This creates undesirable oscillatory moments that force the robots to take small, calculated steps.
|
|
The hips, in particular, generate oscillatory movements that current-generation robots struggle to overcome.
|
|
This led them to imprint an oscillatory pattern of four-point correlations on the sky.
|
|
Finding the oscillatory pattern in the triangles in the sky would confirm that this tower exists.
|
|
There he was hooked up to an oscillatory ventilator, which kept him alive for 10 days.
|
|
In contrast, if this oscillatory signal is important for memory-related spatial coding, then low-frequency oscillations should persist during teleportation.
|
|
As these gravitational waves traverse space they will literally cause distances between objects alternately to decrease and increase in an oscillatory manner.
|
|
As the gels deform under stress—as the material changes shape in response to some stimuli—they undergo an oscillatory reaction known as the Belousov-Zhabotinsky (BZ) reaction.
|
|
Peiris is keen to test a string-inflationary mechanism called axion monodromy, including variants recently developed by Silverstein and collaborators Raphael Flauger, Mehrdad Mirbabayi, and Leonardo Senatore that generate an oscillatory pattern in triangles as a function of their size that can be much more pronounced than the pattern studied by Arkani-Hamed and Maldacena.
|
|
Any Lagrangian distribution can be represented locally by oscillatory integrals (see ). Conversely any oscillatory integral is a Lagrangian distribution. This gives a precise description of the types of distributions which may be represented as oscillatory integrals.
|
|
In mathematical analysis an oscillatory integral is a type of distribution. Oscillatory integrals make rigorous many arguments that, on a naive level, appear to use divergent integrals. It is possible to represent approximate solution operators for many differential equations as oscillatory integrals.
|
|
An oscillatory neural network (ONN) is an artificial neural network that uses coupled oscillators as neurons. Oscillatory neural networks are closely linked to the Kuramoto model, and are inspired by the phenomenon of neural oscillations in the brain. Oscillatory neural networks have been trained to recognize images. An oscillatory autoencoder has also been demonstrated, which uses a combination of oscillators and rate-coded neurons.
|
|
Both single neurons and groups of neurons can generate oscillatory activity spontaneously. In addition, they may show oscillatory responses to perceptual input or motor output. Some types of neurons will fire rhythmically in the absence of any synaptic input. Likewise, brain-wide activity reveals oscillatory activity while subjects do not engage in any activity, so-called resting-state activity.
|
|
Krylov–Bogoliubov averaging can be used to approximate oscillatory problems when a classical perturbation expansion fails. That is singular perturbation problems of oscillatory type, for example Einstein's correction to the perihelion precession of Mercury.
|
|
"Auditory stream segregation based on oscillatory correlation". Proceedings of the IEEE International Workshop on Neural Networks for Signal Processings, 624-632.Wang, D.(1996), "Primitive auditory segregation based on oscillatory correlation". Cognitive Science 20, 409-456.
|
|
ENO (essentially non-oscillatory) methods are classes of high-resolution schemes in numerical solution of differential equations.
|
|
Gilles Laurent and colleagues showed that oscillatory synchronization has an important functional role in odor perception. Perceiving different odors leads to different subsets of neurons firing on different sets of oscillatory cycles. These oscillations can be disrupted by GABA blocker picrotoxin, and the disruption of the oscillatory synchronization leads to impairment of behavioral discrimination of chemically similar odorants in bees and to more similar responses across odors in downstream β-lobe neurons. Recent follow-up of this work has shown that oscillations create periodic integration windows for Kenyon cells in the insect mushroom body, such that incoming spikes from the antennal lobe are more effective in activating Kenyon cells only at specific phases of the oscillatory cycle.
|
|
Such processes would involve exponential decay of the amplitudes, but the solutions of the two-state system are oscillatory.
|
|
In numerical solution of differential equations, WENO (weighted essentially non-oscillatory) methods are classes of high-resolution schemes. WENO are used in the numerical solution of hyperbolic partial differential equations. These methods were developed from ENO methods (essentially non-oscillatory). The first WENO scheme is developed by Liu, Chan and Osher in 1994.
|
|
The primary advantage of using oscillatory droplet deformation to improve these engineering processes is that the phenomenon does not require sophisticated machinery or the introduction of heat sources. This effectively means that improving performance via oscillatory droplet deformation is simple and in no way diminishes the effectiveness of the existing engineering system.
|
|
But when cornering, the rotational movement causes the upper part of the tuning fork to leave the oscillatory plane, creating an alternating voltage (and thus an alternating current) proportional to the yaw rate and oscillatory speed. The output signal's sign depends on the direction of rotation. In the micromechanical type, the Coriolis acceleration is measured by a micromechanical capacitive acceleration sensor placed on an oscillating element. This acceleration is proportional to the product of the yaw rate and oscillatory velocity, the latter of which is maintained electronically at a constant value.
|
|
He is most well known for his work with Percy Deift on the steepest descent method for oscillatory Riemann–Hilbert problems.
|
|
The amplitude a_0 satisfies a transport equation. The small parameter \varepsilon\, enters the scene due to highly oscillatory initial conditions. Thus, when initial conditions oscillate much faster than the coefficients of the differential equation, solutions will be highly oscillatory, and transported along rays. Assuming coefficients in the differential equation are smooth, the rays will be too.
|
|
He hoped to solve the horizon problem in a natural way by showing that the early universe underwent an oscillatory, chaotic epoch.
|
|
In homogenization theory, a branch of mathematics, stochastic homogenization is a technique for understanding solutions to partial differential equations with oscillatory random coefficients.
|
|
In addition to irreversible schooling, self- propelled particles also display reversible collective motion, such as predator–prey behavior and oscillatory clustering and dispersion.
|
|
This oscillation is known as the Babcock-Leighton dynamo cycle, amounting to the oscillatory exchange of energy between poloidal and toroidal solar magnetic field ingredients.
|
|
From the 1970s, his interest turned to oscillatory reactions. His international fame is due to his collaboration with Richard J. Field and Richard M. Noyes. In 1972, they published a description of the oscillatory Belousov–Zhabotinsky reaction involving 11 reactions and 12 species (21 intermediate species and 18 elementary steps). The FKN mechanism served as a starting point for the development of the Oregonator.
|
|
Retrieved on 13 May 2009. Oscillatory motion of the physical line can be termed conductor gallop or flutter depending on the frequency and amplitude of oscillation.
|
|
The Airy pattern, caused by Fraunhofer diffraction. Many special functions exhibit oscillatory decay, and thus convolving with such a function yields ringing in the output; one may consider these ringing, or restrict the term to unintended artifacts in frequency domain signal processing. Fraunhofer diffraction yields the Airy disk as point spread function, which has a ringing pattern. A few Bessel functions of the first kind, showing oscillatory decay.
|
|
This includes stiff and highly oscillatory linear equations. Moreover, the LL schemes (4.6)-(4.9) are regular for linear ODEs and inherit the symplectic structure of Hamiltonian harmonic oscillators.
|
|
Glycophorin C normally shows oscillatory movement in the erythrocyte membrane. This is reduced in Southeast Asian ovalocytosis a disease of erythrocytes due to a mutation in band 3.
|
|
The oscillatory dynamics of neuronal spiking as identified in the Hodgkin–Huxley model closely agree with empirical findings. In addition to periodic spiking, subthreshold membrane potential oscillations, i.e. resonance behavior that does not result in action potentials, may also contribute to oscillatory activity by facilitating synchronous activity of neighboring neurons. Like pacemaker neurons in central pattern generators, subtypes of cortical cells fire bursts of spikes (brief clusters of spikes) rhythmically at preferred frequencies.
|
|
An increase in neurotransmitters causes spasms to occur in the neck, resulting in spasmodic torticollis. Studies of local field potentials have also shown an increase of 4–10 Hz oscillatory activity in the globus pallidus internus during myoclonic episodes and an increase of 5–7 Hz activity in dystonic muscles when compared to other primary dystonias. This indicates that oscillatory activity in these frequency bands may be involved in the pathophysiology of spasmodic torticollis.
|
|
The incident and reflected waves superimpose to cause oscillatory fluid motion in the plane of the interface, thereby generating an AC streaming current at the frequency of the sound waves.
|
|
As glucose increases, the production of insulin increases, which thereby increases the utilization of the glucose, which maintains the glucose levels in an efficient manner and creates an oscillatory behavior.
|
|
Her research interests are in applications of pure mathematics to the physical sciences. She has worked in applications of geometry to robotics, numerical computation of highly oscillatory integrals and dynamical systems.
|
|
Without lubricant, wear is increased when the small oscillatory movements occur again. It is possible for the resulting wear debris to oxidize and form an abrasive compound which further accelerates wear.
|
|
Functional Analysis has chapters on several advanced topics in analysis: Lp spaces, distributions, the Baire category theorem, probability theory including Brownian motion, several complex variables, and oscillatory integrals.Stein & Shakarchi, Functional Analysis.
|
|
Goodwin's model and its extensions have been widely used over the years as the basic skeleton for other models of oscillatory behavior, including circadian clocks, cell division or physiological control systems.
|
|
For instance, the flow around a circular cylinder generates a Kármán vortex street: vortices being shed in an alternating fashion from the cylinder's sides. The oscillatory nature of the flow produces a fluctuating lift force on the cylinder, even though the net (mean) force is negligible. The lift force frequency is characterised by the dimensionless Strouhal number, which depends on the Reynolds number of the flow. For a flexible structure, this oscillatory lift force may induce vortex-induced vibrations.
|
|
Certain network structures promote oscillatory activity at specific frequencies. For example, neuronal activity generated by two populations of interconnected inhibitory and excitatory cells can show spontaneous oscillations that are described by the Wilson-Cowan model. If a group of neurons engages in synchronized oscillatory activity, the neural ensemble can be mathematically represented as a single oscillator. Different neural ensembles are coupled through long-range connections and form a network of weakly coupled oscillators at the next spatial scale.
|
|
400px The thalamocortical loop starts with oscillatory thalamic cells. These cells receive both sensory input from the body as well as input from feedback pathways in the brain. In a sense, these cells serve to integrate these multiple inputs by changing their inherent oscillatory properties in response to depolarization by these many different inputs. TC neurons exhibit gamma oscillation when depolarized to greater than -45 mV, and the frequency of oscillation is related to the degree of depolarization.
|
|
Experiments in locusts have shown that Kenyon cells have their activity synchronized to 20-Hz neural oscillations and are particularly responsive to projection neuron spikes at specific phases of the oscillatory cycle.
|
|
In addition to fast direct synaptic interactions between neurons forming a network, oscillatory activity is regulated by neuromodulators on a much slower time scale. That is, the concentration levels of certain neurotransmitters are known to regulate the amount of oscillatory activity. For instance, GABA concentration has been shown to be positively correlated with frequency of oscillations in induced stimuli. A number of nuclei in the brainstem have diffuse projections throughout the brain influencing concentration levels of neurotransmitters such as norepinephrine, acetylcholine and serotonin.
|
|
Oscillatory rhythms at 10 Hz have been recorded in a brain area called the inferior olive, which is associated with the cerebellum. These oscillations are also observed in motor output of physiological tremor and when performing slow finger movements. These findings may indicate that the human brain controls continuous movements intermittently. In support, it was shown that these movement discontinuities are directly correlated to oscillatory activity in a cerebello-thalamo-cortical loop, which may represent a neural mechanism for the intermittent motor control.
|
|
In acoustics, the pressure gradient is proportional to the sound particle acceleration according to Euler's equation. Sound waves and shock waves can induce very large pressure gradients, but these are oscillatory, and often transitory disturbances.
|
|
Animation of a de Broglie wave incident on a barrier. For a constant potential, , the solution is oscillatory for and exponential for , corresponding to energies that are allowed or disallowed in classical mechanics. Oscillatory solutions have a classically allowed energy and correspond to actual classical motions, while the exponential solutions have a disallowed energy and describe a small amount of quantum bleeding into the classically disallowed region, due to quantum tunneling. If the potential grows to infinity, the motion is classically confined to a finite region.
|
|
Weakly coupled oscillators can generate a range of dynamics including oscillatory activity. Long-range connections between different brain structures, such as the thalamus and the cortex (see thalamocortical oscillation), involve time-delays due to the finite conduction velocity of axons. Because most connections are reciprocal, they form feed-back loops that support oscillatory activity. Oscillations recorded from multiple cortical areas can become synchronized to form large scale brain networks, whose dynamics and functional connectivity can be studied by means of spectral analysis and Granger causality measures.
|
|
The lateral geniculate nucleus, known as the major relay center from the sensory neurons in the eyes to the visual cortex, is found in the thalamus and has thalamocortical oscillatory properties, forming a feedback loop between the thalamus and the visual cortex. Sensory input can be seen to modulate the oscillatory patterns of thalamocortical activity while awake. In the case of vision, stimulation from light sources can be seen to cause direct changes in the amplitude of the thalamocortical oscillations as measured by EEG.
|
|
Thus, apodization improves the resolution of the resulting mass spectrum. Another way to improve the quality of the transient is to wait to collect data until ions have settled into stable oscillatory motion within the trap.
|
|
Lastly, the TTFL is a limit cycle, meaning that it is a closed loop that will return to its fixed trajectory even if it is disturbed, maintaining the oscillatory path on its fixed 24-hour period.
|
|
In systems biology and mathematical modeling of gene regulatory networks, cell- fate determination is predicted to exhibit certain dynamics, such as attractor-convergence (the attractor can be an equilibrium point, limit cycle or strange attractor) or oscillatory.
|
|
T. Compton and Carl Eckart The Diffusion of Electrons Against an Electric Field in the Non-Oscillatory Abnormal Low Voltage Arc, Phys. Rev. 25 (2) 139 - 146 (1925). Palmer Physical Laboratory, Princeton, New Jersey, Received 29 October 1924. brother of Arthur Compton on low-voltage arcs, particularly the oscillatory phenomena arising in the diffusion of electrons against low-voltage fields. He continued this line of work after receipt of his Ph.D. on a National Research Council Fellowship at the California Institute of Technology (Caltech) during the period 1925 to 1927.
|
|
In this subsection, we focus on phenomena that exhibit a significant oscillatory component: repetition increases understanding and hence confidence in a prediction method that is closely connected with such understanding. Singular spectrum analysis (SSA) and the maximum entropy method (MEM) have been combined to predict a variety of phenomena in meteorology, oceanography and climate dynamics (Ghil et al., 2002, and references therein). First, the “noise” is filtered out by projecting the time series onto a subset of leading EOFs obtained by SSA; the selected subset should include statistically significant, oscillatory modes.
|
|
Neural oscillations, or brainwaves, are rhythmic or repetitive patterns of neural activity in the central nervous system. Neural tissue can generate oscillatory activity in many ways, driven either by mechanisms within individual neurons or by interactions between neurons. In individual neurons, oscillations can appear either as oscillations in membrane potential or as rhythmic patterns of action potentials, which then produce oscillatory activation of post-synaptic neurons. At the level of neural ensembles, synchronized activity of large numbers of neurons can give rise to macroscopic oscillations, which can be observed in an electroencephalogram.
|
|
It has been suggested that one integral facet of brain dynamics underlying conscious thought is the brain’s ability to convert seemingly noisy or chaotic signals into predictable oscillatory patterns. In EEG oscillations of neural networks, neighboring waveform frequencies are correlated on a logarithmic scale rather than a linear scale. As a result, mean frequencies in oscillatory bands cannot link together according to linearity of their mean frequencies. Instead, phase transitions are linked according to their ability to couple with adjacent phase shifts in a constant state of transition between unstable and stable phase synchronization.
|
|
Recurrent thalamo-cortical resonance is an observed phenomenon of oscillatory neural activity between the thalamus and various cortical regions of the brain. It is proposed by Rodolfo Llinas and others as a theory for the integration of sensory information into the whole of perception in the brain. Thalamocortical oscillation is proposed to be a mechanism of synchronization between different cortical regions of the brain, a process known as temporal binding. This is possible through the existence of thalamocortical networks, groupings of thalamic and cortical cells that exhibit oscillatory properties.
|
|
This difference is caused by phase lag, often confused with gyroscopic precession. A rotor is an oscillatory system that obeys the laws that govern vibration—which, depending on the rotor system, may resemble the behaviour of a gyroscope.
|
|
Here are some of the most relevant of his publications and patents: #A. Castellanos, P. Atten, M. G. Velarde. Oscillatory and steady convection in dielectric liquid layers subjected to unipolar injection and temperature gradient. Physics of Fluids, vol.
|
|
In his late years, Burbidge was known mostly for his alternative cosmology "quasi-steady state theory", which contradicts the Big Bang theory. According to Burbidge, the universe is oscillatory and as such, expands and contracts periodically over infinite time.
|
|
Some severely affected babies may be saved with extracorporeal membrane oxygenation (ECMO). Not all specialty hospitals have ECMO, and ECMO is considered the therapy of last resort for pulmonary insufficiency. An alternative to ECMO is high-frequency oscillatory ventilation.
|
|
Central pattern generators can serve many functions in vertebrate animals. CPGs can play roles in movement, breathing, rhythm generation and other oscillatory functions. The sections below focus on specific examples of locomotion and rhythm generation, two key functions of CPGs.
|
|
For instance, gamma activity often increases during increased mental activity such as during object representation. Because induced responses may have different phases across measurements and therefore would cancel out during averaging, they can only be obtained using time-frequency analysis. Induced activity generally reflects the activity of numerous neurons: amplitude changes in oscillatory activity are thought to arise from the synchronization of neural activity, for instance by synchronization of spike timing or membrane potential fluctuations of individual neurons. Increases in oscillatory activity are therefore often referred to as event-related synchronization, while decreases are referred to as event-related desynchronization.
|
|
The functions of neural oscillations are wide- ranging and vary for different types of oscillatory activity. Examples are the generation of rhythmic activity such as a heartbeat and the neural binding of sensory features in perception, such as the shape and color of an object. Neural oscillations also play an important role in many neurological disorders, such as excessive synchronization during seizure activity in epilepsy or tremor in patients with Parkinson's disease. Oscillatory activity can also be used to control external devices in brain–computer interfaces, in which subjects can control an external device by changing the amplitude of particular brain rhythmics .
|
|
Sharp waves and ripple complexes (SWRs) are distinct high frequency oscillatory events in the hippocampus thought to play a role in memory formation and consolidation. These events can be readily detected by following the oscillatory cycles of the on-line recorded local field potential. In this way the onset of the event can be used as a trigger signal for a light flash that is guided back into the hippocampus to inhibit neurons specifically during the SWRs and also to optogenetically inhibit the oscillation itself. These kinds of "closed-loop" experiments are useful to study SWR complexes and their role in memory.
|
|
The frequency domain representation of the contrast transfer function may often have an oscillatory nature, which can be tuned by adjusting the focal value of the objective lens. This oscillatory nature implies that some spatial frequencies are faithfully imaged by the microscope, whilst others are suppressed. By combining multiple images with different spatial frequencies, the use of techniques such as focal series reconstruction can be used to improve the resolution of the TEM in a limited manner. The contrast transfer function can, to some extent, be experimentally approximated through techniques such as Fourier transforming images of amorphous material, such as amorphous carbon.
|
|
Vaithianathan Venkatasubramanian is an electrical engineer at Washington State University in Pullman, Washington. He was named a Fellow of the Institute of Electrical and Electronics Engineers (IEEE) in 2015 for his contributions to online detection of oscillatory behavior of electric power systems.
|
|
In normal/healthy individuals' ION neurons, calcium channels regulate normal oscillatory depolarizations. This pacemaker affects processing and coordination of cerebellar precision movements and motor learning. Damages, both physical and chemical, to the ION affects the Guillain-Mollaret Triangle and leads to tremors.
|
|
In labriform locomotion, seen in the wrasses (Labriformes), oscillatory movements of pectoral fins are either drag based or lift based. Propulsion is generated either as a reaction to drag produced by dragging the fins through the water in a rowing motion, or via lift mechanisms.
|
|
Leach believed that the Gumlau and the Gumsa systems formed an oscillatory model and that gumsa polities would eventually become gumlao and vice versa. However this model has been criticized as being overly theoretical and not taking into account historical events.Sadan, M. 2007. Translating Gumlau.
|
|
Oscillatory and synchronous activity is likely to be a typical pattern of discharge in subthalamic neurons recorded from patients and animal models characterized by the loss of dopaminergic cells in the substantia nigra pars compacta, which is the principal pathology that underlies Parkinson's disease.
|
|
In continuum mechanics, the generalized Lagrangian mean (GLM) is a formalism – developed by – to unambiguously split a motion into a mean part and an oscillatory part. The method gives a mixed Eulerian–Lagrangian description for the flow field, but appointed to fixed Eulerian coordinates.
|
|
Neuronal oscillations that synchronize activity of the neurons in an ensemble appear to be an important encoding mechanism. For example, oscillations have been suggested to underlie visual feature binding (Gray, Singer and others). In addition, sleep stages and waking are associated with distinct oscillatory patterns.
|
|
This was seen by the measuring of action potentials. It was observed that certain groups of neurons synchronized with certain phases of respiration. The overall behavior was oscillatory in nature. This is an example of how an autonomous biorhythm can control a crucial bodily function.
|
|
The first of which is Slow Adapting receptors (SA) that sense steady flow. The second is Rapid Adapting receptors (RA) that sense oscillatory stimuli. ISO can potentially detect direction of disturbance with high accuracy in 3D space. Whiskers in harbor seal is another example.
|
|
A head wave refracts at an interface, travelling along it, within the lower medium and produces oscillatory motion parallel to the interface. This motion causes a disturbance in the upper medium that is detected on the surface. The same phenomenon is utilised in seismic refraction.
|
|
2\rangle at different detunings Δ. In physics, the Rabi cycle (or Rabi flop) is the cyclic behaviour of a two-level quantum system in the presence of an oscillatory driving field. A great variety of physical processes belonging to the areas of quantum computing, condensed matter, atomic and molecular physics, and nuclear and particle physics can be conveniently studied in terms of two-level quantum mechanical systems, and exhibit Rabi flopping when coupled to an oscillatory driving field. The effect is important in quantum optics, magnetic resonance and quantum computing, and is named after Isidor Isaac Rabi. A two-level system is one that has two possible energy levels.
|
|
Neubauer, A.C., Sange, G., Pfurtscheller, G., 1999. Psychometric intelligence and event-related desynchronisation during performance of a letter matching task. In: Pfurtscheller, G., Lopes da Silva, F.H. (Eds.), Event-Related Desynchronization (ERD) and Related Oscillatory EEG-Phenomena of the Awake Brain. Elsevier, Amsterdam, pp. 219–231.
|
|
Multilevel computations of integral transforms and particle interactions with oscillatory kernels. Computer Physics Communications, 65:24-38, 1991. In the IC industry, sparsified integral equation techniques are typically used to solve capacitance and inductance extraction problems. The random-walk methods have become quite mature for capacitance extraction.
|
|
Voräufige Mittheilung.", Poggendorff's Annalen der Physik und Chemie, series 2, volume 140, number 8, pp. 541–552 Professors Elihu Thomson and E. J. Houston in 1876 made a number of experiments and observations on high frequency oscillatory discharges.Thomson, Elihu and Houston, Edwin (April 1876) "The Alleged Etheric Force.
|
|
In undulatory swimming modes, thrust is produced by wave-like movements of the propulsive structure (usually a fin or the whole body). Oscillatory modes, on the other hand, are characterized by thrust produced by swiveling of the propulsive structure on an attachment point without any wave-like motion.
|
|
Often, the Stokes drift velocity is loosely referred to as Stokes drift. Stokes drift may occur in all instances of oscillatory flow which are inhomogeneous in space. For instance in water waves, tides and atmospheric waves. In the Lagrangian description, fluid parcels may drift far from their initial positions.
|
|
The important contribution of Jeffreys, Wentzel, Kramers, and Brillouin to the method was the inclusion of the treatment of turning points, connecting the evanescent and oscillatory solutions at either side of the turning point. For example, this may occur in the Schrödinger equation, due to a potential energy hill.
|
|
Weizhu Bao (, born September 1969 in Shaanxi, China) is a Chinese mathematician at the National University of Singapore (NUS). He is known for his work in applied mathematics with applications in quantum physics and chemistry and materials science, especially Bose-Einstein condensation (BEC) and highly oscillatory partial differential equations.
|
|
Thus the tunnel experiment provided the first dynamical model of oscillatory motion, albeit a purely imaginary one in the first instance, and specifically in terms of A-B impetus dynamics.For statements of the relationship between pendulum motion and the tunnel prediction, see for example Oresme's discussion in his Treatise on the Heavens and the World translated on p. 570 of Clagett's 1959, and Benedetti's discussion on p235 of Drake & Drabkin 1959. For Buridan's discussion of pendulum motion in his Questiones see pp. 537–8 of Clagett 1959 However, this thought-experiment was then most cunningly applied to the dynamical explanation of a real world oscillatory motion, namely that of the pendulum, as follows.
