desmid Vdez-modX Any of a group of one-celled, microscopic green algae characterized by great varia¬ tion in cell shape. Typically the cell is divided symmetrically into semi¬ cells connected at a central point.
Desmids are found worldwide, usu¬ ally in acid bogs or lakes. Since most species have a limited range, the presence of specific desmids is help¬ ful in characterizing water samples.
Desmond Ancient territorial divi¬ sion, Ireland. From the 11th to the
Desmid (Micrasterias), highly magni¬ fied
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Desmoulins ► deuterium I 537
17th century, the name was often used for two quite distinct areas. Gaelic Desmond extended over part of modern Counties Kerry and Cork; Anglo- Norman Desmond extended over northern Kerry, most of the modern county of Limerick, southwestern Tipperary, eastern and southern County Cork, and eastern Waterford.
Desmoulins \da-mu-'la n \, (Lucie-Simplice-) Camille (-Benoist)
(b. March 2, 1760, Guise, France—d. April 5, 1794, Paris) French jour¬ nalist influential in the French Revolution. Though a stammer had impeded him as a lawyer, he suddenly emerged as an inspiring orator when the Revolution began, inciting the storming of the Bastille. In his pamphlets and newspapers he campaigned for the deposition of the king and the establishment of a republic. Elected to the National Convention, he joined other Montagnards in a struggle against the Girondins. Later he and Georges Danton became leaders of a moderate faction, the Indulgents. After attacking the Committee of Public Safety’s Reign of Terror, he was guillotined along with other Dantonists.
Dessalines \,da-s9-Ten\, Jean-Jacques (b. c. 1758, West Africa—d. Oct. 17, 1806, Jacmel, Haiti) Emperor of Haiti who drove out the French in 1804. He was a slave of a black master in Saint-Domingue (Haiti) in 1791 when he joined a slave rebellion. He became a lieutenant of Toussaint-Louverture but submitted to the French expedition that deposed Toussaint in 1802. Napoleon’s decision to reintroduce slavery led Dessa¬ lines and others to rebel, and with British help they expelled the French. In 1804 Dessalines proclaimed the island independent under its Arawa- kan name, Haiti, and proclaimed himself emperor the following year. He made it illegal for whites to own property and killed thousands; he also discriminated against mulattoes. He was killed during a mulatto revolt.
destroyer Fast naval vessel used to protect other ships. The term was first applied to vessels built in the 1890s to protect battleships from tor¬ pedo boats. By World War I destroyers were often sent ahead of the battle fleet to scout for the enemy, beat back its destroyers with cannon fire, and then launch torpedoes against its battleships and cruisers. When the sub¬ marine became the main torpedo-launching vessel, destroyers armed with depth charges protected convoys and battle fleets against submarine attack. In World War II, with the addition of radar and antiaircraft guns, its escort role included air defense. Modern destroyers are run by a crew of about 300 and equipped with surface-to-air missiles, antiship missiles, and one or two big guns. Many carry submarine-hunting helicopters, and some carry cruise missiles.
detached retina Separation of most layers of the retina of the eye from the choroid, the pigmented middle layer of the eyeball. With age, small tears can develop in the retina, and the vitreous humour inside the eye¬ ball leaks through, separating the retina from the choroid. The disease ret- rolental fibroplasia or accidents can also cause retinal detachment. It usually develops slowly, without pain. Floating black spots and flashes of light appear in the affected eye, and vision becomes increasingly blurred. Without prompt treatment, it causes permanent blindness. Draining the fluid behind the retina and applying heat, a laser beam, or extreme cold causes scarring that seals the tears and prevents the retina from detach¬ ing again.
detective story Type of popular literature dealing with the step-by- step investigation and solution of a crime, usually murder. The first detec¬ tive story was Edgar Alian Poe’s “The Murders in the Rue Morgue” (1841). The genre soon expanded to novel length. Sherlock Holmes, the first fictional detective to become a household name, first appeared in Arthur Conan Doyle’s A Study in Scarlet (1887). The 1930s was the golden age of the detective novel, exemplified by the books of Dashiell Hammett. The introduction of mass-produced paperback books in the late 1930s made detective stories readily accessible to a wide public, and well-known fictional detectives were created by G.K. Chesterton, Agatha Christie, Dorothy Sayers, Raymond Chandler, Mickey Spillane, and Georges Simenon. Among present-day mystery writers RD. James and Dick Fran¬ cis rank high.
detente \da-'tant\ Period of the easing of Cold War tensions between the U.S. and the Soviet Union from 1967 to 1979. The era was a time of increased trade and cooperation with the Soviet Union and the signing of the SALT treaties. Relations cooled again with the Soviet invasion of Afghanistan.
detergent Any of various surfactants (substances that reduce surface tension) used to dislodge dirt from soiled surfaces and retain it in suspen¬
sion, allowing it to be rinsed away. The term usually refers to synthetic substances and excludes soaps. The characteristic features of a molecule of any detergent are a hydrophilic (water-attracting) end and a hydrophobic (oil-attracting) end. In ionic detergents, the hydrophilic property is con¬ ferred by the ionized part of the molecule. In nonionic detergents, hydro- philicity is based on the presence of multiple hydroxyl groups or other hydrophilic groups. Besides those used in water to clean dishes and laun¬ dry, detergents that function in other solvents are used in lubricating oils, gasolines, and dry-cleaning solvents to prevent or remove unwanted deposits. They are also used as emulsifying agents (see emulsion).
determinant In linear algebra, a numerical value associated with a matrix having the same number of rows as columns. It is particularly use¬ ful in solving systems of (linear) equations and in the study of vectors. For a two-by-two matrix, the determinant is the product of the upper left and lower right terms minus the product of the lower left and upper right terms. Determinants of larger matrices involve more complicated arith¬ metic combinations of the terms and are usually solved using a calcula¬ tor or computer.
determinism In philosophy, the doctrine that all events, including human decisions, are completely determined by previously existing causes. The traditional free will problem arises from the question, Is moral responsibility consistent with the truth of determinism? Among those who believe it is not consistent, some, maintaining the truth of determinism, have concluded that no one is morally responsible for what he does (and therefore that punishment for criminal actions is unjustified); others, maintaining the reality of moral responsibility, have concluded that deter¬ minism is false. Those who believe that moral responsibility is consistent with determinism are known as compatibilists (see compatibilism). Pierre- Simon Laplace is responsible for the classical formulation of determinism in the 18th century. For Laplace, the present state of the universe is the effect of its previous state and the cause of the state that follows it. If a mind, at any given moment, could know all the laws and all the forces operating in nature and the respective positions and momenta of all its components, it could thereby know with certainty the future and the past of every entity.
deterrence Military strategy whereby one power uses the threat of reprisal to preclude an attack from an adversary. The term largely refers to the basic strategy of the nuclear powers and the major alliance systems. The premise is that each nuclear power maintains a high level of instant and overwhelming destructive capability against any aggressor. It relies on two basic conditions: the ability to retaliate after a surprise attack must be perceived as credible, and retaliation must be perceived as a possibil¬ ity, if not a certainty.