Thursday, June 25, 2009

BATTERY

Battery, also electric cell, device that converts chemical energy into electricity. Strictly speaking, a battery consists of two or more cells connected in series or parallel, but the term is also used for single cells. All cells consist of a liquid, paste, or solid electrolyte and a positive electrode, and a negative electrode. The electrolyte is an ionic conductor; one of the electrodes will react, producing electrons, while the other will accept electrons. When the electrodes are connected to a device to be powered, called a load, an electrical current flows.
Batteries in which the chemicals cannot be reconstituted into their original form once the energy has been converted (that is, batteries that have been discharged) are called primary cells or voltaic cells. Batteries in which the chemicals can be reconstituted by passing an electric current through them in the direction opposite that of normal cell operation are called secondary cells, rechargeable cells, storage cells, or accumulators.

PRIMARY CELLS
The most common form of primary cell is the Leclanché cell, invented by the French chemist Georges Leclanché in the 1860s. It is popularly called a dry cell or flashlight battery. The Leclanché cell in use today is very similar to the original invention. The electrolyte consists of a mixture of ammonium chloride and zinc chloride made into a paste. The negative electrode is made of zinc, as is the outside shell of the cell, and the positive electrode is a carbon rod surrounded by a mixture of carbon and manganese dioxide. The Leclanché cell produces about 1.5 V.
Another widely used primary cell is the zinc-mercuric-oxide cell, more commonly called a mercury battery. It can be made in the shape of a small flat disk and is used in this form in hearing aids, photoelectric cells, and electric wristwatches. The negative electrode consists of zinc, the positive electrode is of mercuric oxide, and the electrolyte is a solution of potassium hydroxide. The mercury battery produces about 1.34 V.
The fuel cell is another type of primary cell. It is unique in that the chemicals are not contained within the cell but are supplied from outside.
SECONDARY CELLS
The storage battery, or secondary cell, which can be recharged by reversing the chemical reaction, was invented in 1859 by the French physicist Gaston Planté. Planté's cell was a lead-acid battery, the type widely used today. The lead-acid battery, which consists of three or six cells connected in series, is used in automobiles, trucks, aircraft, and other vehicles. Its chief advantage is that it can deliver a strong current of electricity for starting an engine; however, it runs down quickly. The electrolyte is a dilute solution of sulfuric acid, the negative electrode consists of lead, and the positive electrode of lead dioxide. In operation, the negative lead electrode dissociates into free electrons and positive lead ions. The electrons travel through the external electric circuit, and the positive lead ions combine with the sulfate ions in the electrolyte to form lead sulfate. When the electrons reenter the cell at the positive lead-dioxide electrode, another chemical reaction occurs. The lead dioxide combines with the hydrogen ions in the electrolyte and with the returning electrons to form water, releasing lead ions in the electrolyte to form additional lead sulfate.
A lead-acid storage cell runs down as the sulfuric acid gradually is converted into water and the electrodes are converted into lead sulfate. When the cell is being recharged, the chemical reactions described above are reversed until the chemicals have been restored to their original condition. A lead-acid battery has a useful life of about four years. It produces about 2 V per cell. Recently, lead batteries with useful lives of 50 to 70 years have been developed for special applications.
Another widely used secondary cell is the alkaline cell, or nickel-iron battery, developed by the American inventor Thomas Edison in the 1900s. The principle of operation is the same as in the lead-acid cell except that the negative electrode consists of iron, the positive electrode is of nickel oxide, and the electrolyte is a solution of potassium hydroxide. The nickel-iron cell has the disadvantage of giving off hydrogen gas during charging. This battery is used principally in heavy industry applications. The Edison battery has a useful life of approximately ten years and produces about 1.15 V.
Another alkaline cell similar to the Edison battery is the nickel-cadmium cell, or cadmium battery, in which the iron electrode is replaced by one consisting of cadmium. It also produces about 1.15 V, and its useful lifetime is about 25 years.
A number of new types of batteries have been designed for use in electric vehicles. Improved versions of conventional storage batteries have been developed for electric cars, but they still suffer the drawbacks of either short range, high expense, bulkiness, or environmental problems. Advanced batteries that show promise for use in electric vehicles include lithium-iron sulfide, zinc-chlorine, nickel metal hydride, and sodium-sulfur. The U.S. Advanced Battery Consortium (USABC), a consortium that includes the U.S. Department of Energy and the three major American automakers, was set up in 1991 to speed development of advanced storage batteries. Such batteries are also being developed by electric utilities to be used for “load leveling,” to compensate for momentary system load fluctuations. Such battery modules could be installed close to sites of variable demand. They cause few environmental problems and occupy little space.
SOLAR BATTERY
Solar batteries produce electricity by a photoelectric conversion process. The source of electricity is a photosensitive semiconducting substance such as a silicon crystal to which impurities have been added. When the crystal is struck by light, electrons are dislodged from the surface of the crystal and migrate toward the opposite surface. There they are collected as a current of electricity. Solar batteries have very long lifetimes and are used chiefly in spacecraft as a source of electricity to operate the equipment aboard..

DEMOCRACY

Democracy (Greek demos,”the people”; kratein, “to rule”), political system in which the people of a country rule through any form of government they choose to establish. In modern democracies, supreme authority is exercised for the most part by representatives elected by popular suffrage. The representatives may be supplanted by the electorate according to the legal procedures of recall and referendum, and they are, at least in principle, responsible to the electorate. In many democracies, such as the United States, both the executive head of government and the legislature are elected. In typical constitutional monarchies such as the United Kingdom and Norway, only the legislators are elected, and from their ranks a cabinet and a prime minister are chosen.


Although often used interchangeably, the terms democracy and republic are not synonymous. Both systems delegate the power to govern to their elected representatives. In a republic, however, these officials are expected to act on their own best judgment of the needs and interests of the country. The officials in a democracy more generally and directly reflect the known or ascertained views of their constituents, sometimes subordinating their own judgment.

DEMOCRACY IN ANCIENT GREECE AND ROME
Rule by the people played an important part in the democracies of the pre-Christian era. The democracies of the city-states of classical Greece and of Rome during the early years of the Republic were unlike the democracies of today. They were direct democracies, in which all citizens could speak and vote in assemblies that resembled New England town meetings. Representative government was unknown and unnecessary because of the small size of the city-states (almost never more than 10,000 citizens). Ancient democracy did not presuppose equality of all individuals; the majority of the populace, notably slaves and women, had no political rights. Athens, the greatest of the city democracies, limited the franchise to native-born citizens. Roman democracy resembled that of the Greeks, although Rome sometimes granted citizenship to men of non-Roman descent. The Roman Stoic philosophy, which defined the human race as part of a divine principle, and the Jewish and Christian religions, which emphasized the rights of the underprivileged and the equality of all before God, contributed to the development of modern democratic theory.
The Roman Republic ended in the despotism of the empire. The free cities of Italy, Germany, and Flanders carried on the democratic tradition and applied some principles of democracy during the Middle Ages. Slaves ceased to constitute a major portion of national populations. As feudalism ended, a rich commercial middle class arose, possessing the money and leisure necessary to participate in governmental affairs. One result was the rebirth of a spirit of freedom based on ancient Greek and Roman principles. Concepts of equal political and social rights were further defined during the Renaissance, when the development of humanism was fostered, and later during the Reformation, in the struggle for religious freedom.

WESTERN EUROPE AND THE U.S.

Beginning with the first popular rebellion against monarchy in England (1642), which was brought to a climax by the execution of King Charles I, political and revolutionary action against autocratic European governments resulted in the establishment of democratic governments. Such action was inspired and guided largely by political philosophers, notably the French philosophers Montesquieu and Jean Jacques Rousseau, and the American statesmen Thomas Jefferson and James Madison. Before the end of the 19th century, every important Western European monarchy had adopted a constitution limiting the power of the Crown and giving a considerable share of political power to the people. In many of these countries, a representative legislature modeled on the British Parliament was instituted. British politics was then possibly the greatest single influence on the organization of world democracies, although the French Revolution also exerted a powerful influence. Later, the success of democratic institutions in the United States served as a model for many peoples.

The major features of modern democracy include individual freedom, which entitles citizens to the liberty and responsibility of shaping their own careers and conducting their own affairs; equality before the law; and universal suffrage and education. Such features have been proclaimed in great historic documents, for example, the U.S. Declaration of Independence, which asserted the right to life, liberty, and the pursuit of happiness; the French Declaration of the Rights of Man and of the Citizen, which affirmed the principles of civil liberty and of equality before the law; and the Atlantic Charter, which formulated the four basic freedoms.

