The temperature gradients in the granular ice layer, caused by solar radiation, also play an important role in the onset of the saltation process [movement of particles over an uneven surface].
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Evidence exists for various forms of saltation in a variety of organisms.
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Eimer, M., B. Foster, and J. Vibell. "Cutaneous Saltation within and across Arms: A New Measure of the Saltation Illusion in Somatosensation." Percept Psychophys 67.3 (2005) 458-68. Web. Visual cues—light flashes placed at particular locations along the arm—can influence the cutaneous rabbit illusion.
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This difference is related to saltation. Other characteristics related to hopping locomotion include a long, but rather thin tail.
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They are all capable of saltation (jumping while in a bipedal stance), a feature that is most highly evolved in the desert-dwelling jerboas.
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Other animals, such as a horse when galloping, or an inchworm, alternate between their front and back legs. In saltation (hopping) all legs move together, instead of alternating. As a main means of locomotion, this is usually found in bipeds, or semi-bipeds. Among the mammals saltation is commonly used among kangaroos and their relatives, jerboas, springhares, kangaroo rats, hopping mice, gerbils, and sportive lemurs.
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Certain tendons in the hind legs of kangaroos are very elastic, allowing kangaroos to effectively bounce along conserving energy from hop to hop, making saltation a very energy efficient way to move around in their nutrient poor environment. Saltation is also used by many small birds, frogs, fleas, crickets, grasshoppers, and water fleas (a small planktonic crustacean). Most animals move in the direction of their head. However, there are some exceptions.
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Traction is the geologic process whereby a current transports larger, heavier rocks by rolling or sliding them along the bottom. Thus, the grains and clasts interact with the substratum during transport. By contrast, saltation, a related sediment transport process, moves grains across the bottom by bouncing or hopping. The actual current carries the sediment load in traction and saltation flows, whereas downslope movement under the force of gravity carries the sediment in gravity flows.
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Bateman RM, WA DiMichele. (2002). Generating and filtering major phenotypic novelties: neoGoldschmidtian saltation revisited. pp. 109–159 in QCB Cronk, RM Bateman, JA Hawkins, eds. Developmental genetics and plant evolution.
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In E. I. Svensson & R. Calsbeek eds. (2012). The Adaptive Landscape in Evolutionary Biology. Oxford University Press. According to Norrström (2006) there is evidence for saltation in some cases of mimicry.
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Evidence of phenotypic saltation has been found in the centipedeMinelli, A, Chagas Junior, A, & Edgecombe, G D. (2009). Saltational evolution of trunk segment number in centipedes. Evolution & development. 11: 318-322.
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Saltation of sand In geology, saltation (from Latin saltus, "leap") is a specific type of particle transport by fluids such as wind or water. It occurs when loose materials are removed from a bed and carried by the fluid, before being transported back to the surface. Examples include pebble transport by rivers, sand drift over desert surfaces, soil blowing over fields, and snow drift over smooth surfaces such as those in the Arctic or Canadian Prairies.
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The University of California in Berkeley observed an adult excitable delma in captivity; without any stimulus the delma was filmed jumping more than 30 times. The jumps reached heights of 11 to 15 cm and lasted 0.41 to 0.45 seconds from initial lift to impact. The excitable delma moves through the different ecosystems it inhabits in a locomotor motion known as saltation. Saltation is common in limbless vertebrates, and in the pygopodids family is a behavioral response to predation.
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These particles are accelerated by the fluid, and pulled downward by gravity, causing them to travel in roughly ballistic trajectories. If a particle has obtained sufficient speed from the acceleration by the fluid, it can eject, or splash, other particles in saltation, which propagates the process. Depending on the surface, the particle could also disintegrate on impact, or eject much finer sediment from the surface. In air, this process of saltation bombardment creates most of the dust in dust storms.
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Saltation normally lifts sand-size particles no more than one centimeter above the ground and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation. The grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert.
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Bed-material load is composed of larger grains than any of the other loads. The rate in which grains travel is dependent on the transporting capacity of the flow. Particles move by rolling, sliding, or saltation (bouncing or jumping of grains) at velocities less than that of the surrounding flow. Rolling is the primary mode of transport in gravel-bed streams, while saltation in which grains hop over the bed in a series of low trajectories is largely restricted to sands and small gravels.
