Ice cream is a sweetened frozen food eaten as a snack or dessert. It may be made from dairy milk or cream, or soy, coconut or almondmilk, is flavored with a sweetener, either sugar or an alternative, any spice, such as cocoa or vanilla. Colourings are added, in addition to stabilizers; the mixture is stirred to incorporate air spaces and cooled below the freezing point of water to prevent detectable ice crystals from forming. The result is a smooth, semi-solid foam, solid at low temperatures, it becomes more malleable as its temperature increases. The meaning of the name "ice cream" varies from one country to another. Terms such as "frozen custard," "frozen yogurt," "sorbet," "gelato," and others are used to distinguish different varieties and styles. In some countries, such as the United States, "ice cream" applies only to a specific variety, most governments regulate the commercial use of the various terms according to the relative quantities of the main ingredients, notably the amount of cream.
Products that do not meet the criteria to be called ice cream are sometimes labelled "frozen dessert" instead. In other countries, such as Italy and Argentina, one word is used for all variants. Analogues made from dairy alternatives, such as goat's or sheep's milk, or milk substitutes, are available for those who are lactose intolerant, allergic to dairy protein, or vegan. Ice cream may be licked from edible cones. Ice cream may be served with other desserts, such as apple pie, or as an ingredient in ice cream floats, milkshakes, ice cream cakes and baked items, such as Baked Alaska. History of ice creams began around 500 BC in the Achaemenid Empire with ice combined with flavors to produce summertime treats. In 400 BC, the Persians invented a special chilled food, made of rose water and vermicelli, served to royalty during summers; the ice was mixed with saffron and various other flavours. During the 5th century BC, ancient Greeks ate snow mixed with honey and fruit in the markets of Athens.
Hippocrates encouraged his Ancient Greek patients to eat ice "as it livens the life-juices and increases the well-being." A frozen mixture of milk and rice was used in China around 200 BC. "They poured a mixture of snow and saltpetre over the exteriors of containers filled with syrup, for, in the same way as salt raises the boiling point of water, it lowers the freezing point to below zero." The Roman Emperor Nero had ice brought from the mountains and combined it with fruit toppings to create chilled delicacies. In the sixteenth century, the Mughal emperors from the Indian subcontinent used relays of horsemen to bring ice from the Hindu Kush to Delhi, where it was used in fruit sorbets. Kulfi is a popular frozen dairy dessert from the Indian subcontinent and is described as "traditional Indian ice cream." It originated in the sixteenth century in the Mughal Empire. When Italian duchess Catherine de' Medici married the Duke of Orléans in 1533, she is said to have brought with her to France some Italian chefs who had recipes for flavoured ices or sorbets.
One hundred years Charles I of England was so impressed by the "frozen snow" that he offered his own ice cream maker a lifetime pension in return for keeping the formula secret, so that ice cream could be a royal prerogative. There is no historical evidence to support these legends, which first appeared during the 19th century; the first recipe in French for flavoured ices appears in 1674, in Nicholas Lemery's Recueil de curiositéz rares et nouvelles de plus admirables effets de la nature. Recipes for sorbetti saw publication in the 1694 edition of Antonio Latini's Lo Scalco alla Moderna. Recipes for flavoured ices begin to appear in François Massialot's Nouvelle Instruction pour les Confitures, les Liqueurs, et les Fruits, starting with the 1692 edition. Massialot's recipes result in a pebbly texture. Latini claims that the results of his recipes should have the fine consistency of snow. Ice cream recipes first appeared in England in the 18th century; the recipe for ice cream was published in Mrs. Mary Eales's Receipts in London in 1718.
