Positive numbers are commonly defined as numbers greater than zero, the numbers to the right of zero on the number line. Zero is not a positive number. The opposite, or additive inverse, of a positive number is a negative number. Negative numbers are always preceded by a negative sign (-), while positive numbers are only preceded by a positive sign (+) when it is required to avoid confusion. Thus …
The history of positivism falls into two nearly independent stages: nineteenth-century French and twentieth-century Germanic, which became the logical positivism or logical empiricism of the Vienna Circle that, in turn, enjoyed an American phase. In the postmodern world, "positivist" is often a term of abuse, but historical research now contests the received characterization. In a br…
Positron emission tomography (PET) is a scanning technique used in conjunction with small amounts of radiolabeled compounds to visualize brain anatomy and function. PET was the first scanning method to provide information on brain function as well as anatomy. This information includes data on blood flow, oxygen consumption, glucose metabolism, and concentrations of various molecules in brain tissu…
Postcolonial studies designates a broad, multidisciplinary field of study that includes practitioners from literary, cultural, and media studies, history, geography, art history, philosophy, anthropology, sociology, and political economy. Postcolonial studies is the analysis of the phenomenon of imperialism and its aftermath: slavery, colonialism, nationalism, independence, and migration. Its ecle…
Postcolonial theory, often said to begin with the work of Edward W. Said, Gayatri Chakravorty Spivak, and Homi K. Bhabha, looks at literature and society from two broad angles: how the writer, artist, cultural worker, and his or her context reflects a colonial past, and how they survive and carve out a new way of creating and understanding the world. One of the earliest critical works to present t…
Few terms in the contemporary critical lexicon have been as vociferously debated and as persistently unstable in meaning and use as postmodernism and its various avatars, such as postmodernity. In spite of this instability, postmodernity may be defined as a broad category designating the culture that historically extends from the late 1960s to the early twenty-first century, and that is economical…
A postulate is an assumption, that is, a proposition or statement, that is assumed to be true without any proof. Postulates are the fundamental propositions used to prove other statements known as theorems. Once a theorem has been proven it is may be used in the proof of other theorems. In this way, an entire branch of mathematics can be built up from a few postulates. Postulate is synonymous with…
There have been many industrial applications of potassium aluminum sulfate. It is an important part of many products created by the pharmaceutical, cosmetic, and food industries because of its astringency property. It is also used in the manufacture of paper, dyes, glue, and explosives. Additionally, it helps in the water purification process, is used to speed up the hardening of concrete and plas…
The potato is a starchy, red or brown skinned, underground stem called a tuber. Tubers are storage areas for nutrient reserves of plants, such as starch or sugars. A widely cultivated species, the potato plant has the scientific name Solanum tuberosum and is a member of the nightshade family of plants, Solanaceae. Potato plants are widely grown for their familiar edible tubers that are a mainstay …
Man first began making pots at the end of the Stone Age (Neolithic Period), about 12,000 years ago in the Old World, and about 5,000 years ago in the New World. Basketry, including clay-lined baskets, probably served adequately for food storage for awhile. It may have been the accidental burning of a clay-lined basket that led to the discovery that clay, which is malleable when wet, becomes hard a…
Practices are actions or activities that are repeatable, regular, and recognizable in a given cultural context. In everyday language, practice is often contrasted with theory, ideas, or mental processes: what is done as opposed to what is thought, the pragmatic as opposed to the ideational. Practices may be discursive (practices that communicate meanings through language), visual (practices that c…
Pragmatism is the collective name for a family of theories emphasizing the practical consequences of holding a belief as a means to evaluating the truth of that belief. This focus on the practical was born of attempts to evade or escape many of the traditional metaphysical and epistemological puzzles and problems of traditional Western philosophy. Rather than continuing to deploy philosophical tal…
A prairie is a natural vegetation type in which perennial herbaceous plants predominate, particularly species of grasses. The word "prairie" comes from the French prérie (later, prairie), meaning meadow. The term was first applied to the swath of mid-continental North American grassland in the 1600s by French Jesuit missionaries and explorers, because the landscape resembled, …
