Tarpons are large silvery fish, measuring 4-8 ft (1.3-2.5 m) in length, with large scales, a compressed body, a deeply forked caudal fin, and a long ray extending from the dorsal fin. The mouth is large, and contains rows of sharp, fine teeth, and the lower jaw protrudes outward. Tarpon are among the best known and most impressive of the sportfish. They can live in both freshwater and saltwater. …
Zebras are members of the horse family (Equidae) that inhabit tropical grasslands (savannas) in much of sub-Saharan Africa. Three of the seven species of equids are zebras. Zebras are herd-living social ungulates (hoofed mammals) recognized by a black-and-white (or cream or yellowish) striped coat, short erect mane, and a tail averaging about 18 in (0.5 m) long. The body length of a zebra is about…
Tarsiers are prosimians, or primitive primates, in the family Tarsiidae, found the islands of Southeast Asia. Tarsiers have only 34 teeth, unlike their closest prosimian relatives, the lemurs and lorises, which have 36 teeth. Also, the upper lip of tarsiers is not fastened to the gum underneath, so that the face can be mobile, rather like the more advanced primates, monkeys and apes. Tarsiers are …
A tree is a woody plant which has three principle characteristics: (a) the potential to grow to 20 ft (6.1 m) or more in height; (b) the formation of one or more trunks arising from the ground; and (c) the ability to stand on its own without support. Trees provide many products which are important to humans, such as timber, fruits, and nuts. They are also the dominant plants in the world's …
Zero is often equated with "nothing," but that is not a good analogy. Zero can be the absence of a quality, but it can also be a starting point, such as 0° on a temperature scale. In a mathematical system, zero is the additive identity. It is a number which can be added to any given number to yield a sum equal to the given number. Symbolically, it is a number 0, such that a + …
The tree shrews (order Scandentia, family Tupaiidae) comprise a small number of species that are only found in South and Southeast Asia. Five genera (19 species) are recognized. All occur in forested areas, ranging from India and Southwest China eastward through Malaysia, Indonesia (west of Wallace's Line), and the Philippines. Three genera and 10 species occur on the island of Borneo alone…
The term zodiacal light is used to describe a faint, glowing band of light that occasionally appears near the eastern or western horizon, which is caused by reflection of sunlight from tiny dust particles in the solar system. Our solar system can be pictured as a huge disk, with the planets, their moons, and asteroids mostly orbiting in or near the same plane. If you look at the sky some evening w…
Zoonoses are diseases caused in humans by bacteria, viruses, parasites, and fungi that have been transmitted from animals, reptiles, or birds to people. Because many of the microorganisms that cause zoonotic disease are normal inhabitants of domestic animals and birds, people who are involved in agriculture and those who work in food processing plants can be at risk for infection. Prevention of su…
Tartaric acid is used making silver mirrors, in the manufacturing of soft drinks, to provide tartness to foods, in tanning leather and in making blueprints. Tartaric acid is used in cream of tartar (for cooking) and as an emetic (a substance used to induce vomiting). It readily dissolves in water and is used in making blueprints. Tartaric acid is a molecule that demonstrates properties of optical …
Zooplankton are small animals that occur in the water column of either marine and freshwater ecosystems. Zooplankton are a diverse group defined on the basis of their size and function, rather than on their taxonomic affinities. Most species in the zooplankton community fall into three major groups—Crustacea, Rotifers, and Protozoas. Crustaceans are generally the most abundant, especially t…
The Tasmanian devil (Sarcophilus harrisii) is the largest surviving marsupial predator, occurring only on the island of Tasmania in dense thickets and forests. The Tasmanian devil is one of about 45 species of marsupial predators that make up the family Dasyuridae. The Tasmanian devil once occurred widely in Australia and Tasmania. However, the Tasmanian devil became extirpated from Australia foll…
A virus is a small, infectious agent that consists of a core of genetic material (either deoxyribonucleic acid [DNA] or ribonucleic acid [RNA]) surrounded by a shell of protein. Viruses cause disease by infecting a host cell and commandeering the host cell's synthetic capabilities to produce more viruses. The newly made viruses then leave the host cell, sometimes killing it in the process, …
Taste is one of the five senses (the others being smell, touch, vision, and hearing) through which all animals interpret the world around them. Specifically, taste is the sense for determining the flavor of food and other substances. One of the two chemical senses (the other being smell), taste is stimulated through the contact of certain chemicals in substances with clusters of taste bud cells fo…
The viscosity of a fluid is a measure of its resistance to continuous deformation caused by sliding or shearing forces. Imagine a fluid between two flat plates; one plate is stationary and the other is being moved by a force at a constant velocity parallel to the first plate. The applied force per unit area of the plate is called the shear stress. The applied shear stress keeps the plate in motion…
Trichinosis is a disease caused by the roundworm (nematode) called Trichinella spiralis (T. spiralis). It is readily avoided by proper handling and cooking of certain meats, particularly pork products. …
Triggerfishes are members of the family Balistidae of the order Tetradontiformes. They derive their name from a unique feature of their dorsal fin. The triggerfish can lock the large dorsal spine in an upright position by supporting it with its smaller secondary spine. This protects the fish from predation by larger fish because the erect spine makes the fish hard to swallow or extract from small …
Fats exist in foods—and are usually stored in the body—as Triglycerides. Recent research relating levels of triglycerides in the blood stream to heart attacks in human presents a sometime confusing picture but a mounting level evidence suggests that, along with other indicators, triglyceride levels can be used to predict heart attack risk, especially in women and diabetics. Although …
Taxonomy is the field of biology which deals with the nomenclature, identification, and classification of organisms. There are over one million known species on Earth and probably several million more not yet identified. Taxonomists are responsible for identifying, naming, and classifying all these different species. Systematics is a discipline of biology that explicitly examines the natural varia…
Tritium is an isotope of the chemical element hydrogen. It has not only a single proton but also two neutrons in the nucleus of its atoms. Although technically it is still the element hydrogen, it has its own chemical symbol, T. Chemically, tritium reacts in exactly the same manner as hydrogen, although slightly slower because of its greater atomic weight. A tritium atom has almost three times the…
Vision is sight, the act of seeing with the eyes. In humans, sight conveys more information to the brain than either hearing, touch, taste, or smell, and contributes enormously to memory and other requirements for our normal, everyday functioning. Because we see objects with two eyes at the same time, human vision is binocular, and therefore stereoscopic. Vision begins when light enters the eye, s…
Trogons are about 35 species of beautiful arboreal birds that constitute the family Trogonidae. Trogons have a number of peculiar features in their morphology, and are not thought to be closely related to any other groups of living birds. This is why their family is the only one in the order Trogoniformes. Species of trogons occur throughout the tropical and subtropical parts of the world, a bioge…
The tea plant Camellia sinensis, which is a member of the plant family Theaceae, is a small evergreen tree that is related to the camellias commonly grown in gardens. Although there are more than 3,000 different types, or grades, of true tea that are produced, nearly all are derived from this single species. Other plants such as peppermint and jasmine, which are also often steeped to yield a hot d…
Tectonics is the study of the deformation of Earth's lithosphere—both the causes of deformation and its effects. Tectonics focuses primarily on mountain-building, but involves other unrelated activities as well. Since the development of the theory of plate tectonics, tectonics has become an especially active area of research in geology. Deformation of rocks, known as tectonism or dia…
A telegraph is any system that transmits encoded information by signal across a distance. Although it is associated with sending messages via an electric current, the word telegraph was coined to describe an optical system of sending coded messages. From its invention until the telephone became a viable system, the telegraph was the standard means of communicating both between and within metropoli…
Trophic levels describe the various stages within ecological food chains or webs. Examples of trophic levels, all of which will be described below, are primary producers, primary consumers or herbivores, and secondary and higher-level consumers, or predators. Food webs are based on the productivity of photosynthetic organisms, such as blue-green bacteria, algae, and plants. These are autotrophic o…
Telemetry is the science of obtaining quantities or making measurements from a distant location and transmitting them to receiving equipment where they are recorded, monitored, or displayed. A basic telemetry system consists of a measuring instrument or detector, a medium of transmission (sending), a receiver, and an output device that records and displays data. Today, telemetric systems are mainl…
Tropic birds are three species of pan-tropical seabirds that make up the family Phaethontidae, in the order Pelecaniformes, which also includes the pelicans, anhingas, cormorants, gannets, and boobies. Tropic birds are medium-sized seabirds, weighing about 0.9 lb (0.4 kg), and having a body length of 16-18.9 in (41-48 cm). This length does not include their greatly elongated tail feathers, which a…
Tropical cyclones are large circulating storm systems consisting of multiple bands of intense showers and thunderstorms and extremely high winds. These storm systems develop over warm ocean waters in the tropical regions that lie within about 25° latitude of the equator. Tropical cyclones may begin as isolated thunderstorms. If conditions are right they grow and intensify to form the storm …
The term telephone (from Greek tele, afar, and phone, sound) in a broad sense means a specific type of Figure 1. Telephone set simplified circuit. Illustration by Hans & Cassidy. Courtesy of Gale Group. telecommunications which permits people to carry direct conversations over almost any distance. The articulate speech is transmitted in a form of either modulated electric current pr…
Vision disorders are irregularities or abnormalities either of the eye, visual pathway, or brain, which affect one's ability to see. In healthy vision, visual acuity—often referred to as "20/20 vision"—develops rapidly by three to six months of age and generally decreases rapidly as people approach 45. Poor visual acuity is often correctable with glasses or conta…
Vitamins are organic molecules that are needed in small amounts in the diet. They are frequently molecules that bind in the active site of an enzyme and thereby alter its structure in a way that permits it to react more readily. Vitamins serve nearly the same role in all forms of life and many are essential in the metabolism of all living organisms. They are synthesized by plants and micro-organis…
Viviparity is a form of reproduction found in most mammals and in several other species. Viviparous animals give birth to living young that have been nourished in close contact with their mothers' bodies. Humans, dogs, and cats are viviparous animals. Viviparous animals differ from egg-laying animals, such as birds and most reptiles. Egg-laying, or oviparous, animals obtain all nourishment …
The telescope is an instrument which collects and analyzes the radiation emitted by distant sources. The most common type is the optical telescope, a collection of lenses and/or mirrors that is used to allow the viewer to see distant objects more clearly by magnifying them or to increase the effective brightness of a faint object. In a broader sense, telescopes can operate at most frequencies of t…
Nowhere is the prevalence of certain illnesses more striking than in areas where tropical diseases flourish. In many parts of Africa, South America, and Asia, diseases exist that are rarely seen in the United States. These include malaria, which infects from 300 to 500 million people annually and kills up to 2.7 million people every year, and leishmaniasis, which affects some 12 million people int…
Vivisection originally meant the dissection of a live animal, usually for the purpose of teaching or research. Historically, the word came also to mean the use of a live animal in any experiment. Vivisection, especially in its broader meaning, is a time-tested tool that has helped humans understand how the bodies of animals function, how disease alters that function, and how such diseases can be t…
The trout-perch belongs to the family Percopsidae, which includes only one genus—Percopsis—with only two species. The fish is found only in the fresh waters of North America. One species (Percopsis omiscomaycus) is found mainly on the eastern side; the other species, the sandroller (P. Transmontana), is native to the west in the regions around the Columbia River Basin. Both species a…
Volatility is the ease with which a substance is converted to the gaseous, or vapor, state. The term is usually used to describe the speed with which a liquid evaporates, but it can also apply to the process of a solid changing to a gas, known as sublimation. Liquids that boil at low temperatures, such as gasoline, are volatile liquids, while liquids that boil at higher temperatures, such as water…
The invention of the cathode ray tube in 1897 by Ferdinand Braun quickly made possible the technology that we call television. Indeed, by 1907, the cathode ray tube was supplying television images. Within 50 years, television had become a dominant form of entertainment and an important way to acquire information. This remains true today, as the average American spends between two and five hours ea…
The true bugs are a large and diverse group of about 35,000 species of insects in the order Hemiptera. About 44 families of bugs occur in North America. Bugs typically have a flattened body, and their folded wings cross over their thorax and abdomen, giving a distinctive, cross-like pattern. Some species of true bugs are of great economic importance as pests of agricultural plants. A few species o…
A volcano is an opening in Earth's surface through which molten rock, hot gases, and rocks are ejected. Volcanoes create new land and islands. They can also produce economically important mineral deposits, fertile soils, and beautiful landscapes. However, volcanoes can also destroy lives and property. Therefore, they constitute significant geologic hazards in many parts of the world. With r…
The true eels are elongate bony fish with a snakelike slimy body in the order Anguilliformes. There is one family of freshwater eels (the Anguillidae), and 25 families of exclusively marine eels. The freshwater eels must return to the oceans to spawn. The general characteristics of eels include soft-rayed fins and elongate dorsal and anal fins which merge with the caudal fin. Eels lack pelvic fins…
Voles are small mouse-like mammals in the family Muridae, order Rodentia. Other members of this family include the gerbils, hamsters, lemmings, rats, and mice. Voles occur in a wide range of open, often grassy habitats, such as alpine and arctic tundra, prairies, savannas, and pastures and other types of agricultural fields. Voles have a body length of about 3-5 in (8-12 cm), and typically weigh 1…
Temperature is intuitively associated with the sense of hot and cold. Put your finger in a pan of hot water and energy flows as heat from the water to your finger; you say that the water is at a higher temperature than your finger. Now put your finger in a glass of ice water and energy flows as heat in the other direction. The direction of energy flow as heat is the basis of our definition of temp…
An organism maintains homeostasis, a steady internal state, only if its body temperature stays within prescribed limits. Cellular activities require an optimum amount of heat. They depend on enzyme action, and enzymes function within a narrow range of temperature. For this reason, living things can only tolerate a limited rise or drop in temperature from the optimum. Mechanisms exist that regulate…
The true flies are a large and diverse group of commonly observed insects in the order Diptera, comprising more than 100,000 species. About 107 families of flies occur in North America. Flies have distinctive, knob-like structures known as halteres on the back of their thorax. Halteres are highly modified from the hind wings of true flies, while the fore wings are membranous and used for flying. T…
Volume is the amount of space occupied by an object or a material. Volume is said to be a derived unit, since the volume of an object can be known from other measurements. In order to find the volume of a rectangular box, for example, one only needs to know the length, width, and depth of the box. Then the volume can be calculated from the formula, V = l × w × d. Volume of most physi…