|
|
A leaky mode or tunneling mode in an optical fiber or other waveguide is a mode having an electric field that decays monotonically for a finite distance in the transverse direction but becomes oscillatory everywhere beyond that finite distance. Such a mode gradually "leaks" out of the waveguide as it travels down it, producing attenuation even if the waveguide is perfect in every respect. In order for a leaky mode to be definable as a mode, the relative amplitude of the oscillatory part (the leakage rate) must be sufficiently small that the mode substantially maintains its shape as it decays. Leaky modes correspond to leaky rays in the terminology of geometric optics.
|
|
In biology, the Goodwin model describes negative feedback oscillators in cellular systems,Goodwin, B. Oscillatory behavior in enzymatic control processes. Advances in Enzyme Regulation, 3, 1965, pages 425-428\. for example, circadian rhythms or enzymatic regulation (such as lactose in bacteria). The Goodwin model, though, shows no stable limit cycles.
|
|
This phenomenon is best seen in local field potentials which reflect the synchronous activity of local groups of neurons, but has also been shown in EEG and MEG recordings providing increasing evidence for a close relation between synchronous oscillatory activity and a variety of cognitive functions such as perceptual grouping.
|
|
Scheel's research is concerned with patterns and waves in spatially extended dynamical systems. His results include existence, stability, and bifurcation results for coherent structures such as wave trains, invasion fronts, pattern forming fronts, defects in oscillatory media, spiral waves, or defects in striped phases such as grain boundaries and dislocations.
|
|
The Morris–Lecar model is a biological neuron model developed by Catherine Morris and Harold Lecar to reproduce the variety of oscillatory behavior in relation to Ca++ and K+ conductance in the muscle fiber of the giant barnacle . Morris–Lecar neurons exhibit both class I and class II neuron excitability.
|
|
Another example of TFL is the internal stresses on a hydraulic ram operating in a vibrational environment.Brown, Samuel, "An Analysis of Hydraulic Ram Dynamics," 1981. Due to the oscillatory nature of the acceleration experienced by the ram, in n-dimensions, the resulting frictional response is described as transient friction loading.
|
|
B, shows the spectrogram of EMI noise shape of voltage output for an RPWM, where it is possible to note (also in Fig. 3.A) that randomization process introduces the continuous EMI noise shape, and in low-frequencies, the EMI noise shape follows oscillatory mode with their noise value decreasing across the spectrum.
|
|
Oscillation is viewed as pectoral-fin-based swimming and is best known as mobuliform locomotion. The motion can be described as the production of less than half a wave on the fin, similar to a bird wing flapping. Pelagic stingrays, such as the manta, cownose, eagle and bat rays use oscillatory locomotion.
|
|
Other phenomena have similar symptoms to ringing, but are otherwise distinct in their causes. In cases where these cause circular artifacts around point sources, these may be referred to as "rings" due to the round shape (formally, an annulus), which is unrelated to the "ringing" (oscillatory decay) frequency phenomenon discussed on this page.
|
|
While oscillatory transcription plays a key role in the progression of the yeast cell cycle, the CDK-cyclin machinery operates independently in the early embryonic cell cycle. Before the midblastula transition, zygotic transcription does not occur and all needed proteins, such as the B-type cyclins, are translated from maternally loaded mRNA.
|
|
Rheometers are instruments used to characterize the rheological properties of materials, typically fluids that are melts or solution. These instruments impose a specific stress field or deformation to the fluid, and monitor the resultant deformation or stress. Instruments can be run in steady flow or oscillatory flow, in both shear and extension.
|
|
The mechanism by which the Lewis pair binds CO₂ in solution. The amount of conjugated Lewis pairs can be measured and reflects the quantity of CO₂ in solution. Inside oscillatory microfluidic tube, the Switchable Hydrophilicity Solvent (SHS) - in this case DBAE - being protonated and becoming hydrophilic. The hydrophilic state contains bound CO₂.
|
|
They are best studied through several other rheological properties that relate stress and strain rate tensors under many different flow conditions—such as oscillatory shear or extensional flow—which are measured using different devices or rheometers. The properties are better studied using tensor-valued constitutive equations, which are common in the field of continuum mechanics.
|
|
Neural oscillation can also arise from interactions between different brain areas coupled through the structural connectome. Time delays play an important role here. Because all brain areas are bidirectionally coupled, these connections between brain areas form feedback loops. Positive feedback loops tend to cause oscillatory activity where frequency is inversely related to the delay time.
|
|
It can be shown that any sufficiently fast decaying smooth solution will eventually split into a finite superposition of solitons travelling to the right plus a decaying dispersive part travelling to the left. This was first observed by and can be rigorously proven using the nonlinear steepest descent analysis for oscillatory Riemann–Hilbert problems.See e.g.
|
|
Llinás gives the evidence of anesthesia of the brain and subsequent stimulation of limbs to demonstrate that qualia can be "turned off" with changing only the variable of neuronal oscillation (local brain electrical activity), while all other connections remain intact, arguing strongly for an oscillatory—electrical origin of qualia, or important aspects of them.
|
|
Example of a simple oscillator that requires a capacitor to function A capacitor can possess spring-like qualities in an oscillator circuit. In the image example, a capacitor acts to influence the biasing voltage at the npn transistor's base. The resistance values of the voltage-divider resistors and the capacitance value of the capacitor together control the oscillatory frequency.
|
|
Example of a simple oscillator incorporating a capacitor A capacitor can possess spring-like qualities in an oscillator circuit. In the image example, a capacitor acts to influence the biasing voltage at the npn transistor's base. The resistance values of the voltage-divider resistors and the capacitance value of the capacitor together control the oscillatory frequency.
|
|
In the absence of the spring, the particles would fly apart. However, the force exerted by the extended spring pulls the particles onto a periodic, oscillatory path. Rotational–vibrational coupling occurs when the rotation frequency of an object is close to or identical to a natural internal vibration frequency. The animation on the right shows a simple example.
|
|
Bass guitar time signal of open string A note (55 Hz). Fourier transform of bass guitar time signal of open string A note (55 Hz). Fourier analysis reveals the oscillatory components of signals and functions. In mathematics, Fourier analysis () is the study of the way general functions may be represented or approximated by sums of simpler trigonometric functions.
|
|
Synaptic depression creates a switch that controls the frequency of an oscillatory circuit. Proceedings Of The National Academy Of Sciences Of The United States Of America, 96(14), 8206-8211. It is important that the recycling of neurotransmitters take place at an effective and efficient rate in order to prevent synaptic fatigue from negatively affecting signal transmission.
|
|
Moreover, since w(x) is generally specified analytically, one can sometimes employ specialized methods to compute W_k. For example, special methods have been developed to apply Clenshaw–Curtis quadrature to integrands of the form f(x) w(x) with a weight function w(x) that is highly oscillatory, e.g. a sinusoid or Bessel function (see, e.g., Evans & Webster, 1999G.
|
|
Professor Giacomin and his group have published on the rheology of polymeric liquids, and especially on their behaviours in large-amplitude oscillatory shear flow (LAOS) (see Self-assembly of nanoparticles). Specifically, Giacomin has explored the role of polymer orientation in LAOS. Giacomin developed the conversions from standardized polymer durometer hardness to Young's modulus using linear elastic indentation mechanics.
|
|
These ongoing rhythms can change in different ways in response to perceptual input or motor output. Oscillatory activity may respond by increases or decreases in frequency and amplitude or show a temporary interruption, which is referred to as phase resetting. In addition, external activity may not interact with ongoing activity at all, resulting in an additive response.
|
|
Next to evoked activity, neural activity related to stimulus processing may result in induced activity. Induced activity refers to modulation in ongoing brain activity induced by processing of stimuli or movement preparation. Hence, they reflect an indirect response in contrast to evoked responses. A well-studied type of induced activity is amplitude change in oscillatory activity.
|
|
Neurons generate action potentials resulting from changes in the electric membrane potential. Neurons can generate multiple action potentials in sequence forming so-called spike trains. These spike trains are the basis for neural coding and information transfer in the brain. Spike trains can form all kinds of patterns, such as rhythmic spiking and bursting, and often display oscillatory activity.
|
|
Despite the great utility of such diagrams, they are very difficult to construct, making them either incomplete or very hard to interpret. This complexity lies in the number of variables needed to quantify the system. Dimensional phase diagram for combined flows. Relationships of combined-flow bed-phases stability fields in a plot of Oscillatory vs Unidirectional velocity.
|
|
"The time dimension of scene analysis". IEEE Transactions on Neural Networks, 16(6), 1401-1426. Temporal or oscillatory correlation addressing the binding problem by focusing on the synchrony and desynchrony between neural oscillations to encode the state of binding among the auditory features. These two solutions are very similar to the debacle between place coding and temporal coding.
|
|
In a typical SST study, brain electrical activity (electroencephalogram or EEG) is recorded while participants view audio visual material and/or perform a psychological task. Simultaneously, a dim sinusoidal visual flicker is presented in the visual periphery. The sinusoidal flicker elicits an oscillatory brain electrical response known as the Steady State Visually Evoked Potential (SSVEP).Regan, D., (1989).
|
|
Information about odors may be encoded in the mushroom body by the identities of the responsive neurons as well as the timing of their spikes. Experiments in locusts have shown that Kenyon cells have their activity synchronized to 20-Hz neural oscillations and are particularly responsive to projection neuron spikes at specific phases of the oscillatory cycle.
|
|
He found the representation of time to be generated by the oscillatory activity of cells in the upper cortex. The frequency of these cells' activity is detected by cells in the dorsal striatum at the base of the forebrain. His model separated explicit timing and implicit timing. Explicit timing is used in estimating the duration of a stimulus.
|
|
A generalization of Plücker's conoid is given by the parametric equations : x=v \cos u,\quad y=v \sin u,\quad z= \sin nu. where n denotes the number of folds in the surface. The difference is that the period of the oscillatory motion along the z-axis is 2π/n. (Figure 5 for n = 3) Figure 4.
|
|
However, it is well known that, in specific parameter ranges of the model under consideration, the oscillatory nature of the weight function can lead to a bad statistical convergence of the numerical integration procedure. The problem is known as the numerical sign problem and can be alleviated with analytical and numerical convergence acceleration procedures (Baeurle 2002, Baeurle 2003a).
|
|
Reticular neurons (RE), on the other hand, are highly interconnected and have their own intrinsic oscillatory properties. These neurons are capable of inhibiting thalamocortical activity via their direct connections to TCs. Corticothalamic neurons are the cortical neurons that TC neurons synapse on. These cells are glutaminergic excitatory cells that exhibit increasing activity as they become more depolarized.
|
|
In another experiment involving a human subject under the influence of hallucinogenic drugs (LSD), the oscillatory behaviour of the distribution of dominance duration was recorded. Similar to the previous study, Manousakis' model was able to accurately predict the frequency by which the subject was able to switch between rivalry states given the neuronal hindering effects of the drug.
|
|
Oscillatory recruitment of signaling proteins to the cell tips promotes coordinated behaviour during cell fusion. PNAS. 106(46): 19387–19392. The filamentous fungus Neurospora crassa (a bread mould and fungal model organism) produces CATs from conidia and conidial germ tubes. In contrast, the fungal plant pathogen, Colletotrichum lindemuthianum, only produces CATs from conidia and not from germ tubes.
|
|
In physics, two objects are said to be coupled when they are interacting with each other. In classical mechanics, coupling is a connection between two oscillating systems, such as pendulums connected by a spring. The connection affects the oscillatory pattern of both objects. In particle physics, two particles are coupled if they are connected by one of the four fundamental forces.
|
|
Neural oscillations are rhythmic or repetitive electrochemical activity in the brain and central nervous system. Such oscillations can be characterized by their frequency, amplitude and phase. Neural tissue can generate oscillatory activity driven by mechanisms within individual neurons, as well as by interactions between them. They may also adjust frequency to synchronize with the periodic vibration of external acoustic or visual stimuli.
|
|
Acoustic waves can be projected to the thin film to produce an oscillatory device, which then follows an equation that is nearly identical to the Sauerbrey equation used in the QCM method. Biomolecules, such as proteins or antibodies can bind and its change in mass gives a measureable signal proportional to the presence of the target analyte in the sample.
|
|
During 1954-1957, Shnoll demonstrated a high probability of oscillatory modes in biochemical reactions. Study of chemical oscillating reactions conducted under his direction gained prominence to his graduate student Anatoly Zhabotinsky, who investigated in detail the reaction previously discovered by Boris Belousov. He later worked in the fields of Chronobiology and Astrobiology. He is author of over 200 scientific papers.
|
|
The firehose instability derives its name from a similar instability in magnetized plasmas. However, from a dynamical point of view, a better analogy is with the Kelvin–Helmholtz instability, or with beads sliding along an oscillating string.In spite of its name, the firehose instability is not related dynamically to the oscillatory motion of a hose spewing water from its nozzle.
|
|
Oscillatory activity in single neurons can also be observed in sub- threshold fluctuations in membrane potential. These rhythmic changes in membrane potential do not reach the critical threshold and therefore do not result in an action potential. They can result from postsynaptic potentials from synchronous inputs or from intrinsic properties of neurons. Neuronal spiking can be classified by their activity patterns.
|
|
Various methods of slitlamp illumination are required to obtain full advantage of slit-lamp biomicroscope. There are mainly six type of illuminating options: # Diffuse illumination, # Direct focal illumination, # Specular reflection, # Transillumination or retroillumination, # Indirect lateral illumination or Indirect proximal illumination and # Sclerotic scatter. Oscillatory Illumination is sometimes considered an illumination technique.Practical Ophthalmology A MANUAL FOR BEGINNING RESIDENTS, Fourth Edition, page 218-228.
|
|
Most experimental data can be explained by the model which considers cool flame just as a slow chemical reaction where the rate of heat generation is higher than the heat loss. This model also explains the oscillatory character of the cool flame: the reaction accelerates as it produces more heat until the heat loss becomes appreciable and temporarily quenches the process.
|
|
A standby switch replaced the output socket on the rear. The modifications suggested by Gallagher formed the basis of the OTR amplifier (Oscillatory Transition Return). In 1998, the AD Series was launched. Initially consisting of the AD30 head without reverb, the AD30R, a 2×12 combo with reverb, and the AD15 combo, which was available with 10" or 12" speakers.
|
|
The stingray uses its paired pectoral fins for moving around. This is in contrast to sharks and most other fish, which get most of their swimming power from a single caudal (tail) fin. Stingray pectoral fin locomotion can be divided into two categories: undulatory and oscillatory. Stingrays who use undulatory locomotion have shorter thicker fins for slower motile movements in benthic areas.
|
|
In the process, a packed bed of beads is formed to drastically increase the adsorption efficiency of chromatin fragments. An automated oscillatory washing is then used to remove nonspecific binding and impurity from the bead surface. Initial version of MOWChIP device contained only one microfluidic chamber. In the more recent demonstration, semi-automated MOWChIP device for running 8 parallel assays was presented.
|
|
Fluid–structure interactions are a crucial consideration in the design of many engineering systems, e.g. aircraft, spacecraft, engines and bridges. Failing to consider the effects of oscillatory interactions can be catastrophic, especially in structures comprising materials susceptible to fatigue. Tacoma Narrows Bridge (1940), the first Tacoma Narrows Bridge, is probably one of the most infamous examples of large-scale failure.
|
|
At the 1/f regime, the brain is in the critical state necessary for a conscious response to weak or chaotic environmental signals because it can shift the random signals into identifiable and predictable oscillatory waveforms. While often transient, these waveforms exist in a stable form long enough to contribute to what can be thought of as conscious response to environmental stimuli.
|
|
Since Drazin's 1974 paper, other authors have studied more realistic problems in fluid dynamics using a global mode analysis. Such problems are often highly nonlinear, and attempts to analyse them have often relied on laboratory or numerical experiment. Examples of global modes in practice include the oscillatory wakes produced when fluid flows past an object, such as a vortex street.
|
|
The HES7 gene is self-regulated by a negative feedback loop in which the gene product can bind to its own promoter. This causes the gene to be expressed in an oscillatory manner. The HES7 protein also represses expression of Lunatic Fringe (LFNG) thereby both directly and indirectly regulating the Notch signalling pathway. Mutations in HES7 can result in deformities of the spine, ribs and heart.
|
|
Cox introduced a new treatment called swinging to effect change in blood flow in the head and body, a practice that had been advocated by Erasmus Darwin (1731-1802), a physician and naturalist. The patient was suspended in a chair or bed and swung in an oscillatory or circular manner at varying tempos. Nausea, vomiting, and convulsions were produced but often refreshing sleep followed.
|
|
For example: if a newborn baby's heart beats at a frequency of 120 times a minute (2 hertz), its period, , — the time interval between beats—is half a second (60 seconds divided by 120 beats). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
|
|
In undulatory swimming modes thrust is produced by wave-like movements of the propulsive structure (usually a fin or the whole body). Oscillatory modes, on the other hand, are characterized by thrust production from swiveling of the propulsive structure on an attachment point without any wave-like motion.Sfakiotakis, Michael, David M. Lane, and J. Bruce C. Davies. (1999) Review of Fish Swimming Modes for Aquatic Locomotion.
|
|
There is also a counter mechanism in the body to stop the secretion of insulin beyond a certain limit. Namely, those counter-regulatory mechanisms are glucagon and epinephrine. The process of the regulation of blood glucose (also known as glucose homeostasis) also exhibits oscillatory behavior. On a pathological basis, this topic is crucial to understanding certain disorders in the body such as diabetes, hyperglycemia and hypoglycemia.
|
|
In perturbation theory, the Poincaré–Lindstedt method or Lindstedt–Poincaré method is a technique for uniformly approximating periodic solutions to ordinary differential equations, when regular perturbation approaches fail. The method removes secular terms—terms growing without bound—arising in the straightforward application of perturbation theory to weakly nonlinear problems with finite oscillatory solutions., pp. 181–186. The method is named after Henri Poincaré,, §123–§128.
|
|
Louis Napoleon George Filon, FRS (22 November 1875 – 29 December 1937) was an English applied mathematician, famous for his research on classical mechanics and particularly the theory of elasticity and the mechanics of continuous media. He also developed a method for the numerical quadrature of oscillatory integrals, now known as Filon quadrature. He was Vice Chancellor of the University of London from 1933–35.
|
|
This coordination compound is used as an indicator in analytical chemistry. The active ingredient is the [Fe(o-phen)3]2+ ion, which is a chromophore that can be oxidized to the ferric derivative [Fe(o-phen)3]3+. The potential for this redox change is +1.06 volts in 1 M H2SO4. It is a popular redox indicator for visualizing oscillatory Belousov–Zhabotinsky reactions.
|
|
When this boost occurs, an acoustic reflex mechanism triggers and acts as a defense against these sounds. This mechanism seeks to reduce the sound energy in the ear by dampening its transfer from eardrum to cochlea. It has been seen that this process can reduce sound waves by up to 50 decibels. Although this mechanism can decrease the sound energy, it does not negate the oscillatory pressure.
|
|
When ventilating at high frequencies, its contribution can be substantial, particularly in people with obstructive lung disease such as asthma or chronic obstructive pulmonary disease (COPD). iPEEP has been measured in very few formal studies on ventilation in ARDS, and its contribution is largely unknown. Its measurement is recommended in the treatment of people who have ARDS, especially when using high-frequency (oscillatory/jet) ventilation.
|
|
Its invention is important in the history of technology, because it made possible the development of all-mechanical clocks. This caused a shift from measuring time by continuous processes, such as the flow of liquid in water clocks, to repetitive, oscillatory processes, such as the swing of pendulums, which had the potential to be more accurate., p.31 Oscillating timekeepers are used in all modern timepieces.
|
|
In 1955 Gray was appointed a Lecturer in Chemistry at the University of Leeds. He was promoted to Reader in 1959 and to a personal chair as Professor of Physical Chemistry in 1962. He became Head of the Department of Physical Chemistry on the resignation of Professor Lord Dainton in 1965. His research interests included combustion flame and explosion oscillatory reactions and chaos in chemistry.
|
|
The modern understanding of sunspots starts with George Ellery Hale, who linked magnetic fields and sunspots. Hale suggested that the sunspot cycle period is 22 years, covering two polar reversals of the solar magnetic dipole field. Horace W. Babcock proposed in 1961 a qualitative model for solar dynamics. On the largest scale, the Sun supports an oscillatory magnetic field, with a quasi-steady periodicity of 22 years.
|
|
The damping ratio is a dimensionless measure describing how oscillations in a system decay after a disturbance. Many systems exhibit oscillatory behavior when they are disturbed from their position of static equilibrium. A mass suspended from a spring, for example, might, if pulled and released, bounce up and down. On each bounce, the system tends to return to its equilibrium position, but overshoots it.
|
|
All four HCN subunits are expressed in the brain. In addition to their proposed roles in pacemaking rhythmic or oscillatory activity, HCN channels may control the way that neurons respond to synaptic input. Initial studies suggest roles for HCN channels in sour taste, coordinated motor behavior and aspects of learning and memory. Clinically, there is evidence that HCN channels play roles in epilepsy and neuropathic pain.
|
|
A. Evans and J. R. Webster, "A comparison of some methods for the evaluation of highly oscillatory integrals," Journal of Computational and Applied Mathematics, vol. 112, p. 55-69 (1999).). This is useful for high-accuracy Fourier series and Fourier–Bessel series computation, where simple w(x)=1 quadrature methods are problematic because of the high accuracy required to resolve the contribution of rapid oscillations.
|
|
In addition to giving a restoring force (which on its own would cause oscillatory motion) a tailplane gives damping. This is caused by the relative wind seen by the tail as the aircraft rotates around the centre of gravity. For example, when the aircraft is oscillating, but is momentarily aligned with the overall vehicle's motion, the tailplane still sees a relative wind that is opposing the oscillation.
|
|
Tei and Shin Yamazaki developed the first rodent model that was used to monitor circadian gene expression rhythms. This was done using a luciferase reporter gene expressed under the Per1. In 2000, using their rodent model, they discovered the existence of circadian clocks in peripheral organs of mammals. This discovery led to the current understanding of mammalian circadian control as a multi-oscillatory system.
|
|
Simon El'evich Shnol (; born 21 March 1930 in Moscow) is a biophysicist, and a historian of Soviet science. He is a professor at Physics Department of Moscow State University and a member of Russian Academy of Natural Sciences. His fields of interest are the oscillatory processes in biology, the theory of evolution, chronobiology, and the history of science. He has mentored many successful scientists, including Anatoly Zhabotinsky.
|
|
After the BCI challenge, in 1988, alpha rhythm was used in a brain rhythm based BCI for control of a physical object, a robot. Alpha rhythm based BCI was the first BCI for control of a robot. In particular, some forms of BCI allow users to control a device by measuring the amplitude of oscillatory activity in specific frequency bands, including mu and beta rhythms.
|
|
In addition to local synchronization, oscillatory activity of distant neural structures (single neurons or neural ensembles) can synchronize. Neural oscillations and synchronization have been linked to many cognitive functions such as information transfer, perception, motor control and memory. Neural oscillations have been most widely studied in neural activity generated by large groups of neurons. Large-scale activity can be measured by techniques such as EEG.
|
|
Oscillatory activity in groups of neurons generally arises from feedback connections between the neurons that result in the synchronization of their firing patterns. The interaction between neurons can give rise to oscillations at a different frequency than the firing frequency of individual neurons. A well- known example of macroscopic neural oscillations is alpha activity. Neural oscillations were observed by researchers as early as 1924 (by Hans Berger).
|
|
Example of the high-frequency oscillation burst recorded from the brain. High frequency oscillations (HFO) are brain waves of the frequency faster than ~80 Hz, generated by neuronal cell population. High frequency oscillations can be recorded during an electroencephalagram (EEG), local field potential (LFP) or electrocorticogram (ECoG) electrophysiology recordings. They are present in physiological state during sharp waves and ripples - oscillatory patterns involved in memory consolidation processes.
|
|
He then studied at the Technical University at Darmstadt until he received his doctorate in 1928. Hollmann's doctoral research included the development of an ultra-short-wave transmitter and receiver for centimetre and decimetre waves. This gained the attention of Telefunken, and ultimately led to their development of the first microwave telecommunication system. In 1930 Hollmann moved to the Heinrich-Hertz Institute for Oscillatory Research in Berlin.
|
|
In similar study where LFPs were recorded from macaque monkeys while they performed a precision grip task, it was seen that the disruption of the PTN resulted in a greatly reduced oscillatory response. Stimulation of the PTN caused the monkeys to not be able to perform the grip task as well. It was concluded that PTNs in the motor cortex directly influence the generation of Beta rhythms.
|
|
Although the exact oscillatory pattern that modulates different sports has not been found, there have been studies done to show a correlation between athletic performance and circadian timing. It has been shown certain times of the day are better for training and gametime performance. Training has the best results when done in the morning, while it is better to play a game at night.
|
|
HES1 can maintain neural stem cells expressing Pax6, but leads cells that are Pax6-negative to an astrocyte differentiation fate. Epigenetic modifications such as DNA methylation also influence HES1's ability to direct differentiation. Demethylation of HES1 target sites in the promoter region of astrocyte- specific genes hastens astrocyte differentiation. The oscillatory nature of Hes1 expression has a role in determining differentiation fate as well.
