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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…

Malfunctions of the paired adrenal glands. The paired adrenal glands are complex endocrine organs in proximity to the kidneys (see illustration), and disorders of the adrenal glands can have serious consequences. Under specific circumstances,…

The cross section of a body that is placed in an airstream to produce a useful aerodynamic force in the most efficient manner possible. The cross sections of wings, helicopter rotor blades (Fig. 1), propeller blades, windmill blades, compressor and…

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…

Loss of sensation with or without loss of consciousness. Anesthesia is used to prevent pain during surgery and other medical procedures. There are several ways of producing anesthesia, with the choice dependent on the type of surgery and the medical…

Any treatment or procedure that includes the in-vitro handling of oocytes (immature ova or egg cells) and sperm or embryos for the purpose of establishing a pregnancy. Assisted reproductive technology (ART) is undertaken as a treatment of…

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…

The common name for a malignant neoplasm or tumor. Cancer is a serious medical condition that develops when the orderly relationship of cell division and cell differentiation becomes disordered, leading to the development of neoplasms. Neoplasms are…

Cells within a tumor that possess the capacity to self-renew and cause the heterogeneous lineages of cancerous cells that comprise the tumor. Cancer stem cells (CSCs) typically represent a small percentage of all cells in a tumor (rarely more than…

A condition caused by the thickening of ligaments and tendon sheaths at the wrist, with consequent compression of the median nerve at the palm. The carpal tunnel is a thin passageway among ligaments and tendon sheaths located in the wrist joint area…

The administration of chemical substances for the treatment of disease, especially cancer, or for the prevention of aberrant growth of cells or tissues (neoplasms). In general, chemotherapy is the use of chemicals to treat any disease, but the term…

Pathologies and abnormal conditions that involve the circulatory system. Circulation disorders include both localized disturbances of circulation and diseases of the circulatory system (Fig. 1). Circulation 1 Illustration of the thickening and…

Structural or functional abnormalities of the body that develop during embryogenesis and the fetal period; also called birth defects. Congenital anomalies, or birth defects, are conditions present at or from birth that deviate from the body's normal…

Any of a group of diseases involving connective tissue as the pathological target. Connective tissue comprises one of the primary tissues of the body and is distinguished by an abundance of fibrillar and nonfibrillar extracellular components, which…

Any of a group of viruses that cause upper and lower respiratory tract diseases, gastroenteritis, hepatitis, and central nervous system infections in birds and mammals, including humans. Coronaviruses (Fig. 1) comprise a major group of common animal…

A genome-engineering technique that allows precise targeting of specific stretches of genetic code and editing of DNA at designated locations. The CRISPR/Cas9 system has been used as a general tool to engineer the genomes of many different…

Inflammation of the skin; also known as eczema. Dermatitis, or eczema, is a general medical term that describes irritation or inflammation of the skin. Typically, the inflammation of the skin involves redness and scaling (see illustration). In acute…

A deleterious set of responses occurring at the subcellular level, stimulated by infection, injury, or genetic or developmental errors, and manifested in altered structure or functioning of the affected organism. Disease is considered to be a…

A condition in space in the vicinity of an electrically charged body such that the forces due to the charge are detectable. An electric field (or electrostatic field) exists in a region if an electric charge at rest in the region experiences a force…

A pathology characterized by abnormal enlargement of air spaces distal to the terminal bronchioles in the lung. Emphysema (see illustration) is a pathologic condition distinguished by loss of elasticity of the lung. The primary cause of this loss of…

The occurrence of cases of disease in excess of what is usually expected for a given period of time. An epidemic is a breakout of disease affecting unusually large numbers of people within a community or population. When an epidemic spreads…

Planets beyond our solar system. For millennia, humankind has known about most of the major planets in our solar system because these worlds are visible to the naked eye. Exoplanets, however, were not indisputably known until 1995, when astronomers…

Disorders of form and function that affect the eye. Eye disorders and diseases are pathological conditions of the eye. Some conditions can result in vision loss and even blindness. In contrast, others are less severe and temporary, being resolved by…

Any interaction between objects that causes motion. Fundamentally, objects interact through the four known physical forces: gravity, electromagnetism, and the strong and weak nuclear interactions. In practice, however, many of the forces worked with…

An organism that has had its genetic material manipulated or altered in a laboratory setting through the use of genetic or genomic engineering techniques. Genetically modified organisms (GMOs) are microorganisms, plants, or animals that have been…

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…

A space telescope mission dedicated to detecting exoplanets. The tenth mission launched under the National Aeronautics and Space Administration's (NASA's) Discovery Program, Kepler was the agency’s first mission dedicated to the search for planets…

