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Natural and artificial substances in the atmosphere that affect human health or well-being, or the well-being of any other organisms in the environment. Air pollution also applies to situations in which contaminants affect structures and artifacts…

The ongoing lower level of species extinction intensity occurring between episodes of mass extinctions. Extinction is a normal part of the history of life. Out of every 100 species that have ever lived on Earth, 99 are no longer in existence.…

Cameras in mobile phones or smartphones that can capture images and videos.The cellphone, the world’s favorite must-have gadget, has been with us for nearly a half-century, while experiencing continuous and often phenomenal improvements. Much of the…

Light emitted by a high-speed charged particle when the particle passes through a transparent, nonconducting, solid material at a speed greater than the speed of light in the material. The emission of Cerenkov radiation—also spelled Cherenkov—is…

The extraction and refining of copper (Cu) from its ores. About 18 million metric tons per year of copper metal is produced from the mining and processing of copper ores, typically containing only about 1% Cu. About 80% of the world's primary copper…

The capture, processing, transmission, and storage of images in electronic form. Digital photography differs from film photography in that images are captured and recorded as electronic files rather than as recognizable images on a light-sensitive…

A general term referring to a system or part of a system of conducting parts and their interconnections through which electric currents are intended to flow. A circuit is made up of a voltage source along with active and passive elements, as well as…

The measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, electrical impedance is the complex ratio of the voltage to the current in an alternating-current (ac)…

The ability of a material to resist or allow the flow of electrical current. Material properties largely determine the resistance and conductance—quantified by electrical resistivity and conductivity—of a given object, such as a circuit or…

The measures of a material's opposition to the flow of electricity and a material's ability to conduct electricity, respectively. Resistivity quantifies resistance, which is a material's opposition to the flow of electrons (an electric current or…

The process in which an electron, which has been excited from the valence band to the conduction band of a semiconductor, falls back into an empty state in the valence band, which is known as a hole. When atoms come together to form a crystal, the…

Typically, an aquatic vertebrate with scales, gills, and paired fins. Fishes (Fig. 1) are found throughout the world's waterways, from saltwater oceans to freshwater streams and ponds. About 35,000 species of fishes have been described to date. Many…

A biological organism whose genetic material has been manipulated artificially through genetic or genomic editing techniques. In contrast to the long history of artificial selection (domestication), in which humans selectively breed organisms to…

A space-traversing unmanned vehicle which contains the means for controlling its flight path and that delivers an explosive warhead with high accuracy. Various kinds of missiles are guided in the sense that they can aerodynamically adjust after…

A vacant electron energy state near the top of an energy band in a solid. A hole, or more formally an electron hole, represents the absence of an electron where one could exist as part of an atom or within a crystal structure (an atomic lattice)…

An applied science and technology concerned with the mechanical properties and practical uses of liquids. The physical description of fluids in motion is based upon the conservation laws of mass, momentum, and energy. The mathematical statement of…

Fundamental laws dealing with electric currents at junctions and voltages around any loop within a network. Also known as Kirchhoff's circuit laws, the laws were first described by German physicist Gustav Kirchhoff in 1845. The laws are divided into…

The process of exploring the deep seabed and recovering minerals from seawater and from deposits on and under the seabed. While the world's demand for mineral commodities is increasing at a rapid rate, most of the developed countries have been…

The relationship stating that the magnitude of the electrical current in a circuit is directly proportional to the applied voltage and inversely proportional to the circuit's resistance. One of the simplest and most intuitive electrical laws, Ohm's…

A naturally occurring geologic body that may contain one or more metals. The metals may be present as native elements, or, more commonly, as oxides, sulfides, sulfates, silicates, or other compounds. The term ore is often used loosely to include…

Substances applied to other materials to change the surface properties, such as color, wear, and chemical or scratch resistance, without changing the bulk properties. The terms paint and coatings often are used interchangeably. However, it has…

