Carbon is a chemical element that has the symbol C and atomic number6. An abundant nonmetallic, tetravalent element, carbon has several allotropic forms.

The abundance of carbon in the universe, along with the unusual polymer-forming ability of carbon-based compounds at the common temperatures encountered on Earth, make this element the basis of the chemistry of all known life.

The name "carbon" comes from Latin language carbo, coal. In some Romance languages, the word can refer both to the element and to coal.

Overview of carbon's importance on Earth

As the free element it forms allotropes from differing kinds of carbon-carbon bonds, such as in graphite and diamond. Coal is the main source of carbon in mineral form, containing up to 95% of carbon in anthracite. Recently discovered nanostructured forms called fullerenes include buckyballs such as C60, nanotubes, and nanofibers. Because of their high strength-to-weight ratio, it is hoped that many of these carbon compounds will soon be practical for use in advanced structural composite materials.

Not only can carbon also bond with itself, but it can also form chains with a wide variety of other elements, forming nearly ten million known compounds.

Carbon-containing polymers, often with oxygen and nitrogen ions included at regular intervals in the main polymer chain, form the basis of nearly all industrial commercial plastics.

Carbon occurs in all organic life and is the basis of organic chemistry. When united with oxygen, carbon forms carbon dioxide, which is the main carbon source for plant growth. When united with hydrogen, it forms various flammable compounds called hydrocarbons which are essential to industry in the form of fossil fuels, and also other important living plant components like carotenoids and terpenes. When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, celluloses, lignans, chitins, alcohols, fats, and aromatic esters. With oxygen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids and proteins. With the addition of phosphorus to these other elements, it forms DNA and RNA, the chemical codes of life.

Notable characteristics of carbon

Carbon exhibits remarkable properties, some paradoxical. Different forms include the hardest naturally occurring substance (diamond) and one of the softest substances (graphite) known. Moreover, it has a great affinity for bonding with other small atoms, including other carbon atoms, and is capable of forming multiple stable covalent bonds with such atoms. Because of these properties, carbon is known to form nearly ten million different compounds, the large majority of all chemical compounds. Carbon compounds form the basis of all life on Earth and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars. Moreover, carbon has the highest melting/sublimation point of all elements. At atmospheric pressure it has no actual melting point as its triple point is at 10 MPa (100 bar) so it sublimates above 4000 K. Thus it remains solid at higher temperatures than the highest melting point metals like tungsten or rhenium irrespective of its allotropic form. Although thermodynamically prone to oxidation, it resists oxidation more effectively than some elements (like iron and even copper) that are weaker reducing agents at room temperature.

Although it forms an incredible variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers (such as fluorine and nitric acid). It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures it of course reacts with oxygen in flames and with sulfur vapors; it also combines with some metals at high temperatures to form metallic carbides and reduces such metal oxides as iron oxide.

Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (helium, nuclei). This happens in temperature and helium concentration conditions that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang. Instead, the interiors of stars in the horizontal branch transform three helium nuclei into carbon by means of this triple-alpha process. In order to be available for formation of life as we know it, this carbon must then later be scattered into space as dust, in supernovae explosions, as part of the material which later forms second-generation star systems which have planets accreted from such dust. The solar system is one such second-generation star, made from carbon in the dust of dozens of supernovae in its local area of the galaxy.

Yalta is a city in Crimea, southern Ukraine, on the north coast of the Black Sea. The city is located on the site of an ancient Greek colony, said to have been founded by Greek sailors who were looking for a safe shore (γιαλος - yalos in Greek) on which to land. It is situated on a shallow bay facing south towards the Black Sea, surrounded by wooded mountains. It enjoys a warm Mediterranean climate with many vineyards and orchards in the vicinity.

The term "Great Yalta" is used to designate a part of the Crimean southern coast spanning from Foros in the west to Gurzuf in the east and including the city of Yalta and multiple adjacent urban settlements (the area of Great Yalta is marked dark blue on the map).