Trumpetfish (Aulostomus maculatus) are bony fish in the family Aulostomidae, found from the Caribbean Sea to as far north as Bermuda. They are named for the trumpet-like shape they exhibit when their mouths are open. Trumpetfish measure up to 2 ft (0.6 m) in length, and have dorsal spines which support separate fins or finlets. They are brownish in color with widespread streaks and spots. Trumpetf…
Twin robotic space probes, Voyager 1 and Voyager 2, were launched by the United States in 1977. Their original mission was to fly by Jupiter and Saturn, but the journey of Voyager 2 was successfully extended to Uranus and Neptune. The Voyagers were the most scientifically fruitful space mission ever launched, collecting, among other data, high-quality photographs of four planets and dozens of moon…
Vulcanization is the process by which rubber molecules (polymers or macromolecules made of repeating units or monomers called isoprene) are cross-linked with each other by heating the liquid rubber with sulfur. Cross-linking increases the elasticity and the strength of rubber by about ten-fold, but the amount of cross-linking must be controlled to avoid creating a brittle and inelastic substance. …
Tenrecs are four-legged nocturnal mammals belonging to the order Insectivora. Tenrecs have evolved into more distinct forms than any other family of animals within the order. Tenrecs can resemble hedgehogs, moles, shrews, or muskrats, depending on the species. Some species of tenrecs have a long tail and long hind legs, while others have a stumpy tail and short hind legs. A stripped tenrec. P…
A teratogen is an environmental agent that can cause abnormalities in a developing organism resulting in either fetal death or congenital abnormality. The human fetus is separated from the mother by the placental barrier, but the barrier is imperfect and permits a number of chemical and infectious agents to pass to the fetus. Well known teratogens include (but are not limited to) alcohol, excess v…
In general, there are three types of algebraic expressions which can be classified as terms. These include expressions made up of a single variable or constant, ones that are the product or quotient of two or more variables and/or constants, and those that are the product or quotient of other expressions. For example, the number 4 and the variable x are both terms because they consist of a single …
Tsunami, or seismic sea waves, are a series of very long wavelength ocean waves generated by the sudden displacement of large volumes of water. The generation of tsunami waves is similar to the effect of dropping a solid object, such as a stone, into a pool of water. Waves ripple out from where the stone entered, and thus displaced, the water. In a tsunami, the "stone" comes from und…
Vultures are large birds of prey specialized to scavenge the bodies of dead animals. Species of vultures are assigned to two families in the order Falconiformes. The vultures of the Americas include seven species in the family Cathartidae. The vultures of Eurasia and Africa, numbering 14 species, are specialized members of the Accipitridae, a family that also includes hawks and eagles. The Cathart…
Tuataras are unusual, lizard-like animals that are the only living representatives of the order Sphenodonta of the vertebrate class Reptilia. The lineage of the sphenodonts is an ancient one, with a fossil record extending back 200 million years, prior even to the evolution of dinosaurs and the lizards. Until the discovery of tuataras in New Zealand, biologists had believed that this reptilian lin…
A tuber is a swollen, underground storage organ that develops on the roots of certain species of plants. Some types of tubers are highly nutritious, mostly because of their energy content in the form of starch. Agricultural species of plants that develop edible tubers include the white potato (Solanum tuberosum), sweet potato (Ipomoea batatas), tapioca or cassava (Manihot esculenta), and yam (Dios…
Tuberculosis is a disease caused by the bacterium Mycobacterium tuberculosis. The organism infects the lungs and causes a debilitating condition that historically was known as consumption. In the 1970s, scientists considered tuberculosis as largely defeated following the widespread use of antibiotics. Today, multi-drug resistant Mycobacterium tuberculosis has developed, and tuberculosis has reemer…
A transuranium (beyond uranium) element is any of the chemical elements with atomic numbers higher than 92, which is the atomic number of uranium. Ever since the eighteenth century when chemists began to recognize certain substances as chemical elements, uranium had been the element with the highest atomic weight; it had the heaviest atoms of all the elements that could be found on Earth. The gene…
The true tumbleweeds are various species of herbaceous plants in the amaranth family (Amaranthaceae). These are usually annual plants that develop a spherical, bush-shaped biomass. At the end of the growing season when their small seeds are ripe, the tumbleweeds wither and detach from their base and are blown about by winds, scattering their seeds widely over the surface of the ground. Therefore, …
Wagtails and pipits are 48 species of terrestrial birds that make up the family Motacillidae. Species in this group occur on all of the continents but Antarctica. The usual habitat of these birds is deserts and semi-deserts, prairies, tundras, shores, and cultivated fields. Many species are migratory, with northern species travelling to the tropics to spend their nonbreeding season, and alpine spe…
Termites are slender, social insects, ranging in size from 0.007-0.072 in (2-22 mm) long. The reproductive members of the species have wing spans of 0.03-0.3 in (10-90 mm). Inhabiting nests of their own construction, they live in permanent and often highly developed communities. While termites thrive in warm, humid environments, some species have also adapted to open savannas and temperate zones. …
A tumor (also known as a neoplasm) is an abnormal tissue growth. Neoplasm means "new formation." Tumors can be either malignant (cancerous) or nonmalignant (benign) but either type may require therapy to remove it or reduce its size. In either case the tumor's growth is unregulated by normal body control mechanisms. Usually the growth is not beneficial to the organ in which it…
Walkingsticks are insects with a long, thin body, lengthy delicate legs and a brown-green color which gives them a striking resemblance to a twig. Walkingsticks are in the family Phasmidae in the order Orthoptera, which also includes the grasshoppers and crickets. There are almost 2,500 species of walkingsticks (phasmids), ranging in size from 1 in (2.5 cm) to 1 ft (30 cm), the largest species occ…
Stem cells are undifferentiated cells that have the capability of self replication as well as being able to give rise to diverse types of differentiated or specialized cell lines. Stem cells are subclassified as embryonic stem cells, embryonic germ cells, or adult stem cells. Embryonic stem cells are cultured cells that were originally collected from the inner cell mass of an embryo at the blastoc…
Tuna are large, fast-swimming bony fish (teleosts of the family Scombridae) found in waters of the world's oceans. All species of tuna are economically important, usually supporting a large commercial fishery, and sometimes a local sport fishery. The largest species is the bluefin tuna (Thunnus thynnus), which can achieve a length of 13 ft (4 m) and weigh up to 1,760 lb (800 kg). Population…
Terns are fast-flying coastal birds in the family Sternidae, which includes some 42 species. Most species of terns are found in the tropics and subtropics, but these birds occur on all continents. They range from the limits Royal terns (Thalasseus maximus) on Estero Island, Florida. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. of land in the highest A…
The walnut family contains about 60 species of trees in the family Juglandaceae, divided among seven genera. North American representatives are the walnuts (Juglans spp.) and hickories (Carya spp.). All of these species produce edible nuts and useful wood, and some are cultivated in orchards for the production of these crops. …
The walrus (Odobenus rosmarus) is one of the largest seals, order Pinnipedia. Although similar in many respects to other seals, particularly the eared seals, the walrus is sufficiently different to merit being placed in its own family, Odobenidae. It is the sole member of that family, with only a few subspecies. The genus name is derived from the Greek words for "tooth" and "I…
Tundra is a generic name for a low-growing ecosystem found in climatically stressed environments with short and cool growing seasons. Latitudinal tundra occurs in the Arctic and to a much lesser extent in the Antarctic, where the environments are characterized by cool, short growing seasons. Altitudinal tundra occurs under a similar climatic regime, but at the tops of mountains. After temperature,…
The word terrace is applied to geological formations, architecture such as a housing complex built on a slope, or an island between two paved roads. However, Rice terraces in Bali, Indonesia. JLM Visuals. Reproduced by permission. the act of terracing specifies an agricultural method of cultivating on steeply graded land. This form of conservation tillage breaks a hill into a series of ste…
Tunneling, also known as the tunnel effect, is a quantum mechanical phenomenon by which a tiny particle can penetrate a barrier that it could not, by any classical or obvious means, pass. Though seemingly miraculous, the effect does have some intuitive characteristics. For instance, thin barriers allow more particles to tunnel than do thick ones, and low barriers permit more tunneling than do high…
Warblers are small, perching song birds with a large number of species distributed throughout the world. There are two families of warblers, one in the New World and one in the Old World. The New World warblers (family Parulidae) comprise 113 species that occur throughout the Americas. The Old World warblers (family Silviidae) occur in Eurasia, Africa, and Australia, and include some 325 species. …
Stereochemistry is the study of the three dimensional shape of molecules and the effects of shape upon the properties of molecules. The term stereochemistry is derived from the Greek word stereos, which means solid. …
Turacos, or touracos, are 18 species of sub-Saharan birds that make up the family Musophagidae, in the order Cuculiformes, which also includes the cuckoos, anis, coucals, and roadrunner. The usual habitat of turacos is dense tropical forests or forest edges. Turacos do not migrate, although they may move locally. Turacos are medium- to large-sized birds, with a body length of 1.2-2.5 ft (38-76 cm)…
Sticklebacks are small, bony fish in the family Gasterosteidae that rarely exceed 3 in (8 cm) in body length. Instead of scales, these fish have bony plates covering their body. Sticklebacks are found in North America and northern Eurasia. The name stickleback is derived from the sharp, thick spines arising in the first dorsal fin. The number of these spines forms part of the basis for the identif…
Territoriality is the behavior by which an animal lays claim to and defends an area against others of its species, and occasionally members of other species as well. The territory defended could be hundreds of square miles in size, or only slightly larger than the animal itself. It may be occupied by a single animal, a pair, family, or entire herd or swarm of animals. Some animals hold and defend …
Tetanus, also known as lockjaw, is a disease caused by a type of bacteria that lives in the soil and the intestines of people and animals. When these bacteria get into the body, the poisons they produce affect the nervous system, causing muscle spasms and, in many cases, death. Tetanus is not contagious and can be prevented with a vaccine. Tetanus is caused by the bacteria Clostridium tetani. Teta…
Wasps are slim-waisted, stinging insects in the order Hymenoptera. There are two main groups of wasps: the solitary wasps are relatively small parasites of other arthropods, while the social wasps are larger and live in colonies. Some other groups of tinier hymenopterans are also commonly known as wasps. Wasps are familiar insects to most people, and they are good insects to know about because was…
Stilts and avocets are long-legged, long-beaked wading birds of the muddy shores of shallow lakes and lagoons, including both fresh and saline waters. There are fewer than ten species of stilts and avocets all of which are included in the family Recurvirostridae. These birds occur in the temperate and tropical zones of all of the continents except Antarctica. The bill of stilts is rather straight,…
A tetrahedron is a polyhedron with four triangular faces. It is determined by four points (the vertices) that are not all in the same plane. A regular tetrahedron is one where all of the faces are congruent equilateral triangles. A tetrahedron is the same as a pyramid with a triangular base. …
A turbine is any of various rotary machines that convert the kinetic energy in a stream of fluid (gas or liquid) into mechanical energy by passing the stream through a system of fixed and moving fans or blades. Turbines are simple but powerful machines that embody Newton's third law of motion which states that for every action there is an equal and opposite reaction. They are classified acc…
The term stimulus has many meanings; very generally, it is any occurrence (be it an external event, or anything perceived or thought) that causes a detectable response. Stimulus is often used with qualifying terms to further specify its meaning, for example, conditioned stimulus and neutral stimulus. Various fields of study use the term stimulus in different ways. In psychology, it is most often u…
Turbulence is the formation of eddies in a fluid (liquid or gas). It is produced whenever a fluid (under certain conditions) is in contact with a solid and there is relative motion between them; for example: when wind flows past a building or past a mountain; when the ocean flows past an island; when a baseball flies by; when a jet plane moves in the stratosphere; or when a river flows past a brid…
Turkeys are relatively large, powerful, ground-feeding, North American birds with colorful, featherless heads, classified in the family Phasianidae. The original range of the common turkey (Meleagris gallopavo) was from extreme southern Ontario to Mexico, but it now occupies a much smaller area. The second species in this family is the ocellated turkey (Agriocharis ocellata), which occurs in south…
It is possible that ever since people first came to be, stone was used in constructing something: a fence, an oven in a hole or trench, or a shelf in a cave. And it is possible that sometime during this era, someone coined the statement: "Leave no stone unturned." The many cairns and stone hedges erected for religious or astronomical uses were the initial attempts at masonry. However…
Stoneflies or salmonflies are a group of insects with aquatic nymphal stages in the order Plecoptera. Stoneflies have a simple metamorphosis, with three life-history stages: egg, nymph or naiad, and adult. Adult stoneflies have two pairs of membranous wings that are folded back over the abdomen when not in use. Stoneflies are rather weak fliers, and are not usually found very far from the aquatic …
Textiles are generally considered to be woven fabrics. They may be woven from any natural or synthetic fibers, filaments, or yarns that are suitable for being spun and woven into cloth. Spinning is the process of making yarn or thread by the twisting of vegetable fibers, animal hairs, or man-made fibers, i.e., filament-like elements only a few inches in length. In the spinning mill, the raw materi…
Waste management is the handling of discarded materials. Recycling and composting, which transform waste into useful products, are forms of waste management. The management of waste also includes disposal, such as landfilling. Waste can be almost anything, including food, leaves, newspapers, bottles, construction debris, chemicals from a factory, candy wrappers, disposable diapers, old cars, or ra…
Storks are large wading birds of the tropics and subtropics. They belong to the order Ciconiiformes, which A white stork and its nest in Turkey. JLM Visuals. Reproduced by permission. also includes the ibises and spoonbills. Storks are in the family Ciconiidae. Unlike most tall wading birds, storks will perch in trees. They also nest in high places, and often return to the same nesting sit…
Thalidomide is a drug that was marketed in the late 1950s and early 1960s in Great Britain and Europe. It was used both as a sleeping pill and as an antidote to morning sickness in pregnant women. In 1962, a host of usually rare limb abnormalities suddenly became much more common. About 10,000 babies were born displaying, in particular, a shortening of the arms and/or legs called phocomelia. In ph…
Toxins are poisonous materials that interfere with vital metabolic processes to sicken or kill living organisms. Toxins can be either general poisons that kill many types of cells and organisms, or they can be extremely specific in their target and mode of action. Some are extremely reactive and can be lethal even in very dilute concentrations. Ricin, for instance, is a protein found in castor bea…