That branch of mechanics which deals with the motion of a system of material particles without reference to the forces which act on the system. Kinematics differs from dynamics in that the latter takes these forces into account. Dynamics Mechanics…

The planet fourth outward from the Sun and the planet most like Earth in terms of geology, climate, and suitability for life. Mars is nicknamed the "Red Planet" for its reddish hue (Fig. 1). Besides Earth, Mars is the most-studied world in the solar…

The change in the position of an object in a physical space over time. A familiarly encountered phenomenon, motion (see illustration) occurs on all levels of reality, from the constant movements of subatomic particles (conveyed by probabilities of…

The branch of acoustics that deals with the generation of sound by musical instruments, the transmission of sound to the listener, and the perception of musical sound. Musical acoustics has fascinated scientists at least since the time of the Greek…

An emerging cancer therapy in which oncolytic viruses are used to target and destroy cancer cells without harming healthy cells. Oncolytic viruses (that is, viruses that destroy cancer cells, but not normal cells) are able to infect, replicate…

Any synthetic or semisynthetic organic chemical compound that resembles opium in its pharmacological action to reduce pain. An opioid is an organic chemical compound, created synthetically or semisynthetically, that duplicates the analgesic…

Any agent capable of causing disease. The term pathogen is usually restricted to living agents or microorganisms that produce disease. Pathogens are infectious and diverse, including bacteria (see illustration), viruses, rickettsia, fungi, yeasts,…

An electron microscope that builds up images of samples via the scanning of the sample's surface with a focused electron beam. The idea of the scanning electron microscope (SEM) dates back to the 1930s, with a great deal of the pioneering…

Related terms used to define the intensity of internal reactive forces in a deformed body and associated unit changes of dimension, shape, or volume caused by externally applied forces.Stress is a measure of the internal reaction between elementary…

The general term applied to the description of a disturbance which propagates from one point in a medium to other points without giving the medium as a whole any permanent displacement. Waves are a common phenomenon in the natural world and manifest…

A departure of an optical image-forming system from ideal behavior. Ideally, such a system will produce a unique image point corresponding to each object point. In addition, every straight line in the object space will have as its corresponding…

The apparent change in direction of a source of light caused by an observer's component of motion perpendicular to the impinging rays.To visualize the effect, first imagine a stationary telescope (illus.a) aimed at a luminous source such as a star,…

The time rate of change of velocity. Acceleration is a physics term that measures the rate of change of velocity per unit of time. Because velocity is a directed or vector quantity involving both magnitude and direction, a velocity may change by a…

The technique of measuring the magnitude and direction of acceleration. Measurement of acceleration (see illustration) includes translational acceleration with tangential and radial components and angular acceleration. Acceleration The May 16, 2011…

The use of a combination of mass spectrometers and an accelerator to measure the natural abundances of very rare radioactive isotopes. These abundances are frequently lower than parts per trillion. The most important applications of accelerator mass…

An instrument that utilizes focused acoustic waves to produce images of surface and subsurface features in materials, and to measure elastic properties on a microscopic scale. It has been used to image and measure local elastic properties in metals,…

Unwanted sound. Noise control is the process of obtaining an acceptable noise environment for people in different situations. These definitions and the words “unwanted” and “acceptable” suggest that criteria need to be established to determine when…

The discipline of acoustic phonetics can be narrowly defined as the study of the acoustic output of the vocal tract for speech, but ultimately it encompasses much more. Acoustic phonetics makes direct contact with, and in many cases is the…

A device to measure the acoustic power or intensity of a sound beam by means of the force or torque that the beam exerts on an inserted object or interface. The underlying theory involves the concept of radiation pressure, which is the…

A discipline that deals generally with the extraction of information from acoustic signals in the presence of noise and uncertainty. Acoustic signal processing has expanded from the improvement of music and speech sounds and a tool to search for oil…

A genus of Gram-negative, immotile and nonspore-forming, oval to rod-shaped, often pleomorphic bacteria that occur as parasites or pathogens in mammals (including humans), birds, and reptiles. Actinobacillus bacteria are facultatively aerobic,…

The ratio of the current to the voltage in an alternating-current circuit.In terms of complex current I and voltageV, the admittance of a circuit is given by Eq. (1), and is related to the impedance of the circuit Z by Eq. (2). Y is a complex number…

The force retarding an airplane, especially in supersonic flight, as a consequence of the formation of shock waves. Although the physical laws governing flight at speeds in excess of the speed of sound are the same as those for subsonic flight, the…

