Wednesday, August 22, 2007
Space Shuttle
NASA's Space Shuttle, officially called Space Transportation System (STS), is the United States government's present manned launch vehicle. At launch, it consists of a rust-colored outer tank, two white, slender solid rocket boosters (SRBs), and a winged orbiter. The orbiter carries astronauts and payload such as satellites or space location parts into low earth orbit. Normally, five to seven astronauts ride in the orbiter, with two pilots, eight have been carried, and eleven could be accommodated in an urgent situation landing. When the orbiter's work is complete, it fires its orbital maneuvering thrusters to drop out of orbit and re-enters the Earth's atmosphere. During the descent and landing, the shuttle orbiter acts as a glider and makes a completely unpowered landing. Five spaceworthy orbiters were build, of which three remain.
The Shuttle is the first orbital spacecraft considered for partial reusability. It carries large payloads to various orbits, provides crew rotary motion for the International Space Station (ISS), and performs servicing missions. The orbiter can also recover satellites and other payloads from orbit and return them to Earth, but this capability has not been used often. However, it has been used to return large payloads from the ISS to Earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a expected lifespan of 100 launches or 10 years' operational life.
The Shuttle is the first orbital spacecraft considered for partial reusability. It carries large payloads to various orbits, provides crew rotary motion for the International Space Station (ISS), and performs servicing missions. The orbiter can also recover satellites and other payloads from orbit and return them to Earth, but this capability has not been used often. However, it has been used to return large payloads from the ISS to Earth, as the Russian Soyuz spacecraft has limited capacity for return payloads. Each Shuttle was designed for a expected lifespan of 100 launches or 10 years' operational life.
Monday, August 13, 2007
Table
In relational databases, SQL databases, and flat file databases, a table is a set of data elements that is controlled using a model of horizontal rows and vertical columns. The columns are identified by name, and the rows are identified by the values appearing in a particular column division which has been identified as a candidate key. Table is another term for family although there is the difference in that a table is usually a multi-set of rows whereas a relation is a set and does not allow duplicates. A table has a particular number of columns but can have any number of rows. Besides the actual data rows, tables generally have related with them some meta-information, such as constraints on the table or on the values within particular columns.
The data in a table does not have to be actually stored in the database. Views are also relational tables, but their data is considered at query time. In non-relational systems, such as hierarchical databases, the isolated counterpart of a table is a structured file, representing the rows of a table in each record of the file and each column in a record.
Wednesday, August 01, 2007
Cloud
A cloud is a visible mass of condensed droplets, frozen crystals suspended in the atmosphere above the surface of the Earth or another earthly body, such as a moon. The branch of meteorology in which exhaust are studied is nephology.
On Earth the condensing matter is typically water vapor, which forms small droplets or ice crystals, typically 0.01 mm in diameter. When surrounded by billions of other droplets or crystals they become observable as clouds. Dense deep clouds exhibit a high reflectance throughout the visible range of wavelengths: they thus appear white, at least from the top. Cloud droplets tend to scatter light professionally, so that the intensity of the solar radiation decreases with depth into the cloud, hence the gray or even sometimes dark exterior of the clouds at their base. Thin clouds may appear to have acquired the color of their environment or background, and clouds illuminated by non-white light, such as through sunrise or sunset, may be colored accordingly. In the near-infrared range, clouds would appear darker because the water that constitutes the cloud droplets muscularly absorbs solar radiation at those wavelengths.
On Earth the condensing matter is typically water vapor, which forms small droplets or ice crystals, typically 0.01 mm in diameter. When surrounded by billions of other droplets or crystals they become observable as clouds. Dense deep clouds exhibit a high reflectance throughout the visible range of wavelengths: they thus appear white, at least from the top. Cloud droplets tend to scatter light professionally, so that the intensity of the solar radiation decreases with depth into the cloud, hence the gray or even sometimes dark exterior of the clouds at their base. Thin clouds may appear to have acquired the color of their environment or background, and clouds illuminated by non-white light, such as through sunrise or sunset, may be colored accordingly. In the near-infrared range, clouds would appear darker because the water that constitutes the cloud droplets muscularly absorbs solar radiation at those wavelengths.