A storm is any disturbance in the atmosphere that has noticeable effects on the earth's surface. The term suggests disagreeable weather conditions that may bring discomfort, inconvenience, economic disaster and loss of human lives. In spite of that fact, storms have a generally positive effect on the environment and on human societies because they are the source of most of the rain and snow…
Storm surge, caused by very low atmospheric pressure, is a volume of oceanic water driven by the wind toward the shore where it "builds up" along the coast producing a localized increase in sea level. Such low atmospheric pressure occurs during cyclonic storms, called typhoons in the Pacific region and hurricanes along the Atlantic seaboard. During these storms, a dome of water forms…
Strata (singular: stratum) are the horizontal layers, or beds, present in most sedimentary rocks. During or immediately after the accumulation of sediments, physical, biological, and chemical processes produce sedimentary structures. Strata are probably the most common sedimentary structures, as almost all sedimentary rocks display some type of bedding. A rock that contains beds is stratified or d…
A theorem (the term is derived from the Greek theoreo, which means I look at) denotes either a proposition yet to be proven, or a proposition proven correct on the basis of accepted results from some area of mathematics. Since the time of the ancient Greeks, proven theorems have represented the foundation of mathematics. Perhaps the most famous of all theorems is the Pythagorean theorem. Mathemati…
Water is the most abundant liquid on Earth. It covers more than 70% of the earth's surface. Including the clouds (which are, of course, also water), it makes our entire planet look blue and white from space. It is impossible to overstate the importance of water to almost every process on Earth, from the life processes of the lowest bacteria to the shaping of continents. Water is the most fa…
Water bears or tartigrades are about 500 species of tiny aquatic invertebrate animals in the phylum Tartigrada, including about 90 species in North America. Water bears have a very widespread distribution, occurring in moist habitats from the Arctic to the Antarctic and on mountains as high as 19,680 ft (6,000 m). Water bears have roughly cylindrical dark-colored bodies with four body segments and…
Stratigraphy is the science of interpreting and describing layers and strata of sediments. Commonly these layers are levels of sedimentary rock, but stratigraphy can also include the study of non-ossified sediments, like those in stream beds and lake bottoms, of inclusions such as volcanic ash and lava, and even the study of different layers of human occupation. Sediment usually forms distinct str…
The most easily observed examples of thermal expansion are size changes of materials as they are heated Figure 1. Representation of thermally induced change in a bimetallic strip made of iron and aluminum. The strip bends because the two materials do not expand or contract equally. Illustration by Hans & Cassidy. Courtesy of Gale Group. or cooled. Almost all materials (solids, liqu…
The hydrosphere refers to that portion of the earth that is made of water, including all oceans, lakes, rivers, streams, glaciers, and underground water. Less than 3% of the water of Earth is freshwater, an amount that includes polar ice caps, glaciers, groundwater, surface water of rivers and freshwater lakes, and even atmospheric water. However, the amount of freshwater useable by people and oth…
Stratigraphy is the study of layered materials (strata) that were deposited over time—their lateral and vertical relations, as well as their composition. The basic law of stratigraphy, the law of superposition, states that lower layers are older than upper layers, unless the sequence has been disturbed. Stratified deposits may include soils, sediments, and rocks, as well as man-made structu…
Turtles are familiar, four-legged reptiles whose body is enclosed within a bony shell. Turtles constitute the reptilian order Testudines. The 257 living species inhabit all continents except Antarctica, plus many islands, and there are marine turtles in all tropical and temperate oceans. The turtles are separated into two major groups (subclasses) that can be readily identified by the way they ret…
Streams channel water downhill under the influence of gravity. Stream capacity is a measure of the total sediment (material other than water) a stream can carry. Stream competence reflects the ability of a stream to transport a particular size of particle (e.g., boulder, pebble, etc). With regard to calculation of stream capacity and competence, streams broadly include all channelized movement of …
The water lily, yellow water lily, lotus, and several other aquatic plants are about 60 species of aquatic herbs that make up the family Nymphaeaceae. These plants occur in shallow, fresh waterbodies from the boreal to the tropical zones. The usual habitats of these plants are ponds and shallow water around lake edges, as well as slowly-flowing pools and stagnant backwaters in streams and rivers. …
Also known as twisted-winged parasites, strepsipterans are small insects which are internal parasites of other insects. Measuring between 0.02-0.16 in (0.5 and 4 mm) long, the males and females lead totally different lives. Males are free, winged insects—resembling some forms of beetles—and females are wingless, shapeless insects living as parasites. Strepsipterans live all over the …
Water microbiology is concerned with the microorganisms that live in water, or can be transported from one habitat to another by water. Water can support the growth of many types of microorganisms. This can be advantageous. For example, the chemical activities of certain strains of yeasts provide us with beer and bread. As well, the growth of some bacteria in contaminated water can help digest the…
Any physical, biological, or chemical change in water quality that adversely affects living organisms or makes water unsuitable for desired uses can be considered pollution. Often, however, a change that adversely affects one organism may be advantageous to another. Conversely, antibiotic designed for use at one site, might pose a pollution threat to non-target or beneficial downstream microorgani…
Accurately measuring temperatures over a wide range is a challenge to engineers, physicists, and other scientists. Many techniques have been devised to deal with a wide range of conditions and temperatures. One such technique is a thermocouple. A thermocouple makes use of one aspect of the thermoelectric effect to measure temperatures, the voltage produced between two different wires with junction…
Typhoid fever is a severe infection causing a sustained high fever, and caused by the bacteria Salmonella typhi. S. typhi is in the same tribe of bacteria as the type spread by chicken and eggs, commonly known as "Salmonella poisoning," or food poisoning. S. typhi bacteria, however, do not multiply directly in food, as do the Salmonella responsible for food poisoning, nor does it hav…
Water is treated to make it safe to drink and to use for other purposes, such as to spray on agricultural plants. Water that contains domestic and industrial waste is often required to be treated to lessen or remove the contaminants prior to the discharge of the water into a river, lake, or ocean. Some industrial processes require water that is free of impurities and microorganisms. One example is…
Stress is mental or physical tension brought about by internal or external pressures. Researchers have found significant biochemical changes that take place in the body during stress. Exaggerated, prolonged, or genetic tendencies to stress cause destructive changes which lower the body's immune system response and can lead to a variety of diseases and disorders. These include depression, ca…
Waterbucks belong to the large family of bovids, plant-eating hooved animals with horns and a four-chambered stomach for extracting nutrients from a diet of grass or foliage. These ruminants regurgitate food that is rechewed (chewing the cud). Domestic cattle, also of the bovid family, chew their cud. …
String theory (also termed "superstring" theory) is a mathematical attempt to describe all fundamental forces and particles as manifestations of a single, underlying entity, the "string." String theory's predictions are consistent with all known experimental data, and it is felt by some physicists to be a candidate for the long-sought "theory of every thin…
A watershed refers to land that is drained by an interconnected system of rivulets, streams, rivers, lakes, and groundwater. Water from a watershed eventually drains into a common destination. Both rain and snow contribute to the watershed. Coastal watersheds that begin as rivulets often end as large rivers that empty into a lake or an ocean. Watersheds can range in size from just a few square mil…
A stroke, also called a cerebral vascular accident or CVA, is a sudden, often crippling disturbance in blood circulation in the brain. Interruption in blood circulation may be the result of a burst artery or of an artery that has become closed off because a blood clot has lodged in it. Blood circulation to the area of the brain served by that artery stops at the point of disturbance, and the brain…
Typhus is a disease caused by a group of bacteria called Rickettsia. Three forms of typhus are recognized: epidemic typhus, a serious disease that is fatal if not treated promptly; rat-flea or endemic typhus, a milder form of the disease; and scrub typhus, another fatal form. The Rickettsia species of bacteria that cause all three forms of typhus are transmitted by insects. The bacteria that cause…
The waterwheel is considered the first rotor mechanism in which an outside force creates power to spin a shaft. The Greeks are said to have first developed the waterwheel, using it to raise water from rivers. Polls or pots were attached around the circumference of a large wheel; then oxen would walk in a circle round a vertical shaft connected through a simple gear to the horizontal shaft of the w…
A stromatolite is a preserved structure in sedimentary rock that is a series of thin layers of sediment. These layers formed when a colony of algae trapped loose sediment particles. Stromatolites occur in rocks that range in age from very recent to more than 3.5 billion years old. Ancient stromatolites are the oldest evidence of life that is visible without a microscope. They are also the most com…
Tyrannosaurus rex or T. rex, is easily the most famous of the Tryannosaurids (tyrant reptile). Despite its popularity, T. rex appears to have had a limited range in North America and Asia, and existed for a relatively short period of time. T. rex appeared during the late Cretaceous Period, about 85 million to 65 million years ago. This was toward the end of the Mesozoic Era or the Age of Reptiles,…
A wave is nothing more than a disturbance that moves from place to place in some medium, carrying energy with it. Since the behavior of waves is so closely related to the concept of oscillations, that is a good place to start. There are many examples of simple oscillations, but a very good one is that of an object attached to the end of a spring. Assume that the other end is held fixed, perhaps by…
Sturgeons are large shark-like fish, with a heterocercal tail like that of a shark and a small ventral mouth behind an extended snout. The mouth has long barbells used for feeding on small animals on the bottom. Sturgeons feed on aquatic insects, snails, crayfish, small clams, and small fish. Sturgeons have a cartilaginous skeleton with bony plates instead of scales in their skin which cover the s…
Waxbills are 107 species of finch-like birds that make up the family Estrilidae. Species of waxbills occur in the tropics of Africa, South and Southeast Asia, New Guinea, Australia, and many islands of the South Pacific. Their usual habitats are grasslands, marshes, savannas, forest edges, and disturbed forests. Waxbills are sedentary, nonmigratory birds. Waxbills are small birds, ranging in body …
The tyrant flycatchers are a large family of perching birds, containing 367 species, and making up the family Tyrannidae in the order Passeriformes. Tyrant flycatchers only breed in the Americas, from the northern boreal forest of Canada, through the rest of North America, Central America, and to South America as far south as Patagonia. Rarely, individual tyrant flycatchers may occur in coastal Eu…
Waxwings are medium-sized, fruit-eating, perching birds found in northern Eurasia and North America that Cedar waxwing (Bombycilla cedrorum). Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. are included in the family Bombycillidae. Waxwings have a crest on the top of their head, and have soft, sleek, often shiny plumage. The secondary feathers often hav…
Weasels, ermines, and stoats are various species of small carnivores in the family Mustelidae, which also includes the otters, badgers, martens, minks, skunks, and wolverine. Species of weasels occur in North America, northern South America, northern Africa, Europe, Asia, and Southeast Asia. Weasels have a long, lithe, almost serpentine body, and short legs. This body shape is highly adaptive for …
Subatomic particles are particles that are smaller than an atom. Early in the twentieth century, electrons, protons, and neutrons were thought to be the only subatomic particles; these were also thought to be elementary (i.e., incapable An electronic display of the decay of an upsilon, a particle made of a bottom quark and an antiquark, in the CLEO detector at the CESR collider at Cornell Uni…
Thermodynamics is the science that deals with work and heat, and the transformation of one into the other. It is a macroscopic theory, dealing with matter in bulk, disregarding the molecular nature of materials. The corresponding microscopic theory, based on the fact that materials are made up of a vast number of molecules, is called statistical mechanics. The conservation of energy is well known …
The first known treatise on submarines was written in 1578. Published by William Bourne in his Inventions or Devices, the document describes a ship with two hulls, the outer made of wood. While no record exists concerning its manufacture, the ship, according to Bourne, could be submerged or raised by taking in or expelling water from between the double hulls. The first known submarine was built by…
A thermometer is a device that registers the temperature of a substance relative to some agreed upon standard. Thermometers use changes in the physical or electronic properties of the device to detect temperature variations. For example, the most common thermometer consists of some sort of liquid sealed into a narrow tube, or capillary, with a calibrated scale attached. The liquid, typically mercu…
An ulcer is a sore that develops in the lining of the stomach or the duodenum, the short section of small intestine that leads away from the stomach, or on the surface of the skin as a result of infection with bacteria. An ulcer in the stomach is called a gastric ulcer; an ulcer in the duodenum is called a duodenal ulcer; and an ulcer on the skin is called a decubitus ulcer. …
Stoicism, from its foundation, has been most famous for its ethical ideas. Even now, stoical suggests a particular ethical stance, endurance of pain or misfortune without complaint. But in antiquity Stoicism was notable also for its unified view of the scope of philosophy and of the nature of reality. …
A thermostat is a device for controlling heating and cooling systems. It consists of a circuit controlled by a temperature sensitive device and connected to the environmental system. The most common thermostat, such as the one seen in homes and offices, is based on a bimetallic strip. As its name suggests, a bimetallic strip consists of thin strips of two different metals bonded together. One meta…
An ultracentrifuge is a mechanical device that separates substances of different densities by spinning them very fast. It greatly reduces the time it would take to separate substances that would eventually separate if left alone. The first successful centrifuge was invented in 1883 by Swedish engineer Carl de Laval. It was used to separate cream from milk. Forty years later, another Swede, chemist…
Structuralism was both an intellectual movement with wide ramifications in the twentieth century and an attempt to provide scientific status to the knowledge of language, culture, and society. Structuralism originated in the work of Ferdinand de Saussure (1857–1913), a Swiss linguist whose lectures, when published by his students in 1916 (Course in General Linguistics), launched the new sch…
Thistle is the common name given to some plants in several genera of the Cynareae tribe, family Asteraceae. These genera include Cirsium, Carduus, Echinops, Onopordum, Silybum, Centaurea, and Cnicus. The name thistle most often refers to the weedy, prickly plants belonging to the genera Cirsium and Carduus. Thistles are composite flowers, which means their flower is actually a group of small flowe…
Structuralism in anthropology is inextricably linked with its founder, Claude Lévi-Strauss. His principal contributions have been in the field of kinship and in the analysis of symbolism, particularly of myths. The characteristic approach of structuralist analysis is to categorize systems, not in terms of the composition or content of their component elements, but in terms of the structure of…
Thoracic surgery refers to surgery performed in the thorax or chest. The anatomy and physiology of the thorax require special procedures to be carried out for the surgery to be done. The thorax is the bony cage consisting of the ribs, the spine, and the breastbone or sternum. The floor of the thorax is formed by the diaphragm. Within the thorax lie the two lungs and the heart, the organs whose fun…
