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A common medicine used to relieve mild to moderate pain and reduce fever. Acetaminophen (N-acetyl-p-aminophenol), or paracetamol, is a white crystalline compound with the molecular formula C8H9NO2 (Fig. 1). It is a member of the aniline family of…

A member of a group of organic compounds that can be considered as derived from ammonia by replacement of one or more hydrogens by organic functional groups. Generally amines are bases of widely varying strengths, but a few that are acidic are…

A conductor whose purpose is to emit and/or receive electromagnetic waves using the bulk oscillations of electric charges within the conductor. The conduction electrons in antennas are free to move throughout the conductor. The electrons form a bulk…

The subfield of computer science concerned with understanding the nature of intelligence and constructing computer systems capable of intelligent behavior. Many activities, such as perception, learning, planning, natural language, and understanding,…

An analytical technique for determining the composition of a sample in terms of the chemical elements present and their quantities or concentrations. Unlike other methods of elemental analysis, however, the sample is decomposed into its constituent…

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.…

A kind of mathematics whose variables can only be True or False. A variable is called Boolean if it can only hold two possible values: True or False. The value True can be represented by the number one and False by zero. For example, if A is a…

A poisonous colorless, odorless, tasteless gas (CO), resulting from the incomplete combustion of carbon-containing materials. Carbon monoxide (Fig. 1) is an indoor hazard causing hundreds of deaths annually, and it is one of the six major air…

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…

The attractive force that holds atoms or ions together. Chemical bonds are very strong. To break one bond in each molecule in a mole of material typically requires an energy of many tens of kilocalories.It is convenient to classify chemical bonding…

A chemical element, Cl, atomic number 17 and atomic weight 35.453. Chlorine exists as a greenish-yellow gas at ordinary temperatures and pressures (see illustration). It is second in reactivity only to fluorine among the halogen elements, and hence…

A branch of computer science that deals with the theory and techniques of computer-generated images. Computers produce images by analyzing a collection of dots, or pixels (picture elements). Computer graphics is used to enhance the transfer and…

A radar system used to measure the relative velocity of targets and their position. The operation of these systems is based on the fact that the Doppler frequency shift in the target echo is proportional to the radial component of target velocity.…

A mathematical system that details the properties and relationships of spatial objects such as points, lines, shapes, and planes. Euclidean geometry is also known as flat geometry or planar geometry, because planes in Euclidean geometry have the…

An interdisciplinary science area that is concerned with modeling aspects of natural evolution in order to solve real-world problems of optimization. Living organisms, as well as those that are long extinct, demonstrate optimized complex behavior at…

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…

In thermodynamics, the amount of useful work that can be extracted from a closed thermodynamic system. The Helmholtz free energy applies to a process that takes place at a constant temperature T (isothermal process). The Gibbs free energy applies 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 salt or ester of lactic acid (CH3CHOHCOOH). In lactates, the acidic hydrogen of the carboxyl group has been replaced by a metal or an organic radical. Lactates are optically active, with a chiral center at carbon 2. The two optical isomers of a…

The inverse function of an exponential function in mathematics. Stated less technically, a logarithm is the opposite of an exponent. Logarithms are used to solve equations in which the variable is an exponent. Historically, tables of logarithms…

An analytical technique for identification of chemical structures, determination of mixtures, and quantitative elemental analysis by measuring the mass-to-charge (m/z) ratio of ions produced when a sample is ionized. Determination of organic and…

A device that is capable of converting chemical energy into electrical energy with the use of whole bacterial cells as the catalyst. Fuels that are produced biologically are known as biofuels. Biofuel cells convert chemical energy from organic…

A chemical element, Os, atomic number 76, atomic weight 190.2. Osmium is a hard white metal of rare natural occurrence, and is usually found in nature alloyed with other platinum metals. Metal Periodic table Platinum The periodic table of the…

A two-component reaction involving the loss of electrons (oxidation) by one chemical species and the gain of electrons (reduction) by another; also known as a redox reaction. Both oxidation and reduction occur simultaneously and in equivalent…