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The resulting powder avalanche contained a central layer of which scientists were unaware. Known as the saltation layer, it was primarily responsible for the destruction of buildings. As new snow fell, the melt-crust became unstable until, on 23 February at 3:59 pm, it failed and caused an enormously powerful powder avalanche to crash down the mountainside, picking up more and more snow as it went. There was also 120 km//hour winds which caused the saltation layer of snow to move causing this disaster.
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The illusion was discovered by Frank Geldard and Carl Sherrick of Princeton University, in the early 1970s, and further characterized by Geldard (1982) and in many subsequent studies. Geldard and Sherrick likened the perception to that of a rabbit hopping along the skin, giving the phenomenon its name. While the rabbit illusion has been most extensively studied in the tactile domain, analogous sensory saltation illusions have been observed in audition and vision. The word "saltation" refers to the leaping or jumping nature of the percept.
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On the Origin of Species. p. 471 From 1860 to 1880 saltation had a minority interest but by 1890 had become a major interest to scientists.Gregory Radick. (2008). The Simian Tongue: The Long Debate about Animal Language.
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Animation showing the global movement of dust from an Asian dust storm. As the force of wind passing over loosely held particles increases, particles of sand first start to vibrate, then to move across the surface in a process called saltation. As they repeatedly strike the ground, they loosen and break off smaller particles of dust which then begin to travel in suspension. At wind speeds above that which causes the smallest to suspend, there will be a population of dust grains moving by a range of mechanisms: suspension, saltation and creep.
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It has been suggested that the extant analogues most similar to L. chanarensis are small bipedal mammals, which are often saltators. Three morphological characteristics in L. chanarensis fossils have been putatively cited as evidence of saltation in this taxon.
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Furthermore, the transition between gliding and flapping flight is not well-understood. More recent studies on basal pterosaur hindlimb morphology seem to vindicate a connection to Scleromochlus. Like this archosaur, basal pterosaur lineages have plantigrade hindlimbs that show adaptations for saltation.
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Cicadas, unlike other Auchenorrhyncha, are not adapted for jumping (saltation). They have the usual insect modes of locomotion, walking and flight. However, they do not walk or run well, and take to the wing to travel distances greater than a few centimetres.
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For example, in 1822 Étienne Geoffroy Saint-Hilaire argued that species could be formed by sudden transformations, or what would later be called macromutation. Darwin opposed saltation, insisting on gradualism in evolution as in geology. In 1864, Albert von Kölliker revived Geoffroy's theory.Sewall Wright. (1984).
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Stream capacity, while linked to stream competency through velocity, is the total quantity of sediment a stream can carry. Total quantity includes dissolved, suspended, saltation and bed loads. The movement of sediment is called sediment transport. Initiation of motion involves mass, force, friction and stress.
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Sand sheets are flat, gently undulating plots of sand surfaced by grains that may be too large for saltation. They form approximately 40 percent of aeolian depositional surfaces. Sand sheets exist where grain size is too large, or wind velocities too low, for dunes to form.
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In these dune systems, dune-forms (featuring dry podzols or undifferentiated soils) such as parabolic dunes and longitudinal dunes alternate with vast deflation planes (featuring wet podzols) with multiple moorland pools. All of the soils are sandy, transported by saltation. Its water is low in minerals and profoundly acid.
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Hamadas are produced by the wind removing the fine products of weathering: an aeolian process known as deflation. The finer-grained products are taken away in suspension, while the sand is removed through saltation and surface creep, leaving behind a landscape of gravel, boulders and bare rock.B.W. Sparks. Geomorphology, 2nd ed.
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567 et seq. # All evolutionary phenomena can be explained in a way consistent with known genetic mechanisms and the observational evidence of naturalists. # Evolution is gradual: small genetic changes, recombination ordered by natural selection. Discontinuities amongst species (or other taxa) are explained as originating gradually through geographical separation and extinction (not saltation).
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Bed load rolls slowly along the floor of the stream. These include the largest and heaviest materials in the stream, ranging from sand and gravel to cobbles and boulders. There are two main ways to transport bed load: traction and saltation. Traction describes the “scooting and rolling” of particles along the bed (Ritter, 2006).
