful balancing of the driving force for precipitation and the thermal activation energy available for both desirable and undesirable processes. Nucleation occurs at a relatively high temperature (often just below the solubility limit) so that the kinetic barrier of surface energy can be more easily overcome and the maximum number of precipitate particles can form. These particles are then allowed to grow at lower temperature in a process called ageing. This is carried out under conditions of low solubility so that thermodynamics drive a greater total volume of precipitate formation.
|
|
These stable clusters constitute the nuclei. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by many different factors (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms or molecules arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms or molecules, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.
|
|
Southsea pearls on the other hand are farmed in larger molluscs, and keshi from these may reach considerable size and value. Freshwater cultivators in pre-1985 Japan commonly used up bits of active mantle tissue left over from in-body bead nucleation by slipping a few keshi into the mantle. Now the market of those keshi farmed in China is so low that they discard the leftovers rather than expending even a tiny fraction of their mussels' strength on producing freshwater keshi. Freshwater keshi pearls from China are for the most part unquestionably cultivated, but in an indirect way.
|
|
In 1962 and 1963, Patashinski, Valery Pokrovsky and Isaak Khalatnikov solved the problem of quasi-classical scattering in three dimensions . In 1963-1965, together with Valery Pokrovsky, Patashinski developed the fluctuating theory of phase transitions. This theory was then applied to a wide range of phase transition problems, including critical slowdown of chemical reactions, brownian motion, electric conductivity near the magnetic ordering point, nucleation in near-critical systems. Other contributions of Patashinski include the theory of gravitational collapse in non-spherically- symmetric systems, the collective tube model for hadron-nucleus collisions at high-energies, nonequilibrium critical phenomena.
|
|
Therefore when put into a calcium chloride environment, S. pasteurii are able to survive since they are halotolerant and alkaliphiles. Since the bacteria remain intact during harsh mineralization conditions, are robust, and carry a negative surface charge, they serve as good nucleation sites for MICP. The negatively charged cell wall of the bacterium provides a site of interaction for the positively charged cations to form minerals. The extent of this interaction depends on a variety of factors including the characteristics of the cell surface, amount of peptidoglycan, amidation level of free carboxyl, and availability of teichoic acids.
|
|
The formation of the magnetosome requires at least three steps: #Invagination of the magnetosome membrane (MM) # Entrance of magnetite precursors into the newly formed vesicle # Nucleation and growth of the magnetite crystal During the first formation of an invagination in the cytoplasmic membrane is triggered by a GTPase. It is supposed this process can take place amongst eukaryotes, as well. The second step requires the entrance of ferric ions into the newly formed vesicles from the external environment. Even when cultured in a Fe3+ deficient medium, MTB succeed at accumulating high intracellular concentrations of this ion.
|
|
A quartz vein, prominent from the surrounding weathered rock at Cape Jervis, South Australia Open space filling is the hallmark of epithermal vein systems, such as a stockwork, in greisens or in certain skarn environments. For open space filling to take effect, the confining pressure is generally considered to be below 0.5 GPa, or less than . Veins formed in this way may exhibit a colloform, agate-like habit, of sequential selvages of minerals which radiate out from nucleation points on the vein walls and appear to fill up the available open space. Often evidence of fluid boiling is present.
|
|
The melting point of ice is at standard pressure; however, pure liquid water can be supercooled well below that temperature without freezing if the liquid is not mechanically disturbed. It can remain in a fluid state down to its homogeneous nucleation point of about . The melting point of ordinary hexagonal ice falls slightly under moderately high pressures, by /atm or about /70 atm as the stabilization energy of hydrogen bonding is exceeded by intermolecular repulsion, but as ice transforms into its polymorphs (see crystalline states of ice) above , the melting point increases markedly with pressure, i.e., reaching at (triple point of Ice VII).
|
|
Supermicelle is a hierarchical micelle structure (supramolecular assembly) where individual components are also micelles. Supermicelles are formed via bottom-up chemical approaches, such as self-assembly of long cylindrical micelles into radial cross-, star- or dandelion-like patterns in a specially selected solvent; solid nanoparticles may be added to the solution to act as nucleation centers and form the central core of the supermicelle. The stems of the primary cylindrical micelles are composed of various block copolymers connected by strong covalent bonds; within the supermicelle structure they are loosely held together by hydrogen bonds, electrostatic or solvophobic interactions.
|
|
A supercooled liquid will stay in a liquid state below the normal freezing point when it has little opportunity for nucleation; that is, if it is pure enough and has a smooth enough container. Once agitated it will rapidly become a solid. During the final stage of freezing, an ice drop develops a pointy tip, which is not observed for most other liquids, arises because water expands as it freezes. Once the liquid is completely frozen, the sharp tip of the drop attracts water vapor in the air, much like a sharp metal lightning rod attracts electrical charges.
|
|
Fig. 1 Actin assembly induced by bacterial protein ActA (shown in green). Mammalian proteins involved in this process are: Profilin (P), Vasodilator-stimulated phosphoprotein (VASP) and actin-related-protein 2 and 3 complex (Arp2/3 complex) as well as actin. ActA is a protein which acts as a mimic of Wiskott- Aldrich syndrome protein (WASP), a nucleation promoting factor (NPF) present in host cells. NPFs in the mammalian cell recruit and bind to the already existing actin-related-protein 2 and 3 complex (Arp2/3 complex) and induce an activating conformational change of the Arp2/3 complex.
|
|
The role of Spc110p is a spacer molecule between the central and inner plaque and γ-tubilin complex binding protein. The essential function of calmodulin is at the SPB where it has been proposed to regulate binding of Spc110p to Spc29p. Spc29 forms in the central plaque a repeating structure. Spc98p and Spc97p are two similar yeast γ –tubulin (Tub4p) binding proteins required for microtubule nucleation. Spc98p, Spc97p and Tub4p are found at the inner and outer plaques of SPB and are involved in microtubules organization. Spc42 faces the cytoplasm and binds to coiled-coil Cnm67p (chaotic nuclear migration).
|
|
Most liquids freeze by crystallization, formation of crystalline solid from the uniform liquid. This is a first-order thermodynamic phase transition, which means that as long as solid and liquid coexist, the temperature of the whole system remains very nearly equal to the melting point due to slow removal of heat when in contact with air, which is a poor heat conductor. Because of the latent heat of fusion, the freezing is greatly slowed and the temperature will not drop any more once the freezing starts but will continue dropping once it finishes. Crystallization consists of two major events, nucleation and crystal growth.
|
|
Use of filler metals is required to introduce alloying materials that serve to form oxides that promote the nucleation of acicular ferrite. The HAZ is still a concern that must be addressed with proper preheat and weld procedures to control the cooling rates. Slow cooling rates can be as detrimental and rapid cooling rates in the HAZ. Rapid cooling will form untempered martensite; however, very slow cooling rates caused by high preheat or a combination of preheat and high heat input from the weld procedures can create a very brittle martensite due to high carbon concentrations that form in the HAZ.
|
|
On Earth, basaltic magmas commonly erupt as highly fluid flows, which either emerge directly from vents or form by the coalescence of molten clots at the base of fire fountains (Hawaiian eruption). These styles are also common on Mars, but the lower gravity and atmospheric pressure on Mars allow nucleation of gas bubbles (see above) to occur more readily and at greater depths than on Earth. As a consequence, Martian basaltic volcanoes are also capable of erupting large quantities of ash in Plinian-style eruptions. In a Plinian eruption, hot ash is incorporated into the atmosphere, forming a huge convective column (cloud).
|
|
The solution to this paradox has been established by computational approaches to protein structure prediction. Levinthal himself was aware that proteins fold spontaneously and on short timescales. He suggested that the paradox can be resolved if "protein folding is sped up and guided by the rapid formation of local interactions which then determine the further folding of the peptide; this suggests local amino acid sequences which form stable interactions and serve as nucleation points in the folding process". Indeed, the protein folding intermediates and the partially folded transition states were experimentally detected, which explains the fast protein folding.
|
|
Magnetization curves dominated by rotation and magnetocrystalline anisotropy are found in relatively perfect magnetic materials used in fundamental research. Domain wall motion is a more important reversal mechanism in real engineering materials since defects like grain boundaries and impurities serve as nucleation sites for reversed-magnetization domains. The role of domain walls in determining coercivity is complicated since defects may pin domain walls in addition to nucleating them. The dynamics of domain walls in ferromagnets is similar to that of grain boundaries and plasticity in metallurgy since both domain walls and grain boundaries are planar defects.
|
|
Throughout the development of a mammal, there are three distinct stages of erythrocyte formation – embryonic, fetal and adult. Adult erythrocytes are the most common blood cell type in mammals, and their characteristic biconcave shape, 7-8 µm diameter and enucleation are amongst the greatest commonalities between mammalian species. However, primitive and fetal erythrocytes, which circulate during early stages of development, are markedly different from their adult counterparts, most obviously through their larger size, shorter lifespan, nucleation, containment of different hemoglobin chains, and higher oxygen affinity. The reasons for and functions of these differences are not well established.
|
|
In geology, it is the textural coarsening, aging or growth of phenocrysts and crystals in solid rock which is below the solidus temperature. It is often ascribed as a process in the formation of orthoclase megacrysts, as an alternative to the physical processes governing crystal growth from nucleation and growth rate thermochemical limitations. In chemistry, the term refers to the growth of larger crystals from those of smaller size which have a higher solubility than the larger ones. In the process, many small crystals formed initially slowly disappear, except for a few that grow larger, at the expense of the small crystals.
|
|
Microscopic organisms are the key component in the formation of bioconcrete as they provide the nucleation site for CaCO to precipitate on the surface. Microorganisms such as Sporosarcina pasteurii are useful in these fabrications as they create alkaline environments where high is pH and dissolved inorganic carbon(DIC) count are both high. These factors are essential for micro biologically induced calcite precipitation(MICP) which is the main mechanism in which bioconcrete is formed. Other organisms that can be used to induce this process are photosynthetic microorganisms such as microalgae and cyanobacteria, or sulphate reducing bacteria(SRB) such as Desulfovibrio desulfuricans.
|
|
They are a set of Integro-partial differential equations which gives the mean-field behavior of a population of particles from the analysis of behavior of single particle in local conditions.Ramkrishna, D.: Population Balances: Theory and Applications to Particulate Systems in Engineering, Academic Press, 2000 Particulate systems are characterized by the birth and death of particles. For example, consider precipitation process (formation of solid from liquid solution) which has the subprocesses nucleation, agglomeration, breakage, etc., that result in the increase or decrease of the number of particles of a particular radius (assuming formation of spherical particles).
|
|
In 2009, Schuh became a group leader at the MRC Laboratory of Molecular Biology in Cambridge, UK. Her work centers around the process of asymmetric oocyte division, in which oocytes mature into eggs by extruding half of their chromosomes in a small cell termed the polar body. This requires the spindle apparatus in these cells to be asymmetric. She discovered a role for proteins that control actin nucleation in the positioning of the spindle. In studying how actin helps position the spindle, she discovered that vesicles carrying specific signals can change the organization and density of actin networks.
|
|
Robert Wolfgang Cahn FRS (9 September 1924 – 9 April 2007) was a British metallurgist whose contributions to physical metallurgy centred on the properties of dislocations. Cahn developed a successful model for the nucleation of recrystallisation, which underpinned research into industrial processes involving high-temperature deformation. He also contributed substantially to the crystallography of uranium.R. W. Cahn, The Art of Belonging (Book Guild Publishing, Sussex, UK, 2005) In later life he made a great contribution to scientific editing, editing both scientific textbooks such as the comprehensive Physical Metallurgy, co-edited, with Peter Haasen, a standard reference work in the field.
