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Turtle

For other uses, see Turtle (disambiguation).
Families
Testudines, Chelonia

Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. The term turtle is usually used for the aquatic species, though aquatic fresh water turtles are also called terrapins. The term is sometimes used (esp. in North America) to refer to all members of the order, including tortoises, which are predominantly land-based. The order of Testudines includes both extant (living) and extinct species. About 300 species are alive today. Some species of turtles are highly endangered.

Description

All turtles have a protective shell around their bodies. The top part of the shell is called the carapace, the bottom is called the plastron, and the two are connected by a bridge. Some are known to be able to breathe through their rectums as well. Reference the Rheodytes leukops species.

Sea turtles grow to large sizes and live in the oceans in the temperate and tropical regions of Earth. Pond turtles (terrapins) are usually much smaller, while some land terrapins (tortoises) are as large as sea turtles. The sizes of turtles vary from a few centimetres (forest and jungle species) to two metres (the leatherback turtle and the Galapagos tortoise).

Turtles generally live a long time; some individuals are known to have lived longer than 150 years. The oldest tortoise on record is Tui Malila, known to have lived at least 188 years.

Sea turtles lay their eggs on dry sandy beaches. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Their albumen is white and will not coagulate when cooked because of the protein it contains which is different to that of bird eggs. Turtle eggs prepared to eat consist mainly of yolk. In some species, temperature of the egg during development determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male.

Although they spend large proportions of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. However, aquatic respiration in Australian freshwater turtles is currently being studied. Some species have large cloacal cavities lined with many finger-like projections. These projections, called "papillae", have a rich blood supply, and increase the surface area of the cloaca. The turtles can take up dissolved oxygen from the water through these papillae, in much the same way that fish use gills.

Turtles have a gelatinous substance in their upper and lower shell, called calipash and calipee respectively, the calipash being of a dull greenish and the calipee of a light yellow color.

Evolution

The first turtles are believed to have existed in the era of the dinosaurs, 200 million years ago. Their exact ancestry is disputed. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. All Anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles).

However, it was recently suggested that the Anapsid-like turtle skull may be due to convergent evolution rather than to anapsid descent. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa were broadly enough for constructing the cladogram. While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles.

Order Testudines - Turtles

Gulf Coast Box Turtle, Terrapene carolina major (Emydidae) A slider of genus Trachemys A Leatherback Sea Turtle. Photo credit: NOAA

Suborder Paracryptodira (extinct)

Suborder Cryptodira

Suborder Pleurodira


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Suborder Pleurodira. In 1887 the Michelson-Morley experiment, using an interferometer to attempt to detect the change in the speed of light caused by the Earth moving with respect to the aether, was a famous null result, showing that there really was no static, pervasive medium throughout space and through which the Earth moved as though through a wind. Suborder Cryptodira. This evolved into the luminiferous aether of the 19th century, but the idea was known to have significant shortcomings - specifically that if the Earth is moving through a material medium, the medium would have to be both extremely tenuous (because the earth is not being detectably slowed in its orbit), and extremely rigid (because vibrations propagate so fast). Suborder Paracryptodira (extinct)
. In the 17th century, theories of the nature of light had required the idea of an aethereal medium which would be the medium to convey waves of light (Newton relied on this idea to explain refraction and radiated heat). While the issue is far from resolved, most scientists now lean towards a Diapsid origin for turtles. This led to the development of the vacuum tube.

Re-analysis of prior phylogenies suggests that they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa were broadly enough for constructing the cladogram. A number of electrical properties become observable at this vacuum level, and this renewed interest in vacuum. All molecular studies have strongly upheld this new phylogeny, though some place turtles closer to Archosauria. The study of vacuum then lapsed until 1855 when Heinrich Geissler invented the mercury displacement pump and achieved a record vacuum of about 0.1 Torr. More recent phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. In 1654, Otto von Guericke conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been evacuated. However, it was recently suggested that the Anapsid-like turtle skull may be due to convergent evolution rather than to anapsid descent. Robert Boyle later conducted experiments on the properties of vacuum.