A branch of mathematics involving numerical measures of how likely it is that a particular event will occur. A probability is a number between 0 and 1. An event that will never occur has a probability of zero, and an event that is certain to occur…

Computation that encodes data in quantum objects to later process that data using operations based on the concepts and principles of quantum mechanics. Quantum objects used in quantum computation include the nuclei of atoms, ions in a crystal,…

The study of chemical changes resulting from the absorption of high-energy ionizing radiation. Such radiation includes alpha particles, electrons, gamma rays, fission fragments, protons, deuterons, helium nuclei, and heavier charged projectiles.…

In medicine and health sciences, a value expected for an individual whose state of health is known and well described, and the interval of values broadly expected for a population, respectively. Results of clinical laboratory tests and other…

The evolving internet technologies for content sharing and collaborating among communities of online users. Since the advent of the Web 2.0—the more dynamic and interactive second generation of the World Wide Web—the term social media has become…

The field of knowledge concerned with collecting, analyzing, and presenting data. Statistical methods are regularly used by researchers in the physical, biological, and social sciences, as well as engineers, business managers, government officials…

The theory of circuits made up of ideal digital devices. Included in switching theory are the theories of circuits and networks for telephone switching, digital computing, digital control, and data processing. Computer Electrical circuit Electronic…

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…

One of the elements of atomic numbers 21–31, 39–49, and 71–81. The symbols of these elements, along with their atomic numbers and valence-shell electronic configurations, are given in Fig. 1. The elements are arranged in the order in which they…

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…

The scattering of x-rays by matter with accompanying variation in intensity for specific directions (or wavelengths) due to interference effects. X-ray diffraction is a powerful and readily available method for determining atomic arrangements in…

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…

The study of systems consisting of arbitrary sets of elements of unspecified type, together with certain operations satisfying prescribed lists of axioms. Abstract algebra has been developed since the mid-1920s and has become a basic idiom of…

A useful carbon-carbon bond-forming reaction in which aldehyde and alcohol functional groups are observed during the reaction. The aldol reaction was first reported by Aleksandr Porfiryevich Borodin, who observed the reaction using pentanal and…

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…

A statistical technique that partitions the total variation in experimental data into components assignable to specific sources. Analysis of variance is applicable to data for which (1) effects of sources are additive, (2) uncontrolled or…

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…

A chemical reaction or series of reactions leading to the predominant or exclusive formation of a single enantiomer, that is, one of an isomeric pair of chemical compounds whose molecules are nonsuperimposable mirror images. Enantiomers are said to…

An aromatic hydro­carbon, molecular formula C6H6, also know as benzol. Benzene is a clear, colorless, and flammable liquid which boils at 80.1°C and freezes at 5.5°C.Benzene (1) is an important chemical intermediate used to produce ethylbenzene…

A discipline that combines biology, mathematics, and computer science to acquire, store, analyze, and disseminate complex biological data. The term bioinformatics was coined by Paulien Hogeweg and Ben Hesper in the early 1970s to describe the "the…

An integrated device consisting of a biological recognition element and a transducer capable of detecting the biological reaction and converting it into a signal that can be processed. Ideally, the sensor should be self-contained, so that it is not…

In its simplest form, a vector is a directed line segment. Physical quantities, such as velocity, acceleration, force, and displacement, are vector quantities, or simply vectors, because they can be represented by directed line segments. The algebra…

The measurement of the quantity of heat transferred during chemical reactions, changes of state, mixing of substances, as well as other chemical and physical processes. The unit of energy in the International System of Units is the joule, symbolized…

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),…

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…

A branch of physical chemistry that seeks to explain time-dependent phenomena, such as energy transfer and chemical reaction, in terms of the detailed motion of the nuclei and electrons that constitute the system. As such, chemical dynamics seeks…

A white or colorless amorphous polysaccharide that forms a base for the hard outer integuments of crustaceans, insects, and other invertebrates. Chitin (see illustration) is an important nitrogenous polysaccharide that is found abundantly in nature.…

