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Electrical and dielectric properties of Na_(1/2)La_(1/2)Cu_3Ti_4O_(12) ceramics prepared by high energy ball-milling and conventional sintering

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Chinese Physics B 2016年第12期25卷 474-480页

作者： h mahfoz Kotb mohamad m Ahmad Department of Physics College of ScienceKing Faisal University Department of Physics Faculty of ScienceAssiut University

We report on the measurements of the electrical and dielectric properties of Na1/2La1/2Cu3Ti4O12 （NLCTO） ce- ramics prepared by high energy ball-milling and conventional sintering without any calcination steps. The x-ray powder diffraction analysis shows that pure perovskite-like CCTO phase is obtained after sintering at 1025 ℃-1075 ℃. higher sintering temperatures result in multi-phase ceramics due to thermal decomposition. Scanning electron microscope observations reveal that the grain size is in a range of - 3 μm-5 μm for these ceramics. Impedance spectroscopy measurements performed in a wide frequency range （1 hz-10 mhz） and at various temperatures （120 K-470 K） are used to study the dielectric and electrical properties of NLCTO ceramics. A good compromise between high ε′ （5.7 ×10^3 and 4.1 × 10^3 at 1.1 khz and 96 khz, respectively） and low tan δ （0.161 and 0.126 at 1.1 khz and 96 khz, respectively） is obtained for the ceramic sintered at 1050 ℃. The observed high dielectric constant behavior is explained in terms of the internal barrier layer capacitance effect.

关键词： ceramics sintering dielectric loss and relaxation electrical

Physicochemical Properties of Nanocrystallite Copper Ferrite Prepared by a Novel Self Flash Combustion of Acetate Precursors

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Journal of materials Science & Technology 2005年第5期21卷 675-680页

作者： m.h.Khedr A.A.Farghali Chemistry Department Faculty of Science(Beni-Suef Branch)Cairo UniversityBeni-Suef EgyptChemistry DepartmentFaculty of Science(Beni-Suef Branch)Cairo UniversityBeni-Suef Egypt

Copper ferrite, CuFe2O4, one of the important ferrites due to its interesting electrical, magnetic and structural properties, is obtained by a novel self flash combustion of a homogeneous mixture of one mole copper acetate monohydrate, Cu（Ch3COO）2·h2O, and two moles of iron （Ⅲ） acetate basic, Fe（ChCOO）2·Oh. Nanocrystalite （89 nm） Copper ferrite （less than 100%） is obtained at lower temperatures, whereas 100% copper ferrite is obtained after calcination at 1000℃. Thermal analysis （TG and DTA）, X-ray diffraction （XRD）, Fourier transform infrared spectroscopy （FTIR）, photo microscopy, magnetic and porosity obtained after calcinations at 700, 800, 900 and 1000℃ to measurements have been carried out for the specimens characterize the conversion efficiency of the powder precursors to copper ferrite. It was found that increasing temperature leads to great improvement in the magnetic properties. By increasing calcination temperature from 700～1000℃saturation magnetic flux density （Bs） increased from 17.8 to 40.8 emu/g, while remnant magnetic flux density （Br） increased from 10.1 to 17.11 emu/g.

关键词： Copper ferrite Flash combustion Synthesis Characterization magnetic properties microstructure

monte-Carlo based cascade control approach with focus on real overactuated space systems

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Journal of Central South University 2016年第12期23卷 3171-3182页

作者： m.Shahi A.h.mazinan Department of Electrical Engineering Birjand BranchIslamic Azad University (IAU) Department of Control Engineering Faculty of Electrical EngineeringSouth Tehran BranchIslamic Azad University (IAU)

The present research relies on a cascade control approach through the monte-Carlo based method in the presence of uncertainties to evaluate the performance of the real overactuated space systems.A number of potential investigations in this area are first considered to prepare an idea with respect to *** insight proposed here is organized to present attitude cascade control approach including the low thrust in connection with the high thrust to be implemented,while the aforementioned monte-Carlo based method is carried out to guarantee the approach *** is noted that the investigated outcomes are efficient to handle a class of space systems presented via the center of mass and the moments of *** also a number of profiles for the thrust vector and the misalignments as the disturbances all vary in its span of nominal *** acquired results are finally analyzed in line with some well-known benchmarks to verify the approach *** key core of finding in the research is to propose a novel 3-axis control approach to deal with all the mentioned uncertainties of space systems under control,in a synchronous manner,as long as the appropriate models in the low-high thrusts are realized.