Weather can be defined as the condition of the atmosphere at any given time and place. Weather conditions are determined by six major factors: air temperature, air pressure, humidity of the air, amount and kind of cloud cover, amount and kind of precipitation, and speed and direction of the wind. Weather condition patterns for any one region or for the whole planet can be charted on a weather map …
Subjectivism's natural antonym is objectivism, and various species of subjectivism have been developed as alternatives to objectivism of various sorts. One can be a subjectivist about a variety of things—ethics, aesthetics, even science. Many of these topics are covered in related entries, however, and the emphasis here will be on subjectivism with respect to ethics in modern and con…
Thrips are minute (less than 0.20 in or 5 mm) slender-bodied insects of the order Thysanoptera, characterized by two pairs of veinless, bristle-fringed wings, which are narrow and held over the back when at rest. Although thrips have wings, they do not fly. There are 4,500 species of thrips worldwide. In North America, there are 694 species of thrips in a number of families in two suborders, the T…
Sufism is the English rendering of the Arabic word tasawwuf, which derives from suf, meaning "wool." Tasawwuf in early Islamic history refers to the attitude of people who used to wear a white woolen garment as a sign of renunciation of worldly possessions. To be properly understood, the emergence of Sufism must be situated in the context of Islamic expansion. During the first and se…
The term subsidence is used in both atmospheric and geological sciences. Atmospheric subsidence refers to the sinking of air that is denser (heavier) than the air below. As it subsides, increasing air pressure compresses the air parcel, causing it to warm. Geologic subsidence is a form of mass wasting that refers to the sinking of geologic materials (rocks or sediments) as underlying materials are…
Thrombosis is the formation of a blood clot, or thrombus, in a blood vessel. The process is an exaggeration of a normal and useful event by which the body prevents the loss of blood from veins and arteries as a result of an injury. During thrombosis, the blood clotting process goes beyond the construction of a blockage for a damaged blood vessel and actually produces a solid clump (the clot) that …
The word suicide is a seventeenth-century English invention put together from Latin elements and meaning literally "self-slaughter," and from English the word spread to other European languages. An isolated scholar around 1130 had in fact coined a Latin word suicida, but it had not gained currency, and that fact highlights the question why so ancient an act should have had to wait so…
Superstition has had different meanings in different cultures and epochs. One thing binding these meanings together is that they are usually negative—superstition is a concept defined principally by its self-declared opponents. A second is that superstition is defined as the opposite of something praiseworthy—usually true religion or true science. The word superstition itself origina…
In view of its global impact, as Anna Balakian has persuasively argued, Surrealism constituted the major poetic and artistic current of the twentieth century. Of the dozens of movements that vied for this honor, Surrealism proved to be the most influential and the most persistent. Although abstraction enjoyed a huge success, it was limited almost entirely to art. Surrealism's most serious r…
The symbolist movement began in France in the 1880s as a literary phenomenon. The term symbolism, however, quickly came to encompass a range of arts, from painting and sculpture to theater and music. While the movement is often said to have spanned the years 1885–1895, the ideas and aesthetic interests of symbolism are often traced back to the middle of the nineteenth century, and many earl…
Syncretism—the process whereby two or more independent cultural systems, or elements thereof, conjoin to form a new and distinct system—is among the most important factors in the evolution of culture in general, but especially in the history of religion. Indeed, all of the so-called world religions, that is, Christianity, Judaism, Islam, Hinduism, Buddhism, and Confucianism, are to a…
Thrushes are a diverse group of about 305 species of common, medium-sized, perching, song birds ranging from 4.5-13 in (11-33 cm) in body length in the family Turdidae. Thrushes occur world-wide in a wide range of habitats, but mostly in forests. Some species of thrushes are common in parks and gardens containing shrubs and trees not intensively treated with insecticides. Examples of these familia…
Ultrasonics or ultrasound, derived from the Latin words "ultra," meaning beyond, and "sonic," meaning sound, is a term used to describe sound waves that vibrate more rapidly than the human ear can detect. Sound waves travel as concentric hollow spheres. The surfaces of the spheres are compressed air molecules, and the spaces between the spheres are expansions of the air…
Weather forecasting is the attempt by meteorologists to predict the state of the atmosphere at some future time and the weather conditions that may be expected. Weather forecasting is the single most important practical reason for the existence of meteorology as a science. It is obvious that knowing the future of the weather can be important for individuals and organizations. Accurate weather fore…
We tend to use the word taste in two different ways. First, to refer to the ability to judge a thing correctly, usually (but not always) a work of art from an aesthetic point of view. Second, we use the word to refer to a particular set of aesthetic preferences, and given the most popular sense of this second usage, we understand that one person's set of preferences may differ from another …
Introduced in the first decades of the nineteenth century, the word technology signified the pursuit of a science to encompass all the industrial arts. Mechanical arts, a term used in medieval and early modern Europe, indicated something different because it included, for example, painting and sculpture. The introduction of the term technology corresponded somewhat contemporaneously with the intro…
Making inferences about the nature and structure of buried rock bodies, without access to them, is called subsurface detection. Using geophysical techniques, we obtain data at the surface that characterize the feature buried below. Then we construct models of the feature, trying to invent combinations of reasonable rock bodies which are consistent with all of the observations. Finally, using intui…
In classical and medieval thought, temperance, or sōphrosynē, could signify one or more of a congeries of traits, such as moderation, self-knowledge, self-restraint, or independence. These virtues were to be cultivated by the individual. In modern history, however, the meaning of temperance has become narrowed to refer only to limits on the consumption of alcoholic beverages, whether t…
A thunderstorm is a strong disturbance in the atmosphere bringing heavy rain, lightning, and thunder to areas from one to hundreds of kilometers across. Thunderstorms are formed when humid air near the surface begins rising and cooling. The rising air forms clouds. Lightning over Tamworth, New South Wales, Australia. Photograph by Gordon Garrado. Science Photo Library, National Audubon Societ…
An apprehension of danger or impending violence, terror is akin to fear in an accentuated or distilled form and is often accompanied by trembling. It underpins many aspects of existence, especially the cut-and-thrust of the evolutionary drive and the predatory nature of the food chain. Lacking the "blood and sawdust" element associated with "horror," it has nevertheless…
Ultraviolet astronomy is the study of astronomical objects in the ultraviolet portion of the electromagnetic spectrum. Because Earth's atmosphere prevents ultraviolet radiation from reaching its surface, ground-based observatories cannot observe in the ultraviolet. Only with the advent of space-based telescopes has this area of astronomy become available for research. Ultraviolet radiation …
Weather mapping is the process of representing existing weather patterns and their future development and movement on a map. The process is only possible if two conditions are met. First, current weather conditions must be available at a number of relatively widely distributed stations. Second, reports of those conditions must be transmitted to a central collecting station within a short time peri…
This is not a definition. Well, of course it is—after all, it is appearing in a dictionary—and yet, in a certain and actually rather important way, it is not. Or, put differently, precisely to the extent that the text is not an idea, this is not a definition. Of course, the text can be treated as an idea, perhaps even one whose time has come, but doing so misses something important …
Working with fiber has generated many seminal ideas in the course of human history, including the first notions of rotary motion, machines, and computers. The fiber arts also have provided an important means of expression of the human condition. …
Subtraction is the operation that is the inverse of addition. Subtracting a number has the effect of nullifying the addition of that same number. For example, if one adds 11 to 41 then subtracts 11, the result is 41 again. Symbolically, for any numbers a and b, (a + b) - b = a Or one can subtract first, then add: (a - b) + b = a Thus, one can say that subtraction and addition are "inverse o…
"Performance" is an influential theoretical paradigm in the arts and humanities, with adherents in disciplines as diverse as anthropology, linguistic philosophy, and theater. Since the early 1980s, thinking about performance has been fostered in "performance studies" programs, disciplinary hybrids with widely variant intellectual genealogies, united by their commitment …
Gottfried Wilhelm Leibniz's (1646–1716) neologism théodicée (from Greek theos, God dike, justice) means divine justice, but the term has long been conflated with John Milton's (1608–1674) promise to "justify the ways of God to men." In 1791 Immanuel Kant (1724–1804) defined theodicy as "the defense of the highest wisdom of the creat…
An unconformity is a widespread surface separating rocks above and below, which represents a gap in the rock record. Unconformities occur when either erosion wears away rocks, or rock deposits never form. Therefore, a time gap exists between when the rocks below the unconformity formed and when those above it formed. Unconformities are classified as three types. The most easily recognized are angu…
"The anti-imperialist struggle of the peoples of the Third World and of their equivalents inside the imperialist countries constitutes today the axis of the world revolution. Third cinema is, in our opinion, the cinema that recognizes in that struggle the most gigantic cultural, scientific and artistic manifestation of our time, the great possibility of constructing a liberated personality …
The term Third World has long served to describe countries of Africa, Asia, and Latin America that have been seen to share relatively low per-capita incomes, high rates of illiteracy, limited development of industry, agriculture-based economies, short life expectancies, low degrees of social mobility, and unstable political structures. The 120 countries of the Third World also share a history of u…
As a term of standard usage, though still minus "literature," Third World dates from the 1950s. (The Oxford English Dictionary's first listing for it—still in its French form of Tiers Monde—is dated 1956.) Supposedly coined by the French sociologist Alfred Sauvy (1898–1990) in 1952, it initially referred to the independent and soon-to-be-independent nation…
Chinese thinkers did not devise philosophies, pedagogies, or keys of the sort developed in the West concerning time, and the context was chiefly driven by the state's need for cosmological and ritual correctness, and in some cases by cosmological and apocalyptic notions conveyed in Buddhist and Daoist scriptures. Yet China also produced its own sophisticated metaphysics of time—more …
Succession is a process of ecological change, involving the progressive replacement of earlier biotic communities with others over time. Succession usually begins with the disturbance of a pre-existing ecosystem, followed by recovery. In the absence of further stand-level disturbance, succession culminates in a stable climax community, the nature of which is determined by climate, soil, and the na…
Tides are deformations in the shape of a body caused by the gravitational force of one or more other bodies. All bodies in the universe exert tidal forces on each other, although the effects are generally too small to observe. As far Earth is concerned, the most important tidal phenomena are the ocean and ground tides that occur as a result of the Moon's and the Sun's gravity. …
In general, the conceptualization of time in Indian religious and philosophical thought is framed by a dichotomy between the phenomenal world and absolute transcendence—that is, the realms of time and the timeless. The former, the sphere of contingent temporality, is usually understood to be the world of suffering, of change and impermanence, of what is known in Sanskrit as samsara. The lat…
The term weather modification refers to any deliberate effort on the part of humans to influence weather patterns for some desirable purpose. Probably the most familiar example of weather modification is the seeding of clouds, most often done in order to increase the amount of precipitation during periods of drought. The earliest scientific programs on weather modification date to the 1940s when V…
A primary distinction separates sequential (or utilitarian) time, which has to do with the relations of before and after, from traditional time, which has to do with the relation of the present to both the past and the future. For Émile Durkheim (1858–1917), traditional societies were based on solidarities in traditional time, and they relegated to the margins of social life practical …
Suckers are cylindrical fish with a downward-pointing suckering mouth in the family Catostomidae, which is in the large suborder Cyprinoidea, which also includes minnows, carps, and loaches. Most species in the sucker family occur in the Americas, over a range that extends from the boreal forest of North America through much of Central America. A few other species occur in eastern Siberia, and the…
Toleration is a policy or attitude toward something that is not approved and yet is not actively rejected. The word comes from the Latin tolerare (to bear or endure), suggesting a root meaning of putting up with something. There is no single and widely accepted definition of the term, and it is hardly an exaggeration to say that every author uses it in his or her own way. Therefore it may be best …
Totalitarianism is a concept rooted in the horror of modern war, revolution, terror, genocide, and, since 1945, the threat of nuclear annihilation. It is also among the most versatile and contested terms in the political lexicon. At its simplest, the idea suggests that despite Fascist/Nazi "particularism" (the centrality of the nation or the master race) and Bolshevist "univer…
Time is a measurement to determine the duration of an event, or to determine when an event occurred. Time has different incremental scales (year, day, second, etc.), and it has different ways by which it is reported (Greenwich Mean Time, Universal Time, Ephemeris Time, etc.). …
Underwater exploration is the relatively recent process of investigating the depths of the sea to understand its physical and chemical characteristics and to learn about the life forms that inhabit this realm. Underwater exploration near the surface and near the shore is an ancient form of earning a livelihood and enjoying the pleasures of the water; but deep-sea exploration is a recent phenomenon…
The word totem is an anglicized rendering of the Ojibwa word ninto:tem. It refers to an animal or plant species emblematic of a specific group, notably a clan. While the term was originally applied only to practices of natives of northeastern North America, it was soon extended to refer to superficially similar phenomena around the globe, whose observances came to be known as "totemism.�…
Ungulates are large grazing animals whose toenails have become enlarged into hooves. There are two orders of ungulates: Perissodactyla and Artiodactyla. Animals in the order Artiodactyla have an even number of toes (usually two) that form a cloven hoof. This order is relatively diverse, containing 82 genera and several hundred species. There are nine families in this order, the most familiar of wh…
Trade is one of the basic processes that link individuals and groups. Trade binds people to one another through the expectations of reciprocal giving, through the formal calculus of wages and markets, and through the desires or needs to obtain items not locally available. In this way, trade is a fundamental element of human culture. Trade and exchange are often used synonymously, but there is a ba…
Tinamous are about 45-50 species of ground-dwelling birds that comprise the family Tinamidae, the only member of the order Tinamiformes. Tinamous have a plump, partridge-like body, but they are not related to the "true" partridges, which are species in the pheasant family (Phasianidae). The evolutionary relationships of tinamous are not well understood, but their closest living relat…
