population inversion, in physics, the redistribution of atomic energy levels that takes place in a system so that laser or maser action can occur. Normally, a system of atoms is in temperature equilibrium and there are always more atoms in low energy states than in higher ones. Although absorption

statistics: Estimation of a population mean: The most fundamental point and interval estimation process involves the estimation of a population mean. Suppose it is of interest to estimate the population mean, μ, for a quantitative variable. Data collected from a simple random sample can be used…

population: Population momentum: An important and often misunderstood characteristic of human populations is the tendency of a highly fertile population that has been increasing rapidly in size to continue to do so for decades after the onset of even a substantial decline in fertility. This results…

population ecology: Metapopulations: …dynamics and evolution of many populations are determined by both the population’s life history and the patterns of movement of individuals between populations. Regional groups of interconnected populations are called metapopulations. These metapopulations are, in turn, connected to one another over broader geographic ranges. The mapped distribution of the perennial…

statistics: Estimation of other parameters: For qualitative variables, the population proportion is a parameter of interest. A point estimate of the population proportion is given by the sample proportion. With knowledge of the sampling distribution of the sample proportion, an interval estimate of a population proportion is obtained in much the same fashion as…

population pyramid, graphical representation of the age and sex composition of a specific population. The age and sex structure of the population determines the ultimate shape of a population pyramid, such that the representation may take the form of a pyramid, have a columnar shape (with vertical

apartheid: Apartheid legislation: …was made possible through the Population Registration Act of 1950, which classified all South Africans as either Bantu (all Black Africans), Coloured (those of mixed race), or white. A fourth category—Asian (Indian and Pakistani)—was later added. One of the other most significant acts in terms of forming the basis of…

Homo sapiens: Bodily structure: Out of Africa 2 (also called the population replacement hypothesis) picks up where Out of Africa 1 leaves off. It posits that H. sapiens also evolved in Africa, but some members of the species exited the continent, spreading to new lands while also replacing the…

minimum viable population: Estimating MVP: …computer simulation model known as population viability analysis (PVA) was developed to estimate the MVP of a species. The method was later found to be useful for providing more-sophisticated estimates of extinction risk and long-term persistence. PVA can be customized by the researcher to incorporate various data related to a…

Milky Way Galaxy: Stars and stellar populations: The concept of different populations of stars has undergone considerable change over the last several decades. Before the 1940s, astronomers were aware of differences between stars and had largely accounted for most of them in terms of different masses, luminosities, and orbital characteristics…

population ecology: Life histories and the structure of populations: An organism’s life history is the sequence of events related to survival and reproduction that occur from birth through death. Populations from different parts of the geographic range that a species inhabits may exhibit marked variations in their life histories. The patterns…

Populations I and II, in astronomy, two broad classes of stars and stellar assemblages defined in the early 1950s by the German-born astronomer Walter Baade. The members of these stellar populations differ from each other in various ways, most notably in age, chemical composition, and location

Cameroon: Moving toward independence: …Union (Union des Populations Camerounaises; UPC), led by Felix-Roland Moumie and Reuben Um Nyobe, demanded a thorough break with France and the establishment of a socialist economy. French officials suppressed the UPC, leading to a bitter civil war, while encouraging alternative political leaders. On January 1, 1960, independence was granted.…

populism, political program or movement that champions, or claims to champion, the common person, usually by favourable contrast with a real or perceived elite or establishment. Populism usually combines elements of the left and the right, opposing large business and financial interests but also

Narodnik, member of a 19th-century socialist movement in Russia who believed that political propaganda among the peasantry would lead to the awakening of the masses and, through their influence, to the liberalization of the tsarist regime. Because Russia was a predominantly agricultural country,

Populist Movement, in U.S. history, politically oriented coalition of agrarian reformers in the Midwest and South that advocated a wide range of economic and political legislation in the late 19th century. Throughout the 1880s, local political action groups known as Farmers’ Alliances sprang up

George II: …in exile until the conservative Populist Party, with the support of the army, gained control of the Assembly and declared the restoration of the monarchy in October 1935; a plebiscite, which was most probably manipulated by the prime minister, General Geórgios Kondílis, was held in November in an effort to…

