Nicotine is so highly addictive that the American Psychiatric Association includes it in their diagnostic manual under substance dependence. Nicotine addiction is also very difficult to break—only 5% of those who attempt to quit smoking are successful on their first try, and only 3% can kick the habit for a whole year. Only 10% of smokers are not addicted. To relieve the physical and psycho…
Night vision enhancement scopes or devices enable machines or people to form images when illumination in the visible band of the electromagnetic spectrum is inadequate. Although it is not possible to form images in absolute darkness, that is, in the absence of any electromagnetic radiation whatsoever, it is possible to form images from radiation wavelengths to which the human eye is insensitive, o…
The family of plants known as nightshades is also known as the Solanacene. It is a large group of plants composed of more than 2,000 species and 75 different genera. Most nightshades are herbs, but some species are shrubs, vines, or trees. Most of the members of the nightshade family are native to parts of Central and South America, but about 100 nightshades can be found in North America. Some spe…
Nitric acid is also formed from the reaction of nitrogen oxides produced during the combustion (burning) of fossil fuels in automobile engines. These nitrogen oxides react with water in the atmosphere and form nitric acid, one cause of acid rain. High levels of nitrates in drinking water can contribute to the formation of nitrosamines, a group of carcinogenic (cancer causing) compounds. …
Nitrification is an aerobic microbial process by which specialized bacteria oxidize ammonium to nitrite and then to nitrate. Nitrification is a very important part of the nitrogen cycle, because for most plants nitrate is the preferred chemical form of nitrogen uptake from soil or water. …
Nitrogen is a critically important nutrient for organisms, being one of the most abundant elements in their tissues, and an integral component of many biochemicals, including amino acids, proteins, and nucleic acids. The availability of biologically useful forms of nitrogen is a common limiting factor in the productivity of plants. This is especially true of plants growing in terrestrial and marin…
Non-Euclidean geometry refers to certain types of geometry which differ from plane and solid geometry which dominated the realm of mathematics for several centuries. There are other types of geometry which do not assume all of Euclid's postulates such as hyperbolic geometry, elliptic geometry, spherical geometry, descriptive geometry, differential geometry, geometric algebra, and multidimen…
Non-point sources refer to situations in which there are numerous, relatively small sources of emission of gases, metals, pesticides, nutrients, or other substances into the environment. Collectively, these many sources can comprise a regional emission of large quantities of Non-point sources. Illustration by Hans & Cassidy. Courtesy of Gale Group. pollutants into the environment. Ho…
A nonmetal is a chemical element that generally does not conduct heat or electricity very well, is usually a solid or a gas at normal temperatures, and (for solids) is difficult to reshape by pounding or beating. Nonmetals include elements such as carbon, sulfur, oxygen, and nitrogen. They are normally defined in contrast to metals, which are bright, shiny, solid elements (with one exception) that…
Gandhian nonviolence (ahimsa) is an active civic virtue that habitually disposes individuals, social groups, and political authorities to resist violence through non-violent means and to resolve conflicts using peaceful methods. It recognizes violence as a fact and nonviolence as a norm of social life. Its normative character arises from the assumed natural sociability of human beings. Its focal p…
The landmass occupied by the present-day countries of Canada, the United States, and the Republic of Mexico make up North America. Greenland (Kalaallit Nunaat), an island landmass to the northeast of Canada, is also included in North America, for it has been attached to Canada for almost two billion years. Plate tectonics is the main force of nature responsible for the geologic history of North Am…
Nova is a Latin word meaning new, and it describes the appearance of a seemingly "new star" in the sky, a brilliant object in a place where there was previously only a very faint star, or perhaps nothing at all. A nova is a phenomenon that happens in a binary star system containing a white dwarf and a stable companion star. A white dwarf is the dead, collapsed core of a star that for…
Procaine hydrochloride was first synthesized by Einhorn in 1905 as a substitute for cocaine, the first local anesthetic. Cocaine, an alkaloid obtained from the leaves of the coca plant, Erythroxylon coca, is highly addictive and toxic. Procaine hydrochloride replaced cocaine as a local anesthetic because it is much less toxic, cheaper and easier to produce, and it is easier to sterilize. In contra…
