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1.
Hot electron transport across graded compound semiconductor heterojunctions has been explored using a two-dimensional formulation of the self-consistent ensemble Monte Carlo method. The AlxGa1-xAs/GaAs heterojunction imbedded into a vertical field effect transistor with two ohmic contacts (source, drain) and two lateral Schottky gates has been used as an example. Lateral space charges modulated by the gates are shown to control ballistic injection of electrons over the heterojunction under steady state conditions. The transient response to a gate pulse is found to be determined by carrier transit from the heavily doped source contact region into the channel. A conceptual one-dimensional section model is used to explain the Monte Carlo results. 相似文献
2.
Phase Transformations in Dicalcium Silicate: II, TEM Studies of Crystallography, Microstructure, and Mechanisms 总被引:2,自引:0,他引:2
Young Joong Kim Ian Nettleship Waltraud M. Kriven 《Journal of the American Ceramic Society》1992,75(9):2407-2419
The crystallography, microstructures, and phase transformation mechanisms in dicalcium silicate (Ca2 SiO4 ) were studied by TEM. Three types of superlattice structures were observed in the α'L and β phases. Almost all β grains were twinned and strained. Symmetry-related domain structures inherited from previous high-temperature transformations were observed in β grains. Both the α→α'H and α'L →β transformations were considered to be ferroelastic, and spontaneous strains were calculated. In terms of the crystal structures, the major driving force for the β→γ transformation is proposed to be strains and cation charge repulsions in the β structure. This mechanism can be displacive, but it needs to overcome a comparatively high energy barrier. 相似文献
3.
Chao M. Huang Dong Zhu Xu Yuren Waltraud M. Kriven Chao Y. Yuh 《Materials Science and Engineering: A》1996,220(1-2)
A composite of O′SiAlON (Si2-xAlxN2-xO1+x, with x 0.14) reinforced with 20 vol.% SiC monofilaments was fabricated by hot-pressing, at 1600°C, for 2 h under 34 MPa pressure. The mechanical and interfacial properties of the composites, as-fabricated as well as post-oxidized, were, investigated. The composite exhibited a significant improvement in ultimate flexure strength (640 MPa) and work of fracture (42 kJ m−2) compared with that (350 MPa and 1.8 kJ m−2, respectively) of the monolithic material. These mechanical properties were slightly increased after the composite was heat treated for 24 h in air at 1200 and 1300°C. However, the composite exhibited a significant degradation in ultimate strength, while the work of fracture (WOF) remained unchanged after exposure in air at temperatures beyond 1400°C. The as-fabricated composite revealed a low interfacial shear strength (6.2 MPa) and a frictional sliding stress (3.2 MPa). After the composite was oxidized at elevated temperatures, the interfacial bonding and sliding stresses were reduced to noticeable extents, resulting from the degradation of the carbon coating layer of the SiC monofilaments. 相似文献
4.
Composites of silicon carbide (SiC) with up to 30 vol% of dysprosia (Dy2 O3 ) were fabricated by hot pressing and hot isostatic pressing. The effects of Dy2 O3 dispersions on the microstructure and on selected mechanical properties of the composites were investigated. When 10-15 vol% of Dy2 O3 was dispersed in the SiC matrix, the fracture toughness increased by ∼40%, whereas the flexural strength was comparable to that of unreinforced SiC. The increased fracture toughness was due to crack deflection, in conjunction with crack-interface grain bridging, and was not related to a phase transformation of Dy2 O3 in the matrix. 相似文献
5.
6.
Andrew J. Steveson Waltraud M. Kriven 《Journal of the American Ceramic Society》2021,104(7):3397-3410
The K[AlSi2O6]-Cs[AlSi2O6] pseudo-binary system was synthesized by geopolymer crystallization. The thermal expansion properties of these materials were studied by in situ high-temperature X-ray diffraction to characterize thermal expansion behavior for potential application as environmental barrier coatings. Tailorable thermal expansion through changing cation stoichiometry allowed reduced thermal expansion mismatch with SiCf/SiC composites compared to rare-earth-based coatings. 相似文献
7.