|
|
The genus was discovered in 2004 by Flemming Ekelund, Niels Daugbjerg, and Line Fredslund, whose phylogenetic analysis of rDNA sequences led them to conclude that the genus Cercomonas should be separated into two taxa, with the new one being named Neocercomonas. In 2006 Karpov et al. determined that there was insufficient evidence for its status as a separate genus and reclassified it as part of Cercomonas, but study of differences in microtubule nucleation by Karpov and Cavalier-Smith in 2012 re-established it as a genus, and more recent genetic analysis seems to support Neocercomonas being a monophyletic group.
|
|
The new paradigm of traffic and transportation science following from the empirical nucleation nature of traffic breakdown (F → S transition) and Kerner's three-phase traffic theory changes fundamentally the meaning of stochastic highway capacity as follows. At any time instant there is a range of highway capacity values between a minimum and a maximum highway capacity, which are themselves stochastic values. When the flow rate at a bottleneck is inside this capacity range related to this time instant, traffic breakdown can occur at the bottleneck only with some probability, i.e., in some cases traffic breakdown occurs, in other cases it does not occur.
|
|
When the flow rate at a bottleneck exceeds the capacity value at this time instant, traffic breakdown must occur at the bottleneck. The new paradigm of traffic and transportation science following from the empirical nucleation nature of traffic breakdown (F → S transition) and Kerner's three-phase traffic theory changes fundamentally the meaning of stochastic highway capacity as followsB.S. Kerner (Ed.), Complex Dynamics of Traffic Management, Encyclopedia of Complexity and Systems Science Series, Springer, Berlin, New York 2019B.S. Kerner, "Complex Dynamics of Management: Introduction", Springer Science+Business Media LLC, R.A. Meyers (ed.), Encyclopedia of Complexity and Systems Science, Springer, Berlin (2019).
|
|
A very localized and produced enzymatically ligand concentration is involved and provides a nucleation site for the onset of biomineral precipitation. This is particularly relevant in precipitations of phosphatase activity-derivate biominerals, which cleavage molecules such as glycerol phosphate on periplasm. In Citrobacter and Serratia genera, this cleavage liberates inorganic phosphates (HPO42−) that precipitates with uranyl ion (UO22+) and cause deposition of polycrystalline minerals around the cell wall. Serratia also form biofilms that promote precipitation of chernikovite (rich in uranium) and additionally, remove up to 85% of cobalt-60 and 97% of cesium-137 by proton substitution of this mineral.
|
|
Liane G. Benning is a biogeochemist studying mineral-fluid-microbe interface processes. She is a Professor of Interface Geochemistry at the GFZ German Research Centre for Geosciences in Potsdam, Germany. Her team studies various processes that shape the Earth Surface with a special focus on two aspects: the nucleation, growth and crystallisation of mineral phases from solution and the role, effects and interplay between microbes and minerals in extreme environments. She is also interested in the characterisation of these systems, developing in situ and time resolved high resolution imaging and spectroscopic techniques to follow microbe-mineral reactions as they occur.
|
|
Inner sphere complex is a type of surface complex that refers to the surface chemistry changing a water-surface interface to one without water molecules bridging a ligand to the metal ion. Formation of inner sphere complexes occurs when ions bind directly to the surface with no intervening water molecules. These types of surface complexes are restricted to ions that have a high affinity for surface sites and include specifically adsorbed ions that can bind to the surface through covalent bonding. Inner sphere complexes describe active surface sites that are involved in nucleation, crystal growth, redox processes, soil chemistry, alongside other reactions taking place between a cation and surface.
|
|
Microcellular plastics, otherwise known as microcellular foam, is a form of manufactured plastic, specially fabricated to contain billions of tiny bubbles less than 50 microns in size (typically from 0.1 to 100 micrometers). This type of plastic is formed by dissolving gas under high pressure into various polymers, relying on "thermodynamic instability phenomena" to cause the uniform arrangement of the gas bubbles, otherwise known as nucleation. Its main purpose was to reduce material usage while maintaining valuable mechanical properties. The main room for variance in these foams is the gas used to create them; the density of the finished product is determined by the gas used.
|
|
In aluminum-induced crystallization, a thin layer of aluminum (50 nm or less) is deposited by physical vapor deposition onto the surface of the amorphous silicon. This stack of material is then annealed at a relatively low temperature between 140 °C and 200 °C in a vacuum. The aluminum that diffuses into the amorphous silicon is believed to weaken the hydrogen bonds present, allowing crystal nucleation and growth.. Experiments have shown that polycrystalline silicon with grains on the order of 0.2 – 0.3 μm can be produced at temperatures as low as 150 °C. The volume fraction of the film that is crystallized is dependent on the length of the annealing process.
|
|
Pure ethylene glycol has a specific heat capacity about one half that of water. So, while providing freeze protection and an increased boiling point, ethylene glycol lowers the specific heat capacity of water mixtures relative to pure water. A 1:1 mix by mass has a specific heat capacity of about 3140 J/(kg·°C) (0.75 BTU/(lb·°F)), three quarters that of pure water, thus requiring increased flow rates in same- system comparisons with water. The formation of large bubbles in cooling passages of internal combustion engines will severely inhibit heat flow (flux) from the area, so that allowing nucleation (tiny bubbles) to occur is not advisable.
|
|
The majority of papers reporting on ABX3 NCs make use of a hot injection procedure in which one of the reagents is swiftly injected into a hot solution containing the other reagents and ligands. The combination of high temperature and rapid addition of the reagent result in a rapid reaction that results in supersaturation and nucleation occurring over a very short period of time with a large number of nuclei. After a short period of time, the reaction is quenched by quickly cooling to room temperature. Since 2015, several articles detailing improvements to this approach with zwitterionic ligands, branched ligands and post-synthetic treatments have been reported.
|
|
When the cluster reaches a certain size, known as the critical radius, it becomes energetically favorable, and thus stable enough to continue to grow. This nucleus then remains in the system and grows as more silver atoms diffuse through the solution and attach to the surface When the dissolved concentration of atomic silver decreases enough, it is no longer possible for enough atoms to bind together to form a stable nucleus. At this nucleation threshold, new nanoparticles stop being formed, and the remaining dissolved silver is absorbed by diffusion into the growing nanoparticles in the solution. As the particles grow, other molecules in the solution diffuse and attach to the surface.
|
|
The mechanism of partition involved here is a pushing mechanism: # ParR binds to parC and pairs plasmids which form a nucleoprotein complex, or partition complex # The partition complex serves as nucleation point for the polymerization of ParM; ParM-ATP complex inserts at this point and push plasmids apart # The insertion leads to hydrolysis of ParM-ATP complex, leading to depolymerization of the filament # At cell division, plasmids copies are at each cell extremity, and will end up in future daughter cell The filament of ParM is regulated by the polymerization allowed by the presence the partition complex (ParR-parC), and by the depolymerization controlled by the ATPase activity of ParM.
|
|
The surface energy becomes more significant when grains are sufficiently small, which converts the creep mechanism from dislocation creep to diffusion creep, thus the grains start to grow. Therefore, the determination of the boundary zone between fields of these two creep mechanisms matter to know when the recrystallized grain size tends to stabilize, as to supplement the above model. The difference between this model and the previous nucleation-and-growth models lies within the assumptions: the field boundary model assumes that grain size reduces in the dislocation creep field, and enlarges in the diffusion creep field, but it is not the case in the previous models.
|
|
If the ionic compound is soluble in a solvent, it can be obtained as a solid compound by evaporating the solvent from this electrolyte solution. As the solvent is evaporated, the ions do not go into the vapour, but stay in the remaining solution, and when they become sufficiently concentrated, nucleation occurs, and they crystallize into an ionic compound. This process occurs widely in nature, and is the means of formation of the evaporite minerals. Another method of recovering the compound from solution involves saturating a solution at high temperature and then reducing the solubility by reducing the temperature until the solution is supersaturated and the solid compound nucleates.
|
|
Mecca-Cola and Pepsi are popular alternatives in the Middle East. A Coca-Cola fountain dispenser (officially a Fluids Generic Bioprocessing Apparatus or FGBA) was developed for use on the Space Shuttle as a test bed to determine if carbonated beverages can be produced from separately stored carbon dioxide, water, and flavored syrups and determine if the resulting fluids can be made available for consumption without bubble nucleation and resulting foam formation. FGBA-1 flew on STS-63 in 1995 and dispensed pre-mixed beverages, followed by FGBA-2 on STS-77 the next year. The latter mixed CO₂, water, and syrup to make beverages.
|
|
Llanybri was a demesne manor of the Lords of Llansteffan and Penrhyn and appears to be an early nucleation around a central open space, adjacent to a chapel dedicated to St Mary that had been established, as ‘Morabrichurch’, by the 14th century at least and was, in the 16th century, called ‘Marbell Church’. An area of common land lay within the village and may have Medieval origins. Pendegy Mill, some 700m west of the village, is the site of the Medieval ‘Mundegy Mill’. Rees (1932) depicts Llanybri as a borough, and though the designation is most unlikely the settlement did lie at the junction of seven routeways.
|
|
In parallel, the lab is studying the sources of microbes that colonize the gut and the flow of microbes between the infant and the surrounding environment. A 2017 study demonstrated low level of overlap in the strain membership of microbial communities in different infants hospitalized in the same neonatal intensive care unit at the same time. The group continues to study nanomaterials, including the process of oriented attachment-based crystal growth that they first described in detail in the mid- to late 1990s. Also of current interest is the impact of salinity on nucleation and growth of iron oxyhydroxides and on the structure of smectite clay materials.
|
|
Recrystallization of a metallic material (a → b) and crystal grains growth (b → c → d). Historically it was assumed that the nucleation rate of new recrystallized grains would be determined by the thermal fluctuation model successfully used for solidification and precipitation phenomena. In this theory it is assumed that as a result of the natural movement of atoms (which increases with temperature) small nuclei would spontaneously arise in the matrix. The formation of these nuclei would be associated with an energy requirement due to the formation of a new interface and an energy liberation due to the formation of a new volume of lower energy material.
|
|
From 1933, Nakaya observed natural snow and created 3,000 photographic plates of snow crystals, classifying them into seven major and numerous minor types. In the course of these observations, taking photographs of natural snow and sorting them by appearance according to weather conditions, Nakaya felt the need to make artificial snow from ice crystals grown in the laboratory. He generated water vapor in a dual-layer hollow glass tube, which was then cooled. Contrary to his initial expectations, creating snow crystals was not an easy task - instead of forming into snowflakes, the ice crystals grew like caterpillars on the cotton string he used for nucleation.
|
|
Together with Frank Glas, he predicted narrow sub-Poissonian size distributions [27] in systems with nucleation antibunching [28], and derived analytical asymptotes for their time-independent shapes. ;Elastic relaxation and plastic deformation in nanostructures He and coauthors developed semi-analytical models for elastic relaxation and misfit dislocations in nanostructures grown on lattice-mismatched substrates [29] and contributed into development of epitaxial techniques for monolithic integration of high quality optical III-V nanostructures with silicon electronic platform [8,18,30]. ;Research style Dubrovskii prefers analytical calculations to computers and tries to present theoretical models for complex growth behavior in a simple analytic form with a minimum number of physically transparent parameters.