Most anapsids became extinct in the late Permian period, except procolophonoids and possibly the precursors of the testudines (turtles). Some people believe that although Torricelli produced the first vacuum, it was Blaise Pascal who recognized it for what it was. All Anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygoid arch). Following work by Galileo, Evangelista Torricelli argued in 1643 that there was a vacuum at the top of a mercury barometer. It was believed that they are the only surviving branch of the ancient clade Anapsida, which includes groups such as procolophonoids, millerettids, protorothyrids and pareiasaurs. Opposition to the idea of a vacuum existing in nature continued into the Scientific Revolution, with scholars such as Paolo Casati taking an anti-vacuist position. Their exact ancestry is disputed. This speculation became irrelevant after the Paris condemnations of Bishop Tempier, which required there to be no restrictions on the powers of God, which led to the conclusion that God could create a vacuum if he so wished.

The first turtles are believed to have existed in the era of the dinosaurs, 200 million years ago. There was much discussion of whether the air moved in quickly enough as the plates were separated, or, following William Burley whether a 'celestial agent' prevented the vacuum arising—that is, whether nature abhorred a vacuum. Turtles have a gelatinous substance in their upper and lower shell, called calipash and calipee respectively, the calipash being of a dull greenish and the calipee of a light yellow color. Medieval thought experiments into the idea of a vacuum considered whether a vacuum was present, if only for an instant, between two flat plates when they were rapidly separated. The turtles can take up dissolved oxygen from the water through these papillae, in much the same way that fish use gills. The absence of anything implied the absence of God, and hearkened back to the void prior to the story of creation in the book of Genesis. These projections, called "papillae", have a rich blood supply, and increase the surface area of the cloaca. In the Middle Ages, the idea of a vacuum was thought to be immoral or even heretical.

Some species have large cloacal cavities lined with many finger-like projections. Later Greek philosophers thought that a vacuum could exist outside the cosmos, but not inside it. However, aquatic respiration in Australian freshwater turtles is currently being studied. Similarly, Aristotle considered the creation of a vacuum impossible—nothing could not be something. Although they spend large proportions of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. He believed that all physical things were instantiations of an abstract Platonic ideal, and could not imagine an "ideal" form of a vacuum. In some species, temperature of the egg during development determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male. Plato found the idea of a vacuum inconceivable.

Turtle eggs prepared to eat consist mainly of yolk. Ancient Greek philosophers did not like to admit the existence of a vacuum, asking themselves "how can 'nothing' be something?". Their albumen is white and will not coagulate when cooked because of the protein it contains which is different to that of bird eggs. Historically, there has been much dispute over whether such a thing as a vacuum can exist. The eggs of the largest species are spherical, while the eggs of the rest are elongated. String theory is believed to be analogous to quantum field theory but one with a huge number of vacua - with the so-called anthropic landscape. Sea turtles lay their eggs on dry sandy beaches. If the theory is obtained by quantization of a classical theory, each stationary point of the energy in the configuration space gives rise to a single vacuum.

The oldest tortoise on record is Tui Malila, known to have lived at least 188 years. In free (non-interacting) quantum field theories, this state is analogous to the ground state of a quantum harmonic oscillator. Turtles generally live a long time; some individuals are known to have lived longer than 150 years. In quantum field theory and string theory, the term "vacuum" is used to represent the ground state in the Hilbert space, that is, the state with the lowest possible energy. The sizes of turtles vary from a few centimetres (forest and jungle species) to two metres (the leatherback turtle and the Galapagos tortoise). The best support for vacuum fluctuations is the Casimir effect. Pond turtles (terrapins) are usually much smaller, while some land terrapins (tortoises) are as large as sea turtles. Vacuum fluctuations may also be related to the so-called cosmological constant in the theory of gravitation, if indeed this entity were to be observed in nature on a macroscopic scale.

Sea turtles grow to large sizes and live in the oceans in the temperate and tropical regions of Earth. While most agree that this represents a significant part of particle physics, it is a concept that would benefit from a deeper understanding than currently available. Reference the Rheodytes leukops species. This is called vacuum fluctuation. Some are known to be able to breathe through their rectums as well. The lowest possible energy state is called the zero-point energy and consists of a seething mass of virtual particles that have brief existence. The top part of the shell is called the carapace, the bottom is called the plastron, and the two are connected by a bridge. More fundamentally, quantum mechanics predicts that vacuum energy can never be exactly zero.