The nuclear age began in mid-July 1945 when an 18.6-kiloton nuclear bomb was detonated at the Trinity test site near Alamogordo, New Mexico. Three weeks later, on 6 August 1945, the world became aware of the existence of nuclear weapons when a U.S. B-29 bomber known as Enola Gay dropped a nuclear bomb on the Japanese city of Hiroshima. That was followed three days later by the dropping of another …
Nuclear magnetic resonance, NMR, is a process in which the nuclei of certain atoms absorb energy from a magnetic field that gyrates, or has a direction which rotates about some fixed axis. NMR provides a means of measuring nuclear properties using ordinary electromagnetic fields rather than high-energy particles as in a particle accelerator. Its applications range from nuclear measurements to medi…
Nuclear medicine is a medical specialty that uses radioactive materials, called radionuclides, to help diagnose and treat a wide variety of diseases, and for biomedical research. The development of nuclear medicine reflects the advances in the fields of nuclear physics, nuclear chemistry, and later, molecular biology. While there was considerable research in the nuclear sciences during the first p…
Nuclear power is any method of doing work that makes use of nuclear fission or nuclear fusion reactions. In its broadest sense, the term refers to both the uncontrolled release of nuclear energy, as in fission or fusion weapons, and to the controlled release of energy, as in nuclear power plants. Most commonly, however, the expression "nuclear power" is reserved for the latter. Appro…
Nuclear weapons are explosive devices that release nuclear energy. An individual nuclear device may have an explosive force equivalent to millions of tons (megatons) of trinitrotoluene (TNT, the chemical explosive traditionally used for such comparisons), and is more than enough to inflict devastating physical damage to a city. The destructive power of nuclear weapons derives from the core of the …
Nuclear winter is a theory estimating the global climatic consequences of a nuclear war: prolonged and worldwide cooling and darkening caused by sunlight-blocking smoke and soot entering the atmosphere. The term nuclear winter was first defined and used by American astronomer Carl Sagan (1934–1996) and his group of colleagues in their 1983 article (later referred to as the TTAPS-article, fr…
Two nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are found in living things which serve to store, translate, and pass on the genetic information of an organism to the next generation. Nucleic acids are universal to all life, in eukaryotic and prokaryotic cells, as well as in viruses. The mitochondria of eukaryotic cells also contain some DNA, known as mitochondrial DNA. N…
Nucleon is a generic word for the heavy particles that make up the atomic nucleus: the protons and neutrons. It is like the generic word fruit, used to include apples, oranges, and many others, except that the class of nucleons contains only two members. The use of the ending -on for the names of subatomic particles began with electron, a word that was coined in 1891 by the Irish physicist George …
Although the English word nude is derived from the Latin nudus meaning "naked," "bare," it connotes, especially in such phrases as "in the nude" or "The Nude," more than a state of undress; rather it indicates a work of art, a cultural convention, and a socioreligious attitude. The term The Nude signifies a Western cultural ideology while nud…
Numbats are the sole members of the family Myrmecobiidae. "Mumbat" is the aborigine name for these small marsupial mammals, otherwise known as banded anteaters. They are slightly larger than rats and weigh about 1 lb (0.5 kg). Considered one of the most attractive marsupials, their general color varies from grayish-brown to reddish-brown, broken by several prominent white bars across…
Number theory is the study of natural, or counting numbers, including prime numbers. Number theory is important because the simple sequence of counting numbers from one to infinity conceals many relationships beneath its surface. Number theory is full of famous formulas that illustrate the relationships between whole numbers from 1 to infinity. Some of these formulas are very complicated, but the …
A nut is a type of fruit. Like all fruits, a nut develops from the ovary of a mature, fertilized flower. A nut is thick, dry, hard, and partly or entirely enclosed by a husk. A nut is indehiscent, in that it does not open along a naturally occurring seam, and remains closed even when fully mature. A nut is a simple fruit, in that it is derived from the pistil of a single flower. Although a nut con…
Nuthatches are small, short-tailed, large-headed birds in the family Sittidae in the order Passeriformes, the perching birds. There are 25 species of nuthatches, occurring on all continents except South America, Africa, or Antarctica. Most species of nuthatches are forest birds which clamber over the bark of trees seeking insects, spiders, and arthropod eggs. Nuthatches can climb in any direction-…
