Eagle: Any of many large, heavy-beaked, big-footed Birds of Prey belonging to the family Accipitridae, found worldwide. Eagles are generally larger and more powerful than hawks and may resemble a vulture in build and flight characteristics, but they have a fully feathered (often crested) head and strong feet equipped with great curved talons. Most species subsist mainly on live prey, which they generally capture on the ground. Eagles have been a symbol of war and imperial power since Babylonian times. They mate for life. They nest in inaccessible places and use the same nest each year. Species vary from 24 in. to 3.3 ft (60 cm–1 m) long. The Sea eagles include the Bald eagle.
Ear: Organ of hearing and balance. The outer ear directs sound vibrations through the auditory canal to the eardrum, which is stretched across the end of the auditory canal and which transmits sound vibrations to the middle ear. There a chain of three tiny bones conducts the vibrations to the INNER EAR. Fluid inside the cochlea of the inner ear stimulates sensory hairs; these in turn initiate the nerve impulses that travel along the auditory nerve to the brain. The inner ear is also an organ of balance: the sensation of dizziness that is felt after spinning is caused when fluid inside the inner ear’s semicircular canals continues to move and stimulate sensory hairs after the body has come to rest. The eustachian tube connects the middle ear with the nasal passages; that connection allows the common cold to spread from the nasal passages to the middle ear, especially in infants and small children. The most common cause of hearing loss is otosclerosis, a surgically correctable disease in which one of the bones of the middle ear loses its capacity to vibrate. See illustration
Early burning: Controlled burning early in the dry season, before the leaves and undergrowth are completely dry or before the leaves are shed, as an insurance against later fire damage. (BCFT)
Earth: 1. Third PLANET in distance outward from the SUN. Believed to be about 4.6 billion years old, it is some 92,960,000 mi (149,600,000 km) from the Sun. It orbits the Sun at a speed of 18.5 mi (29.8 km) per second, making one complete revolution in 365.25 days. As it revolves, it rotates on its axis once every 23 hours 56 minutes 4 seconds. The fifth largest planet of the Solar System, it has an equatorial circumference of 24,902 mi (40,076 km). Its total surface area is roughly 197,000,000 sq mi (509,600,000 sq km), of which about 29% is land. Earth’s Atmosphere consists of a mixture of gases, chiefly nitrogen and oxygen. Its only natural satellite, the Moon, orbits the planet at a distance of about 238,860 mi (384,400 km). Earth’s surface is traditionally subdivided into seven continental masses: Africa, Antarctica, Asia, Australia, Europe, North America, and South America. These continents are surrounded by four major bodies of water: the Arctic, Atlantic, Indian, and Pacific oceans. Broadly speaking, Earth’s interior consists of two regions: a Core composed largely of molten, ironrich metallic alloy; and a rocky shell of silicate minerals comprising both the Mantle and Crust. Fluid motions in the electrically conductive outer core generate a magnetic field around Earth that is responsible for the Van Allen Radiation Belts. According to the theory of Plate tectonics, the crust and upper mantle are divided into a number of large and small plates that float on and travel independently of the lower mantle. Plate motions are responsible for Continental drift and Seafloor spreading and for most volcanic and seismic activity on Earth.
Earthquake: Sudden shaking of the ground caused by a disturbance deeper within the crust of the Earth. Most earthquakes occur when masses of rock straining against one another along Fault lines suddenly fracture and slip. The Earth’s major earthquakes occur mainly in belts coinciding with the margins of tectonic plates. These include the Circum-Pacific Belt, which affects New Zealand, New Guinea, Japan, the Aleutian Islands, Alaska, and the western coasts of North and South America; the Alpide Belt, which passes through the Mediterranean region eastward through Asia; oceanic ridges in the Arctic, Atlantic, and western Indian oceans; and the rift valleys of East Africa. The “size,” or magnitude, of earthquakes is usually expressed in terms of the Richter scale, which assigns levels from 1.0 or lower to 8.0 or higher. The largest quake ever recorded (Richter magnitude 9.5) occurred off the coast of Chile in 1960. The “strength” of an earthquake is rated in intensity scales such as the Mercalli scale, which assigns qualitative measures of damage to terrain and structures that range from “not felt” to “damage nearly total.” The most destructive quake of modern times occurred in 1976, when the city of Tangshan, China, was leveled and more than 250,000 people killed.
Earthquake-resistant structure: Building designed to prevent total collapse, preserve life, and minimize damage in case of an earthquake or tremor. Earthquakes exert lateral as well as vertical forces, and a structure’s response to their random, often sudden motions is a complex task that is just beginning to be understood. Earthquake-resistant structures absorb and dissipate seismically induced motion through a combination of means: damping decreases the amplitude of oscillations of a vibrating structure, while ductile materials (e.g., steel) can withstand considerable inelastic deformation. If a skyscraper has too flexible a structure, then tremendous swaying in its upper floors can develop during an earthquake. Care must be taken to provide built-in tolerance for some structural damage, resist lateral loading through stiffeners (diagonal sway bracing), and allow areas of the building to move somewhat independently.
Earthquake swarm: A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time.
Earthworm: Any of more than 1,800 species of terrestrial Worms, particularly members of the genus Lumbricus (class Oligochaeta of the Annelid order). Earthworms exist in all soils of the world that have sufficient moisture and organic content. The most common U.S. species, L. terrestris, grows to about 10 in. (25 cm), but an Australian species can grow as long as 11 ft (3.3 m). The segmented body is tapered at both ends. Earthworms eat decaying organisms and, in the process, ingest soil, sand, and pebbles, which aerates the soil, promotes drainage, and improves the soil’s nutrient content for plants. Earthworms are eaten by many animals.
Easement: In Anglo-American property law, an interest in land owned by another that entitles its holder to a specific limited use or enjoyment, such as the right to cross the land or have a view over it continues unobstructed. It may be created expressly by a written deed of grant conveying the specific usage right, or it may be created by implication, as when an owner divides property into two parcels in such a way that an already existing, obvious, and continuous use of one parcel (e.g., for access) is necessary for the reasonable enjoyment of the other. Some U.S. states permit the creation of an easement by prescription (acquisition of an interest), as when one person makes continuous use of another’s land for some specified period of time (e.g., 20 years). Utility companies often own easements in gross; these are not dependent on ownership of the surrounding estate. Numerous other kinds of easements have been important in Anglo-American law.
Ecdysis: Shedding of an outer layer or the regular molting of an outer layer by arthropods such as insects and crustaceans, and by reptiles
Eccentricity: A shape which in not in a circular form. Eccentricity implies to a closed shape have a number of centers like paraboloidal shape, elliptical shape, etc. A circle has an eccentricity of zero; for an ellipse it is less than one; for a parabola it is equal to one; and for a hyperbola it is greater than one.
Echidna or spiny anteater: Any of three species of egg laying mammals (Monotremes) of the family Tachyglossidae. Echidnas are stocky and virtually tailless. They have strong-clawed feet and spines on the upper part of the brownish body. The snout is narrow, the mouth very small, and the tongue long and sticky for feeding on termites, ants, and other invertebrates in the soil. The short-beaked echidna common in Australia and Tasmania is 12–21 in. (30–53 cm) long. Two species of long-beaked echidna live only on the island of New Guinea. They are 18–31 in. (45–78 cm) long and have a prominent downward-pointing snout. They are valued for their meat and are declining in numbers. Echidnas exude milk from mammary openings on the skin, and the young lap it up.
