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The Quran most likely existed in scattered written form during Muhammad's lifetime. Several sources indicate that during Muhammad's lifetime a large number of his companions had memorized the revelations. Early commentaries and Islamic historical sources support the above-mentioned understanding of the Quran's early development. The Quran in its present form is generally considered by academic scholars to record the words spoken by Muhammad because the search for variants has not yielded any differences of great significance.[page needed] University of Chicago professor Fred Donner states that "...there was a very early attempt to establish a uniform consonantal text of the Qurʾān from what was probably a wider and more varied group of related texts in early transmission. [...] After the creation of this standardized canonical text, earlier authoritative texts were suppressed, and all extant manuscripts—despite their numerous variants—seem to date to a time after this standard consonantal text was established." Although most variant readings of the text of the Quran have ceased to be transmitted, some still are. There has been no critical text produced on which a scholarly reconstruction of the Quranic text could be based. Historically, controversy over the Quran's content has rarely become an issue, although debates continue on the subject.
Sahih al-Bukhari narrates Muhammad describing the revelations as, "Sometimes it is (revealed) like the ringing of a bell" and Aisha reported, "I saw the Prophet being inspired Divinely on a very cold day and noticed the sweat dropping from his forehead (as the Inspiration was over)." Muhammad's first revelation, according to the Quran, was accompanied with a vision. The agent of revelation is mentioned as the "one mighty in power", the one who "grew clear to view when he was on the uppermost horizon. Then he drew nigh and came down till he was (distant) two bows' length or even nearer." The Islamic studies scholar Welch states in the Encyclopaedia of Islam that he believes the graphic descriptions of Muhammad's condition at these moments may be regarded as genuine, because he was severely disturbed after these revelations. According to Welch, these seizures would have been seen by those around him as convincing evidence for the superhuman origin of Muhammad's inspirations. However, Muhammad's critics accused him of being a possessed man, a soothsayer or a magician since his experiences were similar to those claimed by such figures well known in ancient Arabia. Welch additionally states that it remains uncertain whether these experiences occurred before or after Muhammad's initial claim of prophethood.
Muhammad Husayn Tabatabaei says that according to the popular explanation among the later exegetes, ta'wil indicates the particular meaning a verse is directed towards. The meaning of revelation (tanzil), as opposed to ta'wil, is clear in its accordance to the obvious meaning of the words as they were revealed. But this explanation has become so widespread that, at present, it has become the primary meaning of ta'wil, which originally meant "to return" or "the returning place". In Tabatabaei's view, what has been rightly called ta'wil, or hermeneutic interpretation of the Quran, is not concerned simply with the denotation of words. Rather, it is concerned with certain truths and realities that transcend the comprehension of the common run of men; yet it is from these truths and realities that the principles of doctrine and the practical injunctions of the Quran issue forth. Interpretation is not the meaning of the verse—rather it transpires through that meaning, in a special sort of transpiration. There is a spiritual reality—which is the main objective of ordaining a law, or the basic aim in describing a divine attribute—and then there is an actual significance that a Quranic story refers to.
According to Shia beliefs, those who are firmly rooted in knowledge like Muhammad and the imams know the secrets of the Quran. According to Tabatabaei, the statement "none knows its interpretation except God" remains valid, without any opposing or qualifying clause. Therefore, so far as this verse is concerned, the knowledge of the Quran's interpretation is reserved for God. But Tabatabaei uses other verses and concludes that those who are purified by God know the interpretation of the Quran to a certain extent.
A great power is a sovereign state that is recognized as having the ability and expertise to exert its influence on a global scale. Great powers characteristically possess military and economic strength, as well as diplomatic and soft power influence, which may cause middle or small powers to consider the great powers' opinions before taking actions of their own. International relations theorists have posited that great power status can be characterized into power capabilities, spatial aspects, and status dimensions. Sometimes the status of great powers is formally recognized in conferences such as the Congress of Vienna or an international structure such as the United Nations Security Council (China, France, Russia, the United Kingdom and the United States serve as the body's five permanent members). At the same time the status of great powers can be informally recognized in a forum such as the G7 which consists of Canada, France, Germany, Italy, Japan, the United Kingdom and the United States of America.
The term "great power" was first used to represent the most important powers in Europe during the post-Napoleonic era. The "Great Powers" constituted the "Concert of Europe" and claimed the right to joint enforcement of the postwar treaties. The formalization of the division between small powers and great powers came about with the signing of the Treaty of Chaumont in 1814. Since then, the international balance of power has shifted numerous times, most dramatically during World War I and World War II. While some nations are widely considered to be great powers, there is no definitive list of them. In literature, alternative terms for great power are often world power or major power, but these terms can also be interchangeable with superpower.
Early writings on the subject tended to judge states by the realist criterion, as expressed by the historian A. J. P. Taylor when he noted that "The test of a great power is the test of strength for war." Later writers have expanded this test, attempting to define power in terms of overall military, economic, and political capacity. Kenneth Waltz, the founder of the neorealist theory of international relations, uses a set of five criteria to determine great power: population and territory; resource endowment; economic capability; political stability and competence; and military strength. These expanded criteria can be divided into three heads: power capabilities, spatial aspects, and status.
All states have a geographic scope of interests, actions, or projected power. This is a crucial factor in distinguishing a great power from a regional power; by definition the scope of a regional power is restricted to its region. It has been suggested that a great power should be possessed of actual influence throughout the scope of the prevailing international system. Arnold J. Toynbee, for example, observes that "Great power may be defined as a political force exerting an effect co-extensive with the widest range of the society in which it operates. The Great powers of 1914 were 'world-powers' because Western society had recently become 'world-wide'."
Other important criteria throughout history are that great powers should have enough influence to be included in discussions of political and diplomatic questions of the day, and have influence on the final outcome and resolution. Historically, when major political questions were addressed, several great powers met to discuss them. Before the era of groups like the United Nations, participants of such meetings were not officially named, but were decided based on their great power status. These were conferences which settled important questions based on major historical events. This might mean deciding the political resolution of various geographical and nationalist claims following a major conflict, or other contexts.
Lord Castlereagh, the British Foreign Secretary, first used the term in its diplomatic context, in a letter sent on February 13, 1814: "It affords me great satisfaction to acquaint you that there is every prospect of the Congress terminating with a general accord and Guarantee between the Great powers of Europe, with a determination to support the arrangement agreed upon, and to turn the general influence and if necessary the general arms against the Power that shall first attempt to disturb the Continental peace."
Of the five original great powers recognised at the Congress of Vienna, only France and the United Kingdom have maintained that status continuously to the present day, although France was defeated in the Franco-Prussian War and occupied during World War II. After the Congress of Vienna, the British Empire emerged as the pre-eminent power, due to its navy and the extent of its territories, which signalled the beginning of the Pax Britannica and of the Great Game between the UK and Russia. The balance of power between the Great Powers became a major influence in European politics, prompting Otto von Bismarck to say "All politics reduces itself to this formula: try to be one of three, as long as the world is governed by the unstable equilibrium of five great powers."
