permafrost Perennially frozen earth, with a temperature below 32 °F (0 °C) continuously for two years or more. Permafrost is estimated to underlie 20% of the Earth’s land surface and reaches depths of 5,000 ft (1,500 m) in northern Siberia. It occurs in 85% of Alaska, more than half of Russia and Canada, and probably all of Antarctica. Permafrost has a significant effect on plant and animal life, and it presents special prob¬ lems in engineering projects. All land use in permafrost environments must take into account the terrain’s special sensitivity; if the delicate natural balance is not maintained, extensive degradation and ecological damage may result.
permeability, magnetic See magnetic permeability
Permian Period Interval of geologic time, 290-248 million years ago. The last of the six periods of the Paleozoic Era, it follows the Carbonif¬ erous Period. During the Permian, the continents joined to form a single supercontinent, Pangea. Hot, dry conditions prevailed almost everywhere, and deserts were widespread. Life evolved as a continuation of established lines. Marine invertebrates evolved into several lineages. Marine and freshwater fish and amphibians thrived. Reptiles evolved into three dis¬ tinct groups: the cotylosaurs, the pelycosaurs, and the therapsids. Land plants evolved from ferns and seed ferns to conifers and adapted to drier and well-drained land conditions. Toward the close of the Permian, many forms of life suffered mass extinction, whose causes are unknown.
permutations and combinations Number of ways a subset of objects can be selected from a given set of objects. In a permutation, order is important; in a combination, it is not. Thus, there are six permutations of the letters A, B, C selected two at a time (AB, AC, BC, BA, CA, CB) yet only three combinations (AB, AC, BC). The number of permutations of r objects chosen from a set of n objects, expressed in factorial nota¬ tion, is n\ -j- (n - r)! The number of combinations is n\ 4 [r(n - r)!]. The (r + l)st coefficient in the binomial expansion of (x + y) n coincides with the combination of n objects chosen r at a time (see binomial theorem). Probability theory evolved from the study of gambling, including figuring out combinations of playing cards or permutations of win-place-show possibilities in a horse race, and such counting methods played an impor¬ tant role in its development in the 17th century.
Pernambuco See Recife
pernicious anemia Slow-developing disease in which vitamin B 12 (see vitamin B complex) deficiency impairs red-blood-cell production. It can result from a diet lacking in vitamin B 12 or when intrinsic factor, a sub¬ stance needed for intestinal absorption of B 12 , either is not produced by stomach cells or cannot bind to the vitamin. It causes weakness, waxy pallor, shiny tongue, and stomach, intestinal, and neurological problems. Its slow development can allow anemia to become very severe by the time of diagnosis. Monthly B 12 injections into muscle soon reverses the ane¬ mia, but the injections must be continued for life.
Peron \pa-'ron\, Eva (Duarte de) known as Evita orig. Maria Eva Duarte (b. May 7, 1919, Los Toldos, Arg.—d. July 26, 1952, Buenos Aires) Second wife of Argentine president Juan Peron and a powerful though unofficial political leader. Born into poverty, she was an actress when she married Peron. She was instrumental in the success of his first presidential campaign and won the adulation of the masses. Evita acted as de facto minister of health and labour, awarding generous wage increases to workers. With “voluntary” contributions from businesses.
labour unions, and the elite, she established thousands of hospitals, schools, and orphanages. After her death from cancer at age 33, her grief- stricken working-class followers sought to have her canonized.
Peron, Isabel (Martinez de) orig. Maria Estela Martinez Cartas (b. Feb. 4, 1931, La Rioja, Arg.) Third wife of Juan Peron and president of Argentina (1974-76). Born into a lower-middle-class family, she was a dancer when she met Peron in 1955 or 1956. They married during his exile in 1961, and she became his running mate in the 1973 presidential election. She succeeded him when he died in 1974, inherit¬ ing problems of inflation and political violence, which she tried— ineffectively—to solve by printing money and imposing a state of siege. She was deposed in 1976; after five years of house arrest, she was con¬ victed of corruption but permitted to go into exile in Spain.
Peron, Juan (Domingo) (b. Oct. 8, 1895, Buenos Aires province, Arg.—d. July 1, 1974, Buenos Aires) President of Argentina (1946-55, 1973-74). After attending military school, he served in the 1930s in Italy, where he observed the successes of the Fascists. In 1943 he helped over¬ throw Argentina’s ineffective civilian government. As secretary of labour and social welfare, he built a loyal following among industrial workers, who helped elect him president in 1946. Peron’s political views drew on both the far left and the far right: while he showered workers with much- needed benefits, he restricted civil liberties severely. The charisma of his second wife, Eva Peron, greatly increased the regime’s standing with the populace. He was reelected in 1951, but a disastrous economic decline and increasing disaffection among many elements of Argentine society led to his overthrow in 1955 by democratically inspired military officers. He lived in exile in Spain for two decades but continued to influence Argentine affairs. When the Peronist party was made legal, he was reelected president in absentia; he died less than a year after returning to Argentina and assuming the presidency. See also Isabel Peron.
Peronist \p9-'ro-nist\ Member of Argentina’s Justicialist Nationalist Movement, a supporter of Juan Peron, or an adherent of his populist and nationalist policies. Peron’s poorly defined political philosophy embraced elements of both left- and right-wing ideology, combining a commitment to the redistribution of wealth with authoritarian nationalism and disre¬ gard for civil rights. After his death in 1974, the Justicialist movement was weakened by factionalism, but it continued to play an important role in Argentine politics and had adherents elsewhere. See also Carlos Menem.
Perot \p3-'ro\, H(enry) Ross (b. June 27, 1930, Texarkana, Texas, U.S.) U.S. businessman. After graduating from the U.S. Naval Academy, he served in the navy (1953-57). He worked for IBM from 1957 to 1962, when he formed his own company, Electronic Data Systems; he sold it in 1984 to General Motors for $2.5 billion. In 1992 he became an inde¬ pendent candidate for U.S. president. Appealing to voters dissatisfied with traditional party politics, he won 19% of the popular vote, the best third- party presidential showing since 1912. He ran again in 1996 but received only 8% of the vote. His Reform Party, which he founded in 1995, gradu¬ ally established its autonomy from him.
peroxide Any of a class of chemical compounds in which two oxygen atoms are linked by a single covalent bond. Several organic (see organic compound) and inorganic (see inorganic compound) peroxides are useful as bleaching and oxidizing agents (see oxidation-reduction), as initiators of polymerization reactions, and in the preparation of hydrogen peroxide (a mild bleach and antiseptic) and other oxygen compounds. The perox¬ ide anion (chemical formula 0 2 - ) is present in peroxides of inorganic compounds.
Perpendicular style Phase of late Gothic architecture in England roughly parallel in time to the French Flamboyant style. The style, con¬ cerned with creating rich visual effects through decoration, was charac¬ terized by a predominance of vertical lines in stone window tracery, enlargement of windows to great proportions, and conversion of the inte¬ rior stories into a single unified vertical expanse. Fan vaults, springing from slender columns or pendants, became popular. The oldest surviving example of the style is probably the choir of Gloucester Cathedral (begun c. 1335). Other major monuments include King’s College Chapel, Cam¬ bridge (1446-1515), and the chapel of Henry VII in Westminster Abbey. In the 16th century, the grafting of Renaissance elements onto the Perpen¬ dicular style resulted in the Tudor style.