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Hybridization between microstructure and magnetization improvement in lead and RE co-doped BiFeO_3

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Journal of Rare Earths 2016年第5期34卷 495-506页

作者： m.A.Ahmed s.F.mansour s.I.El-Dek m.m.Karamany materials science Lab.(1) Physics Dept.Faculty of ScienceCairo University Physics Department Faculty of ScienceZagazig University materials science and Nanotechnology Dept. Faculty of Post Graduate Studies for Advanced SciencesBeni-Suef University Basic science Dept. Faculty of EngineeringBritish University in Egypt

The crystal structure,magnetic and electrical properties of Bi（0.96）Pb（0.04） FeO3 and Bi（0.92）Pb（0.04）RE（0.04）FeO3（RE=La,sm,Dy and Yb）polycrystalline samples were prepared by the flash autocombustion technique.X-ray diffraction（XRD）measurements show that the rare-earth doped compositions crystallized in rhombohedral symmetry of space group R3 *** undoped sample consisted needle shape particles while rare earth substitution preferred platelet like particles as clarified from high resolution transmission electron microscopy（HRTEm）.morphological features were examined using field emission scanning electron microscopy（FEsEm）.magnetization measurements showed that Yb^3＋ samples possessed the highest room temperature saturation magnetization while when Bi^3＋ ions were substituted by La^3＋ ions,a smaller ms（0.28 emu/g）was *** coexistence of ferroelectric and magnetic transitions was detected using DsC and χm,indicating the multiferroic characteristics of Bi（0.92）Pb（0.04）RE（0.04）FeO3 *** Néel temperature shifted upwards with decreasing the ionic radius of rare earth *** correlation was established between microstructure,morphology and magnetic properties in view of the contribution of magnetocrystalline and shape anisotropy in the magnetic parameters values.

关键词： BiFeO3 multiferroic rare earths anisotropy dielectric conductivity Neel temperature

Axisymmetric Powell-Eyring fluid flow with convective boundary condition: optimal analysis

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Applied mathematics and mechanics(English Edition) 2016年第7期37卷 919-928页

作者： T.HAYAT s.mAKHDOOm m.AWAIs s.sALEEm m.m.RAsHIDI Department of mathematics Quaid-i-Azam University Department of mathematics COMSATS Institute of Information Technology Department of mathematics Statistics and Physics Qatar University shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal management systems Tongji University

The effects of axisymmetric flow of a Powell-Eyring fluid over an impermeable radially stretching surface are presented. Characteristics of the heat transfer process are analyzed with a more realistic condition named the convective boundary condition. Governing equations for the flow problem are derived by the boundary layer approximations. The modeled highly coupled partial differential system is converted into a system of ordinary differential equations with acceptable similarity transformations. The convergent series solutions for the resulting system are constructed and analyzed. Optimal values are obtained and presented in a numerical form using an optimal homotopy analysis method （OHAm）. The rheological characteristics of different parameters of the velocity and temperature profiles are presented graphically. Tabular variations of the skin friction coefficient and the Nusselt number are also calculated. It is observed that the temperature distribution shows opposite behavior for Prandtl and Biot numbers. Furthermore, the rate of heating/cooling is higher for both the Prandtl and Biot numbers.

关键词： axisymmetric flow optimal homotopy analysis method (OHAm) analysis,convective boundary condition

Effects of bi-kappa distributed electrons on dust-ion-acoustic shock waves in dusty superthermal plasmas

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Chinese Physics B 2013年第11期22卷 390-395页

作者： m.s.Alam m.m.masud A.A.mamun Department of Physics Jahangirnagar University Department of Physics Bangladesh University of Engineering and Technology (BUET)

The basic properties of dust-ion-acoustic （DIA） shock waves in an unmagnetized dusty plasma （containing inertial ions, kappa distributed electrons with two distinct temperatures, and negatively charged immobile dust grains） are investi- gated both numerically and analytically. The hydrodynamic equation for inertial ions has been used to derive the Burgers equation. The effects of superthermal bi-kappa electrons and ion kinematic viscosity, which are found to modify the basic features of DIA shock waves significantly, are briefly discussed.

关键词： bi-kappa electrons shock waves dust-ion-acoustic waves dusty plasma

Newtonian heating in stagnation point flow of Burgers fluid

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Applied mathematics and mechanics(English Edition) 2015年第1期36卷 61-68页

作者： T.HAYAT s.ALI m.AWAIs m.s.ALHUTHALI Department of mathematics Quaid-i-Azam University Nonlinear Analysis and Applied mathematics (NAAm) Research Group Faculty of Science King Abdulaziz University Faculty of Engineering sciences Ghulam Ishaq Khan Institute of Engineering Sciences and Technology Department of mathematics COMSATS Institute of Information Technology

The Newtonian heating effects in the stagnation point flow of a Burgers fluid are addressed in this paper. The boundary layer flow problems are stated in the spatial domain from zero to infinity. The solution expressions for the velocity and the temperature are obtained and examined for the influential variables. The tabulated values show comparison with the previous results. It is observed that the obtained results are in good agreement with the existing results in limiting sense.

关键词： Burgers fluid Newtonian heating series solutions

Relativistic symmetry of position-dependent mass particles in a Coulomb field including tensor interaction

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Chinese Physics B 2013年第3期22卷 122-128页

作者： m.Eshghi m.Hamzavi s.m.Ikhdair Physics Department Imam Hossein Comprehensive UniversityTehranIran Department of science and Engineering Abhar BranchIslamic Azad UniversityAbharIran Department of Electrical and Electronic Engineering Near East University922022NicosiaNorthern CyprusTurkey Department of Physics Faculty of ScienceAn-Najah National UniversityNablusWest BankPalestine

The spatially-dependent mass Dirac equation is solved exactly for attractive scalar and repulsive vector Coulomb potentials,including a tensor interaction under the spin and pseudospin symmetric *** forms of the energy eigenvalue equation and wave functions are obtained for arbitrary spin-orbit quantum number κ.some numerical results are also given,and the effect of tensor interaction on the bound states is *** is shown that tensor interaction removes the degeneracy between two states in the spin *** also investigate the effects of the spatially-dependent mass on the bound states under spin symmetric limit conditions in the absence of tensor interaction.

关键词： Dirac equation spin and pseudospin symmetries spatially-dependent mass tensor interaction

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