Over time, the relative power of these five nations fluctuated, which by the dawn of the 20th century had served to create an entirely different balance of power. Some, such as the United Kingdom and Prussia (as the founder of the newly formed German state), experienced continued economic growth and political power. Others, such as Russia and Austria-Hungary, stagnated. At the same time, other states were emerging and expanding in power, largely through the process of industrialization. These countries seeking to attain great power status were: Italy after the Risorgimento, Japan after the Meiji Restoration, and the United States after its civil war. By the dawn of the 20th century, the balance of world power had changed substantially since the Congress of Vienna. The Eight-Nation Alliance was a belligerent alliance of eight nations against the Boxer Rebellion in China. It formed in 1900 and consisted of the five Congress powers plus Italy, Japan, and the United States, representing the great powers at the beginning of 20th century.
Shifts of international power have most notably occurred through major conflicts. The conclusion of the Great War and the resulting treaties of Versailles, St-Germain, Neuilly, Trianon and Sèvres witnessed the United Kingdom, France, Italy, Japan and the United States as the chief arbiters of the new world order. In the aftermath of World War I the German Empire was defeated, the Austria-Hungarian empire was divided into new, less powerful states and the Russian Empire fell to a revolution. During the Paris Peace Conference, the "Big Four"—France, Italy, United Kingdom and the United States—held noticeably more power and influence on the proceedings and outcome of the treaties than Japan. The Big Four were leading architects of the Treaty of Versailles which was signed by Germany; the Treaty of St. Germain, with Austria; the Treaty of Neuilly, with Bulgaria; the Treaty of Trianon, with Hungary; and the Treaty of Sèvres, with the Ottoman Empire. During the decision-making of the Treaty of Versailles, Italy pulled out of the conference because a part of its demands were not met and temporarily left the other three countries as the sole major architects of that treaty, referred to as the "Big Three".
The victorious great powers also gained an acknowledgement of their status through permanent seats at the League of Nations Council, where they acted as a type of executive body directing the Assembly of the League. However, the Council began with only four permanent members—the United Kingdom, France, Italy, and Japan—because the United States, meant to be the fifth permanent member, left because the US Senate voted on 19 March 1920 against the ratification of the Treaty of Versailles, thus preventing American participation in the League.
When World War II started in 1939, it divided the world into two alliances—the Allies (the United Kingdom and France at first in Europe, China in Asia since 1937, followed in 1941 by the Soviet Union, the United States); and the Axis powers consisting of Germany, Italy and Japan.[nb 1] During World War II, the United States, United Kingdom, and Soviet Union controlled Allied policy and emerged as the "Big Three". The Republic of China and the Big Three were referred as a "trusteeship of the powerful" and were recognized as the Allied "Big Four" in Declaration by United Nations in 1942. These four countries were referred as the "Four Policemen" of the Allies and considered as the primary victors of World War II. The importance of France was acknowledged by their inclusion, along with the other four, in the group of countries allotted permanent seats in the United Nations Security Council.
Since the end of the World Wars, the term "great power" has been joined by a number of other power classifications. Foremost among these is the concept of the superpower, used to describe those nations with overwhelming power and influence in the rest of the world. It was first coined in 1944 by William T.R. Fox and according to him, there were three superpowers: the British Empire, the United States, and the Soviet Union. But by the mid-1950s the British Empire lost its superpower status, leaving the United States and the Soviet Union as the world's superpowers.[nb 2] The term middle power has emerged for those nations which exercise a degree of global influence, but are insufficient to be decisive on international affairs. Regional powers are those whose influence is generally confined to their region of the world.
During the Cold War, the Asian power of Japan and the European powers of the United Kingdom, France, and West Germany rebuilt their economies. France and the United Kingdom maintained technologically advanced armed forces with power projection capabilities and maintain large defence budgets to this day. Yet, as the Cold War continued, authorities began to question if France and the United Kingdom could retain their long-held statuses as great powers. China, with the world's largest population, has slowly risen to great power status, with large growth in economic and military power in the post-war period. After 1949, the Republic of China began to lose its recognition as the sole legitimate government of China by the other great powers, in favour of the People's Republic of China. Subsequently, in 1971, it lost its permanent seat at the UN Security Council to the People's Republic of China.
According to Joshua Baron – a "researcher, lecturer, and consultant on international conflict" – since the early 1960s direct military conflicts and major confrontations have "receded into the background" with regards to relations among the great powers. Baron argues several reasons why this is the case, citing the unprecedented rise of the United States and its predominant position as the key reason. Baron highlights that since World War Two no other great power has been able to achieve parity or near parity with the United States, with the exception of the Soviet Union for a brief time. This position is unique among the great powers since the start of the modern era (the 16th century), where there has traditionally always been "tremendous parity among the great powers". This unique period of American primacy has been an important factor in maintaining a condition of peace between the great powers.
Another important factor is the apparent consensus among Western great powers that military force is no longer an effective tool of resolving disputes among their peers. This "subset" of great powers – France, Germany, Japan, the United Kingdom and the United States – consider maintaining a "state of peace" as desirable. As evidence, Baron outlines that since the Cuban missile crisis (1962) during the Cold War, these influential Western nations have resolved all disputes among the great powers peacefully at the United Nations and other forums of international discussion.
China, France, Russia, the United Kingdom and the United States are often referred to as great powers by academics due to "their political and economic dominance of the global arena". These five nations are the only states to have permanent seats with veto power on the UN Security Council. They are also the only recognized "Nuclear Weapons States" under the Nuclear Non-Proliferation Treaty, and maintain military expenditures which are among the largest in the world. However, there is no unanimous agreement among authorities as to the current status of these powers or what precisely defines a great power. For example, sources have at times referred to China, France, Russia and the United Kingdom as middle powers.
Japan and Germany are great powers too, though due to their large advanced economies (having the third and fourth largest economies respectively) rather than their strategic and hard power capabilities (i.e., the lack of permanent seats and veto power on the UN Security Council or strategic military reach). Germany has been a member together with the five permanent Security Council members in the P5+1 grouping of world powers. Like China, France, Russia and the United Kingdom; Germany and Japan have also been referred to as middle powers.
In addition to those contemporary great powers mentioned above, Zbigniew Brzezinski and Malik Mohan consider India to be a great power too. Although unlike the contemporary great powers who have long been considered so, India's recognition among authorities as a great power is comparatively recent. However, there is no collective agreement among observers as to the status of India, for example, a number of academics believe that India is emerging as a great power, while some believe that India remains a middle power.
Milena Sterio, American expert of international law, includes the former axis powers (Germany, Italy and Japan) and India among the great powers along with the permanent members of the UNSC. She considers Germany, Japan and Italy to be great powers due to their G7 membership and because of their influence in regional and international organizations. Various authors describe Italy as an equal major power, while others view Italy as an "intermittent great power" or as "the least of the great powers".