|
|
Heazlewoodite is formed within terrestrial rocks by metamorphism of peridotite and dunite via a process of nucleation. Heazlewoodite is the least sulfur saturated of nickel sulfide minerals and is only formed via metamorphic exsolution of sulfur from the lattice of metamorphic olivine. Heazlewoodite is thought to form from sulfur and nickel which exist in pristine olivine in trace amounts, and which are driven out of the olivine during metamorphic processes. Magmatic olivine generally has up to ~4000 ppm Ni and up to 2500 ppm S within the crystal lattice, as contaminants and substituting for other transition metals with similar ionic radii (Fe2+ and Mg2+).
|
|
A specialised group of PCMs that undergo a solid/solid phase transition with the associated absorption and release of large amounts of heat. These materials change their crystalline structure from one lattice configuration to another at a fixed and well- defined temperature, and the transformation can involve latent heats comparable to the most effective solid/liquid PCMs. Such materials are useful because, unlike solid/liquid PCMs, they do not require nucleation to prevent supercooling. Additionally, because it is a solid/solid phase change, there is no visible change in the appearance of the PCM, and there are no problems associated with handling liquids, e.g.
|
|
The physical reaction that drives the eruption also causes a chemical reaction that slightly increases the pH of the soda. This is because when carbon dioxide is dissolved in water, carbonic acid is formed: H2O(l) + CO2(aq) <=> H2CO3(aq) Loss of carbon dioxide shifts the above equilibrium to the left, removing carbonic acid and increasing pH. It is the physical reaction (carbon dioxide leaving solution) and not the loss of carbonic acid that causes the eruption. The physical characteristics of Mentos (surface roughness) have the effect of drastically reducing the activation energy for carbon dioxide bubble formation, so that the nucleation rate becomes exceedingly high.
|
|
The activation energy for the release of carbon dioxide from Diet Coke by addition of Mentos has been found to be 25 kJ mol−1. The foaming is aided by the presence of food additives such as potassium benzoate, aspartame, sugars, and flavorings in Diet Coke, all which influence the degree to which water can foam. It has been claimed that gelatin and gum arabic in the Mentos candy enhance the fountain, but experiments have shown that these candy additives have no effect on the fountain. The nucleation reaction can start with any heterogeneous surface, such as rock salt, but Mentos have been found to work better than most.
|
|
When sodium chlorate is allowed to crystallize from water and the collected crystals examined in a polarimeter, each crystal turns out to be chiral and either the L form or the D form. In an ordinary experiment the amount of L crystals collected equals the amount of D crystals (corrected for statistical effects). However, when the sodium chlorate solution is stirred during the crystallization process the crystals are either exclusively L or exclusively D. In 32 consecutive crystallization experiments 14 experiments deliver D-crystals and 18 others L-crystals. The explanation for this symmetry breaking is unclear but is related to autocatalysis taking place in the nucleation process.
|
|
The "New Core Paradox" posits that the new upward revisions to the empirically measured thermal conductivity of iron at the pressure and temperature conditions of Earth's core imply that the dynamo is thermally stratified at present, driven solely by compositional convection associated with the solidification of the inner core. However, wide spread paleomagnetic evidence for a geodynamo older than the likely age of the inner core (~1 Gyr) creates a paradox as to what powered the geodynamo prior to inner core nucleation. Recently it has been proposed that a higher core cooling rate and lower mantle cooling rate can resolve the paradox in part. However, the paradox remains unresolved.
|
|
As a sideline, Oriani independently verified the high pressure technique developed at the GE Laboratory for the synthesis of a diamond. After ten years at GE, Oriani moved on to U.S. Steel's Bain Laboratory for Fundamental Research in which he served as Assistant Director and researcher on irreversible thermodynamics applied to metallurgy, nucleation, thermomigration, electromigration, impact adhesion, and hydrogen embrittlement of steel. In 1980 he retired from U.S. Steel and was invited to serve at the University of Minnesota as Professor and Director of a newly established Corrosion Research Center. He retired in 1999, but maintained an office and conducted research experiments there until 2014.
|
|
ActA proteins associated with the old bacterial cell pole (being a bacillus, L. monocytogenes septates in the middle of the cell, thus has one new pole and one old pole) are capable of binding the Arp2/3 complex, thereby inducing actin nucleation at a specific area of the bacterial cell surface. Actin polymerization then propels the bacterium unidirectionally into the host cell membrane. The protrusion formed may then be internalized by a neighboring cell, forming a double-membrane vacuole from which the bacterium must escape using LLO and PlcB. This mode of direct cell-to-cell spread involves a cellular mechanism known as paracytophagy.
|
|
In the realm of theory, the first appearance of fractals in cosmology was likely with Andrei Linde’s "Eternally Existing Self-Reproducing Chaotic Inflationary Universe" theory (see Chaotic inflation theory), in 1986. In this theory, the evolution of a scalar field creates peaks that become nucleation points which cause inflating patches of space to develop into "bubble universes," making the universe fractal on the very largest scales. Alan Guth's 2007 paper on "Eternal Inflation and its implications" shows that this variety of Inflationary universe theory is still being seriously considered today. And inflation, in some form or other, is widely considered to be our best available cosmological model.
|
|
Cosmics Leaving Outdoor Droplets (CLOUD)CLOUD official website is an experiment being run at CERN by a group of researchers led by Jasper Kirkby to investigate the microphysics between galactic cosmic rays (GCRs) and aerosols under controlled conditions. The experiment began operation in November 2009.CLOUD experiment provides unprecedented insight into cloud formation, CERN The primary goal is to understand the influence of galactic cosmic rays (GCRs) on aerosols and clouds, and their implications for climate. Although its design is optimised to address the cosmic ray question, (as posed by Henrik Svensmark and colleagues in 1997) CLOUD allows as well to measure aerosol nucleation and growth under controlled laboratory conditions.
|
|
In-vitro, tau proteins have been shown to directly bind microtubules, promote nucleation and prevent disassembly, and to induce the formation of parallel arrays. Additionally, tau proteins have also been shown to stabilize microtubules in axons and have been implicated in Alzheimer's disease. The second class is composed of MAPs with a molecular weight of 200-1000 kDa, of which there are four known types: MAP-1, MAP-2, MAP-3 and MAP-4. MAP-1 proteins consists of a set of three different proteins: A, B and C. The C protein plays an important role in the retrograde transport of vesicles and is also known as cytoplasmic dynein.
|
|
After appropriate dissolution of the sample the following steps should be followed for successful gravimetric procedure: 1\. Preparation of the Solution: This may involve several steps including adjustment of the pH of the solution in order for the precipitate to occur quantitatively and get a precipitate of desired properties, removing interferences, adjusting the volume of the sample to suit the amount of precipitating agent to be added. 2\. Precipitation: This requires addition of a precipitating agent solution to the sample solution. Upon addition of the first drops of the precipitating agent, supersaturation occurs, then nucleation starts to occur where every few molecules of precipitate aggregate together forming a nucleus.
|
|
The initial steep-sloped segment corresponds to the FM growth mode while the later, shallow-sloped region is representative of the VW mode. This schematic is characteristic of 'ideal' SK growth where nucleation onset begins at 2 monolayer coverage. Analytical techniques such as Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and reflection high energy electron diffraction (RHEED), have been extensively used to monitor SK growth. AES data obtained in situ during film growth in a number model systems, such as Pd/W(100), Pb/Cu(110), Ag/W(110), and Ag/Fe(110), show characteristic segmented curves like those presented in figure 4.
|
|
Height of the film Auger peaks plotted as a function of surface coverage Θ, initially exhibits a straight line, which is indicative of AES data for FM growth. There is a clear break point at a critical adsorbate surface coverage followed by another linear segment at a reduced slope. The paired break point and shallow line slope is characteristic of island nucleation; a similar plot for FM growth would exhibit many such line and break pairs while a plot of the VW mode would be a single line of low slope. In some systems, reorganization of the 2D wetting layer results in decreasing AES peaks with increasing adsorbate coverage.
|
|
This etching is typically done with acid, a laser, or a glass etching tool from a craft shop to provide nucleation sites for continuous bubble formation (note that not all glasses are etched in this way). In 1662 this method was developed in England, as records from the Royal Society show. Dom Pérignon was originally charged by his superiors at the Abbey of Hautvillers to get rid of the bubbles since the pressure in the bottles caused many of them to burst in the cellar. As sparkling wine production increased in the early 18th century, cellar workers had to wear a heavy iron mask to prevent injury from spontaneously bursting bottles.
|
|
Self-assembly in microscopic systems usually starts from diffusion, followed by the nucleation of seeds, subsequent growth of the seeds, and ends at Ostwald ripening. The thermodynamic driving free energy can be either enthalpic or entropic or both. In either the enthalpic or entropic case, self-assembly proceeds through the formation and breaking of bonds, possibly with non-traditional forms of mediation. The kinetics of the self-assembly process is usually related to diffusion, for which the absorption/adsorption rate often follows a Langmuir adsorption model which in the diffusion controlled concentration (relatively diluted solution) can be estimated by the Fick's laws of diffusion.
|
|
As with unimolecular reactions, the keys to the qualitative and quantitative understanding of the many processes in emulsion polymerisation are the rate coefficients of the individual steps. These steps are initiation (how quickly a growing chain starts), propagation (how quickly individual monomer units are added), radical loss processes (the termination and transfer of radical activity), and particle formation (nucleation). With Prof D Napper, Gilbert applied equations that he had solved in gas-phase chemistry to the area of emulsion polymerisation. This opened the way for him to develop—initially in collaboration with Napper—new theoretical and experimental methods for extracting the rate coefficients of elementary processes.
|
|
Illustration of sources of aerosols found during NAAMES cruisesA clear seasonal difference in the quantity of biogenic sulfate aerosols was discovered in the North Atlantic as a result of the NAAMES campaign. These aerosols were traced to two different biogenic origins, both of them marine due to the lack of continental air mass influences during the study period. The biogenic origin was the production of dimethyl sulfide (DMS) by phytoplankton, which then act as cloud condensation nuclei (CCN) and affect cloud formation. This study classified the sulfates as "New Sulfate", formed by nucleation in the atmosphere; and "Added Sulfate", which were existing aerosols in the atmosphere where sulfate was incorporated.
|
|
To achieve formation of amorphous structure even during slower cooling, the alloy has to be made of three or more components, leading to complex crystal units with higher potential energy and lower chance of formation. The atomic radius of the components has to be significantly different (over 12%), to achieve high packing density and low free volume. The combination of components should have negative heat of mixing, inhibiting crystal nucleation and prolonging the time the molten metal stays in supercooled state. The alloys of boron, silicon, phosphorus, and other glass formers with magnetic metals (iron, cobalt, nickel) have high magnetic susceptibility, with low coercivity and high electrical resistance.
|
|
The Çınarcık Basin is a transtensional basin which runs along the Princes' Islands segment of the northern branch of the North Anatolian Fault (NAF). However, in correspondence with the basin there is no evidence of a single strike-slip Fault, neither is visible a cross-basin fault or a pure strike-slip fault in correspondence of the northern margin; along the southern and northern edges seismic imaging shows many deep-penetrating faults. The basin hosted the nucleation points of many among the strongest earthquakes of the region, like those of 1509 and of 1766, and is expected to host the epicenter of the next large earthquake that will hit Istanbul.
|
|
Sodium perborate is manufactured by reaction of borax and sodium hydroxide to give sodium metaborate , which is then reacted with hydrogen peroxide to give hydrated sodium perborate: Na2B4O7 + 2NaOH -> 4 NaBO2 + H2O NaBO2 + 2H2O2 -> Na2B2O4(OH)4 A surfactant may be added to control crystal size.J. Dugua and B.Simon (1978): "Crystallization of sodium perborate from aqueous solutions: I. Nucleation rates in pure solution and in presence of a surfactant". Journal of Crystal Growth, volume 44, issue 3, pages 265-279.J. Dugua and B.Simon (1978): "Crystallization of sodium perborate from aqueous solutions: II. Growth kinetics of different faces in pure solution and in the presence of a surfactant".