Eclipse: The passage of all or part of one celestial body into the shadow of another, the eclipsing body. Observers on Earth experience two major types—lunar eclipses and solar eclipses—each of which involves the Sun and the Moon. The type observed depends on whether Earth is the eclipsing body or the body in shadow. In a lunar eclipse the orbit of the Moon carries it through Earth’s shadow. Observers see the full Moon dim considerably, but it remains faintly visible. In a solar eclipse the Moon is the eclipsing body, passing between Earth and the Sun while casting a traveling shadow across Earth’s lighted surface. Observers along the shadow’s path see a total or partial obscuring of the Sun’s disk by the Moon’s silhouette. The shadow cast by the eclipsing body consists of the central umbra, into which no direct sunlight penetrates (total eclipse), and the encircling penumbra, reached by light from only part of the Sun’s disk (partial eclipse). Solar eclipses visible from different parts of Earth occur two to five times a year; one total solar eclipse occurs in most years. When Earth is closest to the Sun and the Moon farthest from Earth, the Moon’s silhouette may fall entirely within the Sun’s disk, with a ring of the disk visible around it (annular eclipse). Lunar eclipses occur twice in most years. Other kinds of eclipses include those of the Sun by Mercury or Venus (transits), of distant stars by planets or planetary satellites (occultations), and of stars by orbiting companion stars. See illustration
Eco-agriculture: 1. Ecologically sound agricultural methods 2. The practice of agriculture using ecologically beneficial methods that maintain natural resources, biodiversity, and the landscape
Eco-catastrophe: 1. Environmental disaster 2. An event, usually caused by human actions, that results in very severe damage to the environment
Eco-consumer: Environmentally aware consumer; A consumer who is mindful of the ecological impact of what he or she buys
Eco-efficiency: The ability to manufacture goods efficiently and at competitive prices without harming the environment.
Eco-friendly: Intended or perceived to have no harmful effect on the natural environment and its inhabitants
Eco-label: A label placed on some EU products indicating that they are significantly less harmful to the environment than competing products
Ecology: [Late 19th century/ Greek oikos “house, habitation”] 1. Study of the relationships between organisms and their environment. Physiological ecology focuses on the relationships between individual organisms and the physical and chemical features of their environment. Behavioral ecologists study the behaviours of individual organisms as they react to their environment. Population ecology, including population Genetics, is the study of processes that affect the distribution and abundance of animal and plant populations. Community ecology studies how communities of plant and animal populations function and is organized. Paleoecology is the study of the ecology of Fossil organisms. Ecologists frequently concentrate on particular taxonomic groups or on specific environments. Applied ecology applies ecological principles to the management of populations of crops and animals. Theoretical ecologists provide simulations of particular practical problems and develop models of general ecological relevance. The term ecosystem was coined in 1935 by the British ecologist Sir Arthur George Tansley, 2. The study of the relationships between living organisms and their interactions with their natural or developed environment “A land ethic…should be as honest as Thoreau’s Walden, and as comprehensive as the sensitive science of ecology.” (Stewart Udall The Quiet Crisis 1963)
Econometrics: Statistical and mathematical analysis of economic relationships. Econometrics creates equations to describe phenomena such as the relationship between changes in price and demand. Econometricians estimate Production Functions and cost functions for firms, Supply and Demand functions for industries, income distribution in an economy, macroeconomic models and models of the monetary sector for policy makers, and Business Cycles and growth for forecasting. Information derived from these models helps both private businesses and governments make decisions and set Monetary and Fiscal policy. (See also Macroeconomics; Microeconomics).
Economic development: Process whereby simple, low-income national economies are transformed into modern industrial economies. Theories of economic development—the evolution of poor countries dependent on agriculture or resource extraction into prosperous countries with diversified economies—are of critical importance to Third World nations. Economic development projects have typically involved large capital investments in infrastructure (roads, irrigation networks, etc.), industry, education, and financial institutions. More recently, the realization that creating capital-intensive industrial sectors provides only limited employment and can disrupt the rest of the economy has led to smaller scale economic development programs that aim to utilize the specific resources and natural advantages of developing countries and to avoid disruption of their social and economic structures.
Economic growth: Process by which a nation’s wealth increases over time. The most widely used measure of economic growth is the real rate of growth in a country’s total output of goods and services (gauged by the Gross Domestic Product adjusted for Inflation, or “real GDP”). Other measures (e.g., national income per capita, consumption per capita) are also used. The rate of economic growth is influenced by natural resources, human resources, capital resources, and technological development in the economy along with institutional structure and stability. Other factors include the level of world economic activity and the terms of Trade. (See also Economic Development).
Economic indicator: Statistic used to determine the state of general economic activity or to predict it in the future. A leading indicator is one that tends to turn up or down before the general economy does (e.g., building permits, common stock prices, and business inventories). Coincident indicators move in line with the economy; lagging indicators change direction after the economy does.
Economic planning: Use of government to make economic decisions with respect to the use of resources. In communist countries with a state planning apparatus, detailed and rigid planning results in a Command Economy; Land, Capital, and the means of production are publicly owned and centrally allocated, and the government makes both micro- and macroeconomic decisions. Microeconomic decisions include what goods and services to produce, the quantities to produce, the prices to charge, and the wages to pay. Macroeconomic decisions include the rate of investment and the extent of foreign trade. In most industrialized countries, governments influence their economies indirectly through monetary and fiscal policies. A few key economic sectors may be publicly owned, but the trend has been toward the privatization of industries that were socialized in the aftermath of the Great Depression and World War II. Japan is the most notable example of economic planning in a capitalist framework; government and industry cooperate closely in planning patterns of capital investment, research and development, and export strategies.
Economic Rate of Return (ERR): The percentage of profit that can reasonably be expected by a particular investment. (Compare Internal Rate of Return)
Economics: [15th century Greek oikos “house” + nemein “manage”] Social science that analyzes and describes the consequences of choices made concerning scarce productive resources. Economics is the study of how individuals and societies choose to employ those resources: what goods and services will be produced, how they will be produced, and how they will be distributed among the members of society. Economics is customarily divided into Microeconomics and Macroeconomics. Of major concern to macroeconomists are the rate of Economic Growth, the Inflation rate, and the rate of Unemployment. Specialized areas of economic investigation attempt to answer questions on a variety of economic activity; they include agricultural economics, Economic Development, economic history, environmental economics, industrial organization, international trade, Labour Economics, Money Supply and banking, public finance, urban economics, and Welfare Economics. Specialists in mathematical economics and Econometrics provide tools used by all economists. The areas of investigation in economics overlap with many other disciplines, notably history, Mathematics, Political Science, and Sociology.
Economic system: Set of principles and techniques by which a society decides and organizes the ownership and allocation of economic resources. At one extreme, usually called a free-enterprise system, all resources are privately owned. This system, following Adam Smith, is based on the belief that the common good is maximized when all members of society are allowed to pursue their rational self-interest. At the other extreme, usually called a pure-communist system, all resources are publicly owned. This system, following Karl Marx and Vladimir Ilich Lenin, is based on the belief that public ownership of the means of production and government control of every aspect of the economy are necessary to minimize inequalities of wealth and achieve other agreed-upon social objectives. No nation exemplifies either extreme. As one moves from Capitalism through Socialism to Communism, a greater share of a nation’s productive resources is publicly owned and a greater reliance is placed on Economic Planning. Fascism, more a political than an economic system, is a hybrid; privately owned resources are combined into syndicates and placed at the disposal of a centrally planned state.
Economic threshold: (Entomology) This takes into account the revenue losses resulting from pest damage and the costs of treatment to prevent the damage. Below the economic threshold, the presence of the pest is tolerated. Only when pest numbers increase above the threshold does the farmer take action.
Economic warfare: Use of economic measures by governments engaged in international conflict. These may include export and import controls, shipping controls, trade agreements with neutral nations, and so on. Economic warfare among belligerents began with the Blockade and interception of contraband. In World War II it was broadened to include economic pressure applied to neutral countries from which the enemy obtained its supplies. In the Cold War it often involved using measures such as an Embargo to deny potential enemies goods that might contribute to their war-making ability.
Ecoregion: Area falling under same latitude.
