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Plasma Science and Technology 2013年第4期15卷 376-381页

作者： ali akbar ASHKARRAN Department of Physics Faculty of Basic Sciences University of MazandaranBabolsar Iran

We report studies on the growth of gold nanoparticles by a seed-mediated approach in solution. The synthetic method is adapted from one we published earlier （Ashkarran et al. Appl. Phys. A 2009, 96, 423）. The synthesized gold nanoparticles were characterized by X-ray diffraction （XRD）, dynamic light scattering （DLS）, UV-Vis spectroscopy, optical imaging and atomic force microscopy （AFM）. Optical absorption spectroscopy of the prepared samples at 15 A arc current in HAuCI4 solution shows a surface plasmon resonance around 520 nm. It is found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. The intensity of the plasmonic peak of the prepared gold nanoparticles for 1 minute arc duration gradually increases due to seed mediation for up to 6 hours. The formation time of gold nanoparticles at higher seed concentrations is less than that at lower seed concentrations.

关键词： gold nanoparticles liquid arc discharge seed mediation optical properties

An extended iterative direct-forcing immersed boundary method in thermo-fluid problems with Dirichlet or Neumann boundary conditions

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Journal of Central South University 2017年第1期24卷 137-154页

作者： ali akbar Hosseinjani ali Ashrafizadeh Faculty of Mechanical Engineering K.N.Toosi University of TechnologyP.O.B.19395-1999 TehranIran

An iterative direct-forcing immersed boundary method is extended and used to solve convection heat transfer *** pressure,momentum source,and heat source at immersed boundary points are calculated simultaneously to achieve the best *** of convection heat transfer problems with both Dirichlet and Neumann boundary conditions are *** approaches for the implementation of Neumann boundary condition,*** and indirect methods,are introduced and compared in terms of accuracy and computational *** test cases include forced convection on a heated cylinder in an unbounded flow field and mixed convection around a circular body in a lid-driven ***,the proposed method is applied to study the mixed convection around a heated rotating cylinder in a square enclosure with both iso-heat flux and iso-thermal boundary *** results show that the order of accuracy of the indirect method is less than the direct ***,the indirect method takes less computational time both in terms of the implementation of the boundary condition and the post processing time required to compute the heat transfer variables such as the Nusselt *** is concluded that the iterative direct-forcing immersed boundary method is a powerful technique for the solution of convection heat transfer problems with stationary/moving boundaries and various boundary conditions.

关键词： immersed boundary method direct forcing thermo-fluid problems neumann boundary condition

Flow Confinement Effects on the Wake Structure behind a Pitching Airfoil： A Numerical Study Using an Immersed Boundary Method

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Journal of Bionic Engineering 2017年第1期14卷 88-98页

作者： ali akbar Hosseinjani ali Ashrafizadeh Faculty of Mechanical Engineering K. N. Toosi University of Technology Tehran P.O.B. 19395-1999 Iran

The flow patterns and wake structures behind a pitching airfoil in an un-bounded domain have been studied extensively. In contrast, the flow phenomena associated with a pitching airfoil near a solid boundary have not been adequately studied or reported. This paper aims at filling this research gap by considering the flow confinement effects on the flow pattern around a pitching airfoil. To achieve this goal, the flow fields around a flapping airfoil in un-bounded, bounded and semi-bounded domains are studied and compared. Numerical simulations are carried out at a fixed Reynolds number, Re = 255, and at a fixed oscillation frequency corresponding to St = 0.22. An accurate immersed boundary method is employed to calculate the unsteady flow fields around the airfoil at various flapping amplitudes. It is argued that two flow mechanisms, here called ＂the interaction effect＂ and ＂the induced reverse flow effect＂ are responsible for the variations of the flow field due to the presence of a nearby solid boundary.

