Two families of rodents are called porcupines. They all have at least some hair modified into quills. The Old World porcupines belong to family Hystricidae of Europe, Asia, and Africa. The New World porcupines are 10 species of forest dwellers of the family Erethizontidae. The most common of these is the North American porcupine (Erthizon dorsatum). The name porcupine means "quill pig,�…
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 …
A principle feature of Platonism, which refers to the doctrines or philosophies influenced by Plato, is the belief in the existence of a distinction between the world that appears to the senses and a real realm that can be grasped only by the intellect. This latter realm contains the transcendental Ideas or Forms which, although existing independently of both the empirical world and human consciou…
Pluralism derives from the Latin plures, meaning "several" or "many," and it has formed the central concern of various intellectual traditions throughout the history of the West. Applied in philosophy, political theory, religion, and ethnic and racial relations, pluralism challenges the notion that a single authority or group must dominate all others. Rather than accept…
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…
As a science of interpretation, poetics has consistently been concerned with delineating its proper field of study ("What is a poetic text?") and then subdividing it into genres ("What kind of poetic text is under consideration and what interpretive approaches does it select?"). Although classical writers on the subject of literary types failed to formulate a comprehens…
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…
The word political derives from a Latin cognate (politicus) of the original Greek adjective politikos, which is also sometimes employed as a masculine noun to signify a public official or statesman. …
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…
Radio waves are a form of electromagnetic radiation with long wavelengths and low frequencies. The radio section of the electromagnetic spectrum covers a fairly wide band and includes waves with frequencies ranging from about 10 kilohertz to about 60,000 megahertz (which correspond to wavelengths between 98,000 ft, or 30,000 m, and 0.2 in, or 0.5 cm). The commercial value of radio waves as a means…
Protests disrupt the peace, stop business as usual, and cause disquiet. Protesters in effect withdraw their consent to the way things are. Even if people are poor, unemployed, or seemingly without power, when organized together they can become a force that troubles the powerful. When the powerful are inconvenienced (or worse) by sit-ins, strikes, marches, and occupations, they will often negotiate…
In the nineteenth century, prominent scientists such as Charles Lyell, Charles Darwin, Sir William Thomson (Lord Kelvin), and Thomas Huxley, were in continual debate about the age of the earth. The discovery of the radioactive properties of uranium in 1896 by Henri Becquerel subsequently revolutionized the way scientists measured the age of artifacts and supported the theory that the earth was con…
Political science, as currently conceived, is a relatively new concept that dates to the nineteenth-century United States. Prior to this time, the study of politics in the West remained a part of natural philosophy, and it tended to focus on philosophical, historical, and institutional approaches. The ancient Greek philosopher Aristotle is often named as the first "political scientist,�…
The nucleus of each atom has a specific number of protons and neutrons and is either stable or unstable, depending on the relative number of each. The most stable atoms are those that have an equal number of protons and neutrons. Atoms that are unstable are radioactive. An atom that is radioactive can also be called a radionuclide. Of the known nuclides (approximately 2,000), only 264 are stable, …
The concept of polytheism was a creation of the Enlightenment. Before then, Europeans had characterized the religious universe in terms of Christianity, Judaism, paganism, and (eventually) Islam. As late as the sixteenth century, the Franciscan friar Bernardino de Sahagun, in his remarkably detailed and sensitive account of pre-Columbian Mexican religion and culture, equated various Aztec diviniti…
Perceptions of the meaning, implications, and control of reproduction and sexuality, at both the individual and community levels, are among the most important, but also the most challenging, in the history of ideas. Changes in human population helped shape the twentieth century and are creating new tensions in the twenty-first, but, despite the profound significance of childbearing to individuals …
If the term populism was initially borrowed from radical farmers' movements in the United States in the late nineteenth century to describe early-twentieth-century political developments in Latin America, since then it has certainly acquired a special relevance for understanding this region's politics. The golden era for Latin American populism is usually cited as the 1930s to the 19…
Potassium nitrate, also known as saltpeter or niter, is a chemical compound consisting of potassium, nitrogen, and oxygen. While it has many applications, including use as a fertilizer, its most important usage historically has been as a component of gunpowder. Over time its use as an explosive has been made nearly obsolete by dynamite and TNT, but it is still used today in artilleryshell primers,…
Populism (from the Latin term populus, usually translated as "the people") is the name of a group of ideologies that stresses the need for a more equitable distribution of economic, political, and cultural power. Populists argue that an elite of some form or another holds an unfair concentration of political and economic power and typically that government intervention is required to…
Rates of evolution change vary widely over time, among characteristics, and among species. Evolutionary change can be estimated by examining fossils and species that are related to each other. The rate of change is governed by the life span of the species under examination, short-lived species are capable of changing more quickly than those that have a longer life span and reproduce less often. Ye…
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 …
Radioactive fallout is material produced by a nuclear explosion or a nuclear reactor accident that enters the atmosphere and eventually falls to Earth. This fallout consists of minute, radioactive particles of dust, soil, and other debris. While some fallout results from natural sources, the term is usually used in reference to radioactive particles that were released into the atmosphere by a nucl…
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…
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…
Fluids such as water or air exert pressure in all directions and the amount of pressure depends on the depth of the fluid. The pressure on the bottom of an object immersed in a fluid will be greater than the pressure on the top of the object. The imbalance of pressure acting on the object creates an upward force called the buoyant force. If the buoyant force is greater than the weight of the objec…
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…
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…
As an idea, poverty has had an eventful history. From roughly the eighteenth century onward, a change in moral sensibility caused a shift in the understanding of poverty as being an ideal state (for both individuals and communities) to being an execrable condition that societies should seek to ameliorate. In the twentieth and twenty-first centuries, with the growth of social welfare programs, int…
In its most general sense, power refers to the capacity to have an effect. A powerful hurricane comes ashore uprooting trees and destroying houses; the power of music stirs our emotions; the power of love makes gentle the surly man or woman. We speak of electric or wind power, of powerful machines or human bodies. Many different phenomena with a very wide range of effects are said to be or to hav…
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…
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, …
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…
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…
Certain atoms are radioactive, meaning they emit radioactivity during spontaneous transformation from an unstable isotope to a more stable one. Radioactive pollution results from contamination of the environment with such substances, which may represent a significant health risk to humans and other organisms. Radioactive pollution differs from conventional pollution in that it cannot be detoxified…
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…
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…
Prairie dogs, or barking squirrels, are ground-dwelling herbivores in the genus Cynomys, in the squirrel family Sciuridae, order Rodentia. Prairie dogs are closely related to the ground squirrels, gophers, and marmots. Prairie dogs are widespread and familiar animals of the open, arid prairies, grasslands, and some agricultural landscapes of the western regions of North America. …
Presentism is a neologism coined to identify today's preoccupation with the present age as the essential temporal referent in historical interpretation. (One notes that the term does not appear in the earlier edition of this Dictionary.) As a perspective on the meaning of historical time, it accords the present a privileged status. Presentism therefore stands as a counterpoint to the histor…
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 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 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…
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…
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…
Radioactive tracers are substances labeled with a radioactive atom to allow easier detection and measurement. They have applications in many fields, but we will focus on their use in medicine. …
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…
"There is nothing which so generally strikes the imagination, and engages the affections of mankind, as the right of property; or that sole and despotic dominion which one man claims and exercises over the external things of the world, in total exclusion of the right of any other individual in the universe" (p. 2). So wrote Sir William Blackstone (1723–1780), the great English…