|
|
Aircraft wings and turbine blades can break due to FSI oscillations. Fluid–structure interaction has to be taken into account for the analysis of aneurysms in large arteries and artificial heart valves. A reed actually produces sound because the system of equations governing its dynamics has oscillatory solutions. The dynamic of reed valves used in two strokes engines and compressors is governed by FSI.
|
|
An oscillatory pattern in this spectrum is being caused by a single-armed spiral density wave in the disk. The disk may be precessing from the gravitational influence of the secondary component. Zeta Tauri shows variation in its spectrum and brightness. The General Catalogue of Variable Stars lists it as an eclipsing variable and a Gamma Cassiopeiae variable, but it may not be either.
|
|
CA3 has been implicated in a number of working theories on memory and hippocampal learning processes. Slow oscillatory rhythms (theta-band; 3–8 Hz) are cholinergically driven patterns that depend on coupling of interneurons and pyramidal cell axons via gap junctions, as well as glutaminergic (excitatory) and GABAergic (inhibitory) synapses. Sharp EEG waves seen here are also implicated in memory consolidation.Jerome Engel TAP, ed.
|
|
Andreas Seeger is a mathematician who works in the field of harmonic analysis. He is a professor of mathematics at the University of Wisconsin–Madison. He received his Ph.D. from Technische Universität Darmstadt in 1985 under the supervision of Walter Trebels. He was elected a fellow of the American Mathematical Society in 2014 for his contributions to Fourier integral operators, local smoothing, oscillatory integrals, and Fourier multipliers.
|
|
These saccades are generated by a neuronal mechanism that bypasses time-consuming circuits and activates the eye muscles more directly. Specific pre-target oscillatory (alpha rhythms) and transient activities occurring in posterior-lateral parietal cortex and occipital cortex also characterise express saccades. Saccadic mainsequence, showing single saccades from a participant performing a visually-guided saccade task. The amplitude of a saccade is the angular distance the eye travels during the movement.
|
|
The development of this microscope allowed for a direct observation of the oscillatory structure of a wave function to become possible. Photodetachment is the removal of electrons from an atom using interactions with photons or other particles. Photodetachment microscopy made it possible to image the spatial distribution of the ejected electron. The microscope developed in 1996 was the first to image photodetachment rings of a negative Bromine (Br-) ion.
|
|
Jensen's research mainly focuses on the neuronal oscillatory dynamics supporting cognition in animals and humans. In particular, his work has addressed the role of alpha oscillations (or waves) by demonstrating that these oscillations reflect a gating by inhibition mechanism in attention, language and memory tasks. Other parts of his work has focused on understanding the coupling between slower and faster oscillations and how this kind of neuronal dynamics organize neuronal coding.
|
|
Sometimes referred to as electromagnetic viscometer or EMV viscometer, was invented at Cambridge Viscosity (Formally Cambridge Applied Systems) in 1986. The sensor (see figure below) comprises a measurement chamber and magnetically influenced piston. Measurements are taken whereby a sample is first introduced into the thermally controlled measurement chamber where the piston resides. Electronics drive the piston into oscillatory motion within the measurement chamber with a controlled magnetic field.
|
|
Pendulums are widely used in science education as an example of a harmonic oscillator, to teach dynamics and oscillatory motion. One use is to demonstrate the law of conservation of energy. A heavy object such as a bowling ball or wrecking ball is attached to a string. The weight is then moved to within a few inches of a volunteer's face, then released and allowed to swing and come back.
|
|
It considers the brain a dynamical system and uses differential equations to describe how neural activity evolves over time. In particular, it aims to relate dynamic patterns of brain activity to cognitive functions such as perception and memory. In very abstract form, neural oscillations can be analyzed analytically. When studied in a more physiologically realistic setting, oscillatory activity is generally studied using computer simulations of a computational model.
|
|
The mild-slope equation can be derived by the use of several methods. Here, we will use a variational approach. The fluid is assumed to be inviscid and incompressible, and the flow is assumed to be irrotational. These assumptions are valid ones for surface gravity waves, since the effects of vorticity and viscosity are only significant in the Stokes boundary layers (for the oscillatory part of the flow).
|
|
Amiram Harten (1946 - 1994) was an American/Israeli applied mathematician. Harten made fundamental contribution to the development of high-resolution schemes for the solution of hyperbolic partial differential equations. Among other contributions, he developed the total variation diminishing scheme, which gives an oscillation free solution for flow with shocks. In 1980s, Harten along with Björn Engquist, Stanley Osher, and Sukumar R. Chakravarthy developed the essentially non-oscillatory (ENO) schemes.
|
|
The history of brain–computer interfaces (BCIs) starts with Hans Berger's discovery of the electrical activity of the human brain and the development of electroencephalography (EEG). In 1924 Berger was the first to record human brain activity by means of EEG. Berger was able to identify oscillatory activity, such as Berger's wave or the alpha wave (8–13 Hz), by analyzing EEG traces. Berger's first recording device was very rudimentary.
|
|
During courtship, Cupiennius salei communicate using sex pheromones. Females are usually solitary and to attract males, release the pheromones on trees along a silk thread. When a male detects the pheromone, he shows patterned oscillatory movement that creates vibrations on the leaves (an average frequency of 76 Hz). The female responds to this by creating a counter vibration, and in this way guides the receptive male to her exact location.
|
|
However, the slow cortical potential approach to BCIs has not been used in several years, since other approaches require little or no training, are faster and more accurate, and work for a greater proportion of users. Another research parameter is the type of oscillatory activity that is measured. Gert Pfurtscheller founded the BCI Lab 1991 and fed his research results on motor imagery in the first online BCI based on oscillatory features and classifiers. Together with Birbaumer and Jonathan Wolpaw at New York State University they focused on developing technology that would allow users to choose the brain signals they found easiest to operate a BCI, including mu and beta rhythms. A further parameter is the method of feedback used and this is shown in studies of P300 signals. Patterns of P300 waves are generated involuntarily (stimulus-feedback) when people see something they recognize and may allow BCIs to decode categories of thoughts without training patients first.
|
|
A 1915 example of an early type of resonant circuit known as an Oudin coil which uses Leyden jars for the capacitance. Resonance was noticed early on in experiments with the Leyden jar, invented in 1746. The Leyden jar stores electricity due to its capacitance, and is, in fact, an early form of capacitor. When a Leyden jar is discharged by allowing a spark to jump between the electrodes, the discharge is oscillatory.
|
|
During oscillation within an Orbitrap, ion transient signal may not be stable until the ions settle into their oscillations. Toward the end, subtle ion collisions have added up to cause noticeable dephasing. This presents a problem for the Fourier transformation, as it averages the oscillatory signal across the length of the time-domain measurement. Software allows “apodization”, the removal of the front and back section of the transient signal from consideration in the FT calculation.
|
|
More than 50 years later, intrinsic oscillatory behavior was encountered in vertebrate neurons, but its functional role is still not fully understood. The possible roles of neural oscillations include feature binding, information transfer mechanisms and the generation of rhythmic motor output. Over the last decades more insight has been gained, especially with advances in brain imaging. A major area of research in neuroscience involves determining how oscillations are generated and what their roles are.
|
|
They were able to detect that the multiple proxies were varying in a coherent oscillatory way, indicating both the multidecadal pattern in the North Atlantic and a longer term oscillation of roughly 250 years in the surrounding region. Their study did not calibrate these proxy patterns against a quantitative temperature scale, and a new statistical approach was needed to find how they related to surface temperatures in order to reconstruct past temperature patterns..
|
|
Gamma waves can be detected by electroencephalography or magnetoencephalography. One of the earliest reports of gamma wave activity was recorded from the visual cortex of awake monkeys. Subsequently, significant research activity has concentrated on gamma activity in visual cortex. Gamma activity has also been detected and studied across premotor, parietal, temporal, and frontal cortical regions Gamma waves constitute a common class of oscillatory activity in neurons belonging to the cortico-basal ganglia- thalamo-cortical loop.
|
|
The mechanism by which cats purr is an object of speculation, with different theories proposed. An early theory was that purring is a hemodynamic process where sound is produced as the blood runs through the thorax. There is a unique “neural oscillator” in the cat's brain of uncertain significance. Although the mechanism has not yet been fully elucidated, recent studies have inferred it could be the result of oscillatory mechanisms in the central nervous system.
|
|
Podvigin NF, Bagaeva TV, Boykova EV, Zargarov AA, Podvigina DN, Pöppel E, Three bands of oscillatory activity in the lateral geniculate nucleus of the cat visual system. Neuroscience Letters, 2004, 361(1-3):83-85. and Victor Shklovsky from Moscow, and with the Polish neuroscientist Elżbieta Szeląg from the Nencki Institute in Warsaw.Szelag E, von Steinbüchel N, Pöppel E, Temporal processing disorders in patients with Broca’s aphasia. Neuroscience Letters, 1997, 235(1-2): 33-36.
|
|
In physics, a breather is a nonlinear wave in which energy concentrates in a localized and oscillatory fashion. This contradicts with the expectations derived from the corresponding linear system for infinitesimal amplitudes, which tends towards an even distribution of initially localized energy. A discrete breather is a breather solution on a nonlinear lattice. The term breather originates from the characteristic that most breathers are localized in space and oscillate (breathe) in time.
|
|
She went to the University of Pittsburgh for graduate study, completing her Ph.D. there in 1998. Her dissertation, L^p Estimates for Oscillatory Integral Operators, was supervised by Yibiao Pan. After completing her doctorate, despite having offers for tenure-track faculty positions elsewhere, Cheng worked in temporary positions until getting an offer to return to Bryn Mawr in 2002. She was given the Rachel C. Hale Chair at Bryn Mawr in 2018.
|
|
This function has an essential singularity at the origin. By using cylindrical coordinates in space, we can write the above function into parametric equations : x=v\cos u,\quad y=v\sin u,\quad z=\sin 2u. Thus Plücker's conoid is a right conoid, which can be obtained by rotating a horizontal line about the z-axis with the oscillatory motion (with period 2π) along the segment [−1, 1] of the axis (Figure 4).
|
|
The resulting field theories are well-suited for the application of effective approximation techniques, like the mean field approximation. A major difficulty arising in the simulation with such field theories is their highly oscillatory nature in case of strong interactions, which leads to the well-known numerical sign problem. The problem originates from the repulsive part of the interaction potential, which implicates the introduction of the complex factor via the HS transformation.
|
|
Bao has made contributions to Bose-Einstein condensation (BEC), multiscale methods, computational quantum physics and chemistry, computational fluid dynamics, and computational materials science. In the study of BEC, he and collaborators have established mathematical theory and proposed efficient and accurate computational methods. For highly oscillatory partial differential equations, he and collaborators have developed the uniformly accurate multiscale time integrator method. For solid- state dewetting, he and collaborators have derived sharp interface and phase field models.
|
|
The entire field is the phase portrait, a particular path taken along a flow line (i.e. a path always tangent to the vectors) is a phase path. The flows in the vector field indicate the time-evolution of the system the differential equation describes. In this way, phase planes are useful in visualizing the behaviour of physical systems; in particular, of oscillatory systems such as predator-prey models (see Lotka–Volterra equations).
|
|
Branch pipe a of isolating vibration is a part of a tube with elastic walls for reflection and absorption of waves of the oscillatory energy extending from the working pump over wall of the pipe duct. Is established between the pump and the pipe duct. On an illustration is presented the image a vibration-isolating branch pipe of a series «ВИПБ». In a structure is used the rubber envelope, which is reinforced by a spring.
|
|
Mouton, Hague. The study revealed various parameters which controlled the rate of neuron firing, which were subsequently compared with different qualitative regimes of the quantum model. A PDDD of rivalry states was obtained by inputting the empirically derived time-scale durations of the microsaccades and oscillatory parameters into the proposed formulation. The generated distribution of perceptual state‐switching carried the same graphical shape as the data collected from experiments performed by Levelt (image, right).
|
|
Geology: For marine geologists and geomorphologists, rugosity is a useful characteristic in distinguishing different types of seafloors in remote sensing applications (e.g., sonar and laser altimetry, based from ships, planes or satellites). Oceanography: Among oceanographers, rugosity is recognized to influence small-scale hydrodynamics by converting organized laminar or oscillatory flow into energy-dissipating turbulence. Coral biology: High rugosity is often an indication of the presence of coral, which creates a complex surface as it grows.
|
|
The researchers reported that 62% of respondents synchronized their movements upon being exposed to one another's finger- wagging, but 38% were unaffected and continued gesturing independently. The study demonstrated a clear reduction in occipital lobe alpha wave and mu wave rhythms during social interaction. The evident suppression was independent of whether or not behavior was coordinated. In contrast, a pair of oscillatory components (phi-1 and phi-2) above the right centro-parietal cortex distinguished effective from ineffective coordination.
|
|
As a result, the unambiguous definition of an average Lagrangian velocity and Stokes drift velocity, which can be attributed to a certain fixed position, is by no means a trivial task. However, such an unambiguous description is provided by the Generalized Lagrangian Mean (GLM) theory of Andrews and McIntyre in 1978.See Craik (1985), page 105–113. The Stokes drift is important for the mass transfer of all kind of materials and organisms by oscillatory flows.
|
|
A repetitive visual stimulus is a visual stimulus that has a distinctive property (e.g., frequency or phase). The stimuli are simultaneously presented to the user when focusing attention on the corresponding stimulus. For example, when the user focuses attention on a repetitive visual stimulus, an steady state visually evoked potential is elicited which manifests as oscillatory components in the user's electroencephalogram, especially in the signals from the primary visual cortex, matching the frequency or harmonics of that stimulus.
|
|
Rhythmogenesis in a neuron is due to an instability associated with the resting potential. Such instability can be attributed to properties of low- threshold calcium currents. The current is activated at around −60 mV, making it able to generate a low-threshold spike at or near the resting potential. In a somewhat recent finding, cells maintained at a hyperpolarized level have been shown to exhibit intrinsic rhythmicity, resulting in spontaneous oscillatory behavior due to Ca2+ driven depolarizations.
|
|
The ocean body surrounding the Antarctic is currently the only continuous body of water where there is a wide latitude band of open water. It interconnects the Atlantic, Pacific and Indian oceans, and provide an uninterrupted stretch for the prevailing westerly winds to significantly increase wave amplitudes. It is generally accepted that these prevailing winds are primarily responsible for the circumpolar current transport. This current is now thought to vary with time, possibly in an oscillatory manner.
|
|
Also, the mean solar day is getting longer at a rate of about 1.5 ms per century. These effects will cause the calendar to be nearly a day behind in 3200. The number of solar days in a "tropical millennium" is decreasing by about 0.06 per millennium (neglecting the oscillatory changes in the real length of the tropical year).365242×1.5/8640000. This means there should be fewer and fewer leap days as time goes on.
|
|
While the fast multipole method is useful for accelerating MoM solutions of integral equations with static or frequency-domain oscillatory kernels, the plane wave time-domain (PWTD) algorithm employs similar ideas to accelerate the MoM solution of time-domain integral equations involving the retarded potential. The PWTD algorithm was introduced in 1998 by Ergin, Shanker, and Michielssen.Ergin, A. A., Shanker, B., & Michielssen, E. (1998). Fast evaluation of three-dimensional transient wave fields using diagonal translation operators.
|
|
The Bessel function of the first kind, J_0, which is related to the Airy function, exhibits such decay. Combinations of defocus and spherical aberration exhibit ring artifacts. In cameras, a combination of defocus and spherical aberration can yield circular artifacts ("ring" patterns). However, the pattern of these artifacts need not be similar to ringing (as discussed on this page) – they may exhibit oscillatory decay (circles of decreasing intensity), or other intensity patterns, such as a single bright band.
|
|
GGSE-1 was an ovoid satellite based on a similar bus to SOLRAD 7A, with which it was launched into orbit. GGSE-1 was equipped with a passive oscillatory damping mechanism attached to the spacecraft via a 28-foot rod of metal tape. The entire mechanism and rod together weighed less than 4.5 kg. The damping mechanism, developed by General Electric, comprised a metal sphere, 12.7 cm in diameter, containing another metal sphere with a silicone damping fluid between.
|
|
A periodic travelling wave In mathematics, a periodic travelling wave (or wavetrain) is a periodic function of one-dimensional space that moves with constant speed. Consequently, it is a special type of spatiotemporal oscillation that is a periodic function of both space and time. Periodic travelling waves play a fundamental role in many mathematical equations, including self-oscillatory systems,N. Kopell, L.N. Howard (1973) "Plane wave solutions to reaction–diffusion equations", Stud. Appl. Math. 52: 291–328.
|
|
Certain types of oscillatory activity, such as alpha waves, are part of spontaneous activity. Statistical analysis of power fluctuations of alpha activity reveals a bimodal distribution, i.e. a high- and low- amplitude mode, and hence shows that resting-state activity does not just reflect a noise process. In case of fMRI, spontaneous fluctuations in the blood-oxygen-level dependent (BOLD) signal reveal correlation patterns that are linked to resting states networks, such as the default network.
|
|
These devices can switch hundreds of kiloamperes and hold off as much as 50kV. The anodes in these devices are often fabricated from a refractory metal, usually molybdenum, to handle reverse current during ringing (or oscillatory) discharges without damage. Pulse rated ignitrons usually operate at very low duty cycles. They are often used to switch high energy capacitor banks during electromagnetic forming, electrohydraulic forming, or for emergency short- circuiting of high voltage power sources ("crowbar" switching).
|
|
Waddington suggested visualising increasing irreversibility of cell type differentiation as ridges rising between the valleys where the marbles (analogous to cells) are travelling. In recent times, Waddington's notion of the epigenetic landscape has been rigorously formalized in the context of the systems dynamics state approach to the study of cell-fate. Cell-fate determination is predicted to exhibit certain dynamics, such as attractor-convergence (the attractor can be an equilibrium point, limit cycle or strange attractor) or oscillatory.
|
|
They remained the best way to record high-speed electrical phenomena for more than 40 years when they were replaced by the cathode ray oscilloscope. They paved the way for a greater understanding of the behavior of alternating current. Blondel built a theory of rectification with asymmetrical electrodes. He demonstrated that there were three kinds of electric arc: the primitive arc of William Duddell, the secondary arc of Valdemar Poulsen, and a succession of oscillatory discharges.
|
|
The article on ENO, titled, Uniformly High Order Accurate Essentially Non-oscillatory Schemes, III was published in Journal of Computational Physics, in 1987 and is one of the most cited papers in the field of scientific computing. It was republished in 1997 in the same journal. Harten is listed as an ISI highly cited researcher. In 1990 Harten gave a talk on "Recent developments in shock-capturing schemes" at the International Congress of Mathematicians in Kyoto.
|
|
The character's individuality emerges and creates an oscillatory wave that disturbs the peaceful surface of the image, causing it to waver between seduction and repulsion, sophistication and brutality. These images, with their stripped-back composition, are inhabited by strangely motionless beings, suspended in their own time and space; while lost in their dreams and thoughts, they meander through a land where the imaginary world of the photographer, the character and viewer's imagination project and come together.
|
|
Sufficiently strong resonances of the vocal tract can strongly influence the timbre of the instrument. At some frequencies, whose values depend on the position of the player's tongue, resonances of the vocal tract inhibit the oscillatory flow of air into the instrument. Bands of frequencies that are not thus inhibited produce formants in the output sound. These formants, and especially their variation during the inhalation and exhalation phases of circular breathing, give the instrument its readily recognizable sound.
|
|
Generally, if an disturbance can be replicated by a sinusoidal modulation, it is considered to be an oscillatory component of g-jitter. The most noticeable disturbances being routine crew activity and structural vibrations, and can cause a structural resonance throughout a space vehicle. While the average frequency of the structural vibration of a space station is lesser than a Space Shuttle orbiter, the frequency range can still be between the ranges of 0.1 to 1 Hz.
|
|
For the study of two-dimensional systems with repulsive or oscillatory interactions, his group developed LEED diffractometry. He developed electron stimulated desorption (ESD) and static SIMS for the study of adsorbed layers and ultrathin films on single crystal surfaces; alkali ion scattering (ISS) for structural analysis of surfaces; field ion microscopy (FIM) of single atoms and clusters; UHV-SEM studies of surface melting. Ernst Bauer has pioneering contributions to the most aspects of surface science since its inception.
|
|
The Pegasus was acquired, after one year of probation, by the Leipzig–Dresden Railway Company, which used it until 1861. From 1843 to 1868, Ehrhardt worked in Dresden as the chief machinist for the Saxon-Silesian railway company, renamed Saxon State Railways after its nationalization in 1851. He invented the two-sided brake with oscillatory waves in 1847, and the portable Ehrhardtsche scale to control axle loads in 1879. He also helped to improve the preheating of condensation devices.
|
|
A characteristic broadening and narrowing of the noise during one oscillation period can be observed. The probability distribution of a squeezed state is defined as the norm squared of the wave function mentioned in the last paragraph. It corresponds to the square of the electric (and magnetic) field strength of a classical light wave. The moving wave packets display an oscillatory motion combined with the widening and narrowing of their distribution: the "breathing" of the wave packet.
|
|
Rheometry (from the Greek ῥέος – rheos, n, meaning "stream") generically refers to the experimental techniques used to determine the rheological properties of materials, that is the qualitative and quantitative relationships between stresses and strains and their derivatives. The techniques used are experimental. Rheometry investigates materials in relatively simple flows like steady shear flow, small amplitude oscillatory shear, and extensional flow. The choice of the adequate experimental technique depends on the rheological property which has to be determined.
|
|
A synthetic oscillatory network of transcriptional regulators, Michael B. Elowitz & Stanislas Leibler, Nature 403, 335-338 (20 January 2000), doi:10.1038/35002125 Leibler was a 1997/98 Humboldt Research Award winner at the European Molecular Biology Laboratory (EMBO) in Heidelberg. In 2015 he won the Max Delbruck Prize awarded by the American Physical Society.American Physical Society announces 2015 Prize & Award Recipients, 2015 Max Delbruck PrizeIn Biological Physics In 2016 he was elected to the National Academy of Sciences..
|
|
Sardines use body- caudal fin propulsion to swim, holding their pectoral, dorsal, and anal fins flat against the body, creating a more streamlined body to reduce drag. Most fish swim by generating undulatory waves that propagate down the body through the caudal fin. This form of undulatory locomotion is termed body-caudal fin (BCF) swimming on the basis of the body structures used; it includes anguilliform, sub-carangiform, carangiform, and thunniform locomotory modes, as well as the oscillatory ostraciiform mode.
|
|
In applied mathematics, the numerical sign problem is the problem of numerically evaluating the integral of a highly oscillatory function of a large number of variables. Numerical methods fail because of the near- cancellation of the positive and negative contributions to the integral. Each has to be integrated to very high precision in order for their difference to be obtained with useful accuracy. The sign problem is one of the major unsolved problems in the physics of many-particle systems.
|
|
His deftly rendered and original A Treatise on the Mathematical Theory of the Motions of Fluids (which would later be reprinted as Hydrodynamics in 1895) was first published in 1878. In 1883, Lamb published a paper in the Philosophical Transactions of the Royal Society applying Maxwell's equations to the problem of oscillatory current flow in spherical conductors, an early examination of what was later to be known as the skin effect. Lamb was elected a Fellow of the Royal Society in 1884.
|
|
In 1996, Rychkov obtained his diploma (B.S., M.S.) from the Moscow Institute of Physics and Technology. From 1996 to 1998 he studied at the University of Jena. He received his doctorate in mathematics from Princeton University, under the supervision of Elias Stein, in 2002 with a thesis titled "Estimates for Oscillatory Integral Operators" He was a post-doctoral fellow at the University of Amsterdam (2002-2005) and at the Scuola Normale Superiore in Pisa, where he became assistant professor in 2007.
|
|
As a graduate student at Cornell, Legéndy joined an experimental team which had just discovered an electromagnetic resonance phenomenon at unexpectedly low frequencies (32 Hz and below) inside a metal sample in a magnetic field. Legéndy showed that the resonance was the manifestation of solid-state plasma wave propagation inside the metal,Bowers, R., Legéndy, C. R., and Rose, F. E. (November 1961) "Oscillatory galvanomagnetic effect in metallic Sodium". Physical Review Letters 7 (9): 339-341. DOI: 10.1103/PhysRevLett.7.339.
|
|
The importance of the escapement in the history of technology is that it was the key invention that made the all-mechanical clock possible. The invention of the first all-mechanical escapement, the verge escapement, in 13th-century Europe initiated a change in timekeeping methods from continuous processes, such as the flow of water in water clocks, to repetitive oscillatory processes, such as the swing of pendulums, which could yield more accuracy. Oscillating timekeepers are used in every modern clock.
|
|
They are related to each other by a simple proportion, :\omega_0 = 2 \pi f_0 \,. Resonance occurs because energy for this situation is stored in two different ways: in an electric field as the capacitor is charged and in a magnetic field as current flows through the inductor. Energy can be transferred from one to the other within the circuit and this can be oscillatory. A mechanical analogy is a weight suspended on a spring which will oscillate up and down when released.