Prairie chickens are two North American species of birds in the grouse family (Phasianidae) in the order Galliformes, the game birds. Both the greater prairie chicken (Tympanuchus cupido) and the lesser prairie chicken (T. pallidicinctus) are brownish birds with a black band on the end of the tail. Male birds have colorful air sacs that are inflated during courtship and a ruff of long feathers tha…
Falcons are very swift birds of prey that hunt during the day. Falcons are in the family Falconidae, of which there are 39 species, all in the genus Falco. The prairie falcon (Falco mexicanus) is a medium-sized, light-brown falcon that breeds in wide-open, semiarid and prairie habitats in the western United States, southwestern Canada, and northern Mexico. Prairie falcons generally breed in the vi…
The praying mantis (plural praying mantids) is a carnivorous insects of the order Mantoidea (or Mantodea) named for its typical stance of an upright body with the two front legs held out in a pose of prayer. The long, thick, spiny, legs and the markedly triangular head with two large compound eyes make the mantis one of the most readily identifiable of all insects. The long neck of the praying man…
Knowledge about pre-Columbian civilizations comes from two main sources: archaeological remains and the accounts written by European men. The latter include a first group of explorers who described the alien worlds they encountered (and destroyed), and a second group of priests, scholars, and administrators who interviewed the survivors who remembered the past, and later their descendants, who ret…
The precession of the equinoxes (sometimes simply called precession), is a movement of the celestial equator, the projection of the earth's equator into space, with respect to the fixed stars and the ecliptic, the path of the Sun's motion in space as viewed from the earth. These two great circles in space are inclined to one another by an angle of approximately 23.5°, called t…
Gold, silver, and platinum have historically been valued for their beauty and rarity. They are the precious metals. Platinum usually costs slightly more than gold, and both metals are about 80 times more costly than silver. Precious metal weights are given in Troy ounces (named for Troyes, France, known for its fairs during the Middle Ages) a unit approximately 10% larger than 1 oz (28.35 g). The …
A predator is an organism that hunts and eats its prey. All predators are heterotrophs, meaning they must consume the tissues of other organisms to fuel their own growth and reproduction. The most common use of the term is to describe the many types of carnivorous animals that catch, kill, and eat other animals. There is a great diversity of such predatory animals, ranging in size from small arthr…
A major arena for the pursuit of prehistory ante literam was the study of cultural history (Kulturgeschichte), especially in the work of authors like Herder, Gustav Klemm, Friedrich Hellwald, and Gustav Kolb. It was in the later nineteenth century, however, that such efforts produced the modern discipline of "prehistory," a neologism self-consciously coined by Daniel Wilson in 1851. …
The concept of prejudice emerged during the early twentieth century and soon became the most prominent social scientific and lay concept to describe antipathy for others based on their social group or category membership. Social scientists have typically defined prejudice as a negative intergroup attitude. Many, however, have added the rider that this negative intergroup attitude is bad or unjusti…
Prenatal surgery, also called fetal surgery, is medical treatment of the fetus before birth, while it is still in the womb. Most fetal therapies are "closed" procedures, performed without opening the womb. The rarest type of fetal surgery is known as "open surgery," in which the mother's abdomen and uterus are cut open to reveal the tiny fetus. When doctors began…
Pressure is the amount of force applied to a given area. Acrobats and cheerleaders sometimes stand on each other's shoulders to form a human tower. Even with perfect balance, there is a limit to how high such a tower can be built. Ultimately, the ability of the bottom person to bear the pressure, caused by the weight of all the people stacked above, is the limiting factor. Pressure, then, i…
Prey refers to any living entities that are hunted and consumed by predators. Usually the term is used in reference to animals that are stalked, killed, and consumed by other animals, as when a deer is killed by a mountain lion. However, plants may also be considered to be the prey of herbivorous animals, and hosts may be considered the prey of their parasites. Often, predators are important sourc…
Primates are an order of mammals. Most primates are characterized by well-developed binocular vision, a flattened, forward-oriented face, prehensile digits, opposable thumbs (sometimes the first and second digits on the feet are also opposable), five functional digits on the feet, nails on the tips of the digits (instead of claws), a clavicle (or collarbone), a shoulder joint allowing free movemen…