A natural and extremely useful extension of the familiar real numbers. They can be introduced formally as follows. Consider the two-dimensional real vector space consisting of all ordered pairs (a1, a2) of real numbers. Geometrically this space can…

A device that receives, processes, and presents information. The two basic types of computers are analog and digital. Although generally not regarded as such, the most prevalent computer is the simple mechanical analog computer, in which gears,…

Any device connected internally or externally to a computer and used in the transfer of data to or from a computer. A personal computer (PC) processes information. Data (unprocessed information) must get into the computer, and the processed…

Designing and writing a detailed sequence of operating instructions for a particular problem to be run on a computer; also known as programming. A computer is able to perform useful tasks only by executing computer programs. A programming language…

The process of protecting against threats to computing systems. A threat is an event that can cause harm to computers, data or programs, or computations (Fig. 1). A failure of computer security occurs because of a vulnerability or weakness in a…

The hardware components, both internal and external, of a computer used to read (retrieve) or write (save) digital data. The ability to read and write data is an essential function of a computer and of the so-called von Neumann architecture…

A program or script that is loaded and executed on a computer without the knowledge of the user. A typical computer virus is a very small program, several kilobytes or less in size, constructed in a matter of hours or days. When executed, the virus…

The technology concerned with computational understanding and use of the information present in visual images. In part, computer vision is analogous to the transformation of visual sensation into visual perception in biological vision. For this…

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…

A digital equivalent of paper banknotes. Just like paper banknotes, cryptocurrencies allow users to maintain privacy in digital commercial transactions while ensuring that value is transferred from one party to the other. Cryptocurrencies achieve…

A curve traced in the plane by a point on a circle that rolls, without slipping, on a line. If the line is the x axis of a rectangular coordinate system, at whose origin O the moving point P touches the axis, parametric equations of the cycloid are…

A cycloaddition reaction between a diene and a dienophile. The simplest Diels-Alder reaction (O. Diels and K. Alder, 1928) occurs between butadiene and ethylene and is often referred to as a [4+2] cycloaddition. The numbers, four and two in…

A branch of mathematics that deals with intrinsic properties of curves and surfaces in three-dimensional Euclidean space. The intrinsic properties are those which are independent of the geometrical object's orientation or location in space. The…

The transport of matter from one point to another by random molecular motions. Diffusion occurs in gases, liquids, and solids.Diffusion plays a key role in processes as diverse as permeation through membranes, evaporation of liquids, dyeing textile…

The computer manipulation of visual data to solve a problem. The problems under consideration are of two primary types: (1) those that require a computer to act on the resultant images, and (2) those that provide images for human interpretation. The…

In arithmetic and algebra, the process of finding one of two factors of a number (or polynomial) when their product and one of the factors are given. The symbol ÷ now used mostly in elementary English and American arithmetics to denote division…

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…

A system that delivers controlled amounts of a therapeutic agent over a prolonged period or in a desirable temporal fashion, thereby maintaining required plasma or tissue drug levels. Drug delivery systems are bioengineered mechanisms or devices…

The number e usually defined as the limit approached by the expression as n approaches infinity. If the given expression is expanded by the binomial theorem, and if one uses the theorem that the limit of the quotient of two polynomials of equal…

The manner in which electromagnetic waves travel forward along a path. Electromagnetic waves consist of quantized, traveling, self-sustained, electromagnetic field fluctuations. The high speed of electromagnetic waves makes them useful in…

A volatile, fragrant oil obtained from plants. Essential oils are distinguished from those known as fixed oils, which are mainly triglycerides of fatty acids. Essential oils have been obtained from thousands of plants (Fig. 1) and are designated and…

The simplest cyclic ether or epoxide, with the formula C2H4O. Ethylene oxide is also called epoxyethane and oxirane, and has the below structure. Ethylene oxide was discovered in 1859 by C. A. Wurtz. His preparation from ethylene chlorohydrin and…

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…

A method of quantitative multivariate analysis with the goal of representing the interrelationships among a set of continuously measured variables (usually represented by their intercorrelations) by a number of underlying, linearly independent…

