Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The 40 Ar-39 Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock 87 Rb-86 Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period .

Improved Ni based composite Ohmic contact to n-SiC for high temperature and high power device applications

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We have newly introduced a two-step-growth structure and a ridge stripe with steep sidewalls formed with a dry-etching process in the fabrication of a buried ridge stripe structure of a high-power 660 nm laser diode instead of a conventional three-step-growth structure and a ridge stripe with gentle sidewalls formed with a conventional wet-etching process in order to reduce the operating current. We have found that the two-step-growth structure provides better heat dissipation and the dry-etched ridge stripe structure offers higher characteristic temperature. The operating current under pulsed 200 mW at 70°C of the fabricated laser diode is 270 mA. This is the lowest value ever reported so far, to our knowledge. These laser diodes exhibit a kink level and a maximum light output power of 220 mW and higher than 300 mW, respectively. These laser diodes have also operated stably for 1500 h at 70°C with a light output power of 200 mW under the pulsed condition.

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