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Electrodeless plasma thrusters for spacecraft: a review

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Plasma science and Technology 2017年第8期19卷 1-24页

作者： s N BATHGATE m m m BILEK D R mCKENZIE Applied and Plasma Physics School of PhysicsUniversity of Sydney

The physics of electrodeless electric thrusters that use directed plasma to propel spacecraft without employing electrodes subject to plasma erosion is reviewed. Electrodeless plasma thrusters are potentially more durable than presently deployed thrusters that use electrodes such as gridded ion,Hall thrusters, arcjets and resistojets. Like other plasma thrusters, electrodeless thrusters have the advantage of reduced fuel mass compared to chemical thrusters that produce the same thrust. The status of electrodeless plasma thrusters that could be used in communications satellites and in spacecraft for interplanetary missions is examined. Electrodeless thrusters under development or planned for deployment include devices that use a rotating magnetic field; devices that use a rotating electric field; pulsed inductive devices that exploit the Lorentz force on an induced current loop in a plasma; devices that use radiofrequency fields to heat plasmas and have magnetic nozzles to accelerate the hot plasma and other devices that exploit the Lorentz force. Using metrics of specific impulse and thrust efficiency, we find that the most promising designs are those that use Lorentz forces directly to expel plasma and those that use magnetic nozzles to accelerate plasma.

关键词： spacecraft a review propellant Lorentz thrust rotating radiofrequency erosion presently exploit

Heat transfer enhancement in mOsFET mounted on different FR4 substrates by thermal transient measurement

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Chinese Physics B 2017年第9期26卷 549-556页

作者： Norazlina m s Dheepan Chakravarthii m K shanmugan s mutharasu D shahrom mahmud school of Physics Universiti Sains Malaysia 11800 MindenPenangMalaysia

miniaturization of electronic package leads to high heat density and heat accumulation in electronics device, resulting in short life time and premature failure of the device. Junction temperature and thermal resistance are the critical parameters that determine the thermal management and reliability in electronics cooling. metal oxide field effect transistor（mOsFET）is an important semiconductor device for light emitting diode-integrated circuit（LED IC） driver application, and thermal management in mOsFET is a major challenge. In this study, investigations on thermal performance of mOsFET are performed for evaluating the junction temperature and thermal resistance. suitable modifications in FR4 substrates are proposed by introducing thermal vias and copper layer coating to improve the thermal performance of mOsFET. Experiments are conducted using thermal transient tester（T3ster） at 2.0 A input current and ambient temperature varying from25℃ to 75℃. The thermal parameters are measured for three proposed designs： FR4 with circular thermal vias, FR4 with single strip of copper layer and embedded vias, and FR4 with I-shaped copper layer, and compared with that of plain FR4 substrate. From the experimental results, FR4I-shaped shows promising results by 33.71% reduction in junction temperature and 54.19% reduction in thermal resistance. For elevated temperature, the relative increases in junction temperature and thermal resistance are lower for FR4I-shaped than those for other substrates considered. The introduction of thermal vias and copper layer plays a significant role in thermal performance.

关键词： metal oxide field effect transistor(mOsFET) thermal transient measurement heat transfer path FR4

Nonlinear buckling and postbuckling behavior of cylindrical shear deformable nanoshells subjected to radial compression including surface free energy effects

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Acta mechanica solida sinica 2017年第2期30卷 209-222页

作者： s.sahmani m.m.Aghdam m.Bahrami Department of mechanical Engineering Amirkabir University of Technology P.O. Box 15875-4413 Tehran Iran