With continuing European integration, the European Union is increasingly being seen as a great power in its own right, with representation at the WTO and at G8 and G-20 summits. This is most notable in areas where the European Union has exclusive competence (i.e. economic affairs). It also reflects a non-traditional conception of Europe's world role as a global "civilian power", exercising collective influence in the functional spheres of trade and diplomacy, as an alternative to military dominance. The European Union is a supranational union and not a sovereign state, and has limited scope in the areas of foreign affairs and defence policy. These remain largely with the member states of the European Union, which include the three great powers of France, Germany and the United Kingdom (referred to as the "EU three").
Referring to great power relations pre-1960, Joshua Baron highlights that starting from around the 16th century and the rise of several European great powers, military conflicts and confrontations was the defining characteristic of diplomacy and relations between such powers. "Between 1500 and 1953, there were 64 wars in which at least one great power was opposed to another, and they averaged little more than five years in length. In approximately a 450-year time frame, on average at least two great powers were fighting one another in each and every year." Even during the period of Pax Britannica (or "the British Peace") between 1815 and 1914, war and military confrontations among the great powers was still a frequent occurrence. In fact, Joshua Baron points out that, in terms of militarized conflicts or confrontations, the UK led the way in this period with nineteen such instances against; Russia (8), France (5), Germany/Prussia (5) and Italy (1).
From 1989 through 1996, the total area of the US was listed as 9,372,610 km2 (3,618,780 sq mi) (land + inland water only). The listed total area changed to 9,629,091 km2 (3,717,813 sq mi) in 1997 (Great Lakes area and coastal waters added), to 9,631,418 km2 (3,718,711 sq mi) in 2004, to 9,631,420 km2 (3,718,710 sq mi) in 2006, and to 9,826,630 km2 (3,794,080 sq mi) in 2007 (territorial waters added). Currently, the CIA World Factbook gives 9,826,675 km2 (3,794,100 sq mi), the United Nations Statistics Division gives 9,629,091 km2 (3,717,813 sq mi), and the Encyclopædia Britannica gives 9,522,055 km2 (3,676,486 sq mi)(Great Lakes area included but not coastal waters). These source consider only the 50 states and the Federal District, and exclude overseas territories.
By total area (water as well as land), the United States is either slightly larger or smaller than the People's Republic of China, making it the world's third or fourth largest country. China and the United States are smaller than Russia and Canada in total area, but are larger than Brazil. By land area only (exclusive of waters), the United States is the world's third largest country, after Russia and China, with Canada in fourth. Whether the US or China is the third largest country by total area depends on two factors: (1) The validity of China's claim on Aksai Chin and Trans-Karakoram Tract. Both these territories are also claimed by India, so are not counted; and (2) How US calculates its own surface area. Since the initial publishing of the World Factbook, the CIA has updated the total area of United States a number of times.
The United States shares land borders with Canada (to the north) and Mexico (to the south), and a territorial water border with Russia in the northwest, and two territorial water borders in the southeast between Florida and Cuba, and Florida and the Bahamas. The contiguous forty-eight states are otherwise bounded by the Pacific Ocean on the west, the Atlantic Ocean on the east, and the Gulf of Mexico to the southeast. Alaska borders the Pacific Ocean to the south, the Bering Strait to the west, and the Arctic Ocean to the north, while Hawaii lies far to the southwest of the mainland in the Pacific Ocean.
The capital city, Washington, District of Columbia, is a federal district located on land donated by the state of Maryland. (Virginia had also donated land, but it was returned in 1849.) The United States also has overseas territories with varying levels of independence and organization: in the Caribbean the territories of Puerto Rico and the U.S. Virgin Islands, and in the Pacific the inhabited territories of Guam, American Samoa, and the Northern Mariana Islands, along with a number of uninhabited island territories.
The five Great Lakes are located in the north-central portion of the country, four of them forming part of the border with Canada, only Lake Michigan situated entirely within United States. The southeast United States contain subtropical forests and, near the gulf coast, mangrove wetlands, especially in Florida. West of the Appalachians lies the Mississippi River basin and two large eastern tributaries, the Ohio River and the Tennessee River. The Ohio and Tennessee Valleys and the Midwest consist largely of rolling hills and productive farmland, stretching south to the Gulf Coast.
The Great Plains lie west of the Mississippi River and east of the Rocky Mountains. A large portion of the country's agricultural products are grown in the Great Plains. Before their general conversion to farmland, the Great Plains were noted for their extensive grasslands, from tallgrass prairie in the eastern plains to shortgrass steppe in the western High Plains. Elevation rises gradually from less than a few hundred feet near the Mississippi River to more than a mile high in the High Plains. The generally low relief of the plains is broken in several places, most notably in the Ozark and Ouachita Mountains, which form the U.S. Interior Highlands, the only major mountainous region between the Rocky Mountains and the Appalachian Mountains.
The Great Plains come to an abrupt end at the Rocky Mountains. The Rocky Mountains form a large portion of the Western U.S., entering from Canada and stretching nearly to Mexico. The Rocky Mountain region is the highest region of the United States by average elevation. The Rocky Mountains generally contain fairly mild slopes and wider peaks compared to some of the other great mountain ranges, with a few exceptions (such as the Teton Mountains in Wyoming and the Sawatch Range in Colorado). The highest peaks of the Rockies are found in Colorado, the tallest peak being Mount Elbert at 14,440 ft (4,400 m). The Rocky Mountains contain some of the most spectacular, and well known scenery in the world. In addition, instead of being one generally continuous and solid mountain range, it is broken up into a number of smaller, intermittent mountain ranges, forming a large series of basins and valleys.
West of the Rocky Mountains lies the Intermontane Plateaus (also known as the Intermountain West), a large, arid desert lying between the Rockies and the Cascades and Sierra Nevada ranges. The large southern portion, known as the Great Basin, consists of salt flats, drainage basins, and many small north-south mountain ranges. The Southwest is predominantly a low-lying desert region. A portion known as the Colorado Plateau, centered around the Four Corners region, is considered to have some of the most spectacular scenery in the world. It is accentuated in such national parks as Grand Canyon, Arches, Mesa Verde National Park and Bryce Canyon, among others. Other smaller Intermontane areas include the Columbia Plateau covering eastern Washington, western Idaho and northeast Oregon and the Snake River Plain in Southern Idaho.
The Intermontane Plateaus come to an end at the Cascade Range and the Sierra Nevada. The Cascades consist of largely intermittent, volcanic mountains, many rising prominently from the surrounding landscape. The Sierra Nevada, further south, is a high, rugged, and dense mountain range. It contains the highest point in the contiguous 48 states, Mount Whitney (14,505 ft or 4,421 m) It is located at the boundary between California's Inyo and Tulare counties, just 84.6 mi or 136.2 km west-northwest of the lowest point in North America at the Badwater Basin in Death Valley National Park at 279 ft or 85 m below sea level.