|
|
The explanation of traffic breakdown at a highway bottleneck by a F → S transition in a metastable free flow at the bottleneck is the basic assumption of Kerner’s three-phase theory. However, none of earlier traffic- flow theories incorporates a F→S transition in a metastable free flow at the bottleneck. Therefore, none of the classical traffic flow theories is consistent with the empirical nucleation nature of real traffic breakdown at a highway bottleneck. The F→S phase transition in metastable free flow at highway bottleneck does explain the empirical evidence of the induced transition from free flow to synchronized flow together with the flow-rate dependence of the breakdown probability.
|
|
Cubic boron nitride or c-BN was first synthesized in 1957 by Robert H. Wentorf at General Electric, shortly after the synthesis of diamond. The general process for c-BN synthesis is the dissolution of hexagonal boron nitride (h-BN) in a solvent- catalyst, usually alkali or alkaline earth metals or their nitrides, followed by spontaneous nucleation of c-BN under high pressure, high temperature (HPHT) conditions. The yield of c-BN is lower and substantially slower compared to diamond's synthetic route due to the complicated intermediate steps. Its insolubility in iron and other metal alloys makes it more useful for some industrial applications than diamond.
|
|
Recent research at CERN's CLOUD facility examined links between cosmic rays and cloud condensation nuclei, demonstrating the effect of high-energy particulate radiation in nucleating aerosol particles that are precursors to cloud condensation nuclei. Kirkby (CLOUD team leader) said, "At the moment, it [the experiment] actually says nothing about a possible cosmic-ray effect on clouds and climate." After further investigation, the team concluded that "variations in cosmic ray intensity do not appreciably affect climate through nucleation." 1983–1994 global low cloud formation data from the International Satellite Cloud Climatology Project (ISCCP) was highly correlated with galactic cosmic ray (GCR) flux; subsequent to this period, the correlation broke down.
|
|
It may last for a very long time in that state (a property known as metastability), and might eventually move to a more stable state, an event known as vacuum decay. The most common suggestion of how such a change might happen is called bubble nucleation – if a small region of the universe by chance reached a more stable vacuum, this "bubble" (also called "bounce")Tommi Markkanen et al., Cosmological Aspects of Higgs Vacuum Metastability would spread. A false vacuum exists at a local minimum of energy and is therefore not stable, in contrast to a true vacuum, which exists at a global minimum and is stable.
|
|
However, some saturation decompression schedules specifically do not allow an decompression to start with an upward excursion. Neither the excursions nor the decompression procedures currently in use (2016) have been found to cause decompression problems in isolation, but there appears to be significantly higher risk when excursions are followed by decompression before non-symptomatic bubbles resulting from excursions have totally resolved. Starting decompression while bubbles are present appears to be the significant factor in many cases of otherwise unexpected decompression sickness during routine saturation decompression. Application of a bubble model in 1985 allowed successful modelling of conventional decompressions, altitude decompression, no-stop thresholds, and saturation dives using one setting of four global nucleation parameters.
|
|
Decompression (altitude) refers to the reduction in ambient pressure due to ascent above sea level. Decompression has physical effects on gas filled spaces and on liquids, particularly when they contain dissolved gases. Physiological effects of decompression are due to these physical effects and the consequential effects on the living tissues, mostly as a result of the formation and growth of bubbles, and the expansion of gas filled spaces. Formation and growth of bubbles due to reduced pressure can be due to reduction in solubility as described by Henry's Law, nucleation and growth of bubbles in supersaturated liquids and boiling of liquids when the pressure is reduced below the vapour pressure for the temperature of the liquid.
|
|
Injection molding and blow molding differ in regards to the type of product in need of being manufactured. Injection molding, much like casting, is centered around creating a mold for a solid object, which is to later be filled in with the molten plastic. Blow molding on the other hand, is more specialized for hollow objects, although it is less accurate regarding wall thickness with this dimension being an undefined feature (unlike in an injection mold where all dimensions are predetermined). In respect to MuCell® and microcellular plastics, these processes vary from that of traditional plastics due to the additional steps of gas dissolving and cell nucleation before the molding process can begin.
|
|
Scale crystals are initially dispersed in production systems until accumulation of stable crystals of insoluble sulfates and scale growth occur at nucleation centers. Uneven pipeline surfaces and production equipment such as pumps and valves cause rapid scale growth to levels that can block pipelines. The scaling-tendency of an oil-well can be predicted based on the prevailing conditions such as pH, temperature, pressure, ionic strength and the mole fraction of CO2 in the vapor and aqueous phases. For instance the saturation index for CaCO3 scale is calculated using the formula; Fs= {[Ca2+][CO32−]}/Ksp Where Fs is the scale saturation ratio, defined as the ratio of the activity product to the solubility product of the salt.
|
|
As a long-lasting in vivo effect, cofilin recycles older ADP-F-actin, helping cell to maintain ATP-G-actin pool for sustained motility. pH, phosphorylation and phosphoinositides regulate cofilin's binding and associating activity with actin The Arp2/3 complex and cofilin work together to reorganize the actin filaments in the cytoskeleton. Arp 2/3, an actin binding proteins complex, binds to the side of ATP-F-actin near the growing barbed end of the filament, causing nucleation of a new F-actin branch, while cofilin-driven depolymerization takes place after dissociating from the Arp2/3 complex. They also work together to reorganize actin filaments in order to traffic more proteins by vesicle to continue the growth of filaments.
|
|
If the surface cannot reach equilibrium in the presence of a driving force, then it will continue to advance without waiting for the lateral motion of steps. Thus, Cahn concluded that the distinguishing feature is the ability of the surface to reach an equilibrium state in the presence of the driving force. He also concluded that for every surface or interface in a crystalline medium, there exists a critical driving force, which, if exceeded, will enable the surface or interface to advance normal to itself, and, if not exceeded, will require the lateral growth mechanism. Thus, for sufficiently large driving forces, the interface can move uniformly without the benefit of either a heterogeneous nucleation or screw dislocation mechanism.
|
|
For example, using AFM–based nanoindentation it has been shown that a single collagen fibril is a heterogeneous material along its axial direction with significantly different mechanical properties in its gap and overlap regions, correlating with its different molecular organizations in these two regions. Collagen fibrils/aggregates are arranged in different combinations and concentrations in various tissues to provide varying tissue properties. In bone, entire collagen triple helices lie in a parallel, staggered array. 40 nm gaps between the ends of the tropocollagen subunits (approximately equal to the gap region) probably serve as nucleation sites for the deposition of long, hard, fine crystals of the mineral component, which is hydroxylapatite (approximately) Ca10(OH)2(PO4)6.
|
|
The fact that small domains of ice XI can exist at temperatures up to 111 K has some scientists speculating that it may be fairly common in interstellar space, with small 'nucleation seeds' spreading through space and converting regular ice, much like the fabled ice- nine mentioned in Vonnegut's Cat's Cradle. The possible roles of ice XI in interstellar space and planet formation have been the subject of several research papers. Until observational confirmation of ice XI in outer space is made, the presence of ice XI in space remains controversial owing to the aforementioned criticism raised by Iitaka. The infrared absorption spectra of ice XI was studied in 2009 in preparation for searches for ice XI in space.
|
|
Ankyrin-repeat proteins present an unusual problem in the study of protein folding, which has largely focused on globular proteins that form well-defined tertiary structure stabilized by long-range, nonlocal residue-residue contacts. Ankyrin repeats, by contrast, contain very few such contacts (that is, they have a low contact order). Most studies have found that ankyrin repeats fold in a two-state folding mechanism, suggesting a high degree of folding cooperativity despite the local inter-residue contacts and the evident need for successful folding with varying numbers of repeats. Some evidence, based on synthesis of truncated versions of natural repeat proteins, and on the examination of phi values, suggests that the C-terminus forms the folding nucleation site.
|
|
According to Natural England, modern settlement closely follows a medieval pattern of nucleation as is what is common in Western Europe, much of which was established and planned in the 12th and 13th centuries. This leads to small villages sited on ridges in the south-west or at the crossing points of rivers, and houses clustered around greens where stock were kept relatively safe from border raids.. Due to Northumberland's low density Northumberland is home to a great deal of country houses. In terms of agriculture, the lowlands regions in the south are home to crop farming and cattle herding, meanwhile in the uplands of the north and west shepherding is more common.
|
|
However, some saturation decompression schedules specifically do not allow an decompression to start with an upward excursion. Neither the excursions nor the decompression procedures currently in use (2016) have been found to cause decompression problems in isolation, but there appears to be significantly higher risk when excursions are followed by decompression before non- symptomatic bubbles resulting from excursions have totally resolved. Starting decompression while bubbles are present appears to be the significant factor in many cases of otherwise unexpected decompression sickness during routine saturation decompression. Application of a bubble model in 1985 allowed successful modelling of conventional decompressions, altitude decompression, no-stop thresholds, and saturation dives using one setting of four global nucleation parameters.
|
|
Most IPNs do not interpenetrate completely on a molecular scale, but rather form small dispersed or bicontinuous phase morphologies with characteristic length scales on the order of tens of nanometers. However, since these length scales are relatively small, they are often considered homogeneous on a macroscopic scale. The characteristic lengths associated with these domains often scale with the length of chains between crosslinks, and thus the morphology of the phases is often dictated by the crosslinking density of the constituent networks. The kinetics of phase separation in IPNs can arise from both nucleation and growth and spinodal decomposition mechanisms, with the former producing discrete phases akin to dispersed spheres and the latter forming bicontinuous phases akin to interconnected cylinders.
|
|
Geometrical differences between jogs and kinks A Jog describes the steps of a dislocation line that are not in the glide plane of a crystal structure. A dislocation line is rarely uniformly straight, often containing many curves and steps that can impede or facilitate dislocation movement by acting as pinpoints or nucleation points respectively. Because jogs are out of the glide plane, under shear they cannot move by glide (movement along the glide plane). They instead must rely on vacancy diffusion facilitated climb to move through the lattice.. Away from the melting point of a material, vacancy diffusion is a slow process, so jogs act as immobile barriers at room temperature for most metals.
|
|
Most animal cells have one MTOC during interphase, usually located near the nucleus, and generally associated closely with the Golgi apparatus. The MTOC is made up of a pair of centrioles at its center, and is surrounded by pericentriolar material (PCM) that is important for microtubule nucleation. Microtubules are anchored at the MTOC by their minus ends, while their plus ends continue to grow into the cell periphery. The polarity of the microtubules is important for cellular transport, as the motor proteins kinesin and dynein typically move preferentially in the "plus" and "minus" directions respectively, along a microtubule, allowing vesicles to be directed to or from the endoplasmic reticulum and Golgi apparatus.
|
|
The purpose of this modification is to make synthetic protein cages more biocompatible; this post synthetic modification makes the protein cage less susceptible to an immune response and stabilizes the cage from degradation from proteases. Virus-like protein (VLP) cages have also been synthesized and recombinant DNA technology is used to form non-native virus-like proteins. The first reported case of the formation of non-native VLP constructs into a capsid-like structure utilized a functionalized gold core for nucleation. The self-assembly of the VLP was initiated by the electrostatic interaction of the functionalized gold nanoparticles which is similar to the interaction of a native virus with its nucleic acid component.
