Any of a group of techniques used to purify an element or a compound or to control its composition by melting a short region (called a zone) and causing this liquid zone to travel slowly through a relatively long ingot, or charge, of the solid. In zone refining, the most important of the zone-melting techniques, a solid is refined by multiple molten zones being passed through it in one direction. Each zone carries a fraction of the impurities to the end of the solid charge, thereby purifying the remainder. Zone refining is particularly important as a method of purifying crystals, especially for use in semiconductor devices.
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Long, narrow, and mountainous submarine lineation that generally separates ocean-floor ridges differing in depth by as much as 1 mi (1.6 km). The largest fracture zones, in the eastern Pacific, are more than 1,000 mi (1,600 km) long and 60–125 mi (100–200 km) wide. Numerous shorter fracture zones in the Atlantic are associated with the Mid-Atlantic Ridge.
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Oceanic trench area in which, according to the theory of plate tectonics, the seafloor underthrusts an adjacent plate, dragging the accumulated trench sediments downward into the Earth's upper mantle. Seealso deep-sea trench.
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Area within which goods may be landed, handled, and re-exported freely. The purpose is to remove obstacles to trade and to permit quick turnaround of ships and planes. Only when the goods are moved to consumers within the country in which the zone is located do they become subject to tariffs and customs regulation. Free-trade zones are found around major seaports, international airports, and national frontiers; there are more than 200 such zones in the U.S. alone.
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Region of apparent absence of galaxies near the plane of the Milky Way Galaxy. Millions of external galaxies are in this region of the sky but are obscured by interstellar dust within the Milky Way. The zone's obscuration can be penetrated at the infrared portion of the electromagnetic spectrum. Seealso infrared astronomy.
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Strip of territory, a historic administrative entity in Panama over which the U.S. formerly exercised jurisdictional rights (1903–79). The zone came into being in 1904 when Panama granted the U.S., in return for annual payments, sole right to operate and control the Panama Canal, including a strip of land 10 mi (16 km) wide along the canal extending from the Atlantic to the Pacific Ocean and bisecting the Isthmus of Panama. The zone was abolished by treaty in 1979, and civil control of the territory was returned to Panama. By the same treaty a commission under joint U.S.-Panamanian ownership was established to operate the canal until the year 2000, when Panama assumed full control.
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Zone may refer to:
In other uses: