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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…

Technologies to optimize the performance of optical systems wherein controllable optical elements maintain a sharply focused image in the presence of wavefront aberrations. The practical development of adaptive optics started in the late 1960s. Main…

Natural and artificial substances in the atmosphere that affect human health or well-being, or the well-being of any other organisms in the environment. Air pollution also applies to situations in which contaminants affect structures and artifacts…

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 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…

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…

A quantum-mechanical theory of the motion of electrons in solids. The band theory of solids' name comes from the fact that it predicts certain restricted ranges, or bands, for the energies of electrons in solids. In a solid, the energy level of an…

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…

Any of the 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…

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…

Any clouding or opacity of the crystalline lens of the eye. Loss of the transparency of the lens (see illustration) prevents the normal passage of light onto the light-sensitive retina at the back of the eye and thus a loss of visual ability.…

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…

An apparent outward force on a particle rotating about an axis which, by Newton's third law, is equal and opposite to the centripetal force. In classical mechanics, a particle that is rotating about an axis experiences an apparent outward…

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 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…

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…

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…

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 basic quantitative law of electrostatics that quantifies the physical force that exists between two electrically charged points. For electrostatics, Coulomb's law states that the direct force F of point charge q1 on point charge q2, when the…

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…

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…

A range of physical phenomena that involve electric charges, their motions, and their effects. In conventional usage, the term “electricity” often refers to the energy that powers lighting, appliances, and other electronic devices in homes,…

The process in which an electron, which has been excited from the valence band to the conduction band of a semiconductor, falls back into an empty state in the valence band, which is known as a hole. When atoms come together to form a crystal, the…

A 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…

The branch of physics and engineering science concerned with the relation between the forces acting on fluids (liquids and gases), the motions of fluids, and the forces caused by fluids on their surroundings. Fluid mechanics is comprised of two…

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 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…

Pathologies or aberrations in structure or function of blood cells or the blood-clotting mechanism. Hematologic disorders affect the blood and blood-forming organs. Although many diseases and abnormal conditions may be reflected by the blood and its…

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…

The process of tissue death (necrosis) resulting from a failure of blood supply and lack of oxygen (anoxia) reaching the tissue's cells. The usual cause of infarction is occlusion (blockage or closing) of an artery by a thrombus (blood clot; see…

The entrance, growth, and multiplication of a microorganism or pathogen in the body of a host. Infection may or may not result in the establishment of a disease process, depending on many variables including the pathogen involved, the health of the…

One of the three fundamental particles that transmit the weak force. The three intermediate vector bosons are known as the W+, W− , and Z0 particles or bosons. were discovered in 1983 in very high energy proton-antiproton collisions. It is through…

Any scientific law in which a physical quantity varies with distance from a source inversely as the square of that distance. When energy is being radiated by a point source (see illustration), an inverse-square law holds, provided the space between…

Fundamental laws dealing with electric currents at junctions and voltages around any loop within a network. Also known as Kirchhoff's circuit laws, the laws were first described by German physicist Gustav Kirchhoff in 1845. The laws are divided into…

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…

A transparent object that uses refraction in order to alter the light that passes through the object. In general, when a ray of light crosses the interface between two different transparent materials, the ray experiences a bending of its path. This…

The spectrum of a beam of light when only a few isolated colors are present. A beam of light (technically, a beam of electromagnetic radiation) typically contains a mixture of pure colors. The particular pure colors that are present in the beam…

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 disease caused by members of the protozoan genus Plasmodium (a widespread group of protists that parasitize the human liver and red blood cells) and transmitted by the bite of the female Anopheles mosquito. Malaria is a serious mosquito-borne…

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…

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 procedure used to remove toxins, fluids, and other substances from the body when the kidneys are unable to handle this removal naturally. In the medical field, medical dialysis is simply referred to as dialysis. The removal of toxins, fluids, 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…

An autoimmune disease resulting from an abnormality in neuromuscular transmission, characterized by a fluctuating degree of muscle weakness. Myasthenia gravis is a chronic autoimmune neuromuscular disorder (see illustration) characterized by varying…