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排序方式: 共有390条查询结果,搜索用时 62 毫秒
41.
Triratna Shrestha Srikant Gollapudi Indrajit Charit K. Linga Murty 《Journal of Materials Science》2014,49(5):2127-2135
Creep properties of three Sn–Zn solder alloys (Sn–9Zn, Sn–20Zn, and Sn–25Zn, wt%) were studied using the impression creep technique. Microstructural characteristics were examined using a scanning electron microscope. The alloys exhibited stress exponents of about 5.0. The activation energy for creep was calculated to be ~50–75 kJ/mol with a mean value of 66.3 kJ/mol. The likely creep mechanism was identified to be the low temperature viscous glide of dislocations. 相似文献
42.
J. Kumar P. Bera A. Khalili 《International Journal of Heat and Mass Transfer》2010,53(23-24):5261-5273
In this paper, we report the influence of different terms appearing in the momentum equation on the stability of buoyancy-assisted mixed convection in a vertical channel filled with a porous medium. Four different models: (i) Darcy–Brinkman (DB), (ii) Darcy–Brinkman–Forchheimer (DBF), (iii) Darcy–Brinkman–Wooding (DBW), and (iv) Darcy–Brinkman–Forchheimer–Wooding (DBFW) are considered and a comparative study is made based on a linear stability analysis. We consider a Prandtl number range of Pr = 0.1–10, which corresponds to water and gases. Judged from the instability boundary curves, it is found that with reduction of Darcy number there exists an equivalence of DB with DBF model from one side, and an equivalence of DBW with DBFW model from the other side. When the medium is a gas, a significant difference between DB and DBW (or DBF and DBFW) is visible, which is not the case for water. Furthermore, it is found that in case of a gas, inertia force destabilizes the flow, whereas, form drag stabilizes it. In contrast to a fluid-filled channel (where inertia term always destabilizes the buoyancy-assisted flow), here this destabilizing property might turn into a stabilizing one when fluid viscosity and permeability of the medium are changed. In the case of water, for Da = 10?2, the inertia term stabilizes the flow beyond Re = 25. When Da is reduced by one order of magnitude, the destabilizing effect continued up to Re = 220. The combined effect of form drag (Forchheimer term) and inertia (Wooding term) on the stability of the flow is more intensive than their individual effects provided the medium is highly permeable. In most cases studied here, the disturbance flow patterns are similar for DB and DBF from one side, and DBW and DBFW from the other side. 相似文献
43.
P.R SarodeK.R Priolkar Parthasarathi Bera S EmuraR Kumashiro 《Materials Research Bulletin》2002,37(9):1679-1690
The combustion synthesized Ag/CeO2 catalysts have been characterized by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at the Ag K-edge. It has been found that Ag+ like species is present in 1% Ag/CeO2 catalyst, whereas mostly Ag metal clusters are found in 3% Ag/CeO2. The analysis of EXAFS spectra indicates that about one oxygen atom is coordinated to Ag central atom at a distance of 2.19 Å in 1% Ag/CeO2 catalyst along with eight coordinated AgAg bond at 2.86 Å. The AgO bond is absent in 3% Ag/CeO2. 相似文献
44.
45.
Chinmay K. Maiti L.K. Bera S.S. Dey D.K. Nayak N.B. Chakrabarti 《Solid-state electronics》1997,41(12):1863-1869
The growth of a high quality, step-graded lattice-relaxed SiGe buffer layer on a Si(100) substrate is investigated. p-MOSFETs were fabricated on strained-Si grown on top of the above layer. Carrier confinement at the type-II strained-Si/SiGe buffer interface is observed clearly from the device transconductance and C-V measurements. At high vertical field, compared to bulk silicon, the channel mobility of the strained-Si device with x=0.18 is found to be about 40% and 200% higher at 300 K and 77 K respectively. Measurements on transconductance enhancement are also reported. Data at 77 K provide evidence of two channels and a large enhancement of mobility at high transverse field. 相似文献
46.
Tapas Gangopadhyay Raj Kumar Ohdar Dilip Kumar Pratihar Indrajit Basak 《The International Journal of Advanced Manufacturing Technology》2011,53(1-4):301-312
Three-dimensional finite element analyses has been carried out using DEFORM 3D software on multi-stage hot forming of railway wheels involving the processes of upsetting, forging, and punching of wheels. Thermal analysis related to heating the blank in furnace and all intermediate heat transfer stages between deforming operations have been conducted. Rigid viscoplastic finite element method has been utilized for coupled thermo-mechanical analysis of the processes. Modeling of punching the wheel bore has been carried out using Cockcroft and Latham fracture criterion. Evolution of thermo-mechanical parameters at selected points within the workpiece has been studied in detail. The method of simulating the effects of various process parameters has been explained using relevant mathematical relations. This study shows that design, optimization, and analysis of process perturbations for multi-stage railway wheel manufacturing process can be done efficiently in three-dimensional finite element simulations instead of conventional time and cost intensive trials. It might be necessary to use the results of finite element analysis in shop-floor to enhance productivity and reduce wheel rejection. 相似文献
47.
S. Chattopadhyay L. K. Bera C. K. Maiti S. K. Ray P. K. Bose D. Dentel L. Kubler J. L. Bischoff 《Journal of Materials Science: Materials in Electronics》1998,9(6):403-407
PtSi/p-strained-Si1-xGex (x=0.19 and x=0.29) Schottky barrier diodes have been fabricated and characterized for the determination of barrier height, ideality factor and the interface state density distribution with energy. Diodes having an epitaxial layer thickness of 20 and 52 nm were modeled with emphasis on comparison with experiment. To achieve better agreement with experimental data, an interfacial layer and associated series resistance were included in the model. The capacitance–voltage (C–V) technique has been used for the determination of the energy distribution of interface state density. The interface state density distribution for the Si0.81Ge0.19 and Si0.71Ge0.29 diodes is found to decrease with increasing energy from the valence band edge. 相似文献
48.
Random night blood samples were examined from 528 subjects in an endemic zone of lymphatic filariasis, in the coastal region of West Bengal. There were 136 cases out of 528 who were symptomatic, with or without recurrent episodes of fever, lymphangitis and lymphadenitis and with various degrees of lymphoedema. Examination of blood samples revealed microfilaria in 43 cases of which 42 were asymptomatic and only one was symptomatic with lymphoedema. All the microfilariae were of the species Brugia malayi. 相似文献
49.
C.L AravindaParthasarathi Bera V JayaramA.K Sharma S.M Mayanna 《Materials Research Bulletin》2002,37(3):397-405
Electrochemically deposited Cu-Ni black coatings on molybdenum substrate from ethylenediaminetetraacetic acid (EDTA) bath solution are shown to exhibit good optical properties (α=0.94, ε = 0.09). The deposit is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Cu is present in metallic and +2 oxidation states in the as-prepared Cu-Ni black coating, whereas Ni2+ as well as Ni3+ species are observed in the same coating. Cu and Ni are observed in their metallic state after 10 and 20 min sputtering. X-ray initiated Auger electron spectroscopy (XAES) of Cu and Ni also agrees well with XPS investigations. 相似文献
50.
Experimental results obtained with GaAs f.e.t. oscillators at X band are described. It is demonstrated that the output power of f.e.t. oscillators is sufficient to drive X band mixers. The noise measure of these oscillators is competitive with Gunn devices, and can be reduced further. 相似文献