The root of the English word prophecy is derived from the Greek prophēteia, Latin prophetia. The root of prophēteia is derived from prophēmi, which means to speak before or for someone or something. A cognate Greek word is prophētazō, which indicates the reception of the gift of interpreting the will of the gods—that is, the gift of prophecy. The gift of prophe…
Protest, in the context of this entry, is understood as more or less public visual dissent from an official governmental authority or from customs sanctioned socially by the dominant classes. The protesting voice may be that of a minority or a majority but is here defined, following historiographical and ethical norms, as being directed toward "good causes": democracy, civil rights, …
Pseudoscience is a term applied to a field of inquiry by critics claiming that it is a pretended or spurious science because it does not meet established standards. The term pseudoscience is reserved for fields that claim to be a science, that make claims about the world and give explanations of natural processes. Statements of personal values or beliefs are neither scientific nor pseudoscientific…
In a 1928 entry on the subject for the Handwörterbuch der Sexualwissenschaft (Concise dictionary of sexual research), Sigmund Freud (1856–1939) defined psychoanalysis as "the name (1) of a procedure for the investigation of mental processes which are almost inaccessible in any other way, (2) of a method (based upon that investigation) for the treatment of neurotic disorders and …
Psychiatry in the United States has undergone a number of sweeping changes since the middle of the twentieth century. The settings in which psychiatrists practice, the range of diseases they seek to treat, their theoretical understandings of these diseases, and the treatments they apply are all radically different from those of their predecessors. These changes have had an impact not only on the p…
Radioactive waste is generated during the production of electricity by nuclear power plants, by the eventual disposal of those facilities, and during the manufacturing and disposal of nuclear weapons and machines used in medical diagnosis and treatments, academic and industrial research, and certain industrial applications. Radioactive waste produces ionizing radiation, which can damage or destroy…
The term public sphere is the English translation of the German term Öffentlichkeit. This term's significance in the late twentieth and early twenty-first century stems initially from its use in Jürgen Habermas's Strukturwandel der Öffentlichkeit (The structural transformation of the public sphere) in 1962. In spite of its foreign origin, the term public sphere actuall…
Radioisotopes are extensively used in nuclear medicine to allow physicians to explore bodily structures and functions in vivo (in the living body) with a minimum of invasion to the patient. Radioisotopes are also used in radiotherapy (radiation therapy) to treat some cancers and other medical conditions that require destruction of harmful cells. Radioisotopes, containing unstable combinations of p…
Punishment is best defined as an authorized agent or institution intentionally inflicting pain on an offender or depriving the offender of something in response to an offense or crime the offender is said to have committed. But definitions, however broad, need to be approached with caution, since it is impossible to perfectly capture the myriad constellations of social practices labeled punishment…
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 …
Puritanism is the set of religious beliefs and practices retroactively ascribed to Puritans by modern scholars. Since Puritan was originally a term of abuse toward people considered excessively, narrow-mindedly, or hypocritically religious, not an embraced identity, the definitions of both Puritan and Puritanism have been and remain inescapably vague. Roughly, we may take the term Puritans to refe…
The most central teaching of the Pythagorean school—that there is an underlying mathematical structure to the universe—is a foundational idea of Western civilization, particularly in the sciences. Because of this, the entire history of Western scientific and cosmological thought has been intertwined with Pythagorean ideas. Certainly many of the greatest physicists and mathematicians …
The German physicist Max Planck (1858–1947) introduced the quantum of action h (Planck's constant) into physics in his successful theory of blackbody radiation in 1900 and thus started quantum theory, one of several revolutionary discoveries that occurred in physics at the turn of the twentieth century. Others were Albert Einstein's (1879–1955) special theory of relativ…
Since the early 1990s, the term queer has been strategically taken up to signify a wide-ranging and unmethodical resistance to normative models of sex, gender, and sexuality. Although this use of queer marks a process of resignification as new meanings and values are associated with what was once a term of homophobic abuse, there is always an important sense in which queer maintains, even in chang…
The interrelated terms of race and racism should be examined separately before their connection is explored. This entry defines both terms and explores their meanings and new approaches to these concepts in the twenty-first century. …
To discuss race in Asia, race must first be defined. Changes in definitions of race over the centuries in the West make this difficult. The earliest uses of race in sixteenth-century Europe usually focused on differences arising from common ancestry, descent, or origin. These were perceived in kinship and lineage relationships, physiological differences, or even religious or mythical ancestors. Th…
Of the ideas that have appeared in Europe over the centuries, race remains one of the most politically charged and difficult to define. Almost all scholars agree that race is a social construction, signifying no actual or important human difference. Yet, no one would argue that racism, or the process of viewing human groups as defined by inherited differences and acting in such as way as to reinfo…
Asian America is a meaningful social construct in understanding and analyzing Western colonialism in Asia, and immigration policy and racial hierarchy in American society. As a group identity, Asian-American is an externally imposed label because it is based on race rather than culture. The most misleading reference to Asians is the term Oriental. Derogatory in nature, the term refers to people an…
Radiology is a branch of medical science that uses x rays and other forms of technology to image internal structures in the body. For nearly 80 years radiology was based primarily on the x ray, but since the 1970s several new imaging techniques have been developed. Some, like computed tomography, integrates x-ray and computer technology. Others, like ultrasound and magnetic resonance imaging are n…
Radix, the Latin word for root, is the origin of the word radical. In contemporary political philosophy, the term describes activists who challenge established views and who operate outside the parameters of social convention to achieve political aims, sometimes employing extreme or violent methods in that pursuit. The concept of political radicalism evolved out of the language and logic of the sc…
Radon (usually in the form of the radon-222 isotope) is a colorless and odorless radioactive gas formed from radioactive decay. Denoted by the atomic symbol, Rn. radon has an atomic number of 86 and the atomic weight of its most stable isotope is 222. It is a colorless, odorless gas that emits radioactivity. It is classified as a noble gas based on its location on the periodic table. Radon is the …
People constantly make choices or decisions in an uncertain world: should I buy life insurance, marry, change jobs? Rational decision making is an important topic in the social sciences, cognitive science, and philosophy, and for many years classical decision theory has dominated competing accounts of decision making. …
In the final section of the Critique of Pure Reason, Immanuel Kant distinguishes empiricism and rationalism: The School of Athens (1510–1511) by Raphael. In Raphael's fresco, Plato is pointing towards the heavens, indicating what he saw as the unchanging truths of knowledge, while Aristotle points downwards, symbolizing his belief that learning came from human experience. SCALA /…
In meteorology, precipitation is water in either solid or liquid form that falls in Earth's atmosphere. Major forms of precipitation include rain, snow, and hail. When air is lifted in the atmosphere, it expands and cools. Cool air cannot hold as much water in vapor form as warm air, and the condensation of vapor into droplets or ice crystals may eventually occur. If these droplets or cryst…
The question "Who read what—and how?" is fundamental to intellectual history. No idea can have a history until someone reads it somewhere, and its impact on society will depend on the readings of individual readers. It was inevitable, then, that the historiography of ideas would turn toward the historiography of reading. That trend picked up momentum in the 1980s, when postmod…
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…
Realism was a movement in nineteenth century Western culture that claimed to represent ordinary people and their everyday reality based on accurate observation. It challenged centuries of tradition when the highest art aspired to idealized pictorial forms and heroic subjects. Supporters considered its visual veracity to be an indication of an artist's "sincerity." Realism acqu…
Rails are small, shy, marshland birds in the family Rallidae, which includes about 129 species. This family has a worldwide distribution, occurring on all continents except Antarctica. Many species of rails occur only on certain remote, oceanic islands, where many of these isolated species have evolved a flightless condition because of the lack of predators. Unfortunately, this characteristic make…
Realism in Africa is often expressed as a concern with the authentic and full representation of African cognitive, experiential, historical, and cultural reality, focusing on the fundamental nature of African identity as expressed in its thought, art and culture. …