|
|
Researchers has also successfully developed multi layer nanocables with a silver core nanowire, a peptide insulation layer and a gold outer coat, This is done by reducing AgNO3 inside nanotubes, and then bounding a layer of thiol containing peptides with gold particles attached. This layer acts as a nucleation site during the next step where process of electroless deposition layers a coating of gold on the nanotubes to form metal-insulator-metal trilayer coaxial nanocables. Peptide nanotubes are able to produce nanowires of uniform size and this is particularly useful in the nanoelectric applications as electrical and magnetic properties are sensitive to size. Nanotube's exceptional mechanical strength and stability makes them excellent materials for application in this area.
|
|
When polymers crystallize from an isotropic, bulk of melt or concentrated solution, the crystalline lamellae (10 to 20 nm in thickness) are typically organized into a spherulitic morphology as illustrated above. However, when polymer chains are confined in a space with dimensions of a few tens of nanometers, comparable to or smaller than the lamellar crystal thickness or the radius of gyration, nucleation and growth can be dramatically affected. As an example, when a polymer crystallizes in a confined ultrathin layer, the isotropic spherulitic organization of lamellar crystals is hampered and confinement can produce unique lamellar crystal orientations. Sometimes the chain alignment is parallel to the layer plane and the crystals are organized as ‘‘on-edge’’ lamellae.
|
|
Quantum dot manufacturing relies on a process called high temperature dual injection which has been scaled by multiple companies for commercial applications that require large quantities (hundreds of kilograms to tonnes) of quantum dots. This reproducible production method can be applied to a wide range of quantum dot sizes and compositions. The bonding in certain cadmium-free quantum dots, such as III-V-based quantum dots, is more covalent than that in II-VI materials, therefore it is more difficult to separate nanoparticle nucleation and growth via a high temperature dual injection synthesis. An alternative method of quantum dot synthesis, the molecular seeding process, provides a reproducible route to the production of high quality quantum dots in large volumes.
|
|
The process utilises identical molecules of a molecular cluster compound as the nucleation sites for nanoparticle growth, thus avoiding the need for a high temperature injection step. Particle growth is maintained by the periodic addition of precursors at moderate temperatures until the desired particle size is reached. The molecular seeding process is not limited to the production of cadmium-free quantum dots; for example, the process can be used to synthesise kilogram batches of high quality II-VI quantum dots in just a few hours. Another approach for the mass production of colloidal quantum dots can be seen in the transfer of the well-known hot-injection methodology for the synthesis to a technical continuous flow system.
|
|
The eruption is caused by a physical reaction, rather than any chemical reaction. The addition of the Mentos leads to the rapid nucleation of carbon dioxide gas bubbles precipitating out of solution:New Demonstrations and New Insights on the Mechanism of the Candy-Cola Soda Geyser Thomas S. Kuntzleman, Laura S. Davenport, Victoria I. Cothran, Jacob T. Kuntzleman, and Dean J. Campbell Journal of Chemical Education Article ASAP :CO2(aq) -> CO2(g) SEM image of the surface of a Mentos candy. The conversion of dissolved carbon dioxide to gaseous carbon dioxide forms rapidly expanding gas bubbles in the soda, which pushes the beverage contents out of the container. Gases, in general, are more soluble in liquids at elevated pressures.
|
|
Crystal formation can be divided into two types, where the first type of crystals are composed of a cation and anion, also known as a salt, such as sodium acetate. The second type of crystals are composed of uncharged species, for example menthol. Crystal formation can be achieved by various methods, such as: cooling, evaporation, addition of a second solvent to reduce the solubility of the solute (technique known as antisolvent or drown-out), solvent layering, sublimation, changing the cation or anion, as well as other methods. The formation of a supersaturated solution does not guarantee crystal formation, and often a seed crystal or scratching the glass is required to form nucleation sites.
|
|
The Moche civilization flourished in northern Peru with its Huacas del Sol y de la Luna from about AD 100 to 800, during the Regional Development Epoch. The people likely had formed into a group of autonomous polities that shared a common elite culture, as seen in the rich iconography and monumental architecture that survive today. They are particularly noted for their elaborately-painted ceramics, gold work, monumental constructions (huacas) and irrigation systems. Moche history is broadly divided into three periods – the emergence of the Moche culture in the Early Moche (AD 100–300), its expansion and florescence during the Middle Moche (300–600), and the urban nucleation and subsequent collapse in the Late Moche (500–750).
|
|
It can be created artificially with aerosol canisters if the humidity and temperature conditions are right. It can also occur as part of natural weather, when humid air cools rapidly, for example when the air comes into contact with surfaces that are much cooler than the air. The formation of mist, as of other suspensions, is greatly aided by the presence of nucleation sites on which the suspended water phase can congeal. Thus even such unusual sources as small particulates from volcanic eruptions, releases of strongly polar gases, and even the magnetospheric ions associated with polar lights can in right conditions trigger the formation of mist and can make mirrors appear foggy.
|
|
The third recognized mechanism for tufa development is the active role played by the biota. Algae and mosses, along with higher plants and some insects, often trap tiny particles within their sinuous roots, fronds, and shelter/feeding structures, acting as nucleation points for further precipitation. This may explain some of the deposition locations, but the biota plays a larger role as photosynthetic plants remove CO2 from the water, further concentrating the Ca2+ and CO32− and driving precipitation. The Portneuf through this reach is rich in plant life not only due to the nutrient accumulation as it travels through farmland but from the warm water inputs that protect the stream from the effects of the harsh cold of winter temperatures.
|
|
At this point, addition of extra precipitating agent will either form new nuclei or will build up on existing nuclei to give a precipitate. This can be predicted by Von Weimarn ratio where, according to this relation the particle size is inversely proportional to a quantity called the relative supersaturation where Relative supersaturation = (Q – S)/S The Q is the concentration of reactants before precipitation, S is the solubility of precipitate in the medium from which it is being precipitated. Therefore, to get particle growth instead of further nucleation we must make the relative supersaturation ratio as small as possible. The optimum conditions for precipitation which make the supersaturation low are: a.
|
|
The Southern African Special Administrative Region is a political concept proposing the creation of an autonomous self-governing region - or special administrative region (SAR) - in southern Africa. The proposal, made to encourage political discourse, was put forward in late 2007 following popular concern that southern Africa was at risk of losing political, social and economic headway. Much of the discussion to date has surrounded the need for the nucleation of an economic and social example for southern Africa, as well as innovative approaches to reducing crime and poverty in the region. The concept of a special administrative region in southern African is based in the theory of Paul Romer, professor of economics at New York University.
|
|
These patterns describe only the statistical behavior of aftershocks; the actual times, numbers and locations of the aftershocks are stochastic, while tending to follow these patterns. As this is an empirical law, values of the parameters are obtained by fitting to data after a mainshock has occurred, and they imply no specific physical mechanism in any given case. The Utsu-Omori law has also been obtained theoretically, as the solution of a differential equation describing the evolution of the aftershock activity, where the interpretation of the evolution equation is based on the idea of deactivation of the faults in the vicinity of the main shock of the earthquake. Also, previously Utsu-Omori law was obtained from a nucleation process.
|
|
Circular widget etched in the base of a standard pint glass Comparison of bubbles formed in a glass containing a widget (left) and one with a smooth base (right). The term widget glass can be used to refer to a laser-etched pattern at the bottom of a beer glass which aids the release of carbon dioxide bubbles. The pattern of the etching can be anything from a simple circular or chequered design to a logo or text. The widget in the base of a beer glass works by creating a nucleation point, allowing the CO2 to be released from the liquid which comes into contact with it, thus assisting in maintaining head on the beer.
|
|
Moche society was agriculturally based, with a significant level of investment in the construction of a network of irrigation canals for the diversion of river water to supply their crops. Their culture was sophisticated; and their artifacts express their lives, with detailed scenes of hunting, fishing, fighting, sacrifice, sexual encounters and elaborate ceremonies. The Moche are particularly noted for their elaborately painted ceramics, gold work, monumental constructions (huacas) and irrigation systems. Moche history may be broadly divided into three periods – the emergence of the Moche culture in Early Moche (100–300 AD), its expansion and fluorescence during Middle Moche (300–600 AD), and the urban nucleation and subsequent collapse in Late Moche (500–750 AD).
|
|
In 1995, he accepted a post doctoral position at Bell Labs in Murray Hill, working in the group of Yves Chabal, in the Physical Sciences research laboratory, headed by Horst Stormer. He studied the surface oxidation of silicon"Heterogeneous nucleation of oxygen on silicon: Hydroxyl-mediated interdimer coupling on Si(100)-(2x1)", Alejandra B. Gurevich, Boris B. Stefanov, Marcus K. Weldon, Yves J. Chabal, and Krishnan Raghavachari, Physical Review B 58, 15 November 1998, retrieved 20 Feb 2015. and the science of wafer bonding"Interfacial chemistry in direct wafer bonding", Yves J. Chabal and Marcus K. Weldon, Materials Research Society, 16 April 2001, retrieved 20 Feb 2015. and splitting by hydrogen implantation, winning multiple awards for his work.
|
|
Most of tropospheric gases are treated as ideal gases and water vapor, with its ability to change phase from vapor, to liquid, to solid, and back is considered as one of the most important trace components of air. Advanced topics are phase transitions of water, homogeneous and in- homogeneous nucleation, effect of dissolved substances on cloud condensation, role of supersaturation on formation of ice crystals and cloud droplets. Considerations of moist air and cloud theories typically involve various temperatures, such as equivalent potential temperature, wet-bulb and virtual temperatures. Connected areas are energy, momentum, and mass transfer, turbulence interaction between air particles in clouds, convection, dynamics of tropical cyclones, and large scale dynamics of the atmosphere.
|
|
Although the ability of ice to reject suspended particles in the growth process has long been known, the mechanism remains the subject of some discussion. It was believed initially that during the moments immediately following the nucleation of the ice crystals, particles are rejected from the growing planar ice front, leading to the formation of a constitutionally super-cooled zone directly ahead of the growing ice. This unstable region eventually results in perturbations, breaking the planar front into a columnar ice front, a phenomenon better known as a Mullins-Serkerka instability. After the breakdown, the ice crystals grow along the temperature gradient, pushing ceramic particles from the liquid phase aside so that they accumulate between the growing ice crystals.
|
|
In 2004 Kerner introduced congested pattern control approach. Contrarily to standard traffic control at a network bottleneck in which a controller (for example, through the use of on-ramp metering, speed limit, or other traffic control strategies) tries to maintain free flow conditions at the maximum possible flow rate at the bottleneck, in congested pattern control approach no control of traffic flow at the bottleneck is realized as long as free flow is realized at the bottleneck. Only when an F → S transition (traffic breakdown) has occurred at the bottleneck, the controller starts to work trying to return free flow at the bottleneck. Congested pattern control approach is consistent with the empirical nucleation nature of traffic breakdown.
|
|
The existence of these two phases F and S at the same flow rate does not result from the stochastic nature of traffic: Even if there were no stochastic processes in vehicular traffic, the states F and S do exist at the same flow rate. However, classical stochastic approaches to traffic control do not assume a possibility of an F→S phase transition in metastable free flow. For this reason, these stochastic approaches cannot resolve the problem of the inconsistence of classical theories with the nucleation nature of real traffic breakdown. According to Kerner, this inconsistence can explain why network optimization and control approaches based on these fundamentals and methodologies have failed by their applications in the real world.