To ice cream. Take Tin Ice-Pots, fill them with any Sort of Cream you like, either plain or sweeten’d, or Fruit in it; when you wou’d freeze any Sort of Fruit, either Cherries, Currants, or Strawberries, fill your Tin-Pots with the Fruit, but as hollow as you can. An early reference to ice cream given by the Oxford English Dictionary is from 1744, reprinted in a magazine in 1877. "1744 in Pennsylvania Mag. Hist. & Biogr. I. 126 Among the rarities..was some fine ice cream, with the strawberries and milk, eat most deliciously."The 1751 edition of The Art of Cookery made Plain and Easy by Hannah Glasse features a recipe for ice cream. O
A hydrogen bond is a electrostatic force of attraction between a hydrogen atom, covalently bound to a more electronegative atom or group the second-row elements nitrogen, oxygen, or fluorine —the hydrogen bond donor —and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor. Such an interacting system is denoted Dn–H···Ac, where the solid line denotes a covalent bond, the dotted line indicates the hydrogen bond. There is general agreement that there is a minor covalent component to hydrogen bonding for moderate to strong hydrogen bonds, although the importance of covalency in hydrogen bonding is debated. At the opposite end of the scale, there is no clear boundary between a weak hydrogen bond and a van der Waals interaction. Weaker hydrogen bonds are known for hydrogen atoms bound to elements such as chlorine; the hydrogen bond is responsible for many of the anomalous physical and chemical properties of compounds of N, O, F. Hydrogen bonds can be intramolecular.
Depending on the nature of the donor and acceptor atoms which constitute the bond, their geometry, environment, the energy of a hydrogen bond can vary between 1 and 40 kcal/mol. This makes them somewhat stronger than a van der Waals interaction, weaker than covalent or ionic bonds; this type of bond can occur in inorganic molecules such as water and in organic molecules like DNA and proteins. Intermolecular hydrogen bonding is responsible for the high boiling point of water compared to the other group 16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is responsible for the secondary and tertiary structures of proteins and nucleic acids, it plays an important role in the structure of polymers, both synthetic and natural. It was recognized that there are many examples of weaker hydrogen bonding involving donor Dn other than N, O, or F and/or acceptor Ac with close to or the same electronegativity as hydrogen. Though they are quite weak, they are ubiquitous and are recognized as important control elements in receptor-ligand interactions in medicinal chemistry or intra-/intermolecular interactions in materials sciences.
Thus, there is a trend of gradual broadening for the definition of hydrogen bonding. In 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, published in the IUPAC journal Pure and Applied Chemistry; this definition specifies: The hydrogen bond is an attractive interaction between a hydrogen atom from a molecule or a molecular fragment X–H in which X is more electronegative than H, an atom or a group of atoms in the same or a different molecule, in which there is evidence of bond formation. Most introductory textbooks still restrict the definition of hydrogen bond to the "classical" type of hydrogen bond characterized in the opening paragraph. A hydrogen atom attached to a electronegative atom is the hydrogen bond donor. C-H bonds only participate in hydrogen bonding when the carbon atom is bound to electronegative substituents, as is the case in chloroform, CHCl3. In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named proton acceptor, whereas the one covalently bound to the hydrogen is named the proton donor.
In the donor molecule, the H center is protic. The donor is a Lewis base. Hydrogen bonds are represented as H · · · Y system. Liquids that display hydrogen bonding are called associated liquids; the hydrogen bond is described as an electrostatic dipole-dipole interaction. However, it has some features of covalent bonding: it is directional and strong, produces interatomic distances shorter than the sum of the van der Waals radii, involves a limited number of interaction partners, which can be interpreted as a type of valence; these covalent features are more substantial when acceptors bind hydrogens from more electronegative donors. Hydrogen bonds can vary in strength from weak to strong. Typical enthalpies in vapor include: F−H···:F, illustrated uniquely by HF2−, bifluoride O−H···:N, illustrated water-ammonia O−H···:O, illustrated water-water, alcohol-alcohol N−H···:N, illustrated by ammonia-ammonia N−H···:O, illustrated water-amide HO−H···:OH+3 The strength of intermolecular hydrogen bonds is most evaluated by measurements of equilibria between molecules containing donor and/or acceptor units, most in solution.