关键词： immersed boundary method pitching airfoil vortex street induced momentum aligned vortex

EFFECT OF POLYANILINE AS A SURFACE MODIFIER OF TiO_2 NANO-PARTICLES ON THE PROPERTIES OF POLYVINYL CHLORIDE/TiO_2 NANOCOMPOSITES

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Chinese Journal of Polymer Science 2013年第3期31卷 481-494页

作者： ali Olad Sepideh Behboudi ali akbar Entezami Polymer Composite Research Laboratory Department of Applied ChemistryFaculty of ChemistryUniversity of Tabriz Polymer Research Laboratory Department of Organic ChemistryFaculty of ChemistryUniversity of Tabriz

Surface of TiO2 nanoparticles was modified with the in situ chemical oxidative polymerization of aniline. Polyaniline modified TiO2 nanoparticles （PANI-TiO2） were characterized with the FT-IR, XRD, SEM and TEM techniques. Results confirmed that PANI was grafted successfully on the surface of TiO2 nanoparticles, therefore agglomeration of nanoparticles decreased dramatically. Polyvinyl chloride nanocomposites filled with 1 wt%-5 wt% of PANI-TiO2 and TiO2 nanoparticles were prepared via the solution blending method. PVC nanocomposites were analyzed with FT-IR, XRD, SEM, TG/DTA, DSC and tensile test techniques. Effect of PANI as surface modifier of nanoparticles was discussed according to the final properties of PVC nanocomposites. Results demonstrated that deposition of PANI on the surface of TiO2 nanoparticles improved the interfacial adhesion between the constituents of nanocomposites, which resulted in better dispersion of nanoparticles in the PVC matrix. Also PVC/PANI-TiO2 nanocomposites showed higher thennal resistance, tensile strength and Young＇s modulus compared to those of unfilled PVC and PVC/TiO2 nanocomposites.

关键词： Polymer nanocomposite Polyvinyl chloride Polyaniline TiO2 nano-additive Surface modification.

Relativistic symmetries in the Hulthn scalar-vector-tensor interactions

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Chinese Physics B 2013年第8期22卷 257-263页

作者： Majid Hamzavi ali akbar Rajabi Department of Science and Engineering Abhar Branch Islamic Azad UniversityAbhar Iran Physics Department Shahrood University of TechnologyShahrood Iran

In the presence of spin and pseudospin （p-spin） symmetries, the approximate analytical bound states of the Dirac equation for scalar-vector-tensor Hulth6n potentials are obtained with any arbitrary spin-orbit coupling number using the Pekeris approximation. The Hulth6n tensor interaction is studied instead of the commonly used Coulomb or linear terms. The generalized parametric Nikiforov-Uvarov （NU） method is used to obtain energy eigenvalues and corresponding wave functions in their closed forms. It is shown that tensor interaction removes degeneracy between spin and p-spin doublets. Some numerical results are also given.

关键词： Dirac equation Hulth6n scalar-vector-tensor potential spin and p-spin symmetry NU method

GIS based ArcPRZM-3 model for bentazon leaching towards groundwater

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Journal of Environmental Sciences 2010年第12期22卷 1854-1859页

作者： Tahir ali akbar Henry Lin College of Natural Resources University of Wisconsin-Stevens Point Department of Civil Engineering Schulich School of EngineeringUniversity of Calgary2500 University Drive NWCalgaryAlbertaT2N 1N4Canada Department of Crop and Soil Sciences The Pennsylvania State UniversityUniversity ParkPA 16802USA

Groundwater contamination due to pesticide applications on agricultural lands is of great environmental concern. The mathematical models help to understand the mechanism of pesticide leaching in soils towards groundwater. We developed a user-friendly model called ArcPRZM-3 by integrating widely used Pesticide Root Zone Model version 3 （PRZM-3） using Visual Basic and Geographic Information System （GIS） based Avenue programming. ArcPRZM-3 could be used to simulate pesticide leaching towards groundwater with user-friendly input interfaces coupled with databases of crops, soils and pesticides. The outputs from ArcPRZM-3 could be visualized in user-friendly formats of tables, charts and maps. In this study we evaluated ArcPRZM-3 model by simulating bentazon leaching in soil towards groundwater. ArcPRZM-3 was applied to 37 sites in Woodruff County, Arkansas, USA to observe the daily average dissolved bentazon concentration for soybean, sorghum and rice at a depth of 1.8 m for a period of two years. Nineteen ranks of bentazon leaching potential were obtained using ArcPRZM-3 for all sites having different soil and crop combinations. ArcPRZM-3 simulation results for bentazon were compatible with the field monitored data in term of relative ranking and trend, although some uncertainties exist. This study indicated that macropore flow mechanism would be important in analyzing the effect of irrigation on groundwater contamination due to pesticides. Overall, ArcPRZM-3 could be used to simulate pesticide leaching towards groundwater more efficiently and effectively as compared to PRZM-3.

