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排序方式: 共有508条查询结果,搜索用时 15 毫秒
1.
Reddy C.J. Deshpande M.D. Cockrell C.R. Beck F.B. 《Antennas and Propagation, IEEE Transactions on》1998,46(8):1229-1233
The method of moments (MoM) in conjunction with the asymptotic waveform evaluation (AWE) technique is applied to obtain the radar cross section (RCS) of an arbitrarily shaped three-dimensional (3-D) perfect electric conductor (PEC) body over a frequency band. The electric field integral equation (EFIE) is solved using the MoM to obtain the equivalent surface current on the PEC body. In the AWE technique, the equivalent surface current is expanded in a Taylor's series around a frequency in the desired frequency band. The Taylor series coefficients are then matched via the Pade approximation to a rational function. Using the rational function, the surface current is obtained at any frequency within the frequency range, which is in turn used to calculate the RCS of the 3-D PEC body. A rational function approximation is also obtained using the model-based parameter estimation (MBPE) method and compared with the Pade approximation. Numerical results for a square plate, a cube, and a sphere are presented over a frequency bandwidth. Good agreement between the AWE and the exact solution over the bandwidth is observed 相似文献
2.
P. Ohodnicki B. Webler A. Deshpande J.M.K. Wiezorek 《Metallurgical and Materials Transactions A》2007,38(10):2479-2487
3.
Bilirubin, a bile pigment, was studied for its extent of adsorption on substituted aminechloromethyl polystyrene by UV spectrophotometry. By performing simple displacement reactions on chloromethyl polystyrene with secondary and tertiary amines, the amount of charge density and steric factor on substituted nitrogen atom have been varied. Adsorption isotherms of bilirubin at 0°C by different amine–chloromethyl polystyrene homologs suggest the existence of electrostatic interaction of polymeric resin with bilirubin moiety. Results of adsorption of bilirubin to polymeric resin have shown that the extent of adsorption of bilirubin depends on the unit charge, and on the structure of the substituted amine–chloromethyl polystyrene. The effects of porosity of resin on bilirubin adsorption have also been discussed. 相似文献
4.
Kiran B. Deshpande 《Chemical engineering science》2003,58(16):3829-3835
As the holdup of dispersed phase in an agitated liquid-liquid dispersion is increased at fixed agitation, a point is reached (called inversion holdup) when the dispersion inverts—the dispersed phase becomes continuous and vice versa. In this work, we present experimental data which suggest that the inversion holdup for sufficiently intense turbulence is independent of all the operational parameters associated with a stirred tank, e.g., stirrer speed, vessel volume, impeller size, and impeller type; it depends only on the properties of the liquid-liquid system. The inversion holdup was verified to remain unchanged even for inversion in turbulent flow field in the annular space between two coaxial cylinders. A hypothesis involving drops in near contact with each other at high holdups is used to explain the experimental data. The new finding may also provide a qualitative basis for selecting a liquid-liquid system with desired extent of mixing in the dispersed phase for carrying out transport and reactions in multiphase systems. 相似文献
5.
Detailed studies were carried out on the electrowinning of antimony from SbCl3–HCl–H2SO4 and SbCl3–HCl baths using a graphite anode and a tantalum cathode, the anode being enclosed in a cylindrical glass compartment provided with a sintered disc. Disintegration of the graphite anode increased with increase in anode current density and duration of electrolysis. Analysis of gas evolved at the anode indicated that the presence of sulphuric acid increased the production of CO2. The anodic disintegration was reduced to a negligibly low value by circulation of 6m HCl through the anode compartment. Optimum conditions were determined for electrowinning of antimony from a SbCl3–HCl bath. The tantalum content in the metal was 0.1–0.2 p.p.m. 相似文献
6.
J. H. Li P. Deshpande R. Y. Lin 《Journal of Materials Engineering and Performance》2004,13(4):445-450
The objective of this study is to investigate an innovative infrared (IR) technique to enhance adhesion of electroplated copper
(Cu) on Ti-6Al-4V without dichromate dipping. The ultimate goal is to develop a Cu coating process on Ti-6Al-4V without hazardous
hexavalent chromium (Cr) solution treatments. Cu coatings of around 50 μm were electroplated on Ti-6Al-4V specimens at a current
density of 0.03 A/cm2 in an acidic Cu solution. To improve adhesion of coatings, IR heat treatments were performed on the Cu-coated samples at
different temperatures and durations: 860 °C for 600 s and 875 °C for 20–120 s. This process was accomplished in an attempt
to replace the use of dichromate dipping before electroplating. For samples heat treated at 860 °C, no bonding existed, even
after 600 s. It is believed that solid-state diffusion prevailed at 860 °C and that 600 s was not enough for sufficient diffusion
to occur. Adhesion was poor when samples were heat treated at 875 °C for 20 s. Excellent adhesion was observed when the heat
treatment holding time was increased to 40 s. For 90 s, the surface appearance of coatings partially changed from Cu-colored
to a grayish color. There was no Cu left on the surface after a 120 s heat treatment. From optical microscopic observations
on sample cross sections, an interlayer between the Cu and Ti-6Al-4V formed when heat treated at 875 °C for 40 s and longer.