The objective of the present investigation is to predict the nonlinear buckling and postbuckling characteristics of cylindrical shear deformable nanoshells with and without initial imperfection under hydrostatic pressure load in the presence of surface free energy *** this end, Gurtin-murdoch elasticity theory is implemented into the irst-order shear deformation shell theory to develop a size-dependent shell model which has an excellent capability to take surface free energy effects into account. A linear variation through the shell thickness is assumed for the normal stress component of the bulk to satisfy the equilibrium conditions on the surfaces of nanoshell. On the basis of variational approach and using von Karman-Donnell-type of kinematic nonlinearity, the non-classical governing differential equations are derived. Then a boundary layer theory of shell buckling is employed incorporating the effects of surface free energy in conjunction with nonlinear prebuckling deformations, large delections in the postbuckling domain and initial geometric imperfection. Finally, an eficient solution methodology based on a two-stepped singular perturbation technique is put into use in order to obtain the critical buckling loads and postbuckling equilibrium paths corresponding to various geometric parameters. It is demonstrated that the surface free energy effects cause increases in both the critical buckling pressure and critical end-shortening of a nanoshell made of silicon.

关键词： Nanoscale structures size effect Nonlinear buckling surface free energy Boundary layer theory

Numerical and experimental analysis of the closed-cell aluminium foam under low velocity impact using computerized tomography technique

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Acta mechanica sinica 2019年第1期35卷 144-155,I0005页

作者： s.Talebi m.sadighi m.m.Aghdam Department of mechanical Engineering Amirkabir University of TechnologyTehranIran

In the present work, the response of closed-cell aluminum foams under low-velocity impact has been studied numerically and experimentally. Computerized tomography is employed to access three-dimensional (3D) microstructure of the closed-cell aluminum foam. Effective parameters including foam density and the velocity of impactor on foam dynamic behavior are investigated. In order to show the validity and accuracy of results, some static experiments and low-velocity impact tests have been conducted. Results in dicate a remarkable agree me nt between the simulation and experimental data. moreover, the results show that by increasing the density of foam samples, the highest difference between numerical and experimenidi results for peak stress and absorbed energy are 35.9% and 6.9%, respectively, which is related to the highest density. For impact velocities ranging from 3.1 to 4.2 m/s, the maximum discrepancy in peak stress and absorbed energy occur at an inipact velocity of 3.1 m/s in which corresponding errors are 33.3% and 6.6%, respectively. For the impact velocity of 40 m/s, the highest increase in peak stress and absorbed energy are 667.9% and 370.3% associated with the density of 0.5 and 0.3 g/cm^3, respectively.

关键词： Finite element analysis Impact Aluminum foam Experimental analysis Energy absorption

Hermitian-Einstein metrics on Parabolic stable Bundles

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Acta mathematica sinica,English series 1999年第1期15卷 93-114页

作者： m.s.Narasimhan mathematics section International Centre for Theoretic PhysicsP.O.Box 58634100 TriesteItaly

Let be a compact complex manifold of complex dimension two with a smooth K?hler metric and D a smooth divisor on . If E is a rank 2 holomorphic vector bundle on with a stable parabolic structure along D, we prove the existence of a metric on (compatible with the parabolic structure) which is Hermitian-Einstein with respect to the restriction of the K?hler metric to ěD. A converse is also proved.

关键词： Hermitian-Einstein metrics on Parabolic stable Bundles math

THE OPTImAL PRECONDITIONING IN THE DOmAIN DECOmPOsITION mETHOD FOR WILsON ELEmENT

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Journal of Computational mathematics 1997年第3期15卷 193-202页

作者： Wang, m Zhang, s BEIJING UNIV DEPT MATHBEIJING 100871PEOPLES R CHINA CHINEsE ACAD sCI ICMSECBEIJINGPEOPLES R CHINA

This paper discusses the optimal preconditioning in the domain decomposition method for Wilson element. The process of the preconditioning is composed of the resolution of a small scale global problem based on a coarser grid and a number of independent local subproblems, which can be chosen arbitrarily. The condition number of the preconditioned system is estimated by some characteristic numbers related to global and local subproblems. With a proper selection, the optimal preconditioner can be obtained, while the condition number is independent of the scale of the problem and the number of subproblems.

