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排序方式: 共有508条查询结果,搜索用时 15 毫秒
21.
Matilda Zemanov Emmanuel Lecomte Pavol
ajgalík Ralf Riedel 《Journal of the European Ceramic Society》2002,22(16):2963-2968
The pyrolised polysilazanes poly(hydridomethyl)silazane NCP 200 and poly(urea)silazane CERASET derived Si–C–N amorphous powders were used for preparation of micro/nano Si3N4/SiC composites by hot pressing. Y2O3–Al2O3 and Y2O3–Yb2O3 were used, as sintering aids. The resulting ceramic composites of all compositions were dense and polycrystalline with fine microstructure of average grain size <1 μm of both Si3N4 and SiC phases. The fine SiC nano-inclusions were identified within the Si3N4 micrograins. Phase composition of both composites consist of , β modifications of Si3N4 and SiC. High weight loss was observed during the hot pressing cycle, 12 and 19 wt.% for NCP 200 and CERASET precursors, respectively. The fracture toughness of both nanocomposites (NCP 2000 and CERASET derived) was not different. Indentation method measured values are from 5 to 6 MPa m1/2, with respect to the sintering additive system. Fracture toughness is slightly sensitive to the SiC content of the nanocomposite. Hardness increases with the content of SiC in the nanocomposite. The highest hardness was achieved for pyrolysed CERASET precursor with 2 wt.% Y2O3 and 6 wt.% Yb2O3, HV 23 GPa. This is a consequence of the highest SiC content as well as the chemical composition of additives. 相似文献
22.
We consider large-scale dynamical systems in which both the initial state and some parameters are unknown. These unknown quantities must be estimated from partial state observations over a time window. A data assimilation framework is applied for this purpose. Specifically, we focus on large-scale linear systems with multiplicative parameter-state coupling as they arise in the discretization of parametric linear time-dependent partial differential equations. Another feature of our work is the presence of a quantity of interest different from the unknown parameters, which is to be estimated based on the available data. In this setting, we employ a simplicial decomposition algorithm for an optimal sensor placement and set forth formulae for the efficient evaluation of all required quantities. As a guiding example, we consider a thermo-mechanical PDE system with the temperature constituting the system state and the induced displacement at a certain reference point as the quantity of interest. 相似文献
23.
24.
E. R. Gertner A. M. Andrews L. O. Bubulac D. T. Cheung M. J. Ludowise R. A. Riedel 《Journal of Electronic Materials》1979,8(4):545-554
Reported here, for the first time, is the lattice matched growth of InAs1-xSbx on GaSb. The thermodynamic incompatibility of the system, i.e., the strong tendency for the In-As-Sb liquid to dissolve the
GaSb substrate, was solved via a novel liquid phase epitaxial growth technique. Liquid compositions for lattice matching conditions
have been determined in the 400-600°C range. Epitaxial growth has been examined for (100), (111)B and (111)A orientations.
Dislocation etch pit densities for lattice matched, and near lattice matched conditions are shown to be less than 104-cm−2 and 105-cm−4, respectively. The composition of the epitaxial layers are determined by the Gandolfi X-ray diffraction technique and compositional
homogeneity has been confirmed by SEM X-ray analysis. Some material related device properties which demonstrate the reproducibility
of the growth technique are presented. 相似文献
25.
Attempted to devise essentially nonverbal procedures for the measurement of a person's role constructs as defined by G. H. Kelly. This procedure was adopted to allow the extension of personal construct theory to the social psychological realm. The graphic procedure would have the additional value of opening up approaches to personality measurement with S groups (i.e., young children and handicapped Ss) that cannot adequately respond to verbal materials. 2 studies compared 49 6th graders with 49 12th graders and 50 neuropsychiatric with 50 medical patients on the Personal Construct Inventory, specifically constructed for this purpose and pretested with 177 Ss. 6 hypotheses were tested in each study, with 5 out of 6 finding confirmation in both investigations. Results indicate the hypotheses about the nature of role constructs are tenable and merit further investigation. The feasibility of the graphic approach to measurement is illustrated. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
26.
Comtet G Dujardin G Hellner L Lastapis M Martin M Mayne AJ Riedel D 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2004,362(1819):1217-1226
The electronic or quantum control of individual molecules with the scanning tunnelling microscope offers exciting perspectives on operating molecular nanomachines. This implies the use of semiconductor surfaces rather than metallic surfaces which would rapidly quench the electronic excitations. We review recent results illustrating the state of the art and the main problems which need to be solved: the choice, design and properties of functionalized organic molecules on semiconductor surfaces; the control of the inelastic electronic channels through a single molecule; and the search for well-controlled atomic-scale wide-band-gap semiconductor surfaces. 相似文献
27.
28.
High-pressure synthesis is a powerful method for the preparation of novel materials with high elastic moduli and hardness. Additionally, such materials may exhibit interesting thermal, optoelectronic, semiconductuing, magnetic or superconducting properties. Here, we report on the high-pressure synthesis of zirconium and hafnium nitrides with the stoichiometry M3N4, where M = Zr, Hf. Synthesis experiments were performed in a laser-heated diamond anvil cell at pressures up to 18 GPa and temperatures up to 3,000 K. We observed formation of cubic Zr3N4 and Hf3N4 (c-M3N4) with a Th3P4-structure, where M-cations are eightfold coordinated by N anions. The c-M3N4 phases are the first binary nitrides with such a high coordination number. Both compounds exhibit high bulk moduli around 250 GPa, which indicates high hardness. Moreover, the new nitrides, c-Zr3N4 and c-Hf3N4, may be the first members of a larger group of transition metal and/or lanthanide nitrides with interesting ferromagnetic or superconducting behaviour. 相似文献
29.
Time-Resolved Temperature Measurement of AlGaN/GaN Electronic Devices Using Micro-Raman Spectroscopy
Kuball M. Riedel G. J. Pomeroy J. W. Sarua A. Uren M. J. Martin T. Hilton K. P. Maclean J. O. Wallis D. J. 《Electron Device Letters, IEEE》2007,28(2):86-89
We report on the development of time-resolved Raman thermography to measure transient temperatures in semiconductor devices with submicrometer spatial resolution. This new technique is illustrated for AlGaN/GaN HFETs and ungated devices grown on SiC and sapphire substrates. A temporal resolution of 200 ns is demonstrated. Temperature changes rapidly within sub-200 ns after switching the devices on or off, followed by a slower change in device temperature with a time constant of ~10 and ~140 mus for AlGaN/GaN devices grown on SiC and sapphire substrates, respectively. Heat diffusion into the device substrate is also demonstrated 相似文献
30.
Marin-Perianu M. Meratnia N. Havinga P. de Souza L.M.S. Muller J. Spiess P. Haller S. Riedel T. Decker C. Stromberg G. 《Wireless Communications, IEEE》2007,14(6):57-66
Massively deployed wireless sensor and actuator networks, co-existing with RFID technology, can bring clear benefits to large-scale enterprise systems, by delegating parts of the business functionality closer to the point of action. However, a major impediment in the integration process is represented by the variety of customized platforms and proprietary technologies. In this article, we present a three-layer, service-oriented architecture that accommodates different sensor platforms and exposes their functionality in a uniform way to the business application. Our work is motivated by real business cases from the oil and gas industry. In our implementation, we use three sensor platforms (particle, muNode, and Sindrion) integrated through the universal plug and play (UPnP) standard and incorporated into an enterprise software system. The practical tests and application trials confirm the feasibility of our solution but also reveal a number of challenges to be taken into account when deploying wireless sensor and actuator networks at industrial sites. 相似文献