|
|
Sharp waves and ripples (SWRs) are oscillatory patterns in the mammalian brain hippocampus seen on an EEG during immobility and sleep. There are three major network oscillation patterns in the hippocampus: theta waves, SWRs and gamma waves. Gamma oscillations are found in all major brain structures, whereas theta and sharp waves are specific to the hippocampus and its neighbouring areas. SWRs are composed of large amplitude sharp waves in local field potential and associated fast field oscillations known as ripples.
|
|
If the perturbation to the oscillatory cycle is infinitesimally small, it is possible to derive a response function of the neural oscillator. This response function can be classified into different classes (Type 1 and Type 2) based upon its response. #Type I Phase Response Curves are non-negative and strictly positive thus perturbations are only able to enhance a spike in phase, but never delay it. This occurs through a slight depolarization, such as postsynaptic potentials that increase the excitation of an axon.
|
|
Apart from intrinsic properties of neurons, biological neural network properties are also an important source of oscillatory activity. Neurons communicate with one another via synapses and affect the timing of spike trains in the post-synaptic neurons. Depending on the properties of the connection, such as the coupling strength, time delay and whether coupling is excitatory or inhibitory, the spike trains of the interacting neurons may become synchronized. Neurons are locally connected, forming small clusters that are called neural ensembles.
|
|
A neural network model describes a population of physically interconnected neurons or a group of disparate neurons whose inputs or signalling targets define a recognizable circuit. These models aim to describe how the dynamics of neural circuitry arise from interactions between individual neurons. Local interactions between neurons can result in the synchronization of spiking activity and form the basis of oscillatory activity. In particular, models of interacting pyramidal cells and inhibitory interneurons have been shown to generate brain rhythms such as gamma activity.
|
|
A group of neurons can also generate oscillatory activity. Through synaptic interactions, the firing patterns of different neurons may become synchronized and the rhythmic changes in electric potential caused by their action potentials will add up (constructive interference). That is, synchronized firing patterns result in synchronized input into other cortical areas, which gives rise to large-amplitude oscillations of the local field potential. These large-scale oscillations can also be measured outside the scalp using electroencephalography (EEG) and magnetoencephalography (MEG).
|
|
In non-relativistic quantum mechanics, therefore, any atom with an atomic number greater than 137 would require its 1s electrons to be traveling faster than the speed of light. Even in the Dirac equation, which accounts for relativistic effects, the wave function of the electron for atoms with Z > 137 is oscillatory and unbounded. The significance of element 137, also known as untriseptium, was first pointed out by the physicist Richard Feynman. Element 137 is sometimes informally called feynmanium (symbol Fy).
|
|
In the olfactory system, responsible for sense of smell, according to the study, subthreshold membrane potential oscillations present in mitral cells, which are neurons in the olfactory system, are said to influence the timing of the spikes of action potentials, which in turn allows for the synchronization of multiple mitral cells. The study also mentions how this oscillatory activity is thought to also impact excitatory postsynaptic potentials in the way that they act as refinement tools to this post neural activity.
|
|
On the other hand, a wave-front can be regarded as a level surface of displacement of some quantity, such as electric field intensity, hydrostatic pressure, particle number density, oscillatory phase, or probability amplitude. Then the physical meaning of the rays is less evident. This is wave–particle duality for a single particle in ordinary three-dimensional physical space or for a wave of some property of a medium with a spatial distribution of properties that is mostly continuous but not homogeneous.
|
|
The absorption of an X-ray photon by the atom excites a core level electron, thus generating a core hole. This generates a spherical electron wave with the excited atom as the center. The wave propagates outwards and get scattered off from the neighbouring atoms and is turned back towards the central ionized atom. The oscillatory component of the photoabsorption originates from the coupling of this reflected wave to the initial state via the dipole operator Mfs as in (1).
|
|
In astronomy, secular variations are contrasted with periodic phenomena. In particular, astronomical ephemerides use secular to label the longest-lasting or non-oscillatory perturbations in the motion of planets, as opposed to periodic perturbations which exhibit repetition over the course of a time frame of interest. In this context it is referred to as secular motion. Solar System ephemerides are essential for the navigation of spacecraft and for all kinds of space observations of the planets, their natural satellites, stars and galaxies.
|
|
It is important that the results obtained were interpreted as discovering new properties of physical systems. Thousands of papers were published that examine and predict properties of systems based on the use of control, identification and other cybernetic methods. Notably, most of those papers were published in physical journals, their authors representing university physics departments. It has become clear that such types of control goals are important not only for the control of chaos, but also for the control of a broader class of oscillatory processes.
|
|
The Fig. 3.A shows the spectrum of EMI noise shape of voltage output for RPWM with the switching frequency implemented in one Buck- Converter, and in accordance with CISPR A standard. It shows the spectrogram of EMI noise shape of voltage output for an RPWM, where it is possible to note (also in Fig. 3. A) that aleatory process inserts the continuous EMI noise shape, in low-frequencies, the EMI noise shape follows oscillatory mode with their noise value decreasing across the spectrum. Fig. 3.
|
|
An intrapulmonary percussive ventilator machine Mechanical devices used include positive expiratory pressure (PEP), intrapulmonary percussive ventilators, mechanical insufflation-exsufflation known as a mechanically assisted cough, and airway oscillatory devices. Several mechanical techniques are used to dislodge mucus and encourage its expectoration. Chest percussion can be administered as a manual technique but can also be performed using specific devices that use chest wall oscillation or intrapulmonary percussive ventilation. Intrapulmonary percussive ventilators (IPVs) are machines which deliver short bursts of air through a mouthpiece to help to clear mucus.
|
|
As an adaptation for living in the open ocean, the pelagic stingray swims more by flapping than undulating its disc. In adopting a midwater lifestyle, the pelagic stingray exhibits several characteristics different from those of its bottom-dwelling relatives. While most stingrays propel themselves by undulating their disc margins, this species swims by oscillating (flapping) its pectoral fins in a manner approaching the "underwater flying" employed by eagle rays. Oscillatory fin motions generate lift, thus improving cruising efficiency in open water at a cost to maneuverability.
|
|
S. Thompson and R. A. Fail, "Measurements of Oscillatory Derivatives at Mach Numbers up to 2.6 on a Model of a Supersonic Transport Design Study (Bristol Type 198)", RAE Bedford, 1964. but evolved into the larger Type 223. To test the new wing, NASA privately assisted the team by modifying a Douglas F5D Skylancer with temporary wing modifications to mimic the wing selection. In 1965 the NASA test aircraft successfully tested the wing, and found that it reduced landing speeds noticeably over the standard delta wing.
|
|
Flippers on humpback whales (Megaptera novaeangliae) have non-smooth leading edges, yet demonstrate superior fluid dynamics to the characteristically smooth leading edges of artificial wings, turbines and other kinds of blades. The whale’s surprising dexterity is due primarily to its non-conventional flippers, which have large, irregular looking bumps called tubercles across their leading edges. The tubercles break up the passage of water, maintaining even channels of the fast-moving water, limiting turbulence and providing greater maneuverability. The foreflippers used by the pinnipeds act as oscillatory hydrofoils.
|
|
The Sine integral for positive values, exhibiting oscillation. The central example, and often what is meant by "ringing artifacts", is the ideal (brick-wall) low-pass filter, the sinc filter. This has an oscillatory impulse response function, as illustrated above, and the step response – its integral, the sine integral – thus also features oscillations, as illustrated at right. These ringing artifacts are not results of imperfect implementation or windowing: the ideal low-pass filter, while possessing the desired frequency response, necessarily causes ringing artifacts in the time domain.
|
|
The Coulombic repulsion of particles having the same electric charge can break the bonds that hold solids together. When done with a narrow laser beam, a small amount of solid explodes into a plasma of ionized atomic particles. It may be shown that the Coulomb explosion occurs in the same critical parameter regime as the superradiant phase transition i.e. when the destabilizing interactions become overwhelming and dominate over the native oscillatory phonon solid cluster binding motions which is also characteristic for the diamond synthesis.
|
|
This structure is formed under a combination of unidirectional and oscillatory flow that is generated by relatively large storm waves in the ocean. Deposition involves fallout from suspension and lateral tractive flow due to wave oscillation. As the large waves drape sand over an irregular scoured surface, this strong storm-wave action erodes the seabed into low hummocks and swales that lack any significant orientation. It is usually formed by redeposition below normal fair weather wave base delivered offshore by flooding rivers and shoals by large waves.
|
|
After some time new grass replaces the burnt grass, and the field acquires again the ability for igniting. This is an example of an excitation wave. There are a great deal of other natural objects that are also considered among autowave processes: oscillatory chemical reactions in active media (e.g., Belousov–Zhabotinsky reaction), the spread of excitation pulses along nerve fibres, wave chemical signalling in the colonies of certain microorganisms, autowaves in ferroelectric and semiconductor films, population waves, spread of epidemics and of genes, and many other phenomena.
|
|
Underdamped spring–mass system with Damping is an influence within or upon an oscillatory system that has the effect of reducing, restricting or preventing its oscillations. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples include viscous drag in mechanical systems, resistance in electronic oscillators, and absorption and scattering of light in optical oscillators. Damping not based on energy loss can be important in other oscillating systems such as those that occur in biological systems and bikes.
|
|
Convergence can be slow, rapid, oscillatory, regular, highly erratic or simply non-existent, depending on the precise chemical system or basis set. The density matrix for the first-order and higher MP2 wavefunction is of the type known as response density, which differs from the more usual expectation value density. The eigenvalues of the response density matrix (which are the occupation numbers of the MP2 natural orbitals) can therefore be greater than 2 or negative. Unphysical numbers are a sign of a divergent perturbation expansion.
|
|
In 1989 Stuart Parkin discovered the phenomenon of oscillatory interlayer coupling in magnetic multilayers, by which magnetic layers are magnetically coupled via an intervening non-magnetic metallic spacer layer. Parkin found that the sign of the exchange coupling oscillates from ferromagnetic to antiferromagnetic with an oscillation period of just a few atomic layers. Remarkably, Parkin discovered this phenomenon in thin film magnetic heterostructures that he prepared in a simple home-made sputtering system. Parkin, moreover, showed that this phenomenon is displayed by almost all metalllic transition elements.
|
|
The Schwartz research group focused on understanding the neural regulation of circadian rhythmicity in mammals. They focused on tissue, organismal, and supra-organismal levels of analysis to see how individual processes interact in the circadian system to produce observable emergent properties. The Schwartz lab investigated light induced and endogenous gene expression, and the underlying dual oscillatory structure of the circadian pacemaker. His research group has focused on defining the mechanisms by which dysrhythmias occur and how social interactions may impact circuits and cells in the master clock.
|
|
Scientists have identified some intrinsic neuronal properties that play an important role in generating membrane potential oscillations. In particular, voltage-gated ion channels are critical in the generation of action potentials. The dynamics of these ion channels have been captured in the well-established Hodgkin–Huxley model that describes how action potentials are initiated and propagated by means of a set of differential equations. Using bifurcation analysis, different oscillatory varieties of these neuronal models can be determined, allowing for the classification of types of neuronal responses.
|
|
The temporal evolution of resting state networks is correlated with fluctuations of oscillatory EEG activity in different frequency bands. Ongoing brain activity may also have an important role in perception, as it may interact with activity related to incoming stimuli. Indeed, EEG studies suggest that visual perception is dependent on both the phase and amplitude of cortical oscillations. For instance, the amplitude and phase of alpha activity at the moment of visual stimulation predicts whether a weak stimulus will be perceived by the subject.
|
|
Oscillations have been commonly reported in the motor system. Pfurtscheller and colleagues found a reduction in alpha (8-12 Hz) and beta (13-30 Hz) oscillations in EEG activity when subjects made a movement. Using intra- cortical recordings, similar changes in oscillatory activity were found in the motor cortex when the monkeys performed motor acts that required significant attention. In addition, oscillations at spinal level become synchronised to beta oscillations in the motor cortex during constant muscle activation, as determined by cortico-muscular coherence.
|
|
Neural oscillation has been applied as a control signal in various brain–computer interfaces (BCIs). For example, a non-invasive BCI can be created by placing electrodes on the scalp and then measuring the weak electric signals. Although individual neuron activities cannot be recorded through non-invasive BCI because the skull damps and blurs the electromagnetic signals, oscillatory activity can still be reliably detected. The BCI was introduced by Vidal in 1973 as challenge of using EEG signals to control objects outside human body.
|
|
The term "autapse" was first coined in 1972 by Van der Loos and Glaser, who observed them in Golgi preparations of the rabbit occipital cortex while originally conducting a quantitative analysis of rabbit neocortex circuitry. Also in the 1970s, autapses have been described in dog and rat cerebral cortex, monkey neostriatum, and cat spinal cord. In 2000, they were first modeled as supporting persistence in recurrent neural networks. In 2004, they were modeled as demonstrating oscillatory behavior, which was absent in the same model neuron without autapse.
|
|
NAMPT is part of a series of enzymatic reactions that covert niacin (also called nicotinamide) to NAD. SIRT1, which requires NAD for its enzymatic activity, then uses increased NAD levels to suppress BMAL1 through deacetylation. This suppression results in less transcription of the NAMPT, less NAMPT protein, less NAD made, and therefore less SIRT1 and less suppression of the CLOCK-BMAL dimer. This dimer can again positively activate the Nampt gene transcription and the cycle continues, creating another oscillatory loop involving CLOCK-BMAL as positive elements.
|
|
There was structural damage evidence compatible with oscillatory motion of the No. 1 QEC and the left wing. ::4. First stage compressor blades of No. 1 engine rubbed the air inlet housing supports. ::5. The probable cause of a similar accident of another Electra was due to whirl mode. ::If prior damage is a requirement for the necessary reduction in stiffness, it must be assumed that the evidence of such damage was either obliterated in the crash or never existed in a discernible form.
|
|
Whereas in a usual flame molecules break down to small fragments and combine with oxygen producing carbon dioxide (i.e. burn), in a cool flame, the fragments are relatively large and easily recombine with each other. Therefore, much less heat, light and carbon dioxide is released; the combustion process is oscillatory and can sustain for a long time. A typical temperature increase upon ignition of a cool flame is a few tens of degrees Celsius whereas it is on the order of 1000 °C for a conventional flame.
|
|
Different mechanism by fixing different link of slider crank chain are as follows : ;First inversion This inversion is obtained when link 1 (ground body) is fixed. Application- Reciprocating engine, Reciprocating compressor etc... ;Second inversion This inversion is obtained when link 2 (crank) is fixed. Application- Whitworth quick return mechanism, Rotary engine, etc... ;Third inversion This inversion is obtained when link 3 (connecting rod) is fixed. Application- Slotted crank mechanism, Oscillatory engine etc.., ;Fourth inversion This inversion is obtained when link 4 (slider) is fixed.
|
|
A gravimeter or gravitometer, is an instrument used in gravimetry for measuring the local gravitational field. A gravimeter is a type of accelerometer, except that accelerometers are susceptible to all vibrations including noise, that cause oscillatory accelerations. This is counteracted in the gravimeter by integral vibration isolation and signal processing. Though the essential principle of design is the same as in accelerometers, gravimeters are typically designed to be much more sensitive than accelerometers in order to measure very tiny changes within the Earth's gravity, of 1 g.
|
|
A Continuous Oscillatory Baffled Reactor (COBR) is a specially designed chemical reactor to achieve plug flow under laminar flow conditions. Achieving plug flow has previously been limited to either a large number of continuous stir tank reactors (CSTR) in series or conditions with high turbulent flow. The technology incorporates annular baffles to a tubular reactor framework to create eddies when liquid is pushed up through the tube. Likewise, when liquid is on a downstroke through the tube, eddies are created on the other side of the baffles.
|
|
A standard COBR consists of a 10-150mm ID tube with equally spaced baffles throughout. There are typically two pumps in a COBR; one pump is reciprocating to generate continuous oscillatory flow and a second pump creates net flow through the tube. This design offers a control over mixing intensity that conventional tubular reactors cannot achieve. Each baffled cell acts as a CSTR and because a secondary pump is creating a net laminar flow, much longer residence times can be achieved relative to turbulent flow systems.
|
|
Closed form formulas are rare, except when there is some geometric symmetry that can be exploited, and the numerical calculations are difficult because of the oscillatory nature of the integrals, which makes convergence slow and hard to estimate. For practical calculations, other methods are often used. The twentieth century has seen the extension of these methods to all linear partial differential equations with polynomial coefficients, and by extending the notion of Fourier transformation to include Fourier integral operators, some non-linear equations as well.
|
|
The TOC1 gene was initially discovered by Prof. Andrew Millar and colleagues in 1995 while Millar was a graduate student. Millar developed an innovative forward genetic screen in which he linked a bioluminescent reporter, firefly (luciferase), to expression of CAB (chlorophyll-a,b binding protein—see Light-harvesting complexes of green plants) in Arabidopsis. By measuring bioluminescence over the course of the day, Millar found CAB expression to display oscillatory patterns in constant light and to oscillate with a shorter period in toc1 mutant plants.
|
|
Gymnura micrura alter their swimming habits depending on where they are swimming in the water column. They tend to change between an undulation pattern and an oscillation pattern. They use small amplitude undulations of their fins when they are swimming along the bottom, but switch to an oscillatory approach when they are swimming freely in the water. When swimming freely in the water column, they use a quick, powerful downstroke to increase their speed; this means they move their fins down and then quickly back up.
|
|
According to string theory, every particle in the universe, at its most microscopic level (Planck length), consists of varying combinations of vibrating strings (or strands) with preferred patterns of vibration. String theory further claims that it is through these specific oscillatory patterns of strings that a particle of unique mass and force charge is created (that is to say, the electron is a type of string that vibrates one way, while the up quark is a type of string vibrating another way, and so forth).
|
|
New lithosphere is made when hot material beneath ocean ridges is brought to the surface by these cells. As the new lithosphere moved horizontally away from the ridges, the new crust added to the Gulf of Mexico and the Atlantic caused the continents of North America and South America to move apart. Seafloor spreading in the Gulf of Mexico ceased by the beginning of the Cretaceous and spreading shifted to the proto-Caribbean. Around 110-85 Ma, there was worldwide oscillatory increases in ocean floor spreading rates.
|
|
Anesthetic-induced oscillations are also akin to what happens when a hum in a phone line makes it impossible to sustain a normal conversation. Brown has performed many studies on the properties of propofol-induced anesthesia in particular. He found that propofol-induced unconsciousness is mediated simultaneously by two different oscillatory processes. The first is strong coherent alpha oscillations (8 to 10 cycles per second) between the cortex and the thalamus (26-28) and the second are strong incoherent cortical slow-wave oscillations (<1 cycle per second).
|
|
The artificial induction of increased beta waves over the motor cortex by a form of electrical stimulation called Transcranial alternating-current stimulation consistent with its link to isotonic contraction produces a slowing of motor movements. Investigations of reward feedback have revealed two distinct beta components; a high beta (low gamma) component . Marco-Pallerés, J., Cucurell, D., Cunillera, T., García, R., Andrés-Pueyo, A., Münte, T. F., et al. (2008).Human oscillatory activity associated to reward processing in a gambling task, Neuropsychologia, 46, 241-248.
|
|
In mathematical analysis, microlocal analysis comprises techniques developed from the 1950s onwards based on Fourier transforms related to the study of variable-coefficients-linear and nonlinear partial differential equations. This includes generalized functions, pseudo-differential operators, wave front sets, Fourier integral operators, oscillatory integral operators, and paradifferential operators. The term microlocal implies localisation not only with respect to location in the space, but also with respect to cotangent space directions at a given point. This gains in importance on manifolds of dimension greater than one.
|
|
Non-rapid eye movement (NREM) sleep differs from REM in that gamma activity is no longer prominent, stepping aside for lower frequency oscillations. While electrical activity at gamma frequencies can occasionally be detected in NREM, it is infrequent and comes in bursts. The exact purpose of its appearance in NREM is not understood. In NREM sleep, thalamocortical oscillatory activity is still present, but the overall frequencies range from the slow (<1 Hz), to the delta (1–4 Hz), and theta (4–7 Hz) range.
|
|
Based on the selection pressure, the different simulations were categorized into the following groups: \- Delayed Gates: Signals and resource are related by OR, AND, XOR, NAND, NOR dynamic logic functions. \- Multi- gates: Signals and resource are interchangeably related by combinations of OR, AND, XOR, NAND, NOR dynamic logic functions. -Oscillators: Selection pressure to evolve oscillatory expression of RP1 with or without a periodic guiding signal. \- Bi-stable switches: Selection pressure to evolve bi-stability in environments where two environmental signals operate as ON/OFF pulse switches.
|
|
The combined effects of seiches (resonant standing waves)Saylor, James H. and Sloss, Peter W. (1976) Water Volume Transport and Oscillatory Current Flow through the Straits of Mackinac, Journal of Physical Oceanography, v. 6, p. 229-237 and of differing weather conditions (atmospheric pressure, wind) over each basin act to drive water either way through the Straits on a variety of characteristic timescales, at amounts sometimes exceeding for several hours in either direction. However, the long-term average flow through the Straits is eastwards at .
|
|
Different mechanism by fixing different link of slider crank chain are as follows : ;First inversion This inversion is obtained when link 1 (ground body) is fixed. Application- Reciprocating engine, Reciprocating compressor etc... ;Second inversion This inversion is obtained when link 2 (crank) is fixed. Application- Whitworth quick return mechanism, Rotary engine, etc... ;Third inversion This inversion is obtained when link 3 (connecting rod) is fixed. Applications - Slotted crank mechanism, Oscillatory engine etc.., ;Fourth inversion This inversion is obtained when link 4 (slider) is fixed.
|
|
In biochemistry, a glycolytic oscillation is the repetitive fluctuation of in the concentrations of metabolites, classically observed experimentally in yeast and muscle. The first observations of oscillatory behaviour in glycolysis were made by Duysens and Amesz in 1957. The problem of modelling glycolytic oscillation has been studied in control theory and dynamical systems since the 1960s since the behaviour depends on the rate of substrate injection. Early models used two variables, but the most complex behaviour they could demonstrate was period oscillations due to the Poincaré–Bendixson theorem, so later models introduced further variables.
|
|
Also in the series, he developed non-oscillatory interpolation using limiters, an approximate Riemann solver, and discontinuous-Galerkin schemes for unsteady advection. Since joining the University of Michigan’s Aerospace Engineering Department (1986), he has worked on convergence acceleration by local preconditioning and multigrid relaxation for Euler and Navier-Stokes problems, unsteady adaptive grids, space-environment modeling, atmospheric flow modeling, extended hydrodynamics for rarefied flows, and discontinuous-Galerkin methods. He retired in 2012, forced to give up research because of progressive blindness. Throughout his career, van Leer's work has had interdisciplinary characteristic.
|
|
Cheyne–Stokes respiration is an abnormal pattern of breathing characterized by progressively deeper, and sometimes faster, breathing followed by a gradual decrease that results in a temporary stop in breathing called an apnea. The pattern repeats, with each cycle usually taking 30 seconds to 2 minutes. It is an oscillation of ventilation between apnea and hyperpnea with a crescendo- diminuendo pattern, and is associated with changing serum partial pressures of oxygen and carbon dioxide. Cheyne–Stokes respiration and periodic breathing are the two regions on a spectrum of severity of oscillatory tidal volume.
|
|
Graph showing mechanical resonance in a mechanical oscillatory system Mechanical resonance is the tendency of a mechanical system to respond at greater amplitude when the frequency of its oscillations matches the system's natural frequency of vibration (its resonance frequency or resonant frequency) than it does at other frequencies. It may cause violent swaying motions and even catastrophic failure in improperly constructed structures including bridges, buildings and airplanes. This is a phenomenon known as resonance disaster. Avoiding resonance disasters is a major concern in every building, tower and bridge construction project.
|
|
Illustration of Empirical Mode Decomposition's sifting process. The EMD method is a necessary step to reduce any given data into a collection of intrinsic mode functions (IMF) to which the Hilbert spectral analysis can be applied. IMF represents a simple oscillatory mode as a counterpart to the simple harmonic function, but it is much more general: instead of constant amplitude and frequency in a simple harmonic component, an IMF can have variable amplitude and frequency along the time axis. The procedure of extracting an IMF is called sifting.
|
|
Leapfrog integration is a second-order method, in contrast to Euler integration, which is only first-order, yet requires the same number of function evaluations per step. Unlike Euler integration, it is stable for oscillatory motion, as long as the time-step \Delta t is constant, and \Delta t \leq 2/\omega.C. K. Birdsall and A. B. Langdon, Plasma Physics via Computer Simulations, McGraw-Hill Book Company, 1985, p. 56. Using Yoshida coefficients, applying the leapfrog integrator multiple times with the correct timesteps, a much higher order integrator can be generated.