An electric circuit in which the elements, branches (elements in series), or components are connected between two points, with one of the two ends of each component connected to each point. The illustration shows a simple parallel circuit. In more…

A solid crystalline material whose electrical conductivity is intermediate between that of a metal and an insulator. Semiconductors exhibit conduction properties that may be temperature-dependent, permitting their use as thermistors…

The penetration by humans into the reaches of the universe above Earth's atmosphere through the use of crewed vehicles. Human space flight poses significant challenges as an enterprise, given the technical rigors and costs associated with achieving…

A management technology involving the interactions of science, an organization, and its environment as well as the information and knowledge that support each. The purpose of systems engineering is to support organizations that desire improved…

A subdiscipline of paleobiology that investigates the processes of preservation and their influence on information in the fossil record. Taphonomy is the study of fossilization and considers the processes at work in the incorporation of living…

A branch of engineering concerned with the development of sources of supply, transmission, distribution, and treatment of water. The term is used most frequently for municipal water works, but applies also to water systems for industry, irrigation,…

A sequence of physical and chemical processes used to transform various water sources into water that is safe for human consumption and is aesthetically pleasing. Water treatment is designed to remove particulate matter, chemicals, and…

An extensively used electrical network of four resistances R1–4 (or impedances Z1–4) if alternating currents are involved. A Wheatstone bridge network (see Fig. 1), was first described by British physicist and mathematician Samuel Hunter Christie in…

A chemical obtained from wood. Woody plants comprise the greatest part of the organic materials produced by photosynthesis on a renewable basis. Replacement of fossil hydrocarbons, from which most organic chemicals are derived, is possible in many…

A process of making physical objects directly from digital models, usually layer by layer; also known as additive manufacturing (AM). 3D printing has been hailed by many as the technology that will revolutionize how we live. As information…

Mechanized systems of food and fiber production used in agriculture. The mechanized systems comprising agricultural machinery are utilized in numerous aspects of agriculture, including the initial tillage of the soil (Fig. 1), planting, cultural…

The process for selecting an air-pollution monitoring site. Historically, the Clean Air Act was concerned only with criteria air pollutants, the six common air pollutants for which the U.S. Environmental Protection Agency (EPA) had set standards. In…

The movement of passengers and cargo by aircraft such as airplanes and helicopters. Air transportation (Fig. 1) provides efficiency and value when long distances are traveled, high-value payloads are moved, immediate needs must be met, or surface…

The process of designing an aircraft. All new aircraft designs (Fig. 1) are aimed at a specification that is meant to satisfy potential customers and be better than designs from competitors. In the case of civil aircraft, the manufacturer undertakes…

A large aquatic reptile of the family Alligatoridae. Alligators belong to the family Alligatoridae in the reptilian order Crocodylia (Crocodilia). Common usage generally restricts the name alligator to the two extant species of the genus Alligator…

A small, tropical, evergreen tree (Pimenta dioica) and its dried, unripe fruit (berry). Allspice (Pimenta dioica; alternatively, P. officinalis) [see illustration] is a member of the myrtle family (Myrtaceae). Allspice, which is also known as…

Substances formed by the addition of one or more elements, usually metals, to aluminum. The principal alloying elements in aluminum-base alloys are magnesium (Mg), silicon (Si), copper (Cu), zinc (Zn), and manganese (Mn) [Fig. 1]. In wrought…

Most commonly, a generic name for all fossil resins, although it has been restricted by some to refer only to succinite, the mineralogical species of fossil resin that includes most of the Baltic Coast deposits. The time necessary to transform resin…

Any protozoan moving by means of protoplasmic flow. In their entirety, ameboid protozoans (or ameboid protists) include naked amebas, those enclosed within a shell or test, and more highly developed representatives, such as heliozoians,…

Any of the substances containing esters of higher fatty acids and long-chain monohydric alcohols. From a practical standpoint, this definition is inadequate because it allows liquids such as sperm whale oil and jojoba oil to be called waxes, and it…