Populonia, ancient Roman city that had originally been Etruscan and named Pupluna or Fufluna after the Etruscan wine god, Fufluns. It was situated on the western coast of central Italy on the Monte Massoncello Peninsula—the only large Etruscan city directly on the sea. The reason for the city’s

St. Paul VI: Vatican II and Paul VI’s pontificate: …insistent theme of his celebrated Populorum progressio (“Progress of the Peoples”), March 26, 1967. This encyclical was such a pointed plea for social justice that in some conservative circles the pope was accused of Marxism.

poplar, (genus Populus), genus of some 35 species of trees in the willow family (Salicaceae), native to the Northern Hemisphere. The poplar species native to North America are divided into three loose groups: the cottonwoods, the aspens, and the balsam poplars. The name Populus refers to the fact

poplar: Common species: The white poplar (P. alba)—also known as silver poplar for its leaves, which have white felted undersides, and as maple leaf poplar for the leaves’ lobed margins—is widely spreading or columnar in form, reaching 30 metres (100 feet) in height. The gray poplar (P. ×canescens), a…

balsam poplar, North American poplar (Populus balsamifera), native from Labrador to Alaska and across the extreme northern U.S. Often cultivated as a shade tree, it has buds thickly coated with an aromatic resin that is used to make cough syrups. It grows best in northwestern

poplar: Common species: The gray poplar (P. ×canescens), a close relative of the white poplar, has deltoid (roughly triangular) leaves with woolly grayish undersides. The black poplar, or black cottonwood (P. nigra), has oval fine-toothed leaves, is long-trunked, and grows to a height of 35 metres (115 feet). Columnar…

cottonwood: Eastern cottonwood (P. deltoides), nearly 30 metres (100 feet) tall, has thick glossy leaves. A hybrid between this and Eurasian black poplar (P. nigra) is P. canadensis. Alamo, or Fremont cottonwood (P. fremontii), tallest of the group, is found in southwestern North America. Great Plains…

poplar: Common species: …Fremont, or Alamo, cottonwood (P. fremontii) is the tallest of the cottonwoods and is found throughout southwestern North America.

aspen: The American big-tooth aspen (P. grandidentata), up to 18 metres (59 feet), has larger, somewhat rounded, coarse-toothed leaves. See also cottonwood.

poplar: Common species: The buds of the balm of Gilead poplar (P. ×jackii), which is similar, are used to make an ointment. The western balsam poplar, also called black cottonwood (P. trichocarpa), grows some 60 metres (195 feet) tall and is one of the largest deciduous trees of northwestern North America.

poplar: Common species: The black poplar, or black cottonwood (P. nigra), has oval fine-toothed leaves, is long-trunked, and grows to a height of 35 metres (115 feet). Columnar black poplars are widely used in ornamental landscape plantings, particularly among the villas of Italy and elsewhere in southern Europe. White…

Roman law: Corporations: The populus Romanus, or the “people of Rome,” collectively could acquire property, make contracts, and be appointed heir. Public property included the property of the treasury.

cottonwood: Great Plains cottonwood (P. sargentii), of North America, has thick coarse-toothed leaves. Many species and hybrids have wood with a variety of uses, including for matches and matchboxes. Lombardy poplar (P. nigra) is a columnar form that is much planted. See also aspen.

aspen: The common European aspen (P. tremula) and the American quaking, or trembling, aspen (P. tremuloides) are similar, reaching a height of 27 metres (90 feet). P. tremuloides is distinguished by its leaves, which have more pointed tips, and it grows by root suckers. Individual clones of the…

aspen: tremula) and the American quaking, or trembling, aspen (P. tremuloides) are similar, reaching a height of 27 metres (90 feet). P. tremuloides is distinguished by its leaves, which have more pointed tips, and it grows by root suckers. Individual clones of the plants persist for thousands of years even…

poplar: Common species: The western balsam poplar, also called black cottonwood (P. trichocarpa), grows some 60 metres (195 feet) tall and is one of the largest deciduous trees of northwestern North America.

fellow traveler, originally, a writer in the Soviet Union who was not against the Russian Revolution of 1917 but did not actively support it as a propagandist. The term was used in this sense by Leon Trotsky in Literature and the Revolution (1925) and was not meant to be pejorative. Implicit in the