Water droplets and light form the basis of all rainbows, which are circular arcs of color with a common center. Because only water and light are required for rainbows, one will see them in rain, spray, or even fog. A raindrop acts like a prism and separates sunlight into its individual color components through refraction, as light will do when it passes from one medium to another. When the white l…
Aristotle relates that Socrates brought philosophy down from the heavens and into the cities of humans. More prosaically, Socrates invented the problem of practical reason by asking whether reasoning could guide action, and, raising the stakes, whether a life devoted to reasoning could be the best way to live. Aristotle closes the Ethics by ridiculing a too-close connection between reasoning and v…
Reflexivity first entered into anthropological discourse in the late 1970s in response to several problematics that had emerged in the previous decade, but its use in the humanities and in sociology has a longer history. In the words of Barbara Myerhoff and Jay Ruby, two of its advocates, reflexivity "describes the capacity of any system of signification to turn back on itself, to make itse…
Reform, from the Latin reformare, to recast or reshape, denotes the overhaul of an existing state or condition with a view to its improvement. Until the eighteenth century the terms reform and revolution were used interchangeably. In the wake of the French Revolution, however, they took on distinct meanings. Reform came to denote substantial change through an orderly and lawful process; revolution…
Contemporary Islamic reform movements often trace their roots to the founding era of Islam. Several verses of the Koran encourage reform (islah), and a statement of the prophet Muhammad predicts that a renewer (mujaddid) will arise in each century to reform the community of Muslims. Among the scholars cited by various reform movements as fulfilling this prediction are Abu Hamid Muhammad al-Ghazali…
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…
Rainforests are temperate or tropical forests, usually occurring as old-growth ecosystems. The world sustains many types of rainforests, which differ geographically in terms of their species composition and the environmental conditions in which they occur. However, the various rainforests have broad ecological similarities. A such, temperate and tropical rainforests are considered to represent bio…
The Reformation was a movement in Europe of the sixteenth and seventeenth centuries that broke the monopoly over religion held by the Roman Catholic Church since the later years of the Roman Empire and that created a new set of alternative Protestant churches that have henceforth helped supply the needs of Christians in Western Europe and in countries influenced by Europe. Each of these churches d…
The word "random" is used in mathematics much as it is in ordinary speech. A random number is one whose choice from a set of numbers is purely a matter of chance; a random walk is a sequence of steps whose direction after each step is a matter of chance; a random variable (in statistics) is one whose size depends on events which take place as a matter of chance. Random numbers and ot…
It would be difficult to find two people today—even two historians or political scientists—who would completely agree on the meaning of the phrase Eastern Europe. Unlike such phrases as Great Britain, the former Yugoslavia, or the Baltic states, Eastern Europe varies widely in what it denotes. The variation occurs in part because what the phrase denotes has changed frequently over ti…
Although relativism is most often associated with ethics, one can find defenses of relativism in virtually any area of philosophy. The following article first discusses the general structure of relativist positions and arguments. It then examines several influential ideas concerning relativism in the late twentieth century. Finally, it ends by considering the rise of relativism in one area outside…
The first thing to note about the theory of relativity is that there are two different theories of relativity, the special theory put forward in Albert Einstein's (1879–1955) famous 1905 paper, "On the Electrodynamics of Moving Bodies," and the general theory, completed in November 1915 and first presented systematically in a review article published in March 1916. Spec…
Prescribed fire involves the controlled burning of vegetation to achieve some desired management effect. Prescribed burns can be used to encourage a desired type of forest regeneration, to prevent the invasion of prairies by shrubs and trees, to decrease the abundance of pathogens, to prevent catastrophic wildfires by reducing the accumulation of fuel, or to create or maintain habitat for certain …
Rangeland is uncultivated land that is suitable for grazing and browsing animals. Rangeland is one of the major types of land in the world. (Other types are: forest, desert, farmland, pasture, and urban/industrial.) Rangelands are the principal source of forage for livestock, and they also provide habitat for a great variety of native plants and animals. Rangelands are also used by people for recr…
Like all items of culture, words have a history; meanings and usages change over time. So too, "religion," and the assumption that the world is neatly separated between religious and nonreligious spheres (i.e., Church/State), is a product of historical development and not a brute fact of social life. In the early twenty-first century, long after the modern usage of the word was first…
The modern academic study of indigenous African religions began with the publication of ethnographic, missionary, and travel monographs by Leo Frobenius, R. S. Rattray, H. A. Junod, W. C. Willoughby, Edwin Smith, E. E. Evans-Pritchard, John Middleton, Godfrey Liendhardt, Geoffrey Parrinder, and Marcel Griaule, among others. The African scholars Bolajii Idowu, John Mbiti, and Gabriel Setiloane also…
The term African-derived religions (ADR) is used to identify various religions transplanted to the Americas with the enslavement of Africans. For simplicity, ADR will be used in this entry to denote Afro-Caribbean and Afro-Brazilian religions, whose traditions survived cultural and ideological assault and continued to provide spiritual resources for a civilization rooted in African cosmologies. Wi…
Raptors, or birds of prey, are birds having the following three distinctive characteristics: strong grasping feet equipped with sharp talons, a hooked upper beak, and keen vision. Raptors are called birds of prey because these features allow them to be predators that hunt for their food. Many raptors are, in fact, predators. Some raptors actually hunt for and consume other birds. Other members of …
When speaking of religion in East and Southeast Asia, a series of unique problems arises. What the West views as religion in Asia might well pass as philosophy and vice versa. The Harper Collins Dictionary of Philosophy views religion as oscillating between two extremes: Hence, the philosophy of religion studies a variety of topics from existence of "god" and moral thought to the rel…
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…
Unlike Western systems of worship, religious thought and action from South American indigenous perspectives pervade every aspect of existence. As cultural systems, indigenous South American religions encompass quotidian life and become especially salient at times of life crises and during festival and protest activity. With more than three hundred languages grouped into a dozen or more macro famil…
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…
Religion is a system of beliefs that explains what happens in the world, justifies order, and (usually) prescribes certain behaviors. In Latin America, the Spanish and Portuguese imported and spread Catholicism, the predominant religion, starting with the voyages of Columbus in 1492. The belief in and practice of Christianity gradually replaced the native belief systems; at the beginning of the tw…
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…
The Arabian peninsula was one of the last places to accept monotheism, and it did so in a distinctive form that was to dominate the Middle East thereafter. From about 610 until 632 Muhammad, a caravan merchant in Mecca, received verbal messages that he and his followers understood to come from God and that were collected together to form the Koran, the Muslim scripture. The Koran is considered to …
Almost every culture in human history has had a religious framework. Almost every religion offers some form of cosmology, some account of the origin of the world and of humanity, and some sort of scientia, some wisdom about how to relate to the world. The reason why the interaction of religion and science has been of such interest since the mid–nineteenth century is that modern Western scie…
The rare gases, also known as the noble gases, are a group of six gaseous elements found in small amounts in the atmosphere: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). Collectively they make up about one percent of the earth's atmosphere. They were discovered by scientists around the turn of the century and because they were so unreactive were initially ca…
The modern African state system is a new political concept that came about from the struggle for independence. These states are organized in the matrix of the two great religious traditions: Islam and Christianity. The secular hegemonic nature of the founding of these states brings into play the political meaning of these religious traditions. Religion in Africa is projected as a part of a continu…
A prime number is any number greater than 1 that is divisible only by itself and 1. The only even prime number is 2, since all other even numbers are at least divisible by themselves, 1, and 2. …
The rare genotype advantage hypothesis asserts that genotypes (the set of genes (alleles) carried by an organism) that have been rare in the recent past should have particular advantages over common genotypes under certain new and challenging environmental conditions. Rare genotype advantage can be best illustrated by a host-parasite interaction. Successful parasites are those carrying genotypes t…