Uniformitarianism is commonly oversimplified where stated in geological textbooks as "the present is a guide to interpreting the past" (or words to that effect). This explanation, however, is not correct about the true meaning of uniformitarianism. In order to understand uniformitarianism, one must examine its roots in the Enlightenment era (c. 1750–1850) and how the term has …
Weathering is the process by which rocks and minerals are broken down into simpler materials by means of physical (mechanical), chemical, and biological processes. Weathering is an extremely important phenomenon for the human species since it is the mechanism by which one of the planet's most important natural resources—soil—is formed. The exact way in which weathering occurs …
The basic sense of the term tradition remains quite close to its etymological roots. The Latin noun traditio describes the handing over of an item or an idea, while the English tradition refers to a social or cultural institution that is handed down from the past. This much seems straightforward. Sacrificing cattle, singing at graduation, celebrating the New Year with fireworks: all these appear q…
A tissue is a collection of similar cells grouped to perform a common function. Different tissues are made of their own specialized cells that are adapted for a given function. All animal cells are basically similar. Each cell has a cell wall or plasma membrane that surrounds the cell and contains various receptors that interact with the outside area. A nucleus, Golgi apparatus, mitochondria, and …
Various ideas have been associated with the term tragedy and the term comedy over the centuries, including tragedy that is not tragic, in the sense of "sad" or "disastrous," and comedy that is not comic, in the modern prevalent meaning of "amusing." The modern English meaning of comedy as a synonym for humor is largely a twentieth-century development. …
The tit family, Paridae, consists of 46 species of small birds, variously known as tits, titmice, and chickadees. These are all song birds, in the order Passeriformes. All are rather small birds, ranging in body length from about 4–8 in (11–20 cm), and mostly occurring in forests, shrubby woodlands, and in urban and suburban habitats. This family of birds is widespread, and its repre…
What may summarily be called translation has been practiced in many parts of the world for centuries and even millennia. The rendering of Buddhist texts into literary Chinese and the Latinization of the Bible in the first millennium are two instances of celebrated achievements in the long history of translation. There are countless cases where translations are known to have played a decisive role …
Sudden infant death syndrome (SIDS), also called crib death, is the death without apparent organic cause of an infant under the age of one year. A diagnosis of SIDS can only be made after experts have investigated the death scene, autopsied the dead infant, reviewed the baby's medical history, and ruled out all other possible explanations. About 7,000 babies die of SIDS each year in the Uni…
Weaver finches are a relatively large family of 156 species of perching birds, comprising the family Ploceidae. Weaver finches are native to Africa, Madagascar, Eurasia, and Malaysia. This group is richest in species in Africa. However, some species have been widely introduced outside of their natural range. Species of weaver finches occur in a wide range of terrestrial habitats, including semi-de…
The genre of epic structures the oldest European travel narratives extant, from the voyages of Ulysses to that of Beowulf. The epic as a form connects travel to conflict and cultural threat, as well as to the landscape of fantasy and to the epic hero. Just as the epic hero is larger and more marvelous than life, so the epic landscape is both marvelous and dangerous. The epic hero and those who acc…
The possibility of beet sugar was first discovered in 1605 when a French scientist found that the boiled root of garden beet (Beta vulgaris) yielded a syrup similar to that obtained from sugarcane (Saccharum officinarum). It was not until the mid-1700s, however, that the commercial potential of sugar beets was recognized. Once realized, sugar beets quickly became a major crop in Europe and elsewhe…
Weevils (Curculionidae) comprise a very large group of insects that are closely related to beetles (order Coleoptera); more than 40,000 species are recognized worldwide, ranging in size from 0.2-2 in (0.5-5 cm). A weevil is easily distinguished from a beetle by its extended head, which forms a rostrum, and long, segmented antennae that are clubbed at the end and are usually bent in an elbow fashio…
Although the word treaty can be etymologically traced back to the Latin tractus, meaning treatment, handling, discussion, and management, there was no Latin word with that root having the notion of an (international) agreement. If anything, tractus sometimes had the sense of a disagreement, of a violent handling of affairs, such as the dragging by the hair of the priestess of Apollo. A common Lati…
The sugarcane (Saccharum officinale) is a 12-26 ft tall (4-8 m), perennial, tropical grass (family Poaceae). The tough, semi-woody stems of sugarcane are up to 2 in (5 cm) in diameter, with leafy nodes and a moist internal Harvesting sugarcane. Photo Researchers, Inc. Reproduced by permission. pith containing 15-20% sucrose-sugar. The sugar concentration is highest just before the plant flo…
The term tribe, derived from the Latin tribus, refers to a group of persons forming a community and claiming descent from a common ancestor. In the Middle East and North Africa, unlike many other parts of the world, claiming tribal affiliation often positively affirms community, identity, and belonging. In the mid-to late twentieth century, nationalist leaders in some regions rejected claims to tr…
The trope concept, which is used increasingly in the social sciences to conceptualize the dynamics of definitions (and redefinitions) of social situations involved in communicative interaction, is derived from the Greek tropos (a turning), tropë (a turn), or trepein (to turn). It has long been used as a technical term in rhetoric to designate the use of a word or expression in a different sen…
Titanium is a transition metal, one of the elements found in Rows 4, 5, and 6 of the periodic table. It has an atomic number of 22, an atomic mass of 47.88, and a chemical symbol of Ti. …
A unit of measurement is some specific quantity that has been chosen as the standard against which other measurements of the same kind are made. For example, the meter is the unit of measurement for length in the metric system. When an object is said to be 4 m long, that means that the object is four times as long as the unit standard (1 m). The term "standard" refers to the physical…
The concept of truth is central to Western philosophical thought, especially to such branches of philosophy as metaphysics, epistemology, and the philosophy of language. In particular, the correspondence theory of truth has long been associated with a realist metaphysics, according to which objects exist independently of cognition by the human mind. Alternatives to the correspondence theory have, …
Sulfur is the non-metallic chemical element of atomic number 16. It has a symbol of S, an atomic weight of 32.07, and a specific gravity of 2.07 (rhombic form) or 1.96 (monoclimic form). Sulfur boils at 832.5°F (444.7°C) and consists of four stable isotopes of mass numbers 32 (95.0%), 33 (0.75%), 34 (4.2%) and 36 (0.015%). Sulfur atoms found in different locations have slightly diffe…
Toadfish are a poorly known group of marine fishes, the vast majority of which live close to the shoreline but remain close to the sea bed. Unlike most fish, these animals are extremely vocal, with some authorities even reporting that their loud calls can be heard out of water. One North American genus, Porichthys, is more commonly known as the singing midshipman. The calls are produced by muscula…
Uplift is the process by which the earth's surface slowly rises either due to increasing upward force applied from below or decreasing downward force (weight) from above. During uplift, land, as well as the sea floor, rises. The outer shell of the earth, the crust, divides into moving sections called plates. Uplift, forming mountains and plateaus, usually results as these plates crash into …
Since the late nineteenth century, the debate around issues concerning universalism and universalizability has intensified. Against the claims to universal knowledge made on behalf of Christianity, the West, rationality, and mankind, feminist, critical race, and postcolonial scholars and activists have shown that the issues are more complicated. Notwithstanding the validity of their criticism, uni…
Upwellings are a flow to the surface of deep, cold, nutrient-rich waters from greater depths in the ocean. The most extensive upwellings are associated with persistent coastal currents that draw surface water away from or along the coast to be replaced by a surface-ward flow of deeper waters. The most famous of these sorts of regional upwellings are found off the west coast of southern South Ameri…
The university is a legal corporation empowered by civil or ecclesiastical authorities to award degrees certifying that the recipients have achieved significant levels of expertise in various disciplines. Teachers instruct students of various ages and preparation in higher learning in several subjects. Many, but not all, teachers are scholars who carry on original research in order to add to the b…
Sulfur is an important nutrient for organisms, being an key constituent of certain amino acids, proteins, and other biochemicals. Plants satisfy their nutritional needs for sulfur by assimilating simple mineral compounds from the environment. This mostly occurs as sulfate dissolved in soil water that is taken up by roots, or as gaseous sulfur dioxide that is absorbed by foliage in environments whe…
Welding is a group of processes used to join non-metallic and metallic materials, by applying heat, pressure, or a combination of both. Most welding procedures require heat, although some procedures require only extreme pressure (cold welding). The welding process chosen to join materials together depends upon the mechanical, physical, and chemical properties of the materials to be joined, and the…
The late twentieth century saw a renewed interest in the postcolonial development of higher education systems within broader literature on globalization and education policies. Particularly, efforts by international institutions, such as the World Bank, to prevent the global and local effects of the so-called knowledge divide, led to a number of policy documents and initiatives aimed at leveling t…
One drawback to this approach is that for every ton of sulfur dioxide that reacts, two tons of solid calcium sulfite are produced, and they must be disposed of. Sulfur dioxide is used widely to prevent dried fruits (especially apricots and peaches) from becoming discolored. Sulfur dioxide is a strong reducing agent, and prevents the formation of discolored oxidation products in the fruits. It…
West Nile virus is a member of the family of viruses that is called Flaviviridae. The virus is similar to other members of this viral family, is passed to humans from birds by the bite of a mosquito, and is capable of causing disease in humans. For example, another mosquito borne flavivirus causes St. Louis encephalitis in humans. West Nile virus is endemic in Africa. Periodic outbreaks have occur…
Parallel to the varnas and outside scripture were jatis, meaning "by birth" and also translated as castes. A jati is an endogamous group, sharing many customs and often an occupation, usually based in one language area. There were hundreds of jatis within each varna, and while untouchables were avarna, without varna, they were members of specific jatis. …
One of the major uses of sulfuric acid is in the production of fertilizers. Phosphate rock is treated with sulfuric acid to produce water soluble phosphates, which are essential for plant growth and survival. It is also the acid used in car batteries. Automobile batteries contain lead, lead oxide, and sulfuric acid. These lead storage batteries are used because they can not only provide the electr…
The true toads are amphibians in the order Anura, family Bufonidae. There are 355 species of toads in 25 genera. The largest group is the genus Bufo, which includes 205 species. Toads are characterized by thick, dry, warty skin, with large poison glands on the side of the head and a relatively terrestrial habit as adults. In contrast, adult frogs have a smooth, slimy skin, and a more aquatic habit…
Menstruation is a physiological process often imbued with powerful cultural and religious symbols. For men, it is a mysterious and sometimes frightening phenomenon—the shedding of blood without visible injury. For women, it has been a double-edged sword. Far too often, it has been used in misogynist ideologies as evidence of the defiling and ungodly nature of the female body, leading many s…
The tomato, or nightshade family (Solanaceae), contains about 85 genera and 2,300 species. Most of the species are tropical or subtropical in distribution, and a Tomatoes in the field. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. few are of great economic importance. The region of greatest species richness is Central and South America, but representativ…
Uranium is the metallic chemical element with an atomic number of 92. Its symbol is U, atomic weight is 238.0, and specific gravity is 18.95. It melts at 2,071.4°F (1,133°C) and boils at 6,904.4°F (3,818°C). Natural uranium consists of three isotopes of mass numbers 234 (0.00054%), 235 (0.711%) and 238 (99.275%). All are radioactive. …
The notion of taboo has a peculiar history: it was originally a Polynesian term referring to a ritual prohibition against contact with a thing, an animal, or a person. The term eventually became a widely discussed anthropological concept, and finally, in its last avatar, has been adopted by most languages to refer to something that is strictly and collectively forbidden. This wide recognition ste…
Tongue worms are bloodsucking endoparasites with a flattened, tongue-like body, and are in the phylum Linguatulida. The final host of these parasites is a predaceous vertebrate, usually a reptile, but sometimes a mammal or a bird. The intermediate host (in which the parasite lives as a larva) can be any of a number of animals, including insects, fish, amphibians, reptiles, and mammals. The 70 spec…
Utilitarianism is the name of a group of ethical theories that judges the rightness of acts, choices, decisions, and policies by their consequences for human (and possibly animal) welfare. These theories have been widely influential among philosophers, economists, and political and social scientists, and, in the early twenty-first century, in the general area of applied or practical ethics. It wou…
Tonsillitis is an inflammation or infection of the tonsils, caused by either bacteria or viruses. The tonsils usually become swollen and very painful, making swallowing difficult. Sometimes the tonsils have spots of exudates (usually leukocytes) or pus on the surface. The surface of the tonsils is covered by recesses or crypts (cryptae tonsillares) that may branch and extend deep into the tonsil. …
The word utopia was coined by Thomas More (1478–1535) as the name of the island described in his Libellus vere aureus nec minus salutaris quam festivus de optimo reip[ublicae] statu, deq[ue] noua Insula Vtopia (1516). While More wrote in Latin, he based his new word on Greek. More combined topos (place or where) with u or ou (no or not) to create nowhere, but in "Six Lines on the Isl…
The Sun is the star at the center of our solar system. It has a diameter of about 420,000 mi (700,000 km) and a surface temperature of 9,981°F (5,527°C). Its visible "surface" is actually a thin gas, as is the rest of its atmosphere and interior. The Sun shines as a result of thermonuclear fusion reactions in its core, and the energy produced by these reactions heats th…
Even seemingly unshakeable axioms are prone to reassessment by historians, and Victorianism is no exception. Even the very period of Victorianism itself stands challenged: historians no longer refer unquestioningly to the North-West Passage (1874) by John Everett Millais. Oil on canvas. A strong patriarchal influence and the importance of family were prominent values in the Victorian Age, possi…
Sunbirds are 105 species of small, lovely birds that make up the family Nectariniidae. Sunbirds occur in Africa, South and Southeast Asia, New Guinea, and Australia. They occupy a wide range of habitats, from forests and savannas to shrubby grasslands, and some agricultural habitats. Sunbirds range in body length from 4-9 in (9-22 cm). The wings are short and rounded, and the tail is quite long in…
Virtual reality, a term that became popularized in the late 1980s with the advent of critical research and new technologies developed by Scott Fisher at NASA-Ames Research Center, has its roots in a broad and colorful evolution of art, technology, and communications. The creation of virtual reality is essentially concerned with the quality and experience of immersion, whether real or simulated. Th…
Virtue ethics is one of the three major ethical approaches in modern moral philosophy, the other two being utilitarianism and deontology. Unlike the latter two, it focuses on the virtues. In the Western tradition of philosophy, virtue ethics begins with the ethical writings of Plato and Aristotle, but in the Eastern tradition its origins are even earlier. Confucius discussed in detail what might b…