By the middle of the 20th century, every independent country in the world, with only a few exceptions, had a government that, in form if not in practice, embodied some of the principles of democracy. Although the ideals of democracy have been widely professed, the practice and fulfillment have been different in many countries.

VAMPIRE

Vampire, in folklore, a corpse that rises from the grave during the night, often in the form of a bat, and, for nourishment, sucks the blood of sleeping humans. Various talismans and herbs supposedly avert vampires, but, according to tradition, they can be destroyed only by cremation or by stakes driven through their hearts. Belief in vampires originated in ancient times and was especially widespread among the Slavs. The novel Dracula (1897) by the British writer Bram Stoker tells the story of the Transylvanian vampire Count Dracula, who became one of the most popular subjects of horror films.

ASOKA

Ashoka or Asoka (?-232 bc), third king of the Maurya dynasty, who ruled almost the whole of the Indian subcontinent from about 269 to 232 bc (see Mauryan Empire). Ashoka stands unique among emperors in world history: After successfully concluding a major military campaign, he was so disturbed by the suffering that it had caused that he forsook war and thereafter endorsed nonviolence and peaceful persuasion in consolidating his vast empire.

The major source of documentation for Ashoka’s reign is the succession of edicts that he issued to his subjects in every part of his empire. These edicts were inscribed on rock surfaces and on specially polished columns with handsomely sculpted capitals. They were written in Prakrit languages (a group of ancient Indian dialects) for the Indian population, and in Greek and Aramaic for the Hellenistic Greeks and Iranians in the northwestern part of the empire (see Indian Languages; Greek Language; Aramaic Language). Historians have established the extent of Ashoka’s empire through the location of these edicts, as well as by archaeological excavations of artifacts, monuments, and urban sites associated with the Mauryas. In one of his edicts, Ashoka named as his contemporaries five Hellenistic kings, some of whom he had diplomatic contacts with, and this has provided a chronological cross-reference for his reign.
Buddhist texts composed by monks in Sri Lanka and northwestern India color the narrative of Ashoka’s life and depict him as concerned closely with the spread of Buddhism, which was then a relatively new religion. One of these narratives associates him with astutely handling a rebellion against oppression by local officers in the city of Takshasila, in Gandhara, an ancient region in northwestern India. Ashoka’s administrative experience may have begun with the control of Gandhara. Another source describes him in a similar capacity in central India, governing from the city of Ujjain.

ASHOKA’S EMPIRE
Ashoka’s grandfather, Chandragupta Maurya (321?–298?), had established a large kingdom in northern India. This kingdom was further expanded by Ashoka’s father, Bindusara (298?-273?). As a younger son, Ashoka had to fight his elder brothers to reach the throne, possibly with the help of some ministers in Pātaliputra (modern Patna), the capital of the Mauryan Empire. This may have resulted in an interregnum of four years between his father’s death and Ashoka’s formal acceptance as emperor. On becoming king in about 269, Ashoka inherited a vast empire stretching from the Kashmīr region in the north to modern Karnātaka state in the south, and from the Ganges delta in the east to southern and eastern Afghanistan in the northwest.
Historians previously thought that a highly centralized bureaucracy functioning from Pātaliputra uniformly controlled all parts of the empire. They now suggest that the degree of control may have been different in different areas. It is likely that the central government directly administered the region around the capital, which had long been ruled by the Mauryas and their predecessors as the ancient kingdom of Magadha. Close communication would likewise have been maintained with the empire’s major cities, such as Takshasila, Ujjain, Vidisha, Tosali, and Suvarnagiri. Peripheral areas may have been more loosely controlled.
After eight years as king, Ashoka conquered Kalinga (in modern Orissa state). He did this in order to control a part of the subcontinent that was rich in ores and agrarian revenue, as well as to secure the sea route along the eastern coast to the Krishna valley, where major goldfields and veins of semiprecious stones were located. Ashoka’s remorse at the suffering caused by this campaign led him to reject violent conquest as a means to any end. His interest in Buddhism, which had begun earlier, gradually increased.
ASHOKA’S EDICTS
Ashoka began to issue his edicts after the 12th year of his reign. In them, he expressed his policies, concerns, and administrative changes, as well as his aspirations of instituting a new social ethic.
Ashoka’s edicts fall into various categories. A small number relate to the activities of the Buddhist sangha, or order, and of these some are addressed to local officers and some to monks. Those known as the Minor Edicts describe Ashoka’s general involvement with Buddhism, among other matters. The Greek and Aramaic versions of these edicts are useful in shedding fresh light on the meaning of certain words in Prakrit. For example, it has been debated whether Ashoka’s use of the word dhamma (dharma in Sanskrit, a term incorporating a number of interrelated precepts such as piety and virtue) refers specifically to the Buddha’s teaching or to a wider understanding of social ethics, as is suggested by the term eusebeia in the Greek version.
The Major Rock Edicts and the Pillar Edicts are more extensive and more detailed. They reveal Ashoka’s definition of social ethics, which emphasized tolerance for diverse ideologies; respect for all religious teachers; and harmonious relationships between parents and children, teachers and pupils, and employers and employees. The Pillar Edicts, which Ashoka issued in the 27th and 28th years of his reign, were a review of his activities and a testament to his policies. They show that he promoted the welfare of his subjects by building an extensive network of roads lined with shade trees and provided with wells and rest houses at regular intervals. This road system facilitated both trade and administration in the Mauryan Empire. Ashoka also established hospitals and planted medicinal herbs. With the aim of improving conditions for his subjects, he appointed special officers, the mahamairas, to attend to their various problems, and he gave additional powers to rural and judicial administrators.
Whereas Ashoka is largely ignored in Hindu sources, in Buddhist texts he is presented as a pious Buddhist king whose principal concern was the well-being of the sangha. Among the legends of his later years are stories about the evil acts of his young queen. However, these stories contain considerable exaggeration and were meant to be read not only as historical accounts but also as morality tales. Ashoka’s legendary fame in Buddhist societies arises from his later association with the concept of the chakraqvartin, or the righteous ruler in whose reign the wheel of law, the symbol representing the fundamental teachings of Buddhism, rolls across the kingdom ensuring the welfare of all.

BUSINESS

Business, organized approach to providing customers with the goods and services they want. The word business also refers to an organization that provides these goods and services. Most businesses seek to make a profit—that is, they aim to achieve revenues that exceed the costs of operating the business. Prominent examples of for-profit businesses include Mitsubishi Group, General Motors Corporation, and Royal Dutch/Shell Group. However, some businesses only seek to earn enough to cover their operating costs. Commonly called nonprofits, these organizations are primarily nongovernmental service providers. Examples of nonprofit businesses include such organizations as social service agencies, foundations, advocacy groups, and many hospitals.

Business plays a vital role in the life and culture of countries with industrial and postindustrial (service- and information-based) free-market economies such as the United States. In free-market systems, prices and wages are primarily determined by competition, not by governments. In the United States, for example, many people buy and sell goods and services as their primary occupations. In 2001 American companies sold in excess of $10 trillion worth of goods and services. Businesses provide just about anything consumers want or need, including basic necessities such as food and housing, luxuries such as whirlpool baths and wide-screen televisions, and even personal services such as caring for children and finding companionship.


TYPES OF BUSINESSES

There are many types of businesses in a free-market economy. The three most common are (1) manufacturing firms, (2) merchandisers, and (3) service enterprises.


A Manufacturing Firms

Manufacturing firms produce a wide range of products. Large manufacturers include producers of airplanes, cars, computers, and furniture. Many manufacturing firms construct only parts rather than complete, finished products. These suppliers are usually smaller manufacturing firms, which supply parts and components to larger firms. The larger firms then assemble final products for market to consumers. For example, suppliers provide many of the components in personal computers, automobiles, and home appliances to large firms that create the finished or end products. These larger end-product manufacturers are often also responsible for marketing and distributing the products. The advantage that large businesses have in being able to efficiently and inexpensively control any parts of a production process is known as economies of scale. But small manufacturing firms may work best for producing certain types of finished products. Smaller end-product firms are common in the food industry and among artisan trades such as custom cabinetry.