These areas contain some spectacular scenery as well, as evidenced by such national parks as Yosemite and Mount Rainier. West of the Cascades and Sierra Nevada is a series of valleys, such as the Central Valley in California and the Willamette Valley in Oregon. Along the coast is a series of low mountain ranges known as the Pacific Coast Ranges. Much of the Pacific Northwest coast is inhabited by some of the densest vegetation outside of the Tropics, and also the tallest trees in the world (the Redwoods).
The Atlantic coast of the United States is low, with minor exceptions. The Appalachian Highland owes its oblique northeast-southwest trend to crustal deformations which in very early geological time gave a beginning to what later came to be the Appalachian mountain system. This system had its climax of deformation so long ago (probably in Permian time) that it has since then been very generally reduced to moderate or low relief. It owes its present-day altitude either to renewed elevations along the earlier lines or to the survival of the most resistant rocks as residual mountains. The oblique trend of this coast would be even more pronounced but for a comparatively modern crustal movement, causing a depression in the northeast resulting in an encroachment of the sea upon the land. Additionally, the southeastern section has undergone an elevation resulting in the advance of the land upon the sea.
The east coast Appalachian system, originally forest covered, is relatively low and narrow and is bordered on the southeast and south by an important coastal plain. The Cordilleran system on the western side of the continent is lofty, broad and complicated having two branches, the Rocky Mountain System and the Pacific Mountain System. In between these mountain systems lie the Intermontaine Plateaus. Both the Columbia River and Colorado River rise far inland near the easternmost members of the Cordilleran system, and flow through plateaus and intermontaine basins to the ocean. Heavy forests cover the northwest coast, but elsewhere trees are found only on the higher ranges below the Alpine region. The intermontane valleys, plateaus and basins range from treeless to desert with the most arid region being in the southwest.
The Laurentian Highlands, the Interior Plains and the Interior Highlands lie between the two coasts, stretching from the Gulf of Mexico northward, far beyond the national boundary, to the Arctic Ocean. The central plains are divided by a hardly perceptible height of land into a Canadian and a United States portion. It is from the United States side, that the great Mississippi system discharges southward to the Gulf of Mexico. The upper Mississippi and some of the Ohio basin is the semi-arid prairie region, with trees originally only along the watercourses. The uplands towards the Appalachians were included in the great eastern forested area, while the western part of the plains has so dry a climate that its native plant life is scanty, and in the south it is practically barren.
Due to its large size and wide range of geographic features, the United States contains examples of nearly every global climate. The climate is temperate in most areas, subtropical in the Southern United States, tropical in Hawaii and southern Florida, polar in Alaska, semiarid in the Great Plains west of the 100th meridian, Mediterranean in coastal California and arid in the Great Basin. Its comparatively favorable agricultural climate contributed (in part) to the country's rise as a world power, with infrequent severe drought in the major agricultural regions, a general lack of widespread flooding, and a mainly temperate climate that receives adequate precipitation.
The Great Basin and Columbia Plateau (the Intermontane Plateaus) are arid or semiarid regions that lie in the rain shadow of the Cascades and Sierra Nevada. Precipitation averages less than 15 inches (38 cm). The Southwest is a hot desert, with temperatures exceeding 100 °F (37.8 °C) for several weeks at a time in summer. The Southwest and the Great Basin are also affected by the monsoon from the Gulf of California from July to September, which brings localized but often severe thunderstorms to the region.
Much of California consists of a Mediterranean climate, with sometimes excessive rainfall from October–April and nearly no rain the rest of the year. In the Pacific Northwest rain falls year-round, but is much heavier during winter and spring. The mountains of the west receive abundant precipitation and very heavy snowfall. The Cascades are one of the snowiest places in the world, with some places averaging over 600 inches (1,524 cm) of snow annually, but the lower elevations closer to the coast receive very little snow.
On average, the mountains of the western states receive the highest levels of snowfall on Earth. The greatest annual snowfall level is at Mount Rainier in Washington, at 692 inches (1,758 cm); the record there was 1,122 inches (2,850 cm) in the winter of 1971–72. This record was broken by the Mt. Baker Ski Area in northwestern Washington which reported 1,140 inches (2,896 cm) of snowfall for the 1998-99 snowfall season. Other places with significant snowfall outside the Cascade Range are the Wasatch Mountains, near the Great Salt Lake, the San Juan Mountains in Colorado, and the Sierra Nevada, near Lake Tahoe.
In the east, while snowfall does not approach western levels, the region near the Great Lakes and the mountains of the Northeast receive the most. Along the northwestern Pacific coast, rainfall is greater than anywhere else in the continental U.S., with Quinault Rainforest in Washington having an average of 137 inches (348 cm). Hawaii receives even more, with 460 inches (1,168 cm) measured annually on Mount Waialeale, in Kauai. The Mojave Desert, in the southwest, is home to the driest locale in the U.S. Yuma, Arizona, has an average of 2.63 inches (6.7 cm) of precipitation each year.
In central portions of the U.S., tornadoes are more common than anywhere else on Earth and touch down most commonly in the spring and summer. Deadly and destructive hurricanes occur almost every year along the Atlantic seaboard and the Gulf of Mexico. The Appalachian region and the Midwest experience the worst floods, though virtually no area in the U.S. is immune to flooding. The Southwest has the worst droughts; one is thought to have lasted over 500 years and to have hurt Ancestral Pueblo peoples. The West is affected by large wildfires each year.
Occasional severe flooding is experienced. There was the Great Mississippi Flood of 1927, the Great Flood of 1993, and widespread flooding and mudslides caused by the 1982-1983 El Niño event in the western United States. Localized flooding can, however, occur anywhere, and mudslides from heavy rain can cause problems in any mountainous area, particularly the Southwest. Large stretches of desert shrub in the west can fuel the spread of wildfires. The narrow canyons of many mountain areas in the west and severe thunderstorm activity during the summer lead to sometimes devastating flash floods as well, while Nor'Easter snowstorms can bring activity to a halt throughout the Northeast (although heavy snowstorms can occur almost anywhere).
The West Coast of the continental United States and areas of Alaska (including the Aleutian Islands, the Alaskan Peninsula and southern Alaskan coast) make up part of the Pacific Ring of Fire, an area of heavy tectonic and volcanic activity that is the source of 90% of the world's earthquakes.[citation needed] The American Northwest sees the highest concentration of active volcanoes in the United States, in Washington, Oregon and northern California along the Cascade Mountains. There are several active volcanoes located in the islands of Hawaii, including Kilauea in ongoing eruption since 1983, but they do not typically adversely affect the inhabitants of the islands. There has not been a major life-threatening eruption on the Hawaiian islands since the 17th century. Volcanic eruptions can occasionally be devastating, such as in the 1980 eruption of Mount St. Helens in Washington.
Compact Disc (CD) is a digital optical disc data storage format. The format was originally developed to store and play only sound recordings but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. Audio CDs and audio CD players have been commercially available since October 1982.
