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91.
92.
Kuttan Prabhakaran Anand Melkeri Mohd Oveas Beigh Nitin Madhusudan Gokhale Suresh Chandra Sharma 《Journal of the American Ceramic Society》2007,90(2):622-625
A porous NiO–YSZ substrate for anode-supported solid oxide fuel cells has been prepared by gelcasting of NiO–YSZ powders using urea–formaldehyde monomers, followed by humidity-controlled drying, binder removal, and sintering of the gelled bodies. The gelled bodies had sufficient strength to remove even 2-mm-thick samples from the mold immediately after gelation. A gelcast NiO–YSZ sample sintered at 1450°C for 2 h showed an open porosity of ∼53 vol%, and the porosity increased to ∼58% upon reduction with hydrogen. Pore sizes measured on the scanning electron microscopy photomicrograph of NiO–YSZ and Ni–YSZ cermet substrates are in the range of 2–5 μm. Urea–formaldehyde polymer, present in a high amount (∼13 wt%) in the gelcast body, acts as a template for pores. 相似文献
93.
Anand Jagota Kurt R. Mikeska Rajendra K. Bordia 《Journal of the American Ceramic Society》1990,73(8):2266-2273
This paper presents an isotropic model for the effective viscosities of sintering particle packings. The relationship between the macroscopic stress and deformation rate is based on the behavior of individual interparticle contacts, represented by contact viscosities, and the statistics of the packing. The contact viscosities depend on the contact area, which is the primary variable used to describe the state of the packing. A direct consequence of this choice of state variable is that the effective viscosities are identically zero for an undeformed and unsintered packing. Specific results are presented for the case of Newtonian viscous materials. The model is compared with existing models for porous Newtonian viscous materials. Experiments conducted with spherical glass powder packings show good agreement with the model. Finite-element simulations using the model have been used to study forging of a pellet. 相似文献
94.
The viscous sintering of two initially spherical particles is modeled as creeping flow in response to surface tension. The governing equations are solved using the finite-element method. The condensed results of this simulation, the center-to-center approach velocity, and the rate of change of contact area were presented earlier. Some details of the flow field during sintering and the evolution of the neck geometry in the early stages of sintering are presented here. Important numerical issues are detailed. 相似文献
95.
In this work, an analytical relationship is derived for a doubly-clamped microbeam when it buckles after release from the substrate. In terms of the relationship, compressive residual stress in the doubly-clamped microbeam can be determined according to its buckled shape, allowing one to find the compressive residual stress directly without much experimental effort. This relationship has been used to determine compressive residual stresses in four types of doubly-clamped SiO2 microbeams. In addition, four methods have been applied to find the elongations of these SiO2 microbeams, and the corresponding results are compared. Finally, the residual stresses in doubly-clamped SiO2 microbeams predicted according to the derived relationship are compared with those found in SiO2 microcantilevers, and the results have a good match. 相似文献
96.
Micro-measurement using grating microscopy 总被引:2,自引:0,他引:2
In this paper, two quantitative methods to measure micro-deformation using grating microscopy are proposed, a grating diffraction method and a full-field grating phase-shift method. A compact optical transmitting microscope with white light source is reconstructed by developing a loading and recording system. For direct strain measurement, a grating diffraction method is presented. With the help of a Bertrand lens, the Fourier spectrum of the grating is formed on the CCD sensor plane with high image quality. Software for precise, fast and automatic determination of the diffraction spot centroids is developed. Local strains are thus measured with high resolution. For the deformation measurement, a phase-shifting grating microscope method with high sensitivity and spatial resolution is proposed. Phase-shifting is based on the slab refraction effect and is realized via a tilting compensator. The system possesses a high spatial resolution (1 μm), and a displacement precision of 0.1–0.03 μm. The combination of the grating diffraction method and the phase-shifting method in the same test provides simultaneous measurement of strain and displacement, thus demonstrating that the grating techniques are viable in the microscope environment. 相似文献
97.
98.
A GaAs monolithic planar chip consisting of two antiparallel Schottky junctions has been designed, processed and tested as a millimetre-wave crossbar mixer. The planar chip exhibited a broadband RF performance with a low conversion loss of 5.2013;70dB and noise temperature of 750 K at 94 GHz. The structure also exhibits a high burnout capability at W-band frequencies. 相似文献
99.
Electron beam welding plays an important role in the aerospace industry where components like sensors,gears,actuators and air frames used in aircraft and rocket engines were welded using this technique.Welding is normally performed in a vacuum to avoid the scatter of electron due to the presence of gas molecules in the atmosphere and hence electron beam welding process provides the greater results.But still joining of dissimilar metals is challenging.This paper represents review of process,generation and distribution of heat source various input parameters,materials,microstructure,mechanical strength and the possibilities of joining dissimilar metals using electron beam welding. 相似文献
100.
Anand Dersingh Ramiro Liscano Allan Jost John Finnson Rajiv Senthilnathan 《Mobile Networks and Applications》2010,15(2):267-282
Controlling access in pervasive environments is crucial and a significant challenge because users and devices can connect
from anywhere which results in users and resources becoming available at any point of time and location depending on the situation.
Access control policies for this type of environment are required to conform to high-level business notions. In pervasive
environments, these high-level notions refer to contexts of the situation which can change unpredictably and must be interpreted
semantically to maintain proper access control. Therefore, it is necessary to have a formal representation that represents
semantics of the contexts, reflects the change of the situation, and can be shared and understood by a policy system. This
paper addresses these issues by introducing a context management system that uses a semantic web approach as an underlying
mechanism to model and represent semantics of the contexts. The system stores current contexts in a semantic knowledge base
which is used by a semantic access control system in order to form access control policies and evaluate policies at run time.
The approach is validated through a proof of concept implementation that includes performance results of the context management
system as it responds to a change of the situation. 相似文献