The strength of intramolecular hydrogen bonds can be studied with equilibria between conformers with and without hydrogen bonds. The most important method for the identification of hydrogen bonds in complicated molecules is crystallography, sometimes NMR-spectroscopy. Structural details, in particular distances between donor and acceptor which are smaller than the sum of the van der Waals radii can be taken as indication of the hydrogen bond strength. One scheme gives the following somewhat arbitrary classification: those that are 15 to 40 kcal/mol, 5 to 15 kcal/mol, >0 to 5 kcal/mol are considered strong, moder
The Antarctic is a polar region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other island territories located on the Antarctic Plate or south of the Antarctic Convergence; the Antarctic region includes the ice shelves and all the island territories in the Southern Ocean situated south of the Antarctic Convergence, a zone 32 to 48 km wide varying in latitude seasonally. The region covers some 20 percent of the Southern Hemisphere, of which 5.5 percent is the surface area of the Antarctic continent itself. All of the land and ice shelves south of 60°S latitude are administered under the Antarctic Treaty System. Biogeographically, the Antarctic ecozone is one of eight ecozones of the Earth's land surface; the maritime part of the region constitutes the area of application of the international Convention for the Conservation of Antarctic Marine Living Resources, where for technical reasons the Convention uses an approximation of the Convergence line by means of a line joining specified points along parallels of latitude and meridians of longitude.
The implementation of the Convention is managed through an international Commission headquartered in Hobart, Australia, by an efficient system of annual fishing quotas and international inspectors on the fishing vessels, as well as satellite surveillance. Most of the Antarctic region is situated south of 60°S latitude parallel, is governed in accordance with the international legal regime of the Antarctic Treaty System; the Treaty area covers the continent itself and its adjacent islands, as well as the archipelagos of the South Orkney Islands, South Shetland Islands, Peter I Island, Scott Island and Balleny Islands. The islands situated between 60°S latitude parallel to the south and the Antarctic Convergence to the north, their respective 200-nautical-mile exclusive economic zones fall under the national jurisdiction of the countries that possess them: South Georgia and the South Sandwich Islands, Bouvet Island, Heard and McDonald Islands. Kerguelen Islands are situated in the Antarctic Convergence area, while the Falkland Islands, Isla de los Estados, Hornos Island with Cape Horn, Diego Ramírez Islands, Campbell Island, Macquarie Island and Saint Paul Islands, Crozet Islands, Prince Edward Islands, Gough Island and Tristan da Cunha group remain north of the Convergence and thus outside the Antarctic region.
A variety of animals live in Antarctica for at least some of the year, including: Seals Penguins South Georgia pipits Albatrosses Antarctic petrels Whales Fish, such as Antarctic icefish, Antarctic toothfish Squid, including the colossal squid Antarctic krillMost of the Antarctic continent is permanently covered by ice and snow, leaving less than 1 percent of the land exposed. There are only two species of flowering plant, Antarctic hair grass and Antarctic pearlwort, but a range of mosses, liverworts and macrofungi; the first Antarctic land discovered was the island of South Georgia, visited by the English merchant Anthony de la Roché in 1675. Although myths and speculation about a Terra Australis date back to antiquity, the first confirmed sighting of the continent of Antarctica is accepted to have occurred in 1820 by the Russian expedition of Fabian Gottlieb von Bellingshausen and Mikhail Lazarev on Vostok and Mirny; the first human born in the Antarctic was Solveig Gunbjørg Jacobsen born on 8 October 1913 in Grytviken, South Georgia.
The Antarctic region had no indigenous population when first discovered, its present inhabitants comprise a few thousand transient scientific and other personnel working on tours of duty at the several dozen research stations maintained by various countries. However, the region is visited by more than 40,000 tourists annually, the most popular destinations being the Antarctic Peninsula area and South Georgia Island. In December 2009, the growth of tourism, with consequences for both the ecology and the safety of the travellers in its great and remote wilderness, was noted at a conference in New Zealand by experts from signatories to the Antarctic Treaty; the definitive results of the conference was presented at the Antarctic Treaty states' meeting in Uruguay in May 2010. The Antarctic hosts the world's largest protected area comprising 1.07 million km2, the South Georgia and the South Sandwich Islands Marine Protection Area created in 2012. The latter exceeds the surface area of another vast protected territory, the Greenland National Park’s 972,000 km2.