B Merchandisers
Merchandisers are businesses that help move goods through a channel of distribution—that is, the route goods take in reaching the consumer. Merchandisers may be involved in wholesaling or retailing, or sometimes both.
A wholesaler is a merchandiser who purchases goods and then sells them to buyers, typically retailers, for the purpose of resale. A retailer is a merchandiser who sells goods to consumers. A wholesaler often purchases products in large quantities and then sells smaller quantities of each product to retailers who are unable to either buy or stock large amounts of the product. Wholesalers operate somewhat like large, end-product manufacturing firms, benefiting from economies of scale. For example, a wholesaler might purchase 5,000 pairs of work gloves and then sell 100 pairs to 50 different retailers. Some large American discount chains, such as Kmart Corporation and Wal-Mart Stores, Inc., serve as their own wholesalers. These companies go directly to factories and other manufacturing outlets, buy in large amounts, and then warehouse and ship the goods to their stores.
The division between retailing and wholesaling is now being blurred by new technologies that allow retailing to become an economy of scale. Telephone and computer communications allow retailers to serve far greater numbers of customers in a given span of time than is possible in face-to-face interactions between a consumer and a retail salesperson. Computer networks such as the Internet, because they do not require any physical communication between salespeople and customers, allow a nearly unlimited capacity for sales interactions known as 24/7—that is, the Internet site can be open for a transaction 24 hours a day, seven days a week and for as many transactions as the network can handle. For example, a typical transaction to purchase a pair of shoes at a shoe store may take a half-hour from browsing, to fitting, to the transaction with a cashier. But a customer can purchase a pair of shoes through a computer interface with a retailer in a matter of seconds.
Computer technology also provides retailers with another economy of scale through the ability to sell goods without opening any physical stores, often referred to as electronic commerce or e-commerce. Retailers that provide goods entirely through Internet transactions do not incur the expense of building so-called brick-and-mortar stores or the expense of maintaining them.

C Service Enterprises
Service enterprises include many kinds of businesses. Examples include dry cleaners, shoe repair stores, barbershops, restaurants, ski resorts, hospitals, and hotels. In many cases service enterprises are moderately small because they do not have mechanized services and limit service to only as many individuals as they can accommodate at one time. For example, a waiter may be able to provide good service to four tables at once, but with five or more tables, customer service will suffer.
In recent years the number of service enterprises in wealthier free-market economies has grown rapidly, and spending on services now accounts for a significant percentage of all spending. By the late 1990s, private services accounted for more than 21 percent of U.S. spending. Wealthier nations have developed postindustrial economies, where entertainment and recreation businesses have become more important than most raw material extraction such as the mining of mineral ores and some manufacturing industries in terms of creating jobs and stimulating economic growth. Many of these industries have moved to developing nations, especially with the rise of large multinational corporations. As postindustrial economies have accumulated wealth, they have come to support systems of leisure, in which people are willing to pay others to do things for them. In the United States, vast numbers of people work rigid schedules for long hours in indoor offices, stores, and factories. Many employers pay high enough wages so that employees can afford to balance their work schedules with purchased recreation. People in the United States, for example, support thriving travel, theme park, resort, and recreational sport businesses.

BANKING

Banking, the business of providing financial services to consumers and businesses. The basic services a bank provides are checking accounts, which can be used like money to make payments and purchase goods and services; savings accounts and time deposits that can be used to save money for future use; loans that consumers and businesses can use to purchase goods and services; and basic cash management services such as check cashing and foreign currency exchange. Four types of banks specialize in offering these basic banking services: commercial banks, savings and loan associations, savings banks, and credit unions.

A broader definition of a bank is any financial institution that receives, collects, transfers, pays, exchanges, lends, invests, or safeguards money for its customers. This broader definition includes many other financial institutions that are not usually thought of as banks but which nevertheless provide one or more of these broadly defined banking services. These institutions include finance companies, investment companies, investment banks, insurance companies, pension funds, security brokers and dealers, mortgage companies, and real estate investment trusts. This article, however, focuses on the narrower definition of a bank and the services provided by banks in Canada and the United States. (For information on other financial institutions, see Insurance; Investment Banking; and Trust Companies.)
Banking services are extremely important in a free market economy such as that found in Canada and the United States. Banking services serve two primary purposes. First, by supplying customers with the basic mediums-of-exchange (cash, checking accounts, and credit cards), banks play a key role in the way goods and services are purchased. Without these familiar methods of payment, goods could only be exchanged by barter (trading one good for another), which is extremely time-consuming and inefficient. Second, by accepting money deposits from savers and then lending the money to borrowers, banks encourage the flow of money to productive use and investments. This in turn allows the economy to grow. Without this flow, savings would sit idle in someone’s safe or pocket, money would not be available to borrow, people would not be able to purchase cars or houses, and businesses would not be able to build the new factories the economy needs to produce more goods and grow. Enabling the flow of money from savers to investors is called financial intermediation, and it is extremely important to a free market economy.

BANKING REGULATION

Banking is one of the most heavily regulated industries in the United States, and the regulatory structure is quite complex. This owes in part to the fact that the United States has a dual banking system. A dual banking system means that banks and thrifts can be chartered and therefore regulated either by the state in which they operate or by a national chartering agency.
The Office of the Comptroller of the Currency (OCC) in the U.S. Department of Treasury is the federal chartering agency for national banks. The Office of the Comptroller of the Currency provides general supervision of national banks, including periodic bank examinations to determine compliance with rules and regulations and the soundness of bank operations. The Office of Thrift Supervision (OTS) in the Treasury Department charters national savings and loans (SLAs) and savings banks.
The agencies that insure deposits in banks and thrifts also have a role in regulating them. Almost all banks and thrifts are federally insured by the Federal Deposit Insurance Corporation (FDIC). The FDIC insures each depositor (not each separate deposit) for up to $100,000 in each bank or thrift in which the depositor has deposits. The Bank Insurance Fund (BIF) in the FDIC insures commercial bank and savings bank deposits. The Savings Association Insurance Fund (SAIF) in the FDIC insures savings and loan deposits. The National Credit Union Share Insurance Fund (NCUSIF) in the National Credit Union Association (NCUA) insures credit union deposits.
The Federal Reserve is also responsible for regulating commercial banks that are members of the Federal Reserve System and bank holding companies. As a result, a nationally chartered, federally insured, Federal Reserve member bank is subject to the regulations of the OCC, BIF, and the Federal Reserve.
The regulatory landscape is complicated further by the fact that state banking authorities regulate state-chartered banks and frequently conduct their own examinations of state banks. To help sort out the maze of potential regulators, banks are assigned one regulator with primary responsibility for examining the bank. The primary regulator of nationally chartered banks and thrifts is the OCC. The primary regulator of state-chartered banks that belong to the Federal Reserve is the Federal Reserve. The primary regulator of state-chartered banks that are not Fed members but are FDIC insured is the FDIC, while the primary regulator of state-chartered, noninsured banks is the state.
The regulatory agencies also enforce legislation passed by the U.S. Congress. Such legislation attempts to ensure that lending institutions act fairly and that bank customers are well informed about banking services and practices. For example, the Truth-in-Lending Act (1968) and the Fair Credit and Charge Card Disclosure Act (1988) require lenders to disclose the true interest rate on loans on a uniform basis so that borrowers know the true cost of credit.
The Fair Housing Act (1968) and the Equal Credit Opportunity Act (1976) prohibit discrimination against borrowers on the basis of race, color, religion, national origin, sex, marital status, age, or receipt of public assistance. The Community Reinvestment Act (1977) requires banks, savings and loans, and savings banks to meet the credit needs of their local communities. This act was intended to prevent banks located in low-income areas from refusing loans to local residents, who were often members of minority groups. The Truth-in-Savings Act (1991) mandates uniform disclosure of the terms and conditions that banking institutions impose on their deposit accounts so that depositors know the true interest rate they receive on their deposits.

ASTRONOMY

Astronomy, study of the universe and the celestial bodies, gas, and dust within it. Astronomy includes observations and theories about the solar system, the stars, the galaxies, and the general structure of space. Astronomy also includes cosmology, the study of the universe and its past and future. People who study astronomy are called astronomers, and they use a wide variety of methods to perform their research. These methods usually involve ideas of physics, so most astronomers are also astrophysicists, and the terms astronomer and astrophysicist are basically identical. Some areas of astronomy also use techniques of chemistry, geology, and biology.


Astronomy is the oldest science, dating back thousands of years to when primitive people noticed objects in the sky overhead and watched the way the objects moved. In ancient Egypt, the first appearance of certain stars each year marked the onset of the seasonal flood, an important event for agriculture. In 17th-century England, astronomy provided methods of keeping track of time that were especially useful for accurate navigation. Astronomy has a long tradition of practical results, such as our current understanding of the stars, day and night, the seasons, and the phases of the Moon. Much of today's research in astronomy does not address immediate practical problems. Instead, it involves basic research to satisfy our curiosity about the universe and the objects in it. One day such knowledge may well be of practical use to humans. See also History of Astronomy.