The historical division between religion and politics that leads to the problem of their proper ordering and relation emerges only in coincidence with the phenomenon of divine revelation, and hence only with the so-called Abrahamic religions of Judaism, Christianity, and Islam. Religions that rest on a direct relationship between individual human beings and a deity effectively circumvent the monop…
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…
A rate is a comparison of the change in one quantity, such as distance, temperature, weight, or time, to the change in a second quantity of this type. The comparison is often shown as a formula, a ratio, or a fraction, dividing the change in the first quantity by the change in the second quantity. When the changes being compared occur over a measurable period of time, their ratio determines an ave…
Church-state relations in Latin America since the arrival of the Spanish in 1492 and then the Portuguese can be discussed in four periods: (1) evangelicization and orthodoxy, 1492–c.1750, (2) the secular state, c.1750–1892, (3) Rerum Novarum, 1892 to 1962, and (4) Vatican II, 1962 on. The Roman Catholic Church has been the dominant religious institution and Catholics remain a majorit…
The ratio of a to b is a way to convey the idea of relative magnitude of two amounts. Thus if the number a is always twice the number b, we can say that the ratio of a to b is "2 to 1." This ratio is sometimes written 2:1. Today, however, it is more common to write a ratio as a fraction, in this case 2/1. At one time, ratios were in common use in solving problems and the terms …
The relationship between religious and political domains in Islam is extraordinarily complex and is rooted in a rich conceptual and a long (although conflicting) institutional tradition. Koranic verses clearly endorse the prophet Muhammad's spiritual and temporal authority. Muslims agree that he was the sole transmitter of the divine message, the most qualified person to decide the meaning …
Rational numbers are needed because there are many quantities or measures which natural numbers or integers alone will not adequately describe. Measurement of quantities, whether length, mass, or time, is the most common situation. Rational numbers are needed, for example, if a farmer produces and wants to sell part of a bushel of wheat or a workman needs part of a pound of copper. The reason that…
Citizens of the United States quite properly regard the ideas and practices relating religion to the state in their nation as being sharply distinguished from those that prevailed in Europe at the time of the national founding. The sources of these ideas were European as opposed to African, Asian, or Native American. They arrived in America through literary imports and in the minds of colonists ch…
Rationalization is a process applied most often to the denominators of fractions, such as 5/(1 + √+2). There are two reasons for this. If someone wanted to compute a rational approximation for such an expression, doing so would entail dividing by a many-place decimal, in this case 2.41421... With a calculator it would be easy to do, but if it must be done without a calculator, the process i…
The term Renaissance (English, French, German; rinascità in Italian) refers to (1) "a rebirth of arts and letters" noticed by authors and artists living between the 1300s and the 1600s; (2) Italian cultural history from about 1300 to 1520 ("La Rinascimento"), as in the period concept of Jacob Burckhardt's The Civilization of the Renaissance in Italy (1860); …
The fundamental physical properties of a gas are related to its temperature, pressure and volume. These properties can be described and predicted by a set of equations, known as the gas laws. While these laws were originally based on mathematical interpretations for an ideal or perfect gas, modern atomic and kinetic theory of gases has led to a modified expression that more accuratel…
Humans are surrounded by representations. Some of these occur naturally—for example, tree rings and footprints—while others are artificial—for example, words and photographs. Whatever their origins, all share a fundamental feature: they stand for something. Tree rings stand for the age of the tree; footprints stand for the entity that made them; a photograph stands for that wh…
Although in the early twenty-first century representative government is synonymous with democracy, the concept of political representation arose separately from the idea of the rule of the people. Broadly political representation refers to an arrangement whereby one is enabled to speak and act with authority in the behalf of some other. There are two issues that must be addressed in any theory of …
Republicanism advocates a government headed by commoners rather than a hereditary monarchy. It is similar to democracy in that it favors a representative form of government that receives its legitimacy from the people it rules, but democracy in theory also champions political, social, and economic equality. All of the Latin American countries (as well as the United States) are established as repub…
The term republic derives from the Latin phrase res publica ("matter" or "thing of the people"). Most generally, the word refers to any political regime in which no king or hereditary dynasty rules over subjects in a state of submission or servility. A republic is thus populated by "citizens" who enjoy some manner of political and legal rights to govern th…
The path of resistance has been neither straight nor narrow. First adopted by the political right, and then crossing the aisle to the left, resistance is sometimes considered a means and other times an end. Its modern history traces the evolution of an idea and a transformation in politics. The English word resistance is a derivation of "resist," stemming from the Latin—via th…
Until recently, definitions of accommodation and resistance, particularly in relation to slavery and colonialism, have reproduced the stark decisions that faced the Melians more than two thousand years ago. To accommodate was to agree, however tacitly, with the existing order of things—to compromise, to oblige, to be pliable. Accommodation entailed the avoidance of further conflict, as in a…
Rats are members of the order Rodentia, which also encompasses beavers, mice, hamsters, and porcupines. Two major families of rats and mice are recognized: the Sigmodontinae; the New World rats and mice, comprising 369 species in 73 genera, and the Murinae, the Old World rats and mice, comprising 408 species in 89 genera. The major taxonomic difference between the two subfamilies is the presence o…
The term responsibility has several related meanings. First, there is causal responsibility. To say that the short circuit is responsible for the fire is simply to say that the short circuit caused the fire. Second, there is personal responsibility. This comes in two forms, prospective and retrospective. To say that the lifeguard is responsible for the swimmers' safety is to say that the li…
Why is the sky blue? Why are sunsets red? The answer involves Rayleigh scattering. When light strikes small particles, it bounces off in a different direction in a process called scattering. Rayleigh scattering is the scattering that occurs when the particles are smaller than the wavelength of the light. Blue light has a wavelength of about 400 nanometers, and red light has a wavelength of about 7…
It is tempting to give a definition of revolution at the outset of an account such as this. This is a temptation to be resisted. The great sociologist Max Weber (1864–1920) was right to say that "definition can be attempted, if at all, only at the conclusion of the study." Another great thinker, Friedrich Nietzsche (1844–1900), declared that "only that which has …
Rays are members of the class Chondrichthyes, the cartilaginous fish, that includes sharks, skates, and chimeras. The flattened shape of rays makes them unique among fish. Their pectoral fins are much larger than those of other fish, and are attached the length of the body, from the head to the posterior. Rays, and their relatives the skates, comprise the order Rajiformes, which includes 318 speci…
Rhetoric governs the effective use of verbal and nonverbal communication designed to influence an audience. Understood in its broadest sense, it is practiced more or less deliberately in all societies. Even the animal world seems to apply some of its principles. But in its original and historical form, rhetoric is associated with the use of human discourse to persuade and can be defined as the art…
In photogravure, ink is held in the hollows of a plate rather than on high relief. This method of printing is known as intaglio. The photogravure plate, like the halftone plate, is produced with the aid of a camera and an acid to etch away parts of the metal plate. The acid creates hollows of different depths. The deepest hollows hold the most ink and print the darkest areas in the picture. Shallo…
A real number is any number which can be represented by a point on a number line. The numbers 3.5, −0.003, 2/3, π, and √2 are all real numbers. The real numbers include the rational numbers, which are those which can be expressed as the ratio of two integers, and the irrational numbers, which cannot. (In the list above, all the numbers except pi and the square root of 2 are ra…
Invention (inventio) is the devising of matter, true or plausible, that would make the (legal) case convincing. Arrangement (dispositio) is the ordering and distribution of the matter, making clear the place to which everything is to be assigned. Style (elocutio) is the adaptation of suitable words and sentences to the matter devised. Memory (memoria) is the firm retention in the mind of the matte…
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,…
The reciprocal of a number is 1 divided by the number. Thus the reciprocal of 3 is 1/3; of 3/2 is 1 ÷ (3/2)= 2/3, of a/b is b/a. If a number a is the reciprocal of the number b, then b is the reciprocal of a. The product of a number and its reciprocal is 1. Thus, 3 × 1/3 = 1, (3/2) × (2/3) = 1, and (a/b) × (b/a) = 1. …
The study of ritual performed in communal life encompasses the wealth of world history and cosmology. Yet, few linguistic or conceptual categories of analysis address fully the diversity of ritual as an enactment of belief in the divine, inclusive of the mythologies of magic, associated with the liminal moments of human experience. For modern societies, the historical celebration of ritual as a dr…
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) …