|
|
A chiming clock's mechanism. The invention of the mechanical clock in the 13th century initiated a change in timekeeping methods from continuous processes, such as the motion of the gnomon's shadow on a sundial or the flow of liquid in a water clock, to periodic oscillatory processes, such as the swing of a pendulum or the vibration of a quartz crystal, which had the potential for more accuracy. All modern clocks use oscillation. Although the mechanisms they use vary, all oscillating clocks, mechanical, digital and atomic, work similarly and can be divided into analogous parts.
|
|
The transcription factor NF-κB regulates various genes that play essential roles in signaling, stress responses, cell growth and apoptosis. The temporal control of NF-κB activation by the degradation and synthesis of its inhibitor isoforms, I-κBα, -β, - ε has been computationally modeled. The model suggested that I-κBα results in robust negative feedback that leads to a fast turn off of NF-κB response. On the other hand, the oscillatory potential and stabilization of NF-κB during long stimulations has been shown to be reduced by I-κBβ and –ε.
|
|
Clopath uses mathematical models to predict synaptic plasticity and to study the implications of synaptic plasticity in artificial neural networks. These models can explain the origins of vibrations in neural networks, and could determine the activities of excitatory and inhibitory neurons. She used this model to explain that inhibitory neurons are important in the determination of the oscillatory frequency of a network. She hopes that the models she generates of the brain will be able to be used in medical applications as well as designing machines that can achieve human-like learning.
|
|
Evoked activity is brain activity that is the result of a task, sensory input or motor output. It is opposed to spontaneous brain activity during the absence of any explicit task. Most experimental studies in neuroscience investigate brain functioning by administering a task or stimulus and measure the resulting changes in neuronal activity and behavior. In EEG research, evoked activity or evoked responses specifically refers to activity that is phase-locked to the stimulus onset and is opposed to induced activity, which is a stimulus-related change in (the amplitude of) oscillatory activity.
|
|
Another possibility is to use Monte Carlo (MC) algorithms and to sample the full partition function integral in field-theoretic formulation. The resulting procedure is then called a polymer field-theoretic simulation. In a recent work, however, Baeurle demonstrated that MC sampling in conjunction with the basic field- theoretic representation is impracticable due to the so-called numerical sign problem (Baeurle 2002). The difficulty is related to the complex and oscillatory nature of the resulting distribution function, which causes a bad statistical convergence of the ensemble averages of the desired thermodynamic and structural quantities.
|
|
The ekpyrotic and cyclic models are also considered adjuncts to inflation. These models solve the horizon problem through an expanding epoch well before the Big Bang, and then generate the required spectrum of primordial density perturbations during a contracting phase leading to a Big Crunch. The Universe passes through the Big Crunch and emerges in a hot Big Bang phase. In this sense they are reminiscent of Richard Chace Tolman's oscillatory universe; in Tolman's model, however, the total age of the Universe is necessarily finite, while in these models this is not necessarily so.
|
|
Based on the intercomparison of the test data obtained from the VMCM and from other measuring instruments such as Aandera, VACM, electromagnetic current meters, and ACM, it has been experienced that VMCM sensor introduces the least error in relatively small mean flows when high frequency oscillatory fluctuations are also present. (because of surface waves, mooring motion, or both). This quality, together with the accuracy of the propeller sensors experienced in steady, unsteady flows, and combinations of both, make the VMCM appropriate to make accurate measurements in the upper ocean.
|
|
Norman Foster Ramsey Jr. (August 27, 1915 – November 4, 2011) was an American physicist who was awarded the 1989 Nobel Prize in Physics, for the invention of the separated oscillatory field method, which had important applications in the construction of atomic clocks. A physics professor at Harvard University for most of his career, Ramsey also held several posts with such government and international agencies as NATO and the United States Atomic Energy Commission. Among his other accomplishments are helping to found the United States Department of Energy's Brookhaven National Laboratory and Fermilab.
|
|
Retrieved on 2012-01-27. Recent evidence has suggested that the inner core of Earth may rotate slightly faster than the rest of the planet; however, more recent studies in 2011 found this hypothesis to be inconclusive. Options remain for the core which may be oscillatory in nature or a chaotic system. In August 2005 a team of geophysicists announced in the journal Science that, according to their estimates, Earth's inner core rotates approximately 0.3 to 0.5 degrees per year faster relative to the rotation of the surface.
|
|
An important question is whether a periodic travelling wave is stable or unstable as a solution of the original mathematical system. For partial differential equations, it is typical that the wave family subdivides into stable and unstable parts.K. Maginu (1981) "Stability of periodic travelling wave solutions with large spatial periods in reaction-diffusion systems", J. Diff. Eqns. 39: 73–99. 10.1016/0022-0396(81)90084-XM. J. Smith, J.A. Sherratt (2007) "The effects of unequal diffusion coefficients on periodic travelling waves in oscillatory reaction-diffusion systems", Physica D 236: 90–103. DOI:10.1016/j.physd.2007.07.
|
|
In what is often referred to as "Parkin's Periodic Table", Parkin showed that the strength of this oscillatory interlayer exchange interaction varied systematically across the Periodic Table of the elements. Parkin made numerous other fundamental discoveries which continued the development of the field of "spintronics" of which he is recognised as a prolific scientist. Later Parkin improved magnetic tunnelling junctions, a device invented in the 1970s by julliere, and revolutionized by Jagadeesh Moodera of MIT. This element can create a high performance magnetic random access memory in 1995.
|
|
These studies have pointed to abnormalities in oscillatory activity in schizophrenia, particularly in the gamma band (30–80 Hz). Gamma band activity appears to originate from intact functioning parvalbumin-positive interneuron. Together with the post-mortem findings, these EEG abnormalities point to a role for dysfunctional parvalbumin interneurons in schizophrenia. The largest meta-analysis on copy-number variations (CNVs), structural abnormalities in the form of genetic deletions or duplications, to date for schizophrenia, published in 2015, was the first genetic evidence for the broad involvement of GABAergic neurotransmission.
|
|
William Moulton Marston studied blood-pressure and noted increase in systolic blood pressure of 10 mm Hg or over indicated guilt through using the tycos sphygmomanometer, with which he reported 90–100% accuracy. His studies used students and actual court cases. Then in 1913 W.M. Marston determined systolic blood-pressure by oscillatory methods and his findings cite definite changes in blood pressure during the deception of criminal suspects. In 1921, John Augustus Larson criticized Marston's intermittent blood pressure method because emotional changes were so brief they could be lost.
|
|
The study of neuron synchrony could provide information on the differences that occur in neural states such as normal and diseased states. Neurons that are involved significantly in diseases such as Alzheimer's disease or Parkinson's disease are shown to undergo phase resetting before launching into phase locking where clusters of neurons are able to begin firing rapidly to communicate information quickly. phase of ongoing oscillatory activity is reset. A phase response curve can be calculated by noting changes to its period over time depending on where in the cycle the input is applied.
|
|
In a limit-cycle oscillator, the amplitude tends to be more or less constant but the frequency can vary greatly. A heartbeat is an example of a limit-cycle oscillation in that the frequency of beats varies widely, while each individual beat continues to pump about the same amount of blood. Computational models adopt a variety of abstractions in order to describe complex oscillatory dynamics observed in brain activity. Many models are used in the field, each defined at a different level of abstraction and trying to model different aspects of neural systems.
|
|
The Kuramoto model is widely used to study oscillatory brain activity and several extensions have been proposed that increase its neurobiological plausibility, for instance by incorporating topological properties of local cortical connectivity. In particular, it describes how the activity of a group of interacting neurons can become synchronized and generate large-scale oscillations. Simulations using the Kuramoto model with realistic long-range cortical connectivity and time- delayed interactions reveal the emergence of slow patterned fluctuations that reproduce resting-state BOLD functional maps, which can be measured using fMRI.
|
|
In response to input, a neuron or neuronal ensemble may change the frequency at which it oscillates, thus changing the rate at which it spikes. Often, a neuron's firing rate depends on the summed activity it receives. Frequency changes are also commonly observed in central pattern generators and directly relate to the speed of motor activities, such as step frequency in walking. However, changes in relative oscillation frequency between different brain areas is not so common because the frequency of oscillatory activity is often related to the time delays between brain areas.
|
|
Synchronization of neuronal firing may serve as a means to group spatially segregated neurons that respond to the same stimulus in order to bind these responses for further joint processing, i.e. to exploit temporal synchrony to encode relations. Purely theoretical formulations of the binding-by-synchrony hypothesis were proposed first, but subsequently extensive experimental evidence has been reported supporting the potential role of synchrony as a relational code. The functional role of synchronized oscillatory activity in the brain was mainly established in experiments performed on awake kittens with multiple electrodes implanted in the visual cortex.
|
|
Oscillatory activity in the brain is widely observed at different levels of organization and is thought to play a key role in processing neural information. Numerous experimental studies support a functional role of neural oscillations; a unified interpretation, however, is still lacking. Hz. Upper panel shows spiking of individual neurons (with each dot representing an individual action potential within the population of neurons), and the lower panel the local field potential reflecting their summed activity. Figure illustrates how synchronized patterns of action potentials may result in macroscopic oscillations that can be measured outside the scalp.
|
|
As such, the frequency of large-scale oscillations does not need to match the firing pattern of individual neurons. Isolated cortical neurons fire regularly under certain conditions, but in the intact brain cortical cells are bombarded by highly fluctuating synaptic inputs and typically fire seemingly at random. However, if the probability of a large group of neurons is rhythmically modulated at a common frequency, they will generate oscillations in the mean field (see also figure at top of page). Neural ensembles can generate oscillatory activity endogenously through local interactions between excitatory and inhibitory neurons.
|
|
An example of such a feedback loop is the connections between the thalamus and cortex – the thalamocortical radiations. This thalamocortical network is able to generate oscillatory activity known as recurrent thalamo-cortical resonance. The thalamocortical network plays an important role in the generation of alpha activity. In a whole-brain network model with realistic anatomical connectivity and propagation delays between brain areas, oscillations in the beta frequency range emerge from the partial synchronisation of subsets of brain areas oscillating in the gamma-band (generated at the mesoscopic level).
|
|
Evidence from zoned garnets can give insight into the metamorphic history of an area. What one scientist found was that there were three main episodes of garnet growth in the Isua Greenstone Belt, meaning there were three main metamorphic events. Specifically, the garnets were studied in terms of overgrowth patterns using iron-magnesium rich rim, manganese rich cores, then by a calcium-rich rims and cores. In addition, the presence of these overgrowths and their oscillatory zoned nature leads scientists to believe that the metamorphism occurred due to fluid-like metasomatism.
|
|
In the 1950s, he constructed a crossed circle wide line NMR spectrometer which could detect deuterium and oxygen-17 isotopes in their natural abundance. Using oxygen-17 as a probe, he demonstrated chemical shifts in organic liquids due to electronic bonding. He subsequently developed an interdisciplinary group which used NMR and susceptibility measurements in metals to show that susceptibility and the hyperfine field at the nucleus were related and could be modified by alloying. The oscillatory nature of the conduction electron polarisation was established in rare earth alloys.
|
|
The term phonation has slightly different meanings depending on the subfield of phonetics. Among some phoneticians, phonation is the process by which the vocal folds produce certain sounds through quasi-periodic vibration. This is the definition used among those who study laryngeal anatomy and physiology and speech production in general. Phoneticians in other subfields, such as linguistic phonetics, call this process voicing, and use the term phonation to refer to any oscillatory state of any part of the larynx that modifies the airstream, of which voicing is just one example.
|
|
Diffraction in time is a phenomenon associated with the quantum dynamics of suddenly released matter waves initially confined in a region of space. It was introduced in 1952 by Marcos Moshinsky with the shutter problem . A matter- wave beam stopped by an absorbing shutter exhibits an oscillatory density profile during its propagation after removal of the shutter. Whenever this propagation is accurately described by the time-dependent Schrödinger equation, the transient wave functions resemble the solutions that appear for the intensity of light subject to Fresnel diffraction by a straight edge.
|
|
Specifically in the analysis of layered media, derivation of spatial-domain Green's function necessitates the inversion of analytically-derivable spectral-domain Green's function through Sommerfeld path integral. This integral can not be evaluated analytically and its numerical integration is costly due to its oscillatory and slowly-converging behaviour. For a robust analysis, spatial Green's functions are approximated as complex exponentials with methods such as Prony's method or generalized pencil of function, and the integral is evaluated with Sommerfeld identity. This method is known as discrete complex image method.
|
|
In the eternal inflation theory, which is a variant of the cosmic inflation theory, the multiverse or space as a whole is stretching and will continue doing so forever, but some regions of space stop stretching and form distinct bubbles (like gas pockets in a loaf of rising bread). Such bubbles are embryonic level I multiverses. Different bubbles may experience different spontaneous symmetry breaking, which results in different properties, such as different physical constants. Level II also includes John Archibald Wheeler's oscillatory universe theory and Lee Smolin's fecund universes theory.
|
|
In the classical treatment of viscoelasticity, the load-displacement (P-h) response measured from the sample is fitted to predictions from an assumed constitutive model (e.g. the Maxwell model) of the material comprising spring and dashpot elements. Such an approach can be very time consuming, and cannot in general prove the assumed constitutive law in an unambiguous manner. Dynamic indentation with an oscillatory load can be performed, and the viscoelastic behavior of the sample is presented in terms of the resultant storage and loss moduli, often as variations over the load frequency.
|
|
Shallow water equations are especially suitable to model tides which have very large length scales (over hundred of kilometers). For tidal motion, even a very deep ocean may be considered as shallow as its depth will always be much smaller than the tidal wavelength. Tsunami generation and propagation, as computed with the shallow water equations (red line; without frequency dispersion)), and with a Boussinesq-type model (blue line; with frequency dispersion). Observe that the Boussinesq-type model (blue line) forms a soliton with an oscillatory tail staying behind.
|
|
This resolved the solar neutrino problem: the electron neutrinos produced in the Sun had partly changed into other flavors which the experiments could not detect. Although individual experiments, such as the set of solar neutrino experiments, are consistent with non-oscillatory mechanisms of neutrino flavor conversion, taken altogether, neutrino experiments imply the existence of neutrino oscillations. Especially relevant in this context are the reactor experiment KamLAND and the accelerator experiments such as MINOS. The KamLAND experiment has indeed identified oscillations as the neutrino flavor conversion mechanism involved in the solar electron neutrinos.
|
|
The machine used to generate the pips in 1970 The pips have been broadcast daily since 5 February 1924, and were the idea of the Astronomer Royal, Sir Frank Watson Dyson, and the head of the BBC, John Reith. The pips were originally controlled by two mechanical clocks located in the Royal Greenwich Observatory that had electrical contacts attached to their pendula. Two clocks were used in case of a breakdown of one. These sent a signal each second to the BBC, which converted them to the audible oscillatory tone broadcast.
|
|
If we solve the time-independent Schrödinger equation for an energy E>V_0, the solutions will be oscillatory both inside and outside the well. Thus, the solution is never square integrable; that is, it is always a non-normalizable state. This does not mean, however, that it is impossible for a quantum particle to have energy greater than V_0, it merely means that the system has continuous spectrum above V_0. The non-normalizable eigenstates are close enough to being square integrable that they still contribute to the spectrum of the Hamiltonian as an unbounded operator.
|
|
The self re-excitation of hyperactive stretch reflexes theory involves a repetitive contract-relax cycle in the affected muscle, which creates oscillatory movements in the affected limb. In order for self re-excitation to exist, both an increase in motor neuron excitability and nerve signal delay are required. Increased motor neuron excitability is likely accomplished by alterations to the net inhibition of neurons occurring as a result of injury to the CNS (stroke/ spinal cord injury). This lack of inhibition biases neurons to a net excitatory state, therefore increasing total signal conduction.
|
|
Many power processing systems can be improved by the application of resistive elements. Resistors may be applied for waveshaping, damping of oscillatory waveforms, stabilization of nonstable systems, and power flow balancing. The losses involved by the application of conventional resistors may be eliminated by the synthesis of artificial, loss-free resistive elements which replace the conventional ones. The conventional resistor converts the electrical energy absorbed at its terminals into heat; however, it has been found that creation of a resistive characteristic is not necessarily followed by such energy conversion.
|
|
Flow forces according to the Morison equation for a body placed in a harmonic flow, as a function of time. Blue line: drag force; red line: inertia force; black line: total force according to the Morison equation. Note that the inertia force is in front of the phase of the drag force: the flow velocity is a sine wave, while the local acceleration is a cosine wave as a function of time. In fluid dynamics the Morison equation is a semi-empirical equation for the inline force on a body in oscillatory flow.
|
|
It was first pointed out by Felix Bloch and Clarence Zener while studying the electrical properties of crystals. In particular, they predicted that the motion of electrons in a perfect crystal under the action of a constant electric field would be oscillatory instead of uniform. While in natural crystals this phenomenon is extremely hard to observe due to the scattering of electrons by lattice defects, it has been observed in semiconductor superlattices and in different physical systems such as cold atoms in an optical potential and ultrasmall Josephson junctions.
|
|
EEG measures the gross electrical activity of the brain that can be observed on the surface of the skull. In the metastability theory, EEG outputs produce oscillations that can be described as having identifiable patterns that correlate with each other at certain frequencies. Each neuron in a neuronal network normally outputs a dynamical oscillatory waveform, but also has the ability to output a chaotic waveform. When neurons are integrated into the neural network by interfacing neurons with each other, the dynamical oscillations created by each neuron can be combined to form highly predictable EEG oscillations.
|
|
Frank also undertook important work into the physiological basis of the arterial pulse waveform and may have coined the term essential hypertension in 1911. His work on the Windkessel extended the original ideas of Stephen Hales and provided a sound mathematical framework for this approach. Frank also published on waves in the arterial system but his attempts to produce a theory that incorporated waves and the Windkessel are not considered to have been successful. Frank also did work on the oscillatory characteristics of the auditory apparatus of the ear and the thermodynamics of muscle.
|
|
Gamma-range oscillations are not the only rhythms associated with conscious thought and activity. Thalamocortical alpha frequency oscillations have been noted in the human occipital-parietal cortex. This activity could be originated by the pyramidal neurons in layer IV. It has been shown that alpha rhythms seem to be related to the focus of one's attention: external focus on visual tasks diminishes alpha activity while internal focus as in heavy working memory tasks show an increase in alpha magnitudes. This is contrary to gamma wave oscillatory frequencies which emerge in selective focus tasks.
|
|
A repeated burst of action potentials occurs at lower frequencies in the 4–10 Hz range. These bursts can be sustained by inhibition from the thalamic reticular nucleus and may cause an activation of cortical regions that are normally inhibited by gamma-band activity during resonance column formation. While the effect of the deviation from normal patterns of gamma oscillatory activity during conscious perception is not entirely settled, it is proposed that the phenomenon can be used to explain chronic pain in cases where there is no specific peripheral nerve damage.
|
|
Furthermore, polynomial interpolation may exhibit oscillatory artifacts, especially at the end points (see Runge's phenomenon). Polynomial interpolation can estimate local maxima and minima that are outside the range of the samples, unlike linear interpolation. For example, the interpolant above has a local maximum at x ≈ 1.566, f(x) ≈ 1.003 and a local minimum at x ≈ 4.708, f(x) ≈ −1.003. However, these maxima and minima may exceed the theoretical range of the function—for example, a function that is always positive may have an interpolant with negative values, and whose inverse therefore contains false vertical asymptotes.
|
|
The awards Ying has received include a Sloan Fellowship in 2007, an NSF Career Award in 2009, the James H. Wilkinson Prize in Numerical Analysis and Scientific Computing in 2013 (for "his outstanding contributions in many areas, including the rapid evaluation of oscillatory integral transforms, high frequency wave propagation and the computation of electron structure in metallic systems"),"Awards Spotlight: Lexing Ying, Wilkinson Prize in Numerical Analysis and Scientific Computing", SIAM,7 October 2016. and a silver Morningside Medal in 2016."Lexing Ying, professor of mathematics, awarded James H. Wilkinson Prize", Stanford Daily, 28 July 2013.
|
|
Canted insertion device at the Advanced Photon Source, Argonne National Laboratory. An insertion device (ID) is a component in modern synchrotron light sources, so called because they are "inserted" into accelerator tracks. They are periodic magnetic structures that stimulate highly brilliant, forward-directed synchrotron radiation emission by forcing a stored charged particle beam to perform wiggles, or undulations, as they pass through the device. This motion is caused by the Lorentz force, and it is from this oscillatory motion that we get the names for the two classes of device, which are known as wigglers and undulators.
|
|
However, it is well known that MC sampling in conjunction with the basic field-theoretic representation of the partition function integral, directly obtained via the Hubbard-Stratonovich transformation, is impracticable, due to the so-called numerical sign problem (Baeurle 2002, Fredrickson 2002). The difficulty is related to the complex and oscillatory nature of the resulting distribution function, which causes a bad statistical convergence of the ensemble averages of the desired structural and thermodynamic quantities. In such cases special analytical and numerical techniques are required to accelerate the statistical convergence of the field-theoretic simulation (Baeurle 2003, Baeurle 2003a, Baeurle 2004).
|
|
There are several different techniques that can be utilized to understand the biological basis of economic behavior. Neural imaging is used in human subjects to determine which areas of the brain are most active during particular tasks. Some of these techniques, such as fMRI or PET are best suited to giving detailed pictures of the brain which can give information about specific structures involved in a task. Other techniques, such as ERP (event-related potentials) and oscillatory brain activity are used to gain detailed knowledge of the time course of events within a more general area of the brain.
|
|
Fourier analysis grew from the study of Fourier series, and is named after Joseph Fourier, who showed that representing a function as a sum of trigonometric functions greatly simplifies the study of heat transfer. Today, the subject of Fourier analysis encompasses a vast spectrum of mathematics. In the sciences and engineering, the process of decomposing a function into oscillatory components is often called Fourier analysis, while the operation of rebuilding the function from these pieces is known as Fourier synthesis. For example, determining what component frequencies are present in a musical note would involve computing the Fourier transform of a sampled musical note.
|
|
Julian Hart Lewis FRS (12 August 1946 - 30 April 2014) was an English developmental biologist and researcher whose work shed light on the nature of cellular timing mechanisms and their role in animal development. He showed that the Notch ligand (a molecule involved in cell-to-cell communication) controls the timing of nerve cell differentiation and the synchronised cycling of neighbouring cell activity. He modelled the cellular oscillatory circuit that determines the segmentation of the developing body, and clarified the importance of delay kinetics in setting the frequency of those oscillations. He was an undergraduate at Balliol College, Oxford from 1964.
|
|
This, in turn, may lead to an increase in (spatial or temporal) autocorrelation and variance, while variance spectra tend to lower frequencies and the 'direction of critical slowing down' in a system's state space may be indicative of a system's future state when delayed negative feedbacks leading to oscillatory or other complex dynamics are weak. Researchers have explored early warning signals in lakes, climate dynamics, food webs, dry land transitions and epilepsy attacks. It remains unclear how well such signals work for all regime shifts, and if the early warnings give time enough to take appropriate managerial corrections to avoid the shift.
|
|
An IMF is defined as a function that satisfies the following requirements: # In the whole data set, the number of extrema and the number of zero-crossings must either be equal or differ at most by one. # At any point, the mean value of the envelope defined by the local maxima and the envelope defined by the local minima is zero. It represents a generally simple oscillatory mode as a counterpart to the simple harmonic function. By definition, an IMF is any function with the same number of extrema and zero crossings, whose envelopes are symmetric with respect to zero.
|
|
Periodic ordered lattices behave as linear viscoelastic solids when subjected to small amplitude mechanical deformations. Okano's group experimentally correlated the shear modulus to the frequency of standing shear modes using mechanical resonance techniques in the ultrasonic range (40 to 70 kHz). In oscillatory experiments at lower frequencies (< 40 Hz), the fundamental mode of vibration as well as several higher frequency partial overtones (or harmonics) have been observed. Structurally, most systems exhibit a clear instability toward the formation of periodic domains of relatively short-range order Above a critical amplitude of oscillation, plastic deformation is the primary mode of structural rearrangement.
|
|
Eur J Cell Biol 2010, 89:225-230.Lau S, Ehrismann JS, Schlereth A, Takada S, Mayer U, Jurgens G: Cell-cell communication in Arabidopsis early embryogenesis. Eur J Cell Biol 2010, 89:225-230. For a good review of the part of the history of morphogen signaling and development see Briscoe J, Making a grade: Sonic Hedgehog signalling and the control of neural cell fate. In systems biology, cell-fate determination is predicted to exhibit certain dynamics, such as attractor-convergence (the attractor can be an equilibrium point, limit cycle or strange attractor) or oscillatory.
|
|
An equivalent dumping coefficient is a mathematical coefficient used in the calculation of the energy dispersed when a structure moves. As a civil engineering term, it defines the percent of a cycle of oscillation that is absorbed (converted to heat by friction) for the structure or sub-structure under analysis. Usually it is assumed that the equivalent dumping coefficient is linear, which is to say invariant compare to oscillatory amplitude. Modern seismic studies have shown this not to be a satisfactory assumption for larger civic structures, and have developed sophisticated amplitude and frequency based functions for equivalent dumping coefficient.