SOLAR SYSTEM



Solar System, the Sun and everything that orbits the Sun, including the nine planets and their satellites; the asteroids and comets; and interplanetary dust and gas. The term may also refer to a group of celestial bodies orbiting another star (see Extrasolar Planets). In this article, solar system refers to the system that includes Earth and the Sun.


The dimensions of the solar system are specified in terms of the mean distance from Earth to the Sun, called the astronomical unit (AU). One AU is 150 million km (about 93 million mi). The most distant known planet, Pluto, orbits about 39 AU from the Sun. Estimates for the boundary where the Sun’s magnetic field ends and interstellar space begins—called the heliopause—range from 86 to 100 AU.


The most distant known planetoid orbiting the Sun is Sedna, whose discovery was reported in March 2004. A planetoid is an object that is too small to be a planet. At the farthest point in its orbit, Sedna is about 900 AU from the Sun. Comets known as long-period comets, however, achieve the greatest distance from the Sun; they have highly eccentric orbits ranging out to 50,000 AU or more.

The solar system was the only planetary system known to exist around a star similar to the Sun until 1995, when astronomers discovered a planet about 0.6 times the mass of Jupiter orbiting the star 51 Pegasi. Jupiter is the most massive planet in our solar system. Soon after, astronomers found a planet about 8.1 times the mass of Jupiter orbiting the star 70 Virginis, and a planet about 3.5 times the mass of Jupiter orbiting the star 47 Ursa Majoris. Since then, astronomers have found planets and disks of dust in the process of forming planets around many other stars. Most astronomers think it likely that solar systems of some sort are numerous throughout the universe.

CELL(biology)




Cell (biology), basic unit of life. Cells are the smallest structures capable of basic life processes, such as taking in nutrients, expelling waste, and reproducing. All living things are composed of cells. Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a single cell. Plants, animals, and fungi are multicellular; that is, they are composed of a great many cells working in concert. But whether it makes up an entire bacterium or is just one of trillions in a human being, the cell is a marvel of design and efficiency. Cells carry out thousands of biochemical reactions each minute and reproduce new cells that perpetuate life.



Cells vary considerably in size. The smallest cell, a type of bacterium known as a mycoplasma, measures 0.0001 mm (0.000004 in) in diameter; 10,000 mycoplasmas in a row are only as wide as the diameter of a human hair. Among the largest cells are the nerve cells that run down a giraffe’s neck; these cells can exceed 3 m (9.7 ft) in length. Human cells also display a variety of sizes, from small red blood cells that measure 0.00076 mm (0.00003 in) to liver cells that may be ten times larger. About 10,000 average-sized human cells can fit on the head of a pin.
Along with their differences in size, cells present an array of shapes. Some, such as the bacterium Escherichia coli, resemble rods. The paramecium, a type of protozoan, is slipper shaped; and the amoeba, another protozoan, has an irregular form that changes shape as it moves around. Plant cells typically resemble boxes or cubes. In humans, the outermost layers of skin cells are flat, while muscle cells are long and thin. Some nerve cells, with their elongated, tentacle-like extensions, suggest an octopus.
In multicellular organisms, shape is typically tailored to the cell’s job. For example, flat skin cells pack tightly into a layer that protects the underlying tissues from invasion by bacteria. Long, thin muscle cells contract readily to move bones. The numerous extensions from a nerve cell enable it to connect to several other nerve cells in order to send and receive messages rapidly and efficiently.
By itself, each cell is a model of independence and self-containment. Like some miniature, walled city in perpetual rush hour, the cell constantly bustles with traffic, shuttling essential molecules from place to place to carry out the business of living. Despite their individuality, however, cells also display a remarkable ability to join, communicate, and coordinate with other cells. The human body, for example, consists of an estimated 20 to 30 trillion cells. Dozens of different kinds of cells are organized into specialized groups called tissues. Tendons and bones, for example, are composed of connective tissue, whereas skin and mucous membranes are built from epithelial tissue. Different tissue types are assembled into organs, which are structures specialized to perform particular functions. Examples of organs include the heart, stomach, and brain. Organs, in turn, are organized into systems such as the circulatory, digestive, or nervous systems. All together, these assembled organ systems form the human body.
The components of cells are molecules, nonliving structures formed by the union of atoms. Small molecules serve as building blocks for larger molecules. Proteins, nucleic acids, carbohydrates, and lipids, which include fats and oils, are the four major molecules that underlie cell structure and also participate in cell functions. For example,
a tightly organized arrangement of lipids, proteins,
and protein-sugar compounds forms the plasma
membrane, or outer boundary, of certain cells. The
organelles, membrane-bound compartments in cells,
are built largely from proteins. Biochemical reactions
in cells are guided by enzymes, specialized proteins that
speed up chemical reactions. The nucleic acid
deoxyribonucleic acid (DNA) contains the hereditary
information for cells, and another nucleic acid, ribonucleic
acid(RNA), works with DNA to build the thousands
of proteins the cell needs.

Wednesday, June 24, 2009

LORD BUDDHA



Buddha (563?-483?bc), Indian philosopher and the founder of Buddhism, born in Lumbini, Nepal. He was the son of the head of the Sakya warrior caste, with the private name of Siddhartha; in later life he was known also as Sakyamuni (Sage of the Sakyas). The name Gautama Buddha is a combination of the family name Gautama and the appellation Buddha, meaning “Enlightened One.”
All the surviving accounts of Buddha's life were written many years after his death by idealizing followers rather than by objective historians. Consequently, it is difficult to separate facts from the great mass of myth and legend in which they are embedded. From the available evidence, Buddha apparently showed an early inclination to meditation and reflection, displeasing his father, who wanted him to be a warrior and ruler rather than a religious philosopher. Yielding to his father's wishes, he married at an early age and participated in the worldly life of the court. Buddha found his carefree, self-indulgent existence dull, and after a while he left home and began wandering in search of enlightenment. One day in 533, according to tradition, he encountered an aged man, a sick man, and a corpse, and he suddenly and deeply realized that suffering is the common lot of humankind. He then came upon a mendicant monk, calm and serene, whereupon he determined to adopt his way of life and forsake family, wealth, and power in the quest for truth. This decision, known in Buddhism as the Great Renunciation, is celebrated by Buddhists as a turning point in history. Gautama was then 29 years old, according to tradition.
Wandering as a mendicant over northern India, Buddha first investigated Hinduism. He took instruction from some famous Brahman teachers, but he found the Hindu caste system repellent and Hindu asceticism futile. He continued his search, attracting but later losing five followers. About 528, while sitting under a bo tree near Gaya, in what is now Buddh Gaya in the state of Bihār, he experienced the Great Enlightenment, which revealed the way of salvation from suffering. Shortly afterward he preached his first sermon in the Deer Park near Benares (now Vārānasi). This sermon, the text of which is preserved, contains the gist of Buddhism. Many scholars regard it as comparable, in its tone of moral elevation and historical importance, to Jesus Christ's Sermon on the Mount.
The five disciples rejoined Buddha at Benares. Accompanied by them, he traveled through the valley of the Ganges River, teaching his doctrines, gathering followers, and establishing monastic communities that admitted anyone regardless of caste. He returned briefly to his native town and converted his father, his wife, and other members of his family to his beliefs. After 45 years of missionary activity Buddha died in Kusinagara, Nepal, as a result of eating contaminated pork. He was about 80 years old.
Buddha was one of the greatest human beings, a man of noble character, penetrating vision, warm compassion, and profound thought. Not only did he establish a great new religion, but his revolt against Hindu hedonism, asceticism, extreme spiritualism, and the caste system deeply influenced Hinduism itself. His rejection of metaphysical speculation and his logical thinking introduced an important scientific strain heretofore lacking in Oriental thought. Buddha's teachings have influenced the lives of millions of people for nearly 2500 years.

MOUNT EVEREST



Everest, Mount, mountain peak in the Himalayas of southern Asia, considered the highest mountain in the world. Mount Everest is situated at the edge of the Tibetan Plateau (Qing Zang Gaoyuan), on the border of Nepal and the Tibet Autonomous Region of China.


Mount Everest was known as Peak XV until 1856, when it was named for Sir George Everest, the surveyor general of India from 1830 to 1843. The naming coincided with an official announcement of the mountain's height, taken as the average of six separate measurements made by the Great Trigonometrical Survey in 1850. Most Nepali people refer to the mountain as Sagarmatha, meaning “Forehead in the Sky.” Speakers of Tibetan languages, including the Sherpa people of northern Nepal, refer to the mountain as Chomolungma, Tibetan for “Goddess Mother of the World.”