Deoxyribonucleic acid (DNA) is the information blueprint that exists in most living organisms. Some viruses instead contain ribonucleic acid (RNA). Even these viruses require the production of DNA at some stage of their replication. DNA from different organisms of the same species combines together naturally to yield an organism that has traits from both parent organisms. There is also evidence ac…
A rectangle is a quadrilateral whose angles are all right angles. The opposite sides of a rectangle are parallel and equal in length. Any side can be chosen as the Figure 1. Illustration by Hans & Cassidy. Courtesy of Gale Group. base and the altitude is the length of a perpendicular line segment between the base and the opposite side (see Figure 1). A diagonal is either of the line s…
Probability theory is a branch of mathematics concerned with determining the long run frequency or chance that a given event will occur. This chance is determined by dividing the number of selected events by the number of total events possible. For example, each of the six faces of a die has one in six probability on a single toss. Inspired by problems encountered by seventeenth century gamblers, …
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…
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…
Recycling is a method of reusing materials that would otherwise be disposed in a landfill or incinerator. Discarded materials that contain glass, aluminum, paper, or plastic can be recycled by collecting and processing them into raw materials that are then used to manufacture new products. Recycling has many benefits: it saves money in production and energy costs, helps to conserve stocks of virgi…
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…
A red giant is a star that has exhausted the primary supply of hydrogen fuel at its core and is now using another element such as helium as the fuel for its energy-producing thermonuclear fusion reactions. Hydrogen fusion continues outside the core and causes the star to expand dramatically, making it a giant. Expansion also cools the star's surface, which makes it appear red. Red giant sta…
Propane is a gas produced primarily from various refinery processes. It is often mixed with butane, a four carbon atomalkane, and sold as bottled gas or liquefied petroleum gas, LPG. The bottled gas is used as an inexpensive fuel for cooking and heating homes not located near natural gas lines. Since liquefied petroleum gas burns very cleanly, it is being used as an alternate fuel for cars, trucks…
Prosimians are the most primitive of the living primates, which also include the monkeys and apes. The name prosimian means pre-monkey. The living prosimians are placed in the suborder Prosimii, which includes four families of lemurs, (the Lemuridae, the Cheirogaleidae, the Indriidae, and the Daubentoniidae), the bush babies, lorises and pottos (family Lorisidae), and the tarsiers (family Tarsiida…
Red tides are a marine phenomenon in which water is stained a red, brown, or yellowish color because of the temporary abundance of a particular species of pigmented dinoflagellates (these events are known as "blooms"). Also called phytoplankton, or planktonic algae, these single-celled organisms of the class Dinophyceae move using a tail-like structure called a flagellum. They also p…
A redshift is caused by the Doppler effect, which is the change in wavelength and frequency of either light or sound as the source and observer are moving either closer together or farther apart. In astronomy a redshift indicates that the source is moving away, and a blueshift indicates that the source is moving closer to us. Doppler shifts have many important applications in astronomy. They help …
A reflection is one of the three kinds of transformations of plane figures which move the figures but do not change their shape. It is called a reflection because figures after a reflection are the mirror images of the original ones. The reflection takes place across a line called the "line of reflection." Figure 1 shows a triangle ABC and its image A'B'C'. Each individual point and …
Reflexes are set motor responses to specific sensory stimuli. All reflexes share three classical characteristics: they have a sensory inflow pathway, a central relay site, and a motor outflow pathway. Together, these three elements make up the reflex arc. Reflexes can also be characterized according to how much neural processing is involved in eliciting a response. Some reflexes, like the short re…
Refrigerated trucks and railroad cars have had a great impact on the economy and eating habits of Americans. As the United States became more urbanized, the demand for fresh food shipped over long distances increased. Meat products were especially in demand. In the mid-1800s, cattle raised in Texas were shipped by rail to Chicago, Illinois. Although it was more efficient to slaughter the cattle i…
Illness and trauma that lead to disability or functional loss can lead to an individual's need for a changed lifestyle to accommodate his reduced level of ability. A stroke, for example, can lead to partial paralysis; chronic arthritis can result in the inability to stand or to use one's hands; an automobile accident can cause blindness or can result in an individual's confine…
Prosthetics is a branch of surgery that is involved in devising and fabricating a prosthesis for a missing or infirm body part. A prosthesis is an artificial part used to restore some amount of normal body function. The classic example of a prosthesis is a false leg or arm to replace one that has been amputated. A diseased heart valve can be removed and replaced by an artificial one. Artificial bo…
Proteas are evergreen trees and shrubs belonging to the dicotyledonous plant family Proteaceae and, in particular, to members of the genus Protea. They grow mostly in dry regions of the southern hemisphere, especially in Australia and South Africa. The family is divided into five subfamilies, 75 genera, and 1,350 species. The Proteaceae are distinguished from closely related families by having one…
Reinforcement is a term used to refer to the procedure of removing or presenting stimuli (reinforcers) to maintain or increase the frequency or likelihood of a response. The term is also applied to refer to an underlying process that leads to reinforcement or to the actual act of reinforcement, but many psychologists discourage such a broad application of the term. Reinforcement is usually divided…
In mathematics, a relation is any collection of ordered pairs. The fact that the pairs are ordered is important, and means that the ordered pair (a, b) is different from the ordered pair (b, a) unless a = b. For most useful relations, the elements of the ordered pairs are naturally associated or related in some way. More formally, a relation is a subset (a partial collection) of the set of all pos…
Protected areas are parks, ecological reserves, and other tracts set aside from intense development to conserve their natural ecological values. These areas protect the habitat of endangered species, threatened ecological communities, or representative examples of widespread ecosystems, referred to as indigenous (native) biodiversity values. Some protected areas are intended to conserve places of …
Proteins are linear chains of amino acids connected by chemical bonds between the carboxyl group of each amino acid and the amine group of the one following. These bonds are called peptide bonds, and chains of only a few amino acids are referred to as polypeptides rather than proteins. Different authorities set the protein/polypeptide dividing line at anywhere from 10 to 100 amino acids. Many prot…
Proteome is a complement of proteins expressed in a cell at given time and proteomics means global analysis of this protein complement. Proteomics investigates the global changes of proteins in cells and tissues in response to a stimulus (for example temperature change, drug or nutrient treatment, or growth phase). It also studies protein-protein interactions. Proteomics came into prominence after…
Remote sensing is the science and art of obtaining and interpreting information about an object, area, or phenomenon through the analysis of data acquired by a sensor that is not in contact with the object, area, or phenomenon being observed. There are four major characteristics of a remote sensing system, namely, an electromagnetic energy source, transmission path, target, and sensor. The Sun is…
The Kingdom Protista is the most diverse of all six kingdoms. There are more than 200,000 known species of protists with many more yet to be discovered. The protists can be found in countless colors, sizes, and shapes. They inhabit just about any area where water is found some or all of the time. They form the base of ecosystems by making food, as is the case with photosynthetic protists, or by th…
The proton is a positively charged subatomic particle. Protons are one of the fundamental constituents of all atoms. Protons, in addition to neutrons, are found in a very concentrated region of space within atoms referred to as the nucleus. The discovery of the proton, neutron, and electron revolutionized the way scientists viewed the atom. Recent research has shown that protons are themselves mad…
Protozoa are a very varied group of single-celled organisms, with more than 50,000 different types represented. The vast majority are microscopic, many measuring less than 1/200 mm, but some, such as the freshwater Spirostomun, may reach 0.17 in (3 mm) in length, large enough to enable it to be seen with the naked eye. Scientists have even discovered some fossil specimens that measured 0.78 in (20…
Psychiatry is the branch of medicine concerned with the study, diagnosis, and treatment of mental illnesses. The word, psychiatry, comes from two Greek words that mean mind healing. Those who practice psychiatry are called psychiatrists. In addition to their M.D.s, these physicians have post-graduate education in the diagnosis and treatment of behaviors that are considered abnormal. They tend to v…
The reproductive system is the structural and physiological network whose purpose is the creation of a new life to continue the species. It is the only body system that is not concerned with supporting the life of its host. Human reproduction is sexual—meaning that both a male and a female are required to produce a life. Gender is determined at conception by the sex chromosome in the sperm …