All turtles have a protective shell around their bodies. Even the space between molecules is not a perfect vacuum. . Each atom exists as a probability function of space, which has a certain non-zero value everywheres in a given volume. Some species of turtles are highly endangered. Another reason that perfect vacuum is impossible is the Heisenberg uncertainty principle which states that no particle can ever have an exact position. About 300 species are alive today. If this soup of photons is in thermodynamic equilibrium with the walls, it can be said to have a particular temperature, as well as a pressure.

The order of Testudines includes both extant (living) and extinct species. One reason is that the walls of a vacuum chamber emit light in the form of black-body radiation: visible light if they are at a temperature of thousands of degrees, infrared light if they are cooler. in North America) to refer to all members of the order, including tortoises, which are predominantly land-based. Even an ideal vacuum, thought of as the complete absence of anything, will not in practice remain empty. The term is sometimes used (esp. 1913, p.720). The term turtle is usually used for the aquatic species, though aquatic fresh water turtles are also called terrapins. (See "Polar Magnetic Phenomena and Terrella Experiments", in The Norwegian Aurora Polaris Expedition 1902-1903 (publ.

Turtles are reptiles of the order Testudines (all living turtles belong to the crown group Chelonia), most of whose body is shielded by a special bony or cartilagenous shell developed from their ribs. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in "empty" space. Superfamily Pelomedusoidea. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. Superfamily Chelonioidea. He wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. Superfamily Kinosternoidea. In 1913, Norwegian explorer and physicist Kristian Birkeland may have been the first to predict that space is not only a plasma, but also contains "dark matter".

Superfamily Trionychoidea. The deep vacuum of space could make it an attractive environment for certain processes, for instance those that require ultraclean surfaces. Superfamily Testudinoidea. The idea of using this wind with a solar sail has been proposed for interplanetary travel. Spacecraft can be buffeted by solar winds, but planets are too massive to be affected. Beyond planetary atmospheres, the pressure from photons and other particles from the sun become significant.

[2]. Studies have discovered that some satellites retrieved from orbit are coated with a very thin layer of urine and fecal matter evidently released from Russian and US space missions. The atmosphere in Low Earth Orbit is increasingly being polluted with man-made debris. Most Earth satellites operate in this region, and they need to fire their engines every few days to maintain orbit.

In Low Earth Orbit (about 300 km altitude) the atmospheric density is still sufficient to produce significant drag on satellites. The density of gas decreases with distance from the object. Stars, planets and moons keep their atmosphere by gravitational attraction, so atmospheres have no firm boundary. Neither these photons nor the neutrinos produce a significant interaction with matter, so stars, planets and spacecraft move freely in this near perfect vacuum of interstellar space.

The current temperature is about 3 K, being merely 3 degrees above the absolute zero of temperature. All of the observable universe is also filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. A perfect vacuum is an ideal state that cannot practically be obtained in a laboratory, nor even in outer space, where there are a few hydrogen atoms per cubic centimeter at 10−14 Pascal or 10−16 Torr. The properties of the vacuum remain largely unknown.

It is cold and has no friction. Much of outer space has the density and pressure of an almost perfect vacuum. The lowest pressures currently achievable in laboratory are about 10-13 Pa. Vessels lined with a highly gas-permeable material such as palladium (which is a high-capacity hydrogen sponge) create special outgassing problems.

Your system may be able to evacuate nitrogen, (the main component of air,) to the desired vacuum, but your chamber could still be full of residual atmospheric hydrogen and helium. Smaller molecules can leak in more easily and are more easily absorbed by certain materials, and molecular pumps are less effective at pumping gases with lower molecular weights. The impact of molecular size must be considered. The porosity of the metallic chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.

Some oils and greases will boil off in extreme vacuums. The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the absorptivity of hard metals such as stainless steel or titanium must be considered. In ultra-high vacuum systems, some very odd leakage paths and outgassing sources must be considered. Some systems are cooled well below room temperature by liquid nitrogen to shut down residual outgassing and simultaneously cryopump the system.