Mount Everest was known as Peak XV until 1856, when it was named for Sir George Everest, the surveyor general of India from 1830 to 1843. The naming coincided with an official announcement of the mountain's height, taken as the average of six separate measurements made by the Great Trigonometrical Survey in 1850. Most Nepali people refer to the mountain as Sagarmatha, meaning “Forehead in the Sky.” Speakers of Tibetan languages, including the Sherpa people of northern Nepal, refer to the mountain as Chomolungma, Tibetan for “Goddess Mother of the World.”



HELL



Hell, in theology, any place or state of punishment and privation for human souls after death. More strictly, the term is applied to the place or state of eternal punishment of the damned, whether angels or human beings. The doctrine of the existence of hell is derived from the principle of the necessity for vindication of divine justice, combined with the human experience that evildoers do not always appear to be punished adequately in their lifetime. Belief in a hell was widespread in antiquity and is found in most religions of the world today.
Among the early Teutons the term hell signified a place under the earth to which the souls of all mortals, good or bad, were consigned after death; it thus denoted a conception similar to that of the Hebrew Sheol. Among the early Jews, as in other Semitic nations, existence in Sheol was regarded as a shadowy continuation of earthly life where all of the problems of earthly life came to an end. Later the dictum of the prophet Isaiah that the king of Babylon shall be “brought down to Sheol, to the depths of the Pit” (14:15) gave rise to the concept of various depths of Sheol, with corresponding degrees of reward and punishment.
Early Christian writers used the term hell to designate (1) the limbo of infants, where the unbaptized enjoy a natural bliss but are denied the supernatural bliss of the vision of God; (2) the limbo of the fathers, in which the souls of the just who died before the advent of Christ await their redemption, and which is mentioned in the Apostles' Creed, “He [Christ] descended into hell”; (3) a place of purgation from minor offenses leading inevitably to heaven (see Purgatory) and (4) the place of punishment of Satan and the other fallen angels and of all mortals who die unrepentant of serious sin. The last of these interpretations has the greatest acceptance today.
The duration of the punishments of hell has been a subject of controversy since early Christian times. The 3rd century Christian writer and theologian Origen and his school taught that the purpose of these punishments was purgatorial, and that they were proportionate to the guilt of the individual. Origen held that, in time, the purifying effect would be accomplished in all, even devils; that punishment would ultimately cease; and that everyone in hell eventually would be restored to happiness. This doctrine was condemned by the Second Council of Constantinople in 553, and a belief in the eternity of the punishments in hell became characteristic of both the Orthodox church and the Roman Catholic church. It also passed into the creeds of the churches of the Reformation but the doctrine of hell was rejected by many of the more radical thinkers of the Renaissance.
In modern times the belief in physical punishment after death and the endless duration of this punishment has been rejected by many. The question about the nature of the punishment of hell is equally controversial. Opinions range from holding the pains of hell to be no more than the remorse of conscience to the traditional belief that the “pain of loss” (the consciousness of having forfeited the vision of God and the happiness of heaven) is combined with the “pain of sense” (actual physical torment).
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MIRROR


Mirror, optical device, commonly made of glass, with a smooth, polished surface that forms images by the reflection of rays of light (see Light; Optics; Reflection).
Mirrors made of brass are mentioned in the Bible, and mirrors of bronze were in common use among the ancient Egyptians, Greeks, and Romans. Polished silver was also used by the Greeks and Romans to produce reflections. Crude forms of glass mirrors were first made in Venice in 1300. By the end of the 17th century mirrors were made in Britain and the manufacture of mirrors developed subsequently into an important industry in the other European countries and in the United States.
The original method of making glass mirrors consisted of backing a sheet of glass with an amalgam of mercury and tin. The surface was overlaid with sheets of tinfoil that were rubbed down smooth and covered with mercury. A woolen cloth was held firmly over the surface by means of iron weights for about a day. The glass was then inclined and the excess mercury drained away, leaving a lustrous inner surface. The first attempt to back the glass with a solution of silver was made by the German chemist Justus von Liebig in 1836; various methods have been developed since then that depend on the chemical reduction of a silver salt to metallic silver. In the manufacture of mirrors today, in cases where this principle is utilized, the plate glass is cut to size, and all blemishes are removed by polishing with rouge. The glass is scrubbed and flushed with a reducing solution such as stannous chloride before silver is applied, and the glass is then placed on a hollow, cast-iron tabletop, covered with felt, and kept warm by steam. A solution of silver nitrate is poured on the glass and left undisturbed for about 1 hour. The silver nitrate is reduced to a metallic silver and a lustrous deposit of silver gradually forms. The deposit is dried, coated with shellac, and painted. In other methods of mirror production, the silver solution is added with a reducing agent, such as formaldehyde of glucose. Silvering chemicals are often applied in spray form. Special mirrors are sometimes coated with the metal in the form of vapor obtained by vaporizing silver electrically in a vacuum. Large mirrors are often coated with aluminum in the same way (see Electroplating).
None of these types of mirrors is perfect; that is, some of the light that strikes the surface is either absorbed by the mirror or travels through it. In 1998, scientists at the Massachusetts Institute of Technology made a perfect mirror, a mirror that reflects 100 percent of the light that strikes its surface. They used alternating, microscopic layers of tellurium and the plastic polystyrene. A tube lined with this type of mirror would transmit light better over long distances than an optical fiber (see Fiber Optics).
In addition to their general household use, mirrors are used in scientific apparatus, for example, as important components in microscopes and telescopes (see Microscope; Telescope).
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VOLCANO

Volcano, mountain or hill formed by the accumulation of materials erupted through one or more openings (called volcanic vents) in the earth's surface. The term volcano can also refer to the vents themselves. Most volcanoes have steep sides, but some can be gently sloping mountains or even flat tablelands, plateaus, or plains. The volcanoes above sea level are the best known, but the vast majority of the world's volcanoes lie beneath the sea, formed along the global oceanic ridge systems that crisscross the deep ocean floor (see Plate Tectonics). According to the Smithsonian Institution, 1511 above-sea volcanoes have been active during the past 10,000 years, 539 of them erupting one or more times during written history. On average, 50 to 60 above-sea volcanoes worldwide are active in any given year; about half of these are continuations of eruptions from previous years, and the rest are new.

Volcanic eruptions in populated regions are a significant threat to people, property, and agriculture. The danger is mostly from fast-moving, hot flows of explosively erupted materials, falling ash, and highly destructive lava flows and volcanic debris flows (see Volcano Hazards below). In addition, explosive eruptions, even from volcanoes in unpopulated regions, can eject ash high into the atmosphere, creating drifting volcanic ash clouds that pose a serious hazard to airplanes.

VOLCANO FORMATION
All volcanoes are formed by the accumulation of magma (molten rock that forms below the earth's surface). Magma can erupt through one or more volcanic vents, which can be a single opening, a cluster of openings, or a long crack, called a fissure vent. It forms deep within the earth, generally within the upper part of the mantle (one of the layers of the earth’s crust), or less commonly, within the base of the earth's crust. High temperatures and pressures are needed to form magma. The solid mantle or crustal rock must be melted under conditions typically reached at depths of 80 to 100 km (50 to 60 mi) below the earth’s surface.

Once tiny droplets of magma are formed, they begin to rise because the magma is less dense than the solid rock surrounding it. The processes that cause the magma to rise are poorly understood, but it generally moves upward toward lower pressure regions, squeezing into spaces between minerals within the solid rock. As the individual magma droplets rise, they join to form ever-larger blobs and move toward the surface. The larger the rising blob of magma, the easier it moves. Rising magma does not reach the surface in a steady manner but tends to accumulate in one or more underground storage regions, called magma reservoirs, before it erupts onto the surface. With each eruption, whether explosive or nonexplosive, the material erupted adds another layer to the growing volcano. After many eruptions, the volcanic materials pile up around the vent or vents. These piles form a topographic feature, such as a hill, mountain, plateau, or crater, that we recognize as a volcano. Most of the earth's volcanoes are formed beneath the oceans, and their locations have been documented in recent decades by mapping of the ocean floor..

VOLCANIC MATERIALS
Three different types of materials may erupt from an active volcano. These materials are lava, tephra (rock fragments), and gases. The type and amount of the material that erupts from an active volcano depends on the composition of the magma inside the volcano.
A Lava
Lava is magma that breaks the surface and erupts from a volcano. If the magma is very fluid, it flows rapidly down the volcano’s slopes. Lava that is more sticky and less fluid moves slower. Lava flows that have a continuous, smooth, ropy, or billowy surface are called pahoehoe (pronounced pah HOH ee hoh ee) flows, while aa (pronounced ah ah) flows have a jagged surface composed of loose, irregularly shaped lava chunks. Once cooled, pahoehoe forms smooth rocks, while aa forms jagged rocks. The words pahoehoe and aa are Hawaiian terms that describe the texture of the lava. Lava may also be described in terms of its composition and the type of rock it forms. Basalt, andesite, dacite, and rhyolite are all different kinds of rock that form from lava. Each type of rock, and the lava from which it forms, contains a different amount of the compound silicon dioxide. Basaltic lava has the least amount of silicon dioxide, andesitic and dacitic lava have medium levels of silicon dioxide, while rhyolitic lava has the most.