Because Antarctica surrounds the South Pole, it is theoretically located in all time zones. For practical purposes, time zones are based on territorial claims or the time zone of a station's owner country or supply base. Antarctic Circle History of Antarctica Krupnik, Michael A. Lang, Scott E. Miller, eds. Smithsonian at the Poles: Contributions to International Polar Year Science. Washington, D. C.: Smithsonian Institution Scholarly Press, 2009. British Services Antarctic Expedition 2012 Committee for Environmental Protection of Antarctica Secretariat of the Antarctic Treaty CCAMLR Commission Antarctic Heritage Trusts International Association of Antarctica Tour Operators Map of the Antarctic Convergence The South Atlantic and Subantarctic Islands
Rabbits are small mammals in the family Leporidae of the order Lagomorpha. Oryctolagus cuniculus includes the European rabbit species and its descendants, the world's 305 breeds of domestic rabbit. Sylvilagus includes 13 wild rabbit species, among them the 7 types of cottontail; the European rabbit, introduced on every continent except Antarctica, is familiar throughout the world as a wild prey animal and as a domesticated form of livestock and pet. With its widespread effect on ecologies and cultures, the rabbit is, in many areas of the world, a part of daily life—as food, clothing, a companion, as a source of artistic inspiration. Male rabbits are called bucks. An older term for an adult rabbit is coney. Another term for a young rabbit is bunny, though this term is applied informally to rabbits especially domestic ones. More the term kit or kitten has been used to refer to a young rabbit. A group of rabbits is known as a nest. A group of baby rabbits produced from a single mating is referred to as a litter, a group of domestic rabbits living together is sometimes called a herd.
Rabbits and hares were classified in the order Rodentia until 1912, when they were moved into a new order, Lagomorpha. Below are some of the species of the rabbit. Order Lagomorpha Family Leporidae Hares are precocial, born mature and mobile with hair and good vision, while rabbits are altricial, born hairless and blind, requiring closer care. Hares live a solitary life in a simple nest above the ground, while most rabbits live in social groups underground in burrows or warrens. Hares are larger than rabbits, with ears that are more elongated, with hind legs that are larger and longer. Hares have not been domesticated, while descendants of the European rabbit are bred as livestock and kept as pets. Rabbits have long been domesticated. Beginning in the Middle Ages, the European rabbit has been kept as livestock, starting in ancient Rome. Selective breeding has generated a wide variety of rabbit breeds, many of which are kept as pets; some strains of rabbit have been bred as research subjects. As livestock, rabbits are bred for their fur.
The earliest breeds were important sources of meat, so became larger than wild rabbits, but domestic rabbits in modern times range in size from dwarf to giant. Rabbit fur, prized for its softness, can be found in a broad range of coat colors and patterns, as well as lengths; the Angora rabbit breed, for example, was developed for its long, silky fur, hand-spun into yarn. Other domestic rabbit breeds have been developed for the commercial fur trade, including the Rex, which has a short plush coat; because the rabbit's epiglottis is engaged over the soft palate except when swallowing, the rabbit is an obligate nasal breather. Rabbits have two sets of one behind the other; this way they can be distinguished from rodents, with which they are confused. Carl Linnaeus grouped rabbits and rodents under the class Glires. However, recent DNA analysis and the discovery of a common ancestor has supported the view that they do share a common lineage, thus rabbits and rodents are now referred to together as members of the superorder Glires.
Since speed and agility are a rabbit's main defenses against predators, rabbits have large hind leg bones and well developed musculature. Though plantigrade at rest, rabbits are on their toes while running, assuming a more digitigrade form. Rabbits use their strong claws for defense; each front foot has four toes plus a dewclaw. Each hind foot has four toes. Most wild rabbits have full, egg-shaped bodies; the soft coat of the wild rabbit is agouti in coloration. The tail of the rabbit is dark on white below. Cottontails have white on the top of their tails; as a result of the position of the eyes in its skull, the rabbit has a field of vision that encompasses nearly 360 degrees, with just a small blind spot at the bridge of the nose. The anatomy of rabbits' hind limbs are structurally similar to that of other land mammals and contribute to their specialized form of locomotion; the Bones of the hind limbs consist of long bones as well as short bones. These bones are created through endochondral ossification during development.