In algebra, the term "field" is used to designate an algebraic system or structure containing at least two elements and having two binary rules of composition: addition and multiplication (that is, if a and b are any two elements of the field, then…

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…

Qualitative identifications and quantitative determinations of substances essential for the evaluation of the air quality in the ambient air and in the industrial workplace.The terms air pollution and gas analysis are used here in the broad sense.…

A branch of mathematics concerned with the properties of space, including points, lines, curves, planes and surfaces in space, and figures bounded by them. Multiple kinds of geometry exist, dealing with everyday concepts such as lengths, angles, and…

The discovery, development, and application of sustainable chemical reactions that create no waste or generate only benign wastes. The idea that toxic chemicals, once created, can be contained or prevented from entering the environment is…

The responsible use of computer and related resources with the objective of curbing the negative effects that the increasing use of computers and their associated technologies have on the Earth's limited natural resources. Green computing is part of…

Optical instruments that establish an optical line or axis for the purpose of aiming a weapon. The axis includes the observer's eye, a suitable mark in the instrument, and the target. For a pistol, the traditional iron sights employ a rear notch and…

An aliphatic or aromatic hydrocarbon in which one or more hydrogen atoms are substituted by halogen atoms. Alkyl halides Alkyl halides are compounds in which one hydrogen of an alkane has been replaced by halogen [fluorine (F), chlorine (Cl),…

An interdisciplinary field focused on the interactions between human users and computer systems, including the user interface and the underlying processes that produce the interactions. The contributing disciplines include computer science,…

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…

A chemical element, Fe, atomic number 26, and atomic weight 55.845. Iron is a malleable, tough, silver-gray, magnetic metal. It melts at 1540°C, boils at 2800°C, and has a density of 7.86 g/cm3. The four stable, naturally occurring isotopes have…

Intentional generation of interfering signals in the electromagnetic spectrum by powerful transmitters as a countermeasure intended to block a communication, radar, or infrared system or to impair its effectiveness appreciably. Radio broadcasts or…

The common name for a member of the agnathan fishes. The fish superclass Agnatha (subphylum Vertebrata, phylum Chordata) comprises the jawless vertebrates (agnathans). Members include cyclostomes (modern lampreys and hagfishes), various extinct…

A topological group with only countably many connected components whose identity component is open and is an analytic group. An analytic group or connected Lie group is a topological group with the additional structure of a smooth manifold such that…

That branch of mathematics which deals with solutions of systems of linear equations and the related geometric notions of vector spaces and linear transformations. It is fundamental in the theory of the calculus of functions of several variables and…

A branch of artificial intelligence (AI) based on the notion that machines (software applications) can learn from examples and can teach themselves how to solve specific problems without being programmed manually. Recent successes in artificial…

A lineage of true elephants in the extinct genus Mammuthus that occupied Eurasia and North America in the late Cenozoic Era. Mammoths (genus Mammuthus) are extinct elephants assigned to the mammalian order Proboscidea (Fig. 1). They inhabited…

The widespread, catastrophic loss of many species in a relatively short period of geological time. Earth has supported life for approximately 3.5 billion years, and it is normal for species to become extinct and for new species to arise through…

The application of mathematics to biological systems. Just as physics underlies many engineering technologies, biology serves as a foundation for such disciplines as medicine, agriculture, animal husbandry, and environmental sciences, in which…

The study of the patterns and relationships that arise between abstract concepts. Though studied purely for its own sake, mathematics is the language with which all rigorous science is discussed. As the German-born U.S. theoretical physicist Albert…

A solid or liquid (molten), opaque material with a lustrous surface and good electrical and thermal conductivities. Solid metal is usually crystalline and ductile and can be permanently deformed by shear on crystal planes (Fig. 1); permanent…

A type of protein that shuttles metal ions to specific sites within a cell. Metallochaperones are molecular facilitators that transport metal ions to target proteins (see illustration). The target sites for metal delivery include a number of…

The smallest unit of a compound, which consists of atoms bonded together in a unique arrangement. A diatomic molecule consists of two atoms linked together by chemical bonds. Examples include the oxygen and nitrogen of the air (O2 and N2,…