A bacterial genus in the family Vibrionaceae comprising oxidase-positive, facultatively anaerobic, monotrichously flagellated Gram-negative rods. The mesophilic species of Aeromonas are A. hydrophila, A. caviae, and A. sobria; the psychrophilic one…

Helium nuclei, which are abundant throughout the universe both as radioactive-decay products and as key participants in stellar fusion reactions. Alpha particles can also be generated in the laboratory, either by ionizing helium or from nuclear…

Any of the organic compounds possessing one or more basic amino groups and one or more acidic carboxyl groups. Of the more than 80 amino acids that have been found in living organisms, approximately 20 serve as the building blocks for proteins.…

Any of a group of drugs of diverse chemical structure and physiological effects that are used for the relief of pain. Analgesics are drugs, including opiates, synthetic opioids, and salicylates, that are used primarily for pain relief (see…

The closest spiral galaxy to the Milky Way Galaxy. The name of the Andromeda Galaxy (Fig. 1) derives from its appearance in the constellation of Andromeda. The galaxy is also known as M31 and NGC 224, based on its entries in two widely used…

The analog of linear momentum for rotational motion. A particle with mass m moving with velocity v has linear momentum p = m v (Note: This article follows the convention of using bold, non-italicized variables for vectors and using non-bold,…

A small infectious agent that is unable to replicate outside a living animal cell. Animal viruses infect animals and require animal cells as their host. Unlike other intracellular obligatory parasites (for example, chlamydiae and rickettsiae…

A chemical substance, produced by microorganisms, plants, marine organisms, and synthetically, that has the capacity in dilute solutions to inhibit the growth of bacteria or destroy bacteria. Antibiotics are important antibacterial agents. Most are…

The capability that a bacterium acquires to counteract an inhibitory chemical molecule or compound that was formerly effective in killing it or preventing its growth. Antibiotic resistance in bacteria (Fig. 1) is a hot topic in the media and in…

Chemical compounds biosynthetically or synthetically produced that destroy or usefully suppress the growth or metabolism of a variety of microscopic or submicroscopic forms of life. On the basis of their primary activity, antimicrobial agents (see…

A group of diseases affecting joints or their component tissues. Arthritis is the collective term used to describe any joint disorder or process; it also typically involves inflammation. In common usage, arthritis often refers to any joint pain.…

A nonsteroidal anti-inflammatory drug used to control pain, fever, and inflammation. Aspirin is one of the most prevalent medicines in the world and is used to reduce fever and treat minor aches, pains, and inflammation. Furthermore, it is the only…

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 most common type of arrhythmia (any disorder of the heart rate or rhythm). Atrial fibrillation, often abbreviated AFib or AF, is a heart condition that can lead to potentially serious complications. It is associated with decreased quality of…

The study of bacteria. The science of bacteriology is a specialized branch of microbiology concerned with bacteria (Fig. 1). Although bacteria are different in some important respects from all other kinds of cells, their basic processes of…

The study of behavior change in response to drugs, chemicals, or other environmental conditions or agents. Behavioral toxicology investigates the effect of toxic exposure on organismal behavior. The toxic exposure can involve various chemicals,…

A sound-reproducing system in which sound is recorded or transmitted by using two microphones mounted at the ears of a dummy human head. To preserve the binaural effect, the sound must be monitored by a listener wearing a set of earphones…

The application of principles from applied and physical sciences to problems in healthcare and biology. As a field, biomedical engineering draws from a variety of disciplines including mechanical, chemical, electrical, and computer engineering, as…

A form of terrorism in which there is the intentional release of biological agents (viruses, bacteria, fungi, or toxins) from living organisms or agents in order to cause death or disease in humans, animals, and/or plants; also referred to as…

The practice of fertility control, including contraception, which is intended to prevent pregnancy, and the means of interrupting early pregnancy. The efficacy of the various methods of birth control and their consistency of use vary widely (see…

A process in which a liquid phase is converted into a vapor phase. The energy for phase change is generally supplied by the surface on which boiling occurs. Boiling differs from evaporation at predetermined vapor/gas–liquid interfaces because it…

A device for detecting and measuring small amounts of thermal radiation. The bolometer is a simple electric circuit, the essential element of which is a slab of material with an electrical property, most often resistance, that changes with…

A constant occurring in practically all statistical formulas and having a numerical value of 1.3807 × 10−23 joule/K. It is represented by the letter k. If the temperature T is measured from absolute zero, the quantity kT has the dimensions of an…

To describe a system consisting of a large number of particles in a physically useful manner, recourse must be had to so-called statistical procedures. If the mechanical laws operating in the system are those of classical mechanics, and if the…

