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A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

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,…

A neurodevelopmental condition that impairs the way that a person relates to and communicates with other people. Persons with autism have difficulties with social communication and interaction. They also can have unusual behaviors, such as…

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…

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…

A psychotherapy with roots in both cognitive science and behavioral science. Cognitive-behavioral therapy (CBT) is the most widely used evidence-based psychotherapeutic practice for a variety of mental health disorders, including anxiety, depression…

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…

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…

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…

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…

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…

Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

Any disorder of recognition. Agnosia is a rare neurological condition in which an individual fails to recognize and identify persons or objects (see illustration). Typically, agnosia is the result of damage to specific areas of the brain.…

The repeated and/or excessive use of alcohol (ethanol) that continues despite negative physical, psychiatric, or social consequences. Alcoholism is characterized by consuming alcohol more often, in larger amounts, or over longer periods than…

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 significant, yet relatively selective loss of memory. Amnesia is a type of memory loss, often resulting from brain disease or injury (see illustration). The inability to remember can be temporary or permanent. In general, amnesia can be…

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 disorder of language acquired as a result of brain disease. Aphasia is impairment in the use of spoken or written language caused by brain disorders (see illustration) that cannot be explained by paralysis or incoordination of the articulatory…

An impairment in the performance of voluntary actions despite intact motor power and coordination, sensation and perception, and comprehension. Apraxia is a neurological condition in which there is difficulty with skilled tasks or learned movements…

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 common psychiatric disorder (especially in children) characterized by attentional difficulties, impulsivity, and hyperactivity. Attention deficit hyperactivity disorder (ADHD) is a mental disorder marked by an individual's inability to pay…

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…

A major mental disorder in which there are lifelong episodes of both mania and depression; also known as manic-depressive illness. Bipolar disorder, also termed manic-depressive illness or manic depression, is characterized by sudden and often…

A mental health illness characterized by a compulsive or obsessive focus on a perceived flaw in appearance. Body dysmorphic disorder (often abbreviated BDD) is a psychiatric illness in which a person has a severe, excessive preoccupation with a…

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…

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 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 syndrome characterized by a generalized decline in cognition that is severe enough to cause functional impairment in daily activities. Dementia is a term used to describe a collection of symptoms of severe cognitive decline. Individuals suffering…

A heterogeneous affective disorder involving a depressed mood and/or a loss of interest in daily activities. The most common form of affective disorder is depression (also termed clinical depression) [Fig. 1]. A major depressive episode is defined…

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 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…

Impairment of the ability to read. Developmental dyslexia, which is a learning disorder with a neurobiological basis, is characterized by unexpected difficulty in reading in children and adults who otherwise possess the intelligence and motivation…

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 controlled induction of a grand mal seizure under anesthesia to treat individuals suffering from certain psychiatric illnesses. Electroconvulsive therapy (ECT; Fig. 1) was introduced as a treatment for psychiatric disorders by the Italian…

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…

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 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…

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 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…

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…

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 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…

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 major phylum of the animal kingdom comprising a diverse group of unsegmented, soft-bodied invertebrates. The phylum Mollusca is one of the most significant groupings of invertebrate animals. Members of the Mollusca, termed mollusks or molluscs,…

A mammalian order containing the egg-laying platypus and echidnas. Members of the order Monotremata (monotremes) are egg-laying mammals belonging to the subclass Prototheria (in some alternative classifications, the monotremes have been assigned to…

Weapons that arm warships. Of the wide variety of such weapons, three important categories are exclusively naval: antiship missiles, torpedoes, and mines. Other weapons all correspond to land-based types, but submarine-launched ballistic missiles…

A small extinct order of articulated brachiopods that ranges in age from Early to Middle Cambrian and includes the earliest known calcitic brachiopods. Classification The order Obolellida is included within the class Obolellata, subphylum…

An order of coleoid cephalopods, characterized by eight appendages (which encircle the mouth), a saclike body, and an internal shell that is much modified or reduced from that of its ancestors. Members of the order Octopoda (subclass Coleoidea,…

A morphologically distinct type of trace fossil left by boring organisms in hard biogenic substrates. Oichnus Bromley 1981 is a formal taxonomic name with the rank of ichnogenus (a trace fossil genus). Oichnus is a Latin-derived term that…

A suborder of trilobites (a class of extinct arthropods) and a diverse clade consisting of roughly 100 distinct species. The trilobites constituting the suborder Olenellina belong to the order Redlichiida in the class Trilobita. These extinct…

One of the chemical senses, specifically the sense of smell. Olfaction comprises the action or capacity of smelling, and is a form of chemoreception (the ability of organisms to detect changes in the chemical composition of their exterior or…

Computer software that is licensed by the copyright holder, granting the rights to examine, change, and distribute it to anyone and for any purpose as long as the original copyright statement in any redistributed software is preserved. The…

A class of the subphylum Asterozoa (phylum Echinodermata), comprising the brittle stars and basket stars, in which the arms are usually clearly demarcated from a central disk and perform whiplike locomotor movements, and the tube feet are…

A taxonomic fish group comprising the bony fishes. The Osteichthyes grouping (often considered a superclass) consists of the classes Actinopterygii (ray-finned fishes) and Sarcopterygii (lungfishes and lobefins, or coelacanths, but excluding…

Fossil lobe-finned (sarcopterygian) fishes of Devonian to Permian age (395–270 million years ago), the ancestral group for the land vertebrates, or “tetrapods.” Phylogeny The term “osteolepiforms” is applied to a range of fossil fishes, found…

An order of extinct jawless vertebrate fishes, also called Cephalaspida, known from the Middle Silurian to Upper Devonian of Europe, Asia, and North America. They were mostly small, about 2 in. (5 cm) to 2 ft (60 cm) in length. The head and part of…

A major taxon of the Crustacea containing small bivalved animals 0.004–1.4 in. (0.1–33 mm) long, with most between 0.04 and 0.08 in. (1 and 2 mm). Members of the Ostracoda inhabit aquatic environments in nearly all parts of the world.…

A popular name applied to several groups of extinct jawless vertebrates (fishes). Most ostracoderms were covered with an external skeleton or armor of bone, from which is derived their name, meaning “shell-skinned” (see illustration). They are known…

A peculiar arthropod, evidently related to the Pycnogonida and represented by a number of well-preserved fossils from the Devonian Hunsrück shales. Palaeoisopus was formerly considered by a number of paleontologists to have an anterior jointed…

A large, extinct assemblage of primitive ray-finned (actinopterygian) fishes known from the Silurian to Cretaceous, which were most numerous in Carboniferous and Permian times. They are known as fossils from all continents except Antarctica.…

A tiny fossil fish found only in rocks of Middle Devonian age within a small geographic region of Caithness, Scotland, and principally at one site, Achanarras Quarry, where it is surprisingly abundant. One of the most enigmatic of all fossil fishes,…

The study of chemical processes used by organisms that lived in the geological past. Most information on the nature of life in the geological past comes from the study of fossils; a record of biochemical processes that occurred can be found in the…

The study of pollen grains and spores, both extant and extinct, as well as other organic microfossils. Although the origin of the discipline dates back to the seventeenth century, when modern pollen was first examined microscopically, the term…

A fossil lobe-finned (sarcopterygian) fish from rock strata of the Baltic region dating to the Middle–Late Devonian Period (about 372–368 million years ago), which provides key evidence about the evolutionary transition from fish to land vertebrates…