B Tephra
Tephra, or pyroclastic material, is made of rock fragments formed by explosive shattering of sticky magma (see Pyroclastic Flow). The term pyroclastic is of Greek origin and means "fire-broken" (pyro, “fire”; klastos, “broken”). Tephra refers to any airborne pyroclastic material regardless of size or shape. The best-known tephra materials include pumice, cinders, and volcanic ash. These fragments are exploded when gases build up inside a volcano and produce an explosion. The pieces of magma are shot into the air during the explosion. Ash refers to fragments smaller than 2 mm (0.08 in) in diameter. The finest ash is called volcanic dust and is made up of particles that are less than 0.06 mm (0.002 in) in diameter. Volcanic blocks, or bombs, are the largest fragments of tephra, more than 64 mm (2.5 in) in diameter (baseball size or larger). Some bombs can be the size of a small car.
C Gases
Gases, primarily in the form of steam, are released from volcanoes during eruptions. All eruptions, explosive or nonexplosive, are accompanied by the release of volcanic gas. The sudden escape of high-pressure volcanic gas from magma is the driving force for eruptions. Gases come from the magma itself or from the hot magma coming into contact with water in the ground. Volcanic plumes can appear dark during an eruption because the gases are mixed with dark-colored materials such as tephra. Most volcanic gases predominantly consist of water vapor (steam), with carbon dioxide (CO2) and sulfur dioxide (SO2) being the next two most common compounds along with smaller amounts of chlorine and fluorine gases.

WATER

Water, common name applied to the liquid state of the hydrogen-oxygen compound H2O. The ancient philosophers regarded water as a basic element typifying all liquid substances. Scientists did not discard that view until the latter half of the 18th century. In 1781 the British chemist Henry Cavendish synthesized water by detonating a mixture of hydrogen and air. However, the results of his experiments were not clearly interpreted until two years later, when the French chemist Antoine Laurent Lavoisier proved that water was not an element but a compound of oxygen and hydrogen. In a scientific paper presented in 1804, the French chemist Joseph Louis Gay-Lussac and the German naturalist Alexander von Humboldt demonstrated jointly that water consisted of two volumes of hydrogen to one of oxygen, as expressed by the present-day formula H2O.

Almost all the hydrogen in water has an atomic weight of 1. The American chemist Harold Clayton Urey discovered in 1932 the presence in water of a small amount (1 part in 6000) of so-called heavy water, or deuterium oxide (D2O); deuterium is the hydrogen isotope with an atomic weight of 2. In 1951 the American chemist Aristid Grosse discovered that naturally occurring water contains also minute traces of tritium oxide (T2O); tritium is the hydrogen isotope with an atomic weight of 3. See Atom.

PROPERTIES

Pure water is an odorless, tasteless liquid. It has a bluish tint, which may be detected, however, only in layers of considerable depth. Under standard atmospheric pressure (760 mm of mercury, or 760 torr); the freezing point of water is 0° C (32° F) and its boiling point is 100° C (212° F). Water attains its maximum density at a temperature of 4° C (39° F) and expands upon freezing. Like most other liquids, water can exist in a supercooled state; that is, it may remain a liquid although its temperature is below its freezing point. Water can easily be cooled to about -25° C (-13° F) without freezing, either under laboratory conditions or in the atmosphere itself. Supercooled water will freeze if it is disturbed, if the temperature is lowered further, or if an ice crystal or other particle is added to it. Its physical properties are used as standards to define the calorie and specific and latent heat (see Heat) and in the metric system for the original definition of the unit of mass, the gram.

Water is one of the best-known ionizing agents (see Ionization). Because most substances are somewhat soluble in water, it is frequently called the universal solvent. Water combines with certain salts to form hydrates. It reacts with metal oxides to form acids (see Acids and Bases). It acts as a catalyst in many important chemical reactions.



OCCURRENCE

Water is the only substance that occurs at ordinary temperatures in all three states of matter, that is, as a solid, a liquid, and a gas. As a solid, or ice, it is found as glaciers and ice caps, on water surfaces in winter, as snow, hail, and frost, and as clouds formed of ice crystals. It occurs in the liquid state as rain clouds formed of water droplets, and on vegetation as dew; in addition, it covers three-quarters of the surface of the earth in the form of swamps, lakes, rivers, and oceans. As gas, or water vapor, it occurs as fog, steam, and clouds. Atmospheric vapor is measured in terms of relative humidity, which is the ratio of the quantity of vapor actually present to the greatest amount possible at a given temperature. See Atmosphere; Cloud; Fog; Humidity; Rain.
Water occurs as moisture in the upper portion of the soil profile, in which it is held by capillary action to the particles of soil. In this state, it is called bound water and has different characteristics from free water See Soil; Soil Management. Under the influence of gravity, water accumulates in rock interstices beneath the surface of the earth as a vast groundwater reservoir supplying wells and springs and sustaining the flow of some streams during periods of drought.


WATER IN LIFE

Water is the major constitutent of living matter. From 50 to 90 percent of the weight of living organisms is water. Protoplasm, the basic material of living cells, consists of a solution in water of fats, carbohydrates, proteins, salts, and similar chemicals. Water acts as a solvent, transporting, combining, and chemically breaking down these substances. Blood in animals and sap in plants consist largely of water and serve to transport food and remove waste material. Water also plays a key role in the metabolic breakdown of such essential molecules as proteins and carbohydrates. This process, called hydrolysis, goes on continually in living cells.


NATURAL WATER CYCLE
Hydrology is the science concerned with the distribution of water on the earth, its physical and chemical reactions with other naturally occurring substances, and its relation to life on earth; the continuous movement of water between the earth and the atmosphere is known as the hydrological cycle. Under several influences, of which heat is predominant, water is evaporated from both water and land surfaces and is transpired from living cells. This vapor circulates through the atmosphere and is precipitated in the form of rain or snow. See Meteorology.
On striking the surface of the earth, the water follows two paths. In amounts determined by the intensity of the rain and the porosity, permeability, thickness, and previous moisture content of the soil, one part of the water, termed surface runoff, flows directly into rills and streams and thence into oceans or landlocked bodies of water; the remainder infiltrates into the soil. A part of the infiltrated water becomes soil moisture, which may be evaporated directly or may move upward through the roots of vegetation to be transpired from leaves. The portion of the water that overcomes the forces of cohesion and adhesion in the soil profile percolates downward, accumulating in the so-called zone of saturation to form the groundwater reservoir, the surface of which is known as the water table. Under natural conditions, the water table rises intermittently in response to replenishment, or recharge, and then declines as a result of continuous drainage into natural outlets such as springs. See Spring.

BLACK HOLE



Black Hole, an extremely dense celestial body that has been theorized to exist in the universe. The gravitational field of a black hole is so strong that, if the body is large enough, nothing, including electromagnetic radiation, can escape from its vicinity. The body is surrounded by a spherical boundary, called a horizon, through which light can enter but not escape; it therefore appears totally black.