关键词： ArcPRZM-3 PRZM-3 GIS pesticide leaching groundwater contamination bentazon

Hot Ductility of Severe Plastic Deformed AA6061 Aluminum Alloy

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Acta Metallurgica Sinica(English Letters) 2015年第3期28卷 322-330页

作者： ali akbar Khamei Kamran Dehghani Mining and Metallurgical Engineering Department Amirkabir University of Technology

The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain *** tensile tests were carried out at the temperature range of 300-500 ℃ and at the strain rates of 0.0005-0.01 s^（-1）.The microstructure evolution was characterized using optical microscopy,transmission electron microscopy and X-ray diffraction *** influences of the microstructure after SPD,thermomechanical parameters（temperature and strain rate） and specimen size on the hot formability of this alloy were then *** results show that a decrease in grains/subgrains exhibited significant effect on the hot ductility of SPDed *** constitutive equations were then developed to model the hot formability of the studied *** developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation *** the changes of elongation to failure and Zener-Hollomon parameter indicate that the hot ductility of the alloy is more sensitive to the temperature rather than to the strain *** uniform elongation is independent of the specimen size,but the postnecking elongation increases dramatically as the ratio of l/A^（1/2） decreases.

关键词： Al-Mg-Si alloy Deformation behavior Equal channel angular pressing(ECAP) Rolling Hot tensile deformation

Soil-Structure Interaction Analysis of Jack-up Platforms Subjected to Monochrome and Irregular Waves

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China Ocean Engineering 2015年第1期29卷 65-80页

作者： Maziar Gholami KORZANI ali akbar AGHAKOUCHAK Faculty of Civil and Environmental Engineering Tarbiat Modares University

As jack-up platforms have recently been used in deeper and harsher waters, there has been an increasing demand to understand their behaviour more accurately to develop more sophisticated analysis techniques. One of the areas of significant development has been the modelling of spudean performance, where the load-displacement behaviour of the foundation is required to be included in any numerical model of the structure. In this study, beam on nonlinear winkler foundation （BNWF） modeling--which is based on using nonlinear springs and dampers instead of a continuum soil media--is employed for this purpose. A regular monochrome design wave and an irregular wave representing a design sea state are applied to the platform as lateral loading. By using the BNWF model and assuming a granular soil under spudcans, properties such as soil nonlinear behaviour near the structure, contact phenomena at the interface of soil and spudcan （such as uplifting and rocking）, and geometrical nonlinear behaviour of the structure are studied. Results of this study show that inelastic behaviour of the soil causes an increase in the lateral displacement at the hull elevation and permanent unequal settlement in soil below the spudcans, which are increased by decreasing the friction angle of the sandy soil. In fact, spudeans and the underlying soil cause a relative fixity at the platform support, which changes the dynamic response of the structure compared with the case where the structure is assumed to have a fixed support or pinned support. For simulating this behaviour without explicit modelling of soil-structure interaction （SSI）, moment- rotation curves at the end of platform legs, which are dependent on foundation dimensions and soil characteristics, are obtained. These curves can be used in a simplified model of the platform for considering the relative fixity at the soil- foundation interface.

关键词： jack-up platforms wave loading nonlinear dynamic analysis soil-structure interaction (SS1) beam on nonlinear winkler foundation (BNWF)

CONTINUOUS FRAME WAVELETS

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Acta Mathematica Scientia 2012年第2期32卷 807-812页

作者： ali akbar Arefijamaal Narguess Tavallaei Department of Mathematics and Computer Science Sabzevar Tarbiat Moallem UniversitySabzevarIran Department of Pure Mathematics School of Mathematics and Computer ScienceDamghan UniversityDamghanIran

Let π be a unitary representation of a locally compact topological group G on a separable Hilbert space H. A vector ψ∈ H is called a continuous frame wavelet if there exist A, B 〉 0 such that A｜｜Ф｜｜2≤fG｜〈π（G）ψ,Ф｜2dg≤B｜｜Ф｜｜2（Ф∈H）,in which dg is the left Haar measure of G. Similar to the study of wavelets, an essential problem in the study of continuous frame wavelets is how to characterize them under the given unitary representation. Moreover, we investigate a relation between admissible vectors of π and its components.

关键词： Locally compact group unitary representation continuous frame wavelettransform direct integral