Modern Yalta

Following the collapse of the Soviet Union in 1991, Yalta has struggled economically. Many of the nouveaux riche started going to other European holiday resorts, now that they had the freedom and money to travel; conversely, the impoverishment of many ex-Soviet citizens meant that they could no longer afford to go to Yalta. The town's transport links have been significantly reduced with the end of almost all passenger traffic by sea. A main form of transportation to and from Yalta is the Crimean Trolleybus line, which runs from Simferopol—Alushta—Yalta. In recent years, Yalta has staged a recovery, as economic conditions have improved and tourists have returned. It is still almost entirely frequented by Russian and Ukrainian tourists, with relatively few visitors from Western Europe.

Today, Yalta has a beautiful embankment along the Black Sea. People can be seen strolling there all seasons of the year, and it also serves as a place to gather and talk. There are several beaches along the embankment where people relax and go swimming. Some hardy souls even do this in the winter. This embankment is also the site of several hotels and amusement-park-like rides. In addition, the city has several movie theaters, and many restaurants and cafés, as well as a large open-air market.

Leukemia or leukaemia (see spelling differences) is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation (production by multiplication) of blood cells, usually white blood cells (leukocytes). It is part of the broad group of diseases called hematological neoplasms.

Symptoms

Damage to the bone marrow, by way of displacing the normal bone marrow cells with higher numbers of immature white blood cells, results in a lack of blood platelets, which are important in the blood clotting process. This means people with leukemia may become bruised, bleed excessively, or develop pinprick bleeds (petechiae).

White blood cells, which are involved in fighting pathogens, may be suppressed or dysfunctional. This could cause the patient's immune system (white blood cells etc.) to start attacking other body cells.

Finally, the red blood cell deficiency leads to anemia, which may cause dyspnea. All symptoms can be attributed to other diseases; for diagnosis, blood tests and a bone marrow examination are required.

Some other related symptoms

• Fever, chills, night sweats and other flu-like symptoms
• Weakness and fatigue
• Loss of appetite and/or weight
• Swollen or bleeding gums
• Excess bleeding (from a minor cut)
• Neurological symptoms (headache)
• Enlarged liver and spleen
• Easy bruising
• Frequent infection
• Bone pain
• Joint pain
• Swollen tonsils

The word leukemia, which means 'white blood,' is derived from the disease's namesake high white blood cell counts that most leukemia patients have before treatment. The high number of white blood cells are apparent when a blood sample is viewed under a microscope. Frequently, these extra white blood cells are immature or dysfunctional. The excessive number of cells can also interfere with the normal function of other cells.

Some leukemia patients do not have high white blood cell counts visible during a regular blood count. This less-common condition is called aleukemia. The bone marrow still contains cancerous white blood cells, and they are disrupting the normal production of blood cells. However, they are staying in the marrow instead of entering the bloodstream, where they would be visible in a blood test. For an aleukemic patient, the white blood cell counts in the bloodstream can be normal or low. Aleukemia can occur in any of the four major types of leukemia, and is particularly common in hairy cell leukemia.

Causes and risk factors

There is no single known cause for all of the different types of leukemia. The different leukemias likely have different causes, and very little is certain about what causes them. Researchers have strong suspicions about four possible causes:

• natural or artificial ionizing radiation
• certain kinds of chemicals
• some viruses
• genetic predispositions

Leukemia, like other cancers, result from somatic mutations in the DNA which activate oncogenes or deactivate tumor suppressor genes, and disrupt the regulation of cell death, differentiation or division. These mutations may occur spontaneously or as a result of exposure to radiation or carcinogenic substances and are likely to be influenced by genetic factors. Cohort and case-control studies have linked exposure to petrochemicals, such as benzene, and hair dyes to the development of some forms of leukemia.

Viruses have also been linked to some forms of leukemia. For example, certain cases of ALL are associated with viral infections by either the human immunodeficiency virus (HIV, responsible for AIDS)^{[citation needed]} or human T-lymphotropic virus (HTLV-1 and -2, causing adult T-cell leukemia/lymphoma).

Fanconi anemia is also a risk factor for developing acute myelogenous leukemia.