关键词： monte-Carlo based method cascade control approach overactuated space systems low-high thrusts models

Fallopian tube assessment of the peristaltic-ciliary flow of a linearly viscous fluid in a finite narrow tube

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Applied mathematics and mechanics(English Edition) 2018年第3期39卷 437-454页

作者： h.AShRAF A.m.SIDDIQUI m.A.RANA Department of mathematics and Statistics Riphah International University Department of mathematics York CampusPennsylvania State University

The present theoretical assessment deals with the peristaltic-ciliary trans- port of a developing embryo within a fallopian tubal fluid in the human fallopian tube. A mathematical model of peristalsis-cilia induced flow of a linearly viscous fluid within a fallopian tubal fluid in a finite two-dimensional narrow tube is developed. The lubrica- tion approximation theory is used to solve the resulting partial differential equation. The expressions for axial and radial velocities, pressure gradient, stream function, volume flow rate, and time mean volume flow rate are derived. Numerical integration is performed for the appropriate residue time over the wavelength and the pressure difference over the wavelength. moreover, the plots of axial velocity, the appropriate residue time over wavelength, the vector, the pressure difference over wavelength, and the streamlines are displayed and discussed for emerging parameters and constants. Salient features of the pumping characteristics and the trapping phenomenon are discussed in detail. Yhrther- more, a comparison between the peristaltic flow and the peristaltic-ciliary flow is made as the special case. Relevance of the current results to the transport of a developing embryo within a fallopian tubal fluid from ampulla to the intramural in the fallopian tube is also explored. It reveals the fact that cilia along with peristalsis helps to complete the required mitotic divisions while transporting the developing embryo within a fallopian tubal fluid in the human fallopian tube.

关键词： peristaltic-ciliary flow linearly viscous fluid analytic solution human fal-lopian tube

Thermoelastic Analysis of Non-uniform Pressurized Functionally Graded Cylinder with Variable Thickness Using First Order Shear Deformation Theory(FSDT) and Perturbation method

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Chinese Journal of mechanical Engineering 2015年第6期28卷 1149-1156页

作者： KhOShGOFTAR m J mIRZAALI m J RAhImI G h Faculty of mechanical Engineering Tarbiat Modares University Department of mechanical Engineering Faculty of Engineering Arak University Department of mechanical Engineering Politecnico di Milano

Recently application of functionally graded materials（FGms） have attracted a great deal of interest. These materials are composed of various materials with different micro-structures which can vary spatially in FGms. Such composites with varying thickness and non-uniform pressure can be used in the aerospace engineering. Therefore, analysis of such composite is of high importance in engineering problems. Thermoelastic analysis of functionally graded cylinder with variable thickness under non-uniform pressure is considered. First order shear deformation theory and total potential energy approach is applied to obtain the governing equations of non-homogeneous cylinder. Considering the inner and outer solutions, perturbation series are applied to solve the governing equations. Outer solution for out of boundaries and more sensitive variable in inner solution at the boundaries are considered. Combining of inner and outer solution for near and far points from boundaries leads to high accurate displacement field distribution. The main aim of this paper is to show the capability of matched asymptotic solution for different non-homogeneous cylinders with different shapes and different non-uniform pressures. The results can be used to design the optimum thickness of the cylinder and also some properties such as high temperature residence by applying non-homogeneous material.