The nutmeg family, Myristicaceae, order Magnoliales, consists of evergreen trees of the tropical rain forests. The genus Myristica includes about 120 species, the best known of which is the nutmeg tree (Myristica fragrans). The nutmeg tree is native to the Moluccas, a group of islands in eastern Indonesia, also known as the Spice Islands. However, nutmeg is now cultivated in much of southern Asia,…
Nutrient deficiency diseases occur when there is an absence of nutrients which are essential for growth and health. Lack of food leading to either malnutrition or starvation gives rise to these diseases. Another cause for a deficiency disease may be due to a structural or biological imbalance in the individual's metabolic system. There are more than 50 known nutrients in food. Nutrients ena…
Nutrients are any chemicals that are required for life. Nutrients can be of two basic types: (1) inorganic substances absorbed by autotrophic organisms such as plants and certain microorganisms for use in their synthetic reactions and metabolism; or (2) biomass ingested as nourishment by animals and heterotrophic microorganisms. Plants absorb a wide range of mineral nutrients, which they utilize i…
Nutrition is the means by which organisms obtain and use nutrients. Nutrition is also the determination of the kinds and quantities of substances (nutrients) needed by organisms to sustain life. Some organisms such as plants require only a supply of light, water, and a few other molecules and ions in order to thrive, and are known as autotrophs, or self nourishers, for they literally build their o…
The nux vomica tree (Strychnos nux-vomica) is a species in the tropical family Loganiaceae. The range of the nux vomica in cultivation extends from Sri Lanka, India, southern China, southeast Asia, and northern Australia. The nux vomica grows as tall as 49.2 ft (15 m). The nux vomica has roundish, opposite leaves and attractive white flowers. The roughly spherical fruits of the nux vomica are larg…
Oaks (Quercus spp.), members of the Beech family (Fagacea), are trees and shrubs having simple, alternate leaves found throughout the world. Characterized by their strong, complex wood, wind-pollinated flowers, fruits called acorns, and their ability to live for centuries, oaks have played an important role in temperate landscapes. Of the 500 species in the genus Quercus, approximately 90 are foun…
Obesity can be defined as a body weight that is greater than 30% above a favorable target weight. In order to fit the definition of obesity, the excess weight must be due to adipose, or fat, tissue. Muscle mass does not account for the weight attributed to obesity. Therefore, a body-builder with tremendous muscle mass for example is not, by definition, obese. A deleterious condition, obesity is ha…
Since Plato wrote of political obligation in his dialogue Crito, obligation in general has been of ongoing interest to philosophers. In that dialogue, Socrates argues that he was under an obligation to obey the laws of Athens and comply with a sentence of death. During the course of the argument, he raises and offers solutions to many of the central issues about obligation that philosophers still …
The term Occidentalism refers primarily to the many ways in which non-Western intellectuals, artists, and the general public perceive and present the West. Though it seems to be an inversion of Orientalism, it has acquired some unique aspects defying a simple definition. In fact, the practices and discourses of Occidentalism vary a great deal, from time to time and region to region. If we can arbi…
Ocean basins are that part of Earth's surface that extends seaward from the continental margins, ranging from an average water depth of about 6,500 ft (2,000 m) down into the deepest trenches. The ocean basins constitute one of the two major topographic features of Earth's surface, the other being the continents. Ocean basins cover about 70% of the total sea area and about half of th…
The ocean sunfish (Mola mola), also called the headfish, is so named because of its unique shape: it looks as if it is all head and no body. The ocean sunfish is a very large species that lives in tropical and temperate waters. The ocean sunfish has a flattened, oval body that may measure 11 ft (3.5 m) in length and weigh as much as 2,000 lb (1,000 kg). In contrast to its huge size, it has a verte…
Ocean zones are layers within the seas that contain distinctive plant and animal life. They are sometimes referred to as ocean layers or environmental zones. A system of zonation frequently used by oceanographers grew out of suggestions made by Joel Hedgpeth in 1957. According to that system, the ocean environment is first divided into two broad categories, known as realms, the benthic realm, cons…
Oceanography, the study of the oceans, is a combination of the sciences of biology, chemistry, geology, physics, and meteorology. Ancient explorers of the ocean were sailors and fishermen who learned about marine biology by observing the sea life and discovering when it was most plentiful. They observed the effects of wind, currents, and tides, and learned how to use them to their advantage, or to…