Ecospecies: Species distinguished by ecological features: a species made up of several subgroups ecotypes and characterized by its ecological traits
Ecosphere: (Syn Biosphere) 1. Planet Earth and its life. 2. The whole area of Earth’s surface, atmosphere, and sea that is inhabited by living things
Ecosystem: 1. Complex of living organisms, their physical environment, and all their interrelationships in a particular unit of space. An ecosystem’s abiotic (nonbiological) constituents include minerals, climate, soil, water, sunlight, and all other nonliving elements; its biotic constituents consist of all its living members. Two major forces link these constituents: the flow of energy and the cycling of nutrients. The fundamental source of energy in almost all ecosystems is radiant energy from the sun; energy and organic matter are passed along an ecosystem’s Food Chain. The study of ecosystems became increasingly sophisticated in the later 20th century; it is now instrumental in assessing and controlling the environmental effects of agricultural development and industrialization. (See also Biome). 2. The sum of the plants, animals, environmental influences, and their interactions within a particular habitat. 3. Stable, though not necessarily permanent, community of plants that have developed interrelationships with each other and with native wildlife to form a distinct, self-sustaining system. A few examples of ecosystems are tallgrass prairie, boreal forest, estuary, and oak savannah. Though ecosystems are a useful concept, in real life a “pure” ecosystem is unusual; more common are areas in which several ecosystems overlap to various degrees.
Ecoterrorism or ecological terrorism or environmental terrorism: The destruction, or the threat of destruction, of the environment in order to intimidate or coerce governments. The term has also been applied to crimes committed against companies or government agencies in order to prevent or interfere with activities allegedly harmful to the environment. Ecoterrorism includes threats to contaminate water supplies or to destroy or disable energy utilities, for example, and practices such as the deployment of Anthrax. Another form of ecoterrorism, often referred to as environmental warfare, consists of the deliberate and illegal destruction, exploitation, or modification of the environment as a strategy of war or in times of armed conflict. Examples include the U.S. military’s use of the defoliant Agent Orange during the Vietnam War and the destruction of Kuwaiti oil wells by retreating Iraqi military forces during the 1991 Persian Gulf War. The activities of some environmental activists also have been described as ecoterrorism. These activities include criminal trespass on the property of logging companies and other firms and obstruction of their operations through sabotage as well as the environmentally harmless modification of natural resources in order to make them unsuitable for commercial use (a practice known as “monkeywrenching”).
Ecotone: 1. A transition area between two distinct, but adjoining, communities. 2. A zone of transition between two different ecosystems, e.g. where the sea meets the land
Ecotoxicology: Study of substances harmful to environment: the study of how organisms are affected by chemicals released into the environment by human activities.
Ecotourism: A form of tourism that strives to minimize ecological or other damage to areas visited for their natural or cultural interest.
Ecotoxic: Causing severe damage to the environment
Ecotoxiology: The study of how organisms are affected by chemicals released into the environment by human activities
Ecotype: 1. Subgroup of a species OR; a subgroup of a species of organism whose members show genetically determined adaptations to some environmental conditions in their habitat. 2. A race (provenance) adapted to the selective action of a particular environment. Ecotypes are described in terms of the primary environmental influence, e.g., climatic or edaphic. Ecotypes may only be evident when different provenances are tested in a uniform environment.
Ecowarrior: An activist who takes direct, often unlawful, action on an environmental issue
Ectoderm: the outermost of three cell layers of an embryo, from which the epidermis, nervous tissue, and sense organs develop
Ectogenesis: The development of an organism in an artificial environment, e.g. outside the body in which it would normally be found.
Ectomere: A cell blastomere produced during the division of a fertilized egg that develops with others into the outer cell layer ectoderm of an embryo.
Ectoparasite: A parasite that lives on the outside of its host, e.g. on the skin or in the hair. Fleas are ectoparasites
Ectophyte: A parasitic plant that lives on the outer surface of its host.
Ectoplasm: Outer layer of cytoplasm: the dense outer layer of the substance cytoplasm that surrounds the nucleus of a cell
Ectosymbiont: An organism that lives on the surface of another organism to the benefit of both, e.g. any of the microbes that normally live on the skin
Ectotherm: 1. Any so-called cold-blooded animal; that is, any animal whose regulation of body temperature depends on external sources, such as sunlight or a heated rock surface. The ectotherms include the Fishes, Amphibians, Reptiles, and Invertebrates. The body temperatures of aquatic ectotherms are usually very close to those of the water. Ectotherms do not require as much food as warm-blooded animals (Endotherms) of the same size, but most cannot deal as well with cold surroundings.
Ectotrophic: describes an association mycorrhiza between a fungus and the roots of a plant, in which the fungus obtains its nourishment by enveloping the roots in a sheath. (See Endotrophic)
Edaphic: [Late 19th century. < Greek edaphos “floor, ground, soil”] Describes the effect of soil characteristics, especially chemical or physical properties, on plants and animals
Edaphic climax: A stable ecological community that results from the content or properties of the soil rather than the climate
Edge: The transition between two different types or ages of vegetation.
Eelworm: Any of several species of Nematode, named for their resemblance to miniature eels. Eelworms are either free-living or parasitic, and most are about 0.005–0.05 in. (0.1–1.5 mm) long. They are found in all parts of the world. Free-living forms inhabit salt water, freshwater, and damp soil. Parasitic forms are found in the roots of many plant species; the potato-root eelworm, for example, is a serious pest of potatoes. Some species occur in both plants and animals.
Effective seedling: Any seedling, whether natural or planted, that has survived in reasonable vigor for some arbitrary time and is so sited that it should make an effective contribution to the crop. All those seedlings in relation to the optimum are considered elements of the effective stocking.
Egg: In biology, the female sex cell, or gamete. In zoology, the Latin term ovum is often used to refer to the single cell, whereas the word egg may be applied to the entire specialized structure or capsule that consists of the ovum, its various protective membranes, and any accompanying nutritive materials. The egg or ovum, like the male gamete (sperm), bears only a single (haploid) set of Chromosomes. When female and male gametes unite during fertilization, the double (diploid) set of chromosomes is restored in the resulting zygote. In humans, the ovum matures inside one of the ovary’s follicles (hollow group of cells) and is released when the follicle ruptures (ovulation). The ovum passes into the fallopian tube and will degenerate if not fertilized within about 24 hours. In animals, the amount of nutritive material (yolk) deposited in an egg is dependent on the length of time before the developing animal can feed itself or, in the case of mammals, begins to receive nourishment from the maternal circulation. Most animal eggs are enclosed by one or more membranes. Insect eggs are covered by a thick, hard outer membrane, and amphibian eggs are surrounded by a jellylike layer. The term egg also refers to the content of the hard-shelled reproductive body produced by a bird or reptile.
Egg gallery: A long, narrow tunnel along the sides of which eggs are deposited in small niches; the pattern of construction is often diagnostic of a particular species of insect.
Egg mass: Cluster of eggs, usually in a matrix of body hairs or wing scales from the female adult and/or a mucilaginous cementing secretion.
Egret: Any of several species (mainly in the genus Egretta) of wading birds in the same family (Ardeidae) as Herons and Bitterns. Egrets live in marshes, lakes, humid forests, and other wetland environments worldwide. They catch and eat small fishes, amphibians, reptiles, mammals, and crustaceans. They nest in trees and bushes or on the ground. Most are white and develop long plumes for the breeding season. The value of plumes as ornamental objects once drove egrets to near extinction, but changes in fashion and strict conservation measures have allowed their numbers to increase. The great white egret is about 35 in. (90 cm) long; other common species average 20–24 in. (50–60 cm) long.
Einstein’s mass-energy relation: Relationship between Mass (m) and Energy (E) in Albert Einstein’s special theory of Relativity, expressed E = mc2, where c equals 186,000 mi/second (300,000 km/second), the speed of Light. Whereas mass and energy were viewed as distinct in earlier physical theories, in special relativity a body’s mass can be converted into energy in accordance with Einstein’s formula. Such a release of energy decreases the body’s mass.
Eland: Either of two species of easily tamed, oxlike Antelope (genus Taurotragus) found in herds on the plains or in lightly wooded areas of central and southern Africa. The largest of the antelope, they may stand up to 6 ft (1.8 m) tall at the shoulder and weigh as much as 2,200 lbs (1,000 kg). They have a short, dark mane, a dewlap hanging from the throat, and long horns twisted in a tight spiral. The common eland is pale brown, becoming blue-gray with age, and often marked with narrow, vertical white stripes. The giant, or Derby, eland is reddish brown with a blackish neck and vertical white stripes and horns heavier than those of the common eland.
