Tuesday, November 27, 2007


A coin is normally a piece of hard material, generally metal, usually in the shape of a disc, and most often issued by a government, to be used as a form of money in transactions of various kinds,from the everyday circulation of the US quarter, to the storage of vast amounts of bullion coins.In modern times coins along with banknotes, coins construct the cash forms of all modern money systems. Coins made for circulation (general monetized use) are usually used for lower-valued units, and banknotes are usually used for the higher values; also, in most money systems, the highest value coin is worth less than the lowest-value note. The face value of circulation coins is usually higher than the gross value of the metal used in manufacturing them.

Exceptions to these rules take place for non-monetized "bullion coins" made of silver or gold (and, rarely, other metals, such as platinum or palladium), intended for collectors or investors in precious metals.Historically, a enormous number of coinage metals (including alloys) and other materials have been used practically, impractically (i.e., rarely), artistically, and experimentally in the construction of coins for both circulation, assortment, and metal investment

Tuesday, November 20, 2007

Dot matrix printer

Unlike a typewriter or daisy wheel printer, letters are tired out of a dot matrix, and thus, varied fonts and random graphics can be produced. Because the printing involves mechanical pressure, these printers can create carbon copies and carbonless copies. A dot matrix printer or impact matrix printer refers to a type of computer printer with a print head that runs back and forth on the page and prints by impact, outstanding an ink-soaked cloth ribbon beside the paper, much like a typewriter.

Each dot is formed by a tiny metal rod, also called a "wire" or "pin", which uses the power of a tiny electromagnet or solenoid to drive it forward, either directly or through small levers .Facing the ribbon and the paper is a small guide plate (often made of an artificial jewel such as sapphire or garnet) pierced with hole to provide as guides for the pins. The moving portion of the printer is called the print head, and prints one line of text at a time.The majority dot matrix printers have a single vertical line of dot-making apparatus on their print heads; others have a few interleaved rows in order to improve dot density.

These machines can be highly durable, but eventually wear out. Ink invades the direct plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less correct guidance to the printing wires. After about a million characters, even with tungsten blocks and titanium pawls, the printing becomes too unclear to read.

Tuesday, November 13, 2007

Transportation is the movement of people and goods from one place to another. The term is derived from the portare ("to carry") and Latin trans ("across") . Industries which have the business of providing equipment, actual transport, transport of people or goods and services used in transport of goods or people make up a huge broad and important segment of most national economies, and are collectively referred to as transport industries.

The field of transport has several aspects: loosely they can be divided into a triad of infrastructure, vehicles, and operations. Infrastructure includes the transport networks (roads, railways, airways, waterways, canals, pipelines, etc.) that are used, as well as the nodes or terminals (such as airports, railway stations, bus stations and seaports). The vehicles generally traverse on the networks, such as automobiles, bicycles, buses, trains, and aircrafts.

Monday, November 05, 2007

An escalator is a transport machine for transporting people, consisting of a staircase whose steps move up or down on tracks that stay the surfaces of the individual steps horizontal.A moving walkway, moving sidewalk, revelator, or moderator is a slow conveyor belt that transports people straightly or on a bigotry in a similar manner to an escalator. In both cases, riders can wander or stand. The walkways are often whole in pairs, one for each direction. Modern escalators have metal steps in a stable loop that moves on tracks. Escalators are typically used in pairs with one going up and the other going down.