Central Powers World War I coalition that was defeated by the Allied Powers. Its primary members were the German empire and Austria- Hungary, the “central” European states that were at war from August 1914 against France, Britain, and Russia. The Ottoman empire entered the war on the side of the Central Powers in October 1914, followed by Bulgaria in October 1915.
central processing unit See CPU
Central Treaty Organization (CENTO) originally Middle East Treaty Organization or Baghdad Pact Organization Mutual- security organization, originally composed of Turkey, Iran, Iraq, Pakistan, and Britain. It was formed in 1955, at the urging of the U.S. and Britain, to counter the threat of Soviet expansion into the Middle East. CENTO was never very effective. Iraq withdrew after its anti-Soviet monarchy was overthrown in 1959. In that same year the U.S. became an associate member, and CENTO’s headquarters were moved to Ankara, Tur. After the fall of Mohammad Reza Shah Pahlavi in 1979, Iran withdrew and CENTO was dissolved.
Central Valley Spanish Valle Central \'ba-ya-sen-'tral\ Valley, Chile. Located in central Chile between the Western Cordillera of the Andes Mountains and the coastal range, it extends about 400 mi (650 km) from the Chacabuco Range in the north to the Bio-Bio River in the south. The agricultural heartland of Chile, it was the original centre of European colonization beginning in the mid-1500s, and it continues to be home to most Chileans. Santiago is at its northern end.
Central Valley Valley, California, U.S. Located between the Sierra Nevada and the Coast Ranges, it is more than 400 mi (640 km) long and 20-50 mi (32-80 km) wide. The Sacramento and San Joaquin rivers, which run through the valley, are fed by abundant rains and melting snows of the Sierras. Because of the irrigation made possible by numerous dams and canals, the area now contains some of the richest farmland in the U.S.
centrifugal \sen-'trif-y3-g3l\ force Fictitious force, peculiar to circu¬ lar motion, that is equal but opposite to the centripetal force that keeps a particle on a circular path (see centripetal acceleration). For example, a stone attached to a string and whirling in a horizontal circular path is accelerated toward the centre of its path by the tension in the string, the only force acting on the string. However, in a reference frame at rest with the stone, another force—the centrifugal force—must be introduced for Newton's laws of motion to apply. Centrifugal force is a useful concept in analyzing behaviour in rotating systems.
centrifugal \sen-'trif-y3-g9l\ pump Machine for moving liquids and gases. Its two major parts are the impeller (a wheel with vanes) and the cir¬ cular pump casing around it. In the most common type, called the volute centrifugal pump, fluid enters the pump at high speed near the centre of the rotating impeller and is thrown against the casing by the vanes. The cen¬ trifugal pressure forces the fluid through an opening in the casing; this out¬ let widens progressively in a spiral fashion, which reduces the speed of the fluid and thereby increases pressure. Centrifugal pumps are used for many purposes, such as pumping liquids for water supply, irrigation, and sewage disposal systems. They are also used as gas compressors.
centrifuge Vsen-tro-.fyujV Machine that applies a sustained centrifugal force. Effectively, the centrifuge substitutes a similar, stronger force for that of gravity. Every centrifuge contains a spinning vessel; there are many configurations, depending on use. A revolving object exerts a force away from the centre of rotation (see Newton's laws of motion), called the cen¬ trifugal force; it is usually stated as so many “times gravity” or so many
“G,” and may range from a few G for the basket in a home washing machine or an industrial separator to hundreds of thousands of G for cen¬ trifuges to separate isotopes of uranium or to purify vaccines.
centripetal \sen-'trip-3-t3l\ acceleration Property of the motion of an object traveling in a circular path. Centripetal describes the force on the object, directed toward the centre of the circle, which causes a con¬ stant change in the object’s direction and thus its acceleration. The mag¬ nitude of centripetal acceleration a is equal to the square of the object’s velocity v along the curved path divided by the object’s distance r from the centre of the circle, or a = v 2 /r.
centroid In geometry, the centre of mass of a two-dimensional figure or three-dimensional solid. Thus the centroid of a two-dimensional fig¬ ure represents the point at which it could be balanced if it were cut out of, for example, sheet metal. The centroid of a circle or sphere is its cen¬ tre. More generally, the centroid represents the point designated by the mean (see mean, median, and mode) of the coordinates of all the points in a set. If the boundary is irregular, finding the mean requires using calcu¬ lus (the most general formula for the centroid involves an integral).
centromere Vsen-tro-.mhA Structure in a chromosome that holds together the two chromatids. It is the point of attachment to the structure that pulls the chromatids to opposite ends of the cell during cell division (see mitosis). During the middle stage of mitosis, the centromere dupli¬ cates and the chromatid pair separates, each chromatid becoming a sepa¬ rate chromosome. Thus, when the cell divides, both daughter cells have complete sets of chromosomes.
century plant or American aloe or maguey \m9-'ga\ Species of AGAVE (Agave americana), of Mexico and the southwestern U.S. It takes many years (from five to 100) to mature, flowers only once, and then dies. It is widely cultivated for its large spiny leaves and enormous flower clus¬ ter, and may reach 20 ft (6 m) in height. Century plants provide the dis¬ tinctive ingredient for the alcoholic drinks pulque and mescal.
Cephalonia or Cephallenia Largest of the Ionian Islands, western Greece. With Ithaca and smaller nearby islands, it forms the Kefallima department. The mountainous island occupies 302 sq mi (781 sq km) and rises to 5,341 ft (1,628 m) at Mount Amos. Argostolion, the chief town and a port on the southwestern coast, is the department capital. The island was an important Mycenaean centre, which the Romans seized in 189 bc. In the Middle Ages it was captured by Robert Guiscard. Later it was ruled by various Neapolitan and Venetian families. In 1809 it was taken by the British, then ceded to Greece in 1864. It experienced a devastating earth¬ quake in 1953.
cephalopod Vse-fo-lo-.padX Any marine mollusk of the class Cepha¬ lopoda (e.g., cuttlefish, nautilus, octopus, and squid), which includes the most active and largest living invertebrates. Cephalopods are bilaterally symmetrical and typically have a highly developed centralized nervous system. Their image-forming eyes are similar in structure to vertebrate eyes, and their heads are armed with tentacles that have rows of round suction disks. Most cephalopods can change skin colour to blend in with their surroundings. All can swim, propelling themselves backward by expelling water forcefully. Most are carnivores that feed on fish, crusta¬ ceans, and other mollusks.
Cepheid \'sef-e-od\ variable One of a class of variable stars whose period of variation is closely related to its luminosity and is therefore use¬ ful in measuring the distances to clusters of stars and galaxies. Named for the prototype of this class found in the constellation Cepheus, classical Cepheids have periods from about 1.5 days to over 50 days and are Popu¬ lation I stars (see Populations I and II). The longer the period of such a star, the greater its natural brightness; this relationship was discovered in 1912 by the American astronomer Henrietta Leavitt (b. 1868—d. 1921).
Ceram or Seram Vsa-.rairA Island of the central Moluccas, Indonesia. It has an area of 6,621 sq mi (17,148 sq km). The terrain is mountainous and covered with tropical forests; seismic activity is common. Portuguese missionaries arriving in the 15th century found Hindu and Islamic influ¬ ences present; the island came under nominal Dutch control c. 1650. Dur¬ ing World War II the Japanese occupied it; after the war it became part of Indonesia.