Speed limit and the Design speed for vehicle

A speed limit is the maximum speed allowable for vehicle by law on a road. The Speed limits are only peripherally connected to the intend speed of the road. In the United States, the plan speed is "a chosen speed used to determine the different geometric design features of the roadway" according to the 2001 AASHTO Green Book of the highway design manual. It has been altered from previous versions which considered it the "maximum secure speed that can be maintained over a definite section of highway when conditions are so positive that the design features of the highway govern."

The design speed has basically been discredited as an only basis for establishing a speed limit. The Current U.S. standards for design speed derive from outdated, less-capable automotive technology. In addition, the design speed of a given roadway is the theoretical maximum secure speed of the roadway's worst feature (e.g., a curve, bottleneck, hill, etc.). The design speed generally underestimates the maximum secure and safe speed for a roadway and is as a result considered only a very conservative "first guess" at a limit.

Properties and uses of glasses

Glass can be made form transparent and flat, or into added shapes and colors as made known in this ball from the Verrerie of Brehat in Brittany. One of the nearly all obvious characteristics of ordinary glass is that it is clear to visible light. The clearness is due to an absence of electronic transition states in the range of visible light, and to the truth that such glass is homogeneous on all length scales greater than about a wavelength of noticeable light. Ordinary glass does not let light at a wavelength of lower than 400 nm, also recognized as ultraviolet light or UV, to pass. This is due to the addition of compounds for instance soda ash (sodium carbonate).

Pure SiO2 glass (also called fused quartz) does not absorb UV light and is used for applications that necessitate transparency in this region, although it is more costly. This kind of glass can be made so pure that hundreds of kilometers of glass are clear at infrared wavelengths in fiber optic cables. Individual fibers are given a uniformly transparent cladding of SiO2/GeO2 glass, which has only somewhat different optical properties (the germanium causative to a lower index of refraction). Undersea cables have sections doped with Erbium, which intensify transmitted signals by laser release from within the glass itself.

Amorphous SiO2 is also used as a dielectric substance in integrated circuits, owing to the smooth and electrically unbiased interface it forms with silicon. Glasses used for making visual devices are commonly categorized by means of a letter-number code from the Schott Glass catalog. For model, BK7 is a low-dispersion borosilicate crown glass, and SF10 is a high-dispersion opaque flint glass. The glasses are placed by composition, refractive indicator, and Abe number.

Glass is sometimes created obviously from volcanic magma. This glass is called obsidian, and is generally black with impurities. Obsidian is a raw substance for flint knappers, who have used it to make particularly sharp knives since the Stone Age. Obsidian collection is prohibited by law in some places (together with the United States), but the same tool making techniques can be useful to industrially-made glass.

The facts about Venus

Venus (Greek: Aphrodite; Babylonian: Ishtar) is the goddess of love and beauty. The planet is so named most likely because it is the brightest of the planets recognized to the ancients. Venus has been known since prehistoric times. It is the brightest object in the sky except for the Sun and the Moon. Like Mercury, it was commonly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the sunset star, but the Greek astronomers knew better.

Venus' rotary motion is somewhat unusual in that it is both very slow (243 Earth days per Venus day, somewhat longer than Venus' year) and retrograde. Additionally, the periods of Venus' rotary motion and of its orbit are synchronized such that it for all time presents the same face in the direction of Earth when the two planets are at their neighboring approach. Whether this is a resonance effect or just a coincidence is not known.

Venus is at times regarded as Earth's sister planet. In some ways they are especially similar:

* Venus is only somewhat smaller than Earth (95% of Earth's diameter, 80% of Earth's mass).
* Both have a small number of craters indicating relatively young surfaces.
* Their densities and chemical compositions are alike.

Because of these similarities, it was considered that below its dense clouds Venus might be very earthlike and might even have life. However, unfortunately, more detailed study of Venus reveals that in lots of important ways it is radically different from Earth. It may be the slightest hospitable place for life in the solar system.

The force of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a deepness of 1 km in Earth's oceans). It is composed generally of carbon dioxide. There are numerous layers of clouds many kilometers thick composed of sulfuric acid. These clouds entirely obscure our view of the surface. This dense atmosphere creates a run-away greenhouse effect that raises Venus' face temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is truly hotter than Mercury's in spite of being nearly twice as far from the Sun. The oldest terrains on Venus appear to be about 800 million years old. Extensive volcanism at that time wiped out the in advance surface counting any large craters from early in Venus' history.