Once the bulk of the outgassing materials are boiled off and evacuated, the system may be cooled to lower vapour pressures and minimize residual outgassing during actual operation. If necessary, this outgassing of the system can also be performed at room temperature, but this takes much more time. The system is usually baked, preferably under vacuum, to temporarily raise the vapour pressure of all outgassing materials in the system and boil them off. Ultra-high vacuum systems are usually made of stainless steel with metal-gasketed conflat flanges.

On a larger scale, the principles are the same as in a Cryomodule. Cryopumping incorporates the use of introducing cryogenics and a vacuum system. One such method to create a high vacuum to ultra high vacuum is by the use of cryopumps. Yet more specialized pumps become useful:.

Even higher vacuums are possible, but they generally require custom-built equipment, strict operational procedures, and a fair amount of trial-and-error. With careful design and operation, 1μPa is possible. With these standard precautions, vacuums of 1 mPa are easily achieved with off-the-shelf molecular pumps. As a result, many materials that work well in low vacuums, such as epoxy, will become a problematic source of outgassing when attempting to achieve high vacuums.

All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. The system must be clean and free of organic matter to minimize outgassing. High vacuum systems generally require metal chambers with metal O-ring seals such as Klein flanges or ISO flanges. As with mechanical pumps, the base pressure will be reached when leakage, outgassing, and backstreaming equal the pump speed, but now minimizing leakage and outgassing to a level comparable to backstreaming becomes much more difficult.

Both of these pumps will stall and fail to pump if exhausted directly to atmospheric pressure, so they must be exhausted to a lower grade vacuum created by a mechanical pump. Diffusion pumps blow out molecules with jets of oil, while turbomolecular pumps use high speed fans. Both types of pumps blow out gas molecules that diffuse into the pump. The two main types of molecular pumps are the diffusion pump and the turbomolecular pump.

In high vacuum, however, pressure gradients have little effect on fluid flows, and molecular pumps can attain their full potential. Since there is no seal, a small pressure at the exhaust can easily force flow backstream through the pump; this is called stall. They do this at the expense of the seal between the vacuum and their exhaust. Molecular pumps sweep out a larger area than mechanical pumps, and do so more frequently, making them capable of much higher pumping speeds as measured in volume per time.

This regime is generally called high vacuum.. When the distance between the molecules increases, the molecules interact with the walls of the chamber more often than the other molecules, and molecular pumping becomes more effective than compression pumping. At atmospheric pressure and mild vacuums, molecules interact with each other and push on their neighboring molecules in what is known as viscous flow. Matter flows differently at different pressures based on the laws of fluid dynamics.

Fortunately, once the pressure has dropped below 1 kPa or so, another vacuum pumping technique becomes possible. Better pumping technologies must be used to go beyond this barrier. Adding more pumps in parallel or bigger pumps of the same type can still improve the pump-down speed, but they will not reduce the base pressure below ultimate. In this situation, the vacuum will approach the pump's ultimate pressure - the best vacuum that this type of pump can achieve under ideal conditions.

However, there is a point where backstream leakage through the pump and outgassing of the pump oils become the dominant mass flows into the chamber. If the dominant mass flow into the vacuum system is chamber leakage or outgassing of materials under vacuum, then the vacuum can be improved simply by installing bigger pumps with a higher volume flow rate. The base pressure of a rubber- and plastic-sealed piston pump system is typically 1 to 50 kPa, while a scroll pump might reach 10 Pa and a rotary vane oil pump with a clean and empty metallic chamber can easily achieve 0.1 Pa. Outgassing can be reduced by desiccation prior to vacuum pumping.

When the pump's mass flow drops to the same level as the mass flows into the chamber, the system asymptotically approaches a constant pressure called the base pressure. Evaporation and sublimation into a vacuum is called outgassing, and the most common source is water absorbed by materials in the chamber. Meanwhile, the leakage rates, evaporation rates, and sublimation rates produce a constant mass flow into the system. So although the pumping speed remains constant when measured in litres/second, it drops exponentially when measured in kilograms/second. A mechanical vacuum pump moves the same volume of gas with each cycle, but as the chamber's pressure drops, this volume contains less and less mass.