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What Makes Biology Unique?: Considerations on the Autonomy of a Scientific Discipline. Cambridge University Press; 1 edition Saltation was originally denied by the "modern synthesis" school of neo- Darwinism which favoured gradual evolution but has since been accepted due to recent evidence in evolutionary biology (see the current status section).Bateman, R. M. and DiMichele, W. A. (1994).
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William Bateson's 1894 book Materials for the Study of Variation, Treated with Especial Regard to Discontinuity in the Origin of Species marked the arrival of mutationist thinking, before the rediscovery of Mendel's laws. He examined discontinuous variation (implying a form of saltation) where it occurred naturally, following William Keith Brooks, Galton, Thomas Henry Huxley and St. George Jackson Mivart.
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When suspended sediment is returned to the ground, granules physically impact the grounded grains. Due to physics principles, the grounded grains are receiving energy from the once suspended sediment. This impact leads to the dislodgement of grounded grains or creep of coarser grains. Saltation is the movement of grains being picked up by the wind and dropped in a cycling repetitive motion.
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Michelle Lampl is an American physician scientist, academic, and author. She is a distinguished professor and the Director of Emory University’s Center for the Study of Human Health. She is also the co-Director of the Emory-Georgia Tech Predictive Health Institute. Lampl is internationally recognized for her work identifying normal human growth to be a pattern of saltation and stasis.
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The process of geological saltation is quite important on Mars as a mechanism for adding particulates to the atmosphere. Saltating sand particles have been observed on the MER Spirit rover.G. Landis, et al., "Dust and Sand Deposition on the MER Solar Arrays as Viewed by the Microscopic Imager," 37th Lunar and Planetary Science Conference, Houston TX, March 13–17, 2006.
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It may be due to "saltation" - ballistic movement of sand grains which travel further in the weaker Mars gravity. The lee fronts of the dunes in this region move on average 0.5 meters per year (though the selection may be biased here as they only measured dunes with clear lee edges to measure) and the ripples move on average 0.1 meters per year.
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Small particles may be held in the atmosphere in suspension. Upward currents of air support the weight of suspended particles and hold them indefinitely in the surrounding air. Typical winds near Earth's surface suspend particles less than 0.2 millimeters in diameter and scatter them aloft as dust or haze. Saltation is downwind movement of particles in a series of jumps or skips.
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When a slab avalanche forms, the slab disintegrates into increasingly smaller fragments as the snow travels downhill. If the fragments become small enough the outer layer of the avalanche, called a saltation layer, takes on the characteristics of a fluid. When sufficiently fine particles are present they can become airborne and, given a sufficient quantity of airborne snow, this portion of the avalanche can become separated from the bulk of the avalanche and travel a greater distance as a powder snow avalanche.SATSIE Final Report (large PDF file – 33.1 Mb), page 94, October 1, 2005 to May 31, 2006 Scientific studies using radar, following the 1999 Galtür avalanche disaster, confirmed the hypothesis that a saltation layer forms between the surface and the airborne components of an avalanche, which can also separate from the bulk of the avalanche.
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Saltating sand acquires a negative charge relative to the ground which in turn loosens more sand particles which then begin saltating. This process has been found to double the number of particles predicted by previous theory.Electric Sand Findings, University of Michigan Jan. 6, 2008 This is significant in meteorology because it is primarily the saltation of sand particles which dislodges smaller dust particles into the atmosphere.
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In biology, saltation (from Latin, saltus, "leap") is a sudden and large mutational change from one generation to the next, potentially causing single- step speciation. This was historically offered as an alternative to Darwinism. Some forms of mutationism were effectively saltationist, implying large discontinuous jumps. Speciation, such as by polyploidy in plants, can sometimes be achieved in a single and in evolutionary terms sudden step.
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In that sense, it includes the termination of transport by saltation or true bedload transport. Settling is the falling of suspended particles through the liquid, whereas sedimentation is the termination of the settling process. In estuarine environments, settling can be influenced by the presence or absence of vegetation. Trees such as mangroves are crucial to the attenuation of waves or currents, promoting the settlement of suspended particles.
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Sand granules are transported in three ways: suspension, saltation, and creep. Suspended grains are fine granules that can easily be picked up by wind and carried for variable distances. Most visitors to coastal beach environments can attest to having sand blown in their face or leaving with a gritty feeling on their skin. This is due to fine sediment suspended in the moisture rich air.