Like most land mammals, the round head of the femur articulates with the acetabulum of the ox coxae. The femur articulates with the tibia, but not the fibula, fused to the tibia; the tibia and fibula articulate with the tarsals of the pes called the foot. The hind limbs of the rabbit are longer than the front limbs; this allows them to produce their hopping form of locomotion. Longer hind limbs are more capable of producing faster speeds. Hares, which have longer legs than cottontail rabbits, are able to move faster. Rabbits stay just on their toes; the hind feet have four long toes that allow for this and are webbed to prevent them from spreading when hopping. Rabbits do not have paw
Liquid nitrogen is nitrogen in a liquid state at an low temperature. It is a colorless liquid with a density of 0.807 g/ml at its boiling point and a dielectric constant of 1.43. Nitrogen was first liquefied at the Jagiellonian University on 15 April 1883 by Polish physicists, Zygmunt Wróblewski and Karol Olszewski, it is produced industrially by fractional distillation of liquid air. Liquid nitrogen is referred to by the abbreviation, LN2 or "LIN" or "LN" and has the UN number 1977. Liquid nitrogen is a diatomic liquid, which means that the diatomic character of the covalent N bonding in N2 gas is retained after liquefaction. Liquid nitrogen is a cryogenic fluid; when appropriately insulated from ambient heat, liquid nitrogen can be stored and transported, for example in vacuum flasks. The temperature is held constant at 77 K by slow boiling of the liquid, resulting in the evolution of nitrogen gas. Depending on the size and design, the holding time of vacuum flasks ranges from a few hours to a few weeks.
The development of pressurised super-insulated vacuum vessels has enabled liquefied nitrogen to be stored and transported over longer time periods with losses reduced to 2% per day or less. The temperature of liquid nitrogen can be reduced to its freezing point 63 K by placing it in a vacuum chamber pumped by a vacuum pump. Liquid nitrogen's efficiency as a coolant is limited by the fact that it boils on contact with a warmer object, enveloping the object in insulating nitrogen gas; this effect, known as the Leidenfrost effect, applies to any liquid in contact with an object hotter than its boiling point. Faster cooling may be obtained by plunging an object into a slush of liquid and solid nitrogen rather than liquid nitrogen alone. Liquid nitrogen is a compact and transported source of dry nitrogen gas, as it does not require pressurization. Further, its ability to maintain temperatures far below the freezing point of water makes it useful in a wide range of applications as an open-cycle refrigerant, including: in cryotherapy for removing unsightly or malignant skin lesions such as warts and actinic keratosis to store cells at low temperature for laboratory work in cryogenics in a cryophorus to demonstrate rapid freezing by evaporation as a backup nitrogen source in hypoxic air fire prevention systems as a source of dry nitrogen gas for the immersion and transportation of food products for the cryopreservation of blood, reproductive cells, other biological samples and materials to preserve tissue samples from surgical excisions for future studies to facilitate cryoconservation of animal genetic resources to freeze water and oil pipes in order to work on them in situations where a valve is not available to block fluid flow to the work area.
See molecular gastronomy. in container inerting and pressurisation by injecting a controlled amount of liquid nitrogen just prior to sealing or capping as a cosmetic novelty giving a smoky, bubbling "cauldron effect" to drinks. See liquid nitrogen cocktail; as an energy storage medium branding cattle The culinary use of liquid nitrogen is mentioned in an 1890 recipe book titled Fancy Ices authored by Mrs. Agnes Marshall, but has been employed in more recent times by restaurants in the preparation of frozen desserts, such as ice cream, which can be created within moments at the table because of the speed at which it cools food; the rapidity of chilling leads to the formation of smaller ice crystals, which provides the dessert with a smoother texture. The technique is employed by chef Heston Blumenthal who has used it at his restaurant, The Fat Duck to create frozen dishes such as egg and bacon ice cream. Liquid nitrogen has become popular in the preparation of cocktails because it can be used to chill glasses or freeze ingredients.