In 2004, worldwide sales of audio CDs, CD-ROMs and CD-Rs reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide. CDs are increasingly being replaced by other forms of digital storage and distribution, with the result that audio CD sales rates in the U.S. have dropped about 50% from their peak; however, they remain one of the primary distribution methods for the music industry. In 2014, revenues from digital music services matched those from physical format sales for the first time.
The Compact Disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals. Prototypes were developed by Philips and Sony independently in the late 1970s. In 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. After a year of experimentation and discussion, the Red Book CD-DA standard was published in 1980. After their commercial release in 1982, compact discs and their players were extremely popular. Despite costing up to $1,000, over 400,000 CD players were sold in the United States between 1983 and 1984. The success of the compact disc has been credited to the cooperation between Philips and Sony, who came together to agree upon and develop compatible hardware. The unified design of the compact disc allowed consumers to purchase any disc or player from any company, and allowed the CD to dominate the at-home music market unchallenged.
In 1974, L. Ottens, director of the audio division of Philips, started a small group with the aim to develop an analog optical audio disc with a diameter of 20 cm and a sound quality superior to that of the vinyl record. However, due to the unsatisfactory performance of the analog format, two Philips research engineers recommended a digital format in March 1974. In 1977, Philips then established a laboratory with the mission of creating a digital audio disc. The diameter of Philips's prototype compact disc was set at 11.5 cm, the diagonal of an audio cassette.
Heitaro Nakajima, who developed an early digital audio recorder within Japan's national public broadcasting organization NHK in 1970, became general manager of Sony's audio department in 1971. His team developed a digital PCM adaptor audio tape recorder using a Betamax video recorder in 1973. After this, in 1974 the leap to storing digital audio on an optical disc was easily made. Sony first publicly demonstrated an optical digital audio disc in September 1976. A year later, in September 1977, Sony showed the press a 30 cm disc that could play 60 minutes of digital audio (44,100 Hz sampling rate and 16-bit resolution) using MFM modulation. In September 1978, the company demonstrated an optical digital audio disc with a 150-minute playing time, 44,056 Hz sampling rate, 16-bit linear resolution, and cross-interleaved error correction code—specifications similar to those later settled upon for the standard Compact Disc format in 1980. Technical details of Sony's digital audio disc were presented during the 62nd AES Convention, held on 13–16 March 1979, in Brussels. Sony's AES technical paper was published on 1 March 1979. A week later, on 8 March, Philips publicly demonstrated a prototype of an optical digital audio disc at a press conference called "Philips Introduce Compact Disc" in Eindhoven, Netherlands.
As a result, in 1979, Sony and Philips set up a joint task force of engineers to design a new digital audio disc. Led by engineers Kees Schouhamer Immink and Toshitada Doi, the research pushed forward laser and optical disc technology. After a year of experimentation and discussion, the task force produced the Red Book CD-DA standard. First published in 1980, the standard was formally adopted by the IEC as an international standard in 1987, with various amendments becoming part of the standard in 1996.
The Japanese launch was followed in March 1983 by the introduction of CD players and discs to Europe and North America (where CBS Records released sixteen titles). This event is often seen as the "Big Bang" of the digital audio revolution. The new audio disc was enthusiastically received, especially in the early-adopting classical music and audiophile communities, and its handling quality received particular praise. As the price of players gradually came down, and with the introduction of the portable Walkman the CD began to gain popularity in the larger popular and rock music markets. The first artist to sell a million copies on CD was Dire Straits, with their 1985 album Brothers in Arms. The first major artist to have his entire catalogue converted to CD was David Bowie, whose 15 studio albums were made available by RCA Records in February 1985, along with four greatest hits albums. In 1988, 400 million CDs were manufactured by 50 pressing plants around the world.
The CD was planned to be the successor of the gramophone record for playing music, rather than primarily as a data storage medium. From its origins as a musical format, CDs have grown to encompass other applications. In 1983, following the CD's introduction, Immink and Braat presented the first experiments with erasable compact discs during the 73rd AES Convention. In June 1985, the computer-readable CD-ROM (read-only memory) and, in 1990, CD-Recordable were introduced, also developed by both Sony and Philips. Recordable CDs were a new alternative to tape for recording music and copying music albums without defects introduced in compression used in other digital recording methods. Other newer video formats such as DVD and Blu-ray use the same physical geometry as CD, and most DVD and Blu-ray players are backward compatible with audio CD.
Meanwhile, with the advent and popularity of Internet-based distribution of files in lossily-compressed audio formats such as MP3, sales of CDs began to decline in the 2000s. For example, between 2000 - 2008, despite overall growth in music sales and one anomalous year of increase, major-label CD sales declined overall by 20%, although independent and DIY music sales may be tracking better according to figures released 30 March 2009, and CDs still continue to sell greatly. As of 2012, CDs and DVDs made up only 34 percent of music sales in the United States. In Japan, however, over 80 percent of music was bought on CDs and other physical formats as of 2015.
Replicated CDs are mass-produced initially using a hydraulic press. Small granules of heated raw polycarbonate plastic are fed into the press. A screw forces the liquefied plastic into the mold cavity. The mold closes with a metal stamper in contact with the disc surface. The plastic is allowed to cool and harden. Once opened, the disc substrate is removed from the mold by a robotic arm, and a 15 mm diameter center hole (called a stacking ring) is created. The time it takes to "stamp" one CD is usually two to three seconds.
This method produces the clear plastic blank part of the disc. After a metallic reflecting layer (usually aluminium, but sometimes gold or other metal) is applied to the clear blank substrate, the disc goes under a UV light for curing and it is ready to go to press. To prepare to press a CD, a glass master is made, using a high-powered laser on a device similar to a CD writer. The glass master is a positive image of the desired CD surface (with the desired microscopic pits and lands). After testing, it is used to make a die by pressing it against a metal disc.
The die is a negative image of the glass master: typically, several are made, depending on the number of pressing mills that are to make the CD. The die then goes into a press, and the physical image is transferred to the blank CD, leaving a final positive image on the disc. A small amount of lacquer is applied as a ring around the center of the disc, and rapid spinning spreads it evenly over the surface. Edge protection lacquer is applied before the disc is finished. The disc can then be printed and packed.
The most expensive part of a CD is the jewel case. In 1995, material costs were 30 cents for the jewel case and 10 to 15 cents for the CD. Wholesale cost of CDs was $0.75 to $1.15, which retailed for $16.98. On average, the store received 35 percent of the retail price, the record company 27 percent, the artist 16 percent, the manufacturer 13 percent, and the distributor 9 percent. When 8-track tapes, cassette tapes, and CDs were introduced, each was marketed at a higher price than the format they succeeded, even though the cost to produce the media was reduced. This was done because the apparent value increased. This continued from vinyl to CDs but was broken when Apple marketed MP3s for $0.99, and albums for $9.99. The incremental cost, though, to produce an MP3 is very small.
CD-R recordings are designed to be permanent. Over time, the dye's physical characteristics may change causing read errors and data loss until the reading device cannot recover with error correction methods. The design life is from 20 to 100 years, depending on the quality of the discs, the quality of the writing drive, and storage conditions. However, testing has demonstrated such degradation of some discs in as little as 18 months under normal storage conditions. This failure is known as disc rot, for which there are several, mostly environmental, reasons.