Elastic wave: A wave that is propagated by some kind of elastic deformation, that is, a change in shape that disappears when the forces are removed. A seismic wave is a type of elastic wave.
Electric charge: Quantity of electricity that flows in electric currents or that accumulates on the surfaces of dissimilar nonmetallic substances that are rubbed together briskly. It occurs in discrete natural units, equal to the charge of an electron or proton. It cannot be created or destroyed. Charge can be positive or negative; one positive charge can combine with one negative charge, and the result is a net charge of zero. Two objects that have an excess of the same type of charge repel each other, while two objects with an excess of opposite charge attract each other. The unit of charge is the coulomb, which consists of 6.24 × 1018 natural units of electric charge.
Electric current: Movement of electric charge carriers. In a wire, electric current is a flow of electrons that have been dislodged from atoms and is a measure of the quantity of electrical charge passing any point of the wire per unit time. Current in gases and liquids generally consists of a flow of positive ions in one direction together with a flow of negative ions in the opposite direction. Conventionally, the direction of electric current is that of the flow of the positive ions. In alternating current (AC) the motion of the charges is periodically reversed; in direct current (DC) it is not. A common unit of current is the ampere, a flow of one coulomb of charge per second, or 6.24 × 1018 electrons per second.
Electric dipole: Pair of equal and opposite electric charges, the centres of which do not coincide. An atom in which the centre of the negative cloud of Electrons has been shifted slightly away from the nucleus by an external electric field is an induced electric dipole. When the external field is removed, the atom loses its dipolarity. A water molecule, in which two hydrogen atoms are situated to one side of an oxygen atom, is a permanent electric dipole. The oxygen side is always slightly negative, the hydrogen side slightly positive.
Electric potential: Amount of work needed to move a unit electric charge from a reference point to a specific point against an electric field. The potential energy of a positive charge increases when it moves against an electric field and decreases when it moves with the field. Electric potential can be thought of as potential energy per unit charge. The work done in moving a unit charge from one point to another, as in an electric circuit, is equal to the difference in potential energies at each point. Electric potential is expressed in units of joules per coulomb, or volts.
Electric ray: Any of the aquatic Rays (families Torpedinidae, Narkidae, and Temeridae) that produce an electrical shock. They are found worldwide in warm and temperate seas, mostly in shallow water but some (genus Benthobatis) at depths greater than 3,000 ft (900 m). Slow-moving bottom-dwellers, they feed on fishes and invertebrates. They range in length from less than 1 ft (30 cm) to about 6 ft (1.8 m) and have a short, stout tail. They are soft and smooth-skinned, with a circular or nearly circular body disk formed by the head and pectoral fins. They are harmless unless touched or stepped on. The electric organs, composed of modified muscle tissue, are in the disk near the head. The shock from these organs, which may reach 220 volts and is strong enough to fell a human adult, is used for defense, sensory location, and capturing prey.
Electrolysis: Process in which electric current passed through a substance causes a chemical change, usually the gaining or losing of Electrons. It is carried out in an electrolytic cell consisting of separated positive and negative Electrodes (anode and cathode, respectively) immersed in an electrolyte solution containing Ions or in a molten ionic compound. Electric current enters through the cathode; positively charged Cations travel to it and combine with electrons. Negatively charged Anions give up electrons at the anode. Both thus become neutral molecules. Electrolysis is used extensively in metallurgy to extract or purify Metals from Ores or compounds and to deposit them from solution (electroplating). Electrolysis of molten sodium chloride yields metallic sodium and chlorine gas; that of a strong solution of sodium chloride in water (brine) yields hydrogen gas, chlorine gas, and sodium hydroxide (in solution); and that of water (with a low concentration of dissolved sodium chloride or other electrolyte) yields hydrogen and oxygen.
Electromagnetic spectrum: Total range of frequencies or wavelengths of electromagnetic radiation. The spectrum ranges from waves of long wavelength (low frequency) to those of short wavelength (high frequency); it comprises, in order of increasing frequency (or decreasing wavelength): very-low-frequency to ultrahigh-frequency Radio Waves, Microwaves, infrared radiation, visible light, ultraviolet radiation, X-Rays, and Gamma Rays. In a vacuum, all waves of the electromagnetic spectrum travel at the same speed: 299,792,458 m/sec (186,282 mi/sec).
Elephant: Any of three Ungulate species in the order Proboscidea (family Elephantidae), characterized by their large size, long trunk, tusks, massive legs, large ears, and huge head. All species are grayish to brown, with sparse, coarse body hair. The trunk is used for breathing, drinking, and reaching for food. Elephants eat grasses, leaves, and fruit. The African savanna, or bush elephant (Loxodonta africana), of sub-Saharan Africa, is the largest living land animal, weighing up to 16,500 lbs (7,500 kg) and standing 10–13 ft (3–4 m) tall at the shoulder. The African forest elephant (L. cyclotis) is smaller. The Indian elephant (Elephas maximus), of South and Southeast Asia, weighs about 12,000 lbs (5,500 kg) and stands about 10 ft (3 m) tall. Elephants live in habitats ranging from thick jungle to savanna, in small family groups led by old cows. Most bulls live in bachelor herds. Elephants migrate seasonally. They may eat more than 500 lbs (225 kg) of vegetation daily. All species are considered endangered by the International Union for Conservation of Nature and Natural Resources (IUCN).
Ellipse: Closed curve, one of the conic sections of Analytic Geometry, consisting of all points whose distances from each of two fixed points (foci) add up to the same value. The midpoint between the foci is the center. One property of an ellipse is that the reflection off its boundary of a line from one focus will pass through the other. In an elliptical room, a person whispering at one focus is easily heard by someone at the other. An oval may or may not fit the definition of an ellipse.
Elm: Any of about 18 species of forest and ornamental shade trees that make up the genus Ulmus (family Ulmaceae), native mostly to northern temperate areas. Many are grown for their height and attractive foliage. The leaves are doubly toothed and often lopsided at the base. The flowers, which lack petals, appear before the leaves and are borne in clusters. Seeds are borne in a samara (dry, winged fruit). The American elm (U. americana) has dark gray, ridged bark and elliptical leaves. Many species are susceptible to Dutch elm disease. Elm wood is important for boats and farm buildings because it is durable in water; it is also used for furniture.
Elytra: The anterior leathery or chitinous wings of beetles and leafhoppers; serve as coverings to the hind wings and commonly meet at rest in a straight line down the middle of the dorsum.
Embryo: Early stage of development of an organism in the Egg or the Uterus, during which its essential form and its organs and tissues develop. In humans, the organism is called an embryo for the first seven or eight weeks after conception, after which it is called a Fetus. In mammals, the fertilized egg or zygote undergoes cleavage (cell division without cell growth) to form a hollow ball or blastocyst. During the second week following fertilization, gastrulation (cell differentiation and migration) results in the formation of three tissue types. These three types of tissue develop into different organ systems: the ectoderm develops into the skin and nervous system; the mesoderm develops into connective tissues, the circulatory system, muscles, and bones; and the endoderm develops into the lining of the digestive system, lungs, and urinary system. In humans, by about the fourth week, the head and trunk can be distinguished and the brain, spinal cord, and internal organs begin to develop. By the fifth week, limbs begin to appear and the embryo is about .33 in. (.8 cm) long. By the end of eight weeks, the embryo has grown to about 1 in. (2.5 cm) long and all subsequent change is limited primarily to growth and specialization of existing structures. Any Congenital Disorders begin in this stage.