It is added to drinks to create a smoky effect, which occurs as tiny droplets of the liquid nitrogen come into contact with the surrounding air, condensing the vapour, present. Because the liquid-to-gas expansion ratio of nitrogen is 1:694 at 20 °C, a tremendous amount of force can be generated if liquid nitrogen is vaporized in an enclosed space. In an incident on January 12, 2006 at Texas A&M University, the pressure-relief devices of a tank of liquid nitrogen were malfunctioning and sealed; as a result of the subsequent pressure buildup, the tank failed catastrophically. The force of the explosion was sufficient to propel the tank through the ceiling above it, shatter a reinforced concrete beam below it, blow the walls of t
In physics, cryogenics is the production and behaviour of materials at low temperatures. A person who studies elements that have been subjected to cold temperatures is called a cryogenicist, it is not well-defined at what point on the temperature scale refrigeration ends and cryogenics begins, but scientists assume a gas to be cryogenic if it can be liquefied at or below −150 °C. The U. S. National Institute of Standards and Technology has chosen to consider the field of cryogenics as that involving temperatures below −180 °C; this is a logical dividing line, since the normal boiling points of the so-called permanent gases lie below −180 °C while the Freon refrigerants and other common refrigerants have boiling points above −180 °C. Discovery of superconducting materials with critical temperatures above the boiling point of liquid nitrogen has provided new interest in reliable, low cost methods of producing high temperature cryogenic refrigeration; the term "high temperature cryogenic" describes temperatures ranging from above the boiling point of liquid nitrogen, −195.79 °C, up to −50 °C, the defined upper limit of study referred to as cryogenics.
Cryogenicists use the Kelvin or Rankine temperature scale, both of which measure from absolute zero, rather than more usual scales such as Celsius or Fahrenheit, with their zeroes at arbitrary temperatures. Cryogenics The branches of engineering that involve the study of low temperatures, how to produce them, how materials behave at those temperatures. Cryobiology The branch of biology involving the study of the effects of low temperatures on organisms. Cryoconservation of animal genetic resources The conservation of genetic material with the intention of conserving a breed. Cryosurgery The branch of surgery applying cryogenic temperatures to destroy malignant tissue, e.g. cancer cells. Cryoelectronics The study of electronic phenomena at cryogenic temperatures. Examples include variable-range hopping. Cryotronics The practical application of cryoelectronics. Cryonics Cryopreserving humans and animals with the intention of future revival. "Cryogenics" is sometimes erroneously used to mean "Cryonics" in the press.
The word cryogenics stems from Greek κρύο – "cold" + γονική – "having to do with production". Cryogenic fluids with their boiling point in kelvins. Liquefied gases, such as liquid nitrogen and liquid helium, are used in many cryogenic applications. Liquid nitrogen is the most used element in cryogenics and is purchasable around the world. Liquid helium is commonly used and allows for the lowest attainable temperatures to be reached; these liquids may be stored in Dewar flasks, which are double-walled containers with a high vacuum between the walls to reduce heat transfer into the liquid. Typical laboratory Dewar flasks are spherical, made of glass and protected in a metal outer container. Dewar flasks for cold liquids such as liquid helium have another double-walled container filled with liquid nitrogen. Dewar flasks are named after James Dewar, the man who first liquefied hydrogen. Thermos bottles are smaller vacuum flasks fitted in a protective casing. Cryogenic barcode labels are used to mark Dewar flasks containing these liquids, will not frost over down to −195 degrees Celsius.
Cryogenic transfer pumps are the pumps used on LNG piers to transfer liquefied natural gas from LNG carriers to LNG storage tanks, as are cryogenic valves. The field of cryogenics advanced during World War II when scientists found that metals frozen to low temperatures showed more resistance to wear. Based on this theory of cryogenic hardening, the commercial cryogenic processing industry was founded in 1966 by Ed Busch. With a background in the heat treating industry, Busch founded a company in Detroit called CryoTech in 1966 which merged with 300 Below in 1999 to become the world's largest and oldest commercial cryogenic processing company. Busch experimented with the possibility of increasing the life of metal tools to anywhere between 200% and 400% of the original life expectancy using cryogenic tempering instead of heat treating; this evolved in the late 1990s into the treatment of other parts. Cryogens, such as liquid nitrogen, are further used for specialty chilling and freezing applications.