The ReWritable Audio CD is designed to be used in a consumer audio CD recorder, which will not (without modification) accept standard CD-RW discs. These consumer audio CD recorders use the Serial Copy Management System (SCMS), an early form of digital rights management (DRM), to conform to the United States' Audio Home Recording Act (AHRA). The ReWritable Audio CD is typically somewhat more expensive than CD-RW due to (a) lower volume and (b) a 3% AHRA royalty used to compensate the music industry for the making of a copy.
Due to technical limitations, the original ReWritable CD could be written no faster than 4x speed. High Speed ReWritable CD has a different design, which permits writing at speeds ranging from 4x to 12x. Original CD-RW drives can only write to original ReWritable CDs. High Speed CD-RW drives can typically write to both original ReWritable CDs and High Speed ReWritable CDs. Both types of CD-RW discs can be read in most CD drives. Higher speed CD-RW discs, Ultra Speed (16x to 24x write speed) and Ultra Speed+ (32x write speed) are now available.
A CD is read by focusing a 780 nm wavelength (near infrared) semiconductor laser housed within the CD player, through the bottom of the polycarbonate layer. The change in height between pits and lands results in a difference in the way the light is reflected. By measuring the intensity change with a photodiode, the data can be read from the disc. In order to accommodate the spiral pattern of data, the semiconductor laser is placed on a swing arm within the disc tray of any CD player. This swing arm allows the laser to read information from the centre to the edge of a disc, without having to interrupt the spinning of the disc itself.
The pits and lands themselves do not directly represent the zeros and ones of binary data. Instead, non-return-to-zero, inverted encoding is used: a change from pit to land or land to pit indicates a one, while no change indicates a series of zeros. There must be at least two and no more than ten zeros between each one, which is defined by the length of the pit. This in turn is decoded by reversing the eight-to-fourteen modulation used in mastering the disc, and then reversing the cross-interleaved Reed–Solomon coding, finally revealing the raw data stored on the disc. These encoding techniques (defined in the Red Book) were originally designed for CD Digital Audio, but they later became a standard for almost all CD formats (such as CD-ROM).
CDs are susceptible to damage during handling and from environmental exposure. Pits are much closer to the label side of a disc, enabling defects and contaminants on the clear side to be out of focus during playback. Consequently, CDs are more likely to suffer damage on the label side of the disc. Scratches on the clear side can be repaired by refilling them with similar refractive plastic or by careful polishing. The edges of CDs are sometimes incompletely sealed, allowing gases and liquids to corrode the metal reflective layer and to interfere with the focus of the laser on the pits. The fungus Geotrichum candidum, found in Belize, has been found to consume the polycarbonate plastic and aluminium found in CDs.
The digital data on a CD begins at the center of the disc and proceeds toward the edge, which allows adaptation to the different size formats available. Standard CDs are available in two sizes. By far, the most common is 120 millimetres (4.7 in) in diameter, with a 74- or 80-minute audio capacity and a 650 or 700 MiB (737,280,000-byte) data capacity. This capacity was reportedly specified by Sony executive Norio Ohga in May 1980 so as to be able to contain the entirety of the London Philharmonic Orchestra's recording of Beethoven's Ninth Symphony on one disc. This is a myth according to Kees Immink, as the code format had not yet been decided in May 1980. The adoption of EFM one month later would have allowed a playing time of 97 minutes for 120 mm diameter or 74 minutes for a disc as small as 100 mm. The 120 mm diameter has been adopted by subsequent formats, including Super Audio CD, DVD, HD DVD, and Blu-ray Disc. Eighty-millimeter discs ("Mini CDs") were originally designed for CD singles and can hold up to 24 minutes of music or 210 MiB of data but never became popular.[citation needed] Today, nearly every single is released on a 120 mm CD, called a Maxi single.[citation needed]
The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in a document produced in 1980 by the format's joint creators, Sony and Philips. The document is known colloquially as the Red Book CD-DA after the colour of its cover. The format is a two-channel 16-bit PCM encoding at a 44.1 kHz sampling rate per channel. Four-channel sound was to be an allowable option within the Red Book format, but has never been implemented. Monaural audio has no existing standard on a Red Book CD; thus, mono source material is usually presented as two identical channels in a standard Red Book stereo track (i.e., mirrored mono); an MP3 CD, however, can have audio file formats with mono sound.
Compact Disc + Graphics is a special audio compact disc that contains graphics data in addition to the audio data on the disc. The disc can be played on a regular audio CD player, but when played on a special CD+G player, it can output a graphics signal (typically, the CD+G player is hooked up to a television set or a computer monitor); these graphics are almost exclusively used to display lyrics on a television set for karaoke performers to sing along with. The CD+G format takes advantage of the channels R through W. These six bits store the graphics information.
SVCD has two-thirds the resolution of DVD, and over 2.7 times the resolution of VCD. One CD-R disc can hold up to 60 minutes of standard quality SVCD-format video. While no specific limit on SVCD video length is mandated by the specification, one must lower the video bit rate, and therefore quality, to accommodate very long videos. It is usually difficult to fit much more than 100 minutes of video onto one SVCD without incurring significant quality loss, and many hardware players are unable to play video with an instantaneous bit rate lower than 300 to 600 kilobits per second.
Photo CD is a system designed by Kodak for digitizing and storing photos on a CD. Launched in 1992, the discs were designed to hold nearly 100 high-quality images, scanned prints and slides using special proprietary encoding. Photo CDs are defined in the Beige Book and conform to the CD-ROM XA and CD-i Bridge specifications as well. They are intended to play on CD-i players, Photo CD players and any computer with the suitable software irrespective of the operating system. The images can also be printed out on photographic paper with a special Kodak machine. This format is not to be confused with Kodak Picture CD, which is a consumer product in CD-ROM format.
The Red Book audio specification, except for a simple "anti-copy" statement in the subcode, does not include any copy protection mechanism. Known at least as early as 2001, attempts were made by record companies to market "copy-protected" non-standard compact discs, which cannot be ripped, or copied, to hard drives or easily converted to MP3s. One major drawback to these copy-protected discs is that most will not play on either computer CD-ROM drives or some standalone CD players that use CD-ROM mechanisms. Philips has stated that such discs are not permitted to bear the trademarked Compact Disc Digital Audio logo because they violate the Red Book specifications. Numerous copy-protection systems have been countered by readily available, often free, software.
A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. First conceived by Julius Lilienfeld in 1926 and practically implemented in 1947 by American physicists John Bardeen, Walter Brattain, and William Shockley, the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel Prize in Physics for their achievement.
The thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony. The triode, however, was a fragile device that consumed a lot of power. Physicist Julius Edgar Lilienfeld filed a patent for a field-effect transistor (FET) in Canada in 1925, which was intended to be a solid-state replacement for the triode. Lilienfeld also filed identical patents in the United States in 1926 and 1928. However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any specific examples of a working prototype. Because the production of high-quality semiconductor materials was still decades away, Lilienfeld's solid-state amplifier ideas would not have found practical use in the 1920s and 1930s, even if such a device had been built. In 1934, German inventor Oskar Heil patented a similar device.
From November 17, 1947 to December 23, 1947, John Bardeen and Walter Brattain at AT&T's Bell Labs in the United States performed experiments and observed that when two gold point contacts were applied to a crystal of germanium, a signal was produced with the output power greater than the input. Solid State Physics Group leader William Shockley saw the potential in this, and over the next few months worked to greatly expand the knowledge of semiconductors. The term transistor was coined by John R. Pierce as a contraction of the term transresistance. According to Lillian Hoddeson and Vicki Daitch, authors of a biography of John Bardeen, Shockley had proposed that Bell Labs' first patent for a transistor should be based on the field-effect and that he be named as the inventor. Having unearthed Lilienfeld’s patents that went into obscurity years earlier, lawyers at Bell Labs advised against Shockley's proposal because the idea of a field-effect transistor that used an electric field as a "grid" was not new. Instead, what Bardeen, Brattain, and Shockley invented in 1947 was the first point-contact transistor. In acknowledgement of this accomplishment, Shockley, Bardeen, and Brattain were jointly awarded the 1956 Nobel Prize in Physics "for their researches on semiconductors and their discovery of the transistor effect."
In 1948, the point-contact transistor was independently invented by German physicists Herbert Mataré and Heinrich Welker while working at the Compagnie des Freins et Signaux, a Westinghouse subsidiary located in Paris. Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II. Using this knowledge, he began researching the phenomenon of "interference" in 1947. By June 1948, witnessing currents flowing through point-contacts, Mataré produced consistent results using samples of germanium produced by Welker, similar to what Bardeen and Brattain had accomplished earlier in December 1947. Realizing that Bell Labs' scientists had already invented the transistor before them, the company rushed to get its "transistron" into production for amplified use in France's telephone network.
Although several companies each produce over a billion individually packaged (known as discrete) transistors every year, the vast majority of transistors are now produced in integrated circuits (often shortened to IC, microchips or simply chips), along with diodes, resistors, capacitors and other electronic components, to produce complete electronic circuits. A logic gate consists of up to about twenty transistors whereas an advanced microprocessor, as of 2009, can use as many as 3 billion transistors (MOSFETs). "About 60 million transistors were built in 2002… for [each] man, woman, and child on Earth."
The essential usefulness of a transistor comes from its ability to use a small signal applied between one pair of its terminals to control a much larger signal at another pair of terminals. This property is called gain. It can produce a stronger output signal, a voltage or current, which is proportional to a weaker input signal; that is, it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a circuit as an electrically controlled switch, where the amount of current is determined by other circuit elements.
There are two types of transistors, which have slight differences in how they are used in a circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals. For a field-effect transistor, the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current between source and drain.
In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base voltage rises, the emitter and collector currents rise exponentially. The collector voltage drops because of reduced resistance from collector to emitter. If the voltage difference between the collector and emitter were zero (or near zero), the collector current would be limited only by the load resistance (light bulb) and the supply voltage. This is called saturation because current is flowing from collector to emitter freely. When saturated, the switch is said to be on.
Providing sufficient base drive current is a key problem in the use of bipolar transistors as switches. The transistor provides current gain, allowing a relatively large current in the collector to be switched by a much smaller current into the base terminal. The ratio of these currents varies depending on the type of transistor, and even for a particular type, varies depending on the collector current. In the example light-switch circuit shown, the resistor is chosen to provide enough base current to ensure the transistor will be saturated.
In a switching circuit, the idea is to simulate, as near as possible, the ideal switch having the properties of open circuit when off, short circuit when on, and an instantaneous transition between the two states. Parameters are chosen such that the "off" output is limited to leakage currents too small to affect connected circuitry; the resistance of the transistor in the "on" state is too small to affect circuitry; and the transition between the two states is fast enough not to have a detrimental effect.
Bipolar transistors are so named because they conduct by using both majority and minority carriers. The bipolar junction transistor, the first type of transistor to be mass-produced, is a combination of two junction diodes, and is formed of either a thin layer of p-type semiconductor sandwiched between two n-type semiconductors (an n–p–n transistor), or a thin layer of n-type semiconductor sandwiched between two p-type semiconductors (a p–n–p transistor). This construction produces two p–n junctions: a base–emitter junction and a base–collector junction, separated by a thin region of semiconductor known as the base region (two junction diodes wired together without sharing an intervening semiconducting region will not make a transistor).
BJTs have three terminals, corresponding to the three layers of semiconductor—an emitter, a base, and a collector. They are useful in amplifiers because the currents at the emitter and collector are controllable by a relatively small base current. In an n–p–n transistor operating in the active region, the emitter–base junction is forward biased (electrons and holes recombine at the junction), and electrons are injected into the base region. Because the base is narrow, most of these electrons will diffuse into the reverse-biased (electrons and holes are formed at, and move away from the junction) base–collector junction and be swept into the collector; perhaps one-hundredth of the electrons will recombine in the base, which is the dominant mechanism in the base current. By controlling the number of electrons that can leave the base, the number of electrons entering the collector can be controlled. Collector current is approximately β (common-emitter current gain) times the base current. It is typically greater than 100 for small-signal transistors but can be smaller in transistors designed for high-power applications.
In a FET, the drain-to-source current flows via a conducting channel that connects the source region to the drain region. The conductivity is varied by the electric field that is produced when a voltage is applied between the gate and source terminals; hence the current flowing between the drain and source is controlled by the voltage applied between the gate and source. As the gate–source voltage (VGS) is increased, the drain–source current (IDS) increases exponentially for VGS below threshold, and then at a roughly quadratic rate (IGS ∝ (VGS − VT)2) (where VT is the threshold voltage at which drain current begins) in the "space-charge-limited" region above threshold. A quadratic behavior is not observed in modern devices, for example, at the 65 nm technology node.
FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The IGFET is more commonly known as a metal–oxide–semiconductor FET (MOSFET), reflecting its original construction from layers of metal (the gate), oxide (the insulation), and semiconductor. Unlike IGFETs, the JFET gate forms a p–n diode with the channel which lies between the source and drain. Functionally, this makes the n-channel JFET the solid-state equivalent of the vacuum tube triode which, similarly, forms a diode between its grid and cathode. Also, both devices operate in the depletion mode, they both have a high input impedance, and they both conduct current under the control of an input voltage.
FETs are further divided into depletion-mode and enhancement-mode types, depending on whether the channel is turned on or off with zero gate-to-source voltage. For enhancement mode, the channel is off at zero bias, and a gate potential can "enhance" the conduction. For the depletion mode, the channel is on at zero bias, and a gate potential (of the opposite polarity) can "deplete" the channel, reducing conduction. For either mode, a more positive gate voltage corresponds to a higher current for n-channel devices and a lower current for p-channel devices. Nearly all JFETs are depletion-mode because the diode junctions would forward bias and conduct if they were enhancement-mode devices; most IGFETs are enhancement-mode types.