|
|
High speed films show the animal expelling two streams of adhesive liquid through a small opening (50 to 200 microns) at a speed of . The interplay between the elasticity of oral papillae and the fast unsteady flow produces a passive oscillatory motion (30–60 Hz) of the oral papillae. The oscillation causes the streams to cross in mid air, weaving a disordered net; the velvet worms can control only the general direction where the net is thrown. The slime glands themselves are deep inside the body cavity, each at the end of a tube more than half the length of the body.
|
|
He identified new rotating modes of nonlinear convection in rotating systems, and in collaboration with Steven Childress, established an MHD dynamo model in a rapidly rotating Bénard layer; he also gave the first demonstration that situations exist where oscillatory MHD dynamos generate magnetic fields more readily than steady flows can. He collaborated with Eric Priest to provide the first mathematically consistent account of the Petschek mechanism of magnetic field line reconnection. Soward also gave the first complete solution of the Stefan (freezing) problem in cylindrical geometry; with C.A. Jones, he provided the first completely correct solution of the spherical Taylor problem.
|
|
His graduate studies in 1963 of the electrophysiology of the olfactory bulb produced one of the first diagrams of a brain microcircuit. Building on this work he collaborated with Wilfrid Rall, just then founding the new field of computational neuroscience, at NIH to construct the first computational models of brain neurons: the mitral and granule cell. This predicted previously unknown dendrodendritic interactions between the mitral and granule cells, subsequently confirmed by electronmicroscopy. These interactions were hypothesized to mediate lateral inhibition in the processing of the sensory input as well as generate oscillatory activity involved in odor processing.
|
|
Shown are Ramsey (left) and Lee Davenport (right) Ramsey's research in the immediate post-war years looked at measuring fundamental properties of atoms and molecules by use of molecular beams. On moving to Harvard, his objective was to carry out accurate molecular beam magnetic resonance experiments, based on the techniques developed by Rabi. However, the accuracy of the measurements depended on the uniformity of the magnetic field, and Ramsey found that it was difficult to create sufficiently uniform magnetic fields. He developed the separated oscillatory field method in 1949 as a means of achieving the accuracy he wanted.
|
|
Since so-called hidden variables are involved, the theory must deal with the Bell inequalities. Hasselmann does this by showing that the theory produces time reversal invariance at the subatomic level, and posits both advanced and retarded potentials, as proposed by Feynman and Wheeler. In his most recent publication, in 2005, he was able to qualitatively reproduce the interference pattern observed in electron double-slit experiments. He was also considering reformulating his theory in four-dimensional spacetime, since the properties associated with the higher dimensions are oscillatory and can be represented as fiber bundles over a 4D Minkowski manifold.
|
|
From single-unit recording scientists have been able to measure the oscillatory neuronal activity and have been able to better their understanding of the grouping or pairing of neurons. Thus, these pairings connect with Gestalt psychology and its theory that objects are seen independently of their separate pieces, in a more global manner. A study done by Gray, Konig, Engel and Singer in 1989 reported that when studying visual cortex cells, light moving in opposite directions had low relation to one another. Yet when the light rays were then pointed in the same direction, the correlative relationship was stronger.
|
|
The GLM method does not suffer from the strong drawback of the Lagrangian specification of the flow field – following individual fluid parcels – that Lagrangian positions which are initially close gradually drift far apart. In the Lagrangian frame of reference, it therefore becomes often difficult to attribute Lagrangian-mean values to some location in space. The specification of mean properties for the oscillatory part of the flow, like: Stokes drift, wave action, pseudomomentum and pseudoenergy – and the associated conservation laws – arise naturally when using the GLM method. The GLM concept can also be incorporated into variational principles of fluid flow.
|
|
False-Brinelling of a bearing False brinelling is a bearing damage caused by fretting, with or without corrosion, that causes imprints that look similar to brinelling, but are caused by a different mechanism. False brinelling may occur in bearings which act under small oscillations or vibrations. The basic cause of false brinelling is that the design of the bearing does not have a method for redistribution of lubricant without large rotational movement of all bearing surfaces in the raceway. Lubricant is pushed out of a loaded region during small oscillatory movements and vibration where the bearings surfaces repeatedly do not move very far.
|
|
Section 357 et seq. The Theory of Sound, Macmillan, London, reprinted by Dover, New York, 1945.); waves on the surface of the sea break discontinuously when they reach the shore (Thom 1975Thom, R. (1975). Structural Stability and Morphogenesis: An outline of a general theory of models, translated from the French by D.H. Fowler, W.A. Benjamin, Reading Ma, ). Helmholtz pointed out that the sounds of organ pipes must arise from such discontinuity of flow, occasioned by the passage of air past a sharp-edged obstacle; otherwise the oscillatory character of the sound wave would be damped away to nothing.
|
|
These two properties are very general and occur for oscillatory systems in many other fields such as population dynamics, oceanography, plasma physics, etc. The weak nonlinearity and the long time scale of the amplitude variation allows the temporal description of the pulsating system to be simplified to that of only the pulsation amplitudes, thus eliminating motion on the short time scale of the period. The result is a description of the system in terms of amplitude equations that are truncated to low powers of the amplitudes. Such amplitude equations have been derived by a variety of techniques, e.g.
|
|
Neural oscillatory output Central pattern generators are biological neural networks organized to produce any rhythmic output without requiring a rhythmic input. In mammals, locomotor CPGs are organized in the lumbar and cervical segments of the spinal cord, and are used to control rhythmic muscle output in the arms and legs. Certain areas of the brain initiate the descending neural pathways that ultimately control and modulate the CPG signals. In addition to this direct control, there exist different feedback loops that coordinate the limbs for efficient locomotion and allow for the switching of gaits under appropriate circumstances.
|
|
The electromagnetic force acts along V just as gravity acts along y. The shape of the mountain and the loop- de-loop act to couple the y and x dimensions to each other. In the neuron, nature has already decided how V and N are coupled, but the relationship is much more complicated than the gravitational example. This property of excitability is what gives neurons the ability to transmit information to each other, so it is important to dynamical neuron networks, but the Morris Lecar can also operate in another parameter regime where it exhibits oscillatory behavior, forever oscillating around in phase space.
|
|
The glutamate hypothesis of schizophrenia models the subset of pathologic mechanisms linked to glutamatergic signaling. The hypothesis was initially based on a set of clinical, neuropathological, and, later, genetic findings pointing at a hypofunction of glutamatergic signaling via NMDA receptors. While thought to be more proximal to the root causes of schizophrenia, it does not negate the dopamine hypothesis, and the two may be ultimately brought together by circuit-based models. The development of the hypothesis allowed for the integration of the GABAergic and oscillatory abnormalities into the converging disease model and made it possible to discover the causes of some disruptions.
|
|
The whole sequence of events takes only a fraction of a second. These pulsations are caused by repeated microexplosions which are the results of the continuous pressure on the reservoir and the oscillatory opening and closing of the valve that controls access to the reaction chamber. This pulsed mechanism is beneficial for the beetles' survival because the system uses pressure instead of muscles to eject the spray at a constant velocity, saving the beetle energy. Also, the reintroduction of new reactants into the vestibule where enzymes are stored, reduces the temperature of the chamber, thereby protecting the peroxidases and catalases from thermal denaturation.
|
|
The original reason for the invention of the superhet was that before the appearance of the screen-grid valve, there was no type of valve which could give good gain at radio frequencies (i.e. frequencies much above 100 kHz), so a technique was applied whereby the incoming RF signal was "mixed" (i.e. multiplied) with a locally generated oscillatory voltage (the local oscillator) so as to produce a beat frequency of about 30 kHz. This intermediate frequency represented the incoming signal in all important respects, but at a significantly lower frequency which could be successfully amplified by the triode amplifiers available then.
|
|
The oscillatory structure extending for hundreds of electron volts past the edges was called the “Kronig structure” after the scientist, Ralph Kronig, who assigned this structure in the high energy range ( i.e., for a kinetic energy range - larger than 100 eV - of the phoelectron in the weak scattering regime) to the single scattering of the excited photoelectron by neighbouring atoms in molecules and condensed matter.X-ray Absorption: principles, applications and techniques of EXAFS, SEXAFS and XANES, edited by D.C. Koeningsberger, R. Prins, John Wiley & Sons 1988.Principles and Applications of EXAFS, Chapter 10 in Handbook of Synchrotron Radiation, pp 995–1014.
|
|
Direct resonance can be equated to someone pushing a child on a swing. If the frequency of the pushing (external forcing) matches the natural frequency of the child-swing system, direct resonance can be achieved. Parametric resonance, on the other hand, is the child shifting his/her own weight with time (twice the frequency of the natural frequency) and building up the oscillatory amplitude of the swing without anyone helping to push. In other words, there is an internal transfer of energy (instead of simply dissipating all available energy) as the system parameter (child's weight) modulates and changes with time.
|
|
MOWChIP-seq (Microfluidic Oscillatory Washing–based Chromatin ImmunoPrecipitation followed by sequencing) is a microfluidic technology used in molecular biology for profiling genome-wide histone modifications and other molecular bindings using as few as 30-100 cells per assay. MOWChIP-seq is a special type of ChIP-seq assay designed for low-input and high-throughput assays. The overall process of MOWChIP-seq is similar to that of conventional ChIP-seq assay except that the chromatin immunoprecipitation (ChIP) and washing steps occur in a small microfluidic chamber. MOWChIP-seq takes advantage of the capability of microfluidics for manipulating micrometer-sized beads.
|
|
When the TSC is turned on ("deblocked") again, care must be taken to choose the correct instant in order to avoid creating very large oscillatory currents. Since the TSC is a resonant circuit, any sudden shock excitation will produce a high frequency ringing effect which could damage the thyristor valve. The optimum time to turn on a TSC is when the capacitor is still charged to its normal peak value and the turn-on command is sent at the minimum of valve voltage. If the TSC is deblocked at this point, the transition back into the conducting state will be smooth.
|
|
The averaged Lagrangian approach applies to wave motion – possibly superposed on a mean motion – that can be described in a Lagrangian formulation. Using an ansatz on the form of the wave part of the motion, the Lagrangian is phase averaged. Since the Lagrangian is associated with the kinetic energy and potential energy of the motion, the oscillations contribute to the Lagrangian, although the mean value of the wave's oscillatory excursion is zero (or very small). The resulting averaged Lagrangian contains wave characteristics like the wavenumber, angular frequency and amplitude (or equivalently the wave's energy density or wave action).
|
|
This is an outstanding advantage.S.E. Hamamci, I. Kaya and D.P. Atherton, "Smith predictor design by CDM", Proceedings of the ECC’01 European Control Conference, Semina´rio de Vilar, Porto, Portugal, 2001. 4\. It is particularly hard to design robust controllers realizing the desired performance properties for unstable, integrating and oscillatory processes having poles near the imaginary axis. It has been reported that successful designs can be achieved even in these cases by using CDM.S. Manabe, "A low cost inverted pendulum system for control system education", The 3rd IFAC Symposium on advances in Control Education, Tokyo, 1994. 5\.
|
|
This oscillation is caused by the activation of leaky P/Q-type calcium channels found in the dendrites of the cells. Because of the leaky channel properties, spontaneous, inherent oscillation can also occur independent of any rhythmic input as well, though the ramifications of this capability are not entirely known and may add nothing but background noise to the thalamocortical loop. The cortex provides feedback to the thalamus through links to dendrites of these thalamocortical cells and serves as the source of constant thalamic oscillation. Oscillatory behavior depends on the conscious/unconscious state of the brain.
|
|
The human visual pathway. The lateral geniculate nucleus, a region of the thalamus, exhibits thalamocortical oscillation with the visual cortex. Thalamocortical oscillation is thought to be responsible for the synchronization of neural activity between different regions of the cortex and is associated with the appearance of specific mental states depending on the frequency range of the most prominent oscillatory activity, gamma most associated with conscious, selective concentration on tasks, learning (perceptual and associative), and short-term memory. Magnetoencephalography (MEG) has been used to show that during conscious perception, gamma-band frequency electrical activity and thalamocortical resonance prominently occurs in the human brain.
|
|
Typically the open-loop phase lag (relative to input, < 0) varies with frequency, progressively increasing to exceed 180°, at which frequency the output signal becomes inverted, or antiphase in relation to the input. The PM will be positive but decreasing at frequencies less than the frequency at which inversion sets in (at which PM = 0), and PM is negative (PM < 0) at higher frequencies. In the presence of negative feedback, a zero or negative PM at a frequency where the loop gain exceeds unity (1) guarantees instability. Thus positive PM is a "safety margin" that ensures proper (non-oscillatory) operation of the circuit.
|
|
UX Lyncis is a star in the constellation Lynx. It is a red giant of spectral type M3. It has been classified as a semiregular variable ranging from magnitude 6.6 to 6.78, Its changes in brightness are complex, with a shorter period of 37.3 days due to the star's pulsations, and a longer period of 420 days possibly due to the star's rotation or convectively induced oscillatory thermal (COT) mode. Located around 800 light-years distant, it shines with a luminosity approximately 2240 times that of the Sun and has a surface temperature of 3323 K.
|
|
To assess the bubbling behaviour of the vibrating fluidized bed, factors such as the size of the bubble and its velocity were also taken into account. For various vibration amplitudes and frequencies, numerical simulations of the vibrating fluidized bed was conducted to better understand the behaviour of the bubbles under the vibrating conditions. The results showed that due to the oscillatory displacement of the vibrating fluidized bed causes the mean bubble diameter to increase but lowers the acceleration rate of the bubbles. Thus, it was concluded that bubbling behaviour in a vibrating fluidized bed in dependent on the vibrations.
|
|
Moreover, the effective inductive reactance of the crystal can be reduced by adding a capacitor in series with the crystal. This latter technique can provide a useful method of trimming the oscillatory frequency within a narrow range; in this case inserting a capacitor in series with the crystal raises the frequency of oscillation. For a crystal to operate at its specified frequency, the electronic circuit has to be exactly that specified by the crystal manufacturer. Note that these points imply a subtlety concerning crystal oscillators in this frequency range: the crystal does not usually oscillate at precisely either of its resonant frequencies.
|
|
Similarly to the aerodynamics of flight, powered swimming requires animals to overcome drag by producing thrust. Unlike flying, however, swimming animals often do not need to supply much vertical force because the effect of buoyancy can counter the downward pull of gravity, allowing these animals to float without much effort. While there is great diversity in fish locomotion, swimming behavior can be classified into two distinct "modes" based on the body structures involved in thrust production, Median-Paired Fin (MPF) and Body-Caudal Fin (BCF). Within each of these classifications, there are numerous specifications along a spectrum of behaviours from purely undulatory to entirely oscillatory.
|
|
Hepler’s research is currently aimed at finding the ionic and molecular components that make up the pacemaker that regulates the oscillatory growth of pollen tubes. He has shown that calcium ions and protons are essential for growth. The intracellular free calcium ions exist in a gradient dropping from 3000 nM at the tip to 200 nM 20 μm from the tip and the intracellular H+ gradient falls from pH 6.8 at the tip to pH 7.5 10–30 μm from the tip. The higher concentrations of intracellular Ca2+ and H+ at the tip result from the localization of the influx of these ions at the tip.
|
|
Similarly to the aerodynamics of flight, powered swimming requires animals to overcome drag by producing thrust. Unlike flying, however, swimming animals do not necessarily need to actively exert high vertical forces because the effect of buoyancy can counter the downward pull of gravity, allowing these animals to float without much effort. While there is great diversity in fish locomotion, swimming behavior can be classified into two distinct "modes" based on the body structures involved in thrust production, Median-Paired Fin (MPF) and Body-Caudal Fin (BCF). Within each of these classifications, there are numerous specifications along a spectrum of behaviors from purely undulatory to entirely oscillatory based.
|
|
Timothy P. Lodge was born in Manchester, England, a son of Helen and Arthur S. Lodge. He moved permanently to the United States in 1968. He received his A. B. degree in applied mathematics from Harvard University in 1975. Working under the mentorship of Professor John Schrag at the University of Wisconsin, Madison, Lodge received his Ph.D. in chemistry in 1980. His dissertation was titled, “Oscillatory Flow Birefringence of Dilute Polymer Solutions: Concentration Dependence and High Frequency Behavior.” Upon graduation, Lodge collaborated with Dr. Charles Han as a National Research Council Postdoctoral Associate at the National Bureau of Standards (now the National Institute of Standards and Technology).
|
|
Besides a nearly periodic motion, mode-mode interactions with very irregular (also chaotic) behaviour and spreading of the wavepacket may also occur. Near a conical intersection this will be accompanied/complemented by nonradiative transitions (termed internal conversion) to other APESs occurring on the same ultrafast time scale. For the JT case the situation is somewhat special, as compared to a general conical intersection, because the different JT potential sheets are symmetry-related to each other and have (exactly or nearly) the same energy minimum. The "transition" between them is thus more oscillatory than one would normally expect, and their time-averaged populations are close to 1/2.
|
|
Because of a historical accident, the term "theta rhythm" is used to refer to two different phenomena, "hippocampal theta" and "human cortical theta". Both of these are oscillatory EEG patterns, but they may have little in common beyond the name "theta". In the oldest EEG literature dating back to the 1920s, Greek letters such as alpha, beta, theta, and gamma were used to classify EEG waves falling into specific frequency ranges, with "theta" generally meaning a range of about 4–7 cycles per second (Hz). In the 1930s–1950s, a very strong rhythmic oscillation pattern was discovered in the hippocampus of cats and rabbits (Green & Arduini, 1954).
|
|
Furthermore, nocturnal reactivation seems to share the same neural oscillatory patterns as reactivation during wakefulness, processes which might be coordinated by theta activity. During wakefulness, theta oscillations have been often related to successful performance in memory tasks, and cued memory reactivations during sleep have been showing that theta activity is significantly stronger in subsequent recognition of cued stimuli as compared to uncued ones, possibly indicating a strengthening of memory traces and lexical integration by cuing during sleep. However, the beneficial effect of TMR for memory consolidation seems to occur only if the cued memories can be related to prior knowledge.Groch, S., Schreiner, T., Rasch, B., Huber, R., & Wilhelm, I. (2017).
|
|
Unlike RF band detection, optical frequencies oscillate too rapidly to directly measure and process the electric field electronically. Instead optical photons are (usually) detected by absorbing the photon's energy, thus only revealing the magnitude, and not by following the electric field phase. Hence the primary purpose of heterodyne mixing is to down shift the signal from the optical band to an electronically tractable frequency range. In RF band detection, typically, the electromagnetic field drives oscillatory motion of electrons in an antenna; the captured EMF is subsequently electronically mixed with a local oscillator (LO) by any convenient non-linear circuit element with a quadratic term (most commonly a rectifier).
|
|
Earth batteries tap a useful low voltage current from telluric currents, and were used for telegraph systems as far back as the 1840s. In industrial prospecting activity that uses the telluric current method, electrodes are properly located on the ground to sense the voltage difference between locations caused by the oscillatory telluric currents.Dobrin, "Introduction to Geophysical Prospecting", McGraw Hill (3rd Ed. 1976) pg. 592., C. L. Kober, Passive geophysical prospection system based upon the detection of the vertical electric field component of telluric currents and method therefore It is recognized that a low frequency window (LFW) exists when telluric currents pass through the earth's substrata.
|
|
Stable limit cycle (shown in bold) and two other trajectories spiraling into it Stable limit cycle (shown in bold) for the Van der Pol oscillator In mathematics, in the study of dynamical systems with two-dimensional phase space, a limit cycle is a closed trajectory in phase space having the property that at least one other trajectory spirals into it either as time approaches infinity or as time approaches negative infinity. Such behavior is exhibited in some nonlinear systems. Limit cycles have been used to model the behavior of a great many real-world oscillatory systems. The study of limit cycles was initiated by Henri Poincaré (1854–1912).
|
|
Once the cells of the pre-somitic mesoderm are in place following by cell migration during gastrulation, oscillatory expression of many genes begins in these cells as if regulated by a developmental "clock." This has led many to conclude that somitogenesis is coordinated by a "clock and wave" mechanism. More technically, this means that somitogenesis occurs due to the largely cell-autonomous oscillations of a network of genes and gene products which causes cells to oscillate between a permissive and a non-permissive state in a consistently timed-fashion, like a clock. These genes include members of the FGF family, Wnt and Notch pathway, as well as targets of these pathways.
|
|
Static loads have been shown to be detrimental to biosynthesis while oscillatory loads at low frequencies (similar that of a normal walking gait) have been shown to be beneficial in maintaining health and increasing matrix synthesis. Due to the complexity of in-vivo loading conditions and the interplay of other mechanical and biochemical factors, the question of what an optimal loading regimen may be or whether one exists remain unanswered. Although studies have shown that, like most biological tissues, cartilage is capable of mechanotransduction, the precise mechanisms by which this is done remain unknown. However, there exist a few hypotheses which begin with the identification of mechanoreceptors.
|
|
With his colleagues he created a comprehensive description of the Peierls and spin-Peierls transition in magnetic field, predicted the possibility of multi-quanta vortices attached to columnar defects, demonstrated the possibility of tilted vortex attraction in layered superconductors which has received an experimental confirmation. These findings open perspectives for the nano-fabricated superconducting materials and present an important contribution to the general theory of superconductivity . Bouzdine contributed into the theory of the inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov phase in the superconducting state. In his pioneering theoretical studies of superconductor-ferromagnet (S-F) multilayer systems he found a damped oscillatory behaviour of the superconducting order parameter in the ferromagnetic layer.
|
|
The function of the epithalamus is to connect the limbic system to other parts of the brain. The epithalamus also serves as a connecting point for the dorsal diencephalic conduction system, which is responsible for carrying information from the limbic forebrain to limbic midbrain structures. Some functions of its components include the secretion of melatonin and secretion of hormones from the pituitary gland (by the pineal gland circadian rhythms), regulation of motor pathways and emotions, and how energy is conserved in the body. A study has shown that the lateral habenula, an epithalamic structure, produces spontaneous theta oscillatory activity that was correlated with theta oscillation in the hippocampus.
|
|
Jellium is the simplest model of interacting electrons. It is employed in the calculation of properties of metals, where the core electrons and the nuclei are modeled as the uniform positive background and the valence electrons are treated with full rigor. Semi-infinite jellium slabs are used to investigate surface properties such as work function and surface effects such as adsorption; near surfaces the electronic density varies in an oscillatory manner, decaying to a constant value in the bulk. Within density functional theory, jellium is used in the construction of the local-density approximation, which in turn is a component of more sophisticated exchange-correlation energy functionals.
|
|
These experiments showed that groups of spatially segregated neurons engage in synchronous oscillatory activity when activated by visual stimuli. The frequency of these oscillations was in the range of 40 Hz and differed from the periodic activation induced by the grating, suggesting that the oscillations and their synchronization were due to internal neuronal interactions. Similar findings were shown in parallel by the group of Eckhorn, providing further evidence for the functional role of neural synchronization in feature binding. Since then, numerous studies have replicated these findings and extended them to different modalities such as EEG, providing extensive evidence of the functional role of gamma oscillations in visual perception.
|
|
The first demonstration that glutamate could induce the formation of molecules belonging to a major second messenger system was in 1985, when it was shown that it could stimulate the formation of inositol phosphates. This finding allowed in 1987 to yield an explanation for oscillatory ionic glutamate responses and to provide further evidence for the existence of metabotropic glutamate receptors. In 1991 the first metabotropic glutamate receptor of the seven transmembrane domain family was cloned. More recent reports on ionotropic glutamate receptors able to couple to metabotropic transduction systems suggest that metabotropic responses of glutamate might not be limited to seven transmembrane domain metabotropic glutamate receptors.
|
|
The relativistic Dirac equation has problems for elements with more than 137 protons. For such elements, the wave function of the Dirac ground state is oscillatory rather than bound, and there is no gap between the positive and negative energy spectra, as in the Klein paradox. More accurate calculations taking into account the effects of the finite size of the nucleus indicate that the binding energy first exceeds the limit for elements with more than 173 protons. For heavier elements, if the innermost orbital (1s) is not filled, the electric field of the nucleus will pull an electron out of the vacuum, resulting in the spontaneous emission of a positron.
|
|
As indicated here, even most simple liquids will exhibit some elastic response at shear rates or frequencies exceeding 5 x 106 cycles per second. Experiments on such short time scales probe the fundamental motions of the primary particles (or particle clusters) which constitute the lattice structure or aggregate. The increasing resistance of certain liquids to flow at high stirring speeds is one manifestation of this phenomenon. The ability of a condensed body to respond to a mechanical force by viscous flow is thus strongly dependent on the time scale over which the load is applied, and thus the frequency and amplitude of the stress wave in oscillatory experiments.
|
|
However, in moving the mass back to the equilibrium position, it has acquired momentum which keeps it moving beyond that position, establishing a new restoring force in the opposite sense. If a constant force such as gravity is added to the system, the point of equilibrium is shifted. The time taken for an oscillation to occur is often referred to as the oscillatory period. The systems where the restoring force on a body is directly proportional to its displacement, such as the dynamics of the spring- mass system, are described mathematically by the simple harmonic oscillator and the regular periodic motion is known as simple harmonic motion.
