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Preparation and Structural Properties of ZnAl_xFe_2-xO₄ Spinel Oxide

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American Journal of Analytical Chemistry 2016年第2期7卷 203-209页

作者： Shahzad Hossain Goutam Dev Mst. Sanjida Aktar Muhammad Kamrul Hasan A. K. M. Zakaria Tapash Kumar Datta imtiaz kamal Sk. Md. Yunus Md. Habibul Ahsan Abul Kalam Azad Institute of Nuclear Science & Technology Bangladesh Atomic Energy Commission Dhaka Bangladesh Faculty of Integrated Technologies Universiti Brunei Darussalam Gadong Brunei Darussalam Department of Physics Shahjalal University of Science and Technology Sylhet Bangladesh

The ZnAlxFe2-xO4 (x = 0.0, 0.2 and 0.4) spinel ferrites were prepared by the conventional solid state reaction in air at 1350°C. The X-ray diffraction of all the three samples showed sharp Bragg peaks indicating the formation of a single phase spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using the Nelson-Riley extrapolation method. The lattice parameters, cation distribution and oxygen position parameters have also been determined by refining the data by the Rietveld method. Rietveld refinement of the XRD data reveals all the samples to possess cubic symmetry corresponding to the space group Fd3m. Lattice parameters were found to decrease with increasing Al concentration, i.e. 8.4322, 8.4002, and 8.3984 Åfor x = 0.0, 0.2 and 0.4, respectively.

关键词： Polycrystalline Ferrite X-Ray Diffraction Spinel Ferrite Rietveld Refinement Space Group Fd3m Lattice Parameter

An Effective Runge-Kutta Optimizer Based on Adaptive Population Size and Search Step Size

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Computers, Materials & Continua 2023年第9期76卷 3443-3464页

作者： Ala Kana imtiaz Ahmad Department of Computer Engineering College of Engineering and PetroleumKuwait UniversityKuwait CityKuwait

A newly proposed competent population-based optimization algorithm called RUN,which uses the principle of slope variations calculated by applying the Runge Kutta method as the key search mechanism,has gained wider interest in solving optimization ***,in high-dimensional problems,the search capabilities,convergence speed,and runtime of RUN *** work aims at filling this gap by proposing an improved variant of the RUN algorithm called the *** size plays a vital role in both runtime efficiency and optimization effectiveness of metaheuristic *** the original RUN where population size is fixed throughout the search process,Adaptive-RUN automatically adjusts population size according to two population size adaptation techniques,which are linear staircase reduction and iterative halving,during the search process to achieve a good balance between exploration and exploitation *** addition,the proposed methodology employs an adaptive search step size technique to determine a better solution in the early stages of evolution to improve the solution quality,fitness,and convergence speed of the original ***-RUN performance is analyzed over 23 IEEE CEC-2017 benchmark functions for two cases,where the first one applies linear staircase reduction with adaptive search step size(LSRUN),and the second one applies iterative halving with adaptive search step size(HRUN),with the original *** promote green computing,the carbon footprint metric is included in the performance evaluation in addition to runtime and *** results based on the Friedman andWilcoxon tests revealed that Adaptive-RUN can produce high-quality solutions with lower runtime and carbon footprint values as compared to the original RUN and three recent ***,with its higher computation efficiency,Adaptive-RUN is a much more favorable choice as compared to RUN in time stringent applications.

关键词： Optimization Runge Kutta(RUN) metaheuristic algorithm exploration exploitation population size adaptation adaptive search step size

Partial slip effects in flow over nonlinear stretching surface

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Applied Mathematics and Mechanics(English Edition) 2015年第11期36卷 1513-1526页

作者： T.HAYAT M.imtiaz A.ALSAEDI Department of Mathematics Quaid-i-Azam University 45320Islamabad 44000 Pakistan Department of Mathematics Faculty of Science King Abdulaziz University

The two-dimensional flow of a viscous nanofluid is investigated. The flow is caused by a nonlinear stretching surface with the slip effects of the velocity, the temperature, and the concentration. The fluid is electrically conducted in the presence of an applied magnetic field. Appropriate transformations reduce the nonlinear partial differential system to an ordinary differential system. The convergent solutions of the governing nonlinear problems are computed. The results of the velocity, the temperature, and the concentration fields are calculated in series forms. The effects of the different parameters on the velocity, the temperature, and the concentration profiles are shown and analyzed. The skin friction coefficient, the Nusselt number, and the Sherwood number are also com-puted and investigated for different embedded parameters in the problem statements.