The interlayer thickness increased as the holding time increased, until depletion of Cu. The sheet resistivity of coated specimens
was on the order of pure Cu for samples heat treated at 875 °C and less than 90 s. During the 875 °C heat treatment, the following
occurred: solid-state diffusion of Cu in Ti-6Al-4V, formation of eutectic solutions, dissolution of Cu and Ti-6Al-4V into
the liquid phase, and the formation of intermetallic compounds. The lowest eutectic temperature of 875 °C played a key role
in this innovative process of Cu coating on Ti-6Al-4V.
This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September
15–17, 2003, in Indianapolis, Indiana and appears on pp. 403–10 of the Proceedings. 相似文献
7.
Kostas Tzoumas Amol Deshpande Christian S. Jensen 《The VLDB Journal The International Journal on Very Large Data Bases》2013,22(1):3-27
Query optimizers rely on statistical models that succinctly describe the underlying data. Models are used to derive cardinality estimates for intermediate relations, which in turn guide the optimizer to choose the best query execution plan. The quality of the resulting plan is highly dependent on the accuracy of the statistical model that represents the data. It is well known that small errors in the model estimates propagate exponentially through joins, and may result in the choice of a highly sub-optimal query execution plan. Most commercial query optimizers make the attribute value independence assumption: all attributes are assumed to be statistically independent. This reduces the statistical model of the data to a collection of one-dimensional synopses (typically in the form of histograms), and it permits the optimizer to estimate the selectivity of a predicate conjunction as the product of the selectivities of the constituent predicates. However, this independence assumption is more often than not wrong, and is considered to be the most common cause of sub-optimal query execution plans chosen by modern query optimizers. We take a step towards a principled and practical approach to performing cardinality estimation without making the independence assumption. By carefully using concepts from the field of graphical models, we are able to factor the joint probability distribution over all the attributes in the database into small, usually two-dimensional distributions, without a significant loss in estimation accuracy. We show how to efficiently construct such a graphical model from the database using only two-way join queries, and we show how to perform selectivity estimation in a highly efficient manner. We integrate our algorithms into the PostgreSQL DBMS. Experimental results indicate that estimation errors can be greatly reduced, leading to orders of magnitude more efficient query execution plans in many cases. Optimization time is kept in the range of tens of milliseconds, making this a practical approach for industrial-strength query optimizers. 相似文献
8.
In this paper, we present the design and development of a real-time interactive virtual classroom multimedia distance learning system at the University of Washington. There has been rapid progress in digital media compression research, and the delivery of media data on the public Internet is becoming widespread. A real-time interactive virtual classroom allows a remote participant to not only receive a live class feed, but also to interact in a live class by asking questions with audio, video in real-time using an Internet connection. Many instructors use electronically prepared slides during their class. The traditional video coding algorithms are not able to compress this slide data very well at low bit-rates. We propose a Web-based real-time presentation system for the electronic slides. Instructors also write text on a white board or a piece of paper during the class. At low bit-rates, conventional video encoding algorithms cannot encode this handwritten text video with enough fidelity, resulting in an illegible decoded video. We propose an extension of the well known bilevel image encoding algorithms to handle the handwritten text video. Our method results in decoded video frames which can be read very clearly when encoded at low bit-rates. We have developed a set of tools which allows recording the live classroom session and automatic creation of a synchronized multimedia integration language (SMIL) presentation, which can be used for a later viewing 相似文献
9.
S K Sathe S S Deshpande D K Salunkhe 《Critical reviews in food science and nutrition》1984,21(1):41-93
Beans of Phaseolus are an important food crop both economically and nutritionally, and are cultivated and consumed worldwide. With ever rising costs of meats and fresh fruits and vegetables, dry beans are expected to contribute more to the human nutrition in coming years. Traditionally, they have been referred to as "poor man's meat" and have contributed significantly to the diets of many people of several countries in Asia, Africa, Middle East, and South America. In recent years, a renewed interest in bean research in Western European countries and the U.S. is evident. In this review, certain biochemical, technological, nutritional, and toxicological aspects are discussed and the limitations and problems associated with dry beans of Phaseolus as human food are addressed. 相似文献
10.
Upadhyay J Joshi MJ Deshpande PP Sharma ML Navathe CP 《The Review of scientific instruments》2008,79(5):054701
In this paper, a ramp generator with programmable slope is presented. It consists of a high voltage step generator, followed by integrator. The capacitor and inductor in the integrator are designed such that they can be varied by a microcontroller. This circuit generates two bipolar ramps with fastest speed <1 ns and provides continuous speed variation from 6 to 30 ns for a ramp of 500 V. This is being developed as a part of automated streak camera for deflection of electron beam. 相似文献