|
|
This is a special category of chain-growth supramolecular polymerization, where the monomer nucleates only in an early stage of polymerization to generate “seeds” and becomes active for polymer chain elongation upon further addition of a new batch of monomer. A secondary nucleation is suppressed in most of the case and thus possible to realize a narrow polydispersity of the resulting supramolecular polymer. In 2007, Ian Manners and Mitchell A. Winnik introduced this concept using a polyferrocenyldimethylsilane–polyisoprene diblock copolymer as the monomer, which assembles into cylindrical micelles. When a fresh feed of the monomer is added to the micellar “seeds” obtained by sonication, the polymerization starts in a living polymerization manner.
|
|
Working on thin films and nanomatter, Chopra did pioneering studies through which he established specular scattering of electrons in epitaxial metal films, discovered field induced nucleation and growth process as well as giant photocontraction effect in amorphous chalcogenide films, developed semiconducting metallopolymer films and proposed new process protocols for low dimensional nanomaterials and high temperature superconductors. He published his findings through more than 430 research articles and ten books, which include Thin film phenomena, Thin Film Solar Cells, Thin Film Device Applications and Vacuum Science and Technology. He has also edited two books, Thin Film Technology and Applications: International Workshop, New Delhi, Nov. 1984, Proceedings and Thin Films 7: Proceedings of the 7th International Conference on Thin Films, New Delhi, India, December 7–11, 1987.
|
|
Even professionals experience periodic mishaps during evaporation, especially bumping, though experienced users become aware of the propensity of some mixtures to bump or foam, and apply precautions that help to avoid most such events. In particular, bumping can often be prevented by taking homogeneous phases into the evaporation, by carefully regulating the strength of the vacuum (or the bath temperature) to provide for an even rate of evaporation, or, in rare cases, through use of added agents such as boiling chips (to make the nucleation step of evaporation more uniform). Rotary evaporators can also be equipped with further special traps and condenser arrays that are best suited to particular difficult sample types, including those with the tendency to foam or bump.
|
|
If the concentrations of phosphate and UO22+ are sufficiently high, minerals such as autunite (Ca(UO2)2(PO4)2•10-12H2O) or polycrystalline HUO2PO4 may form thus reducing the mobility of UO22+. Compared to the direct addition of inorganic phosphate to contaminated groundwater, biomineralization has the advantage that the ligands produced by microbes will target uranium compounds more specifically rather than react actively with all aqueous metals. Stimulating bacterial phosphatase activity to liberate phosphate under controlled conditions limits the rate of bacterial hydrolysis of organophosphate and the release of phosphate to the system, thus avoiding clogging of the injection location with metal phosphate minerals. The high concentration of ligands near the cell surface also provides nucleation foci for precipitation, which leads to higher efficiency than chemical precipitation.
|
|
If the number of lung capillaries blocked by these bubbles is relatively small, the diver will not display symptoms, and no tissue will be damaged (lung tissues are adequately oxygenated by diffusion). The bubbles which are small enough to pass through the lung capillaries may be small enough to be dissolved due to a combination of surface tension and diffusion to a lowered concentration in the surrounding blood, though the Varying Permeability Model nucleation theory implies that most bubbles passing through the pulmonary circulation will lose enough gas to pass through the capillaries and return to the systemic circulation as recycled but stable nuclei. Bubbles which form within the tissues must be eliminated in situ by diffusion, which implies a suitable concentration gradient.
|
|
However, there could also be phosphorylation-independent structural aspects contributing to binding. Plo1 (the Plk found in fission yeast) is part of a positive-feedback loop that controls the expression of genes that are required for cell division. Plk has also been shown to be needed at the G2/M transition. Spindle pole formation needs Plk1, and some proteins such as gamma-tubulin fail to recruit spindle poles in the absence of Plk1 for centrosome maturation. Several other potential Plk1 substrates and binding partners that are implicated in microtubule nucleation and dynamics have also been identified including the microtubule-severing protein katanin,McNally, K. P., Buster, D. & McNally, F. J. Katanin-mediated microtubule severing can be regulated by multiple mechanisms.
|
|
TPX2 is also important in activating and recruiting Aurora A kinase, a kinase responsible for phosphorylating TPX2 and essential for cell proliferation. In the presence of nuclear import factor importin α, TPX2 is bound and prevented from binding Aurora A kinase, though it is still able to bind microtubules via its amino-terminal domain. This leads to inhibition of M phase microtubule nucleation. In contrast, TPX2 is freed from inhibition by displacement of importin α via RanGTP, though RanGTP is not required for free TPX2 activity, as TPX2 has been shown to induce microtubule assembly in the absence of exogenous and depletion of endogenous RanGTP. This suggests that TPX2 is downstream of RanGTP activity, but whether TPX2 is directly regulated by RanGTP still remains to be determined.
|
|
Lindow, now a plant pathologist at the University of California- Berkeley, found that when this particular bacterium was introduced to plants where it is originally absent, the plants became very vulnerable to frost damage. He would go on to identify the bacterium as P. syringae, investigate P. syringaes role in ice nucleation and in 1977, discover the mutant ice-minus strain. He was later successful at developing the ice-minus strain of P. syringae through recombinant DNA technology as well. In 1983, a biotech company, Advanced Genetic Sciences (AGS) applied for U.S. government authorization to perform field tests with the ice-minus strain of P. syringae, but environmental groups and protestors delayed the field tests for four years with legal challenges.
|
|
The freezing of organic matter in these aerosols promotes the formation of clouds in warmer and drier environments than where they would otherwise form, especially at high latitudes such as the North Atlantic Ocean. Organic matter in these aerosols help nucleation of water droplets at these regions, yet plenty of unknowns remain, such as what fraction contain ice-freezing organic materials, and from what biological sources. Nevertheless, the role of phytoplankton blooms as a source of enhanced ice nucleating particles has been confirmed in laboratory experiments, implying the important role of these aerosols in cloud radiative forcing. Primary marine aerosols created through bubble-bursting emission have been measured in the North Atlantic during spring 2008 by the International Chemistry Experiment in the Arctic Lower Troposphere (ICEALOT).
|
|
Kerner developed the three-phase theory as an explanation of the empirical nature of traffic breakdown at highway bottlenecks: a random (probabilistic) F → S phase transition that occurs in metastable state of free flow. Herewith Kerner explained the main prediction, that this metastability of free flow with respect to the F → S phase transition is governed by the nucleation nature of an instability of synchronized flow. The explanation is a large enough local increase in speed in synchronized flow (called a S → F instability), that is a growing speed wave of a local increase in speed in synchronized flow at the bottleneck. The development of the S → F instability leads to a local phase transition from synchronized flow to free flow at the bottleneck (S → F transition).
|
|
Other alloys, binary eutectics (e.g. Pb88.8Sb11.1, Sn61.9Pd38.1, or Ag71.9Cu28.1), form a metal-matrix composite material with ductile matrix with brittle dendrites; such materials reduce slug formation but are difficult to shape. A metal-matrix composite with discrete inclusions of low-melting material is another option; the inclusions either melt before the jet reaches the well casing, weakening the material, or serve as crack nucleation sites, and the slug breaks up on impact. The dispersion of the second phase can be achieved also with castable alloys (e.g., copper) with a low-melting-point metal insoluble in copper, such as bismuth, 1–5% lithium, or up to 50% (usually 15–30%) lead; the size of inclusions can be adjusted by thermal treatment.
|
|
The COX14 gene encodes for a core protein component of the MITRAC (mitochondrial translation regulation assembly intermediate of cytochrome c oxidase complex) complex, which is required for the proper regulation of complex IV assembly. Complex IV of the mitochondrial respiratory chain is essential in catalyzing the oxidation of cytochrome c by molecular oxygen. COX14 has been shown to contribute to the early stages of complex IV assembly by coelution with COX1 and COX4 for nucleation of the assembly. The protein participates in the coupling synthesis of COX1 followed by an assembly of nascent subunits into the holoenzyme complex IV. The knockdown of the protein COX14 involving small interfering RNA in regular human fibroblast has been shown to result in a complex IV defect with reduced activity.
|
|
Geopolymerization occurs at ambient or slightly elevated temperature, where the leaching of solid aluminosilicate raw materials in alkaline solutions leads to the transfer of leached species from the solid surfaces into a growing gel phase, followed by nucleation and condensation of the gel phase to form a solid binder.' For geopolymer ceramic chemistsPeigang He, Dechang Jia, Meirong Wang, Yu Zhou, (2011) (Harbin Institute of Technology, Harbin, PR China:), Thermal evolution and crystallization kinetics of potassium-based geopolymer, Ceramics International, 37, 59–63. :'…Although geopolymer is generally X-ray amorphous if cured at standard pressures and temperatures, it will convert into crystalline ceramic phases like leucite or pollucite upon heating.' For ceramic scientistsBell, Jonathan L.; Driemeyer, Patrick E. and Kriven, Waltraud M. (2009) (University of Illinois, USA), Formation of Ceramics from Metakaolin-Based Geopolymers.
|
|
These impurities contribute to the optical loss through absorption and scattering as well as serving as nucleation sites for crystallization. Although high purity raw elements are now commercially available, with 99.9999% purity routine for many metals, even this level of purity is often not sufficient, particularly for optical fiber applications.J.S. Sanghera and I. D. Aggarwal, Editors, “Infrared Fiber Optics”, CRC Press, LLC, Florida (1998) More of a concern are commercially available chalcogenide compounds such as germanium sulfide, gallium sulfide or arsenic sulfide. Although these may have been synthesized from high purity elements, the conversion process itself can readily introduce oxide, water or organic impurities. It is not unheard of to find for example, commercial gallium sulphide contaminated with 45% or more gallium oxide through incomplete reaction of the precursors during production.
|
|
If cosmological inflation had never happened, and radiation domination continued back until a gravitational singularity, then the mode would never have been inside the horizon in the very early universe, and no causal mechanism could have ensured that the universe was homogeneous on the scale of the perturbation mode. Guth proposed that as the early universe cooled, it was trapped in a false vacuum with a high energy density, which is much like a cosmological constant. As the very early universe cooled it was trapped in a metastable state (it was supercooled), which it could only decay out of through the process of bubble nucleation via quantum tunneling. Bubbles of true vacuum spontaneously form in the sea of false vacuum and rapidly begin expanding at the speed of light.
|
|
Fis causes mild condensation of a single DNA molecule at <1 mM, but induces substantial folding through the formation of DNA loops of an average size of ~800 bp at >1 mM. The loops in magnetic tweezers experiments are distinct from the micro-loops created by coherent DNA bending at cognate sites, as they require the formation of high-density DNA- protein complexes achieved by sequence-independent binding. Although, occurrence of such loops in vivo remains to be demonstrated, high-density binding of Fis may occur in vivo through concerted action of both specific and non-specific binding. The in-tandem occurrence of specific sites might initiate a nucleation reaction similar to that of H-NS, and then non-specific binding would lead to the formation of localized high-density Fis arrays.
|
|
Lina Mendoni and Harikleia Papageorgiadou, "A Surface Survey of Roman Kea," in Susan Walker and Averil Cameron (eds), The Greek Renaissance in the Roman Empire: Papers from the Tenth British Museum Classical Colloquium (University of London, Institute of Classical Studies, 1989), p. 172. A process of nucleation reduced the number of population centers: "By the 2nd century BC the poleis of Koressos and Poieessa were absorbed by their neighbours Ioulis and Karthaia, and in the Late Roman period Karthaia ceased to exist, leaving Ioulis (Chora) as the single polis of the island."Helle Damgaard Andersen, Urbanization in the Mediterranean in the Ninth to Sixth Centuries BC (Museum Tusculanum Press, 1997: ), p. 32. In the thirteenth century it seems to have been still the only town on the island.