PROPERTIES
The black-hole concept was developed by the German astronomer Karl Schwarzschild in 1916 on the basis of physicist Albert Einstein’s general theory of relativity. The radius of the horizon of a Schwarzschild black hole depends only on the mass of the body, being 2.95 km (1.83 mi) times the mass of the body in solar units (the mass of the body divided by the mass of the Sun). If a body is electrically charged or rotating, Schwarzschild’s results are modified. An “ergosphere” forms outside the horizon, within which matter is forced to rotate with the black hole; in principle, energy can be emitted from the ergosphere.
According to general relativity, gravitation severely modifies space and time near a black hole. As the horizon is approached from outside, time slows down relative to that of distant observers, stopping completely on the horizon. Once a body has contracted within its Schwarzschild radius, it would theoretically collapse to a singularity—that is, a dimensionless object of infinite density.
FORMATION
Black holes are thought to form during the course of stellar evolution. As nuclear fuels are exhausted in the core of a star, the pressure associated with their energy production is no longer available to resist contraction of the core to ever-higher densities. Two new types of pressure, electron and neutron pressure, arise at densities a million and a million billion times that of water, respectively, and a compact white dwarf or a neutron star may form. If the star is more than about five times as massive as the Sun, however, neither electron nor neutron pressure is sufficient to prevent collapse to a black hole.
In 1994 astronomers used the Hubble Space Telescope (HST) to uncover the first convincing evidence that a black hole exists. They detected an accretion disk (disk of hot, gaseous material) circling the center of the galaxy M87 with an acceleration that indicated the presence of an object 2.5 to 3.5 billion times the mass of the Sun. By 2000, astronomers had detected supermassive black holes in the centers of dozens of galaxies and had found that the masses of the black holes were correlated with the masses of the parent galaxies. More massive galaxies tend to have more massive black holes at their centers. Learning more about galactic black holes will help astronomers learn about the evolution of galaxies and the relationship between galaxies, black holes, and quasars.
The English physicist Stephen Hawking has suggested that many black holes may have formed in the early universe. If this were so, many of these black holes could be too far from other matter to form detectable accretion disks, and they could even compose a significant fraction of the total mass of the universe. For black holes of sufficiently small mass it is possible for only one member of an electron-positron pair near the horizon to fall into the black hole, the other escaping (see X Ray: Pair Production). The resulting radiation carries off energy, in a sense evaporating the black hole. Any primordial black holes weighing less than a few thousand million metric tons would have already evaporated, but heavier ones may remain.

The American astronomer Kip Thorne of California Institute of Technology in Pasadena, California, has evaluated the chance that black holes can collapse to form "wormholes," connections between otherwise distant parts of the universe. He concludes that an unknown form of "exotic matter" would be necessary for such wormholes to survive.




COMMAND

Command, in computer science, an instruction that initiates a computer function, operation, or program. All computer programs respond to some sort of specific commands, with more complicated programs generally having a larger quantity and variety of commands. Commands for similar functions differ depending on the computer system and operating system being used.
Commands are an integral part of the interface between the user and computer. Computers usually employ one of two types of user interfaces: command-line interfaces or graphical user interfaces (GUIs). Command-line interfaces are based on text. An example of a command-line interface is Microsoft Corporation’s Disk Operating System (MS-DOS). In programs that respond to commands through a command-line interface, the user must enter an exact command, usually in the form of a keyword, into the computer. An example is the command MEM in MS-DOS, which displays information about the amount and the various types of memory in the main computer memory.
Graphical user interfaces, such as the Apple Computer Inc. operating system and Microsoft’s Windows 95 operating system, enable the user to enter commands into the computer by single-or double-clicking a mouse button once an appropriate icon or keyword has been selected. The icon or keyword is selected from a menu, from the desktop, or from a window.
Once a user enters a command into the computer, the command is read by the computer’s operating system. The operating system is the most important program running on a computer because it performs basic functions, such as memory allocation, and allows other computer programs to run. One of the functions of the operating system is to interpret commands. This function is performed by a program running within each computer’s operating system called the command interpreter. The command interpreter reads the commands from the user or from a file and executes them.

KEYBOARD

Keyboard, in computer science, a keypad device with buttons or keys that a user presses to enter data characters and commands into a computer. Keyboards emerged from the combination of typewriter and computer-terminal technology. They are one of the fundamental pieces of personal computer (PC) hardware, along with the central processing unit (CPU), the monitor or screen, and the mouse or other cursor device.
The most common English-language key pattern for typewriters and keyboards is called QWERTY, after the layout of the first six letters in the top row of its keys (from left to right). In the late 1860s, American inventor and printer Christopher Sholes invented the modern form of the typewriter. Sholes created the QWERTY keyboard layout by separating commonly used letters so that typists would type slower and not jam their mechanical typewriters. Subsequent generations of typists have learned to type using QWERTY keyboards, prompting manufacturers to maintain this key orientation on typewriters.
Computer keyboards copied the QWERTY key layout and have followed the precedent set by typewriter manufacturers of keeping this convention. Modern keyboards connect with the computer CPU by cable or by infrared transmitter. When a key on the keyboard is pressed, a numeric code is sent to the keyboard’s driver software and to the computer’s operating system software. The driver translates this data into a specialized command that the computer’s CPU and application programs understand. In this way, users may enter text, commands, numbers, or other data. The term character is generally reserved for letters, numbers, and punctuation, but may also include control codes, graphical symbols, mathematical symbols, and graphic images.
Almost all standard English-language keyboards have keys for each character of the American Standard Code for Information Interchange (ASCII) character set, as well as various function keys. Most computers and applications today use seven or eight data bits for each character. Other character sets include ISO Latin 1, Kanji, and Unicode. Each character is represented by a unique number understood by the computer. For example, ASCII code 65 is equal to the letter A. The function keys generate short, fixed sequences of character codes that instruct application programs running on the computer to perform certain actions. Often, keyboards also have directional buttons for moving the screen cursor, separate numeric pads for entering numeric and arithmetic data, and a switch for turning the computer on and off. Some keyboards, including most for laptop computers, also incorporate a trackball, mouse pad, or other cursor-directing device. No standard exists for positioning the function, numeric, and other buttons on a keyboard relative to the QWERTY and other typewriting keys. Thus layouts vary on keyboards.
An alternative keyboard design not yet widely used but broadly acknowledged for its speed advantages is the Dvorak keyboard. In the 1930s, American educators August Dvorak and William Dealy designed this key set so that the letters that make up most words in the English language are in the middle row of keys and are easily reachable by a typist’s fingers. Common letter combinations are also positioned so that they can be typed quickly. Most keyboards are arranged in rectangles, left to right around the QWERTY layout. Newer, innovative keyboard designs are more ergonomic in shape. These keyboards have separated banks of keys and are less likely to cause carpal tunnel syndrome, a disorder often caused by excessive typing on less ergonomic keyboards.

MOUSE(computer)

Mouse (computer), a common pointing device, popularized by its inclusion as standard equipment with the Apple Macintosh. With the rise in popularity of graphical user interfaces (Graphical User Interface) in MS-DOS; UNIX, and OS/2, use of mice is growing throughout the personal computer and workstation worlds. The basic features of a mouse are a casing with a flat bottom, designed to be gripped by one hand; one or more buttons on the top; a multidirectional detection device (usually a ball) on the bottom; and a cable connecting the mouse to the computer. See the illustration. By moving the mouse on a surface (such as a desk), the user typically controls an on-screen cursor. A mouse is a relative pointing device because there are no defined limits to the mouse's movement and because its placement on a surface does not map directly to a specific screen location. To select items or choose commands on the screen, the user presses one of the mouse's buttons, producing a “mouse click.”See also bus mouse; Mechanical Mouse; Optical Mouse; Optomechanical Mouse; Serial Mouse; Trackball.

BIRD

Bird, animal with feathers and wings. Birds are the only animals with feathers, although some other animals, such as insects and bats, also have wings. Nearly all birds can fly, and even flightless birds, such as ostriches and penguins, evolved from flying ancestors.

Birds are members of a group of animals called vertebrates, which possess a spinal column or backbone. Other vertebrates are fish, amphibians, reptiles, and mammals. Many characteristics and behaviors of birds are distinct from all other animals, but there are some similarities. Like mammals, birds have four-chambered hearts and are warm-blooded—having a relatively constant body temperature that enables them to live in a wide variety of environments. Like reptiles, birds develop from embryos in eggs outside of the mother’s body.
Birds are found worldwide in many habitats. They can fly over some of the highest mountains on earth as well as both of the earth’s poles, dive through water to depths of more than 250 m (850 ft), and occupy habitats with the most extreme climates on the planet, including arctic tundra and the Sahara Desert. Certain kinds of seabirds are commonly seen over the open ocean thousands of kilometers from the nearest land, but all birds must come ashore to raise their young.
Highly developed animals, birds are sensitive and responsive, colorful and graceful, with habits that excite interest and inquiry. People have long been fascinated by birds, in part because birds are found in great abundance and variety in the same habitats in which humans thrive. And like people, most species of birds are active during daylight hours. Humans find inspiration in birds’ capacity for flight and in their musical calls. Humans also find birds useful—their flesh and eggs for food, their feathers for warmth, and their companionship. Perhaps a key basis for our rapport with birds is the similarity of our sensory worlds: Both birds and humans rely more heavily on hearing and color vision than on smell. Birds are useful indicators of the quality of the environment, because the health of bird populations mirrors the health of our environment. The rapid decline in bird populations and the accelerating extinction rates of birds in the world’s forests, grasslands, wetlands, and islands are therefore reasons for great concern.

MUSIC

Music, artful arrangement of sounds across time. This definition is obviously very broad, but a narrower one would exclude too much. Music is part of virtually every culture on Earth, but it varies widely among cultures in style and structure. Definitions of music can change dramatically over a short time, as they have across the world during the 20th century.