Primroses are perennial, herbaceous plants in the genus Primula, family Primulaceae. There are about 500 species of primroses. Most of these occur in arctic, boreal, and cool-temperate climates, including mountain-tops in tropical latitudes. The greatest species numbers occur Bloom of the shooting star, a member of the primrose family. Photograph by Robert J. Huffman. Field Mark Publications. R…
The term prion (derived from "proteinaceous infectious particle") refers to an infectious agent consisting of a tiny protein that lacks genes, but can proliferate inside the host, causing slowly developing neurodegenerative diseases in animals and humans. Prions are thought to cause several diseases that attack the brain, such as Creutzfeldt-Jakob disease in humans, scrapie in sheep,…
In Euclidean geometry, a prism is a three dimensional figure, or solid, having five or more faces, each of which is a polygon. Polygons, in turn, consist of any number of straight line segments, arranged to form a flat, closed, two-dimensional figure. Thus, triangles, rectangles, pentagons, hexagons, and so on are all polygons. In addition, a prism has at least two congruent (same size and shape) …
The volume of studies on privacy has increased tremendously since the 1970s, especially in the United States, and their geographical spread has become wider. These studies address new topics, including celebrity privacy for political and other public figures and privacy rights in international human rights law. Developments in advanced technology, such as electronic storage and DNA testing, have a…
The American economist Steve Hanke defines privatization as "the transfer of assets and service functions from public to private hands. It includes, therefore, activities that range from selling state-owned enterprises to contracting out public services with private contractors" (p. 4). At one extreme, privatization might entail the wholesale transfer to the private sector of both ow…
"Probability is the very guide of life," Bishop Butler wrote in 1736. Probability judgments of the efficacy and side effects of a pharmaceutical drug determine whether it is approved for release to the public. The outcome of a civil trial hinges on the jurors' opinions about the probabilistic weight of evidence. Geologists calculate the probability that an earthquake of a cert…
The proboscis monkey (Nasalis larvatus) of Borneo belongs to the primate family Cercopithecidae. It is grouped with the langurs, leaf monkeys, and colobus monkeys in the subfamily Colobinae. The feature that gives this odd-looking monkey its common name is the large, tongue-shaped nose of the adult male. This nose can be as much as 4 in (10 cm) long. It sometimes hangs down over the mouth, but ext…
The idea of progress—the idea that human society can be made ever better by conscious effort, or that society is becoming ever better by spontaneous laws of history—is relatively new. The idea was virtually unknown in classical antiquity. In each of the three greatest books of that period, what we think of as progress is explicitly denied. In Plato's Republic, even the best po…
Projective geometry is the study of geometric properties which are not changed by a projective transformation. A projective transformation is one that occurs when: points on one line are projected onto another line; points in a plane are projected onto another plane; or points in space are projected onto a plane, etc. Projections can be parallel or central. For example, the Sun shining behind a pe…
Prokaryotes are single-celled organisms such as bacteria that have no distinct nucleus. In addition to the lack of a nucleus, prokaryotes lack many of the other small organelles found in the larger eukaryotic cells. A typical prokaryote is bound by a plasma membrane and a cell wall. Within this double boundary, the fluid material inside the cell (the cytoplasm) is studded with small, rounded bodie…
The pronghorn antelope (Antilocapra americana) is a species of ruminant that is the sole living representative of its family, the Antilocapridae. This family was much more diverse during the Pliocene and early to mid-Pleistocene periods. The Antilocapridae is an exclusively North American family, and pronghorns are not closely related to the true antelopes, which are members of the Bovidae, a …
A proof is a logical argument demonstrating that a specific statement, proposition, or mathematical formula is true. It consists of a set of assumptions, or premises, which are combined according to logical rules, to establish a valid conclusion. This validation can be achieved by direct proof that verifies the conclusion is true, or by indirect proof that establishes that it cannot be false. Each…
Since the twentieth century, propaganda has largely had pejorative associations. The term continues to imply something sinister; synonyms for propaganda frequently include lies, falsehood, deceit, and brainwashing. In recent years unfavorable references have been made to "spin doctors" and the manner in which "propaganda" has devalued democratic politics. The psychologi…