The bipolar junction transistor (BJT) was the most commonly used transistor in the 1960s and 70s. Even after MOSFETs became widely available, the BJT remained the transistor of choice for many analog circuits such as amplifiers because of their greater linearity and ease of manufacture. In integrated circuits, the desirable properties of MOSFETs allowed them to capture nearly all market share for digital circuits. Discrete MOSFETs can be applied in transistor applications, including analog circuits, voltage regulators, amplifiers, power transmitters and motor drivers.
The Pro Electron standard, the European Electronic Component Manufacturers Association part numbering scheme, begins with two letters: the first gives the semiconductor type (A for germanium, B for silicon, and C for materials like GaAs); the second letter denotes the intended use (A for diode, C for general-purpose transistor, etc.). A 3-digit sequence number (or one letter then 2 digits, for industrial types) follows. With early devices this indicated the case type. Suffixes may be used, with a letter (e.g. "C" often means high hFE, such as in: BC549C) or other codes may follow to show gain (e.g. BC327-25) or voltage rating (e.g. BUK854-800A). The more common prefixes are:
The JEDEC EIA370 transistor device numbers usually start with "2N", indicating a three-terminal device (dual-gate field-effect transistors are four-terminal devices, so begin with 3N), then a 2, 3 or 4-digit sequential number with no significance as to device properties (although early devices with low numbers tend to be germanium). For example, 2N3055 is a silicon n–p–n power transistor, 2N1301 is a p–n–p germanium switching transistor. A letter suffix (such as "A") is sometimes used to indicate a newer variant, but rarely gain groupings.
Manufacturers of devices may have their own proprietary numbering system, for example CK722. Since devices are second-sourced, a manufacturer's prefix (like "MPF" in MPF102, which originally would denote a Motorola FET) now is an unreliable indicator of who made the device. Some proprietary naming schemes adopt parts of other naming schemes, for example a PN2222A is a (possibly Fairchild Semiconductor) 2N2222A in a plastic case (but a PN108 is a plastic version of a BC108, not a 2N108, while the PN100 is unrelated to other xx100 devices).
The junction forward voltage is the voltage applied to the emitter–base junction of a BJT in order to make the base conduct a specified current. The current increases exponentially as the junction forward voltage is increased. The values given in the table are typical for a current of 1 mA (the same values apply to semiconductor diodes). The lower the junction forward voltage the better, as this means that less power is required to "drive" the transistor. The junction forward voltage for a given current decreases with increase in temperature. For a typical silicon junction the change is −2.1 mV/°C. In some circuits special compensating elements (sensistors) must be used to compensate for such changes.
Because the electron mobility is higher than the hole mobility for all semiconductor materials, a given bipolar n–p–n transistor tends to be swifter than an equivalent p–n–p transistor. GaAs has the highest electron mobility of the three semiconductors. It is for this reason that GaAs is used in high-frequency applications. A relatively recent FET development, the high-electron-mobility transistor (HEMT), has a heterostructure (junction between different semiconductor materials) of aluminium gallium arsenide (AlGaAs)-gallium arsenide (GaAs) which has twice the electron mobility of a GaAs-metal barrier junction. Because of their high speed and low noise, HEMTs are used in satellite receivers working at frequencies around 12 GHz. HEMTs based on gallium nitride and aluminium gallium nitride (AlGaN/GaN HEMTs) provide a still higher electron mobility and are being developed for various applications.
Discrete transistors are individually packaged transistors. Transistors come in many different semiconductor packages (see image). The two main categories are through-hole (or leaded), and surface-mount, also known as surface-mount device (SMD). The ball grid array (BGA) is the latest surface-mount package (currently only for large integrated circuits). It has solder "balls" on the underside in place of leads. Because they are smaller and have shorter interconnections, SMDs have better high-frequency characteristics but lower power rating.
In the Pre-Modern era, many people's sense of self and purpose was often expressed via a faith in some form of deity, be that in a single God or in many gods. Pre-modern cultures have not been thought of creating a sense of distinct individuality, though. Religious officials, who often held positions of power, were the spiritual intermediaries to the common person. It was only through these intermediaries that the general masses had access to the divine. Tradition was sacred to ancient cultures and was unchanging and the social order of ceremony and morals in a culture could be strictly enforced.
The term "modern" was coined in the 16th century to indicate present or recent times (ultimately derived from the Latin adverb modo, meaning "just now). The European Renaissance (about 1420–1630), which marked the transition between the Late Middle Ages and Early Modern times, started in Italy and was spurred in part by the rediscovery of classical art and literature, as well as the new perspectives gained from the Age of Discovery and the invention of the telescope and microscope, expanding the borders of thought and knowledge.
The term "Early Modern" was introduced in the English language in the 1930s. to distinguish the time between what we call Middle Ages and time of the late Enlightenment (1800) (when the meaning of the term Modern Ages was developing its contemporary form). It is important to note that these terms stem from European history. In usage in other parts of the world, such as in Asia, and in Muslim countries, the terms are applied in a very different way, but often in the context with their contact with European culture in the Age of Discovery.
In the Contemporary era, there were various socio-technological trends. Regarding the 21st century and the late modern world, the Information age and computers were forefront in use, not completely ubiquitous but often present in daily life. The development of Eastern powers was of note, with China and India becoming more powerful. In the Eurasian theater, the European Union and Russian Federation were two forces recently developed. A concern for Western world, if not the whole world, was the late modern form of terrorism and the warfare that has resulted from the contemporary terrorist acts.
In Asia, various Chinese dynasties and Japanese shogunates controlled the Asian sphere. In Japan, the Edo period from 1600 to 1868 is also referred to as the early modern period. And in Korea, from the rising of Joseon Dynasty to the enthronement of King Gojong is referred to as the early modern period. In the Americas, Native Americans had built a large and varied civilization, including the Aztec Empire and alliance, the Inca civilization, the Mayan Empire and cities, and the Chibcha Confederation. In the west, the European kingdoms and movements were in a movement of reformation and expansion. Russia reached the Pacific coast in 1647 and consolidated its control over the Russian Far East in the 19th century.
In China, urbanization increased as the population grew and as the division of labor grew more complex. Large urban centers, such as Nanjing and Beijing, also contributed to the growth of private industry. In particular, small-scale industries grew up, often specializing in paper, silk, cotton, and porcelain goods. For the most part, however, relatively small urban centers with markets proliferated around the country. Town markets mainly traded food, with some necessary manufactures such as pins or oil. Despite the xenophobia and intellectual introspection characteristic of the increasingly popular new school of neo-Confucianism, China under the early Ming dynasty was not isolated. Foreign trade and other contacts with the outside world, particularly Japan, increased considerably. Chinese merchants explored all of the Indian Ocean, reaching East Africa with the treasure voyages of Zheng He.

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