Reproductive toxicants are substances that adversely affect fertility or a developing embryo or fetus. Toxicants, strictly speaking, are poisons. However, reproductive toxicants loosely include any infectious, physical, chemical, or environmental agent that has a damaging effect on fertility or embryonic development. Some substances that have a beneficial effect on one occasion (such as a dental x…
The class Reptilia includes over 6,000 species grouped into four orders: the turtles (Chelonia), the snakes and lizards (Squamata), the crocodiles and alligators (Crocodilia), and the tuataras (Sphenodonta). Other, now extinct, reptilian orders included Earth's largest terrestrial animals, and some enormous marine creatures. The fishlike ichthyosaurs were large marine reptiles, as were the …
Historically, the term resin has been applied to a group of substances obtained as gums from trees or manufactured synthetically. Strictly speaking, however, resins are complex mixtures, whereas gums are compounds that can be represented by a chemical formula. The word gum was originally applied to any soft sticky product derived from trees; for example, the latex obtained from Hevea trees, which …
The term psychoanalysis has three meanings: 1) a theory of personality with an emphasis on motivation, or why we behave the way we do; 2) a method of treatment for various psychological problems; and 3) a group of techniques used to explore human nature or the mind. …
There are many instances in which we want to add energy to the motion of an object which is oscillating. In order for this transfer to be efficient, the oscillation and the source of new energy have to be "matched" in a very specific way. When this match occurs, we say that the oscillation and source are in resonance. A simple example of an oscillation that we have all seen is that o…
"Psychology" comes from the Greek words psyche, meaning "mind" or "soul," and logos, meaning word. It is the scientific study of human and animal behavior and mental processes. Behavior refers here to easily observable activities such as walking, talking, or smiling. Mental processes, such as thinking, feeling, or remembering, often cannot be directly obse…
Psychometry or psychometrics is a field of psychology which uses tests to quantify psychological aptitudes, reactions to stimuli, types of behavior, etc., in an effort to devlop reliable scientific models that can be applied to larger populations. Currently many new psychometric theories and statistical models are being proposed that will probably lead to changes in test construction. In addition,…
Respiration is the physiological process by which organisms supply oxygen to their cells and the cells use that oxygen to produce high energy molecules. Respiration occurs in all types of organisms, including bacteria, protists, fungi, plants, and animals. In higher animals, respiration is often separated into three separate components: (a) external respiration, the exchange of oxygen and carbon d…
A psychotic state is one in which a person suffering from one of several mental illnesses loses touch with reality. People experiencing psychosis may be diagnosed as schizophrenic, manic-depressive, or delusional. Psychosis can also be induced from drug or alcohol abuse, reaction to medication, from exposure to some toxic substance, or from trauma to the brain. Psychotic episodes have a duration t…
A respirator is a means to provide needed oxygen to a patient, to infuse medication directly into the lungs, or to provide the power to breathe to someone who is unable to do so on his own. A respirator may be needed following a serious trauma that interferes with the individual's breathing or for a person who has contracted a disease such as poliomyelitis that has affected the nerves that …
Psychosurgery is the alteration or destruction of brain matter in order to alleviate severe, long-lasting, and harmful psychiatric symptoms that do not respond to psychotherapy, behavioral, physical, or drug treatments. Psychosurgery involves opening up the skull or entering the brain through natural fissures such as the eye sockets, and injecting various tissue-altering solutions, removing or des…
There are many different types of respiratory diseases that interfere with the vital process of breathing. Respiratory obstructions arising from diseases can occur in the nasal area, the regions of the throat and windpipe (upper respiratory system), or in the bronchial tubes and lungs (lower respiratory system). The common cold and allergic reactions to airborne pollens block the nasal passages by…
Puberty is the period of sexual maturity when sexual organs mature and secondary sexual characteristics develop. Puberty is also the second major growth period of life—the first being infancy. A number of hormones under the control of the hypothalamus, pituitary, ovaries, and testes regulate this period of sexual growth, which begins for most boys and girls between the ages of nine and 15. …
Puffbirds are 32 species of birds that make up the family Bucconidae. This family is in the order Piciformes, which also contains the woodpeckers, toucans, barbets, jacamars, and honey-guides. Puffbirds are native to lowland tropical forests from southern Mexico, through to Paraguay and northern Argentina in South America. Most species occur in Amazonia. Puffbirds are short, squat birds, with a la…
Puffer fish or globe fish (family Tetraodontidae) are a group of tropical- and warm-temperate-dwelling species that are almost exclusively marine in their habits. A few freshwater species occur in tropical Africa and Asia. Most are typically found in shallow waters, often on coral reefs, in beds of sea grass, and in estuaries, swimming and feeding during daylight. A few species are oceanic. Their …
A pulsar is a celestial object that emits radiation pulses (bursts) of very short (one to a few milliseconds, or thousandths of a second) duration at very regular intervals from a fraction of a second to ten seconds. The first pulsar was discovered in 1967 by Jocelyn Bell and Antony Hewish at Cambridge, England, with radio telescopes equipped to study the twinkling (scintillation) of radio stars. …
Punctuated equilibrium is a theory about how new species evolve that was first advanced by American paleontologists Niles Eldredge and Stephen Jay Gould (1941–2002) in 1972. Although controversial, punctuated equilibrium has stimulated fruitful debate about speciation (the birth of new species) and the fossil record and has, in recent years, won at least partial acceptance among most evolut…
A pyramid is a geometric solid of the shape made famous by the royal tombs of ancient Egypt. It is a solid whose base is a polygon and whose lateral faces are triangles with a common vertex (the vertex of the pyramid). In the case of the Egyptian pyramid of Cheops, the base is an almost perfect square 755 ft (230 m) on an edge, and the faces of triangles that are approximately equilateral. Pyr…
Aerobic organisms take in oxygen from the external environment and release carbon dioxide in a process known as respiration. At the most basic level, this exchange of gases takes place in cells and involves the release of energy from food materials by oxidation. Carbon dioxide is produced as a waste product of these oxidation reactions. The gas exchange in cells is called cellular respiration. In …
This theorem was likely to have been known earlier to be the Babylonians, Pythagoras is said to have traveled to Babylon as a young man, where he could have learned the famous theorem. Nevertheless, Pythagoras (or some member of his school) is credited with the first proof of the theorem. …
Plate tectonics, is the theory explaining geologic changes that result from the movement of lithospheric plates over the asthenosphere (the molten, ductile, upper portion of Earth's mantle). Plates move and shift their positions relative to one another. Movement of and contact between plates either directly or indirectly accounts for most of the major geologic features at Earth's sur…
Pythons are nonvenomous constricting snakes in the family Boidae that are found only in the Old World. Like the boas, pythons retain lizard-like features such as paired lungs and the remnants of the hind limbs. Pythons are egg-laying snakes which distinguishes them from boas and sandboas which typically bear live young. Fossil species of pythons are known from Cretaceous period, some 200 million y…
A quadrilateral is a polygon with four sides. Special cases of a quadrilateral are: (1) A trapezium—A quadrilateral Illustration by Hans & Cassidy. Courtesy of Gale Group. Illustration by Hans & Cassidy. Courtesy of Gale Group. with no pairs of opposite sides parallel. (Figure A) (2) A trapezoid—A quadrilateral with one pair of sides parallel. (Figure B) (3) A…
The term platonic solids refers to regular polyhedra. In geometry, a polyhedron, (the word is a Greek neologism meaning many seats) is a solid bounded by plane surfaces, which are called the faces; the intersection of three or more edges is called a vertex (plural: vertices). What distinguishes regular polyhedra from all others is the fact that all of their faces are congruent with one another. (I…
Restoration ecology refers to activities undertaken to increase populations of an endangered species or to manage or reconstruct a threatened ecosystem. Ecological restoration is an extremely difficult and expensive endeavor, and only attempted when the population of an endangered species is considered too small to be self-maintaining or the area of a threatened ecosystem is not large enough to al…
Retrograde motion means "moving backward," and describes the loop or Z-shaped path that planets farther from the Sun than Earth appear to trace in the sky over Figure 1. Illustration by Hans & Cassidy. Courtesy of Gale Group. Figure 2. Illustration by Hans & Cassidy. Courtesy of Gale Group. the course of a few months. All the visible planets farther from …
Quail are relatively small species of fowl in the family Phasianidae, which also includes pheasants, partridges, peafowl, turkeys, guinea fowl, and francolins. Like other members of their family, quail have a chunky body with short, rounded wings, and a short, thick, hooked bill, in which the tip of the upper mandible hangs slightly over that of the lower. The legs and feet are stout, and are used…