Can music exist without sound? Some philosophers argue that music should be defined as a kind of “mental image” and that the physical aspects of sound are simply by-products of this image. If you think you can have a musical experience by imagining the sound of a piece of music, then you think music can exist without sound. But most musical experiences involve producing or listening to physical characteristics of sound such as pitch and timbre (quality comparable to texture or color in sight).

Is the tape-recorded sound of a large metal-stamping machine music? Are 4 minutes and 33 seconds of silence music? Is the activity of reading a list of hundreds of seemingly unrelated objects, activities, and states of mind music? Each of these “works”, as well as many other sounds (or nonsounds), has been copyrighted as a musical composition, performed, and recorded in the 20th century. One of the legacies of 20th-century music is to have blurred the definition of music as never before.


Other experts argue that whether any particular pattern of sounds (or our mental image of this pattern) is or is not music hinges on the musical culture into which we were born and in which we have grown up. In other words, whether sounds are music or not has more to do with learning than with anything about the physical characteristics of the sounds or the inborn characteristics of people. An American or European, hearing for the first time a Javanese gamelan performance or singing by the Ewe people of West Africa, might feel disoriented and disappointed by the unfamiliar and seemingly meaningless sounds of these kinds of music. Similarly, Javanese or Ghanaian listeners might feel every bit as disappointed when they first hear the music of Austrian composer Franz Schubert or the songs of a popular rock group, and they might find these equally meaningless.

Like language, another arrangement of sounds, music is a uniquely human form of communication with well-developed rules of construction much like grammar. Some language experts would say that you can listen to someone speaking a language you do not understand and still know whether the speaker is excited or tired, angry or delighted. You would be making interpretations based upon the speech patterns: loud or soft, high-pitched or low-pitched, rapid and bitten off, or slow and smooth. Corresponding to these elements of speech are musical variables such as dynamics (force and volume), register (range of music or voice), mode (arrangement of a set of tones), and articulation (such as staccato, meaning abrupt and crisp; or legato, smooth and even). On the other hand, most people would agree that a meaningful conversation can only take place when both the speaker and the listener speak the same language. The conversation becomes even more meaningful when the parties are talking about something or someone they both know well.

Although there is no general agreement as to exactly what music communicates or how it communicates it, some individuals and governments have believed that music possesses great powers of communication. Most ancient Greek philosophers believed that listening to music based on certain of the modes in use at the time was beneficial to the development of a young person’s character, and warned that listening to music based on certain other modes would have harmful effects. For centuries Chinese beliefs about music were influenced by the philosophy of Confucius, whichmusic was not to entertain but to purify one's thoughts.

SINGING

Singing, the use of the human voice to produce music. In singing, the lungs act as an air reservoir and bellows, forcing air between the vocal cords (see Larynx) and causing them to vibrate, much like the double reed of an oboe. The resulting sound is amplified as it resonates in the cavities of the chest, neck, and head, and it is articulated (given vowels and consonants) by the singer's lips, teeth, tongue, and palate (see Speech and Speech Disorders). Vocal training allows a singer to develop breath control, to regulate the degree of relaxation or tension in the body, and to resonate and articulate sound. Whether trained or not, singers in every culture exercise choice in their use of the voice. American, Swiss, and African Pygmy yodelers intuitively alternate rapidly between high and low registers, for example, and most men can produce falsetto tones without knowing that these tones depend on only partial vibration of the vocal cords.

STYLISTIC VARIATION

Among the world's many singing styles, cultural choices are observable in the variations in tone, color, physical tension, and acoustical intensity. Cultural differences also exist in preferences for high- or low-pitched ranges, solo or choral singing, extensive or sparse melodic ornamentation, and the use or avoidance of rasps, yelps, growls, and other colorful voice modifications.


The rich variety of vocal styles found in the U.S. includes the trained, resonant, well-projected tone of operatic singers; the relaxed, intimate sound of popular crooners; the tensely sung, high, ornamented melodic style of Appalachian folk singers; the relaxed, subtly ornamented, rubato singing of black folk musicians, sometimes augmented with rough, guttural effects; and the tense, electronically distorted sound of much rock singing. Where ancient Mediterranean and Asian civilizations once flourished, singing tends to be high-pitched, tense, and ornamented, and solo singing predominates; within this broad geographical area, however, sounds vary from the moderate-range, highly ornamented style of Indian classical singing to the thin, extremely high, well-projected tone found in Chinese opera. In sub-Saharan Africa, where an abundance of choral music is found, low voices for women and high, penetrating voices for men are favored. Many agricultural regions in central Europe also have strong choral traditions, characterized by a straightforward, open vocal tone.




GAMES

Games, activities or contests governed by sets of rules. People engage in games for recreation and to develop mental or physical skills.

Games come in many varieties. They may have any number of players and can be played competitively or cooperatively. They also may involve a wide range of equipment. Some games, such as chess, test players’ analytic skills. Other games, such as darts and electronic games, require hand-eye coordination. Some games are also considered sports, especially when they involve physical skill.


CATEGORIES OF GAMES

Games may be classified in several ways. These include the number of players required (as in solitaire games), the purpose of playing (as in gambling games), the object of the game (as in race games, to finish first), the people who play them (as in children’s games), or the place they are played (as in lawn games). Many games fall into more than one of these categories, so the most common way of classifying games is by the equipment that is required to play them.

Board games probably make up the largest category of games. They are usually played on a flat surface made of cardboard, wood, or other material. Players place the board on a table or on the floor, then sit around it to play. In most board games, pieces are placed on the board and moved around on it. Dice, cards, and other equipment can be used.

In strategy board games, pieces are placed or moved in order to capture other pieces (as in chess or checkers) or to achieve such goals as gaining territory, linking pieces to one another, or aligning pieces together. Other major groups of board games include race games (such as backgammon), word games (Scrabble), games of deduction (Clue), trivia games (Trivial Pursuit), party games (Pictionary), family games (Life), financial games (Monopoly), sports games (Strat-O-Matic Baseball), action games (Operation), and games of conflict (Risk).

Many games fall into more than one category. The board game Life, for example, has elements of race games, and Trivial Pursuit is often played at parties. Other types of board games include topical games, which can be based on currently popular movies, television programs, or books; and simulation games, which range from historical war games to civilization-building games.

Role-playing games, which can be played without boards or with playing fields drawn by hand on paper, are often considered a distinct game category. In these games, each player assumes the role of a character with particular strengths and weaknesses. Another player known as the gamemaster leads the character-players through adventures. The most famous role-playing game is Dungeons & Dragons (now called Advanced Dungeons & Dragons), which was invented in the 1970s.
Some games, such as billiards and table tennis, are played on larger surfaces than board games, typically tables with legs. These table games also require different kinds of equipment from board games. In billiards, players use a cue stick to knock balls into one another. Table tennis players use paddles to hit a light ball back and forth over a net strung across the table.

Card games require a deck of cards, and sometimes paper and pencil (or occasionally other equipment, such as a cribbage board) for keeping score. Many popular games, including poker, bridge, and rummy, call for a standard deck of 52 playing cards. Some card games, such as canasta, use more than one deck or a larger deck. And other games use a deck from which certain cards have been removed, or decks with cards designed specifically for the game.
The major kinds of card games include trick-taking games, in which players try to take (or avoid taking) specific cards; melding games, in which players try to form winning combinations with their cards; betting games, in which players wager on the outcome; and solitaire games, which are played alone. A new category, collectible card games, became an overnight sensation in 1993 with the publication of Magic: The Gathering. In Magic and similar games, players buy a starter set of cards that they use to compete against other players. They can supplement the starter kit with additional purchases of random assortments of cards.
Tile games can be similar to card games, but they use pieces made of harder materials, such as wood, plastic, or bone. Popular tile games include Mah Jongg and dominoes. Dice games involve throwing a set of dice in an attempt to achieve certain combinations or totals. Paper and pencil games use only paper and pencil. Two such games, tic-tac-toe and dots-and-boxes, are among the first games that many children learn. Target games, in which players aim at a target, are tests of hand-eye coordination. Examples of target games are marbles, horseshoe pitching, and bowling.
Electronic games (video games and computer games) grew in popularity in the late 20th century, as the power of computers increased. In most electronic games, players use a keyboard, joystick, or some other type of game controller. Video games are played on specially designed arcade machines, handheld devices, or systems that are hooked to television screens. Computer games are played on home computers. With electronic games, the computer itself can serve as the opponent, allowing people to play traditional games such as chess or bridge against the computer.

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