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Styrene undergoes efficient epoxidation to styrene epoxide on the Cu{111} surface. At the optimum condition (Θo = 0.03 ML) ∼20% of the styrene is converted to the epoxide with almost 100% selectivity. Comparison with Ag{111} shows that
the epoxidation activity and selectivity of Cu greatly exceed those of Ag. Incipient oxidation of the Cu{111} surface does
not suppress the adsorption of styrene, but the oxidised metal is catalytically inert. Submonolayer amounts of Cs enhance
styrene uptake and increase conversion to the epoxide without adversely affecting epoxidation selectivity. This effect is
due to inhibition of Cu oxidation by Cs. Our findings are discussed in the light of current understanding of Ag‐catalysed
alkene epoxidation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
114.
The design of a high speed, broadband packet switch with two priority levels for application in integrated voice/data networks is presented. The packet switch can efficiently cope with 128 byte packets converging on it from eight 140 Mbit/s dynamic time division multiplexed fibre optic links. The packet switch throughput varies with the load and traffic composition, and the delay experienced by voice and data packets is within 300 μs and 3 ms, respectively. The design is implemented by task-sharing in a multi-processor configuration. The design of the packet switch, including its subsystems, is detailed here. 相似文献
115.
P. N. Kotru Anima Jain Ashok K. Razdan B. M. Wanklyn 《Journal of Materials Science》1989,24(4):1413-1420
Results of topographical studies carried out on (100) and (110) faces of lanthanum borate crystals grown from the PbO-B2O3 flux system are illustrated and discussed. The habit faces display the formation of cavities, microcrystals, elliptical etch pits, elliptical hillocks, circular hillocks and irregular structures. Also described are a various number of elevated structures identified as impurity phases. Energy dispersive X-ray (EDAX) studies have confirmed that these impurity phases in the growth of lanthanum borate (LaBO3) crystals are enriched by lead (Pb). The habit faces also exhibit some elevated regions which are reported to be more imperfect in comparison with others. It is inferred that independent growth on the habit faces has taken place during the last stage of crystal growth by a two-dimensional nucleation mechanism. 相似文献
116.
This paper presents two mathematical models to predict the performance of the man—machine systems under different weather conditions. The operator may be in good or poor physical condition which also affects the performance of the system. Failure rate of the system, rate of change of weather conditions as well as rate of change of physical conditions of the operator are assumed to be constant while the repair time distributions are general. Regenerative technique in MRP is applied to obtain several reliability characteristics of interest. 相似文献
117.
Virpal Singh V. N. Singh Ashok Mittal 《Journal of Infrared, Millimeter and Terahertz Waves》2000,21(3):421-428
This paper describes the Integrated Finline Front-end Radar Receivers at Ka-Band. The Front-receivers developed for Radar applications include combining of finline components on a single MIC substrate with various planar transmission lines. The integrated systems so developed have better noise figure and control over phase and gain imbalances as compared to discrete component systems. Two types of Integrated Front-ends Radar receivers are described here. The developed systems are highly compact and reliable. 相似文献
118.
C. P. Navathe B. L. Dashora Archana Jaiswal D. S. Thakur U. N. Roy L. M. Kukreja 《Sadhana》2001,26(3):213-225
An indigenous and simple electronic control system for Langmuir-Blodgett (LB) film deposition set-up has been developed. This
set-up consists of a microstepping circuit to drive the stepper motors with precision and smooth motion, essential for controlled
movement of the barriers and substrate in the LB set-up. Linear variable differential transformer (LVDT)-based displacement
measuring device has been developed and used to measure the surface pressure of the monolayer material spread on the water
surface. A control program is written which incorporates all operational modes required to drive the set-up and to acquire
the datain situ using a set of user-friendly commands. This control set-up has been successfully used to plot the pressure-area isotherm
of various amphiphilic compounds such as ferric stearate, zinc arachidate etc. and for deposition of ordered LB films of ferric
stearate. 相似文献
119.
120.
Ashok D. Belegundu Jasbir S. Arora 《International journal for numerical methods in engineering》1985,21(9):1583-1599
A comprehensive study of various mathematical programming methods for structural optimization is presented. In recent years, many modern optimization techniques and convergence results have been developed in the field of mathematical programming. The aim of this paper is twofold: (a) to discuss the applicability of modern optimization techniques to structural design problems, and (b) to present mathematical programming methods from a unified and design engineers' viewpoint. Theoretical aspects are considered here, while numerical results of test problems are discussed in a companion paper. Special features possessed by structural optimization problems, together with recent developments in mathematical programming (recursive quadratic programming methods, global convergence theory), have formed a basis for conducting the study. Some improvements of existing methods are noted and areas for future investigation are discussed. 相似文献