Retroviruses are spherical viruses that contain ribonucleic acid (RNA) as their genetic material. In contrast, most other organisms, including humans, store their genetic information in the form of deoxyribonucleic acid (DNA). Retroviruses are of concern to humans because of their disease causing ability. Examples of retroviruses include human T cell leukemia virus, which causes cancer in humans, …
The value of a material is determined in part by the substances of which it is composed. The operations necessary to determine this composition are known as qualitative analysis. Qualitative analysis is a series of tests; responses to these tests identify the elements and compounds that make up the material. Every substance is unique. Each has, for example, a certain color, texture, and appearance…
Reye's syndrome is a serious medical condition associated with viral infection and aspirin intake. It usually strikes children under age 18, most commonly those between the ages of five and 12. Symptoms of Reye's syndrome develop after the patient appears to have recovered from the initial viral infection. Symptoms include fatigue, irritability, and severe vomiting. Eventually, neuro…
The platypus is an egg laying mammal that is well adapted to the water. Physically, it looks like a mole or otter, with a beaver's flattened tail and a duck's bill. It also has short, powerful legs and webbed feet. While the fur on its back is dense, bristly, and reddish or blackish brown, the fur on its underbelly is soft and gray. Its eyes are very small, and it does not have exter…
Plovers are shore birds in the family Charadriidae, order Charadriiformes. Plovers have short, straight bills, with a small swelling towards the tip. Their wings are pointed at the tips, usually with a white wing-stripe on the underside, and the flight of these birds is fast and direct. Plovers and the closely related sandpipers (family Scolopacidae) are affectionately known as "peeps…
Quantitative analysis is a chemical analysis performed to find the amount of each component present in a material. It is done by either a classical or instrumental procedure. A quantitative investigation means that the amount (quantity) or relative amount of each component present is determined. In a pure substance, the entire mass, or 100%, is composed of a single component. In materials composed…
The computers of today are smaller, faster, and more powerful than their predecessors from the 1940s. The underlying philosophy of the ancient computers and their modern cousins, however, is exactly the same. The task remains the same: to manipulate and interpret information that is expressed as either a 0 or a 1. This packaging of information is referred to as the binary bit. Binary bit computers…
Quantum electrodynamics (QED) is a complex and highly mathematical theory regarding the interaction of electromagnetic radiation with matter. The development of QED theory was essential in the verification and development of quantum field theory and it allows physicists to predict how subatomic particles are created or destroyed. QED is a fundamentally important scientific theory that accounts for…
Rh factor is a blood protein that plays a critical role in some pregnancies. People without Rh factor are known as Rh negative, while people with the Rh factor are Rh positive. If a woman who is Rh negative is pregnant with a fetus who is Rh positive, her body will make antibodies against the fetus's blood. This can cause Rh disease, also known as hemolytic disease of the newborn, in the ba…
Rhesus monkeys (Macaca mulatta) are macaques belonging to the primate family Cercopithecidae. These medium-sized monkeys are colored from golden-brown to gray-brown. Rhesus monkeys spend most their time on the ground, although they take to trees readily, and have great agility in climbing and leaping. Typical body weights range from 11 to 26.5 lb (5-12 kg) for adult male rhesus monkeys, and from 9…
Quantum mechanics is the theory used to provide an understanding of the behavior of microscopic particles such as electrons and atoms. More importantly, quantum mechanics describes the relationships between energy and matter on atomic and subatomic scale. At the beginning of the twentieth century, German physicist Maxwell Planck (1858–1947) proposed that atoms absorb or emit electromagnetic…
The ninth planet from the Sun, Pluto is one of the least well understood objects in the solar system. It is the smallest of the major planets, and has a most unusual orbit. Pluto's companion moon, Charon, is so large that the pair essentially form a binary system. How the Pluto-Charon system formed and how the system acquired its special 2-to-3 orbital resonance with Neptune are unanswered …
A quantum number is a number that specifies the particular state of motion an atom or molecule is in and, usually, the energy of that motion. By 1900, several phenomena were recognized that could not be explained by accepted scientific theories. One such phenomenon was the behavior of light itself. In 1900, however, Max Planck (1858-1947) developed a new theory that successfully described the natu…
Rheumatic fever is a rare complication that occurs after an infection with Streptococcus pyogenes bacteria. The most common type of S. pyogenes infection is "strep throat," in which the tissues that line the pharynx become infected with the bacteria. Rheumatic fever does not occur if the initial strep infection is treated with antibiotics. Major symptoms of rheumatic fever include in…
Rhinos are heavily built, thick-skinned, herbivorous mammals with one or two horns, and three toes on each foot. The family Rhinocerotidae includes five species found in Asia or Africa, all of which are threatened by extinction. The two-ton, one-horned Great Indian rhinoceroses (Rhinoceros unicornis) is a shy and inoffensive animal that seldom acts aggressively. This rhino was once abundant in Pak…
A rhizome is a root-like, underground stem, growing horizontally on or just under the surface of the ground, and capable of producing shoots and roots from its nodes. Rhizomes are most commonly produced by perennial, herbaceous species of plants, that die back to the ground at the end of the growing season, and must grow a new shoot at the beginning of the next season. Rhizomes are capable of stor…
Quarks are, according to the modern theory of subatomic particles, one of the three basic building blocks of all matter. The others are the leptons (which include the electron and the three types of neutrinos) and the intermediate vector bosons (which mediate the forces that bind other particles together). The stable particles of which ordinary matter is mostly composed—protons and neutrons…
Rhubarbs are several species of large-leaved, perennial, herbaceous plants in the buckwheat family (Polygonaceae). Rhubarbs originated in eastern Asia and were not cultivated in Europe until the nineteenth century. Rhubarbs have been used as medicinal plants, as food, and as garden ornamentals. The initial uses of rhubarb were medicinal, for which both the medicinal rhubarb (Rheum officinale) and,…
Ribbon worms, also called bootlace worms or proboscis worms, derive their common names from their threadlike or ribbonlike form, and from the characteristic reversible proboscis which they use in prey capture or in burrowing. The phylum Nemertea (or Rhynchocoela) includes approximately 900 described species of these worms. Most of them are marine, living in sand or mud, or under shells and rocks; …
Quasi-stellar radio sources (quasars) are the most distant cosmic objects observed by astronomers. Although not visible to the naked eye, quasars are also among the most energetic of cosmic phenomena. Although some quasars may be physically smaller in size than our own solar system, some quasars are calculated to be brighter than hundreds of galaxies combined. Quasars and active galaxies appear to…
The quetzal (Pharomachrus mocinno), also known as the resplendent quetzal or magnificent quetzal, is an astonishingly beautiful bird of tropical forests. It is a member of the trogon family (Trogonidae). The quetzal has a body length of 14 in (36 cm); in addition, the male has impressive tail streamers as long as 25 in (64 cm). The mature male has a shining green body color, with a crimson belly, …
Pneumonia is an infection of the lung, and can be caused by nearly any class of organism known to cause human infections, including bacteria, viruses, fungi, and parasites. In the United States, pneumonia is the sixth most common disease leading to death, and the most common fatal infection acquired by already hospitalized patients. In developing countries, pneumonia ties with diarrhea as the most…
Podiatry is a medical specialty that focuses on the diagnosis and treatment of foot disease and deformity. The term is from the Greek word for foot (podos) and means "to heal the foot." Until recent years this specialty was called chiropody, literally meaning "to heal the hand and foot." References to physicians who treated abnormalities or injuries in the foot are foun…
A point is an undefined term in geometry that expresses the notion of an object with position but with no size. Unlike a three-dimensional figure, such as a box (whose dimensions are length, width, and height), a point has no length, no width, and no height. It is said to have dimension 0. Geometric figures such as lines, circles, planes, and spheres, can all be considered as sets of points. …
Quinine is an alkaloid obtained from the bark of several species of the cinchona tree. Until the development of synthetic drugs, quinine was used as the primary treatment of malaria, a disease that kills over 100 million people a year. The cinchona tree is native to the eastern slopes of the Andes Mountains in South America. Today, the tree is cultivated throughout Central and South America, Indon…
A point source is a situation where large quantities of pollutants are emitted from a single, discrete source, such as a smokestack, a sewage or thermal outfall into a waterbody, or a volcano. If the emissions from a point source are large, the environment will be characterized by strong but continuous gradients of ecological stress, distributed more-or-less concentrically around the source, and d…