We present an efficient implementation of the Modified SParse Approximate Inverse (MSPAI) preconditioner. MSPAI generalizes the class of preconditioners based on Frobenius norm minimizations, the class of modified preconditioners such as MILU, as well as interface probing techniques in domain decomposition: it adds probing constraints to the basic SPAI formulation, and one can thus optimize the preconditioner relative to certain subspaces. We demonstrate MSPAI’s qualities for iterative regularization problems arising from image deblurring.Such applications demand for a fast and parallel preconditioner realization. We present such an implementation introducing two new optimization techniques: First, we avoid redundant calculations using a dictionary. Second, our implementation reduces the runtime spent on the most demanding numerical parts as the code switches to sparse QR decomposition methods wherever profitable. The optimized code runs in parallel with a dynamic load balancing. 相似文献
8.
C. Richter P. Weinzierl W. Engl C. Penzkofer B. Irmer T. Sulzbach 《Microsystem Technologies》2012,18(7-8):1119-1126
Since the invention in 1986 atomic force microscopy (AFM) has become the most widely used scanning probe microscopy (Binnig et al. in Phys Rev Lett 56:930–933, 1986). The microscope images the interaction of forces like Van der Waals or Coulomb forces between a sample and the apex of a small tip integrated near the free end of a flexible cantilever. But as all other scanning probe techniques the AFM requires serial data acquisition and suffers therefore from a low temporal resolution. Enhancing the speed to video rate imaging makes high demands on scanner technology, control electronics and on the key feature the cantilever with integrated sharp stylus. For the cantilever probes, fundamental resonance frequencies in the MHz regime are envisaged while the force constant of a few nN/nm shall be maintained. We present different novel AFM probes with ultrashort cantilevers and integrated sharp tips for high speed AFM while focusing on widely dispersed applications and on aspects of mass fabrication. 相似文献
9.
ZUSAMMENFASSUNG: Anders als die weitgehend in der Geschichtsschreibung belegte psychiatrische Anstalt für Europ?er und Europ?erinnen mit ihrem englischen Leiter Owen Berkeley-Hill ist die weitaus gr??ere Institution für indische Patienten und Patientinnen im nordindischen Ranchi bisher nicht untersucht worden. Im Mittelpunkt dieses Beitrags steht die Karriere des Leiters dieser Institution, Jal E. Dhunjibhoy, zu Beginn des 20. Jahrhunderts als von der britischen Kolonialregierung eine Indianisierung der medizinischen Einrichtungen angestrebt wurde. Im Gegensatz zu bisherigen Studien über intermediaries und middles konzentriert sich dieser Aufsatz auf einen hochrangigen einheimischen Mitarbeiter. Die verbreitete Annahme zwangsl?ufiger historischer Prozesse wird dabei differenziert, eine regionale Kontextualisierung vorgenommen und die Kontinuit?t offener und versteckter Diskriminierung indischer Mediziner in Bezug auf Entlohnung, gesellschaftliche Stellung, fachliche Anerkennung, posthume Würdigung und historiographischer Berücksichtigung herausgearbeitet. Es wird verdeutlicht, in welcher Weise koloniale Akteure in bestehende gesellschaftliche Disparit?ten und soziopolitische Prozessen verstrickt waren und wie die Karriere eines leitenden Mediziners von einer Vielzahl von au?ermedizinischen Zusammenh?ngen bestimmt wurde. Gleichzeitig wird hervorgehoben, dass ihre strukturelle Positionierung als inbetweens, Kollaborateure oder Repr?sentanten einer erfolgreichen Dekolonisierung für ein nuancierteres Verst?ndnis ihrer beruflichen und pers?nlichen Identit?tsformierung nicht ausreicht. 相似文献
10.
原材料成本推动Autocoro纺纱工艺发展.最近几年纱线生产成本在总成本中的份额不断地在增加.以前纱线生产成本也许占总成本的一半,目前已达75%.介绍了纺纱厂应对这种趋势的方法. 相似文献