|
|
His approach to Femtosecond pulse shaping has been crucial for applications from the demonstration of control in the gas phase fragmentation reactions to 2D IR spectroscopy and quantum computing . His work has built upon a history of over thirty years of working on pulsed laser experiments and has established other milestones in the field. He developed the self-calibrated femtosecond optical tweezers method for reproducible pulsed laser optical tweezers experiments with an additional forced oscillatory mode of motion. He went on to use the femtosecond optical tweezers to provide a direct measure and control of 'in situ' temperature and viscosity at micro-scale volumes .
|
|
However, there is relatively little exchange of water between channels; experimental studies and mathematical modelling of the coastline near Hopkins Marine Station in California have shown that water is rapidly mixed within each channel, but that it mostly moves in an oscillatory manner. Surge channels have been likened to 'containment vessels', retaining water borne gametes and probably enhancing the effectiveness of external fertilisation of marine species dwelling within them. Surge channels can form in reefs, and the term is sometimes also applied to breaches of coastal dunes by storms. Surge channels can range from a few inches across to ten feet or more across.
|
|
Around the same time, intrinsic oscillatory behavior in vertebrate neurons was observed in cerebellar Purkinje cells, inferior olivary nucleus and thalamus. In the 1990s, with the advent of positron emission tomography (PET) scans, researchers began to notice that when a person is involved in perception, language, and attention tasks, the same brain areas become less active compared to passive rest, and labeled these areas as becoming "deactivated". In 1995, Bharat Biswal, a graduate student at the Medical College of Wisconsin in Milwaukee, discovered that the human sensorimotor system displayed "resting-state connectivity," exhibiting synchronicity in functional magnetic resonance imaging (fMRI) scans while not engaged in any task.
|
|
In the field of computational neuroscience, the theory of metastability refers to the human brain’s ability to integrate several functional parts and to produce neural oscillations in a cooperative and coordinated manner, providing the basis for conscious activity. Metastability, a state in which signals (such as oscillatory waves) fall outside their natural equilibrium state but persist for an extended period of time, is a principle that describes the brain’s ability to make sense out of seemingly random environmental cues. In the past 25 years, interest in metastability and the underlying framework of nonlinear dynamics has been fueled by advancements in the methods by which computers model brain activity.
|
|
Thalamocortical dysrhythmia (TCD) is a proposed explanation for certain cognitive disorders. It occurs upon the disruption of normal gamma-band electrical activity between the cortex and thalamic neurons during awakened, conscious states. This disorder is associated with diseases and conditions such as neuropathic pain, tinnitus, and Parkinson's disease and is characterized by the presence of unusually low- frequency resonance in the thalamocortical system. TCD is associated with disruption of many brain functions including cognition, sensory perception, and motor control and occurs when thalamocortical neurons become inappropriately hyperpolarized, allowing T-type calcium channels to activate and the oscillatory properties of the thalamocortical neurons to change.
|
|
In these models the phase paths can "spiral in" towards zero, "spiral out" towards infinity, or reach neutrally stable situations called centres where the path traced out can be either circular, elliptical, or ovoid, or some variant thereof. This is useful in determining if the dynamics are stable or not. Other examples of oscillatory systems are certain chemical reactions with multiple steps, some of which involve dynamic equilibria rather than reactions that go to completion. In such cases one can model the rise and fall of reactant and product concentration (or mass, or amount of substance) with the correct differential equations and a good understanding of chemical kinetics.
|
|
The radiation stress tensor describes the additional forcing due to the presence of the waves, which changes the mean depth-integrated horizontal momentum in the fluid layer. As a result, varying radiation stresses induce changes in the mean surface elevation (wave setup) and the mean flow (wave-induced currents). For the mean energy density in the oscillatory part of the fluid motion, the radiation stress tensor is important for its dynamics, in case of an inhomogeneous mean-flow field. The radiation stress tensor, as well as several of its implications on the physics of surface gravity waves and mean flows, were formulated in a series of papers by Longuet-Higgins and Stewart in 1960–1964.
|
|
Rife claimed to have documented a "Mortal Oscillatory Rate" for various pathogenic organisms, and to be able to destroy the organisms by vibrating them at this particular rate. According to the San Diego Evening Tribune in 1938, Rife stopped short of claiming that he could cure cancer, but did argue that he could "devitalize disease organisms" in living tissue, "with certain exceptions". In a 1931 profile, Rife warned against "medical fakers" who claim to cure disease using "electrical 'vibrations'", stating that his work did not uphold such claims. Rife machine from 1922 Rife's claims about his beam ray could not be independently replicated, and were discredited by independent researchers during the 1950s.
|
|
On the other hand, negative circuits, involving an odd number of negative interactions, can generate oscillatory behaviour or homeostasis. In a further step, considering the regulatory graph associated with a gene network, modelled in terms of logical or differential formalism, Thomas proposed general rules stating that (i) a positive circuit is necessary to display multiple stable states, and (ii) a negative circuit is necessary to have robust sustained oscillations. This has major biological implications since, as first pointed out by Max Delbrück and amply confirmed since, cell differentiation essentially results from successive choices between multiple steady states. Thus, any model for a differentiation process has to involve at least one positive circuit.
|
|
Arieh Iserles (born 2 September 1947) is a computational mathematician, currently Professor of the Numerical Analysis of Differential Equations at the University of Cambridge and a member of the Department of Applied Mathematics and Theoretical Physics. He studied at the Hebrew University of Jerusalem and Ben-Gurion University of the Negev and wrote his PhD dissertation on numerical methods for stiff ordinary differential equations. His research comprises many themes in computational and applied mathematics: ordinary and partial differential equations, approximation theory, geometric numerical integration, orthogonal polynomials, functional equations, computational dynamics and the computation of highly oscillatory phenomena. He has written a textbook, A First Course in the Numerical Analysis of Differential Equations (Cambridge University Press, 2nd ed. 2009).
|
|
Direct ionization corresponds to electrons ejected down-field towards the bottleneck in the Coulomb + dc electric field potential, whereas indirect ionization corresponds to electrons ejected away from the bottleneck in the Coulomb + dc electric field and only ionize upon further Coulomb interactions. The different trajectories caused by direct and indirect ionization give rise to a distinct pattern that can be detected by a two-dimensional flux detector and subsequently imaged. The images exhibited an outer ring, which corresponded to the indirect ionization process and an inner ring, which corresponded to the direct ionization process. This oscillatory pattern can be interpreted as being interferences among the trajectories of the electrons moving from the atom to the detector.
|
|
Phase response curve analysis can be used to understand the intrinsic properties and oscillatory behavior of regular-spiking neurons. The neuronal PRCs can be classified as being purely positive (PRC type I) or as having negative parts (PRC type II). Importantly, the PRC type exhibited by a neuron is indicative of its input–output function (excitability) as well as synchronization behavior: networks of PRC type II neurons can synchronize their activity via mutual excitatory connections, but those of PRC type I can not. Experimental estimation of PRC in living, regular-spiking neurons involves measuring the changes in inter-spike interval in response to a small perturbation, such as a transient pulse of current.
|
|
169, 738–747van Nes, E., and Scheffer, M. (2005) Implications of spatial heterogeneity for catastrophic regime shifts in ecosystems. Ecology 86, 1797–1807Hastings, A., and Wysham, D.B. (2010) Regime shifts in ecological systems can occur with no warning. Ecol Lett, 1–9 Systems approaching a bifurcation point show a characteristic behaviour called critical slowing down leading to an increasingly slow recovery from perturbations. This, in turn, may lead to an increase in (spatial or temporal) autocorrelation and variance, while variance spectra tend to lower frequencies, and the 'direction of critical slowing down' in a system's state space may be indicative of a system's future state when delayed negative feedbacks leading to oscillatory or other complex dynamics are weak.
|
|
In turn the oscillating voltage on the tank circuit varies the potential of the grid, causing the electrons to bunch into a cloud of electrons moving back and forth through the grid in phase at the resonant frequency. The oscillatory motion of the electron cloud continues; this cloud constitutes the alternating output current. Some electrons are lost to the grid on each pass, but the electron supply is continually replenished by new electrons emitted by the cathode. Compared to a conventional triode oscillator, the number of electrons actually hitting the anode plate and grid is small, so the plate and grid alternating currents are small, and the output power of the B-K oscillator is low.
|
|
These functions are special because no matter where we evaluate the action of the Hoperator on the wave function, we always get the same number E. These functions are called stationary states, because the time derivative at any point x is always the same, so the amplitude of the wave function never changes in time. Since the overall phase of a wave function is not measurable, the system does not change in time. We are usually interested in the wave function with the lowest energy eigenvalue, the ground state. We're going to write a slightly different version of the Schrödinger equation that will have the same energy eigenvalue, but, instead of being oscillatory, it will be convergent.
|
|
Most notably in 1955 he published an article which described a dimensionless parameter (α) which characterised the nature of unsteady flow; subsequently this has been called the Womersley number. In July 1955, as planned, he moved to WADC to take a post as acting chief of the Analysis Section, System Dynamics Branch Aeronautical Research Laboratory. In 1956, he was promoted to Supervisory Mathematician and then Supervisory Aeronautical Research Engineer (Flight Systems), although he continued to publish on mathematical aspects of blood flow until his early death in 1958. His 1957 monograph on 'An elastic tube theory of pulse transmission and oscillatory flow in mammalian arteries' is widely regarded as a major influence in the field.
|
|
In general, it is difficult to decompose a combined wave–mean motion into a mean and a wave part, especially for flows bounded by a wavy surface: e.g. in the presence of surface gravity waves or near another undulating bounding surface (like atmospheric flow over mountainous or hilly terrain). However, this splitting of the motion in a wave and mean part is often demanded in mathematical models, when the main interest is in the mean motion – slowly varying at scales much larger than those of the individual undulations. From a series of postulates, arrive at the (GLM) formalism to split the flow: into a generalised Lagrangian mean flow and an oscillatory-flow part.
|
|
Windhorst's research has revolved around the control of skeletal muscle contraction based on sensory signal arising in muscles and skin and on neuronal networks predominantly in the spinal cord and brainstem. In this wider context, one line of research strived to elucidate the dynamic signal processing of the participating neurons, such as muscle spindles, motoneurons and interneurons (particularly Renshaw cells) and their importance for oscillatory process such as tremor. Related issues were the plastic properties of such networks and their modulation by signals arising in the peripheral and central nervous system, specifically in the context of muscle fatigue. A related aspect of research concerned the origin of muscle pain and its effects on spinal neurons.
|
|
Shifts in phase (or behavior of neurons) caused due to a perturbation (an external stimulus) can be quantified within a Phase Response Curve (PRC) to predict synchrony in coupled and oscillating neurons. These effects can be computed, in the case of advances or delays to responses, to observe the changes in the oscillatory behavior of neurons, pending on when a stimulus was applied in the phase cycle of an oscillating neuron. The key to understanding this is in the behavioral patterns of neurons and the routes neural information travels. Neural circuits are able to communicate efficiently and effectively within milliseconds of experiencing a stimulus and lead to the spread of information throughout the neural network.
|
|
In general, EEG signals have a broad spectral content similar to pink noise, but also reveal oscillatory activity in specific frequency bands. The first discovered and best-known frequency band is alpha activity (8–12 Hz) that can be detected from the occipital lobe during relaxed wakefulness and which increases when the eyes are closed. Other frequency bands are: delta (1-4 Hz), theta (4-8 Hz), beta (13-30 Hz), low gamma (30-70 Hz), and high gamma (70-150 Hz) frequency bands, where faster rhythms such as gamma activity have been linked to cognitive processing. Indeed, EEG signals change dramatically during sleep and show a transition from faster frequencies to increasingly slower frequencies such as alpha waves.
|
|
At the age of 20, interrupting a lecture during his signals training, Muggleton corrected an assertion about limits of the reflective nature of the ionosphere. He was asked to prove his claim to a group of British Army generals and succeeded in demonstrating Appleton's theoretical prediction that radio signals could be reflected from the Heaviside layer of the ionosphere even when transmitted vertically. His demonstration went on to be significant in its use for troop communications between the fjords in the Allied liberation of Norway during the winter of 1944-1945. In work published in 1968 and 1969 Muggleton studied long-term oscillatory variations in the relationship between F-region ionization and visible solar activity.
|
|
An unexpected series of experimental results for the rate of decay of heavy highly charged radioactive ions circulating in a storage ring has provoked theoretical activity in an effort to find a convincing explanation. The rates of weak decay of two radioactive species with half lives of about 40 s and 200 s are found to have a significant oscillatory modulation, with a period of about 7 s. The observed phenomenon is known as the GSI anomaly, as the storage ring is a facility at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. As the decay process produces an electron neutrino, some of the proposed explanations for the observed rate oscillation invoke neutrino properties.
|
|
Once the cells of the pre-somitic mesoderm are in place following cell migration during gastrulation, oscillatory expression of many genes begins in these cells as if regulated by a developmental "clock." As mentioned previously, this has led many to conclude that somitogenesis is coordinated by a "clock and wave" mechanism. In technical terms, this means that somitogenesis occurs due to the largely cell-autonomous oscillations of a network of genes and gene products, which causes cells to oscillate between a permissive and a non-permissive state in a consistently timed-fashion, like a clock. These genes include members of the FGF family, Wnt and Notch pathway, as well as targets of these pathways.
|
|
An unexpected series of experimental results for the rate of decay of heavy highly charged radioactive ions circulating in a storage ring has provoked theoretical activity in an effort to find a convincing explanation. The rates of weak decay of two radioactive species with half lives of about 40 seconds and 200 seconds are found to have a significant oscillatory modulation, with a period of about 7 seconds. The observed phenomenon is known as the GSI anomaly, as the storage ring is a facility at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt Germany. As the decay process produces an electron neutrino, some of the proposed explanations for the observed oscillation rate invoke neutrino properties.
|
|
As the solar cycle progresses towards its maximum, sunspots tend to form closer to the solar equator, following Spörer's law. The 11-year sunspot cycle is half of a 22-year Babcock–Leighton solar dynamo cycle, which corresponds to an oscillatory exchange of energy between toroidal and poloidal solar magnetic fields. At solar-cycle maximum, the external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength, but an internal toroidal quadrupolar field, generated through differential rotation within the tachocline, is near its maximum strength. At this point in the dynamo cycle, buoyant upwelling within the convection zone forces emergence of the toroidal magnetic field through the photosphere, giving rise to pairs of sunspots, roughly aligned east–west with opposite magnetic polarities.
|
|
For orbits that do not have an eccentricity close to zero, the rotation rate tends to become locked with the orbital speed when the body is at periapsis, which is the point of strongest tidal interaction between the two objects. If the orbiting object has a companion, this third body can cause the rotation rate of the parent object to vary in an oscillatory manner. This interaction can also drive an increase in orbital eccentricity of the orbiting object around the primary - an effect known as eccentricity pumping. In some cases where the orbit is eccentric and the tidal effect is relatively weak, the smaller body may end up in a so-called spin–orbit resonance, rather than being tidally locked.
|
|
Yuwen Zhang's research area is in the field of heat and mass transfer with applications in nanomanufacturing, thermal management, and energy storage and conversion. He has published on topics including latent heat thermal energy storage systems,Zhang, Y., and Faghri, A., 1996, “Heat Transfer Enhancement in Latent Heat Thermal Energy Storage System by Using the Internally Finned Tube,” Int. J. Heat Mass Transfer, 39(15), pp. 3165-3173. additive manufacturing (AM),Zhou, J., Zhang, Y., and Chen, J.K., 2009, “Numerical Simulation of Laser Irradiation to a Randomly Packed Bimodal Powder Bed,” Int. J. Heat Mass Transfer, 52(13-14), pp. 3137-3146. oscillating heat pipes,Zhang, Y., and Faghri, A., 2003, “Oscillatory Flow in Pulsating Heat Pipes with Arbitrary Numbers of Turns,” J. Thermophys.
|
|
During an active Madden–Julian oscillatory period over Australian longitudes in late November, a broad low- pressure area developed within the monsoon trough in the southeastern Arafura Sea, west of Cape York Peninsula. Due to its potential for development, the Bureau of Meteorology Tropical Cyclone Warning Center in Darwin (TCWC Darwin) began monitoring the system on 28 November. Tracking westward, the low eventually moved into the Timor Sea three days later and became quasi- stationary in forward motion. Situated within a good outflow environment, the Joint Typhoon Warning Center (JTWC) began monitoring the disturbance at 0300 UTC on 1 December, assessing it with a 'poor' likelihood of cyclogenesis; these probabilities as assessed by the JTWC would increase up until eventual formation.
|
|
It has recently been proposed that even if phases are not aligned across trials, induced activity may still cause event-related potentials because ongoing brain oscillations may not be symmetric and thus amplitude modulations may result in a baseline shift that does not average out. This model implies that slow event-related responses, such as asymmetric alpha activity, could result from asymmetric brain oscillation amplitude modulations, such as an asymmetry of the intracellular currents that propagate forward and backward down the dendrites. Under this assumption, asymmetries in the dendritic current would cause asymmetries in oscillatory activity measured by EEG and MEG, since dendritic currents in pyramidal cells are generally thought to generate EEG and MEG signals that can be measured at the scalp.
|
|
The Big Bounce is a hypothesized cosmological model for the origin of the known universe. It was originally suggested as a phase of the cyclic model or oscillatory universe interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe. In the early 2000s, inflation was found by some theorists to be problematic and unfalsifiable in that its various parameters could be adjusted to fit any observations, so that the properties of the observable universe are a matter of chance.
|
|
The Gladstone–Dale relation requires a particle model of light because the continuous wave-front required by wave theory cannot be maintained if light encounters atoms or molecules that maintain a local electric structure with a characteristic refractivity. Similarly, the wave theory cannot explain the photoelectric effect or absorption by individual atoms and one requires a local particle of light (see wave–particle duality). A local model of light consistent with these electrostatic refraction calculations occurs if the electromagnetic energy is restricted to a finite region of space. An electric-charge monopole must occur perpendicular to dipole loops of magnetic flux, but if local mechanisms for propagation are required, a periodic oscillatory exchange of electromagnetic energy occurs with transient mass.
|
|
His contributions in the field of electrical engineering began with the completion of his PhD at MIT under the supervision of Prof. Fred Schweppe, in which he formulated a new technique for the dynamic analysis of small perturbations of electric power systems known as Selective Modal Analysis. This analytical framework allows approaching large and complex linear time-invariant dynamic system problems (such as dynamic stability analysis, or the determination of coherent generator groups and dynamic equivalents in transient stability studies) through a reduction technique that extracts the relevant quantitative and qualitative information. This framework was later applied intensively to solve different power system stability and control problems, such as the analysis of the oscillatory stability and control, subsynchronous resonance or multi-area analysis of small signal stability.
|
|
Zitterbewegung ("jittery motion" in German) is a predicted rapid oscillatory motion of elementary particles that obey relativistic wave equations. The existence of such motion was first proposed by Erwin Schrödinger in 1930 as a result of his analysis of the wave packet solutions of the Dirac equation for relativistic electrons in free space, in which an interference between positive and negative energy states produces what appears to be a fluctuation (up to the speed of light) of the position of an electron around the median, with an angular frequency of , or approximately radians per second. For the hydrogen atom, zitterbewegung can be invoked as a heuristic way to derive the Darwin term, a small correction of the energy level of the s-orbitals.
|
|
Although adding noise may result in smaller signal to-noise ratio, the added white noise will provide a uniform reference scale distribution to facilitate EMD; therefore, the low signal-noise ratio does not affect the decomposition method but actually enhances it to avoid the mode mixing. Based on this argument, an additional step is taken by arguing that adding white noise may help to extract the true signals in the data, a method that is termed Ensemble Empirical Mode Decomposition (EEMD) The EEMD consists of the following steps: # Adding a white noise series to the original data. # Decomposing the data with added white noise into oscillatory components. # Repeating step 1 and step 2 again and again, but with different white noise series added each time.
|
|
There are a number of different causes of noise from shipping. These can be subdivided into those caused by the propeller, those caused by machinery, and those caused by the movement of the hull through the water. The relative importance of these three different categories will depend, amongst other things, on the ship type reducing underwater noise pollution from large commercial vessels One of the main causes of hydro acoustic noise from fully submerged lifting surfaces is the unsteady separated turbulent flow near the surface's trailing edge that produces pressure fluctuations on the surface and unsteady oscillatory flow in the near wake. The relative motion between the surface and the ocean creates a turbulent boundary layer (TBL) that surrounds the surface.
|
|
The absence of long-range order in liquids and glasses is evidenced by the absence of Bragg peaks in X-ray and neutron diffraction. For these isotropic materials, the diffraction pattern has circular symmetry, and in the radial direction, the diffraction intensity has a smooth oscillatory shape. This diffracted intensity is usually analyzed to give the static structure factor, S(q), where q is given by q=4πsin(θ)/λ, where 2θ is the scattering angle (the angle between the incident and scattered quanta), and λ is the incident wavelength of the probe (photon or neutron). Typically diffraction measurements are performed at a single (monochromatic) λ, and diffracted intensity is measured over a range of 2θ angles, to give a wide range of q.
|
|
On this analysis then impetus dynamics was to be preferred if the Aristotelian science of motion was to incorporate a dynamical explanation of pendulum motion. And indeed it was also to be preferred more generally if it was to explain other oscillatory motions, such as the to and fro vibrations around the normal of musical strings in tension, such as those of a zither, lute or guitar. For here the analogy made with the gravitational tunnel experiment was that the tension in the string pulling it towards the normal played the role of gravity, and thus when plucked i.e. pulled away from the normal and then released, this was the equivalent of pulling the cannonball to the Earth's surface and then releasing it.
|
|
They also found several new rings, such as rings coincident with the orbits of Atlas, Janus and Epimetheus (the Saturnian 'co-orbitals') and Pallene; a diffuse ring between Atlas and the F ring; and new rings within several of the gaps in Saturn's rings. In 2013, Cassini data confirmed a 1993 prediction by Porco and Mark Marley that acoustic oscillations within the body of Saturn are responsible for creating particular features in the rings of Saturn. This confirmation, the first to demonstrate that planetary rings can act like a seismograph in recording oscillatory motions within the host planet, should provide new constraints on the interior structure of Saturn. Such oscillations are known to exist in the sun as well as other stars.
|
|
The main idea behind spectral regularization is that each regularization operator can be described using spectral calculus as an appropriate filter on the eigenvalues of the operator that defines the problem, and the role of the filter is to "suppress the oscillatory behavior corresponding to small eigenvalues". Therefore, each algorithm in the class of spectral regularization algorithms is defined by a suitable filter function (which needs to be derived for that particular algorithm). Three of the most commonly used regularization algorithms for which spectral filtering is well- studied are Tikhonov regularization, Landweber iteration, and truncated singular value decomposition (TSVD). As for choosing the regularization parameter, examples of candidate methods to compute this parameter include the discrepancy principle, generalized cross validation, and the L-curve criterion.
|
|
As a matter of principle a power source (such as a waterwheel) is installed as close as possible to the equipment that it drives (such as a water pump), to minimise the inevitable loss of power incurred in its transmission. When the distance between source and target is significant an efficient means of transferring the power is necessary, and in the 19th century the best method available was the flatrod system. This was used at a number of mines and consisted of a series of linked iron or wooden rods connected to a crank on a waterwheel (or steam engine). The crank converted the circular motion of the wheel into an oscillatory back-and-forth motion of the rods which, suitably supported, could be extended for some distance along the ground.
|
|
Ramsey and his PhD student Daniel Kleppner developed the atomic hydrogen maser, looking to increase the accuracy with which the hyperfine separations of atomic hydrogen, deuterium and tritium could be measured, as well as to investigate how much the hyperfine structure was affected by external magnetic and electric fields. He also participated in developing an extremely stable clock based on a hydrogen maser. From 1967 until 2019, the second has been defined based on 9,192,631,770 hyperfine transition of a cesium-133 atom; the atomic clock which is used to set this standard is an application of Ramsey's work. He was awarded the Nobel Prize in Physics in 1989 "for the invention of the separated oscillatory fields method and its use in the hydrogen maser and other atomic clocks".
|
|
A small bar magnet attached to the inner sphere aligned that sphere with the earth's magnetic field. As the satellite oscillated about its local vertical because of gravity gradient forces, the outer sphere of the damper rotated about the inner sphere, dissipating the oscillatory energy in the form of heat from the viscous drag of the fluid. This system was more effective than the damping spring-and-weight system used on a previously launched Transit satellite in that it provided equal damping about all three axes of the satellite while the older damper provided no damping about the yaw axis and less damping of the roll axis than for pitch. The new damper also was effective immediately whereas the older technique required several weeks for the spring-mass to compress into operational position.