The use of live nonhuman animals for scientific research and experimentation. Animal testing has been a cornerstone of biomedical research, having contributed greatly to the understanding of human biology, to the unraveling of the complex underlying…

One of the three living orders of the class Amphibia, encompassing the frogs and toads. Anura is the largest order of amphibians (class Amphibia), containing more than 7000 species of frogs (Fig. 1) and toads. Because members of the order Anura…

A natural order of the class Arachnida, commonly known as the spiders. Members of the order Araneae (also called Araneida)—the spiders (Fig. 1)—are widespread over most of the land areas of the world and are well adapted to many different habitats.…

A genus of fossil birds in the extinct order Archaeopterygiformes, characterized by flight feathers like those of modern birds. Archaeopteryx is generally accepted as the oldest known fossil bird. It represents a unique snapshot of evolution; most…

Any vegetable that is prevalent in Asian cuisines, but less well known in Western diets. Asian vegetables (Fig. 1), also referred to as Asian greens or oriental vegetables, are very important in Asian countries, but are not as popular in North…

Frameworks for assessing risk prior to a complete understanding of nanomaterial behavior. Nanotechnology is being used in exciting and potentially revolutionary applications, ranging from sunscreens and drug delivery to more efficient solar cells…

A self-propelled land vehicle, usually having four wheels and an internal combustion engine, used primarily for personal transportation; also known as a car. Other types of motor vehicles include buses, which carry large numbers of commercial…

A nonporous envelope of thin material filled with a lifting gas and capable of lifting any surrounding material and usually a suspended payload into the atmosphere. A balloon (Fig. 1) which is supported chiefly by buoyancy imparted by the…

A structural member that is fabricated from metal, reinforced or prestressed concrete, wood, fiber-reinforced plastic, or other construction materials and that resists loads perpendicular to its longitudinal axis. A beam's length is usually much…

Identifying exposure sources, routes, frequency, duration, and magnitude using biomarker data combined with other approaches, such as computational models and available environmental measurement data. The goal of environmental health science is to…

The application of chemical engineering principles to the solution of medical problems due to physiological impairment. Knowledge of organic chemistry is required of all chemical engineers, and many study biochemistry and molecular biology. This…

The name for two species within the genus Bison of the cattle family Bovidae in the mammalian order Artiodactyla found in North America and Europe. Bison are artiodactyl mammals belonging to the genus Bison (family Bovidae). The North American bison…

A taxonomic order of insects comprising the cockroaches and termites. The order Blattodea, also referred to as Blattaria, contains at least 4500 species of cockroaches (Fig. 1) and 3000 species of termites. Previously, termites were assigned to a…

The name for several members of the family Bovidae in the mammalian order Artiodactyla. The buffalo is an Old World artiodactyl that resembles oxen in general appearance. The North American bison is often called a buffalo, but it is not related to…

A fixed permanent structure, more or less enclosed and designed to be used as housing or shelter or to serve the needs of commerce and industry. The history of buildings is almost as old as human history. Most contemporary building techniques are…

Any terrestrial or aquatic animal that is capable of excavating holes in the ground for protection from adverse environmental conditions, as well as for storing food. Burrowing animals are uniquely adapted species, having the capacity to dig burrows…

A member of the mammalian family Camelidae in the order Artiodactyla. Camels are even-toed, hoofed mammals (ungulates). There are three extant camel species: the Bactrian camel (Camelus bactrianus; Fig. 1), the wild Bactrian camel (C. ferus), and…

A medium-sized, spreading evergreen tree (Anacardium occidentale), which is grown widely in the tropics for its kidney-shaped edible nuts (also called cashews) and the resinous oil in the shells of the nuts. Cashew trees, which are native to Brazil,…

A coarse, erect, annual herb plant, Ricinus communis, belonging to the spurge family (Euphorbiaceae). The castor plant (Ricinus communis) is a member of the spurge family (Euphorbiaceae) in the order Malpighiales. The plant varies greatly in height…