Some chemical reactions, like those used to produce the active ingredients for the popular statin drugs, must occur at low temperatures of −100 °C. Special cryogenic chemical reactors are used to remove reaction heat and provide a low temperature environment; the freezing of foods and biotechnology products, like vaccines, requires nitrogen in blast freezing or immersion freezing systems. Certain soft or elastic materials become hard and brittle at low temperatures, which makes cryogenic milling an option for some materials that cannot be milled at higher temperatures. Cryogenic processing is not a substitute for heat treatment, but rather an extension of the heating–quenching–tempering cycle; when an item is quenched, the final temperature is ambient. The only reason for this is. There is nothing metallurgically significant about ambient temperature; the cryogenic process continues this action from ambient temperature down to −320 °F. In most instances the cryogenic cycle is followed by a heat tempering procedure.
As all alloys do not have the same chemical constituents, the tempering procedure varies according to the material's chemical composition, t
Insects or Insecta are hexapod invertebrates and the largest group within the arthropod phylum. Definitions and circumscriptions vary; as used here, the term Insecta is synonymous with Ectognatha. Insects have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. Insects are the most diverse group of animals; the total number of extant species is estimated at between ten million. Insects may be found in nearly all environments, although only a small number of species reside in the oceans, which are dominated by another arthropod group, crustaceans. Nearly all insects hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts; the immature stages differ from the adults in structure and habitat, can include a passive pupal stage in those groups that undergo four-stage metamorphosis. Insects that undergo three-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages.
The higher level relationship of the insects is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm; the most diverse insect groups appear to have coevolved with flowering plants. Adult insects move about by walking, flying, or sometimes swimming; as it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, composed of the front & rear on one side with the middle on the other side. Insects are the only invertebrates to have evolved flight, all flying insects derive from one common ancestor. Many insects spend at least part of their lives under water, with larval adaptations that include gills, some adult insects are aquatic and have adaptations for swimming; some species, such as water striders, are capable of walking on the surface of water. Insects are solitary, but some, such as certain bees and termites, are social and live in large, well-organized colonies.
Some insects, such as earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyrid beetles communicate with light. Humans regard certain insects as pests, attempt to control them using insecticides, a host of other techniques; some insects damage crops by feeding on sap, fruits, or wood. Some species are parasitic, may vector diseases; some insects perform complex ecological roles. Insect pollinators are essential to the life cycle of many flowering plant species on which most organisms, including humans, are at least dependent. Many insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms produce silk and honey bees produce honey and both have been domesticated by humans.
Insects are consumed as food in 80% of the world's nations, by people in 3000 ethnic groups. Human activities have effects on insect biodiversity; the word "insect" comes from the Latin word insectum, meaning "with a notched or divided body", or "cut into", from the neuter singular perfect passive participle of insectare, "to cut into, to cut up", from in- "into" and secare "to cut". A calque of Greek ἔντομον, "cut into sections", Pliny the Elder introduced the Latin designation as a loan-translation of the Greek word ἔντομος or "insect", Aristotle's term for this class of life in reference to their "notched" bodies. "Insect" first appears documented in English in 1601 in Holland's translation of Pliny. Translations of Aristotle's term form the usual word for "insect" in Welsh, Serbo-Croatian, etc; the precise definition of the taxon Insecta and the equivalent English name "insect" varies. In the broadest circumscription, Insecta sensu lato consists of all hexapods. Traditionally, insects defined in this way were divided into "Apterygota" —the wingless insects—and Pterygota—the winged insects.
However, modern phylogenetic studies have shown that "Apterygota" is not monophyletic, so does not form a good taxon. A narrower circumscription restricts insects to those hexapods with external mouthparts, comprises only the last three groups in the table. In this sense, Insecta sensu stricto is equivalent to Ectognatha. In the narrowest circumscription, insects are restricted to hexapods that are either winged or descended from winged ancestors. Insecta sensu strictissimo is equivalent to Pterygota. For the purposes of this article, the middle definition is used; the evolutionary relationship of insects to other animal groups remains unclear. Although traditionally grouped with millipedes and centiped