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81.
Angle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the ( 2 x 2 x 2) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition. 相似文献
82.
We report a demonstration of distributed-feedback (DFB) optical parametric oscillation (OPO) by writing photorefractive gratings in periodically poled lithium niobate (PPLN). The photorefractive DFB structures were fabricated by illumination of PPLN with UV light through a photomask and by writing of PPLN with UV-light gated interfering laser beams at 532 nm. Evidence of OPO was observed from the spectral narrowing at the 1438.8- and the 619.3-nm signal wavelengths from 1064- and 532-nm-pumped PPLN crystals with the DFB grating periods phase matched to the 4084.5- and 3774-nm idler wavelengths, respectively. 相似文献
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Scattering by a cylindrical cavity in a porous solid is studied by the boundary layer approximation of Mei and Foda. Quantitative results will be presented for two cases: (1) vacuum cavity and (2) cavity filled with fluid. In each case both P and SV incident waves will be studied. Focus will be on the stress distribution near the cavity surface and contrast to the non-porous case will be pointed out. The effect of fluid compressibility due to possible entrainment of air will be discussed. These results should be of interest to the design of long tunnels subject to earthquakes. 相似文献
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The copolymerizations of anhydride-cured epoxy resin on fiberglass surfaces treated with a N-methylaminopropyltrimethoxysilane coupling agent has been investigated using Fourier-transform infrared spectroscopy. The structure of the interface of the silane and the resin in fiber-reinforced composites is composed of copolymers of the epoxy resin with the organofunctionality of the deposited silanes. The number of interfacial bonds formed depends on the amount of silane coupling agent deposited on the fiberglass and the reaction conditions. The silane induces additional esterification and increases the curing density of the epoxy matrix near the fiber surface by about 5–10% relative to the bulk resin. 相似文献
88.
The effect of uniaxial stress on the room temperature electrical conductivity of polymeric sulfur-nitride is reported. The results provide additional evidence of the importance of interchain coupling on the electrical properties of (SN)x and demonstrate that the perpendicular transport is limited by interfiber contacts. 相似文献
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