Dmitri Mendeleev: Other scientific achievements of Dmitri Mendeleev: …khimicheskogo ponimania mirovogo efira (1902; An Attempt Towards a Chemical Conception of the Ether), he explained these phenomena as movements of ether around heavy atoms, and he tried to classify ether as a chemical element above the group of inert gases (or noble gases). This bold (and ultimately discredited) hypothesis…

poker: History of poker: …developed a similar game called poque, first played in French America in 1803, when the Louisiana Purchase made New Orleans and its environs territories of the United States. During the next 20 years, English-speaking settlers in the Louisiana Territory adopted the game, Anglicized its name to poker, and established the…

Molière was a French actor and playwright who became the greatest of all writers of French comedy. Although the sacred and secular authorities of 17th-century France often combined against him, the genius of Molière finally emerged to win him acclaim. Comedy had a long history before Molière, who

Luis Carlos López: …dificiles (1909; “Difficult Situations”), and Por el atajo (1928; “For the Short-Cut”).

Albanian literature: …Albanian literature is the poet Lasgush Poradeci (pseudonym of Llazar Gusho, of which Lasgush is a contraction). Breaking with tradition and conventions, he introduced a new genre with his lyrical poetry, which is tinged with mystical overtones. Writers in post-World War II Albania laboured under state-imposed guidelines summed up by…

Bora-Bora, volcanic island, Îles Sous le Vent (Leeward Islands), in the Society Islands of French Polynesia. It lies in the central South Pacific Ocean, about 165 miles (265 km) northwest of Tahiti. The mountainous island, some 6 miles (10 km) long and 2.5 miles (4 km) wide, has Mount Otemanu

chromatography: Subsequent developments: In 1959 Per Flodin and Jerker Porath in Sweden developed cellulose polymeric materials that acted as molecular sieves for substances dispersed in liquids. This extended the molecular weight range of chromatography to polypeptides, proteins, and high-molecular-weight polymers. The generic term for such separations is size-exclusion chromatography.

Porbandar, city, western Gujarat state, western India. It is situated in the western part of the Kathiawar Peninsula on the Arabian Sea coast. Porbandar was controlled by the Jethwa Rajputs from about the 16th century. It was the capital of the former princely state of Porbandar (1785–1948) before

porbeagle, species of mackerel shark

salmon shark, (Lamna ditropis), species of mackerel shark (Lamnidae) whose geographic range spans the entirety of the North Pacific Ocean. Salmon sharks are found primarily in the waters near the coasts of Japan, North Korea, and South Korea, from the Sea of Okhotsk to the Bering Sea, and southward

Colombia: Relief: …deep transverse cleft of the Porce River, which occupies the U-shaped valley in which is situated the expanding metropolis of Medellín, Colombia’s second city. The batholith contains gold-bearing quartz veins, which were the source of the placer gravels that gave rise to an active colonial mining economy. Beyond Antioquia the…

porcelain, vitrified pottery with a white, fine-grained body that is usually translucent, as distinguished from earthenware, which is porous, opaque, and coarser. The distinction between porcelain and stoneware, the other class of vitrified pottery material, is less clear. In China, porcelain is

porcelain enamelling, process of fusing a thin layer of glass to a metal object to prevent corrosion and enhance its beauty. Porcelain-enamelled iron is used extensively for such articles as kitchen pots and pans, bathtubs, refrigerators, chemical and food tanks, and equipment for meat markets. In

Capodimonte porcelain: …factory is the Rococo “Porcelain Room” originally at the Villa Reale at Portici but moved to the Palazzo of Capodimonte in 1805. Executed between 1757 and 1759, it is still intact except for a chandelier destroyed in World War II. Gricci and Fischer were principally responsible for the room,…

bioceramics: Dental ceramics: …crowns and inlays—are made of porcelain-fused-to-metal (PFM) cermets. These consist of a cast metal substrate, a metal oxide adhesion layer, and several layers of porcelain. The porcelain hides the metal while providing translucency and colour. It must be thermally compatible with the metal to stand up to the multiple firing…