关键词： non-homogenous cylinder First order Shear Deformation Theory matched asymptotic method perturbation method functionally graded material

EFFECT OF NANOSILICA ON ThE KINETICS OF CURE REACTION AND ThERmAL DEGRADATION OF EPOXY RESIN

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Chinese Journal of Polymer Science 2011年第2期29卷 141-148页

作者： m.Ghaemy m.Bazzar h.mighani Faculty of Chemistry University of MazandaranBabolsarIran Department of Chemistry University of GolestanGorganIran

Nanocomposites from nanoscale silica particles（NS）,diglycidylether of bisphenol-A based epoxy（DGEBA）,and 3,5-diamino-N-（4-（quinolin-8-yloxy） phenyl） benzamide（DQPB） as curing agent were obtained from direct blending of these *** effect of nanosilica（NS） particles as catalyst on the cure reaction of DGEBA/DQPB system was studied by using non-isothermal DSC *** activation energy（E_a） was obtained by using Kissinger and Ozawa equations. The E_a value of curing of DGEBA/DQPB/10%NS system showed a decrease of about 10 kJ/mol indicating the catalytic effect of NS particles on the cure *** E_a values of thermal degradation of the cured samples of both systems were 148 kJ/mol and 160 kJ/mol,*** addition of 10%of NS to the curing mixture did not have much effect on the initial decomposition temperature（T_i） but increased the char residues from 20%to 28%at 650℃.

关键词： Thermosets Resins Curing of polymers Thermal properties DSC

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Chinese Physics Letters 2012年第10期29卷 116-119页

作者： m.Erfanian Nakhchi m.R.h.Nobari h.Basirat Tabrizi Department of mechanical Engineering Amirkabir University of Technology15875 TehranIran

Steady non-similarity thermal boundary layer flow over a stretching flat plate is *** velocity and temperature on the surface are assumed to vary with the *** energy equation is solved with the homotopy analysis method which is suitable for strongly non-linear *** approach is more general than the similarity methods and is valid in the whole spatial and temporal *** results are compared with the similarity solutions for special cases of velocity and temperature profiles on the *** effect of different parameters on the Nusselt number and temperature profiles is investigated.

关键词： problems similarity stretching

Parallel propagating modes and anomalous spatial damping in the ultra-relativistic electron plasma with arbitrary degeneracy

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Chinese Physics B 2017年第11期26卷 76-82页

作者： h Farooq m Sarfraz Z Iqbal G Abbas h A Shah Department of Physics Government College University Government College University

The dispersion relations of parallel propagating modes（Langmuir mode, right and left handed circular polarized waves） in the weak magnetic field limit ｜ω-k·v｜〉〉？ are considered for ultra-relativistic arbitrary degenerate electron plasma. The results are presented in terms of moments of Fermi-Dirac distribution. The increase in the electron equilibrium number density from negative large（weakly degenerate） to positive large（highly degenerate） values of μ/Te is observed（where μ is the electron chemical potential and Te is the electron thermal energy）. As a result, shifting of the cutoff points in all the real dispersion branches towards the higher values and increasing in the band gap between unmagnetized longitudinal and transverse modes in k-space are examined. Also, the suppression of the weak magnetic field effects in weakly magnetized right handed and left handed circular polarized waves and a decrease in the longitudinal and transverse screening effects are observed in the graphical patterns due to an increase in the equilibrium number density.

关键词： degenerate Fermi gases relativistic plasmas electromagnetic waves

Is there more than one stickiness criterion?

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Friction 2023年第6期11卷 1027-1039页

作者： Anle WANG martin h.müSER Department of material Science and Engineering Saarland UniversitySaarbrücken66123Germany INm—Leibniz Institute for New materials Saarbrücken66123Germany

Adhesion between an elastic body and a smooth,rigid substrate can lead to large tensile stresses between ***,most macroscopic objects are microscopically rough,which strongly suppresses adhesion.A fierce debate has unfolded recently as to whether local or global parameters determine the crossover between small and large ***,we report simulations revealing that the dependence of the pull-off force Fn on the surface energyγdoes not only have two regimes of high and low adhesion but up to four *** are related to contacts,which at the moment of rupture consist of(i)the last individual hertzian-shaped contact,in which is linear inγ,(ii)a last meso-scale,individual patches with super-linear scaling,(iii)many isolated contact patches with extremely strong scaling,and(iv)a dominating largest contact patch,for which the pull-off stress is no longer negligible compared to the maximum,microscopic pull-off ***(iii)can be seen as a transition *** is located near the point where the surface energy is half the elastic energy per unit area in conformal contact.A criterion for the transition between regimes(i)and(ii)appears difficult to grasp.

关键词： adhesion pull-off force rough contact stickiness