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排序方式: 共有1428条查询结果,搜索用时 15 毫秒
1.
2.
In the catalytic reaction of an iron(III) porphyrin with t-BuOOH, CumOOH, H2O2 and C6F5IO, cyclohexene was used as a probe substrate. The selective hydroxylation of cyclohexene by hydroperoxides proceeds through radical path and this has been utilized for successful dioxygen activation/autooxidation. For other oxidants epoxide was the major product and the reactions proceed through non-radical path. 相似文献
3.
Sirisha Nerella Debendra K. Das Godwin A. Chukwu Abhijit Y. Dandekar Santanu Khataniar Shirish L. Patil 《Petroleum Science and Technology》2003,21(7):1275-1294
Gas-to-liquids (GTL) technology involves the conversion of natural gas to liquid hydrocarbons. In this article, theoretical studies have been presented to determine the feasibility of transporting GTL products through the Trans-Alaska Pipeline System (TAPS). To successfully transport GTL through TAPS, heat loss along the route must be carefully determined. This study presents heat transfer and fluid dynamic calculations to evaluate this feasibility. Because of heat loss, the fluid temperature decreases in the direction of flow and this affects the fluid properties, which in turn influence convection coefficient and pumping power requirements. The temperature and heat loss distribution along the pipeline at different locations have been calculated. Fairly good agreement with measured oil temperatures is observed. The powers required to pump crude oil and GTL individually, against various losses have been calculated. Two GTL transportation modes have been considered; one as a pure stream of GTL and the second as a commingled mixture with crude oil. These results show that the pumping power and heat loss for GTL are less than that of the crude oil for the same volumetric flow rate. Therefore, GTL can be transported through TAPS using existing equipment at pump stations. 相似文献
4.
Michael Osterman Abhijit Dasgupta 《Journal of Materials Science: Materials in Electronics》2007,18(1-3):229-236
The transition from lead (Pb) bearing solder to Pb-free solder has arisen in response to government restrictions on the use
of lead (Pb) by the European Union. As a result, electronic manufacturers have sought a material comparable to the conventional
63Sn37Pb solder that has been traditionally used to assemble electronic hardware. Based on extensive review of various solder
combination, the majority of electronic manufacturers appear to be adopting a tin–silver–copper (SAC) solder as a popular
Pb-free solder replacement. Significant investments have been made by many researchers to characterize the material behavior
and durability of this solder system. While the exact composition of the SAC solder is still in question, it now appears that
the 96.5Sn3.0Ag0.5Cu (SAC305) solder is gaining wider acceptance as the favored Pb-free replacement, for surface mount assemblies
that are going to be subjected predominantly to cyclic thermal environments. This paper presents a review of our current understanding
of the life expectancy of Pb-free SAC solder interconnects for electronic hardware. To this end, the paper focuses on material
characterization of SAC solder, as well as its temperature cycling and vibration fatigue reliability. From this review, SAC
solder interconnects are shown to be suitable for providing adequate life expectancies for temperature cycling in electronic
hardware. However, it is clear that there are differences between SAC and the conventional Sn37Pb solder, that need to be
understood in order to design reliable electronic hardware. 相似文献
5.
6.
The problem of determining the maximum mean response level crossing rate of a linear system driven by a partially specified Gaussian load process has been considered. The partial specification of the load is given only in terms of its total average energy. The critical input power spectral (PSD) function, which maximizes the mean response level crossing rate, is obtained. The critical input PSD turns out to be highly narrow-banded which fails to capture the erratic nature of the excitation. Consequently, the trade-off curve between the maximum mean response level crossing rate and the maximum disorder in the input process, quantified in terms of its entropy rate, has been generated. The method of Pareto optimization is used to tackle the conflicting objectives of the simultaneous maximization of the mean response level crossing rate and the input entropy rate. The non-linear multi-objective optimization has been carried out using a recently developed multi-criteria genetic algorithm scheme. Illustrative example of determining the critical input of an axially vibrating rod, excited by a partially specified stationary Gaussian load process, has been considered. 相似文献
7.
Ashraf Bastawros Abhijit Chandra Yongjin Guo Bo Yan 《Journal of Electronic Materials》2002,31(10):1022-1031
The role of a porous pad in controlling material-removal rate (MRR) during the chemical-mechanical planarization (CMP) process
has been studied numerically. The numerical results are used to develop a phenomenological model that correlates the forces
on each individual abrasive particle to the applied nominal pressure. The model provides a physical explanation for the experimentally
observed domains of pressure-dependent MRR, where the pad deformation controls the load sharing between active-abrasive particles
and direct pad-wafer contact. The predicted correlations between MRR and slurry characteristics, i.e., particle size and concentration,
are in agreement with experimentally measured trends reported by Ouma1 and Izumitani.2 相似文献
8.
Shailendra Joshi Abhijit Mukherjee Siegfried Schmauder 《Computational Materials Science》2003,28(3-4):548-555
The present paper deals with a class of functionally graded materials (FGM), called active FGM that has electro-elastically graded material phases. An active FGM system leads to minimization of stress concentration that arises due to mismatch in the electrical and elastic properties of the constituent phases. This work focuses on the characterization of the through thickness stresses of an active FGM subjected to electrical excitation. The structure is comprised of a substrate, an electro-elastically graded layer and an active layer. A formulation for exact solutions of the system based on Euler–Bernoulli theory is presented. Power-law variation of the composition of the two phases in the graded layer is considered. Performance of linearly gradient FGM for a range of stiffness and electrical property ratios of the active and substrate materials have been studied. It is observed that the electrical strain component and the compositional gradation significantly influence the stress characteristics of the active FGM. 相似文献
9.
Amiya S. Sanyal Joydeb Mukerji Siddhartha Bandyopadhyay 《Journal of the American Ceramic Society》1991,74(9):2312-2314
Mössbauer spectra of the products obtained by carbothermal reduction and distribution of silica in the presence of iron in the temperatures range 1200o to 1540o were studied. The preponderance of β- Si3 N4 over the α form at a higher reaction temperature were assumed to be related to the formation of an Fe-Si-N liquid. The liquid did not alter its composition with the variation of reduction-temprature, Iron had no effect on the reaction mechanism below 1300o C. 相似文献
10.