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Saltation is responsible for the majority (50-70%) of wind erosion, followed by suspension (30-40%), and then surface creep (5-25%). Wind erosion is much more severe in arid areas and during times of drought. For example, in the Great Plains, it is estimated that soil loss due to wind erosion can be as much as 6100 times greater in drought years than in wet years.
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Dust storm approaching Spearman, Texas April 14, 1935. Dust storm in Amarillo, Texas. FSA photo by Arthur Rothstein (1936) A massive sand storm cloud is about to envelop a military camp as it rolls over Al Asad, Iraq, just before nightfall on April 27, 2005. Particles are transported by winds through suspension, saltation (skipping or bouncing) and creeping (rolling or sliding) along the ground.
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Many Auchenorrhyncha including representatives of the cicadas, leafhoppers, treehoppers, planthoppers, and froghoppers are adapted for jumping (saltation). Treehoppers, for example, jump by rapidly depressing their hind legs. Before jumping, the hind legs are raised and the femora are pressed tightly into curved indentations in the coxae. Treehoppers can attain a take-off velocity of up to 2.7 metres per second and an acceleration of up to 250 g.
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Some of these geneticists developed it into the mutation theory of evolution.Peter J. Bowler. (2003). Evolution: The History of an Idea. University of California Press. pp. 265–270 There was also a debate over accounts of the evolution of mimicry and if they could be explained by gradualism or saltation. The geneticist Reginald Punnett supported a saltational theory in his book Mimicry in Butterflies (1915).Reginald Punnett. (1915). Mimicry in Butterflies.
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Megaripple/dune, formed in the upper flow regime, from Utah. There are two kinds of flow structures: bidirectional (multiple directions, back-and-forth) and unidirectional. Flow regimes in single-direction (typically fluvial) flow, which at varying speeds and velocities produce different structures, are called bedforms. In the lower flow regime, the natural progression is from a flat bed, to some sediment movement (saltation etc.), to ripples, to slightly larger dunes.
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A quokka weighs and is long with a tail, which is quite short for a macropod. It has a stocky build, well developed hind legs, rounded ears, and a short, broad head. Its musculoskeletal system was originally adapted for terrestrial bipedal saltation, but over its evolution, its system has been built for arboreal locomotion. Although looking rather like a very small kangaroo, it can climb small trees and shrubs up to .
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In rivers, this process repeats continually, gradually eroding away the river bed, but also transporting-in fresh material from upstream. The speed at which the flow can move particles by saltation is given by the Bagnold formula. Suspension generally affects small particles ('small' means ~70 micrometres or less for particles in air). For these particles, vertical drag forces due to turbulent fluctuations in the fluid are similar in magnitude to the weight of the particle.
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Seen from above, a sandstorm might not look as strong as it really is. Namib Desert (2017) A dust storm, also called sandstorm, is a meteorological phenomenon common in arid and semi-arid regions. Dust storms arise when a gust front or other strong wind blows loose sand and dirt from a dry surface. Fine particles are transported by saltation and suspension, a process that moves soil from one place and deposits it in another.
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A study from 2008 finds that the initial saltation of sand particles induces a static electric field by friction. Saltating sand acquires a negative charge relative to the ground which in turn loosens more sand particles which then begin saltating. This process has been found to double the number of particles predicted by previous theories. Particles become loosely held mainly due to a prolonged drought or arid conditions, and high wind speeds.
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Through a process known as saltation the sand was eventually blown onto the area now known as Jockey's Ridge where something caused it to begin building the dune system. At one time, the dunes of the Outer Banks extended all the way to the southern end of Virginia. Many mariners used the ridge as a landmark in navigation of the area for coastal exploration in the 16th century.Biggs, Jr., W. and Parnell, J. 1989.
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Sand dunes can have a negative impact on humans when they encroach on human habitats. Sand dunes move via a few different means, all of them helped along by wind. One way that dunes can move is by saltation, where sand particles skip along the ground like a bouncing ball. When these skipping particles land, they may knock into other particles and cause them to move as well, in a process known as creep.
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Beaches are the result of wave action by which waves or currents move sand or other loose sediments of which the beach is made as these particles are held in suspension. Alternatively, sand may be moved by saltation (a bouncing movement of large particles). Beach materials come from erosion of rocks offshore, as well as from headland erosion and slumping producing deposits of scree. A coral reef offshore is a significant source of sand particles.