Embryology: Study of the formation and development of an embryo and fetus. Before widespread use of the microscope and the advent of cellular biology in the 19th century, embryology was based on descriptive and comparative studies. From the time of Aristotle it was debated whether the embryo was a preformed, miniature individual or an undifferentiated form that gradually became specialized. The latter theory was proved in 1827 when Karl Ernst Baer discovered the mammalian ovum (egg). The German anatomist Wilhelm Roux (1850–1924), noted for his pioneering studies on frog eggs (from 1885), became the founder of experimental embryology.
Embryonic root: The embryonic root is the structure that will become the root in a mature plant. When it grows out of the seed and into the soil, it grows downward. Its formal name is Radicle.
Embryonic shoot: The embryonic shoot is the structure in the seed that will become the stem of the new plant and grows upward through the soil surface.
Emergence: In the theory of Evolution, the rise of a system that cannot be predicted or explained from antecedent conditions. The British philosopher of science G.H. Lewes (1817–78) distinguished between resultants and emergents—phenomena that are predictable from their constituent parts (e.g., a physical mixture of sand and talcum powder) and those that are not (e.g., a chemical compound such as salt, which looks nothing like sodium or chlorine). The evolutionary account of life is a continuous history marked by stages at which fundamentally new forms have appeared. Each new mode of life, though grounded in the conditions of the previous stage, is intelligible only in terms of its own ordering principle. These are thus cases of emergence. In the philosophy of mind, the primary candidates for the status of emergent properties are mental states and events.
Emergent: A tree whose crown at maturity projects well above the level of the highest canopy.
Empirical yield tables: 1. Representation of actual and forecast volumes at different stocking levels per age class. 2. In Canada, tables are also prepared for average volume and its components, usu without distinction as to site, over large areas; such tables are referred to as “empirical yield tables.”
Emu: Ratite of Australia. After the ostrich, the emu is the secondlargest living bird. They stand more than 5 ft (1.5 m) tall and often weigh more than 100 lbs (45 kg). The common emu (Dromaius novaehollandiae, family Dromaiidae), the only survivor of several forms exterminated by settlers, has a stout body and long legs. Both sexes are brownish, with a dark-gray head and neck. Emus can run up to 30 mph (50 kph); if cornered, they kick with their large feet. They mate for life and forage in small flocks for fruits and insects but sometimes damage crops.
Endangered or Threatened Species: 1. Any species of plant or animal threatened with Extinction. International and national agencies work to maintain lists of endangered species, to protect and preserve natural habitats, and to promote programs for recovery and reestablishment of these species. The Species Survival Commission of the International Union for Conservation of Nature and Natural Resources (IUCN) publishes information online about endangered species worldwide as the Red List of Threatened Species. Separate books for animal and plant species are also published. In the United States, the Fish and Wildlife Service is responsible for the Conservation and management of fish and wildlife, including endangered species, and their habitats. Its list now consists of about 1,200 domestic species of endangered or threatened animals and plants, and some 200 recovery programs are in effect. 2. A species is endangered when the total number of remaining members may not be sufficient to reproduce enough offspring to ensure survival of the species. A threatened species exhibits declining or dangerously low populations but still has enough members to maintain or increase numbers.
Endemic: It describes a species of organism that is confined to a particular geographic region such as an island or river basin like Chiltan Markhor in Hazar Gangi, Mastung – Baluchistan.
Endocarp: The innermost of the three layers of the wall pericarp of a fruit. It may be toughened or hardened, as in a cherry stone or peach pit. (technical)
Endocrine system: Group of ductless Glands that secrete Hormones necessary for normal growth and development, reproduction, and homeostasis. The major endocrine glands are the hypothalamus, pituitary, pineal, thyroid, Parathyroids, Adrenals, islets of langerhans in the pancreas, ovaries, and testes. Secretion is regulated either by regulators in a gland that detect high or low levels of a chemical and inhibit or stimulate secretion or by a complex mechanism involving the hypothalamus and the pituitary. Tumours that produce hormones can throw off this balance. Diseases of the endocrine system result from over- or underproduction of a hormone or an abnormal response to a hormone. (See illustration).
Endoparasite: A parasite that lives inside its host, e.g. a tapeworm
Endophyte: A plant or fungus that lives inside another plant. It may or may not be a parasite of its host plant.
Endoplasm: The inner, more fluid layer of cytoplasm in a cell Endoplasmic reticulum (ER): Membrane system within the Cytoplasm of a eukaryotic cell (see Eukaryote), important in the synthesis of proteins and lipids. The ER usually makes up more than half the membrane of the cell and is continuous with the outer membrane of the nuclear envelope (See Nucleus). There are two distinct regions of ER: the rough ER, or RER (so called because of the protein-synthesizing Ribosomes attached to it), and the smooth ER (SER), which is not associated with ribosomes and is involved in the synthesis of lipids and the detoxification of some toxic chemicals.. (Pic)
Endoscopy: Examination of the body’s interior through an instrument inserted into a natural opening or an incision, usually as an outpatient procedure. Endoscopes include the upper gastrointestinal endoscope (for the esophagus, stomach, and duodenum), the colonoscope (for the colon), and the bronchoscope (for the bronchial tubes).With Fibre Optics, much more maneuverable instruments can reach formerly inaccessible sites, while causing much less discomfort. Attachments can take tissue samples, excise polyps and small tumors, and remove foreign objects.
Endosperm: The tissue that surrounds the embryo inside a plant seed and provides nourishment for it
Endospore an asexual spore that is formed inside the cells of some bacteria and algae.
Endosymbiosis: Symbiosis in which one organism lives inside the body of another and both function as a single organism
Endothecium: The inner tissue of the spore-producing capsule of a moss
Endotherm: So-called warm-blooded animals; that is, those that maintain a constant body temperature independent of the environment. The endotherms include the birds and mammals. If heat loss exceeds heat generation, metabolism increases to make up the loss or the animal shivers to raise its body temperature. If heat generation exceeds the heat loss, mechanisms such as panting or perspiring increase heat loss. Unlike Ectotherms (See Ectotherms), endotherms can be active and survive at quite low external temperatures, but because they must produce heat continuously, they require high quantities of “fuel” (i.e., food).
Energy: Capacity for doing Work. Energy exists in various forms— including Kinetic, Potential, Thermal, Chemical, electrical, and Nuclear—and can be converted from one form to another. For example, fuel-burning heat engines convert chemical energy to thermal energy; batteries convert chemical energy to electrical energy. Though energy may be converted from one form to another, it may not be created or destroyed; that is, total energy in a closed system remains constant. All forms of energy are associated with motion. A rolling ball has kinetic energy, for instance, whereas a ball lifted above the ground has potential energy, as it has the potential to move if released. Heat and work involve the transfer of energy; heat transferred may become thermal energy.
English bond: An arrangement of bricks in a wall in which layers courses of bricks laid end to end stretchers alternate with layers of bricks laid side to side headers. The stretchers of all layers are aligned vertically, and the headers are centered on the stretchers and the mortar joints between them. (See: Flemish bond)
Engraver: Beetle which feeds in the phloem-cambium region of woody plants, often scoring or engraving adjacent sapwood tissues.
Enhanced: Stocked area where density control standards have been met.
Enterprise: [15th century. < Old French entreprise < past participle of entreprendre “undertake” < prendre “take”] commercial business: a commercial company
Entire: Having no teeth or indentations.
Entomology: (from Greek ἔντομος, entomos, “that which is cut in pieces or engraved/segmented”, hence “insect”; and -λογία, -logia) Branch of Zoology dealing with the scientific study of Insects, including their taxonomy, morphology, physiology, and ecology. Applied aspects of entomology, such as the harmful and beneficial impact of insects on humans, are also studied.
Environment: The interaction of climate, soil, topography, and other plants and animals in any given area. An organism’s environment influences its form, behavior, and survival; all the external factors influencing the life and activities of people, plants, and animals
Environmental geology: Scientific field concerned with applying the findings of geologic research to the problems of land use and civil engineering. It is closely allied with urban geology and deals with the impact of human activities on the physical environment. Other important concerns of environmental geology include reclaiming mined lands; identifying geologically stable sites for constructing buildings, nuclear power plants, and other facilities; and locating sources of building materials, such as sand and gravel.