Meissen porcelain, German hard-paste, or true, porcelain produced at the Meissen factory, near Dresden in Saxony (now Germany), from 1710 until the present day. It was the first successfully produced true porcelain in Europe and dominated the style of European porcelain manufactured until about

porcellanite, hard, dense rock that takes its name from its resemblance to unglazed porcelain. Frequently porcellanite is an impure variety of chert containing clay and calcareous matter; when of this nature it is composed chiefly of silica (see chert and flint). The porcellanite of some

Annonaceae: Major genera and species: A South American tree, Porcelia saffordiana, bears immense fruits sometimes weighing 18 kg (40 pounds) or more.

porcellanite, hard, dense rock that takes its name from its resemblance to unglazed porcelain. Frequently porcellanite is an impure variety of chert containing clay and calcareous matter; when of this nature it is composed chiefly of silica (see chert and flint). The porcellanite of some

porch, roofed structure, usually open at the sides, projecting from the face of a building and used to protect the entrance. It is also known in the United States as a veranda and is sometimes referred to as a portico. A loggia may also serve as a porch. There is little material evidence of the

George Edward Stanhope Molyneux Herbert, 5th earl of Carnarvon was a British Egyptologist who was the patron and associate of archaeologist Howard Carter in the discovery of the tomb of King Tutankhamen. Carnarvon was educated at Eton and at Trinity College, Cambridge. He began excavations in

Sergius IV was the pope from 1009 to 1012. He became bishop of Albano, Papal States, about 1004. Elected to succeed Pope John XVIII, he was consecrated on July 31, 1009; he changed his name from Peter to Sergius out of deference to the first pope. He was powerless in the hands of the Roman nobles

ancient Rome: Citizenship and politics in the middle republic: A series of Porcian laws were passed to protect citizens from summary execution or scourging, asserting the citizen’s right of appeal to the assembly (ius provocationis). A descendant of the Porcian clan later advertised these laws on coins as a victory for freedom. Moreover, the massive annual war…

meat processing: PSE meat: A genetic condition known as porcine stress syndrome (PSS) may increase the likelihood that a pig will yield PSE meat.

Andes Mountains: Physiography of the Central Andes: …are much lower, as at Porculla Pass (7,000 feet) east of Piura.

porcupine, any of several species of large, herbivorous, quill-bearing rodents active from early evening to dawn. All have short stocky legs, but their tails range from short to long, some being prehensile. The quills, or spines, take various forms depending on the species, but all are modified

porcupine fish, any of the spiny, shallow-water fishes of the family Diodontidae, found in seas around the world, especially the species Diodon hystrix. They are related to the puffers and, like them, can inflate their bodies when provoked. Porcupine fishes are short and broad-bodied, with large

Porcupine River, major tributary of the Yukon River, in northern Yukon, Can., and northeastern Alaska, U.S. Discovered in 1842 by John Bell of the Hudson’s Bay Company, the Porcupine rises in the Mackenzie Mountains of west central Yukon and flows for 448 mi (721 km) in a great arc, first north and

coconut palm: Uses: …as a cabinet wood called porcupine wood.

Stephen Dobyns: 1966–1992 (1994), Common Carnage (1996), The Porcupine’s Kisses (2002), Winter’s Journey (2010), and The Day’s Last Light Reddens the Leaves of the Copper Beech (2016).

William Cobbett was an English popular journalist who played an important political role as a champion of traditional rural England against the changes wrought by the Industrial Revolution. His father was a small farmer and innkeeper. Cobbett’s memories of his early life were pleasant, and,

rodent: Evolution and classification: Suborder Hystricognatha (porcupine-like rodents) 16 extant families (8 extinct families containing 26 genera). Late Eocene to present. Family Echimyidae (American spiny rats) 71 species in 17 genera, 21 extinct genera. Late Oligocene to present in South America, Pleistocene to present in

Pordenone was a High Renaissance Italian painter chiefly known for his frescoes of religious subjects. Pordenone was a pupil of Pellegrino da S. Daniele and other Friulian masters, but his early style is founded on Venetian models and in particular on Andrea Mantegna. Later he was influenced by

