hydrogen-ion concentration: see pH.

concentration camp, a detention site outside the normal prison system created for military or political purposes to confine, terrorize, and, in some cases, kill civilians. The term was first used to describe prison camps used by the Spanish military during the Cuban insurrection (1868-78), those created by America in the Philippines (1898-1901), and, most widely, to refer to British camps built during the South African War (Boer War) to confine Afrikaners in the Transvaal and Cape Colony (1899—1902). The term soon took on much darker meanings. In the USSR, the Gulag elaborated on the concept beginning as early as 1920. After 1928, millions of opponents of Soviet collectivization as well as common criminals were imprisoned under extremely harsh conditions and many died.

During World War II concentration camps were established throughout Europe by the Nazis, and throughout Indochina and Manchuria by the Japanese. Of the millions of people of many nationalities detained in them, a large proportion died of mistreatment, malnutrition, and disease. In both Nazi and Japanese camps inmates were exploited for slave labor and medical experimentation, but the Nazis also established extermination camps. In the best known of these—Majdanek, Treblinka, and Oświęcim (Auschwitz), in Poland—more than six million mainly Jewish men, women, and children were killed in gas chambers. Among the most notorious Nazi camps liberated by U.S. and British troops in 1945 were Buchenwald, Dachau, and Belsen.

The term has also been applied to the U.S. relocation centers for American citizens of Japanese origin and others interned in the W United States during World War II. In China during the Cultural Revolution (1966-69) millions were sent to euphemistically named "reeducation" camps, and in Cambodia after Pol Pot came to power (1976) an estimated one million civilians died in "reeducation" camps. North Korea maintains a system of political and criminal prison camps in which inmates are sentenced to harsh physical labor and are underfed and mistreated. In 1992, reports of malnutrition and killings in concentration camps for Muslim, Croat, and Serb male civilians in Bosnia led to attempts by international organizations to identify the location of the camps and inspect them.

concentration, in chemistry, measure of the relative proportions of two or more quantities in a mixture. The concentration of a solute is very important in studying chemical reactions because it determines how often molecules collide in solution and thus indirectly determines the rates of reactions and the conditions at equilibrium (see chemical equilibrium).

Concentration may be expressed in a number of ways. The simplest statement of the concentrations of the components of a mixture is in terms of their percentages by weight or volume. Mixtures of solids or liquids are frequently specified by weight percentage concentrations, such as alloys of metals or mixtures used in cooking, whereas mixtures of gases are usually specified by volume percentages. Very low concentrations may be expressed in parts per million (ppm), as in specifying the relative presence of various substances in the atmosphere.

In addition to these means of expressing concentration, several others are defined especially for describing solutions: molarity, molality, mole fraction, formality, and normality. Some of these define the concentration of the solute in reference to the amount of solvent, others in reference to the total amount of solution. The molarity of a solution is the number of moles of solute per liter of solution; e.g., a solution of glucose in water containing 180.16 grams (1 gram-molecular weight, or mole) of glucose per liter of solution is referred to as one molar (1 M). The molality of a solution is the number of moles of solute per 1,000 grams of solvent; a solution prepared by dissolving 180.16 grams of glucose in 1,000 grams of water is one molal (1 m). The mole fraction of a solution is the ratio of moles of solute to the total number of moles in the solution. Since ionic compounds, such as sodium chloride, NaCl, do not occur as molecules, their concentrations cannot be expressed in terms of molarity, molality, or mole fraction. Instead, the concentration of an ionic compound in solution may be given by its formality, the number of gram-formula weights of the compound per liter of solution; e.g., a solution containing 58.44 grams (one gram-formula weight) of NaCl per liter of solution is one formal (1 F). In considering the reactions of certain solutions in combination, for example the neutralization of acids and bases, a useful expression of the concentration is the normality of each solution, the number of gram-equivalent weights of solute per liter of solution (see equivalent weight); e.g., a solution containing 49.04 grams (one gram-equivalent weight) of sulfuric acid, H₂SO₄, per liter of solution is one normal (1 N). Concentrations of solutions may also frequently be given in terms of the weight of solute in a given volume of solvent or solution.

Internment centre established by a government to confine political prisoners or members of national or minority groups for reasons of state security, exploitation, or punishment. The prisoners are usually selected by executive decree or military order. Camps are usually built to house many people, typically in highly crowded conditions. Countries that have used such camps include Britain during the South African War, the Soviet Union (see Gulag), the U.S. (see Manzanar Relocation Center), and Japan, which interned Dutch civilians in the Dutch East Indies during World War II. A variation, called a “reeducation camp,” was used in Vietnam after 1975 and in Cambodia under the Khmer Rouge. Most notorious were the death camps of Nazi Germany, including Auschwitz, Bergen-Belsen, Buchenwald, Dachau, and Treblinka.

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formerly hyperactivity

Behavioral syndrome in children, whose major symptoms are inattention and distractibility, restlessness, inability to sit still, and difficulty concentrating on one thing for any period of time. It occurs in about 5percnt of all schoolchildren, and it is three times more common in boys than in girls. It can adversely affect learning, though many children with ADD can learn to control their behaviour sufficiently to perform satisfactorily in school. It appears to be caused by a combination of genetic and environmental factors. Certain aspects of the syndrome may persist into adulthood. Treatment usually entails counseling and close parental supervision, and it may also include prescription medication.

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In psychology, the act or state of applying the mind to an object of sense or thought. Wilhelm Wundt was perhaps the first psychologist to study attention, distinguishing between broad and restricted fields of awareness. He was followed by William James, who emphasized active selection of stimuli, and Ivan Pavlov, who noted the role attention plays in activating conditioned reflexes. John B. Watson sought to define attention not as an “inner” process but rather as a behavioral response to specific stimuli. Psychologists today consider attention against a background of “orienting reflexes” or “preattentive processes,” whose physical correlates include changes in the voltage potential of the cerebral cortex and in the electrical activity of the skin, increased cerebral blood flow, pupil dilation, and muscular tightening. Seealso attention deficit disorder.

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