Saturday, October 27, 2007

Mounting of traffic lights

A typical exemplar of how traffic lights are mounted in California. Wealthy cities like Cerritos frequently have elaborate traffic light gantries. There are important differences from place to place in how traffic lights are mounted or placed so that they are visible to drivers. Depending upon the place, traffic lights may be mounted on poles positioned on street corners, hung from wires strung over the roadway, or even hung from horizontal poles or installed within large horizontal gantries that make bigger out from the corner and over the right-of-way. In the previous case, such poles or gantries frequently have a lit sign with the name of the cross-street.

In some places mount lights with their multiple faces set horizontally and others vertically. California is particularly fastidious in ensuring that drivers can see the current state of a traffic light. One entrance to a typical large intersection, with three through lanes, two dedicated left-turn lanes, and a crosswalk, may have as many as three traffic lights for the left-turn lanes, three for the through lanes, and a pedestrian signal for the crosswalk. And those numbers must be multipled by four to cover all four ways to enter a typical intersection. Additionally to being positioned and mounted for preferred visibility for their personal traffic, some traffic lights are also meant, louvered, or shaded to reduce mis-interpretation from other lanes. For instance, a Fresnel lens on a neighboring through-lane signal may be intended to prevent left-turning traffic from anticipating its individual green arrow.

The Traffic signals in Germany are placed at the stop line on same side of the intersection as the forthcoming traffic and are often mounted overhead with on the right and left sides of the road. The stop line position is done to stop crosswalk blocking and permit for better pedestrian traffic flow.

Thursday, October 18, 2007

The History of glass

Naturally occurring glass, like obsidian, has been used ever since the Stone Age. The first accepted instructions for glass making are in Egypt about 1500 BC, when glass was used as a glaze for pottery and additional items. In the first century BC the method of blowing glass was developed and what had once been a tremendously rare and expensive item became much more common. During the Roman Empire numerous forms of glass were created, generally for use in vases and bottles.

The Glass was made from sand, plant ash and lime. The most primitive use of glass was as a colored, opaque, or clear glaze applied to ceramics before they were fired. Small pieces of colored glass were considered costly and often rivaled valuable gems as jewelry items. As time passed, it was revealed (most likely by a potter) that if glass is heated in anticipation of it becomes semi-liquid, it can be shaped and left to cool in a new , solid, separately standing shape. In the first century BC, someplace at the eastern end of the Mediterranean, a new discovery caused a true revolution in the glass industry. This was the invention of glassblowing, both free-blowing and mold-blowing. The color of "natural glass" is green to bluish green glass. This color is caused by the changeable amounts of naturally occurring iron impurities in the sand. Common glass at present usually has a slight green or blue tint, arising from these same impurities.

The Glassmakers learned to make colored glass by adding metallic compounds and mineral oxides to make brilliant hues of red, green, and blue - the colors of gemstones. When gem cutters learned to cut glass, they create that clear glass was an outstanding refractor of light, the attractiveness of cut clear glass soared, that of colored glass diminished.

The Glass objects from the 7th and 8th centuries have been found on the island of Torcello close to Venice. These form an essential link between Roman times and the later on importance of that city in the production of the material. About 1000 CE, an essential technological breakthrough was made in Northern Europe when soda glass was replaced by glass made from a much more readily obtainable material: potash obtained from wood ashes. From this point on, northern glass differed considerably from that made in the Mediterranean area, where soda remained in general use.

Thursday, October 11, 2007

The real facts about Mars

Mars (Greek: Ares) is the God of War. The planet perhaps got this name due to its red color; Mars is at times referred to as the Red Planet. The name of the month March obtains from Mars.

Mars has been recognized since prehistoric times. Certainly, it has been broadly studied with ground-based observatories. But even very large telescopes find Mars a hard target, it's just too small. It is still a favorite of science fiction writers as the best place in the Solar System (other than Earth!) for human habitation. But the illustrious "canals" "seen" by Lowell and others were, regrettably, just as fantasy as Barsoomian princesses.

Mars' orbit is considerably elliptical. One result of this is a temperature variation of concerning 30 C at the sub solar point between aphelion and perihelion. This has a most important influence on Mars' climate. While the average temperature on Mars is about 218 K (-55 C, -67 F), and in summer, Martian surface temperatures range broadly from as little as 140 K (-133 C, -207 F) at the winter pole to roughly 300 K (27 C, 80 F) on the day side.

There is dreadfully clear evidence of erosion in many places on Mars together with large floods and small river systems. At some time in the past there was evidently some sort of fluid on the surface. Liquid water is the clear fluid but other possibilities exist. There possibly will have been large lakes or even oceans; the proof for which was strengthened by some extremely nice images of layered terrain taken by Mars Global Surveyor and the mineral logy results from MER Opportunity. Most of these points to wet episodes that occurred only for a short time and very long ago; the age of the erosion channels are estimated at about almost 4 billion years. However, images from Mars Express released in early on 2005 show what appears to be an ice-covered sea that was liquid very recently (maybe 5 million years ago). Confirmation of this interpretation would be an extremely big deal indeed!

Mars has a very thin atmosphere composed more often than not of the tiny amount of remaining carbon dioxide (95.3%) plus nitrogen (2.7%), argon (1.6%) and traces of oxygen (0.15%) and water (0.03%). The average pressure on the surface of Mars is simply about 7 millibars (below 1% of Earth's), but it varies to a great extent with altitude from almost 9 millibars in the deepest basins to about 1 millibar at the top of Olympus Mons. But it is thick enough to support very strong winds and measureless dust storms that on occasion engulf the entire planet for months. Mars' thin atmosphere produces a greenhouse consequence but it is only enough to lift up the surface temperature by 5 degrees (K); much less than what we observe on Venus and Earth.