Pordenone, city, Friuli–Venezia Giulia regione, northeastern Italy. It lies along a small tributary of the Meduna River, southwest of Udine. Originating as the Roman and medieval river port of Portus Naonis, it was a bulwark of the Trevisani in their war against Aquileia until it was destroyed by

coal: Porosity: …part by the presence of pores that persist throughout coalification. Measurement of pore sizes and pore distribution is difficult; however, there appear to be three size ranges of pores: (1) macropores (diameter greater than 50 nanometres), (2) mesopores (diameter 2 to 50 nanometres), and (3) micropores (diameter less than 2…

Polyporales, large order of pore fungi within the phylum Basidiomycota (kingdom Fungi). The 2,300 known species have conspicuous sporophores (fruiting bodies), sometimes mushroomlike, the spore-bearing layer (hymenium) appearing either tube-shaped, gill-like, rough, smooth, or convoluted. Many

permafrost: Types of ground ice: …into five main types: (1) pore ice, (2) segregated, or Taber, ice, (3) foliated, or wedge, ice, (4) pingo ice, and (5) buried ice.

chemoreception: Terrestrial vertebrates: …each eye is a small pore leading to a sac that contains a tentacle. The tentacle can be extended through the pore by hydrostatic pressure to make contact with the surrounding soil. A duct connects the tentacular sac with the vomeronasal organ, and it is believed that this is the…

rock: Rock mechanics: …and internal (pore), due to pressure exerted by pore fluids contained in void space in the rock. Directed applied stress, such as compression, tension, and shear, is studied, as are the effects of increased temperature introduced with depth in the Earth’s crust. The effects of the duration of time and…

plant: Annotated classification: …9,000 species; representative genera include Porella, Frullania, Marchantia, Conocephalum, and Riccia. Division Lycophyta (club mosses,

cephalic disorder: Porencephaly: Porencephaly occurs when CSF-filled cysts or cavities form in the cerebral hemispheres. The condition is very rare and can manifest before birth, when caused by inherited defects in brain development in the prenatal period, or after birth, by destruction of brain tissue by stroke…

Beguines: …the most remarkable Beguines was Marguerite Porete, who was burned for heresy in Paris in 1310. Her mystical work Miroir des simples âmes (c. 1300; The Mirror of Simple Souls) is thought to be the greatest religious tract written in Old French.

history of logic: Other 19th-century logicians: Bobyin (1886) and Platon Sergeevich Poretsky (1884) initiated a school of algebraic logic. In the United Kingdom a vast amount of work on formal and symbolic logic was published in the best philosophical journals from 1870 until 1910. This includes work by William Stanley Jevons, whose intensional logic…

Porfiriato, the period of Porfirio Díaz’s presidency of Mexico (1876–80; 1884–1911), an era of dictatorial rule accomplished through a combination of consensus and repression during which the country underwent extensive modernization but political liberties were limited and the free press was

DuBose Heyward: …and poet whose first novel, Porgy (1925), was the basis for a highly successful play, an opera, and a motion picture.

porgy, any of about 100 species of marine fishes of the family Sparidae (order Perciformes). Porgies, sometimes called sea breams, are typically high-backed snapper- or grunt-like fishes. They have a single dorsal fin, and their small mouths, equipped with strong teeth, can handle a diet of fishes

Porgy and Bess, dramatic folk opera in three acts by George Gershwin. Its English libretto was written by DuBose Heyward (with lyrics by Heyward and Ira Gershwin), based on Heyward’s novel Porgy (1925). The opera—which premiered at the Alvin Theatre in New York City on October 10, 1935—is

Gil Evans: …densely textured Miles Ahead (1957), Porgy and Bess (1958), and Sketches of Spain (1960), all arranged by Evans. The albums “rank with the finest orchestral music of the 20th century,” according to jazz scholar Ian Carr, and Evans’s arrangements were praised as having

Pearl Bailey: …films—among them, Carmen Jones (1954), Porgy and Bess (1959), and All the Fine Young Cannibals (1960). In the 1960s she returned almost exclusively to nightclub work. Her most memorable stage role was as matchmaker Dolly Gallagher Levi in an all-black production of the musical Hello, Dolly!, first on Broadway (1967–69),…

Pori, city, southwestern Finland. It lies along the Kokemäen River near the Gulf of Bothnia, north-northwest of Turku. Originally settled in the 12th century farther up the Kokemäen and chartered as Ulvila in 1365, it was moved to its present site in 1558. It was destroyed by fire in the 16th and

fungus: Structure of the thallus: …pore fungus also known as tuckahoe, may reach a diameter of 20 to 25 cm (8 to 10 inches).