关键词： magnetohydrodynamic (MHD) nanofluid nonlinear stretching sheet slipeffect

Boundary layer flow of Oldroyd-B fluid by exponentially stretching sheet

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Applied Mathematics and Mechanics(English Edition) 2016年第5期37卷 573-582页

作者： T.HAYAT M.imtiaz A.ALSAEDI Department of Mathematics Quaid-i-Azam University Department of Mathematics Faculty of Science King Abdulaziz University

The present paper investigates the steady flow of an Oldroyd-B fluid. The fluid flow is induced by an exponentially stretched surface. Suitable transformations reduce a system of nonlinear partial differential equations to a system of ordinary dif- ferential equations. Convergence of series solution is discussed explicitly by a homotopy analysis method （HAM）. Velocity, temperature and heat transfer rates are examined for different involved parameters through graphs. It is revealed that for a larger retardation time constant, the velocity is enhanced and the temperature is lowered. It is noted that relaxation time constant and the Prandtl number enhance the heat transfer rate.

关键词： Oldroyd-B fluid homotopy analysis method (HAM) exponentially stretch-ing sheet

Fundamental problem in optimizing the biaxial testing specimen

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Science China(Technological Sciences) 2019年第5期62卷 773-780页

作者： imtiaz Haroon FANG YaoPeng DU JianBin LIU Bin Department of Engineering Mechanics Applied Mechanics Lab Tsinghua University

Most of the elements in structural design are subjected to the complex loading conditions that need to be predicted in advance for a reliable design. The failure prediction of these structural elements is based on the failure theories that employ the experimental data of the uniaxial, the biaxial and the shear tests. Among these tests, the biaxial testing is used to model the behavior of the structure loaded in more than one direction. In this study, we discover an interesting fact for the biaxial tension specimen that the thickness reduction of the measuring region cannot increase the stress to a high level. This behavior of the biaxial testing is different from the uniaxial testing where the thickness reduction of the measuring region always increases its stress to a higher level. Therefore, we further investigate the biaxial testing specimen via related fundamental problem, i.e., an axisymmetric plate with varying thickness under axisymmetric tension. We perform the shape optimization based on our analytical solution and the FEM results. For an infinite axisymmetric disk, the optimized design should include a low slope diverging section connecting the inner to outer region. On the contrary, the larger inner measuring region for finite axisymmetric disk would result in higher corresponding stress. These conclusions can be used as a guideline for the design of a biaxial testing specimen.

关键词： uniaxial testing biaxial testing axisymmetric disk problem optimization

Longitudinal and transverse structure functions in decaying nearly homogeneous and isotropic turbulence

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Chinese Physics B 2014年第1期23卷 272-278页

作者： imtiaz Ahmad 卢志明刘宇陆 Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai 200072 China Department of Mathematics University of Azad Jammu and Kashmir Muzaffarabad 13100 Pakistan

Streamwise evolution of longitudinal and transverse velocity structure functions in a decaying homogeneous and nearly isotropic turbulence is reported for Reynolds numbers Reλ up to 720. First, two theoretical relations between longitudinal and transverse structure functions are examined in the light of recently derived relations and the results show that the low-order transverse structure functions can be well approximated by longitudinal ones within the sub-inertial range. Reconstruction of fourth-order transverse structure functions with a recently proposed relation by Grauer et al. is comparatively less valid than the relation already proposed by Antonia et al. Secondly, extended self-similarity methods are used to measure the scaling exponents up to order eight and the streamwise evolution of scaling exponents is explored. The scaling exponents of longitudinal structure functions are, at first location, close to Zybin's model, and at the fourth location, close to She–Leveque model. No obvious trend is found for the streamwise evolution of longitudinal scaling exponents, whereas, on the contrary, transverse scaling exponents become slightly smaller with the development of a steamwise direction. Finally, the stremwise variation of the order-dependent isotropy ratio indicates the turbulence at the last location is closer to isotropic than the other three locations.