|
|
British scientist William Thomson (Lord Kelvin) in 1853 showed mathematically that the discharge of a Leyden jar through an inductance should be oscillatory, and derived its resonant frequency. British radio researcher Oliver Lodge, by discharging a large battery of Leyden jars through a long wire, created a tuned circuit with its resonant frequency in the audio range, which produced a musical tone from the spark when it was discharged. In 1857, German physicist Berend Wilhelm Feddersen photographed the spark produced by a resonant Leyden jar circuit in a rotating mirror, providing visible evidence of the oscillations. In 1868, Scottish physicist James Clerk Maxwell calculated the effect of applying an alternating current to a circuit with inductance and capacitance, showing that the response is maximum at the resonant frequency.
|
|
A decade later Francis Crick & Christof Koch developed the model further by explaining the synchronization of distant neurons by transient gamma wave oscillations being guided by attention. By 1995, Francisco Varela had established the importance of the role of the oscillatory phase in the pairing of neuron assemblies. The Temporal Binding Hypothesis was first proposed as a way of addressing the combinatorial problem of neural binding, which emphasizes the impossibly large number of connections that would have to be made between neurons of overlapping function and association in order to achieve the degree of observable complexity in neural binding. Modern models that are currently being developed often retain the structure of temporal synchrony due to this significant advantage as well as the strong experimental support for the existence of global brain oscillations.
|
|
British scientist William Thomson (Lord Kelvin) in 1853 showed mathematically that the discharge of a Leyden jar through an inductance should be oscillatory, and derived its resonant frequency. British radio researcher Oliver Lodge, by discharging a large battery of Leyden jars through a long wire, created a tuned circuit with its resonant frequency in the audio range, which produced a musical tone from the spark when it was discharged. In 1857, German physicist Berend Wilhelm Feddersen photographed the spark produced by a resonant Leyden jar circuit in a rotating mirror, providing visible evidence of the oscillations. In 1868, Scottish physicist James Clerk Maxwell calculated the effect of applying an alternating current to a circuit with inductance and capacitance, showing that the response is maximum at the resonant frequency.
|
|
Neurons firing in synchrony in circadian pacemaker cells Phase resetting in neurons is a behavior observed in different biological oscillators and plays a role in creating neural synchronization as well as different processes within the body. Phase resetting in neurons is when the dynamical behavior of an oscillation is shifted. This occurs when a stimulus perturbs the phase within an oscillatory cycle and a change in period occurs. The periods of these oscillations can vary depending on the biological system, with examples such as: (1) neural responses can change within a millisecond to quickly relay information; (2) In cardiac and respiratory changes that occur throughout the day, could be within seconds; (3) circadian rhythms may vary throughout a series of days; (4) rhythms such as hibernation may have periods that are measured in years.
|
|
The precession frequency is measured using the Ramsey separated oscillatory field magnetic resonance method, in which a large number of spin polarized ultra-cold neutrons are stored in an electric and magnetic field. An AC magnetic field pulse is then applied to rotate the spins by \pi/2. The signal generator used to apply the pulse is then gated off while the neutron spins precess about the magnetic field axis at the precession frequency; after a period of ~100s, another field pulse is applied to rotate the spins by \pi/2. If the frequency of the applied signal is exactly equal to the precession frequency, the neutrons will all be synchronised with the signal generator, and they will all end up polarized in the opposite direction to how they started.
|
|
Animation of a torsion spring oscillating The balance wheel of a mechanical watch is a harmonic oscillator whose resonant frequency f_n\, sets the rate of the watch. The resonant frequency is regulated, first coarsely by adjusting I\, with weight screws set radially into the rim of the wheel, and then more finely by adjusting \kappa\, with a regulating lever that changes the length of the balance spring. In a torsion balance the drive torque is constant and equal to the unknown force to be measured F\,, times the moment arm of the balance beam L\,, so \tau(t) = FL\,. When the oscillatory motion of the balance dies out, the deflection will be proportional to the force: :\theta = FL/\kappa\, To determine F\, it is necessary to find the torsion spring constant \kappa\,.
|
|
The second lateral motion is an oscillatory combined roll and yaw motion called Dutch roll, perhaps because of its similarity to an ice-skating motion of the same name made by Dutch skaters; the origin of the name is unclear. The Dutch roll may be described as a yaw and roll to the right, followed by a recovery towards the equilibrium condition, then an overshooting of this condition and a yaw and roll to the left, then back past the equilibrium attitude, and so on. The period is usually on the order of 3–15 seconds, but it can vary from a few seconds for light aircraft to a minute or more for airliners. Damping is increased by large directional stability and small dihedral and decreased by small directional stability and large dihedral.
|
|
The star is an aging red giant of spectral type M3IIIab, currently on the asymptotic giant branch, having exhausted the hydrogen at its core and evolved away from the main sequence. It has been classified as a slow irregular variable, after being found to be slightly variable in 1969 by Olin J. Eggen. Its changes in brightness are complex, with two shorter changeable periods of 35–40 and 47–50 days due to the star's pulsations, and a longer period of 1500 days possibly due to the star's rotation or convectively induced oscillatory thermal (COT) mode. The star has expanded to 156 times the Sun's radius and it is radiating 2,848 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 3,485 K.
|
|
In contrast to normal pylons, the two carrying masts at both ends of the crossing are frequently equipped with flight safety lamps, and have stairways for easy access to the top. anchor portal of the River Usk crossing Overhead line crossings of rivers and straits with spans of over 2 km are frequently prohibitively expensive to build and operate; because of the danger of wind-induced oscillatory movements of the conductor cables, it is necessary either to install very large leader distances or to mount insulators between the conductors in the area of the span. Bundle conductors, which are used for almost all extra-high voltage lines, are more susceptible to oscillations from wind forces than single conductors. Therefore, single conductors must be used for the crossing section, which means the crossing section of the power line determines the maximum transmittable power.
|
|
This was not suspected until 1826, when Felix Savary in France, and later (1842) Joseph HenryJoseph Henry, "On induction from ordinary electricity; and on the oscillatory discharge", Proceedings of the American Philosophical Society, vol 2, pp.193–196, 17 June 1842 in the US noted that a steel needle placed close to the discharge does not always magnetise in the same direction. They both independently drew the conclusion that there was a transient oscillation dying with time.Blanchard, pp.415–416 Hermann von Helmholtz in 1847 published his important work on conservation of energyHermann von Helmholtz, Uber die Erhaltung der Kraft (On the Conservation of Force), G Reimer, Berlin, 1847 in part of which he used those principles to explain why the oscillation dies away, that it is the resistance of the circuit which dissipates the energy of the oscillation on each successive cycle.
|
|
Minerals with Na > K are known as natrojarosite. End member formation (jarosite and natrojarosite) is favoured by a low temperature environment, less than 100 °C, and is illustrated by the oscillatory zoning of jarosite and natrojarosite found in samples from the Apex Mine, Arizona, and Gold Hill, Utah. This indicates that there is a wide miscibility gap between the two end members,American Mineralogist (2007) 92:444-447 and it is doubtful whether a complete series exists between jarosite and natrojarosite. In hydroniumjarositeAmerican Mineralogist (2007) 92:1464-1473 the hydronium ion H3O+ can also substitute for K+, with increased hydronium ion content causing a marked decrease in the lattice parameter c, although there is little change in a.American Mineralogist (1965) 50:1595-1607 Hydroniumjarosite will only form from alkali- deficient solutions, as alkali-rich jarosite forms preferentially.
|
|
In further research on place cells, O’Keefe found evidence for a distinctive variation of temporal coding of information by the timing of action potentials in place cells, relative to an oscillatory EEG cycle known as the theta rhythm, as opposed to spike timing within a single cell. In a 1993 paper, he and Michael Recce demonstrated that place cells spike at different phases relative to theta rhythm oscillations in the local field potential of the hippocampus. As a rat enters the firing field of a place cell, the spiking starts at late phases of theta rhythm, and as the rat moves through the firing field, the spikes shift to earlier phases of the theta cycle. This effect has been replicated in numerous subsequent papers, providing evidence for the coding of sensory input by the timing of spikes.
|
|
The Set–Reset NOR latch example A simple example of metastability can be found in an SR NOR latch, when Set and Reset inputs are true (R=1 and S=1) and then both transition to false (R=0 and S=0) at about the same time. Both outputs Q and are initially held at 0 by the simultaneous Set and Reset inputs. After both Set and Reset inputs change to false, the flip-flop will (eventually) end up in one of two stable states, one of Q and true and the other false. The final state will depend on which of R or S returns to zero first, chronologically, but if both transition at about the same time, the resulting metastability, with intermediate or oscillatory output levels, can take arbitrarily long to resolve to a stable state.
|
|
Subthreshold oscillation frequency can vary, from few Hz to over 40 Hz, and their dynamic properties have been studied in detail in relation to neuronal activity coherence and timing in CNS, in particular with respect to the 10 Hz physiological tremor that controls motor execution, Theta rhythm in the entorhinal cortex,Alonso, A. andgwmw> Llinas, R. (1989) "Subthreshold Na+-dependent theta-like rhythmicity in entorhinal cortex layer II stellate cells". Nature, 342: 175-177., gamma band in cortical inhibitory interneurons and gamma band activity in cortical inhibitory interneuronsLlinas R. Grace, A.A. and Yarom, Y. (1991) " In vitro neurons in mammalian cortical layer 4 exhibit intrinsic oscillatory activity in the 10 to 50 Hz frequency range". PNAS, 88, 897-901 and in thalamus neurons.
|
|
Schreiner and Rasch (2017) proposed a model illustrating how the cueing beneficial effect on memory during sleep could function, which includes theta and gamma waves and sleep spindles. Increased theta activity represents the successful reestablishment of the memory after the cueing: if such an increase is observed, it means that the association between the cue and the memory trace is strong enough, and that the cue is presented in an effective way and time. Theta waves interacts with gamma activity, and - during NREM - this oscillatory theta-gamma produces the relocation of the memory representation, from the hippocampus to the cortex. On the other hand, sleep spindles increase occurs right after or in parallel to the theta augmentation, and is a necessary mechanism for the stabilization, the reinforcement and also the integration of the newly encoded memory trace.
|
|
Primidone's mechanism of tremor prevention has been shown significantly in controlled clinical studies. The benzodiazepine drugs such as diazepam and barbiturates have been shown to reduce presentation of several types of tremor, including the essential variety. Controlled clinical trials of gabapentin yielded mixed results in efficacy against essential tremor while topiramate was shown to be effective in a larger double-blind controlled study, resulting in both lower Fahn- Tolosa-Marin tremor scale ratings and better function and disability as compared to placebo. It has been shown in two double-blind controlled studies that injection of botulinum toxin into muscles used to produce oscillatory movements of essential tremors, such as forearm, wrist and finger flexors, may decrease the amplitude of hand tremor for approximately three months and that injections of the toxin may reduce essential tremor presenting in the head and voice.
|
|
In a first author paper published in Science, Giocomo found that grid cells exhibit differences in frequency of subthreshold membrane potential oscillations in the entorhinal cortex across the dorsal to ventral axis. These findings are in line with the Burgess and O’Keefe Model such that differences in the frequency of subthreshold somatic oscillations results in differences in spacial frequency of grid cell fields. Giocomo further explored the differences in intrinsic properties of medial entorhinal cortical grid cells across the dorsal to ventral axis and, in 2008, published another first author paper outlining how experimental data regarding the physiology of grid cells can be understood in the framework of two possible computational models of grid cells. She concluded that, taking into account the experimental data, both the attractor dynamics and oscillatory interference models help to explain the properties of grid cell firing in the entorhinal cortex.
|
|
TRACE image of a coronal arcade Wave and oscillatory phenomena are observed in the hot plasma of the corona mainly in EUV, optical and microwave bands with a number of spaceborne and ground-based instruments, e.g. the Solar and Heliospheric Observatory (SOHO), the Transition Region and Coronal Explorer (TRACE), the Nobeyama Radioheliograph (NoRH, see the Nobeyama radio observatory). Phenomenologically, researchers distinguish between compressible waves in polar plumes and in legs of large coronal loops, flare-generated transverse oscillations of loops, acoustic oscillations of loops, propagating kink waves in loops and in structures above arcades (an arcade being a close collection of loops in a cylindrical structure, see image to right), sausage oscillations of flaring loops, and oscillations of prominences and fibrils (see solar prominence), and this list is continuously updated. Coronal seismology is one of the aims of the Atmospheric Imaging Assembly (AIA) instrument on the Solar Dynamics Observatory (SDO) mission.
|
|
Baltasar Mena Iniesta (born in 1942) is a Spanish-born Mexican mechanical engineer specialized in Rheology. He has been laureated with Mexico's National Prize for Arts and Sciences (1997), UNESCO Science Prize (2001), and has chaired both the International Committee on Rheology (1984–88) and the Mexican Society of Rheology (1976–97). Mena graduated with a bachelor's degree in Mechanical Engineering from the National Autonomous University of Mexico (UNAM, 1964); specialized in Fluid Mechanics at the University of Toulouse (France, 1967); and earned both a master's degree and a Ph.D in Mechanical Engineering from Brown University (United States, 1969–73), where he also received the Brown Engineering Alumni Medal in 2000. He has developed several patents, including an oscillatory die for polymer extrusion used by the henequen industry in the Yucatan peninsula and an hexagonal solar-powered grain elevator used in Mexico, India and Southeast Asia.
|
|
The verge stops the escape wheel by catching one of its teeth with a pallet, say the top pallet for the purpose of the following explanation. The motion of the verge subsequently disengages the top pallet from the escape wheel, allowing the latter to rotate freely for a brief duration until it comes into contact with the bottom pallet which will have moved in its way to catch another of its teeth thus stopping it again. The rotation of the verge then changes direction and disengages on its way back the bottom pallet from the escape wheel, which then rotates freely until coming into contact with the top pallet once again, completing a cycle. The escape wheel in turn provides an impulse to the verge every time it is released from a pallet, replacing the energy lost by the latter due to friction and therefore allowing its continued oscillatory motion.
|
|
In 1971, Varchenko proved that a family of complex quasi- projective algebraic sets with an irreducible base form a topologically locally trivial bundle over a Zariski open subset of the base. This statement, conjectured by Oscar Zariski, had filled up a gap in the proof of Zariski's theorem on the fundamental group of the complement to a complex algebraic hypersurface published in 1937. In 1973, Varchenko proved René Thom's conjecture that a germ of a generic smooth map is topologically equivalent to a germ of a polynomial map and has a finite dimensional polynomial topological versal deformation, while the non-generic maps form a subset of infinite codimension in the space of all germs. Varchenko was among creators of the theory of Newton polygons in singularity theory, in particular, he gave a formula, relating Newton polygons and asymptotics of the oscillatory integrals associated with a critical point of a function.
|
|
Ideally, artificial numerical dissipation needs to be added only in the vicinity of shocks or other sharp features, and regions of smooth flow must be left unmodified. These schemes have proven to be stable and accurate even for problems containing strong shock waves. Some of the well-known classical shock-capturing methods include the MacCormack method (uses a discretization scheme for the numerical solution of hyperbolic partial differential equations), Lax–Wendroff method (based on finite differences, uses a numerical method for the solution of hyperbolic partial differential equations), and Beam–Warming method. Examples of modern shock- capturing schemes include higher-order total variation diminishing (TVD) schemes first proposed by Harten, flux-corrected transport scheme introduced by Boris and Book, Monotonic Upstream-centered Schemes for Conservation Laws (MUSCL) based on Godunov approach and introduced by van Leer, various essentially non-oscillatory schemes (ENO) proposed by Harten et al.
|
|
Although these symptoms may not be readily apparent in well-rested patients, weakness can usually be induced with exercise of the commonly affected muscles (e.g. by having the patient look upward for about 60 seconds). In 75% of MG cases, the initial manifestation is in the eye. Within 2 years, 80% of patients with ocular onset of MG will progress to involve other muscle groups, thereby developing generalized MG. If MG is confined to the ocular muscles for more than 3 years, there is a 94% likelihood that the symptoms will not worsen or generalize. Aside from asymmetric ptosis (which becomes worse with fatigue, sustained upgaze, and at the end of the day) and variable limitation of extraocular muscles/diplopia, other clinical signs of ocular MG include gaze-evoked nystagmus (rapid, involuntary, oscillatory motion of the eyeball) and Cogan’s lid twitch (upper lid twitch present when patient looks straight ahead after looking down for 10–15 seconds).
|
|
Paulsson's lab has made major contributions to the development of experimental techniques for counting plasmids, to extend his previous work on the mathematical aspects of plasmid replication as well as theoretical work on the stochastic processes on gene expression and copy number control and work on muti-level selection by using experimental evolution. His most influential publication is the analysis of all previous noise data and interpretations in one unified framework, which later guided many experimental approaches. More recent results include the effects of partition in phenotypic variability, the details of the stochastic processes that underlie gene expression noise and the limitations of the usual experimental approaches and the fundamental limits of feedback as a noise control mechanism. This set of interests led Paulsson to examine the repressilator, a synthetic gene regulatory network that was designed from scratch to oscillate and reported in 2000A Synthetic Oscillatory Network of Transcriptional Regulators; Michael Elowitz and Stanislas Leibler; Nature.
|
|
Known as the overdamped oscillator model, since it also models the damped CDW response to oscillatory (ac) electric fields, this picture accounts for the scaling of the narrow-band noise with CDW current above threshold. However, since impurities are randomly distributed throughout the crystal, a more realistic picture must allow for variations in optimum CDW phase φ with position - essentially a modified sine-Gordon picture with a disordered washboard potential. This is done in the Fukuyama-Lee-Rice (FLR) model, in which the CDW minimizes its total energy by optimizing both the elastic strain energy due to spatial gradients in φ and the pinning energy. Two limits that emerge from FLR include weak pinning, typically from isoelectronic impurities, where the optimum phase is spread over many impurities and the depinning field scales as ni2 (ni being the impurity concentration) and strong pinning, where each impurity is strong enough to pin the CDW phase and the depinning field scales linearly with ni.
|
|
Tempestite deposits are very useful for aiding in paleoecological and paleogeographical interpretations. As storms that generate tempestite deposits can only form in between 5 degrees and 20 degrees north and south latitude (with even the largest 1000 year storm only being preserved upwards of 35 degrees latitude), accurate recognition of a tempestite deposit within the rock record allows for confident interpretation of a range of latitudes. Since hummocky cross stratification forms during the combined flow and waning oscillatory flow current regimes, the preserved amplitudes of their hummocks and swales are reflective of the storm intensity. Once it is understood where the deposit in question was deposited relative to the paleo-shoreline, which can usually be done using the ichnological data preserved in the same location, the hummock amplitudes/wavelengths, grainsize (decreases with increase in paleo water depth), and bedding thickness (decreases with increase in paleo water depth) can be used to estimate the storm intensity/energy.
|
|
A further level of integration of shaft rotations by either electronic means or by mechanical means, such as a Ball-and-disk integrator, can record the displacement or distance traveled, this latter mechanical method being used by early guidance systems prior to the availability of suitable digital computers. In most implementations of the PIGA the gyroscope itself is cantilevered on the end of the pendulum arm to act as the pendulous mass itself. Up to three such instruments may be required for each dimension of an INS with the three accelerometers mounted orthogonally generally on a platform stabilized gyroscopically within a system of gimbals. Image:PIGA_accelerometer_1.png A critical requirement for accuracy is low static friction (stiction) in the bearings of the pendulum; this is achieved by various means ranging from double ball bearing with a superimposed oscillatory motion to dither the bearing above its threshold or through the use of gaseous or fluid bearings or by the alternative method of floating the gyroscope in a fluid and restraining the residual mass by jewel bearings or electromagnetic means.
|
|
The discovery of this oscillatory behavior > is thus another reinforcement of the Standard Model's durability ... > > CDF physicists have previously measured the rate of the matter-antimatter > transitions for the B meson, which consists of the heavy bottom quark bound > by the strong nuclear interaction to a strange antiquark. Now they have > achieved the standard for a discovery in the field of particle physics, > where the probability for a false observation must be proven to be less than > about 5 in 10 million (). For CDF's result the probability is even smaller, > at 8 in 100 million Ronald Kotulak, writing for the Chicago Tribune, called the particle "bizarre" and stated that the meson "may open the door to a new era of physics" with its proven interactions with the "spooky realm of antimatter". On 14 May 2010, physicists at the Fermi National Accelerator Laboratory reported that the oscillations decayed into matter 1% more often than into antimatter, which may help explain the abundance of matter over antimatter in the observed Universe.
|
|
In late April, a well-developed tropical wave began developing east of Chuuk Lagoon. Tracking westward, the easterly wave was analyzed to have organized into a tropical depression by 0000 UTC on April 29. Twelve hours later, Iris was estimated to have strengthened into a tropical storm. At roughly the same time, a vessel in the vicinity of the storm reported winds in excess of 65 km/h (40 mph), prompting the Guam Fleet Weather Center to initiate reconnaissance flights into the cyclone. Midday on April 30, Iris intensified into the equivalent of a modern-day typhoon as it moved in a slightly oscillatory path towards the Philippines. After a slight fluctuation in intensity during the overnight hours of May 1, Iris rapidly intensified to reach its peak intensity with a minimum pressure of 909 mbar (hPa; 26.85 inHg) and maximum sustained winds of 280 km/h (175 mph) early on May 4, making it the equivalent of a Category 5 super typhoon; at the time this was the first confirmed instance of a typhoon reaching such intensities.
|
|
Copula has many applications in the area of medicine, for example, # Copula has been used in the field of magnetic resonance imaging (MRI), for example, to segment images, to fill a vacancy of graphical models in imaging genetics in a study on schizophrenia, and to distinguish between normal and Alzheimer patients. # Copula has been in the area of brain research based on EEG signals, for example, to detect drowsiness during daytime nap, to track changes in instantaneous equivalent bandwidths (IEBWs), to derive synchrony for early diagnosis of Alzheimer's disease, to characterize dependence in oscillatory activity between EEG channels, and to assess the reliability of using methods to capture dependence between pairs of EEG channels using their time-varying envelopes. Copula functions have been successfully applied to the analysis of neuronal dependencies and spike counts in neuroscience . #A copula model has been developed in the field of oncology, for example, to jointly model genotypes, phenotypes, and pathways to reconstruct a cellular network to identify interactions between specific phenotype and multiple molecular features (e.g.
|
|
He established the theorem of instability for the equations of a perturbed motion. Working on the perturbations of stable motions of Hamiltonian system he formulated and proved the theorem of the properties of the Poincaré variational equations that states: “If the unperturbed motion of a holonomic potential system is stable, then, first, the characteristic numbers of all solutions of the variational equations are equal to zero, second, these equations are regular in the sense of Lyapunov and are reduced to a system of equations with constant coefficients and have a quadratic integral of definite sign”. The Chetaev's theorem generalizes the Lagrange's theorem on an equilibrium and the Poincaré–Lyapunov theorem on a periodic motion. According to the theorem, for a stable unperturbed motion of a potential system, an infinitely near perturbed motion has an oscillatory, wave-like, character. # Chetaev’s method of constructing Lyapunov functions as a coupling (combination) of first integrals. The previous result gave rise to and substantiated the Chetaev’s concept of constructing Lyapunov functions using first integrals initially implemented in his famous book “Stability of Motion” as a coupling of first integrals in quadratic form .
|
|
The Gibbs phenomenon is also closely related to the principle that the decay of the Fourier coefficients of a function at infinity is controlled by the smoothness of that function; very smooth functions will have very rapidly decaying Fourier coefficients (resulting in the rapid convergence of the Fourier series), whereas discontinuous functions will have very slowly decaying Fourier coefficients (causing the Fourier series to converge very slowly). Note for instance that the Fourier coefficients 1, −1/3, 1/5, ... of the discontinuous square wave described above decay only as fast as the harmonic series, which is not absolutely convergent; indeed, the above Fourier series turns out to be only conditionally convergent for almost every value of x. This provides a partial explanation of the Gibbs phenomenon, since Fourier series with absolutely convergent Fourier coefficients would be uniformly convergent by the Weierstrass M-test and would thus be unable to exhibit the above oscillatory behavior. By the same token, it is impossible for a discontinuous function to have absolutely convergent Fourier coefficients, since the function would thus be the uniform limit of continuous functions and therefore be continuous, a contradiction.
|
|
For example, when you see a red ball roll by, cells sensitive to movement fire in the medial temporal cortex, while cells sensitive to color, shape and location fire in other areas. Despite all this distinct neuronal firing, you don't perceive the ball as separated by shape, movement and color perceptions; you experience an integrated experience with all these components occurring together. The question of how these elements are combined is the essence of the binding problem, a central focus of research into the late 1990s. A number of possible mechanisms were envisaged, including grandmother cells responding to specific conjunctions of features that uniquely identify a particular object; local cell assemblies onto which the pathways from different feature maps converge, perhaps with adjustable connections allowing flexible routing of signals; a serial scan of different spatial areas selected by an adjustable attention window, conjoining the features that each contains and excluding features from adjacent areas; detection of temporal contiguity – parts and properties whose onset, offset or motion coincide probably belong to the same object synchronised firing of cells responding to features of the same object, perhaps assisted by oscillatory neural activity.
|
|