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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…

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…

The use of pollen and spore evidence in legal cases. In its broader application, the field of forensic palynology also includes legal information derived from the analysis of a broad range of microscopic organisms that can be found in both fresh and…

A plant that has altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

A commercially grown plant that has altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

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 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…

A plant, Musa textilis, of the banana family that is valuable for its hard fiber (also known as Manila hemp). Abaca (Musa textilis) is a flowering plant native to the Philippines and Borneo. Taxonomically, it is assigned to the order Zingiberales.…

A major plant hormone that plays an important role in plant growth and development. Abscisic acid (ABA), with a chemical formula of C15H20O4 (Fig. 1), is one of the most significant hormones found in plants. It is responsible for regulating various…

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…

An informal assemblage of predominantly aquatic eukaryotes that carry out oxygen-evolving photosynthesis, but lack specialized water-conducting and food-conducting tissues. Algae (Fig. 1) are eukaryotic organisms (having an organized nucleus).…

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…

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 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…

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…

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…

Any of a class of plant growth substances (phytohormones or plant hormones) that have an essential role in coordination of many growth and developmental processes during the life cycle of plants, especially the ability to increase the rate of shoot…

A class of nonflagellate unicellular algae, commonly called diatoms, with boxlike silicified walls. Members of the algal class Bacillariophyceae are commonly termed diatoms (Fig. 1). Diatoms range in maximum dimension from 4 μm (0.00004 in.) to more…

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 drug as well as the plant known as deadly nightshade (Atropa belladonna). The belladonna plant (Atropa belladonna; see illustration) belongs to the nightshade family, Solanaceae, in the order Solanales. The plant is a coarse and poisonous…

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),…

Fungi that exhibit the natural phenomenon of bioluminescence (the ability of an organism to emit visible light). Bioluminescence is the emission of photons of visible light by living organisms via the chemical reaction of molecular oxygen (O2) with…

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 garden for the culture of plants collected chiefly for scientific, educational, and esthetic purposes. A botanical garden (see illustration) is an establishment in which various plants, including trees, are collected, cultivated, and grown for…

The branch of biological science that embraces the study of plants and plant life. Botany is the scientific study of plants (see illustration), encompassing investigations of plant anatomy, physiology, genetics, phylogeny, ecology, pathology, and…

A division that consists of small and relatively simple plants commonly known as mosses, peat mosses, granite mosses, liverworts, and hornworts. Members of the division Bryophyta are referred to as bryophytes (see illustration). These nonvascular…

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 genus comprising yeasts that cause a variety of human diseases referred to as candidiasis. All Candida species are single-celled yeasts (fungal organisms) that are ovoid in shape and 3–5 μm in size, and they multiply by a process called budding.…

An order of flowering plants (angiosperms) including the mustard and caper families. The plant order Capparales contains various families of eurosid dicotyledons. Most notably, mustards, capers, and various ornamental plants (see illustration) are…

A member of a class of common pigments, typically of yellow, orange, or red hues, that serve in both light absorption and the protection against too much light in photosynthesis as well as in the vision process. Carotenoids comprise a class of…

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…

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…

A type of sweet or sour fruit of the Prunus genus, as well as the tree that bears the fruit. Cherry trees belong to the Prunus genus in the order Rosales, and the sweet and sour fruits of these trees are called cherries (Fig. 1). There are…

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…

A large palm, Cocos nucifera, widely grown throughout the tropics and valuable for its fruit and fiber. The coconut (Cocos nucifera) belongs to the plant family Arecaceae. The name coconut can refer to the tree and its fruit. Usually found near the…

Any of various tropical trees belonging to the genus Cola. Members of the genus Cola (family Malvaceae, order Malvales), which are native to tropical Africa, are called cola trees (see illustration). In particular, two species, C. acuminata and C.…

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…

A fiber obtained from the cotton plant Gossypium. The cotton plant (genus Gossypium, order Malvales; Fig. 1) has been used by humans for more than 5000 years. The fiber (cotton) obtained from this plant is the most widely used natural fiber because…

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…

A woody higher plant that regularly loses its leaves at the end of each growing season. Deciduous plants drop (shed) their leaves seasonally, most commonly during the fall (autumn). In general, the dropping of leaves occurs at the inception of an…

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 major clade or natural group of plants, comprising the land plants. The members of the Embryobionta or Embryophyta are commonly termed embryobionts or embryophytes, and they constitute the land plants. Embryophytes form a well-marked clade (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…