The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size. Because of the pressure differential, some air from the chamber is pushed into the pump's small cavity. Inside the pump, a mechanism expands a small sealed cavity to create a deep vacuum. This is the principle behind most mechanical vacuum pumps.

By repeatedly closing off a compartment of the vacuum and exhausting it, it is possible to pump air out of a chamber of fixed size in a manner analogous to pumping a milkshake out of a glass. For example, your muscles expand your lungs to create a partial vacuum inside them, and air rushes in to fill the vacuum. The easiest way to create an artificial vacuum is to expand the volume of a container.
.

Astrophysicists prefer to use density to describe these environments, in units of particles per cubic metre. In interplanetary and interstellar space, isotropic gas pressure is insignificant when compared to solar pressure, solar wind, and dynamic pressure. This vacuum state is called high vacuum, and the study of fluid flows in this regime is called particle gas dynamics. When the MFP is greater than the chamber, pump, spacecraft, or other objects present, the continuum assumptions of fluid mechanics do not apply.

As gas pressure decreases, the mean free path (MFP) of the gas molecules increases. Here, 29.92 inHg means perfect vacuum. Thus a vacuum of 26 inHg is equivalent to a pressure of (29.92 - 26) or 3.92 inHg. This means that the pressure in vacuum, when specified in inches of mercury, is equal to the specified inches of mercury subtracted from 29.92.

For commercial purposes, vacuum is often measured in inches of mercury (inHg). It is often also measured using the barometric scale, or as a percentage of atmospheric pressure in bars or atms. The SI unit of pressure is the pascal (abbreviation Pa), but vacuum is usually measured in millimeters of mercury (mmHg) or Torr, with 1 mmHg or 1 Torr equaling 133.3223684 pascals. Engineers measure the degree of vacuum in units of pressure.

In engineering, a vacuum is any region where the gas pressure is less than atmospheric pressure. The antithesis of a vacuum, which is also an ideal unachievable state, is called a plenum. A complete characterization of the physical state would require further parameters, such as temperature. Physicists use the term partial vacuum to describe real-life non-ideal vacuum.

In modern day usage vacuum is considered to exist in an enclosed space or chamber, when the pressure of gaseous environment is lower than atmospheric pressure (760 Torr or 101 kPa), or has been reduced as much as necessary to prevent the influence of some gas on a process being carried out in that space. A perfect vacuum is an ideal state that cannot practically be obtained in a laboratory, nor even in outer space where there are a few hydrogen atoms per cubic centimeter at 10−14 pascal or 10−16 torr. Vacuum ranges do not have universally agreed definitions and often depend on the size of the vacuum chamber, but a typical distribution is as follows:. .

A perfect vacuum with a gaseous pressure of absolute zero is a philosophical concept with no physical reality; see sections below on Vacuum in Space and The Quantum Mechanical Vacuum. vacua) which means "empty," but space can never be perfectly empty. The root of the word vacuum is the Latin word vacuus (pl.
A vacuum is a volume of space that is empty of matter and radiation, including air, so that gaseous pressure is much less than standard atmospheric pressure.

For other uses, see vacuum cleaner, vacuum exercise and Vacuum (musical group).'. Converting them to solids by electrically combining them with other materials, called ion pumping. Converting the molecules of gas to their solid phase by freezing them, called cryopumping or cryotrapping. light bulb.

vacuum tube. vacuum welding. process purging. ultra-clean inert storage.

adhesive preparation. vacuum deposition as in semiconductor fabrication. thermal insulation as in a thermos. freeze drying.

Interstellar space = approximately 1 fPa (10−17 Torr) [1]. Pressure on the Moon = approximately 1 nPa (10−11 Torr). Cryopumped MBE chamber = 100 nPa to 1 nPa (10−9 Torr to 10−11 Torr). Near earth outer space = approximately 100 µPa (10−6 Torr).

Mechanical vacuum pump = approximately 100 Pa to 100 µPa (1 Torr to 10−6 Torr). Mechanical water-sealed liquid ring vacuum pump = approximately 3.2 kPa (24 Torr). Vacuum cleaner = approximately 80 kPa (600 Torr). Atmospheric pressure = variable, but standardised at 101.325  kPa (760 Torr) or 760 mm of mercury.

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