|
|
The strain energy density is defined as the energy invested into the volume unit of polymeric material for deformation, also known as the elastic energy per unit volume in the solid. In crack nucleation approach, no crack is introduced into the sample initially, and crack initiation is observed under loadings. Crack Growth Approach Unlike crack initiation approach, the crack growth approach introduces a pre-existing crack to the specimen, and calculate for the crack propagation rate under cyclic loadings. Because of the pre- existing crack, the elastic energy released by fracture will associate with the surface energy at new crack surfaces, and it was found that the crack propagation rate can be described by a function of the energy release rate, depending on which regime of crack propagation this relation is in.
|
|
Soluble boron arranges in steels along grain boundaries. This retards the γ-α transformations (austenite to ferrite transformation) by diffusion and therefore increases the hardenability, with an optimal range of ~ 0.0003 to 0.003% B. Additionally Fe2B has been found to precipitate at grain boundaries, which may also retard the γ-α transformations . At higher B values Fe23(CB)6 is thought to form, which promotes ferrite nucleation, and so adversely affects hardenability. Boron is effective at very low concentrations - 30 ppm B can replace an equivalent 0.4% Cr, 0.5% C, or 0.12% V. 30 ppm B has also been shown to increase depth of hardening (~ +50%) in a low alloy steel - thought to be due to its retardation of the transformation from martensite to softer bainite, ferrite, or pearlite.
|
|
Rounding forces are driven by reorganization of F-actin and myosin (actomyosin) into a contractile homogeneous cell cortex that 1) rigidifies the cell periphery and 2) facilitates generation of intracellular hydrostatic pressure (up to 10 fold higher than interphase). The generation of intracellular pressure is particularly critical under confinement, such as would be important in a tissue scenario, where outward forces must be produced to round up against surrounding cells and/or the extracellular matrix. Generation of pressure is dependent on formin-mediated F-actin nucleation and Rho kinase (ROCK)-mediated myosin II contraction, both of which are governed upstream by signaling pathways RhoA and ECT2 through the activity of Cdk1. Due to its importance in mitosis, the molecular components and dynamics of the mitotic actomyosin cortex is an area of active research.
|
|
Along with his colleague and close friend, Dr. David Atlas, Dr. Battan underwent rigorous training in radar engineering and meteorology in the U.S. Army Air Corps, at Harvard University, and the Massachusetts Institute of Technology (MIT) during World War II. He received his B.S. from New York University (NYU) in 1946 and then moved to the University of Chicago where he obtained his M.S. and a Ph.D. in 1953. During the Thunderstorm Project (1946–48), Dr. Battan used radar analysis to show precipitation initiation from coalescence in midlatitude convective clouds. He, along with Dr. Roscoe Braham Jr. and Dr. Horace R. Byers, conducted one of the first randomized experiments on cloud modification by the artificial nucleation of cumulus clouds. After obtaining his Ph.D., he remained at Chicago until 1958.
|
|
Droplet diameter governs the dynamic behaviour of the droplet in flight which in turn determines the time available for in-flight cooling which is critical in controlling the resulting billet microstructure. At a flight distance of 300–400 mm, predictions show droplet velocities of 40-90 ms−1 for droplet diameters in the range 20-150 μm respectively, compared to measured velocities of ~100 ms−1, and at distances of up to 180 mm from the atomiser, droplets were still being accelerated by the gas. Droplets cool in-flight predominantly by convection and radiation, and can experience undercooling of up to prior to nucleation. Models and experimental measurements show that small droplets (<50 μm) very rapidly become fully solid prior to deposition, 50-200 μm droplets will be typically semi-solid and droplets of diameters >200 μm will be liquid at deposition.
|
|
Fallstreak hole over Austria, August 2008 A fallstreak hole (also known as a cavum, hole punch cloud, punch hole cloud, skypunch, cloud canal or cloud hole) is a large gap, usually circular or elliptical, that can appear in cirrocumulus or altocumulus clouds. Such holes are formed when the water temperature in the clouds is below freezing, but the water, in a supercooled state, has not frozen yet due to the lack of ice nucleation. When ice crystals do form, a domino effect is set off due to the Bergeron process, causing the water droplets around the crystals to evaporate: this leaves a large, often circular, hole in the cloud. It is thought that the introduction of large numbers of tiny ice crystals into the cloud layer sets off this domino effect of fusion which creates the hole.
|
|
Later, from 1965 to 1970, the Linde Division of Union Carbide produced completely synthetic emeralds by hydrothermal synthesis. According to their patents (attributable to E.M. Flanigen),Geological Magazine "Hydrothermal process for growing crystals having the structure of beryl in an alkaline halide medium" Issue date: March 2, 1971 acidic conditions are essential to prevent the chromium (which is used as the colorant) from precipitating. Also, it is important that the silicon-containing nutrient be kept away from the other ingredients to prevent nucleation and confine growth to the seed crystals. Growth occurs by a diffusion-reaction process, assisted by convection. The largest producer of hydrothermal emeralds today is Tairus, which has succeeded in synthesizing emeralds with chemical composition similar to emeralds in alkaline deposits in Colombia, and whose products are thus known as “Colombian created emeralds” or “Tairus created emeralds”.
|
|
It binds to Arp2/3 with an aspartic acid-aspartic acid- tryptophan (DDW) sequence in its NTA region, a motif that is often seen in other actin nucleation-promoting factors (NPFs). Certain serine/threonine kinases, such as ERK, can phosphorylate cortactin on Ser405 and Ser418 in the SH3 domain. Activated like this, it still associates with Arp2/3 and F-actin, but will also allow other actin NPFs, most importantly N-WASp (Neuronal Wiskott-Aldrich syndrome protein), to bind to the complex as well; when phosphorylated by tyrosine kinases, other NPFs are excluded. The ability of these other NPFs to bind the Arp2/3 complex while cortactin is also bound could come from new interactions with cortactin's SH3 domain, which is in a different conformation when phosphorylated by Ser/Thr kinases and thus may be more open to interactions with other NPFs.
|
|
Below the Tg, molecular motion is stopped and the polymer chains are essentially frozen in place. In this temperature range, amorphous regions can no longer transition into crystalline regions, and the polymer as a whole has reached its maximum crystallinity. Physical properties of polymers change drastically across thermal transitions Hoffman nucleation theory addresses the amorphous to crystalline polymer transition, and this transition can only occur in the temperature range between the Tm and Tg. The transition from an amorphous to a crystalline single polymer chain is related to the random thermal energy required to align and fold sections of the chain to form ordered regions titled lamellae, which are a subset of even bigger structures called spherulites. The crystallization of polymers can be brought about by several different methods, and is a complex topic in itself.
|
|
In the theory of crystal growth, Cahn concluded that the distinguishing feature is the ability of the surface to reach an equilibrium state in the presence of a thermodynamic driving force (typically in the form of the degree of undercooling). He also concluded that for every surface or interface in a crystalline medium, there exists a critical driving force, which, if exceeded, will enable the surface or interface to advance normal to itself, and, if not exceeded, will require the lateral growth mechanism. Thus, for sufficiently large driving forces, the interface can move uniformly without the benefit of either a heterogeneous nucleation or screw dislocation mechanism. What constitutes a sufficiently large driving force depends upon the diffuseness of the interface, so that for extremely diffuse interfaces, this critical driving force will be so small that any measurable driving force will exceed it.
|
|
Dr Séamus Caulfield, retired professor of archaeology at University College Dublin, has stated that Irish Stone Age rural settlements were dispersed throughout the countryside but that in recent years planners were using British Anglo-Saxon planning models that emphasise "settlement in urban areas – nucleation settlements".One-off housing key for rural living, meeting told, Irish Times, 22 February 2003 (subscription) Minister for the Environment, Dick Roche, has supported the view that one-off housing is a continuation of the traditional land use patterns in Ireland for millennia. > "We have a dispersed pattern of settlement going back thousands of > years."Seanad Debate on Sustainable Rural Housing Guidelines, 28 April, 2005 In contrast, An Tasice has arguedAn Taisce challenges expert on rural plans, Irish Times, 29 April 2002 (subscription) that early settlements were nucleated and communal, often surrounded by ringforts for protection.
|
|
Although the process of subduction as it occurs today is fairly well understood, its origin remains a matter of discussion and continuing study. Subduction initiation can occur spontaneously if denser oceanic lithosphere is able to founder and sink beneath adjacent oceanic or continental lithosphere; alternatively, existing plate motions can induce new subduction zones by forcing oceanic lithosphere to rupture and sink into the asthenosphere. Both models can eventually yield self-sustaining subduction zones, as oceanic crust is metamorphosed at great depth and becomes denser than the surrounding mantle rocks. Results from numerical models generally favor induced subduction initiation for most modern subduction zones, which is supported by geologic studies, but other analogue modeling shows the possibility of spontaneous subduction from inherent density differences between two plates at passive margins, and observations from the Izu-Bonin-Mariana subduction system are compatible with spontaneous subduction nucleation.
|
|
Absence of freezing indicates that their AFPs can inhibit ice nucleators to vary in low temperatures and may inhibit homogenous nucleation resulting in vitrification. Another study reported that if temperatures were held constant, then C. clavipes individuals with the highest water content had the highest probability of freezing, and individuals with the lowest water content had the lowest probability of freezing.Sformo, T., J. McIntyre, K. R. Walters Jr., B. M. Barnes and J. Duman. 2011. The probability of freezing in the freeze-avoiding beetle larvae Cucujus clavipes puniceus (Coleoptera: Cucujidae) from interior Alaska. Journal of Insect Physiology 57:1170-1177 AFPs decrease the temperature at which an ice crystal grows, defined as the hysteretic freezing point, by an average of 2–5 °C below the melting point in insects, which can be as much as 13 °C in C. clavipes in winter when the insect is dehydrated and the AFPs concentrated.
|
|
AKNA is an essential part in the construction, organization, and proliferation of the centrosomal microtubules in order to maintain the neural stem cells during the process of neurogenesis. Due to these functions AKNA plays in the centrosomal microtubules it also has an active role in delamination during the formation of the subventricular zone, and the regulation of the amount of access provided to cells in this zone. Furthermore, because of AKNA's role in the centrosomal microtubules it also plays a part in the management of the modification of epithelial cells losing their polarity and attachment, and transforming into the mobile mesenchymal stem cells, epithelial-mesenchymal transition (EMT). This occurs because the alongside the increase in centrosomal microtubules both nucleation factors and minus end stabilizers are also increasing, causing the apical endfoot to have its constriction regulated because this affects the microtubules found at adherens junctions.
|
|
Freezing does not start until the temperature is low enough to provide enough energy to form stable nuclei. In presence of irregularities on the surface of the containing vessel, solid or gaseous impurities, pre-formed solid crystals, or other nucleators, heterogeneous nucleation may occur, where some energy is released by the partial destruction of the previous interface, raising the supercooling point to be near or equal to the melting point. The melting point of water at 1 atmosphere of pressure is very close to 0 °C (32 °F, 273.15 K), and in the presence of nucleating substances the freezing point of water is close to the melting point, but in the absence of nucleators water can supercool to −40 °C (−40 °F, 233 K) before freezing. Under high pressure (2,000 atmospheres) water will supercool to as low as −70 °C (−94 °F, 203 K) before freezing.