A class in the phylum Mollusca that is exclusively marine and includes squids, octopuses, and cuttlefishes. The molluscan class Cephalopoda is one of the major taxonomic groupings of marine animals and contains both extant members—squids (Fig. 1),…

Any member of the grass family (Poaceae or Gramineae) that produces edible grains usable as food by humans and livestock. Cereals are important cultivated crops. Common cereals include rice, wheat, barley, oats, maize (corn), sorghum, rye, and…

An order of the class Reptilia, including the turtles, terrapins, and tortoises; also termed Testudines. The order Chelonia (often referred to as Testudines) comprises one of the oldest groups of reptiles on Earth. Members of the Chelonia…

The common name for any of 25 species of rodents in the mammalian family Sciuridae. Chipmunks are assigned to three different genera within the mammalian family Sciuridae: Tamias, with 1 species; Eutamias, with 1 species; and Neotamias, with 23…

An evergreen shrub or small tree, particularly Cinnamomum verum, and the spice obtained from the plant's bark. The cinnamon plant (see illustration) is a member of the laurel family (Lauraceae) in the order Laurales. Native to Sri Lanka, the…

A branch of civil engineering concerned with the planning, design, construction, and maintenance of works in the coastal zone. The purposes of these works include control of shoreline erosion; development of navigation channels and harbors; defense…

An order of Insecta comprising the beetles. Beetles belong to the insect order Coleoptera. This is the largest animal order, containing approximately 400,000 species. With so many species, beetles show very great diversity in size, form, color,…

The application of computational biology, using mathematical and computer models, to assess the risk chemicals pose to human health and the environment and to better understand the mechanism through which given chemicals induce harm. Hundreds of…

Any use of computer software to solve engineering problems. With the improvement of graphics displays and graphics standards, computer-aided engineering (CAE) has come to mean the computer solution of engineering problems with the assistance of…

Any living or fossil member of the plant division Pinophyta, consisting chiefly of woody trees or shrubs that produce cones and evergreen needles. Conifers are predominantly cone-bearing, evergreen trees and shrubs belonging to the order Pinales, as…

Interconnections of components forming system configurations which will provide a desired system response as time progresses. The steering of an automobile is a familiar example. The driver observes the position of the car relative to the desired…

The common name used for the large aquatic reptiles included in the family Crocodylidae. Crocodile (see illustration) is the common name used to describe about 17 species of large aquatic reptiles assigned to the family Crocodylidae, which is one of…

The use of data analytics and informatics-based approaches to discriminate between potential environmental contaminants and noncontaminants. New and emerging environmental contaminants are chemicals that have not been previously detected or that are…

An order of insects commonly known as earwigs, in reference to an unfounded superstition that they crawl into the ears of sleeping persons. Earwigs are elongate and flattened, with a pair of forceps-like appendages, or cerci, at the end of the…

An order of mammals comprising one family (Cynocephalidae), one genus (Cynocephalus), and two species—C. variegatus (Malayan colugo) and C. volans (Philippine colugo). These mammals inhabit the rainforests of Southeast Asia from the Malay Peninsula…

An order of the class Insecta comprising the true flies. Members of the order Diptera (class Insecta, phylum Arthropoda) are known as dipterans or flies (Fig. 1). The name Diptera is derived from the Greek di-ptera, for "two wings," because the…

Any member of the carnivorous mammalian family Canidae. All breeds of domestic dogs (Fig. 1), the wild dogs, and related species belong to the family Canidae. Despite the various breeds of domestic dogs that are known, the scientific name for all…

Programmable computers integrated with electrically powered machines that perform household chores. Domestic robots, also known as home or service robots, are essentially programmable computers integrated with electrically powered machines that…

The biological study of insects that have a direct influence on humanity. Economic entomology is a subdiscipline of entomology (the biological science that deals with the investigation of insects) and focuses on the effects of insects on human…