Until the cause or causes of leukemia are found, there is no way to prevent the disease. Even when the causes become known, they may prove to be things which are not readily controllable, such as naturally occurring background radiation, and therefore not especially hel

In ancient geography, Cappadocia or Capadocia, Turkish Kapadokya (from Persian: Katpatuka meaning "the land of beautiful horses"^{[citation needed]}, Greek: Καππαδοκία; see also List of traditional Greek place names) was the name of the extensive inland district of Asia Minor (modern Turkey). The name continued to be used in western sources and in the Christian tradition throughout history and is still widely used as an international tourism concept to define a region of exceptional natural wonders characterized by fairy chimneys and a unique historical and cultural heritage. The term, as used in tourism, roughly corresponds to present-day Nevşehir Province of Turkey.

It is impossible to define Cappadocia's limits with accuracy. In the time of Herodotus, the Cappadocians are supposed to have occupied the whole region from Mount Taurus to the vicinity of the Euxine (Black Sea. Cappadocia, in this sense, was bounded in the south by the chain of Mount Taurus, to the east by the Euphrates, to the north by Pontus, and to the west vaguely by the great salt lake, Lake Tuz, in Central Anatolia. But Strabo, the only ancient author who gives any circumstantial account of the country, greatly exaggerated its dimensions. It is now believed that 250 miles in length by less than 150 in breadth is a more realistic appraisal of Cappadocia's extension.

Venice (Italian: Venezia, Venetian: Venezsia, Latin: Venetia) is a city in northern Italy, the capital of region Veneto, and has a population of 271,251 (census estimate January 1, 2004). Together with Padua, the city is included in the Padua-Venice Metropolitan Area (population 1,600,000). Venice's nicknames include "Queen of the Adriatic", "City of Water", "City of Bridges", and "The City of Light".

The city stretches across numerous small islands in the marshy Venetian Lagoon along the Adriatic Sea in northeast Italy. The saltwater lagoon stretches along the shoreline between the mouths of the Po (south) and the Piave (north) Rivers. The population estimate of 272,000 inhabitants includes the population of the whole Comune of Venezia; around 62,000 in the historic city of Venice (Centro storico); 176,000 in Terraferma (literally firm land, the areas outside the lagoon), mostly in the large frazione of Mestre and Marghera; and 31,000 live on other islands in the lagoon.

The Venetian Republic was a major sea power and a staging area for the Crusades, as well as a very important center of commerce (especially the spice trade) and art in the Renaissance. Though ironically the city-state lost much of its power and importance due to the decline and fall of the Byzantine Empire, which Venice helped to destroy. This was due to the fact that Turkish control of the Eastern Mediterranean gave the European maritime powers incentive to find trade routes elsewhere.

A smaller number of stealth aircraft may replace a large fleet of conventional attack jets with the same or increased combat efficiency, possibly resulting in longer term savings in the military budget.

A stealth aircraft strike capability may deter potential opponents from taking action and keep them in constant fear of strikes, since they can never know if the attack planes are already underway. This may make them more willing to accept a diplomatic solution, although the moral reasoning behind this is disputed.

Stealth aircraft allow raids on important point targets to occur, while maintaining a cover of plausible denial. Since no-one could detect the attackers or at least identify them, the stealth operator would simply refuse to comment and hope to avoid war.

The production and fielding of a stealth combat aircraft design may force an opponent to pursue the same aim, possibly resulting in significant weakening of the economically inferior party. The 1980s American Strategic Defense Initiative ("Star Wars") program served a similar purpose against the USSR.

A computer is a machine for manipulating data according to a list of instructions.

Computers take numerous physical forms. Early electronic computers were the size of a large room, using as much power as several hundred modern computers. ^[1] Today, computers can be made small enough to fit into a wrist watch and be powered from a watch battery. Society has come to recognize personal computers and their portable equivalent, the laptop computer, as icons of the information age; they are what most people think of as "a computer". However, the most common form of computer in use today is by far the embedded computer. Embedded computers are small, simple devices that are often used to control other devices—for example, they may be found in machines ranging from fighter aircraft to industrial robots, digital cameras, and even children's toys.

The ability to store and execute programs makes computers extremely versatile and distinguishes them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: Any computer with a certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore, computers with capability and complexity ranging from that of a personal digital assistant to a supercomputer are all able to perform the same computational tasks as long as time and storage capacity are not considerations.