Cybernetics is a term that was originated by American mathematician Norbert Wiener (1894–1964) in the late 1940s. Based on common relationships between humans and machines, cybernetics is the study and analysis of control and communication systems. As Wiener explains in his 1948 book, Cybernetics: or Control and Communication in the Animal and the Machine, any machine that is "intell…
University of Illinois graduate student Michael Sveda first synthesized cyclamate in 1937. Some say that he discovered its sweet taste by chance when he accidentally got some on the cigarette he was smoking. The university eventually transferred patent rights to Abbott Laboratories, which brought the sweetener to market in 1950. Another reason for combining saccharin with cyclamate is that the swe…
The terms cyclone and anticyclone are used to describe areas of low and high atmospheric pressure, respectively. Air flowing around one or the other of these areas is said to be moving cyclonically in the first case and anticyclonically in the second. In the northern hemisphere, cyclonic winds travel in a counterclockwise direction and anticyclonic winds, in a clockwise direction. When a cyclone o…
Cyclosporines are drugs used in the field of immunosuppressant medicine to prevent the rejection of transplanted organs. They were discovered by Jean F. Borel in 1972. The cyclosporine used for transplant surgery is called cyclosporine A (CsA) and in 1984 it was added to the group of medicines used to prevent transplant rejection. Cyclosporine A is the most common form of the Norwegian fungus Toly…
A cyclotron is a type of particle accelerator designed to accelerate protons and ions to high velocities and then release them so as to strike a target. Observations of such collisions yield information about the nature of atomic particles. In contrast to the enormous particle accelerators used in particle physics today, the first cyclotron, built in 1930 by U.S. physicist E. O. Lawrence (1901…
The word cynic generally conveys negative ideas in modern languages. It describes someone who is unduly critical and suspicious, apathetic about certain issues and rebellious in response to others, selfish, and indifferent toward traditions and accepted beliefs, and unconcerned with the public welfare. The cynic is often viewed as a person who has severed all ties with his social context. To be c…
Cystic fibrosis (CF) is genetic disease characterized by defects in the transport of a molecule called chloride. Abnormalities in CF have been described in several organs and tissues, including the airways, pancreas, bile ducts, gastrointestinal tract, sweat glands, and male reproductive. Lung function is often normal at birth; however, airway obstruction and inflammation as well as bacterial colo…
Cytochromes are electron-transporting protein pigments concerned with cell respiration that contain an iron-containing molecule called heme, allied to that of hemoglobin. When the iron of heme accepts an electron, it changes from the oxidized ferric (Fe III) state to the reduced ferrous (Fe II) state. The oxidation of cytochromes to molecular oxygen and their subsequent reduction by oxidizable sub…
Cytology is the branch of biology that studies cells, the building blocks of life. The name for this science is translated from kytos, the Greek term for "cavity." Cytology's roots travel back to 1665, when British botanist Robert Hooke, examining a cross-section of cork, gave the spaces the name "cells," meaning "little rooms" or "cavities.&…
Presided over by the poet and essayist Tristan Tzara (1896–1963), who served as its principal spokesman, dada was the first truly international avant-garde movement. Although the term dada was invented in Zurich, the movement's origins were by no means limited to Switzerland. The dada spirit existed previously in several other countries, where it expressed itself in outrageous avant-…
Damselflies are the smaller and more delicate members of the insect order Odonata, which includes the dragonflies. The damselfly suborder Zygoptera is characterized by similar fore and hind wings, which are both narrow at the base. Most damselflies can be easily distinguished from their larger and heavier dragonfly relatives in the field by their fluttering flight, and when at rest by their holdin…
Defining the features of Daoism (or Taoism) as one of the predominant trends in the history of Chinese thought involves accounting for its religious traits. As often happens outside the Western hemisphere—Buddhism may be the best-known example, but the same is true of Islam—the boundary between thought and religion in China is tenuous, unstable, and sometimes simply impossible to ide…
Dark matter is the term astronomers use to describe material in the Universe that is non-luminous—that is, material that does not emit or reflect light and that is therefore invisible. Everything seen when looking through a telescope is visible because it is either emitting or reflecting light; stars, nebulae, and galaxies are examples of luminous objects. However, luminous matter appears t…
Dating techniques are procedures used by scientists to determine the age of a specimen. Relative dating methods tell only if one sample is older or younger than another; absolute dating methods provide a date in years. The latter have generally been available only since 1947. Many absolute dating techniques take advantage of radioactive decay, whereby a radioactive form of an element is converted …
Deafness is the lack of functional sense of hearing in both ears. Loss of hearing can result from environmental or genetic causes and it can be temporary or permanent. Environmental loss of hearing results from occupational noise, noise pollution, accidents, or intake of certain drugs. Inherited loss of hearing can be caused by mutations in any of over a hundred of genes known to affect hearing, a…
The idea of death—the irreversible end to life—has preoccupied, fascinated, and struck fear into human beings through the millennia. In the early twenty-first century, artists continue to sing about death, write about death, and depict it in paintings and photographs. Religious leaders are still talking about how to live a meaningful life in the face of death's inevitability. …
