A mutation is an alteration of the genomic sequence of DNA molecules. Mutations may cause altered function in the affected organism, or may cause alteration of inherited traits of...
Arabian Desert and East Sahero-Arabian xeric shrublandsLast Updated on 2013-12-17 20:17:31Located on the Arabian Peninsula, the Arabian Desert and East Sahero-Arabian Xeric Shrublands , and extending north to surround the Dead Sea, is a desert ecoregion, one of the most continuous bodies of sand in the world.
This ecoregion holds little biodiversity, although a few endemic plants grow here. Many faunal species, such as the striped hyaena, jackal, and honey badger have become extinct in this area due to hunting, human encroachment, and habitat destruction. Other species have been successfully re-introduced, such as the endangered white oryx and the sand gazelle, and are protected at a number of reserves. Overgrazing by livestock, off-road driving, and human destruction of habitat are the main threats to this desert ecoregion.
This is the largest ecoregion of the Arabian Peninsula, stretching from the Yemeni border to the Arabian Gulf and from Oman to Jordan and Iraq.... More »
HydrodesulfurizationLast Updated on 2013-12-15 23:43:02Hydrodesulfurization (HDS) or Hydrotreating is a catalytic chemical process widely used to remove sulfur compounds from refined petroleum products such as gasoline or petrol, jet fuel, diesel fuel, and fuel oils. One purpose for removing the sulfur is to reduce the sulfur dioxide emissions resulting from using those fuels in automotive vehicles, aircraft, railroad locomotives, ships, or oil burning power plants, residential and industrial furnaces, and other forms of fuel combustion.
Another important reason for removing sulfur from the intermediate product naphtha streams within a petroleum refinery is that sulfur, even in extremely low concentrations, poisons the noble metal catalysts platinum and rhenium in the catalytic reforming units that are subsequently used to upgrade the of the naphtha streams.
Hydrogenation of the sulfur compounds results in the formation of undesirable,... More »
UraniumLast Updated on 2013-12-15 23:42:25Uranium is a radioactive element that occurs naturally in low concentrations (a few parts per million) in soil, rock, and surface and groundwater. It is the heaviest naturally occurring element, with an atomic number of 92. Uranium in its pure form is a silver-colored heavy metal that is nearly twice as dense as lead and is pyrophoric when finely divided.
Uranium exhibits three crystallographic modifications as follows: alpha --(688°C)→ beta --(776°C)→ gamma. It is a little softer than steel, and is attacked by cold water in a finely divided state. It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis.
Previous Element: Protactinium
Next Element:... More »
Douglas-fir Last Updated on 2013-12-15 23:37:47The Douglas-fir (scientific name: Pseudotsuga) is a genus of tree that includes ar least five species found in North America and Asia:
Bigcone Douglas-fir (Pseudotsuga macrocarpa)
Coast Douglas-fir (Pseudotsuga menziesii)
-- Pseudotsuga menziesii subsp. menziesii – regular Coast Douglas-fir
-- Pseudotsuga menziesii subsp. glauca – Rocky Mountain Douglas-fir
Mexican Douglas-fir (Pseudotsuga lindleyana; included by some within Pseudotsuga menziesii subsp. glauca)
Chinese Douglas-fir (Pseudotsuga sinensis)
-- Pseudotsuga sinensis var. sinensis – regular Chinese... More »
GrassesLast Updated on 2013-12-12 15:24:09
The grass family Poaceae (also known as Gramineae) contains approximately 10,000 distinct species and 650 to 900 genera. Only the sunflower (Asteraceae, or Compositae), legume (Fabaceae, or Leguminosae), and orchid (Orchidaceae) families are larger in terms of number of taxa. The grass family has more individual plants and a wider environmental range than does any other family, occupying the geographic limits of vegetation in polar regions and on mountaintops, enduring extremes of cold, sunlight, heat, and drought, while dominating various landscapes worldwide. Grasses are the most successful monocots (seed-bearing plants with single seed leaves), and the most beneficial plants for humankind, providing highly nutritional grains and livestock forage, and preventing soil erosion. Of the five crops that provide almost two-thirds of the food caloric intake that mankind consumes,... More »
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