关键词： fully developed turbulence longitudinal and transverse structure functions scaling exponents intermittency

Detrended analysis of Reynolds stress in a decaying turbulent flow in a wind tunnel with active grids

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Journal of Hydrodynamics 2014年第1期26卷 122-128页

作者： AHMAD imtiaz 黄永祥卢志明 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Department of Mathematics University of Azad Jammu and Kashmir Shanghai Institute of Applied Mathematics and Mechanics and Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University

Multi-scale properties of Reynolds stress in decaying turbulence in a wind tunnel with high Reynolds number are investi-gated. Two filtering techniques i.e., the zeroth-order and first-order detrending methods are applied to the two velocity components, where the local mean value （resp. local linear trend） is removed in the former （latter） technique. Some basic statistics for thirty mea-surements show that the variation is very large at first two locations and relatively small at last two locations. Moderately good power law is found for the mean value of local Reynolds stress at last three measurement locations with scaling exponents approxi-mately being 1.0 and a dual power law exists for the mean value of standard deviation of local Reynolds stress at all four measureme-nt locations with scaling exponents being 0.53 and 0.58 for zeroth-and first-order filtering respectively. Present results about local Reynolds stress are useful to build and evaluate the model of sub-grid Reynolds stress in large eddy simulations.

关键词： Reynolds stress multi-scale analysis detrended analysis power law

Effects of homogeneous-heterogeneous reactions in flow of Powell-Eyring fluid

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Journal of Central South University 2015年第8期22卷 3211-3216页

作者： T.Hayat M.imtiaz A.Alsaedi Department of Mathematics Quaid-I-Azam University NAAM Research Group Department of Mathematics Faculty of ScienceKing Abdulaziz University

The steady two-dimensional flow of Powell-Eyring fluid is investigated. The flow is caused by a stretching surface with homogeneous-heterogeneous reactions. The governing nonlinear differential equations are reduced to the ordinary differential equations by similarity transformations. The analytic solutions are presented in series forms by homotopy analysis method(HAM). Convergence of the obtained series solutions is explicitly discussed. The physical significance of different parameters on the velocity and concentration profiles is discussed through graphical illustrations. It is noticed that the boundary layer thickness increases by increasing the Powell-Eyring fluid material parameter(ε) whereas it decreases by increasing the fluid material parameter(δ). Further, the concentration profile increases when Powell-Eyring fluid material parameters increase. The concentration is also an increasing function of Schmidt number and decreasing function of strength of homogeneous reaction. Also mass transfer rate increases for larger rate of heterogeneous reaction.

关键词： Powell-Eyring fluid boundary layer flow stretching sheet homogeneous-heterogeneous reactions

A comprehensive physical insight about thermo physical aspects of Carreau fluid flow over a rotated disk of variable thickness by implementing finite difference approach

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Propulsion and Power Research 2022年第1期11卷 143-153页

作者： Sardar Bilal imtiaz Ali Shah Department of Mathematics AIR UniversityP.A.F ComplexSector E-9P.O.44000IslamabadPakistan

Present communication is devoted to analyze thermal characteristics of Carreau liquid flowing on variably thickened non-uniformly rotating *** formulation is constructed in view of complex coupled partial differential ***,boundary layer approach is executed for comprehensive examination of under consideration phenomenon with in boundary layer ***’s transformation is capitalized to convert the attained PDE’s into ordinary differential equations *** of attained ODE’s system is solved numerically by implementing Keller-Box *** of protuberant involved parameters on momentum and thermal distributions is illustrated through *** addition,impact of flow concerning parameters on wall shear stress and thermal flux is also *** assurance of present finding is done by making agreement with published results and by restricting considered problem to Newtonian ***,we observed that radially and tangentially directed wall drag lessen with growing magnitude of power law exponent ***,the consequence of disk thickness parameter grows stresses along radial direction whereas opposite behavior is depicted in case of tangentially directed friction and heat flux factors.

关键词： Carreau viscosity model Rotating disk Non-uniform thickness Keller-Box method