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Lampl M, Thompson AL. (2007) Growth chart curves do not describe individual growth biology. American Journal of Human Biology 19:643-53. Lampl collaborated with Michael Johnson to develop mathematical approaches to investigate and quantify discontinuous vs pulsatile biological signals. Their work initiated mathematical interrogation of the saltation and stasis model of growth in humans, permitting statistical comparisons between different biological models of growth by formal goodness-of-fit comparisons between continuous, pulsatile and discontinuous processes.
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In the early 20th century a mechanism of saltation was proposed as large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection. It was popular with early geneticists such as Hugo de Vries, who along with Carl Correns helped rediscover Gregor Mendel's laws of inheritance in 1900, William Bateson, a British zoologist who switched to genetics, and early in his career Thomas Hunt Morgan.
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Zalambdalestes (meaning much-like-lambda robber) was a eutherian mammal, most likely not a placental due to the presence of an epipubic bone, living during the Upper Cretaceous in Mongolia. Life restoration of Z. lechei Zalambdalestes was a hopping animal with a long snout, long teeth, a small brain and large eyes. It was about long, with a head only long. It had strong front paws and even stronger rear ones, sharing specializations to saltation similar to those of modern rabbits.
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Unlike modern macropodids, which hop (either bipedally or quadrupedally), sthenurines seem to have abandoned saltation as a means of locomotion. Their comparatively inflexible spines, robust hindlimb and pelvic elements, and the lack of capacity for rapid hopping suggest that these animals walked bipedally, somewhat like hominids, even converging with those primates in details of their pelvic anatomy. Furthermore, their hooved single digits and metatarsal anatomy suggest that unlike their plantigrade relatives, sthenurines were unguligrade, walking on the tips of their "toes".
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Darwin's cousin, Francis Galton, considered Darwin's evidence for evolution, and came to an opposite conclusion about the type of variation on which natural selection must act. He carried out his own experiments and published a series of papers and books setting out his views. Already by 1869 when he published Hereditary Genius, he believed in evolution by saltation. In his 1889 book Natural Inheritance he argued that natural selection would benefit from accepting that the steps need not, as Darwin had stated, be minute.
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Global dust storms (area > 106 km2 ) occur on average once every 3 Martial years. Observations showed that larger dust storms are usually the result of merging smaller dust storms, but the growth mechanism of the storm and the role of atmospheric feedbacks are still not well understood. Although it is thought that Martian dust can be entrained into the atmosphere by processes similar to Earth's (e.g. saltation), the actual mechanisms are yet to be verified, and electrostatic or magnetic forces may also play in modulating dust emission.
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It can be sometimes be confused as an escape response but this is not the function of this behaviour. Saltation is the locomotion motion of side-pushing, and the jumping in delmas allows them to move the body at a greater wave-speed. The locomotion movement begins in the tail, and the lizard has evolved to propel itself forward at a 45 degree angle. Another defense mechanism of the delma species, is the capability to vocalize sounds like other lizards in the pygopodids family.
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The leaping of the youths over fire (sobótka) must be a custom derived from remote antiquity. Jan Kochanowski, who died in 1584, mentions it in a song from an ancient tradition. Varro and Ovid relate, that in the Palilia, celebrated in honour of the goddess Pales, on 20 April, the anniversary of the foundation of Rome, the young Romans leaped over burning bundles of hay. In modern Italy, this kind of saltation is continued by the name of Sabatina,"Włochy mają Sobótki pod imieniem Sabatina; znane są i w Niemczech." in: Oskar Kolberg.
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Once sediment transport begins, it continues via gravity and momentum: particles that fall out of the air typically impact the surface with enough force to dislodge further particles (called reptation). These impacts are separated in space by the saltation hop length of the traveling particles, which creates distinct areas of erosion and/or deposition. As time passes, the surface rises in areas with net deposition, and lowers in areas with net erosion, creating initial landforms. Larger aeolian landforms alter the surface wind field in patterns that promote their growth.
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In stream load transport, saltation is a bounce-like movement, occurring when large particles are suspended in the stream for a short distance after which they fall to the bed, dislodging particles from the house. The dislodged particles move downstream a short distance where they fall to the bed, again loosening bed load particles upon impact (Ritter, 2006). Dissolved and suspended load move with the natural stream flow, while the heavier bed load rolls across the floor of the stream. Increased suspended load gives this flooded stream its muddy color.
