Clark

Clark is an English language surname, ultimately derived from the Latin clericus meaning "scribe", "secretary" or a scholar within a religious order, referring to someone who was educated. Clark evolved from "clerk". First records of the name are found in 12th century England. The name has many variants.

Clark is the twenty-seventh most common surname in the United Kingdom, including placing fourteenth in Scotland. Clark is also an occasional given name, as in the case of Clark Gable.

According to the 1990 United States Census, Clark was the twenty-first most frequently encountered surname, accounting for 0.23% of the population. Notable people with the surname include:

Ryan Clark

Ryan Clark may refer to:

See also

Tank

A tank is a large, heavily armoured fighting vehicle with tracks and a large tank gun that is designed for front-line combat. Modern tanks are mobile land weapon platforms, mounting a large-calibre cannon in a rotating gun turret. They combine this with heavy vehicle armour which provides protection for the crew, the vehicle's weapons, and its propulsion systems, and operational mobility, due to its use of tracks rather than wheels, which allows the tank to move over rugged terrain and be positioned on the battlefield in advantageous locations. These features enable the tank to perform well in a tactical situation: the combination of powerful weapons fire from their tank gun and their ability to resist enemy fire means the tank can take hold of and control an area and prevent other enemy vehicles from advancing. In both offensive and defensive roles, they are powerful units able to perform key primary tasks required of armoured units on the battlefield. The modern tank was the result of a century of development from the first primitive armoured vehicles, due to improvements in technology such as the internal combustion engine, which allowed the rapid movement of heavy armoured vehicles. As a result of these advances, tanks underwent tremendous shifts in capability during the World Wars of the 20th century.

Pacific Time Zone

The Pacific Time Zone observes standard time by subtracting eight hours from Coordinated Universal Time (UTC−8). The standard time in this zone is based on the mean solar time of the 120th meridian west of the Greenwich Observatory. During daylight saving time, its time offset is UTC−7 and is thus based on the mean solar time of the 105th meridian west of the Greenwich Observatory.

In the United States and Canada, this time zone is generically called the Pacific Time Zone (PT). Specifically, it uses Pacific Standard Time (PST) when observing standard time (late autumn to early spring), and Pacific Daylight Time (PDT) when observing daylight saving time (early spring to late autumn). Most of Canada uses daylight saving time. In Mexico the UTC−8 time zone is known as the Northwest Zone, which is synchronized with the U.S. PDT daylight saving schedule.

The largest city in the Pacific Time Zone is Los Angeles, California; the city's metropolitan area is the largest in the zone.

Steam

Steam is water in the gas phase, which is formed when water boils. Steam is invisible; however, "steam" often refers to wet steam, the visible mist or aerosol of water droplets formed as this water vapor condenses. At lower pressures, such as in the upper atmosphere or at the top of high mountains, water boils at a lower temperature than the nominal 100 °C (212 °F) at standard temperature and pressure. If heated further it becomes superheated steam.

The enthalpy of vaporization is the energy required to turn water into the gaseous form when it increases in volume by 1,700 times at standard temperature and pressure; this change in volume can be converted into mechanical work by steam engines such as reciprocating piston type engines and steam turbines, which are a sub-group of steam engines. Piston type steam engines played a central role to the Industrial Revolution and modern steam turbines are used to generate more than 80% of the world's electricity. If liquid water comes in contact with a very hot surface or depressurizes quickly below its vapor pressure, it can create a steam explosion. Steam explosions have been responsible for many foundry accidents, and may also have been responsible for much of the damage to the plant in the Chernobyl disaster.