An equation which is used to study the nonequilibrium behavior of a collection of particles. In a state of equilibrium a gas of particles has uniform composition and constant temperature and density. If the gas is subjected to a temperature…

A genus of pathogenic gram-negative bacteria that are coccobacilli and obligate aerobes, and fail to ferment carbohydrates. Bordetella bacteria are respiratory pathogens. Bordetella pertussis, B. parapertussis, and B. bronchiseptica share greater…

A circuit composed of a source and four impedances that is used in the measurement of a wide range of physical quantities. The bridge circuit is useful in measuring impedances (resistors, capacitors, and inductors) and in converting signals from…

A gravitationally bound, condensed body whose mass is too small to sustain nuclear fusion reactions in its core. Brown dwarfs are often likened to "failed stars." The approximate mass range for brown dwarfs is between 13 and 80 times the mass of…

The resultant vertical force exerted on a body by a static fluid in which the body is submerged or floating. Buoyancy is the upward force exerted by a fluid (liquid or gas) on a body that is placed within it (see illustration). The buoyant force FB…

The reaction that occurs when tissue (usually skin) receives more energy (heat, chemical energy, electrical energy, or radiation) than it can absorb without injury. Factors such as the duration of contact, temperature, volume of chemical, and…

An algorithm that gives a name to each day. These day names are generally distinct, but not always. For example, the day of the week is a calendar, in a trivial sense, with infinitely many days having the same day name. The design of calendars has…

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.…

A set of generalized coordinates of a classical dynamical system together with their conjugate momenta, and transformations among these coordinates and momenta that leave the form of Hamilton's equations of motion unchanged. Explanation of some of…

Any of the group of organic compounds consisting of carbon, hydrogen, and oxygen that includes sugars, starches, and cellulose. Carbohydrate compounds consist of carbon, hydrogen, and oxygen, with the general chemical formula Cm(H2O)n [Fig. 1]; the…

The name given to the electrons originating at the cathodes of gaseous discharge devices. The term has now been extended to include low-pressure devices such as cathode-ray tubes. Furthermore, cathode rays are now used to designate electron beams…

A luminescence resulting from the bombardment of a substance with an electron (cathode-ray) beam. The principal applications of cathodoluminescence are in television, computer, radar, and oscilloscope displays. In these a thin layer of luminescent…

In physics, the requirement that interactions in any spacetime region can influence the evolution of the system only at subsequent times; that is, past events are causes of future events, and future events can never be the causes of events in the…

The formation of vapor- or gas-filled cavities in liquids. If understood in this broad sense, cavitation includes the familiar phenomenon of bubble formation when water is brought to a boil under constant pressure and the effervescence of champagne…

An enclosure capable of resounding or resonating and thereby intensifying sound tones or electromagnetic waves. Resonance is the phenomenon which results when the frequency of the impressed driving force is the same as the natural vibration of the…

A set of four numbers used to specify the orientation of a body, or equivalently, the rotation R which produces that orientation, starting from some reference orientation. They can be expressed in terms of the Euler angles ψ, θ, and ϕ, as in Eqs.…

An autoimmune disorder caused by gluten sensitivity that damages the small intestine and leads to the malabsorption of nutrients from food. Celiac disease (CD) is an autoimmune condition of the small intestine that is believed to be T-cell…

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 fixed point in a body of matter through which the resultant force of gravitational attraction acts. The center of gravity is an imaginary point in any given body that is convenient when performing calculations and conducting mechanical studies…

A force whose line of action is always directed toward a fixed point. The central force may attract or repel. The point toward or from which the force acts is called the center of force. If the central force attracts a material particle, the path of…

A fictitious or pseudo outward force on a particle rotating about an axis which by Newton's third law is equal and opposite to the centripetal force. Like all such action-reaction pairs of forces, they are equal and opposite but do not act on the…

The inward force required to keep a particle or an object moving in a circular path. It can be shown that a particle moving in a circular path has an acceleration toward the center of the circle along a radius. This radial acceleration, called 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 blue glow observed in the water of a nuclear reactor, close…

A nuclear fission process in which neutrons produced in earlier fission events cause successive fission events. Fission (splitting) of a large-mass atomic nucleus may be induced when the nucleus absorbs a neutron. Fission results in the release of…

A single-particle detector which in its basic form (Fig. 1) consists of a hollow tube (channel) of either glass or ceramic material with a semiconducting inner surface. The detector responds to one or more primary electron impact events at its…

The steering of positively charged energetic particles between atomic rows or planes of a crystalline solid. The particles can be positive ions, protons, positrons, or muons. If the angle between the direction of the particle and a particular axis…