Environmentalism: Advocacy of the preservation or improvement of the natural environment, especially the social and political movement to control environmental pollution. Other specific goals of environmentalism include control of human population growth, conservation of natural resources, restriction of the negative effects of modern technology, and the adoption of environmentally benign forms of political and economic organization. Environmental advocacy at the international level by Nongovernmental Organizations and some states has resulted in treaties, conventions, and other instruments of environmental law addressing problems such as Global Warming, the depletion of the OZONE LAYER, and the danger of transboundary pollution from nuclear accidents. Influential U.S. and British environmentalists have included Thomas Robert Malthus, John Muir, Rachel Carson, Barry Commoner, Paul R. Ehrlich, and Edward O. Wilson. In the social sciences, the term refers to any theory that emphasizes the importance of environmental factors in the development of culture and society.
Environmental Protection Agency (EPA): U.S. government agency that sets and enforces national pollution-control standards. It was established by Pres. Richard Nixon (1970) to supersede a welter of confusing and ineffective state environmental laws. Its early accomplishments include banning the use of DDT (1972), setting deadlines for the removal of lead from gasoline (1973), establishing health standards for drinking water (1974), and monitoring fuel efficiency in automobiles (1975). The EPA’s enforcement was in large part responsible for a decline of onethird to one-half in most air-pollution emissions in the U.S. from 1970 to 1990, and during the 1980s the pollution standards index improved by half in major cities; water quality and waste disposal also improved significantly. The EPA also oversees the cleanup of abandoned waste sites through Superfund. Its existence has resulted in heightened awareness and concern for the environment worldwide.
Enzyme: Substance that acts as a Catalyst in living organisms, regulating the Rate at which life’s Chemical Reactions proceed without being altered in the process. Enzymes reduce the Activation Energy needed to start these reactions; without them, most such reactions would not take place at a useful rate. Because enzymes are not consumed, only tiny amounts of them are needed. Enzymes catalyze all aspects of cell metabolism, including the digestion of food, in which large nutrient molecules (including proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular materials and components. Almost all enzymes are Proteins; many depend on a nonprotein Cofactor, either a loosely associated organic compound (e.g., a Vitamin) or a tightly bound metal ion (e.g., iron, zinc) or organic (often metal-containing) group. The enzyme-cofactor combination provides an active configuration; usually including an active site into which the substance (substrate) involved in the reaction can fit. Many enzymes are specific to one substrate. If a competing molecule blocks the active site or changes its shape, the enzyme’s activity is inhibited. If the enzyme’s configuration is destroyed, its activity is lost. Enzymes are classified by the type of reaction they catalyze: (1) Oxidation-Reduction, (2) transfer of a chemical group, (3) Hydrolysis, (4) removal or addition of a chemical group, (5) isomerization, and (6) binding together of substrate units (polymerization). Most enzyme names end in -ase. Enzymes are chiral catalysts, producing mostly or only one of the possible stereoisomeric products. The fermentation of wine, leavening of bread, curdling of milk into cheese, and brewing of beer are all enzymatic reactions. The uses of enzymes in medicine include killing disease causing microorganisms, promoting wound healing, and diagnosing certain diseases.
Ephemerals: Plants that emerge and bloom during one season then die back for the remainder of the year. Many spring ephemerals bloom in woodlands, including trillium and ladyslipper.
Epicenter: That point on the Earth’s surface directly above the hypocenter of an earthquake. (Pic at earthquake) Locating Epicenter: Seismologists can locate the epicenter of an earthquake by triangulation, a method that involves taking seismographic measurements from at least three separate seismic stations. Seismologists measure the time it takes seismic waves to reach the recording stations, as well as the magnitude of the waves, and triangulate the measurements to calculate the location of the epicenter.
Epicormic branching: Branches that grow out of the main stem of a tree from buds produced under the bark, most commonly occurring in trees under crown stress; also called watersprouts. Severe epicormic branching increases knottiness and reduces lumber quality.
Epicormic shoot: (syn. Sprout) A shoot arising from a dormant or adventitious bud on the stem or branch of a woody plant.
Epidemic: Widespread insect or disease incidence beyond normal proportions; usually accompanied by excessive damage
Epidermis: The epidermis is a layer of cells on the exterior of stems and leaves as well as other plant organs. This is a protective layer that keeps out bacterial and fungal spores as well as sealing the plant organ from loss of water. Cutin, secreted by the epidermal cell, is a waxy material that allows the epidermal cell to be very effective in preventing water loss. In cross section, the epidermis looks like small bricks. Looking at epidermal cells from the top down, they have the appearance of a jigsaw puzzle pieces. (Pic) (Pic at Cuticle)
Epidemiology: Study of disease distribution in populations. It focuses on groups rather than individuals and often takes a historical perspective. Descriptive epidemiology surveys a population to see what segments (e.g., age, sex, ethnic group, occupation) are affected by a disorder, follows changes or variations in its incidence or mortality over time and in different locations, and helps identify syndromes or suggest associations with risk factors. Analytic epidemiology conducts studies to test the conclusions of descriptive surveys or laboratory observations. Epidemiologic data on diseases is used to find those at high risk, identify causes and take preventive measures, and plan new health services.
Epiphyte: Any plant that grows upon or is attached to another plant or object merely for physical support. Epiphytes are found mostly in the tropics and are also known as air plants because they have no attachment to the ground or other obvious nutrient source. They obtain water and minerals from rain and from debris on the supporting plants. Orchids, ferns, and members of the pineapple family are common tropical epiphytes. Lichens, mosses, liverworts, and algae are epiphytes of temperate regions.
Epigynous: Epigynous ovaries have the flower parts (calyx, corolla, and androecium) attached above the ovary to the top of the ovary. Epigynous and inferior ovaries are synonymous terms. (Pic)
Epistatic gene: Gene that determines whether or not a trait determined by another gene will be expressed. For example, when the gene responsible for albinism occurs, the genes that determine skin color are present but not expressed; the gene for albinism is therefore called an epistatic gene.
Epistemology: Study of the origin, nature, and limits of human knowledge. Nearly every great philosopher has contributed to the epistemological literature. Some historically important issues in epistemology are: (1) whether knowledge of any kind is possible, and if so what kind; (2) whether some human knowledge is innate (i.e., present, in some sense, at birth) or whether instead all significant knowledge is acquired through experience; (3) whether knowledge is inherently a mental state; (4) whether certainty is a form of knowledge; and (5) whether the primary task of epistemology is to provide justifications for broad categories of knowledge claim or merely to describe what kinds of things are known and how that knowledge is acquired. Issues related to (1) arise in the consideration of Skepticism, radical versions of which challenge the possibility of knowledge of matters of fact, knowledge of an external world, and knowledge of the existence and natures of other minds.
Epoch: Unit of geologic time during which a rock series is deposited. It is a subdivision of a geologic period. Additional distinctions can be made by adding relative time terms, such as early, middle, and late. The use of the term is usually restricted to divisions of the Tertiary and Quaternary Periods.
Equator: Great circle around the Earth that is everywhere equidistant from the geographic poles and lies in a plane perpendicular to the Earth’s axis. This geographic, or terrestrial, Equator divides the Earth into the Northern and Southern Hemispheres and forms the imaginary reference line on the Earth’s surface from which Latitude is reckoned (i.e., 0° latitude). In astronomy, the celestial equator is the great circle in which the plane of the terrestrial Equator intersects the celestial sphere; it is thus equidistant from the celestial poles. When the Sun lies in its plane, day and night are everywhere of equal length; this happens at the Equinoxes.
Equinox: Either of two moments in the year when the Sun is exactly above the Equator and day and night are of equal length all over Earth; also, either of two points in the sky where the Ecliptic and the celestial equator intersect. The vernal equinox, when spring begins in the Northern Hemisphere, occurs about March 21, when the Sun moves north across the celestial equator. The autumnal equinox falls about September 23, as the Sun crosses the celestial equator going south.
