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An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

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 response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

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…

The interaction of the behavior and ecology of hosts with the biology of pathogens as relating to the impact of diseases on populations. Although human diseases have been studied from an ecological perspective for centuries, diseases in plant and…

The adaptation of an animal or plant through breeding in captivity to a life intimately associated with and advantageous to humans. Domesticated plants and animals differ genetically and morphologically from their wild counterparts, often in ways…

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…

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…

A species translocated from one region or continent to another outside its normal range, particularly when the translocation is the result of human activity (intentional or otherwise). Many thousands of species, including animals, plants, fungi,…

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 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…

Any of the plant growth forms characteristic of the upper reaches of mountain slopes. Alpine vegetation refers to the plants that grow in mountainous areas above the limit of subalpine trees and other subalpine vegetation. In such environments,…

An intergrading region on a mountain slope characterized by specific plant life forms or species composition, and determined by complex environmental gradients. Along an altitudinal transect of a mountain, there are sequential changes in the…

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…

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 application of ecological principles to the solution of human problems and the maintenance of a high quality of life. Applied ecology is a branch of ecology that applies concepts of ecology to address contemporary problems involving natural…

The application of chemical techniques to the study of archeological materials in order to elucidate aspects of the human past. The materials used in archeological chemistry might be anthropogenic (for example, pottery or metal) or natural (from…

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…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

The study of skeletal remains from archeological sites by biological (or physical) anthropologists. Bioarcheology differs in several ways from traditional skeletal research (see illustration). Previous work focused on individual case studies (for…

The number of different plant and animal species living in a defined ecosystem or study area; a contraction of biological diversity. Biodiversity includes genetic diversity (variability in the genetic makeup among individuals in a single species),…

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…

A nutrient-poor, acid peatland. A bog is a type of peatland, which is a terrestrial wetland ecosystem. Bogs (Fig. 1) are nutrient-poor and acidic, and they contain vegetation in which peat mosses (Sphagnum species) and ericaceous dwarf shrubs play a…

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 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 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…

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…

An unharvested crop grown to improve soil quality or enhance pest management. Increasing numbers of farmers plant cover crops as a means of conserving soil, enhancing subsequent production, and reducing off-farm inputs. The sustainable agriculture…

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…

Marine animal life inhabiting the portion of the oceans below the upper limit of the continental slopes. The marine animals that make up the deep-sea fauna live below the photic zone of the oceans. In general, the deep sea may be regarded as that…

The deliberate conversion of forest to nonforest land that results in the long-term reduction of tree canopy below a minimum level. Deforestation, also known as land clearing, permanently eliminates forests to utilize the land for other purposes…

Any of various species of diving, air-breathing animals. Diving animals, which are found in every class of terrestrial vertebrates (amphibians, reptiles, birds, and mammals), are air-breathing species that have almost complete freedom in the aquatic…

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…

Plants occupying sand dunes and the slacks, or swales, and flats between them. Dunes are mobile accumulations of sand that occur along shorelines and in deserts because of wind action. The formation and stability of dunes are affected significantly…

An assemblage of living organisms occurring together in an area. Ecological communities are aggregations of organisms characterized by a distinctive combination of two or more ecologically related species (Fig. 1). The nature of the forces that knit…

The study of the flow of energy within an ecological system from the time the energy enters the living system until it is ultimately degraded to heat and irretrievably lost from the system. It is also referred to as production ecology, because…

The methods required for the measurement of features of plant and animal populations or for quantifying energy flow or other aspects of ecological communities. Ecologists are concerned with such a wide range of variables that they may use many other…

The use of computer simulations or mathematical equations to address questions that cannot be answered solely by experiments or observations. Ecological models have two major aims: to provide general insight into how ecological systems or ecological…

A directional change in an ecological community. Populations of animals and plants are in a dynamic state. Through the continual turnover of individuals, a population may expand or decline depending on the success of its members in survival and…

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…

A species of animal, plant, or other living organism that is in serious danger of extinction throughout all or a significant portion of its range. When a species is categorized as endangered, its numbers are so small that the species is at risk of…

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…

The process by which water bodies, such as estuaries, coastal waters, and lakes, become enriched in dissolved nutrients, such as phosphorus and nitrogen, resulting in increased growth of algae and aquatic plants as well as the deterioration of the…

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…

An organism that tolerates and grows optimally under extreme environmental conditions. Extremophiles are organisms, predominantly microorganisms, that thrive in environmental conditions hostile to most life, including extremes of temperature (both…

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…

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 subdiscipline in mycology and ecology that examines community composition and structure; responses, activities, and interactions of single fungal species; and the functions of fungi in ecosystems. Fungi (that is, the true fungi, or Eumycota)…

Soil ingestion by animals. Grazing animals such as sheep and cattle ingest varying amounts of soil when they graze herbage contaminated with it.Pastures become contaminated with soil when livestock walk across the herbage, particularly in wet…

The design of products, processes, and systems with explicit consideration of potential environmental impacts. Green engineering does not set environmental objectives as higher priorities than other design requirements, but it does require them to…

An uncrewed, controlled-flight vehicle that is guided to a target by guidance and control equipment. This equipment may be carried in the missile vehicle itself, or guidance may be directed from the launch site. The term is generally reserved for…

A branch of the environmental and occupational safety health sciences and professions concerned with the protection of people and the environment from possibly harmful effects of radiation, while providing for the utilization of radiation for the…

Any chemical used to destroy or inhibit plant growth, especially of weeds or other undesirable vegetation. The control of weeds by means of herbicides has provided many benefits. Freeing agricultural crops from weed competition results in higher…

General terms applied to conditions of dormancy and torpor found in certain animals. Hibernation and estivation are physiological states of reduced metabolic activity exhibited by certain animals. In particular, many cold-blooded (poikilotherm or…

A branch of civil engineering that includes planning, design, construction, operation, and maintenance of roads, bridges, and related infrastructure to ensure effective and efficient movement of people, goods, and services that use this mode of…

A complex system that comprise both humans and machines. Human-machine systems engineering is the analysis, modeling, and design of such systems. It is distinguished from the more general field of human factors and from the related fields of…

An aldehyde synthesis process that falls under the general classification of a Fischer-Tropsch reaction but is distinguished by the addition of an olefin feed along with the characteristic carbon monoxide and hydrogen. In the oxo process for alcohol…

A means for estimating the potential for environmental damage that may be caused by a product or process, ideally before the product or process begins. Life-cycle assessment (LCA) includes all of the steps from extracting natural resources through…

Volatile and airborne chemical and biological contaminants in the indoor environment. Most pollution comes from human sources, although natural sources do exist, including plants, animals, and other living organisms and bodies of water that release…

An interdisciplinary field for preventing occupational illnesses and injuries. The disciplines of engineering, epidemiology, toxicology, medicine, psychology, and sociology provide the methods for study and prevention. Occupational hazards Tens of…

The field of engineering involving computer-based hardware and software systems, and communication systems, to enable the acquisition, representation, storage, transmission, and use of information. Information technology (IT) is critically dependent…

An intelligent transportation system framework rooted in connected and automated technologies. Intelligence is the capacity to acquire and apply knowledge. For intelligent vehicles, this is the capability to sense their surroundings, make decisions…