Rabies is a viral brain disease that is almost always fatal if it is allowed to develop and is not prevented with prompt treatment. The disease, which typically spreads to humans from animals through a scratch or a bite, causes inflammation of the brain. The disease is also called hydrophobia (meaning fear of water) because it causes painful muscle spasms in the throat that prevent swallowing. In …
Raccoons are foxlike carnivores of North and South America that belong to the same family (Procyonidae) as the coatis, kinkajou, and the lesser panda. The most common species is the northern raccoon (Procyon lotor), which has numerous subspecies, all with the famous black mask on their faces and rings of dark color on their tails. They are found throughout the United States, in central Canada, and…
A chemical is said to be a poison if it causes some degree of metabolic disfunction in organisms. Strictly speaking, a toxin is a poisonous chemical of biological origin, being produced by a microorganism, plant, or animal. In common usage, however, the words poison and toxin are often used interchangeably, and in this essay they are also treated as synonyms. It is important to understand that pot…
One of the several systems for addressing points in the plane is the polar-coordinate system. In this system a point P is identified with an ordered pair (r,θ) where r is a distance and θ an angle. The angle is measured counter-clockwise from a fixed ray OA called the "polar axis." The distance to P is measured from the end point O of the ray. This point is called the &…
Radar (RAdio Detection And Ranging) is an electronic detector system that measures distance or velocity by sending a signal out and receiving its return. It can pierce fog, darkness, or any atmospheric disturbance all the way to the horizon. Within its range, it can show an observer clouds, landmass, or objects such as ships, airplanes, or spacecraft. Radar can measure distance or range to a targe…
The polar ice caps cover the north and south poles and their surrounding territory, including the entire continent of Antarctica in the south, the Arctic Ocean, the northern part of Greenland, parts of northern Canada, and bits of Siberia and Scandinavia also in the north. Polar ice caps are dome-shaped sheets of ice that feed ice to other glacial formations, such as ice sheets, ice fields, and ic…
Radial keratotomy (RK) is a surgical procedure that reduces myopia (nearsightedness), or astigmatism (diminished focus) by changing the shape of the cornea—the outermost part of the eyeball. The procedure is particularly attractive to individuals who want to avoid wearing glasses or wish to be rid of the inconvenience of contact lenses. RK is a quick, relatively painless procedure that take…
The word radiation comes from the Latin for "ray of light," and is used in a general sense to cover all forms of energy that travel through space from one place to another as "rays." Radiation may be in the form of a spray of subatomic particles, like miniature bullets from a machine gun, or in the form of electromagnetic waves, which are nothing but pure energy and whi…
Radiation detectors are devices which sense and relay information about incoming radiation. Though the name brings to mind images of nuclear power plants and science fiction films, radiation detectors have found homes in such fields as medicine, geology, physics, and biology. The term radiation refers to energies or particles given off by radioactive matter. Mostly, radiation takes the form of alp…
There are three viruses responsible for the infectious disease now called poliomyelitis. It has been called infantile paralysis and is now commonly referred to as polio. While the disease usually afflicts young children, adults can succumb to it also. A notable example of polio in an adult was the case of President Franklin Delano Roosevelt, the thirty-second president of the United States. He con…
Pollen analysis, or palynology, is the study of fossil pollen (and to a lesser degree, plant spores) preserved in lake sediments, bog peat, or other matrices. Usually, the goal of palynology is to reconstruct the probable character of local plant communities in the historical past, as inferred from the abundance of plant species in dated potions of the pollen record. Palynology is a very important…
Radiation exposure occurs any time that energy in the form of electromagnetic rays or particles interacts with biological tissue. Ionizing radiation is particularly energetic; examples include: x rays, gamma radiation, and subatomic particles. Biological damages caused by exposure to ionizing range from mild tissue burns to cancer, genetic damage, and ultimately, death. However, there are potentia…
Pollination is the transfer of pollen from the male reproductive organs to the female reproductive organs of A honeybee becomes coated in pollen while gathering nectar and transports the pollen as it goes from flower to flower. Photograph by M. Ruckszis. Stock Market/Zefa Germany. Reproduced by permission. a plant, and it precedes fertilization, the fusion of the male and the female sex cell…
The term pollution is derived from the Latin pollutus, which means to be made foul, unclean, or dirty. Anything that corrupts, degrades, or makes something less valuable or desirable can be considered pollution. There is, however, a good deal of ambiguity and contention about what constitutes a pollutant. Many reserve the term for harmful physical changes in our environment caused by human actions…
Pollution control is the process of reducing or eliminating the release of pollutants into the enviroment. It is regulated by various environmental agencies which establish pollutant discharge limits for air, water, and land. Air pollution control strategies can be divided into two categories, the control of particulate emission and the control of gaseous emissions. There are many kinds of equipme…
Polybrominated biphenyls (or PBBs) are chemicals used to make plastics flame retardant. In Michigan in the early 1970s one type of PBB was accidentally mixed into livestock feed and fed to farm animals, resulting in the sickening and/or death of tens of thousands of animals. A large portion of Michigan's nine million residents became ill as a result of eating contaminated meat or poultry. P…
A radical is an uncharged atom or molecule that has an unpaired, or "free," electron. Radicals are formed when a covalent bond in an atom or molecule is split apart and the remaining pieces retain one electron of the original shared pair. These reaction products, called free radicals, are highly reactive entities that can participate in a variety of reactions. In chemical notation, r…
Polychlorinated biphenyls are a mixture of compounds having from one to 10 chlorine atoms attached to a biphenyl ring structure. There are 209 possible structures theoretically; the manufacturing process results in approximately 120 different structures. PCBs resist biological and heat degradation and were once used in numerous applications, including dielectric fluids in capacitors and transforme…
Polycyclic aromatic hydrocarbons, or polynuclear aromatic hydrocarbons, are a family of hydrocarbons containing two or more closed aromatic ring structures, each based on the structure of benzene. The simplest of these chemicals is naphthalene, consisting of two fused benzene rings. Sometimes there is limited substitution of halogens for the hydrogen of polycyclic aromatic hydrocarbons, in which c…
A radical is a symbol for the indicated root of a number, for example a square root or cube root; the term is also synonymous for the root itself. The radical &NA; is the symbol that calls for the root operation; the number or variable under the radical sign is called the radicand. It is common parlance to speak of the radicand as being "under the radical." It is also common to simpl…
Polygons are closed plane figures bounded by three or more line segments. In the world of geometry, polygons abound. The term refers to a multisided geometric form in the plane. The number of angles in a polygon always equals the number of sides. Polygons are named to indicate the number of their sides or number of noncollinear points present in the polygon. A square is a special type of polygon, …
A polyhedron is a three-dimensional closed surface or solid, bounded by plane figures called polygons. The word polyhedron comes from the Greek prefix poly- , which means "many," and the root word hedron which refers to "surface." A polyhedron is a solid whose boundaries consist of planes. Many common objects in the world around us are in the shape of polyhedrons. The c…
Polymers are made up of extremely large, chainlike molecules consisting of numerous, smaller, repeating units called monomers. Polymer chains, which could be compared to paper clips linked together to make a long strand, appear in varying lengths. They can have branches, become intertwined, and can have cross-links. In addition, polymers can be composed of one or more types of monomer units, they …
There are various words that are used in conjunction with polynomials. The degree of a polynomial is the exponent of the highest power of x. Thus the degree of The most general form for a polynomial in one variable is Similar definitions apply to polynomials in 3, 4, 5 ellipsevariables but the term "polynomial" without qualification usually refers to a polynomial in one var…
Poppies belong to a small family of flowering plants called the Papaveraceae. Poppies are annual, biennial, or perennial herbs, although three New World genera (Bocconia, Dendromecon, and Romneya) are woody shrubs or small trees. The leaves are alternate, lack stipules, and are often lobed or deeply dissected. The flowers are usually solitary, bisexual, showy, and crumpled in the bud. The fruit is…
The numbers of humans on Earth have increased enormously during the past several millennia, but especially during the past two centuries. By the end of the twentieth century, the global population of humans was 6.0 billion. That figure is twice the population of 1960, a mere 30 years earlier. Moreover, the human population is growing at about 1.5% annually, equivalent to an additional 89 million p…
Radio is the technology and practice that enables the transmission and reception of information carried by long-wave electromagnetic radiation. Radio makes it possible to establish wireless two-way communication between individual pairs of transmitter and receiver, and it is used for one-way broadcasts to many receivers. Radio signals can carry speech, music, telemetry, or digitally-encoded entert…