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Biology Direct 4: 46. In recent years there are some prominent proponents of saltation, including Carl Woese. Woese, and colleagues, suggested that the absence of RNA signature continuum between domains of bacteria, archaea, and eukarya constitutes a primary indication that the three primary organismal lineages materialized via one or more major evolutionary saltations from some universal ancestral state involving dramatic change in cellular organization that was significant early in the evolution of life, but in complex organisms gave way to the generally accepted Darwinian mechanisms.Roberts, E., A. Sethi, J. Montoya, C.R. Woese and Z. Luthey-Schulten. (2008).
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Gray squirrel (Sciurus carolinensis) in mid-leap Jumping (saltation) can be distinguished from running, galloping, and other gaits where the entire body is temporarily airborne by the relatively long duration of the aerial phase and high angle of initial launch. Many terrestrial animals use jumping (including hopping or leaping) to escape predators or catch prey—however, relatively few animals use this as a primary mode of locomotion. Those that do include the kangaroo and other macropods, rabbit, hare, jerboa, hopping mouse, and kangaroo rat. Kangaroo rats often leap 2 m and reportedly up to 2.75 m at speeds up to almost .
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Hjulstroms Diagram Bed armor is most often transported through entrainment, and more specifically suspension and saltation. Both of these processes involve moving the sediment both near and around the bed of a river. When a sediment is entrained it is being moved downstream through the forces between the layers of water around it, and once it settles it begins to create a layer on the bed of the river. This layer of sediment changes the hydrology of the river around it, as once this layer on the bottom is formed it affects the hydraulics of the river.
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For example, in 1822 Étienne Geoffroy Saint-Hilaire argued that species could be formed by sudden transformations, or what would later be called macromutation. Darwin opposed saltation, insisting on gradualism in evolution as in geology (uniformitarianism). In 1864, Albert von Kölliker revived Geoffroy's theory. In 1901 the geneticist Hugo de Vries gave the name "mutation" to seemingly new forms that suddenly arose in his experiments on the evening primrose Oenothera lamarckiana, and in the first decade of the 20th century, mutationism, or as de Vries named it mutationstheorie, became a rival to Darwinism supported for a while by geneticists including William Bateson, Thomas Hunt Morgan, and Reginald Punnett.
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He then introduced the 'swamping argument' to deny the possibility that an occasional monstrous individual, a saltation, could supply an escape from this state of affairs and give rise to a permanent adaptation. Jenkin made a mathematical calculation for his argument Jenkin made a mistake in his calculation stating the chances are “fifty to one” where it should have been “ten thousand to one”. He continued his essay with a melodramatic story to elaborate on his calculation Darwin agreed that a variation originating in a single individual would not spread across a population, and would invariably be lost. Darwin stated to his colleagues that he was always aware that “swamping” would stamp out saltations.
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Many evolutionary biologists agreed, and suggested that modern flatfishes anatomy arose as a result of saltation. The 2008 discovery of Heteronectes and Amphistium was considered a vindication of the viability of a gradual transition.Minard A. “Odd Fish Find Contradicts Intelligent-Design Argument”, National Geographic News 9/7/2008 Friedman suggested that Heteronectes and Amphistium did not rest completely on the sea floor like modern flatfishes. Instead, they might only held their tail to the sea floor and kept their head lifted into the water above, using one eye to watch for predators, while the other were used to look for prey in the mud below. Janvier P (2008), “Squint of the fossil flatfish”, Nature 454(7201): p.
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SCOPE was then used to construct a synthetic enzyme lineage, which was biochemically characterized to recapitulate the evolutionary divergence of two modern day enzymes. The rapid evolvability of chemical diversity in terpene synthases were demonstrated through processes akin to both Darwinian gradualism and saltation: some mutational pathways show steady, additive changes, whereas others show drastic jumps between contrasting product specificities with single mutational steps. Further, a metric was devised to describe the chemical distance of mutational steps to derive a chemical-based phylogeny relating sequence variation to chemical output. These examples establish SCOPE as a standardized method for the construction of synthetic gene libraries from close or distantly related parental sequences to identify functional novelty among the encoded proteins.