Fungus creates circular patterns on decomposing maple leaves. CORBIS/Gary Braasch. Reproduced by permission. Decomposition is the natural process by which large organic materials and molecules are broken down into simpler ones. The ultimate products of decomposition are simple molecules, such as carbon dioxide and water. Sometimes misunderstood as being undesirable, decomposition is actuall…
Deer are members of the order Artiodactyla, the even-toed ungulates. This order also includes the antelopes, bovines, and giraffes. Deer are generally slender and long-legged, and their most striking characteristic is the presence of antlers, which are often used to differentiate species. The deer family, Cervidae, includes about 45 species, which are divided among 17 genera and five subfamilies: …
The deer mouse (Peromyscus maniculatus) is a small, native rodent with an almost ubiquitous distribution in North America. The deer mouse ranges from the subarctic boreal forest, through wide areas of more southern conifer and mixed-wood forests, to drier habitats as far south as some regions of Mexico. The deer mouse is highly variable in size and color over its range. Its body length ranges from…
Deforestation refers to a longer-term conversion of forest to some other kind of ecosystem, such as agricultural or urbanized land. Sometimes, however, the term is used in reference to any situation in which forests are disturbed, for example by clear-cut harvesting, even if another forest subsequently regenerates on the site. Various human activities result in net losses of forest area and theref…
Dehydroepiandrosterone (DHEA) is one of the androgens secreted by the adrenal cortex. An androgen is a hormone that stimulates masculine characteristics and is present in both males and females. The adrenal glands are small structures located at the tops of the kidneys. The adrenal medulla is the central portion of the adrenal gland and the adrenal cortex is the outer portion. The adrenal glands p…
Deism holds more meanings than one word should be asked to bear. Generally, to the point of almost being meaningless, it refers to the notion that reason plays an important role in determining religious knowledge. By this definition the pre-Socratic philosophers, Plato, Aristotle, Epicurus, the Stoics, Cicero, Lucretius, Buddha, Moses, Jesus, and Muhammad all qualify to varying degrees as Deists. …
A delta is a low-lying, almost flat landform, composed of sediments deposited where a river flows into a lake or an ocean. Deltas form when the volume of sediment deposited at a river mouth is greater than what waves, currents, and tides can erode. Deltas extend the coastline outward, forming new land along the shore. However, even as the delta is constructed, waves, currents, or tidal activity ma…
Dementia is a decline in a person's ability to think and learn. To distinguish true dementia from more limited difficulties due to localized brain damage, the strict medical definition requires that this decline affect at least two distinct spheres of mental activity; examples of such spheres include memory, verbal fluency, calculating ability, and understanding of time and location. Some d…
In the mid-1980s, democratic theory and politics in Africa entered a new phase as struggles for democratization spread across the continent and scholars began to vigorously debate the processes, prospects, and problems of Africa's democratic projects. This process was captured in an important collection edited by Peter Anyang Nyong'o, Popular Struggles for Democracy in Africa (1987),…
Demography is the study of human population and its changes due to deaths, births, marriages and divorces, and migration. The term demos denotes people in Greek—the term demography literally means the systematic study of people. In the early twenty-first century the discipline encompasses a broad array of subject matters, covering, among others, economic, social, public health, and politica…
Some years ago, Richard Cavendish, an eminent demonologist and student of the so-called black arts, observed that "[b]elief in the existence of evil supernatural beings" is so widespread that it "seems to be instinctive" (p. 8). Whether, as Cavendish suggests, these beliefs are in fact instinctive is still very much an open question. However, human beings do indeed app…
Dengue fever is an illness caused by four closely related viruses (DEN-1, DEN-2, DEN-3, and DEN-4). Even though these viruses are closely related, they are recognized by the immune system as being different from each other. Thus, an infection with one virus does not provide immune protection against infections with the remaining three viral types. A person can have four bouts of dengue fever in hi…
The density of an object is defined simply as the mass of the object divided by the volume of the object. For a concrete example, imagine you have two identical boxes. You are told that one is filled with feathers and the other is filled with cement. You can tell when you pick up the boxes, without looking inside, which is the box filled with cement and which is the box filled with feathers. The b…
Dentistry is the medical activity focused on treating the teeth, the gums and the oral cavity. This includes treating teeth damaged due to accidents or disease, filling teeth damaged due to tooth decay, and replacing damaged or injured teeth with replacement teeth. Major disciplines of dentistry include orthodontics, which focuses on the correction of tooth problems such as gaps between the teeth,…
Deoxyribonucleic acid (DNA), "the master molecule," is a natural polymer which encodes the genetic information required for the growth, development, and reproduction of an organism. Found in all cells, it consists of chains of units called nucleotides. Each nucleotide unit contains three components: the sugar deoxyribose, a phosphate group, and a nitrogen-containing amine or base wit…