Wetlands are low-lying, depressional ecosystems that are permanently or periodically saturated with water at or close to the surface. The vegetation of wetlands must be adapted to the physical and chemical stresses associated with flooded substrates. The most common types of wetlands are swamps, marshes, shallow open waters, and mires, the latter consisting of peat-accumulating fens and bogs. Wetl…
While visual culture has certainly been around as long as culture itself, the phrase visual culture used to denote a specific component of culture in general, a set of visual practices, or an academic discipline is quite recent. James Elkins, one of this emerging field's leading scholars, dates the term from 1972, saying that it "was used—perhaps for the first time …&#x…
Topology, which is often described as "rubber-sheet geometry," is a branch of geometry that focuses on distortion. Topology describes mathematically the features of a geometric shape that do not change when the shape is twisted, stretched, or squeezed. Tearing, cutting, and combining shapes do not apply to topology. Topology helps to solve problems about determining the number of col…
Wheat is one of the oldest and most important cereal crops. Wheat is grown for its grain, which is ground into flour used to make breads and pastas. Wheat consists of approximately 20 species in the genus Triticum of the grass family (Poaceae). The most important wheats are: Triticum aestivum, used to make bread; T. durum, used to make pasta; and T. compactum, used to make softer cakes, crackers, …
A generation trained to select icons on a desktop computer is able to take a fresh approach to the visual cues within early rooms of collection. Visual cues often preceded catalogs and inventories, helping users to situate themselves in the room and to locate items of the collection. In searching out the modes of conceptualizing, mapping, and classifying of collections, we shall see that the disti…
The whisk fern (Psilotum spp., family Psilotaceae) splays its leafless, whisk-like branches upward, and is a living fossil from the time before the dinosaurs. It can grow as an epiphyte in moist climates or as a terrestrial plant in drier areas. Found in the tropics from around the world, the whisk fern is descended from the first vascular land plants, the Rhyniophytes, which appeared about 400 mi…
Volksgeist (folk or national spirit) is perhaps the best known of a family of terms referring to sets of mental, intellectual, moral, and cultural traits that define particular human groups represented as being "nations" or "peoples." Additional related words include Volksseele ("folk soul"), "national character," esprit de la nation (…
Sunspots are relatively dark, temporary spots that appear on the Sun from time to time. The largest of these spots are visible to the naked eye and have been noted by Chinese astronomers since antiquity, but their first mention in Western literature is in The Starry Messenger (1610) by Italian astronomer Galileo Galilei (1564–1642). Sunspot activity—the number of spots on the Sun at …
During the first quarter of this century astronomers found that the brightest star in the sky, Sirius, was orbited by a much fainter companion. Analysis of the orbit yielded a mass for the companion similar to that of the sun while an analysis of its light suggested that its size was approximately the same as Earth's. Further observation revealed that these small massive stars are reasonabl…
The meaning of volunteerism is contingent on the nature of government, particularly the extent and ways in which it enables individuals to make uncompensated donations of money and labor to some form of collective activity or shared purpose. Over the course of the five centuries since European colonists first occupied North America, the meaning and practice of volunteerism has changed as part of t…
White-eyes are 85 species of small, perching song-birds that constitute the family Zosteropidae. White-eyes occur in sub-Saharan Africa, South Asia, Japan, Southeast Asia, New Guinea, Australia, New Zealand, and many other islands in the Pacific and Indian Oceans. White-eyes are arboreal birds, occurring in a wide range of forest types, including mangroves, lowland forests, and montane forests. Th…
How does one define a war? How can one distinguish between the war on drugs, the war on terrorism, jihad, anarchy, and wars between states? Definitions are relevant as they provide the rationale for considering a war legitimate and just and contribute to decisions about international interventions, aid, and protocol. This has become particularly important in contemporary international affairs, whe…
Depictions of violence have been part of human culture for millennia. What began as an effort of early humans to come to terms with the awe-inspiring power of weapons to kill their prey, and thus sustain human life, or ward off danger (for example, the cave paintings of Altamira, Spain) has evolved into a complex social code to help us try to make sense of total war, which industrialization and th…
Superclusters are currently the largest structures known in the universe. Stars and clusters of stars group together into galaxies that can contain anywhere from a few million to a few trillion stars. Galaxies collect into groups known as clusters of galaxies. On a larger scale superclusters are clusters of clusters of galaxies. As clusters of galaxies group into superclusters they leave empty spa…
A tornado is a rapidly spinning column of air formed in severe thunderstorms. The rotating column, or vortex, forms inside the storm cloud then grows downward until it touches the ground. Although a tornado is not as large as its parent thunderstorm, it is capable of extreme damage because it packs very high wind speeds into a compact area. Tornadoes have been known to shatter buildings, drive str…
Wealth has been viewed as a blessing and as a curse; as a prerequisite of virtue and an embodiment of vice; as an expression of merit and of fault. This nonexhaustive list illustrates that not only is the history of wealth a history of contention, it is also intimately bound up with moral evaluations. These differing evaluations themselves indicate a range of divergent cultural judgments. "…
According to Isaac Newton, an object at rest will remain at rest, and an object will remain in motion unless acted upon by an outside force. A force, therefore, is what causes any object to move. Any force which causes an object to rotate, turn, or twist is called a torque. Torque is equal to the amount of force being exerted on the object times the object's rotation point to the location w…
As applied to non-Western societies, the term Westernization is almost always equated with modernization. It is important, however, to distinguish between the two, for modernization, considered as an overhauling of African societies, predates the incursion of the West on the continent. Before the Europeans, the most important agents of modernization in Africa were the Arabs, who, after their settl…
A torus is a doughnut-shaped, three-dimensional figure formed when a circle is rotated through 360° about a line in its plane, but not passing through the circle itself. Imagine, for example, that the circle lies in space such that its diameter is parallel to a straight line. The figure that is formed is a hollow, circular tube, a torus. A torus is sometimes referred to as an anchor ring. …
The notion of Westernization in the Middle East raises a number of interrelated issues. First, it refers to a period (nineteenth to twentieth centuries) in which Middle Eastern intellectuals engaged Western political philosophy in a self-conscious search for modernity. Albert Hourani, in his groundbreaking Arabic Thought in the Liberal Age, 1798–1939 (1983), dates this engagement from Napol…
Whooping cough is a highly contagious disease caused by the bacteria Bordatella pertussis. It is characterized by classic paroxysms (spasms) of uncontrollable coughing, followed by a sharp intake of air which creates the characteristic "whoop" of the disease name. B. pertussis is uniquely a human pathogen, meaning that it neither causes disease in other animals, nor survives in human…
Westernization in world history can refer to the transmission and reception of European ideas, technology, lifestyles, and institutions throughout the globe. Much of the scholarly attention has tended to concentrate on the intensity and nature of that transmission during the era of European colonialism and its attempts to transform the very consciousness of the peoples it encountered. Although the…
A superconductor is a material that exhibits zero resistance to the flow of electrical current and becomes diamagnetic (opaque to magnetic fields) when cooled to a sufficiently low temperature. …
Total solar irradiance is defined as the amount of radiant energy emitted by the Sun over all wavelengths that fall each second on 11 sq ft (1 sq m) outside the earth's atmosphere. By way of further definition, irradiance is defined as the amount of electromagnetic energy incident on a surface per unit time per unit area. Solar refers to electromagnetic radiation in the spectral range of ap…
Uranus is the seventh planet from the Sun. It has a large size (its diameter is almost four times that of Earth) and mass, low mean density, fairly rapid rotation, and well-developed ring (11 components) and satellite (15 members) systems. The planet has a strong magnetic field with a large tilt (58.6°) to its rotation axis and offset (0.3 Uranus radius) from its center. Analysis of the obs…
In genetics, the specific types of genes (alleles) carried by individuals in any population comprise that individual's genotype. The actual expression of those genes produces a set of observable characteristics (phenotype). In any population of organisms, the wild type (also often printed in a hyphenated form as "wild-type") represents the most common genotype. With many organ…
Prehistory makes clear that our ancestors continuously conceptualized their relations with the myriad forms of plants and animals with whom their existence was interwoven. These ancient musings, more mythological than scientific, were the first sustained efforts to comprehend the order of nature. The noun wildlife has been in use no more than 125 years. But the swirl of ideas around wildlife, howe…
Wisdom is irretrievably linked with age and experience in human societies. If wisdom comes mainly through age and experience, it also requires "sense" to achieve. It is associated with the capacity to deal with experience in a constructive manner. If someone acts in a way that seems sensible, we may use the phrase "he has sense." Sense is the internal quality that promo…
Toucans are 42 species of familiar, brilliantly colored arboreal birds that make up the family Ramphastidae. Toucans are in the order Piciformes, which also includes the woodpeckers. Toucans range from southern Mexico to northern Argentina and Paraguay. Their usual habitat is tropical and subtropical forests and woodlands, and sometimes more open savanna with clumps of trees. Most species occur in…
The word witchcraft is used in many different ways. The word witch is derived from Old English wicca (masc., "wizard") and wicce (fem., "witch"). The term wiccan ("witchcraft") referred to human acts intended to influence nature, usually through the use of power unavailable to all human beings. This use of the word witchcraft is synonymous with the more ge…
Urea is a white, crystalline solid also known as carbamide. It is highly soluble in water and is the major molecule used by mammals and amphibians as a means of excreting nitrogenous waste (which generally comes from proteins). It is used in making fertilizers (where it serves as source of nitrogen) and in cattle feed, where it also raises the nitrogen levels. Urea is also used in the manufacturin…
Urology is the branch of medicine that deals with the urinary tract in females and with the urogenital tract in males. In both sexes, the urinary tract consists of the kidneys, ureters, bladder, and urethra. In males, additional structures such as the prostate gland are included in the urogenital system. The problems with which a urologist deals tend to fall into three general categories: infectio…
Wildfire is a periodic ecological disturbance, associated with the rapid combustion of much of the biomass of an ecosystem. Once ignited by lightning or by humans, the biomass oxidizes as an uncontrolled blaze, until the fire either runs out of fuel or is quenched. Wildfire is best known as a force affecting forests, although savanna, chaparral, prairie, and tundra also burn. A large wildfire can …
The term womanist first appeared in Alice Walker's In Search of Our Mothers' Gardens: Womanist Prose (1983), in which the author attributed the word's origin to Although Walker states that a womanist is a black feminist or feminist of color, she insists that a black feminist as womanist talks back to feminism, brings new demands and different perspectives to feminism, and comp…
A supernova is the massive explosion of a star, and is one of the most violent events in the Universe. There are two types of supernovae. A Type I supernova happens when a dead star called a white dwarf accretes so much matter from a companion star that it becomes unstable and explodes. A Type II supernova occurs when a high-mass star runs out of thermonuclear fuel. In this case, the star's…
Touch is one of the five senses (the others being smell, taste, vision, and hearing) through which animals and people interpret the world around them. While the other senses are localized primarily in a single area (such as vision in the eyes or taste in the tongue), the sensation of touch (or contact with the outside world) can be experienced anywhere on the body, from the top of the head to the …
A vaccine is a medical preparation providing immunity from a vaccine specific disease. Vaccines generally consist of a weakened (attenuated) or killed antigens, associated with a particular disease that are capable of stimulating the body to make specific antibodies to that disease. Vaccines use a variety of different substances ranging from dead microorganisms to genetically engineered antigens t…
It was once customary to consider all undomesticated species of vertebrate animals as wildlife. Birds and mammals still receive the greatest public interest and concern, consistently higher than those expressed for reptiles and amphibians. Most concern over fishes results from interest in sport and commercial value. The tendency in recent years has been to include more life-forms under the categor…
Before the women's movement and deconstruction, the term femininity was understood as the opposite of the more obvious masculinity. Femininity represented those traits, characteristics, behaviors, or thought patterns not associated with a given society's expectations of men. Until the cultural upheaval of the late 1960s in the United States and elsewhere, the sweetly patient "…
Surface tension is the result of the cohesive forces that attract water molecules to one another. This surface force keeps objects which are more dense than water (meaning they should not float) from sinking into it. The surface tension of water makes it puddle on the ground and keeps it in a droplet shape when it falls. If you use a table fork to carefully place a paper clip on the surface of som…
The towers of Hanoi is an ancient mathematical puzzle likely to have originated in India. It consists of three poles, in which one is surrounded by a certain number of discs with a decreasing diameter. The object of the puzzle is to move all of the discs from one pole onto another pole. The movement of any disc is restricted by two rules. First, discs can only be moved one at a time. Second, a lar…
Vacuum is a term that describes conditions where the pressure is lower than that of the atmosphere. A sealed container is said to be "under vacuum" in this case whereas it is "pressurized" when the pressure is higher than atmosphere. In a vacuum, it becomes necessary to define pressure microscopically. This means that the pressure, or force per unit area, is determined …
Since 1970 the history of African women has developed into a vital and steadily expanding area of research and study, motivated, as with other areas of women's history, by the development of the international feminist movement. African women's history also paralleled the expansion of African history following World War II, as scholars inside and outside of Africa began to focus on hi…
The prominent roles occupied by women in the legends and myths of that complex and diverse part of the world called Asia suggest that "histories" of women in Asia have existed for a very long time. That these legends have been shaped, written, and sometimes performed by men operating in androcentric cultural contexts does not negate the impression of power and consequence their narra…
A vacuum tube is a hollow glass cylinder containing a positive electrode and a negative electrode between which is conducted in a full or partial vacuum. A grid between these electrodes controls the flow of electricity. The hollow cylinder of a vacuum tube contains a filament, typically tungsten coated with another metal. When the filament is sufficiently heated by an electric current, it emits el…
Many endangered species, or their body parts, are extremely valuable for one reason or another. In some cases, they are avidly sought by public zoos or botanical gardens, or by private collectors, who may be willing to pay large sums of money for living or dead specimens to add to their collection. In other cases, parts of an animal or plant may be valuable. This can result in species being killed…
