Ridgeland (CTA station)
Ridgeland is a station on the Chicago Transit Authority's 'L' system, serving the Green Line. It is located in the suburb of Oak Park just west of Chicago. To the north of the station is the triple tracked Union Pacific/West Line.
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CTA
CTA may refer to:
Science
Organisations
Tantalum carbide
Tantalum carbides form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaCx, where x usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metallic electrical conductivity. They appear as brown-gray powders which are usually processed by sintering. Being important cermet materials, tantalum carbides are commercially used in tool bits for cutting applications and are sometimes added to tungsten carbide alloys. The melting points of tantalum carbides peak at about 3880 °C depending on the purity and measurement conditions; this value is among the highest for binary compounds. Only tantalum hafnium carbide may have a slightly higher melting point of about 3942 °C, whereas the melting point of hafnium carbide is comparable to that of TaC.
Preparation
TaCx powders of desired composition are prepared by heating a mixture of tantalum and graphite powders in vacuum or inert gas atmosphere (argon). The heating is performed at temperature of about 2000 °C using a furnace or an arc-melting setup. An alternative technique is reduction of tantalum pentoxide by carbon in vacuum or hydrogen gas atmosphere at a temperature of 1500–1700 °C. This method was used to obtain tantalum carbide back in 1876, but it lacks control over the stoichiometry of the product.
CTA-102
In astronomy, CTA 102, also known by its B1950 coordinates as 2230+114 (QSR B2230+114) and its J2000 coordinates as J2232+1143 (QSO J2232+1143), is a quasar discovered in the early 1960s by a radio survey carried out by the California Institute of Technology. It has been observed by a large range of instruments since its discovery, including WMAP, EGRET, GALEX, VSOP and Parkes, and has been regularly imaged by the Very Long Baseline Array since 1995. It has also been detected in gamma rays, and a gamma-ray flare has been detected from it.
In 1963 Nikolai Kardashev proposed that the then-unidentified radio source could be evidence of a Type II or III extraterrestrial civilization on the Kardashev scale. Follow-up observations were announced in 1965 by Gennady Sholomitskii, who found that the object's radio emission was varying; a public announcement of these results caused a worldwide sensation. The idea that the emission was caused by a civilization was rejected when the radio source was later identified as one of the many varieties of a quasar.
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