Era: Very long span of geologic time; in formal usage, a portion of geologic time of the second-greatest magnitude (eons are longer). Three eras are recognized: Paleozoic, Mesozoic, and Cenozoic. Because of the difficulties involved in establishing accurate chronologies, the Precambrian, or earliest, eras are classified independently. An era is composed of one or more geologic periods.
Ergonomics: Study of workplace design: the study of how a workplace and the equipment used there can best be designed for comfort, efficiency, safety, and productivity
Ergot: Disease of Cereal Grasses, especially Rye, caused by the fungus Claviceps purpurea. An ear of rye infected with ergot exudes a sweet, yellowish mucus. Ergot is the source of drugs used to control postpartum hemorrhage and to treat migraine headaches. Lysergic acid, from which the powerful Hallucinogen LSD is synthesized, comes from ergot. Taking an overdose of ergot-derived medications or eating flour milled from ergot-infected rye can cause ergotism (also called St. Anthony’s fire) in humans and livestock; symptoms may include convulsions, miscarriages in females, and dry gangrene, and may result in death.
Erica: Any of the approximately 500 species of low evergreen shrubs that make up the genus Erica, in the Heath Family, most native to South Africa. Some also occur in the Mediterranean and in northern Europe, and species have been introduced to North America. They have small, narrow leaves arranged in whorls set closely together on the shoots. Some African species are large bushes or trees. The white, or tree, heath (E. arborea) is also known as Brier. Some southern African species are cultivated in cool greenhouses and outdoors in southwestern North America.
Erosion: [Early 17th century Latin erodere “gnaw off”] Removal of surface material from the Earth’s crust and transportation of the eroded materials by natural agencies from the point of removal. Erosion is caused by wind action, river and stream processes, marine processes (sea waves), and glacial processes. The complementary actions of erosion and deposition or sedimentation operate through wind, moving water, and ice to alter existing landforms and create new landforms. Erosion will often occur after rock has been disintegrated or altered through Weathering. Moving water is the most important natural agent of erosion. Sea wave erosion results primarily from the impact of waves striking the shore and the abrasive action of sand and pebbles agitated by wave action. Erosion by rivers is caused by the scouring action of the sediment-containing flowing water. Glacial erosion occurs by surface abrasion as the ice, embedded with debris, moves slowly over the ground accompanied by the plucking of rock from the surface. Wind plays a key role in arid regions as blowing sand breaks down rock and dislodges surface sand from unprotected sand dunes. Human intervention, as by the removal of natural vegetation for farming or grazing purposes, can lead to or accelerate erosion by wind and water. (See also Sheet Erosion).
Erosion strip: (Syn: Erosion Felling) A type of predicted felling by experts in which felling is done in strips along the river banks. This is mainly applied in Sind, Pakistan. In this felling trees are felled leaving behind the stumps.
Error: 1. In applied mathematics, the difference between a value and an estimate of that value. In statistics, a common example is the difference between the mean age of a given group of people (See Mean, Median, and Mode) and that of a sample drawn from the group. In Numerical Analysis, an example of round-off error is the difference between the true value of PI and commonly substituted expressions like 22⁄7 and shorter versions like 3.14159. Truncation error results from using only the first few terms of an infinite series. Relative error is the ratio of the size of an error to the size of the quantity measured, and percentage error is relative error expressed as a percent.
Escalator: Moving staircase used as transportation between floors or levels in stores, airports, subways, and other mass pedestrian areas. The name was first applied to a moving stairway shown at the Paris Exposition of 1900. Modern escalators are electrically powered, driven by chain and sprocket, and held in place by two tracks. As the treads approach a landing, they pass through a comb device; a switch cuts off power if an object becomes jammed between comb and treads.
Essential oil: Any of a class of highly volatile (readily evaporating) organic compounds found in plants and usually named for them (e.g., rose oil, peppermint oil). They have been known and traded since ancient times. Many essential oils contain Isoprenoids. Some, such as oil of wintergreen (methyl salicylate) and orange oil (d-limonene), have one predominant component, but most have dozens or hundreds. Trace components impart oil’s characteristic odour, which synthetic or blended oils can rarely duplicate. Essential oils have three primary commercial uses: as odorants in perfumes, soaps, detergents, and other products; as flavours in baked goods, candies, soft drinks, and many other foods; and as pharmaceuticals, in dental products and many medicines.
Establishment: The process of developing a crop to the stage at which the young trees may be considered established, i.e., safe from juvenile mortality and no longer in need of special protection or special tending, but only routine cleaning, thinning, and pruning.
Establishment period: The time elapsing between the initiation of a new crop and its establishment.
Estate law: Laws governing the nature and extent of an owner’s rights with respect to real and personal property. When used in connection with probate proceedings, it refers to the laws governing the disposition of the total property of whatever kind owned by a person at the time of death. (See also Estate tax, Property, Property Tax).
Estate tax: Levy on the value of property changing hands at the death of the owner, fixed mainly by reference to its total value. Estate tax is generally applied only to estates whose value exceeds a set amount, and it is applied at graduated rates. An estate tax was first instituted in the U.S. in 1898 to help finance the Spanish-American War; it was repealed in 1902 but permanently re-imposed in 1916, initially to help finance mobilization for World War I. Methods of avoiding estate tax (e.g., gifts and trust funds) were largely foiled by the U.S. Tax Reform Act of 1976.
Estimate: The value of a parameter or variate obtained indirectly. The average height of a stand of trees may be estimated by measuring a sample of trees and calculating the average from this sample.
Estuary: Partly enclosed coastal body of water in which river water is mixed with seawater. An estuary is thus defined by salinity rather than geography. Many coastal features designated by other names are in fact estuaries (e.g., Chesapeake Bay). Some of the oldest continuous civilizations have flourished in estuarine environments (e.g., the land between the Tigris and Euphrates rivers, the Nile delta, the Ganges delta, and the lower Huang He valley). Cities such as London (River Thames), New York (Hudson River), and Montreal (St. Lawrence River) developed on estuaries and became important commercial centres.
Ethologists: The biologists who are interested in studying behaviors and Ethology (See Ethology) are the branch of biology, dealing with the study of Animal Behaviour.
Ethology: Study of animal behaviour. It is a combination of laboratory and field science, with strong ties to other disciplines (e.g., Neuroanatomy, Ecology, Evolution). Though many naturalists have studied aspects of animal behaviour through the centuries, the modern science of ethology is considered to have arisen as a discrete discipline with the work in the 1920s of Nikolaas Tinbergen and Konrad Lorenz. Interested in the behavioral process rather than in a particular animal group, ethologists often study one type of behaviour (e.g., aggression) in various unrelated animals.
Eucalyptus: Any of the more than 500 species of mostly very large trees in the genus Eucalyptus, in the Myrtle family, native to Australia, New Zealand, Tasmania, and nearby islands. Many species are grown widely throughout the temperate regions of the world as shade trees or in forestry plantations. Because they grow rapidly, many species attain great height. The leaf glands of many species, especially E. salicifolia and E. globulus, contain a volatile, aromatic oil known as eucalyptus oil, used mostly in medicines. Eucalyptus wood is used extensively in Australia as fuel, and the timber is commonly used in buildings and fencing. The bark of many species is used in papermaking and tanning.
Eugenic: Favorable to the genetic quality of a population. (cf. dysgenic)
Euglena: The euglena is a single-celled alga with two or several flagella (depending on the species) located at one end for locomotion. Other algae, vertebrate sperm cells, and some protozoans and bacteria possess a single flagellum for movement. (Pic)
Eukaryote: Any organism composed of one or more cells, each of which contains a clearly defined nucleus enclosed by a membrane, along with organelles (small, self-contained, cellular parts that perform specific functions). The organelles include mitochondria, Chloroplasts, a Golgi apparatus, an Endoplasmic Reticulum, and Lysosomes. All organisms except Bacteria are eukaryotes; bacteria are Prokaryotes.