In its short history (from the late 1960s in the United States) women's studies has moved around the world as an idea, a concept, a practice, and finally a field or Fach (German for specialty or field). As late as 1982 in Germany Frauenstudium was not considered a Fach and therefore could not be studied in the university but only in special or summer courses. By the early twentieth century …
Valence refers to a number assigned to elements that reflects their ability to react with other elements and the type of reactions the element will undergo. The term valence is derived from the Latin word for strength and can reflect an element's strength or affinity for certain types of reactions. The electrons in an atom are located at different energy levels. The electrons in the highest…
Work as a unitary experience, set off in time and place from the rest of life, is a concept bound in the culture of wage labor (see especially Thompson, 1967, on disciplined promptness and time regulation accompanying factory work). Only when effort—physical and mental—is turned into a commodity sold to an employer who then monitors and controls it can we discern an abstract concept …
Toxic shock syndrome (TSS) is a serious, life-threatening disease caused by bacteria called Staphylococcus aureus and less typically, Streptococcus pyrogenes. Common causes of skin and mucous membrane infections, some strains of Staph. aureus and Strep. pyrogenes secrete toxins that initiate a cascade of immune reactions. These immune reactions lead to overproduction of immune proteins, and the ab…
The term world systems analysis was coined in 1974 by Immanuel Wallerstein to refer to a broad set of ideas about the global political economy, and especially the relationship between Latin America and the dominant economies of Europe and the United States, which were then gaining currency. The phrase world system is explored in detail in Wallerstein's famous book The Modern World-System: C…
In Chinese cosmology, yin and yang are two opposite but complementary principles that regulate the functioning of the cosmos. Their repeated alternation provides the energy necessary for the cosmos to sustain itself, and their continuous joining and separation is at the origin of the rise and the disappearance of the entities and phenomena that exist within the world of the "ten thousand th…
Willows are a diverse group of about 300 species of woody angiosperm plants in the genus Salix, family Salicaceae. Willows are widely dispersed and occur on all continents except Antarctica, but they are most diverse in cooler regions of the Northern Hemisphere. All willows are woody plants, but the species vary greatly in size. Some species of willows are trees that can grow taller than 49 ft (15…
The word yoga comes from a Sanskrit verbal root meaning "to yoke, harness" and in general refers to one or another of the many psycho-physical techniques in Indian religions designed to obtain discipline and control over the body and mind. In its classical contexts, yoga could refer to any one of a whole variety of such self-disciplinary practices. In India, yoga transcended sectaria…
One of the most important scholars of Zen Buddhism, Daisetz Suzuki, cogently explained the origins of Zen Buddhism in 1959: For several centuries in China, it was thought that Buddhism was a form of Daoism returning from India along the Silk Roads. Bernard Faure relates: "At the end of his life Laozi, in the guise of the Buddha, was said to have departed to the west to convert the barbarian…
Toxicology is the scientific study of poisons (or toxins). Major topics in toxicology include the detection and chemical analysis of poisons, the study of the metabolic effects of these substances on organisms, and the investigation of methods for treatment of poisoning. The Swiss physician and alchemist Philippus Aureolus, also known as Paracelsus (1493-1541) and said to be the father of the mode…
Radiation belts are enormous populations of energetic, electrically charged particles—principally protons and electrons—trapped in the external magnetic field of a planet. Durable radiation belts exist at the planets Earth, Jupiter, Saturn, Uranus, and Neptune but not at Mercury, Venus, or Mars. Nine artificial radiation belts of Earth were produced during the period 1958-62 by the i…
The historians of nationalism have reached a consensus that modern nationalism began as a secular movement, but almost all its varieties were affected by an undertow of older religious sentiments and loyalties. In many of the nationalisms (for example, in the battles between Greeks and Turks in the second decade of the nineteenth century or in the quarrel between Catholics and Protestants in North…
Trace elements are chemicals that are required by organisms in very small quantities for proper physiological and biochemical functioning. Trace elements commonly occur in organisms in concentrations smaller than about 0.001% of the dry weight (less than 10 parts per million, or ppm). Listed in alphabetical order, the most commonly required trace elements for healthy animal or plant nutrition are:…
Van der Waals forces are weak attractive forces between electrically neutral atoms or molecules. They are much weaker than the electrostatic forces which bind charged atoms or molecules (ions) of opposite sign or the covalent forces that bond neighboring atoms by sharing electrons. These forces develop because the rapid shifting of electrons within molecules causes some parts of the molecule to be…
Surgery is the part of medicine which employs operative or manual treatment of disease or injury. Although surgery was practiced in ancient times, modern anesthesia was not developed until the nineteenth century. For centuries, most types of operative surgery involved high risk to patients due to infection. With the development of antiseptic surgical methods in the nineteenth century, the risks li…
Tragopans are members of the attractive bird family Phasianidae, which also includes pheasants, peafowl, partridges, guinea fowl, and turkeys. There are various species of tragopans in Afghanistan, eastward as far as Tibet, and in the Himalayas, in the same area as Ithaginus cruentus, a related short-tailed species. Tragopans, however, are more colorful. Tragopans spend much of their time in the c…
The term wind refers to any flow of air relative to the Earth's surface in a roughly horizontal direction. Breezes that blow back and forth from a body of water to adjacent land areas—on-shore and off-shore breezes—are examples of wind. The ultimate cause of Earth's winds is solar energy. When sunlight strikes Earth's surface, it heats that surface differently. N…
Surveying is the apportionment of land by measuring and mapping. It is employed to determine boundaries and property lines, and to plan construction projects. The classic surveyors were the Romans. In order to forge an Empire that stretched from the Scottish border to the Persian Gulf, a large system of roads, bridges, aqueducts, and canals was built, binding the country economically and militaril…
Vapor pressure is a force exerted by the gaseous phase of a two phase—gas/liquid or gas/solid system. All liquids and solids have vapor pressure at all temperatures except at absolute zero, -459°F (-273°C). The pressure of the vapor that is formed above its liquid or solid is called the vapor pressure. If a substance is in an enclosed place the two phase system will arrive to …
Wind chill is the temperature felt by humans as a result of air blowing over exposed skin. The temperature Table 1. Illustration by Hans & Cassidy. Courtesy of Gale Group. that humans actually feel, called the sensible temperature, can be quite different from the temperature measured in the same location with a thermometer. The reason for such differences is that the human body const…
The term "survival of the fittest" was first used by the Victorian naturalist Herbert Spencer as a metaphor to help explain natural selection, the central element of Charles Darwin's revolutionary theory of evolutionary change, first published in 1859 in his famous book, The Origin of Species by Means of Natural Selection. In this extremely influential and important book, Darw…
Wind shear is the difference in speed or direction between two layers of air in the atmosphere. Wind shear may occur in either a vertical or horizontal orientation. An example of the former situation is the case in which one layer of air in the atmosphere is traveling from the west at a speed of 31 mph (50 kph) while a second layer above it is traveling in the same direction at a speed of 6.2 mph …
Wintergreen is the common name for an evergreen shrub belonging to the genus Gaultheria and heath family Ericaceae. Gaultheria procumbens is native to eastern North America and grows wild in sandy, wooded areas or shady clearings. This shrub grows 4-6 in (10-15 cm) high with creeping stems. Stalks grow from the stems and have elliptical, shiny green leaves and leathery leaves. During mid-summer, w…
A variable is a mathematical symbol which is used to represent a member of a given set and is typically denoted by a letter such as x, y, or z. The idea of a variable, invented during the late sixteenth century, is characteristic of modern mathematics and was not widely used in ancient times. Since a variable reflects a quantity which can take on different values, its use has become a critical par…
The wolverine (Gulo gulo) is an uncommonly large member of the weasel family (Mustelidae) that occurs in the subarctic and boreal forests of North America and northern Eurasia. The wolverine is famous for its aggressive, combative nature and its remarkable strength. Although the wolverine is only a medium-sized animal, it can dominate much larger animals during an aggressive encounter at a food so…
Most people regard the stars as constant and unchanging. A character in one of Shakespeare's plays refers to a friend "as constant as the Pole Star." While Shakespeare was probably referring to the constant position of the Pole Star, he did not know about the precession of the equinoxes. Or, if he was referring to the constant light of the Pole Star (Polaris), he was in error …
Wombats are thickset, bear-like, Australian marsupials (order Marsupalial). They dig burrows, are about the size of a small dog, and have perpetually growing teeth (like placental rodents). Wombats are members of the family Vombatidae, which includes three species. The critically endangered Queensland or northern hairy-nosed wombat (Lasiorhinus krefftii) is limited to a small area of Queensland Na…
Variance is one of several measures of dispersion which are used to evaluate the spread of a distribution of numbers. Such measures are important because they provide ways of obtaining information about data sets without considering all of the elements of the data individually. To understand variance, one must first understand something about other measures of dispersion. One measure of dispersion…
Wood, also known as secondary xylem, is a composite of tissues found in trees. Secondary xylem is composed primarily of cells, called vessel elements in angiosperms, or of slightly different cells in gymnosperms called tracheids. These cells of secondary xylem, along with specialized cells of a type called parenchyma, are made by a meristematic tissue called the vascular cambium. As the vascular c…
Sustainable development is the management of renewable resources for the good of the entire human and natural community. Built into this concept is an awareness of the animal and plant life of the surrounding environment, as well as inorganic components such as water and the atmosphere. The goal of sustainable development is to provide resources for the use of present populations without compromis…
Varicella zoster virus is a member of the alphaherpesvirus group and is the cause of both chickenpox (also known as varicella) and shingles (herpes zoster). The virus is surrounded by a covering, or envelope, that is made of lipid. As such, the envelope dissolves readily in solvents such as alcohol. Wiping surfaces with alcohol is thus an effective means of inactivating the virus and preventing sp…
Variola virus (or variola major virus) is the virus that causes smallpox. The virus is one of the members of the poxvirus group (Family Poxviridae). The virus particle is brick shaped and contains a double strand of deoxyribonucleic acid. The variola virus is among the most dangerous of all the potential biological weapons. At the time of smallpox eradication approximately one third of patients di…
Trains were developed during the Industrial Revolution and were arguably that period's most important product. In many ways railroads made the Industrial Revolution possible. Factories could not run without a constant supply of raw materials, or without a method of moving goods to market. More than anything, the progress of the railroads depended on the development of motive power, which wa…
Swallows and martins are small fast-flying agile birds in the family Hirundinidae. There are 74 species in this family worldwide, mostly found in open habitats, where they forage aerially for their prey of flying insects. There is no particular biological difference between swallows and martins. Sometimes these names are used interchangeably, as in the case of Riparia riparia, known as the sand ma…
The word vegetable is not scientifically defined by botanists. Rather, the plants and plant parts that are considered to be vegetables have been specified by a broad consensus among farmers, grocers, and consumers. In general, vegetables are plant tissues that are eaten as a substantial part of the main course of a meal. In contrast, fruits have a culinary definition as relatively sweet, often unc…
Woodpeckers are birds in the family Picidae, which includes about 200 species of true woodpeckers, wrynecks, as well as the diminutive piculets. Woodpeckers are widespread in the world's forested areas, occurring everywhere but Australia, New Zealand, New Guinea, Madagascar, and Antarctica. Birds in the woodpecker family range in size from the relatively enormous imperial woodpecker (Campep…
Veins are vessels designed to collect and return blood, including deoxygenated hemoglobin, from tissues to the heart. In humans, veins and the venous vascular system can be divided in to three separate systems depending on anatomical relationships and function. Initially, veins can be divided into systemic and pulmonary systems. The veins that drain the heart, comprising the coronary venous system…
The woolly mammoth (Mammuthus primigenius) was a large mammal that coexisted with early humans. It became extinct at the end of the last ice age, about 10,000 years ago. One of four species of mammoths, woolly mammoths were abundant on the cold tundra that extended beyond the glaciated ice fields of Europe, Asia, and North America. It is unclear whether the extinction of the woolly mammoth was a r…
The swamp cypress family is more formally called the Taxodiaceae. This is a family of coniferous trees within the Gymnosperms, that is, plants which produce naked seeds (not in a fruit) borne on scales. These scales are usually arranged to form a cone. Within the Taxodiaceae some species are evergreen, and some deciduous. There are nine genera which contain 16 species. These can be found in temper…
Velocity is the time rate of change of the position of a body. Mathematically, velocity is a vector quantity having direction as well as magnitude. Speed, on the other hand, is a scalar quantity which has only magnitude. The magnitude of velocity is expressed in units such as miles per hour or meters per second when describing motion along a straight or curved path. A body which is rotating about …
Who is doing more work: a weight lifter holding up, but not moving, a 200 lb (91 kg) barbell, or an office worker lifting a pen? The weight lifter is certainly exerting more effort, and many people would say he is doing more work. To a physicist, however, the office worker is doing more work as long as the weight lifter does not actually move the barbell. The weight lifter does a considerable amou…
Belonging to the order Synbranchiformes, swamp eels are very slim fish with elongated bodies and reduced fins. Their gill system, which is very small, is linked to other organs to help them breathe air. Swamp eels live in tropical and subtropical habitats. They usually are found in stagnant fresh or brackish water; only one species lives in the sea. These fish are found in Central and South Americ…
The wren-warblers or Australian warblers are 83 species of birds that constitute the family Maluridae. These are nonmigratory birds, occurring in New Guinea, Australia, New Zealand, and nearby islands. Their usual habitat is forests, shrublands, and heaths. Wren-warblers are small birds, with a body length of 3.9-7.9 in (10 to 20 cm), including the long, cocked tail that many species have. Their w…
The medical use of drugs to reduce or relieve anxiety has given rise to a group of medications called an tianxiety agents. These agents include anxiolytics, tranquilizers, and sedatives. Tranquilizers were formerly grouped as either "minor" tranquilizers or "major" tranquilizers. The word major stands for "major psychiatric illness," not heavily sedating o…
Swans are large birds in the waterfowl family, Anatidae, which also includes ducks and geese. There are seven species of swans, occurring on all continents except Antarctica. Three species of swan, the mute swan (Cygnus olor), the tundra swan (C. colombianus), and the trumpeter swan (C. buccinator) breed regularly in North America. Swans have a very long neck, and all North American species have a…
Wrens are 63 species of small, restless perching birds in the family Troglodytidae. Species of wrens are most diverse in North America and South America, although one species, the winter wren, breeds widely in Europe, Asia, and North Africa. Wrens occur in a wide range of habitats, including semidesert, prairie, savanna, forests, and wetlands. Species of wrens breed from the boreal zone to the hum…