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Wind ripples on crescent-shaped sand dunes (Barchans) in Southwest Afghanistan (Sistan). ;Normal ripples: Also known as impact ripples, these occur in the lower part of the lower flow regime sands with grain sizes between 0.3-2.5 mm and normal ripples form wavelengths of 7-14 cm. Normal ripples have straight or slightly sinuous crests approximately transverse to the direction of the wind. ;Megaripples: These occur in the upper part of the lower flow regime where sand with bimodal particle size distribution forms unusually long wavelength of 1-25 m where the wind is not strong enough to move the larger particles but strong enough to move the smaller grains by saltation.
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A dust storm or sandstorm, a meteorological phenomenon common in arid and semi-arid regions, arises when a gust front passes or when the wind force exceeds the threshold value where loose sand and dust are removed from the dry surface. Particles are transported by saltation and suspension, causing soil erosion from one place and deposition in another. Sandstorm usually refers to dust storms in desert areas when, in addition to fine particles obscuring visibility, a considerable amount of larger sand particles moves closer to the surface. The term dust storm is more likely to be used when finer particles are blown long distances, especially when the dust storm affects urban areas.
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The cutaneous rabbit illusion (also known as cutaneous saltation and sometimes the cutaneous rabbit effect or CRE) is a tactile illusion evoked by tapping two or more separate regions of the skin in rapid succession. The illusion is most readily evoked on regions of the body surface that have relatively poor spatial acuity, such as the forearm. A rapid sequence of taps delivered first near the wrist and then near the elbow creates the sensation of sequential taps hopping up the arm from the wrist towards the elbow, although no physical stimulus was applied between the two actual stimulus locations. Similarly, stimuli delivered first near the elbow then near the wrist evoke the illusory perception of taps hopping from elbow towards wrist.
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Such movement mechanism is called saltation and it has been determined that the dunes at Nili Patera, under the existing wind conditions, are active and moving as a unit. Due to the thinner atmosphere of Mars, winds have to be approximately 10 times faster than those on Earth to cause sand movement. These high winds occur very rarely on Mars, but because of the thinner atmosphere and lower gravity of the planet, sand grains, once in motion, can move faster and to a longer distance than on Earth. It is theorised, that on Mars, once high winds initiate the movement of the sand particles, weaker winds can sustain the motion of the dune, due to the lower gravity of the planet and the lower resistance of the thinner atmosphere.
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This friction increases with the speed of the water and the roughness of the bed. Once loosened the smaller particles are actually held in suspension by the force of the flowing water, these suspended particles can scour the sides and bottom of the stream. The scouring action produces distinctive markings on streams beds such as ripple marks, fluting, and crescent marks.Coja Isabelle and Renard, Maurice (2002) Sedimentology (translation of Sédimentologie from French) Lisse, Exton, Pennsylvania, pages 143–144, The larger particles and even large rocks are scooted (dragged) along the bottom in a process known as traction which causes attrition, and are often "bounced" along in a process known as saltation where the force of the water temporarily lifts the rock particle which then crashes back into the bed dislodging other particles.
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Grain flows (sand avalanches) on the slip faces of sand dunes at Kelso in the Mojave desert, California. A grain flow is a type of sediment-gravity flow in which the supporting fluid, which can be either air or water, acts only as a lubricant, and grains within the flow remain in suspension due to grain-to- grain collisions that generate a dispersive pressure to prevent further settling. Grain flows are very common in aeolian settings as grain avalanches on the slip faces of sand dunes. By contrast, pure grain flows are rare in subaqueous settings, where the grains in a flow are generally held in suspension dominantly by traction, saltation, fluid turbulence and/or grain buoyancy when the grains are floating in the clay matrix of a mud flow.
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Presentation on imported dust in North American skies Large dust storm over Libya Atmospheric or wind-borne fugitive dust, also known as aeolian dust, comes from arid and dry regions where high velocity winds are able to remove mostly silt-sized material, deflating susceptible surfaces. This includes areas where grazing, ploughing, vehicle use, and other human activities have further destabilized the land, though not all source areas have been largely affected by anthropogenic impacts. One- third of the global land area is covered by dust-producing surfaces, made up of hyper-arid regions like the Sahara which covers 0.9 billion hectares, and drylands which occupy 5.2 billion hectares. Dust in the atmosphere is produced by saltation and sandblasting of sand-sized grains, and it is transported through the troposphere.
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