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排序方式: 共有7533条查询结果,搜索用时 62 毫秒
21.
Stawarz Sylwester Witek Natalia Kucharczyk Wojciech Bakar Mohamed Stawarz Magdalena 《International Journal of Mechanics and Materials in Design》2019,15(3):585-599
International Journal of Mechanics and Materials in Design - The present work investigates the ablative and thermal properties of an epoxy resin which was modified with titanium dioxide... 相似文献
22.
A 3D target structure along with a coordinate system transformation will enable a high-resolution ground-based radar looking up at a target or an airborne radar looking down on a target to perform target recognition at all azimuth and elevation or look-down angles. Target dimensions such as length, width, and height are characterized by a three-dimensional surface as a function of azimuth and elevation angles. Target signatures for transmitted pulses with beta time variation are obtained as a function of target extent, azimuth, and elevation or look-down angles. An average range resolution is defined to accommodate the large variation in range resolution with target orientation. Target recognition based on target shape can distinguish airplane targets with a variable structure, though the database may not contain a matched sample target signature to the observed one. A distributed ground clutter model has been analyzed to obtain ground clutter variations with azimuth and elevation angles. In addition, the peak magnitude of clutter-to-signal ratio has been determined for a clutter area with a varying number of point scatterers. The analysis and target recognition of a radar receiver consisting of a sliding correlator to suppress noise followed by a three-pulse canceller to eliminate clutter has been carried out in terms of input target signatures 相似文献
23.
An adaptive antenna array is incorporated into a decorrelatingmulti-user detector to effectively increase the DS-CDMA system capacity.Capacity improvement is due to beamforming gain, spatial diversity gain(assuming large angle spread), and the decorrelating effect. Thereceiver has been analyzed for the cases of sufficiently andinsufficiently spaced receiving antennas. The receiver consists of afront-end beamformer for every user in the cell and has knowledge of allusers' signature sequences. The beamformer estimates the desired userchannel vector, enhancing its signal and reducing the co-channelinterference from other directions. The multi-user detection, exploitingknowledge of other users, rejects those interferers whose arrival anglesare close to that of the desired user. The average uncoded Bit ErrorRate (BER) as a function of the number of in-beam active users, theaverage antenna Signal-to-Noise Ratio (SNR), and the number of receivingantennas is examined in both single-path and multi-path Rayleigh fadingchannels. Analysis shows an increase in system capacity proportional tothe number of receiving antennas. 相似文献
24.
The performance of a home made MIS–p-Si solar cell was experimentally studied under various gamma irradiation doses (up to 500 Mrad). The effect of radiation dose on the I−V and C−V characteristics was investigated in this work. The obtained results showed that all the output parameters of the cells under investigation were degraded with gamma radiation exposure. In addition, the effects of fabrication conditions (metal thickness and adding of antireflection coating) on the cell output parameters were also investigated. 相似文献
25.
PHYSICS-BASED SIMULATION OF HIGH SPEED MACHINING 总被引:3,自引:0,他引:3
Eu-Gene Ng Tahany I. El-Wardany Mihaela Dumitrescu Mohamed A. Elbestawi 《Machining Science and Technology》2002,6(3):301-329
Computer simulation of high speed machining processes can provide a unique insight and reduce the number of design iterations required to advance and optimize the process. Predictive modeling of high speed machining of exotic materials has been hindered by the nonlinear behavior of this type of materials at extremely high strain, strain rate, and temperatures. This paper presents a physics-based modeling technology that includes the change in the material constitutive equation and the friction characterization at cutting speeds up to 400 m min-1. The dependence of the accuracy of the predicted parameters, such as the chip formation on cutting forces, chip/tool/workpiece interface temperature, stress and strain distributions are also discussed. The fundamentals of metal cutting were utilized to understand the effect of parameter changes in regimes that are outside current empirical knowledge databases. 相似文献
26.
Abdelbaki Benamor Brahim Si Ali Mohamed Kheireddine Aroua 《Korean Journal of Chemical Engineering》2008,25(3):451-460
The absorption rates of CO2 into aqueous solutions of Diethanolamine (DEA) with varying concentrations from 0.2 to 4M and temperature range from 293
to 323 K were measured by using a laboratory stirred reactor. The CO2 partial pressure was varied in a range that the reaction would occur in pseudo first order regime. Experimental data were
analyzed and the kinetic parameters associated with the reaction were determined. The activation energy for the deprotonation
of the intermediate zwitterion was estimated at about 11.4 kcal/mol. The contribution of carbamate formation to the overall
absorbed CO2 was experimentally evaluated and found to be of the order of 100%. 相似文献
27.
28.
T. S. Srivatsan I. A. Ibrahim F. A. Mohamed E. J. Lavernia 《Journal of Materials Science》1991,26(22):5965-5978
The critical need for high strength, lightweight and high stiffness materials has, in recent years, resurrected much interest in discontinuously reinforced powder metallurgy metal matrix composites. These hybrid materials have combined both standard wrought alloys of aluminium and a wide variety of discontinuous reinforcements such as particulates and whiskers of ceramic materials. Renewed interest in these materials as attractive candidates for use in the aerospace and transportation industry has resulted from an attractive and unique combination of physical and mechanical properties, and an ability to offer near isotropic properties coupled with the low cost of these materials when compared with existing monolithic materials. In this paper, the primary processing categories for discontinuously-reinforced metal-matrix composites are highlighted and the salient features of the various techniques in each category are discussed. The variables involved in each processing technique are examined, and the influence of alloy chemistry highlighted. Novel processing techniques for these materials such as the variable co-deposition method is presented as a means to process these novel engineering materials in order to improve their overall mechanical performance. 相似文献
29.
30.
The non-uniformity of the air temperatures and the slow flow rate at the plane collector exit constitute the main cause of the limitations of the solar drying systems. In order to obtain an uniform and a variable flow rate for different uses, a hot air generator using concentrated solar radiation is proposed. To improve the thermal efficiency of the generator, a study of the influence of different shape parameters is realized. The generator is simulated in the laboratory while investigating the flow induced by a circular disc heated uniformly by Joule effect at constant temperature. This disc is placed at the entrance of an open ended vertical cylinder of a larger diameter. Thermal radiation emitted by the hot disc heats the cylinder wall. The heating of the fluid at the cylinder-inlet generates a thermosiphon flow around the one created by the hot disc. The comparison of the velocity and the temperature profiles of the resulting flow permits to determine the influence of the cylinder height, the vertical source-cylinder spacing and the radius ratio, on the resulting flow at the system exit. Thus, a judicious choice of the shape parameters entails an improvement of the flow rate as well as the thermal flux absorbed by the air and a good homogenization of the air temperature at the generator exit. 相似文献