The sweet gale or bayberry family (Myricaceae) is made up of about 50 species of shrubs and trees. Minor economic uses of some species involve the extraction of a fragrant wax from their fruits and cultivation as ornamental shrubs. The foliage of plants in the Myricaceae can be deciduous or evergreen, and the leaves are commonly fragrant when crushed. The flowers are small and occur in catkin-like…
A transducer is a device which converts one form of energy to another. Typically, one of these forms is electrical while the other is either mechanical, optical, or thermal. Transducers are usually classified as either input or output devices, depending on the direction in which they transfer energy or information. Input transducers convert some property or effect into an electrical signal, while …
Wrynecks are two species of small, woodpecker-like birds. Wrynecks are in the family Picidae, which also includes the woodpeckers and piculets. However, the distinctively different wrynecks are in their own sub-family, the Junginae. Wrynecks received their common name from their habit of twisting their head and neck when disturbed. The plumage of wrynecks is a mottled and cryptic brown, grey, and …
The sweet potato (Ipomoea batatas) is a creeping, vine-like plant that is cultivated in tropical climates for its starchy, nutritious tubers. The sweet potato is in the morning glory family (Convolvulaceae). The sweet potato is sometimes referred to as a yam, but it is quite different from the true yam (Dioscorea batatas), which is another species of tropical root-crop. The sweet potato is a peren…
A transformer is an electrical device which changes or transforms an alternating current (AC) signal from A high voltage transformer. Photograph by Tardos Camesi. Stock Market. Reproduced by permission. one level to another. The device typically consists of two sets of insulated wire, coiled around a common iron core. Electrical power is applied to one of these coils, called the primary co…
Swifts are the fastest fliers of all of the small birds, reaching speeds of 172-218 mph (275-349 kph), although 35-80 mph (56-128 kph) is more common. They belong to the family Apodidae, a name meaning "without feet" and a reference to the fact that a swift in flight appears to have no legs or feet. Indeed, the legs of swifts are small and weak so that a swift that lands on the groun…
The swordfish (Xiphias gladius), also known as the broadbill, or the forktail, is the only species in the bony fish family Xiphiidae. The swordfish is highly prized as a food fish, and as a game fish. Its most distinguishing characteristic is the remarkable elongation of the upper jaw, which resembles a long, flattened, serrated sword and can extend up to one-third of the body length. The sword is…
The term transgenics refers to the process of transferring genetic information from one organism to another. By introducing new genetic material into a cell or individual, a transgenic organism is created that has new characteristics it did not have before. The genes transferred from one organism or cell to another are called transgenes. The development of biotechnological techniques has led to th…
Venus is the second planet from the Sun and is in some superficial geological features like Earth. In many important geochemical features, however, it is quite different. Next to the Sun and Moon, Venus can be the brightest object in the sky. At its most brilliant, Venus is sixteen times brighter than Sirius (α Canis Majoris), the brightest star in the night sky. The extreme brilliance of V…
At the high-energy end of the electromagnetic spectrum, x rays provide a unique window on some of the hottest and most violent objects in the universe. Since the discovery of extra-solar x-ray sources in 1962, scientists have investigated a large number of phenomena which emit x rays. With each new space mission, more sources and more details of the structure of the xray universe have been gleaned…
X-ray crystallography is a laboratory technique used for the study of the internal structure of crystalline materials. More specifically known as x-ray diffraction, the technique is based on the interference pattern produced as x rays pass through the three-dimensional, repeating pattern of atoms within a crystal lattice. The characteristic interference patterns produced are reflective of the mole…
Symbiosis is a word used to refer to intimate relationships among species. Symbioses can involve interactions of individuals of different species, or associations of populations of one or more species. Symbiosis can involve obligate relationships, in which the symbionts cannot live apart in nature, but usually the association is more flexible than this. …
The verbena or vervain family (Verbenaceae) is a diverse group of about 3,000 species of plants, most of which occur in the tropics. Plants in this family can be herbs, shrubs, trees, or lianas (tropical vines). The leaves are usually simple, arranged alternately on the stem, which is often square-sided. The flowers are small, but often occur in attractive inflorescences. Some species of trees in …
Vertebrates are animals classified in the subphylum Vertebrata, phylum Chordata. Vertebrates share a number of features. They all have an internal skeleton of bone and/or cartilage, which includes a bony cranium surrounding the brain and a bony vertebral column enclosing the spinal cord. Vertebrates are all covered by a skin composed of dermal and superficial epidermal layers of scales, feathers o…
When used by botanists and plant breeders, xenogamy (also called outbreeding) generally refers to a form of cross-pollination. Xenogamy is also a term more broadly used in genetics to describe the union of genetically unrelated organisms within the same species. In all cases, xenogamy promotes genetic diversity and thus, also enhances the overall fitness of a species. In some circumstances, xenoga…
The yaks are members of the family Bovidae (oxen), order Artiodactyla, which also includes the domestic cattle and existing wild cattle species such as the aurochs, the gaur or seladang, and the koupray. The generally accepted species name for yak is Bos grunniens, and it seems to have an affinity to bison, which belong to the same genus Bos. Like some other Bos species the yak is a large, massive…
A transistor is a small, solid device capable of amplifying and switching electrical signals. A transistor can be manufactured using a wide variety of materials; most transistors utilize the unique semiconducting properties of silicon or germanium that has been selectively contaminated with other elements (e.g., arsenic, phosophorus, boron, gallium). A transistor is controlled by voltages communic…
Yams are any of the 10 economically important species of Dioscorea, a genus in the monocotyledonous family Dioscoriaceae. These species, all tropical in their origin, are cultivated for their edible tubers (enlarged, fleshy, usually underground storage stems). In the United States, the name yam is often misapplied to the sweet potato (Ipomea batatas). Yams are herbaceous plants whose stems twine u…
The concept of transitivity goes back at least 2,300 years. In the Elements, Euclid includes it as one of his "common notions." He says, "Things which are equal to the same thing are also equal to one another." As Euclid puts it, if a = b and c = b, then a = c, which is equivalent to the modern version, which has "b = c" rather than "c = b." …
The term "video recording" refers to storing a video signal (information designed to specify a moving image) in a recording medium such as magnetic tape, optical disc, or computer memory. Video signals have much larger bandwidths &NA;65 MHz) than do audio signals (&NA;20 kHz), and thus involve a more complex recording and playback technology. The transverse recording technique is bas…
Logic is the study of the rules which underlie plausible reasoning in mathematics, science, law, and other discliplines. Symbolic logic is a system for expressing logical rules in an abstract, easily manipulated form. …
A translation is one of the three transformations that move a figure in the plane without changing its size or shape. (The other two are rotations and reflections.) In a translation, the figure is moved in a single direction without turning it or flipping it over. A translation can, of course, be combined with the two other rigid motions (as transformations which preserve a figure's size an…
Many real objects and forces at all size scales—subatomic particles, atoms, crystals, organisms, stars, and galaxies—exhibit symmetry, of which there are many kinds. Line or bilateral symmetry, the simplest and most familiar, is the symmetry of by any figure or object that can be divided along a central line and then restored (geometrically) to wholeness by reflecting its remaining h…
Yeasts are single-celled fungi, belonging mainly to the Ascomycetes, that serve as nutrient recyclers in nature, but are also important in industry, biotechnology, and as the agents of disease in humans. The term yeast is generically used in reference to many species of single-celled, budding fungi, including Saccharomyces—used in baking and brewing—and Candida—an infectious y…
Nerve impulses are transmitted through a functional gap or intercellular space between neural cells (neurons) termed the synapse (also termed the synaptic gap). Although nerve impulses are conducted electrically within the neuron, in the synapse they are continued (propogated) via a special group of chemicals termed neurotransmitters. The synapse is more properly described in structural terms as a…
The violet family (Violaceae) includes about 900 species of plants. Species in this family occur in all parts of the world, but are mostly in the temperate zones, and at high altitude in the tropics. The largest group in the family is the genus containing violets and pansies (Viola spp.), with about 500 species. Most species in this family are annual or perennial herbs. The leaves are simple, comm…
A syndrome is a collection of signs, symptoms, and other indications which, taken together, characterize a particular disease or abnormal medical condition. Medical workers place a heavy reliance on the collection of such indicators in the diagnosis of health problems and disorders. The usual approach is to question patients about the nature of their complaints and then to conduct examinations and…
Transpiration refers to the evaporation of water from a biological surface, such as leaves, skin, or lungs. In its most common usage, however, transpiration refers to the loss of water from plant foliage, occurring through microscopic pores known as stomata. Transpiration is a component of a larger process known as evapotranspiration, which is the evaporation of water from a landscape, including b…
Vipers are snakes in the family Viperidae, a group of short-tailed, (usually) stout-bodied snakes with long fangs at the front of the mouth, sited on a short jawbone that can be rotated to bring the fangs from their resting position parallel with the palate to an erect position for striking. This efficient venom delivery system allows vipers to eat large (and sometimes dangerous) animals without a…
The earliest known talking machine was developed in 1778 by Wolfgang von Kempelen. Eyewitnesses reported that it could speak several words in a timid, childlike voice. While the talking machine's success appears genuine, Baron von Kempelen's accomplishments are not above suspicion. Nine years earlier, he had built a chess-playing machine, which defeated many players, including Napole…
Viral genetics, the study of the genetic mechanisms that operate during the life cycle of viruses, utilizes biophysical, biological, and genetic analyses to study the viral genome and its variation. The virus genome consists of only one type of nucleic acid, which could be a single or double stranded DNA or RNA. Single stranded RNA viruses could contain positive-sense (+RNA), which serves directly…
Yellow fever is a severe illness that causes outbreaks of epidemic proportions throughout Africa and tropical America. The first written evidence of such an epidemic dates back to a 1648 outbreak in the Yucatan Peninsula in Mexico. Since that time, much has been learned about the interesting transmission patterns of this devastating illness. A very safe, highly effective yellow fever vaccine exist…
There are several different ways to represent compounds in structural formulas, depending on how much detail needs to be shown about the molecule under consideration. Illustration by Hans & Cassidy. Courtesy of Gale Group. We will look at complete structural formulas, condensed formulas, line formulas, and three-dimensional formulas. After you become familiar with the rules for wr…
Systems of equations are a group of relationships between various unknown variables which can be expressed in terms of algebraic expressions. The solutions for a simple system of equation can be obtained by graphing, substitution, and elimination addition. These methods became too cumbersome to be used for more complex systems however, and a method involving matrices is used to find solutions. Sys…
Vireos are 44 species of small arboreal birds that comprise the family Vireonidae, in the order Passeriformes. As it is considered here, the Vireonidae is an assembly of three sub-families: the true vireos or Vireoninae, the shrike vireos or Vireolaniinae, and the pepper shrikes or Cyclarhinae. It should be pointed out, however, that some taxonomic treatments consider these to be separate families…
When a vertebrate encounters substances that are capable of causing it harm, a protective system known as the "immune system" comes into play. This system is a network of many different organs that work together to recognize foreign substances and destroy them. The immune system can respond to the presence of a disease causing agent (pathogen) in two ways. Immune cells called the B c…
A surgical transplant involves the removal of body parts, organs, or tissues from one person and implanting them into the body of another person. Although the idea of transplantation to cure disease dates back several centuries, transplantation has been considered a viable therapy for only a few decades. The relatively recent growth in transplantation stems primarily from expanding knowledge about…
Virtual particles are subatomic particles that form out of "nothing" (vacuum fields conceptually analogous to lines of force between magnetic poles) for extremely short periods of time and then disappear again. Such particles permeate space, mediate particle decay, and mediate the exchange of the fundamental forces (electromagnetic, weak, strong, and—in accord with quantum the…
Yews are various species of tree- or shrub-sized, woody plants that comprise the conifer family, Taxaceae. All yews are in the genus Taxus, and about seven species are known, occurring in moist, temperate forest habitats in North America, Europe, Asia, and Africa. …
A trapezoid is a four-sided, two-dimensional polygon. With four sides, a trapezoid is a quadrilateral, just as a square or rectangle or parallelogram. Unlike those forms, however, a trapezoid does not necessarily have to have parallel sides. In other words, all rectangles are trapezoids, but not all trapezoids are rectangles. A trapezium is a subset of trapezoids in which at least two sides are pa…
Yttrium is not itself a rare earth element; however, its history is closely tied to that of the rare earths, and its chemical properties are similar to those of the members of that family. It also occurs in close association in nature with the rare earths. Yttrium was the first new element to be identified in the complex mineral called ytteriteytterite (now known as gadolinitegadolinite), discover…
Scarlet tanager (Piranga olivacea). Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. Tanagers are 239 species of extremely colorful, perching birds that make up the family Thraupidae. The evolutionary history and phylogenetic relationships of the tanagers and related birds are not well understood. Recent taxonomic treatments have included the tanagers as a…
Taphonomy is the study of how organisms are preserved in the fossil record (the term is derived from the Greek word taphos, which means grave). Taphonomists seek to understand how an organism died and what happened to its body before and during burial. They also try to determine what factors may have contributed to unequal representation of certain groups in the fossil record due to differences in…
Tapirs, of the family Tapiridae, are large, forest-dwelling mammals with a long flexible snout. They are found in tropical South and Central America, and in southeast Asia. There are four species of tapirs in the single genus, Tapirus. Tapirs are grouped with horses and rhinoceroses in the order Perissodactyla, which are the odd-toed, hoofed mammals. Tapirs have a fourth toe on their front feet. E…
Virtual reality is a product of the evolution of the computer from an instrument that merely received input from a user to a machine that can adapt to the user's cues to create an almost lifelike experience. The term virtual reality was coined in 1989 by Jaron Lanier. Others have described the concept as "artificial reality," "cyberspace," and "virtual wor…
As the end of the 1990s approached, the world became preoccupied with the coming of the Year 2000, nicknamed "Y2K" (Y for year and 2 times K, a standard designation for a thousand). Some were superstitious about the turning of year numbers to 2000, but many focused on a predicted technological problem commonly known as the"Y2K Glitch" or the "millennium bug…