关键词： Wang Zhang THE OPTImAL PRECONDITIONING IN THE DOmAIN DECOmPOsITION mETHOD FOR WILsON ELEmENT

Review on sol-Gel Derived Coatings: Process, Techniques and Optical Applications

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Journal of materials science & Technology 2002年第3期18卷 211-218页

作者： s.m.Attia JueWANG 等 PohlInstituteofsolidstatePhysics TongjiUniversityShanghai200092China Phys.Dept.FacultyofEducation KaferEl-SheikhEgypt

sol-gel process is one of the simplest techniques to manufacture thin films. The quality of the prepared films depends on the parameters of the sol-gel process and the used technique for deposition. A great variety of the sol-gel derived films have been prepared for different applications. We present a review on the sol-gel derived coatings. The description of the process is introduced in details. Different sol-gel deposition techniques are mentioned. The optical applications of the sol-gel derived coatings are reviewed.

关键词： sol-gel process Coating Thin film

Nonlinear primary resonance analysis of nanoshells including vibrational mode interactions based on the surface elasticity theory

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Applied mathematics and mechanics(English Edition) 2020年第2期41卷 233-260页

作者： A.sARAFRAZ s.sAHmANI m.m.AGHDAm mechanical Engineering Department Amirkabir University of TechnologyTehran 15875-4413Iran school of science and Technology The University of GeorgiaTbilisi 0171Georgia

The deviation from the classical elastic characteristics induced by the free surface energy can be considerable for nanostructures due to the high surface to volume ratio. Consequently, this type of size dependency should be accounted for in the mechanical behaviors of nanoscale structures. In the current investigation, the influence of free surface energy on the nonlinear primary resonance of silicon nanoshells under soft harmonic external excitation is studied. In order to obtain more accurate results,the interaction between the first, third, and fifth symmetric vibration modes with the main oscillation mode is taken into consideration. Through the implementation of the Gurtin-murdoch theory of elasticity into the classical shell theory, a size-dependent shell model is developed incorporating the effect of surface free energy. With the aid of the variational approach, the governing differential equations of motion including both of the cubic and quadratic nonlinearities are derived. Thereafter, the multi-time-scale method is used to achieve an analytical solution for the nonlinear size-dependent problem. The frequency-response and amplitude-response of the soft harmonic excited nanoshells are presented corresponding to different values of shell thickness and surface elastic constants as well as various vibration mode interactions. It is depicted that through consideration of the interaction between the higher symmetric vibration modes and the main oscillation mode, the hardening response of nanoshell changes to the softening one. This pattern is observed corresponding to both of the positive and negative values of the surface elastic constants and the surface residual stress.

关键词： nanostructure nonlinear dynamics surface stress mode interaction multi-time-scale method

THREE-DImENsIONAL NUmERICAL LOCALIZATION OF ImPERFECTIONs BAsED ON A LImIT mODEL IN ELECTRIC FIELD AND A LImIT PERTURBATION mODEL

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Journal of Computational mathematics 2009年第4期27卷 495-524页

作者： s.m.mefire LAmFA CNRS UMR 6140Université de Picardie33 r.Saint-Leu80039 Amiens Cedex 1France

From a limit model in electric field obtained by letting the frequency vanish in the time-harmonic maxwell equations, we consider a limit perturbation model in the tangential boundary trace of the curl of the electric field for localizing numerically certain small electromagnetic inhomogeneities, in a three-dimensional bounded domain. We introduce here two localization procedures resulting from the combination of this limit perturbation model with each of the following inversion processes： the Current Projection method and an Inverse Fourier method. Each localization procedure uses, as data, a finite number of boundary measurements, and is employed in the single inhomogeneity case; only the one based on an Inverse Fourier method is required in the multiple inhomogeneities case. Our localization approach is numerically suitable for the context of inhomogeneities that are not purely electric. We compare the numerical results obtained from the two localization procedures in the single inhomogeneity configuration, and describe, in various settings of multiple inhomogeneities, the results provided by the procedure based on an Inverse Fourier method.

关键词： Inverse problems maxwell equations Electric fields Inhomogeneities Elec-trical Impedance Tomography Current Projection method FFT Numerical boundarymeasurements Edge elements Least square systems Incomplete modified Gram-schmidt preconditioning.