A System that locates suitably equipped users by means of measurements made by electronic sensors. Typical measurements include distance or bearing from a vehicle to a known point, or direct determination of the present position of the vehicle in a…

The common name for three living species of mammals in the family Elephantidae (order Proboscidea). Elephants are extant members of the mammalian family Elephantidae, which is one of several families included in the order Proboscidea. The remaining…

A source from which energy can be obtained to provide heat, light, or power. The term energy is used to describe an amount of work performed. There are two kinds of energy, kinetic energy, meaning work performed by the movement of matter, and…

The general method and specific techniques for storing energy derived from some primary source in a form convenient for use at a later time when a specific energy demand is to be met, often in a different location.In the past, energy storage on a…

A flexible, collaborative, and iterative process to provide the ability to manufacture quickly, effectively, and at minimal cost a component, assembly, product, or machine that meets particular operating specifications reliably and sustainably.…

A Chemical compound that interferes with the proper function of endocrine systems in humans and other organisms. There has been much scientific and medical research on pharmaceuticals as endocrine disruptors. However, endocrine disruptors are…

The evaluation of a physical system (engineering product) in conditions which simulate one or more of the environments that may harm the system or adversely affect its performance. Such testing is typically undertaken during the development of new…

An active and intentional act or practice of putting to death, in a relatively painless way, of persons suffering severely from medical conditions that are incurable, untreatable, or irreversible. Euthanasia is an act by a person, usually a…

The test of a hypothesis under controlled conditions. The experiment is one of the distinctive tools of the scientist. It enables the scientist to put questions to nature and receive answers. These answers lead to new problems whose solutions…

The death and disappearance of a species. The extinction of a species usually represents an end point in a long series of population extinctions. During the extinction process, unique evolutionary history is lost at every stage, but the death of the…

A method of separating the constituents of a mixture using preferential solubility of one or more components in a second phase. Commonly, this added phase is a liquid, while the mixture to be separated may be either solid or liquid. For example, the…

The detection and diagnosis of malfunctions in technical systems. Such systems include production equipment (chemical plants, steel mills, paper mills, and power stations), transportation vehicles (ships, airplanes, automobiles), and household…

An enzymatic transformation of organic substrates, especially carbohydrates, generally accompanied by the evolution of a gas. Fermentation is a chemical transformation of organic substrates, especially carbohydrates, to alcohol or organic acids,…

A plant grown for its fibrous material, which is used for many commercial purposes and for home industry. Many plants are grown as fiber crops because of their content or yield of fibrous material (see illustration), which is used in the manufacture…

The separation of solid particles from a fluid-solids suspension using a porous material to separate the suspended particulate matter from fluid. The filter material (medium) and the equipment assembly that holds it and provides space for the…

The application of different types of energy and techniques involving equipment and apparatuses to transform agricultural products of plant and animal origin or seafood into food ingredients, semifinished commodities, and finished ready-to-eat…

The study of the physical, chemical, and biological properties of foods as well as the sensory, nutritional, storage properties, and safety of foods. Food properties are influenced by growing, harvesting, and slaughtering practices, preservation and…

Any of the grasses and legumes that make up grasslands and are consumed by grazing livestock. Grasslands represent an ancient renewable natural resource. In general, grasslands form 25% of the world's vegetation and occupy the largest area of any…

A record of earlier life buried in rock. Originally meaning any distinctive object that has been dug up (from Latin fodio, dig), the term “fossil” soon came to refer particularly to things resembling animals and plants. These objects were known…

A hardy perennial, Allium sativum, of Asiatic origin and belonging to the plant order Asparagales. Garlic is grown for its pungent bulbs (see illustration). Segments of these are used primarily for seasoning. Europeans have grown garlic for probably…

The common name for any of the numerous small lizards in the infraorder Gekkota. Members of the reptilian infraorder Gekkota (order Squamata) are called geckos (see illustration). These small lizards are distinguished by a flattened body [never…