Evaporation: Change of a liquid into the gaseous state; in particular, the process by which liquid water enters the atmosphere as water vapour. Evaporation, mostly from the sea and from vegetation, replenishes the humidity of the air. It is an important part of the exchange of energy in the Earth-atmosphere system that produces atmospheric motion, and therefore weather and climate. The rate of evaporation depends on the temperature difference between the evaporating surface and the air, the relative humidity, and wind.
Evaporator: Industrial apparatus for converting liquid into gas or vapour. The single-effect evaporator consists of a container or surface and a heating unit; the multiple-effect evaporator uses the vapour produced in one unit to heat a succeeding unit. Double-, triple-, or quadruple-effect evaporators may be used in industrial and steam heating plants. Some evaporators are used to concentrate a solution by vaporizing and eliminating water (e.g., in a concentration plant for sugar and syrup). In purification processes such as Desalination, evaporators convert the water to vapour, leaving mineral residues behind; the vapour is then condensed into (desalinated) water. In a refrigeration system, the cooling is produced as the rapid evaporation of the liquid refrigerant absorbs heat.
Evapotranspiration: Loss of water from the soil both by evaporation from the soil surface and by Transpiration from the leaves of the plants growing on it. Factors that affect the rate of evapotranspiration include the amount of solar radiation, atmospheric vapor pressure, temperature, wind, and soil moisture. Evapotranspiration accounts for most of the water lost from the soil during the growth of a crop. Estimation of evapotranspiration rates is thus important in planning irrigation schemes.
Even-aged: 1. Applied for a crop which are of the same age. 2. A crop having age difference less than 25% is said to be as even aged crop. 3. Applied to a stand in which relatively small age differences exist between individual trees. The maximum difference in age permitted in an even-aged stand is usu 10 to 20 years, though where a stand will not be harvested until it is 100 to 200 years old, larger difference up to 25 % of the rotation age may be allowed. (SAF)
Even-Aged management: A forest management method in which all trees in an area are harvested at one time or in several cuttings over a short time to produce stands that are all the same age or nearly so. This management method is commonly applied to shade-intolerant conifers and hardwoods.
Even-aged system: Silvicultural systems in which stands have an even-aged structure, e.g., clearcutting method, coppice method, seed-tree method.
Even-flow harvest: A harvesting scheme designed to extract exactly the same volume of wood fiber each period.
Evergreens: Any plant that retains its leaves through the winter and into the following summer or through several years. Many tropical species of broad-leaved Flowering Plants are evergreen, but in cold-temperate and Arctic areas the evergreens commonly are cone-bearing shrubs or trees (Conifers), such as Pines and Firs. The leaves of evergreens usually are thicker and more leathery than those of Deciduous Trees and often are needlelike or scale like in cone-bearing trees. A leaf (or needle) may remain on an evergreen tree for two years or longer and may fall during any season.
Everlasting: Any of several plants that retain their form and colour when dried and are used in dry bouquets and flower arrangements. Popular everlastings include several species of the Composite Family, especially the true everlastings, or immortelles, species of the genus Helichrysum, native to North Africa, Crete, and the parts of Asia bordering on the Mediterranean and cultivated in many parts of Europe. One of the best known everlastings is the strawflower (H. bracteatum) of Australia. Many Grasses with showy plumes or spikes are classified as everlastings.
Evidence: In law, something (e.g., testimony, documents, or physical objects) presented at a judicial or administrative proceeding for the purpose of establishing the truth or falsity of an allegation of fact. To preserve legal due process and to prevent the jury from being misled, an extensive body of rules has sprung up regarding the handling of evidence. In the U.S., all federal and many state courts adhere to the Federal Rules of Evidence, which covers such elements as types of evidence, admissibility, relevance, competency of witnesses, confessions and admissions, expert testimony, and authentication. Most evidence received at trial is in the form of verbal statements of witnesses, who are subject to questioning by attorneys from both sides. Two important categories of evidence are direct evidence, which is offered by a witness whose knowledge of a factual matter is firsthand (as through sight or hearing), and circumstantial evidence.
Evolution: Biological theory that animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations. It is one of the keystones of modern biological theory. In 1858 Charles Darwin and Alfred Russel Wallace jointly published a paper on evolution. The next year Darwin presented his major treatise On the Origin of Species by Means of Natural Selection, which revolutionized all later biological study. The heart of Darwinian evolution is the mechanism of Natural Selection. Surviving individuals, which vary (See Variation) in some way that enables them to live longer and reproduce, pass on their advantage to succeeding generations. In 1937 Theodosius Dobzhansky applied Mendelian genetics (See Gregor Mendel) to Darwinian Theory, contributing to a new understanding of evolution as the cumulative action of natural selection on small genetic variations in whole populations. Part of the proof of evolution is in the fossil record, which shows a succession of gradually changing forms leading up to those known today. Structural similarities and similarities in embryonic development among living forms also point to common ancestry. Molecular biology (especially the study of genes and proteins) provides the most detailed evidence of evolutionary change. Though the theory of evolution is accepted by nearly the entire scientific community, it has sparked much controversy from Darwin’s time to the present; many of the objections have come from religious leaders and thinkers who believe that elements of the theory conflict with literal interpretations of the Bible.
Exchange rate: Price of one country’s money in relation to another’s. Exchange rates may be fixed or flexible. An exchange rate is fixed when two countries agree to maintain a fixed rate through the use of Monetary Policy. Historically, the most famous fixed exchange-rate system was the Gold Standard; in the late 1850s, one ounce of gold was defined as being worth 20 U.S dollars and 4 pounds sterling, resulting in an exchange rate of 5 dollars per pound. An exchange rate is flexible, or “floating,” when two countries agree to let international market forces determine the rate through Supply and Demand. The rate will fluctuate with a country’s exports and imports. Most world trade currently takes place with flexible exchange rates that fluctuate within relatively fixed limits.
Excretion: Bodily process for disposing of undigested food waste products and nitrogenous by-products of metabolism, regulating water content, maintaining acid-base balance, and controlling osmotic pressure to promote Homeostasis. It refers to both Urination and Defecation and to the processes that take place in the digestive and Urinary Systems, as the kidney and liver filter wastes, toxins, and drugs from the blood and food reaches the last stage of digestion. Ammonia from protein digestion, the primary excretory product, is converted to urea to be excreted in urine.
Excurrent: Excurrent branching is the type of branching that exists in a pine tree. There is one main trunk with a whorl of branches at each node. This is also known as Monopodial Branching.
Exfoliation: It is mainly a physical weathering process in which long sheets of rock peel off from an outcrop. In exfoliation, reduction in pressure due to removal of the overlying rock plays an important part. As each stab breaks off, it releases weight from the underlying mass. As a result, its outer layer expands and separates from the rock mass. Exfoliation in commonly seen in homogenous rocks like granite.
Exploitable age: The age at which an individual tree or crop attains the size required to fulfill the objects of management. (Syn: Cutting age; Rotation age)
Exploitable diameter: 1. the minimum diameters at breast height at which trees are considered suitable for conversion. 2. The diameter own to which all portions of a bole or tree must be exploited as a timber or fuel under a permit or license. (BCFT)
Extension forester: A Cooperative Extension Service professional who educates woodland owners on how they can effectively manage their forests.
Extensive forest management: Protection from fire and insects; reliance on natural regeneration.
Extinction (of species): Dying out or termination of a species. It occurs when a species can no longer reproduce at replacement levels. Most past extinctions are thought to have resulted from environmental changes that the doomed species was either unable to adapt to or that caused it to adapt so thoroughly that it became a distinctly new species. The effect of humans on the environment, through hunting, collecting, and habitat destruction, has become the principal factor in plant and animal extinctions.
Extrusive rock: Any Igneous Rock derived from magma that is poured out or ejected at the Earth’s surface. Extrusive rocks are usually distinguished from Intrusive Rocks on the basis of their texture and mineral composition. Lava flows and pyroclastic debris (fragmented volcanic material) are extrusive; they are commonly glassy (e.g., obsidian) or finely crystalline (e.g., basalts and felsites).
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Naeem Javid Muhammad Hassani