|
|
Stranski–Krastanov growth (SK growth, also Stransky–Krastanov or Stranski–Krastanow) is one of the three primary modes by which thin films grow epitaxially at a crystal surface or interface. Also known as 'layer-plus- island growth', the SK mode follows a two step process: initially, complete films of adsorbates, up to several monolayers thick, grow in a layer-by-layer fashion on a crystal substrate. Beyond a critical layer thickness, which depends on strain and the chemical potential of the deposited film, growth continues through the nucleation and coalescence of adsorbate 'islands'. This growth mechanism was first noted by Ivan Stranski and Lyubomir Krastanov in 1938. It wasn’t until 1958 however, in a seminal work by Ernst Bauer published in Zeitschrift für Kristallographie, that the SK, Volmer–Weber, and Frank–van der Merwe mechanisms were systematically classified as the primary thin-film growth processes.
|
|
The development of colleges and universities worldwide, most notably in the United States, would expand food chemistry as well with research of the dietary substances, most notably the Single-grain experiment during 1907-11. Additional research by Harvey W. Wiley at the United States Department of Agriculture during the late 19th century would play a key factor in the creation of the United States Food and Drug Administration in 1906. The American Chemical Society would establish their Agricultural and Food Chemistry Division in 1908 while the Institute of Food Technologists would establish their Food Chemistry Division in 1995. Food chemistry concepts are often drawn from rheology, theories of transport phenomena, physical and chemical thermodynamics, chemical bonds and interaction forces, quantum mechanics and reaction kinetics, biopolymer science, colloidal interactions, nucleation, glass transitions and freezing/disordered or noncrystalline solids, and thus has Food Physical Chemistry as a foundation area.
|
|
They speculated that the change could be due to the birth of Earth's solid inner core. From their age estimate they derived a rather modest value for the thermal conductivity of the outer core, that allowed for simpler models of the Earth's thermal evolution. In 2016, P. Driscoll published an evolving numerical dynamo model that made a detailed prediction of the paleomagnetic field evolution over 0-2 Ga. The evolving dynamo model was driving by time-variable boundary conditions produced by the thermal history solution in Driscoll and Bercovici (2014). The evolving dynamo model predicted a strong-field dynamo prior to 1.7 Ga that is multipolar, a strong-field dynamo from 1.0-1.7 Ga that is predominantly dipolar, a weak-field dynamo from 0.6-1.0 Ga that is a non-axial dipole, and a strong-field dynamo after inner core nucleation from 0-0.6 Ga that is predominantly dipolar.
|
|
Biman Bagchi (born 1954) is an Indian biophysical chemist, theoretical chemist and an Amrut Mody Professor at the Solid State and Structural Chemistry Unit of the Indian Institute of Science. He is known for his studies on statistical mechanics; particularly in the study of phase transition and nucleation, solvation dynamics, mode-coupling theory of electrolyte transport, dynamics of biological macromolecules (proteins, DNA etc.), protein folding, enzyme kinetics, supercooled liquids and protein hydration layer. He is an elected fellow of the Indian National Science Academy, the Indian Academy of Sciences and The World Academy of Sciences. Besides several scientific articles, he has authored two books, Molecular Relaxation in Liquids and Water in Biological and Chemical Processes: From Structure and Dynamics to Function The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, in 1991, for his contributions to chemical sciences.
|
|
Working in Xenopus (frog) egg extracts, Kirschner and Andrew Murray showed that cyclin synthesis drives the cell cycle Pulverer, Bernd "Milestones in cell division (12): Surfing the cyclin wave" Nature Publishing Group (retrieved 16 May 2012) and, later, that ubiquitin regulates levels of cyclin by marking the cell-cycle molecule for destruction.Brooksbank, Cath "Milestones in cell division (20): Disappearing Act" Nature Publishing Group (retrieved 16 May 2012) His lab discovered and purified many of the components involved in cell cycle progression, including anaphase promoting complex (APC), the complex that ubiquitinates cyclin B. A second notedLewin, B "Great experiments: Dynamic instability of microtubules - Marc Kirschner and Tim Mitchison", CELLS! The web site accompanying the Cells textbook (Jones and Bartlett Publishers (2007) finding was his discovery, with Tim Mitchison, of the dynamic instability of microtubules, In mitosis, for example, microtubules form the spindle that separates the chromosomes. The first step in spindle formation is the nucleation of microtubules by microtubule-organizing centers, which then grow in all directions.
|
|
A patch of grass showing crystalline frost in the below-freezing shade (blue, lower right); frost in the warming but still below freezing strip most recently exposed to sunlight (white, center); and a frost-free region: here, the previous frost has melted from a more prolonged exposure to sunlight (green, upper left.) Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a gas) to ice (a solid) as the water vapor reaches the freezing point. In temperate climates, it most commonly appears on surfaces near the ground as fragile white crystals; in cold climates, it occurs in a greater variety of forms. The propagation of crystal formation occurs by the process of nucleation. The ice crystals of frost form as the result of fractal process development.
|
|
Using a single model to simulate all fault behaviours made it possible for Lapusta et al. to demonstrate that during an earthquake the supposedly stable zones behave differently when penetrated by earthquake ruptures, and can in fact contribute to the generation of massive earthquakes through dynamic weakening. Her model could qualitatively reproduce the 2011 Tōhoku earthquake. uncovering the critical role of small scale frictional and hydromechanical processes and pointing to complex feedback interactions between fault slip, friction, and heterogeneous hydraulic properties that may qualitatively and quantitatively alter fault response from what may be inferred from small scale experiments Lapusta's work on small repeating earthquakes, interaction of seismic and aseismic slip in complex fault structures, and dynamic weakening that may potentially control the final size of an earthquake following its nucleation, has demonstrated the importance of rigorous mechanics-based modelling of earthquake processes, and how this may potentially be very informative to seismic hazard calculations particularly when data is scarce as it is the case for large earthquakes.
|
|
These transmembrane transporters are localised both in the cytoplasmic membrane and in the MM, but in an inverted orientation; this configuration allows them to generate an efflux of Fe2+ ions at the cytoplasmic membrane, and an influx of this same ion at the MM. This step is strictly controlled by a cytochrome-dependent redox system, which is not yet fully explained and appears to be species-specific. During the final stage of the process, the magnetite crystal nucleation is by action of transmembrane proteins with acidic and basic domains. One of these proteins, called Mms6, has also been employed for the artificial synthesis of magnetite, where its presence allows the production of crystals homogeneous in shape and size. It is likely that many other proteins associated with the MM could be involved in other roles, such as generation of supersaturated concentrations of iron, maintenance of reducing conditions, oxidisation of iron, and partial reduction and dehydration of hydrated iron compounds.
|
|
A small seed crystal is attached to a rod, which is lowered over the crucible until the crystal contacts the surface of the melted mixture. The seed crystal acts as a site of nucleation; the temperature is kept steady at a point where the surface of the mixture is just below the melting point. The rod is slowly and continuously rotated and retracted, and the pulled mixture crystallizes as it exits the crucible, forming a single crystal in the form of a cylindrical boule. The crystal's purity is extremely high, and it typically measures 5 cm (2 inches) in diameter and 20 cm (8 inches) in length, and weighs 9,000 carats (1.75 kg). YAG hardness (8.25) and lack of brittleness were great improvements over strontium titanate, and although its RI (1.83) and dispersion (0.028) were fairly low, they were enough to give brilliant-cut YAGs perceptible fire and good brilliance (although still much lower than diamond).
|
|
Normally folded proteins have to unfold partially before aggregation can take place through one of these mechanisms. In some cases, however, folded proteins can aggregate without crossing the major energy barrier for unfolding, by populating native-like conformations as a consequence of thermal fluctuations, ligand release or local unfolding occurring in particular circumstances. In these native-like conformations, segments that are normally buried or structured in the fully folded and possessing a high propensity to aggregate become exposed to the solvent or flexible, allowing the formation of native-like aggregates, which convert subsequently into nuclei and fibrils. This process is called ‘native-like aggregation’ (green arrows in the figure) and is similar to the ‘nucleated conformational conversion’ model. A more recent, modern and thorough model of amyloid fibril formation involves the intervention of secondary events, such as ‘fragmentation’, in which a fibril breaks into two or more shorter fibrils, and ‘secondary nucleation’, in which fibril surfaces (not fibril ends) catalyze the formation of new nuclei.
|
|
Considerable understanding of surfaces and thin films has been achieved by laterally averaging measurement techniques, but it has become evident that many problems can be solved only by laterally resolving methods (surface microscopy). Ernst Bauer invented Low Energy Electron Microscopy (LEEM) already in 1962 but he had to overcome intense skepticism of scientists and also many scientific and funding obstacles before finally LEEM came to fruition in 1985. His work was brought to the attention of a much wider general scientific community in the nineteen eighties, when the mature LEEM began producing the very impressive real-time high-resolution dynamic image recordings of atomic processes such as crystal nucleation and growth, sublimation, phase transitions and epitaxy on surfaces. The high signal intensities available in LEEM (compared to X-ray imaging) allowed observing surface structure and dynamic processes in real space and real time at sample temperatures up to 1500 K with 10 nm lateral resolution and atomic depth resolution.
|
|
Like most proteins PrP can exist in two forms, one major and one minor, an alpha helix structure and a beta-pleated sheet structure respectively, that are balanced during nearly all conditions, but with dominance granted to the stable helix form. In certain instances, it may be possible for two beta forms to contact each other at the same time, and in this case the pair can form bonds that successfully stabilize the beta forms thermodynamically and allowing these structures to remain. This is termed the “seed” of polymerization as from this point the continued interaction, or recruitment, amongst the beta forms is increased perpetually, since there is a constant presence of stable beta forms, as well as the fact that beta forms, or beta-pleated sheets, have a greater number of reactive nucleation sites. This progression forms extended fibrils slowly over time that will then cause localized cytopathology, resulting in the characteristic sites of cell degradation or “sponginess”.
|
|
Rare event sampling is an umbrella term for a group of computer simulation methods intended to selectively sample 'special' regions of the dynamic space of systems which are unlikely to visit those special regions through brute- force simulation. A familiar example of a rare event in this context would be nucleation of a raindrop from over-saturated water vapour: although raindrops form every day, relative to the length and time scales defined by the motion of water molecules in the vapour phase, the formation of a liquid droplet is extremely rare. Due to the wide use of computer simulation across very different domains, articles on the topic arise from quite disparate sources and it is difficult to make a coherent survey of rare event sampling techniques. Contemporary methods include Transition Path Sampling (TPS), Replica Exchange Transition Interface Sampling (RETIS), Repetitive Simulation Trials After Reaching Thresholds (RESTART), Forward Flux Sampling (FFS), Generalized Splitting, Adaptive Multilevel Splitting (AMS), Stochastic Process Rare Event Sampling (SPRES), Line sampling, Subset simulation, and Weighted Ensemble (WE).
|
|
Bubbles which are carried back to the heart in the veins will normally pass into the right side of the heart, and from there they will normally enter the pulmonary circulation and eventually pass through or be trapped in the capillaries of the lungs, which are around the alveoli and very near to the respiratory gas, where the gas will diffuse from the bubbles though the capillary and alveolar walls into the gas in the lung. If the number of lung capillaries blocked by these bubbles is relatively small, the diver will not display symptoms, and no tissue will be damaged (lung tissues are adequately oxygenated by diffusion). The bubbles which are small enough to pass through the lung capillaries may be small enough to be dissolved due to a combination of surface tension and diffusion to a lowered concentration in the surrounding blood, though the Varying Permeability Model nucleation theory implies that most bubbles passing through the pulmonary circulation will lose enough gas to pass through the capillaries and return to the systemic circulation as recycled but stable nuclei. Bubbles which form within the tissues must be eliminated in situ by diffusion, which implies a suitable concentration gradient.
|
|