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Anirban Chakraborty James C. Earthman 《Metallurgical and Materials Transactions A》1997,28(4):979-989
Finite element simulations of the high-temperature behavior of single-phase γ, dual-phase α2+γ, and fully lamellar (FL) α2+γTiAl intermetallic alloy microstructures have been performed. Nonlinear viscous primary creep deformation is modeled in
each phase based on published creep data. Models were also developed that incorporate grain boundary and lath boundary sliding
in addition to the dislocation creep flow within each phase. Overall strain rates are compared to gain an understanding of
the relative influence each of these localized deformation mechanisms has on the creep strength of the microstructures considered.
Facet stress enhancement factors were also determined for the transverse grain facets in each model to examine the relative
susceptibility to creep damage. The results indicate that a mechanism for unrestricted sliding of γ lath boundaries theorized
by Hazzledine and co-workers leads to unrealistically high strain rates. However, the results also suggest that the greater
creep strength observed experimentally for the lamellar microstructure is primarily due to inhibited former grain boundary
sliding (GBS) in this microstructure compared to relatively unimpeded GBS in the equiaxed microstructures. The serrated nature
of the former grain boundaries generally observed for lamellar TiAl alloys is consistent with this finding. 相似文献
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Haemangiopericytoma of nose and paranasal sinuses is relatively uncommon tumour. It occurs in adults in sixth and seventh decades of life. In view of paucity of intranasal haemangiopericytoma old in Indian literature and young age of patient, we are reporting one case in 28-year-old female who presented with recurrent, profuse epistaxis. 相似文献
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We have utilized a variable energy positron beam and infrared transmission spectroscopy to study defects in GaAs epilayers
grown at low temperatures (LT-GaAs) by molecular beam epitaxy. We have measured the Doppler broadening of the positron-electron
annihilation gamma ray spectra as a function of positron implantation energy. From these measurements, we have obtained results
for the depth profiles of Ga monovacancies in unannealed LT-GaAs and Ga monovacancies and arsenic cluster related defects
in annealed LT-GaAs. We have also studied the effects of the Si impurities in annealed LT-GaAs. The infrared transmission
measurements on unannealed LT-GaAs furnish a broad defect band, related to As antisites, centered at 0.370 eV below the conduction
band. 相似文献
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Electrochemical impedance measurements have been used to characterize zinc selenide films prepared by electrochemical co-deposition at a platinum rotating disk electrode. Estimations of capacitance and polarization resistance of variously prepared electrodeposits have been carried out to determine charge carrier density and corrosion rates. 相似文献
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Sample preparation for DNA and RNA assays is a prime candidate for laboratory automation. A novel, parallel processing device that performs the three separate liquid-handling functions necessary for such sample preparation-dispensing, pipetting, and pressurizing-is presented. The device comprises an array of fine nozzles connected by fluidic channels to automatically and precisely distribute flow between one source and an array of points. The design principles, as well as the experimental and computational methods used to develop the device, are described. Test results, including accuracy, uniformity, volume range, and timing, are presented. The functionality of the device is demonstrated by performing a solid-phase extraction of DNA with two types of microcolumns. 相似文献