paracanthopterygian: Life cycle and reproduction: …be sexual attractants in the midshipman (Porichthys)—so named because the organs resemble rows of bright buttons on a naval uniform. The northern midshipman (P. notatus), a common species on the eastern Pacific coast, spawns in shallow water, attaching its eggs to a rocky surface. The male guards the eggs. Like…

paracanthopterygian: Life cycle and reproduction: The northern midshipman (P. notatus), a common species on the eastern Pacific coast, spawns in shallow water, attaching its eggs to a rocky surface. The male guards the eggs. Like other batrachoidiforms, the midshipman lives and grows on the ocean bottom.

sponge, any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more. The members of one

sponge, any of the primitive multicellular aquatic animals that constitute the phylum Porifera. They number approximately 5,000 described species and inhabit all seas, where they occur attached to surfaces from the intertidal zone to depths of 8,500 metres (29,000 feet) or more. The members of one

John Crome: …his most important works are The Poringland Oak (c. 1818–20), Slate Quarries (c. 1805), and Moonlight on the Yare (1817). Among his many etchings is the representative series entitled Norfolk Picturesque Scenery (1834).

Porirua, city, southern North Island, New Zealand. It is located about 13 miles (21 km) north of Wellington (the national capital), at the head of Porirua Harbour. The earliest inhabitants were aboriginal moa hunters in the 12th century. European whalers and traders occupied nearby Mana Island from

Pappus of Alexandria: …his commentary on Euclid’s lost Porisms in Book 7 was a subject of living interest for Jean-Victor Poncelet (1788–1867) and Michel Chasles (1793–1880) in their development of projective geometry.

pork, flesh of hogs, usually slaughtered between the ages of six months and one year. The most desirable pork is grayish pink in colour, firm and fine-grained, well-marbled, and covered with an outer layer of firm white fat. About 30 percent of the meat is consumed as cooked fresh meat; the

Lewis Milestone: Later work: He subsequently filmed Pork Chop Hill (1959), a hard-boiled Korean War movie with a cast headed by Gregory Peck, Rip Torn, George Peppard, and Woody Strode. Next was the heist film Ocean’s Eleven (1960), which starred, among others, the “Rat Pack”:

tapeworm: The pork tapeworm (Taenia solium, or Taeniarhynchus solium), found wherever raw pork is eaten, lives in the human intestine in its adult stage. Each proglottid, following fertilization, may contain as many as 40,000 embryos encased in separate capsules. If the embryos, which pass out with the…

John McCain: Political career: …of global warming), reduction of pork-barrel government spending, regressive tax cuts, and the political power of religious conservatives, McCain stood out. His critics claimed that his contrarian stance was calculated and mostly for show and that the favourable impression it made inside the news media far outweighed the political risks.…

grunt: …cm (15 inches) long; the porkfish (Anisotremus virginicus), a western Atlantic reef fish that, when young, is marked with black and serves as a “cleaner,” picking parasites off larger fishes; several species of sweetlips (Plectorhynchus), which are Indo-Pacific fishes, highly variable in colouring and sometimes kept in marine aquariums; and…

Cincinnati, city, seat of Hamilton county, southwestern Ohio, U.S. It lies along the Ohio River opposite the suburbs of Covington and Newport, Kentucky, 15 miles (24 km) east of the Indiana border and about 50 miles (80 km) southwest of Dayton. Cincinnati is Ohio’s third largest city, after

porkpie, round hat with a turned-up brim and a flat crown. The porkpie, so called because of its shape, became popular with both men and women in the mid-19th century, though a similarly shaped hat had been worn in the European Middle Ages. In the 19th century the porkpie worn by men sometimes had

Bugs Bunny: …such as Daffy Duck and Porky Pig, and his most frequent nemeses are Elmer Fudd and Yosemite Sam. Classic Bugs cartoons include Hare Tonic (1945), The Big Snooze (1946), Hair-Raising Hare (1946), Buccaneer Bunny (1948), Mississippi Hare (1949), Mutiny on the Bunny (1950), What’s Up, Doc? (1950), The Rabbit of…