Sunday, April 29, 2007

Nanotechnology

Nanotechnology is a pasture of applied science and technology covering a wide range of topics. The main unifying premise is the control of matter on a scale smaller than 1 micrometer, normally between 1-100 nanometers, as well as the manufacture of devices on this same length scale. It is a highly multidisciplinary field, drawing from fields such as colloidal science, device physics, and supra molecular chemistry. Much hypothesis exists as to what new science and technology might result from these lines of research. Some view nanotechnology as a marketing term that describes pre-existing lines of research applied to the sub-micron size scale.

In spite of the apparent ease of this definition, nanotechnology actually encompasses diverse lines of inquiry. Nanotechnology cuts across many disciplines, together with colloidal science, chemistry, applied physics, materials science, and even mechanical and electrical engineering. It could variously be seen as an extension of existing sciences into the Nanoscale, or as a recasting of existing sciences using a newer, more recent term. Two major approaches are used in nanotechnology: one is a "bottom-up" approach where materials and devices are built from molecular components which gather themselves chemically using principles of molecular gratitude; the other being a "top-down" approach where nano-objects are constructed from larger entities without atomic-level control.

Monday, April 23, 2007

Dot matrix printer

Not like a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary 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, striking an ink-soaked cloth ribbon against the paper, much like a typewriter.

Each dot is produced 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 pierced with holes to serve 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. Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density.

These machines can be highly hard-wearing, but eventually wear out. Ink invades the guide 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, given that less and less accurate guidance to the printing wires. After about a million characters, even with tungsten blocks and titanium pawls, the printing becomes too indistinct to read.

Thursday, April 19, 2007

Croydon Airport

Croydon Airport is in south London on the borders of the London Boroughs of Croydon and Sutton. It was once the main airport for London, before it was replaced by Northolt Aerodrome, London Heathrow Airport and London Gatwick Airport.It originated as two adjacent World War I airfields. Beddington Aerodrome, one of a number of small airfields around London which had been formed for protection against the Zeppelin raids in about May 1915, and Waddon Aerodrome of 1918, a test-flight aerodrome adjoining National Aircraft Factory No1.At the end of that war, the two airfields were joint into London's official airport as the gateway for all international flights to and from the capital. Croydon Aerodrome opened on 29 March 1920.It stimulated a increase in regular scheduled flights carrying passengers, mail and freight, the first destinations being Paris, Amsterdam and Rotterdam. In 1923 Berlin flights were added. It was the operating base for Imperial Airways - remembered in the road name Imperial Way on the site today.In the mid 1920s, the airfield was extended, some adjacent roads being permanently closed to allow heavier airliners to land and depart safely. A new complex of buildings was constructed adjoining Purley Way, including the first purpose-designed air terminal in the world, the Aerodrome Hotel and extensive hangars, all opening on 2 May 1928.The terminal building, the booking hall inside it with its gallery balustraded in the geometrical design typical of the period, and the Aerodrome hotel were all built in the Art Deco style of the 1920s and 1930s. A further item that caught the eye of visitor and traveller alike was the time zone tower in the booking hall with its dials depicting the times in different parts of the world.The aerodrome was known the world over, its fame being spread by the many aviators and pioneers who touched down at Croydon.

Tuesday, April 10, 2007

Postage Stamp

A postage stamp is proof of pre-paying a fee for postal services. Usually a small paper rectangle which is attached to an envelope, signifying that the person sending the letter or package has paid for delivery; it is the most popular option to using a prepaid-postage envelope.

History

In it he argued that it would be well again for the sender to pay the cost of delivery, rather than the addressee who could refuse the letter if they could not or did not want to pay, as occasionally happened at the time. He also argued for a identical rate of one penny per letter, no matter where its end. Accounting costs for the government would thus be cut; postage would no longer be charged according to how far a letter had traveled, which necessary each letter to have an individual entry in the Royal Mail's accounts. Chalmers' ideas were finally adopted by Parliament in August, 1839 and the General Post Office launched the Penny Post service the next year in 1840 with two prepaid-postage symbolic envelopes or wrappers: one valued at a penny and one valued at two pence.

Friday, April 06, 2007

Clock face

100 A clock faces is the part of an analog clock that tells time from side to side the use of a fixed numbered dial or dials and moving hand or hands. Typically, the dial is numbered 1-12 representative the hours in a 12-hour cycle. The term face is also used for the time display on digital clocks and watches.

Certain clocks have 24-hour analog displays and are noticeable consequently. Some special purpose clocks, such darkroom timers and sporting occasion clocks are designed for measuring periods less than one hour. Clocks can indicate the hour with roman numerals or Arabic numerals. The two numbering systems have also been used in mixture with the prior representing the hour and the later the minute. Long case clocks typically use Roman numerals for the hours. Clocks using only Arabic numerals first began to appear in the mid-18th century. In some instances, mainly in the case of watches, the numbers are replaced with undifferentiated hour markings. Infrequently markings of any sort are dispensed with. The face of the Movado "Museum Watch" is known for a single dot at the 12 o'clock position.

Historical and Stylistic Development
Before the late 15th century, a fixed hand indicated the hour by pointing to rotating numbers. Minute hands only came into use in the late 17th century after the discovery of the pendulum allowed for increased accuracy in time telling. Until the last quarter of the 17th century hour markings were etched into metal faces and the recesses filled with black wax. Subsequently, higher contrast and improved readability was achieved with white enamel plaques painted with black numbers. Initially, the numbers were printed on small, individual plaques mounted on a brass substructure. This was not a stylistic decision; rather enamel production technology had not yet achieved the skill to create large pieces of enamel. The "13 piece face" was an early attempt to create an completely white enamel face. As the name suggests, it was composed of 13 enamel plaques: 12 numbered wedges en suite around a circle. The first single piece enamel faces, not unlike those in production today, began to appear c. 1735.

Monday, April 02, 2007

Sunglasses

Sunglasses are a kind of visual correction aid, variously termed spectacles or glasses, which feature lenses that are coloured or darkened to screen out strong light from the eyes.Many people find direct sunlight too bright to be comfortable, particularly when reading from paper on which the sun directly shines. In outdoor activities like skiing and flying, the eye can receive more light than usual. It has been recommended to wear these kind of glasses on sunny days to protect the eyes from ultraviolet radiation, which can lead to the development of a cataract. Sunglasses have also been linked with celebrities and film actors mainly due to the desire to mask identity, but in part due to the lighting involved in production being typically stronger than natural light and uncomfortable to the naked eye.Augusto Pinochet sits with sunglasses in the front of the Chilean JuntaContents