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Cross-focusing of two chirped Gaussian laser beams and THz wave generation in plasmas of multi-ion species under a weakly relativistic and ponderomotive regime

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Plasma Science and Technology 2022年第10期24卷 1-11页

作者： m R jafari mILANI S REZAEI m J jafari Photonics and Quantum Technologies Research School Nuclear Science and Technology Research InstituteTehran 14665-678Iran Plasma and Fusion Research School Nuclear Science and Technology Research InstituteTehran 14399-51113Iran

The generation of terahertz(THz)waves via the beating of two high-intensity chirped Gaussian lasers in a multi-ion-species plasma is numerically studied by taking into account the weak relativistic and ponderomotive regime of *** coupled differential equations for beamwidth parameters are extracted by introducing the dielectric function of such plasma and using WkB and paraxial ray *** amplitude of THz radiation at beat frequency resulting from the nonlinear current density induced by the beat ponderomotive force of the cross-focusing of beams was *** impacts of the chirp frequency parameter,initial laser intensity and initial ionic species density(specifically,the presence of singly and doubly charged ions)in the plasma on THz generation were *** numerical results reveal that THz radiation generation strongly depends on the chirp frequency parameter.A specific range of chirp frequencies exists for self-focusing as well as THz generation with a'turning point',where the THz emission reaches its maximum *** results show that the strength of self-focusing and consequently the generated THz radiation are reduced by increasing the density of doubly charged ionic species in the plasma due to the suppression of the nonlinear effects.

关键词： laser–plasma interaction THz generation chirped Gaussian laser beams

Hygroelasticity analysis of an elastically restrained functionally graded porous metamaterial circular plate resting on an auxetic material circular plate

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Applied mathematics and mechanics(English Edition) 2020年第9期41卷 1359-1380页

作者： A.BEHRAVAN-RAD m.jafari Faculty of mechanical and mechatronics Engineering Shahrood University of TechnologyShahrood ***Iran

The main objective of this research is to investigate the hygroelastic behavior of a non-homogeneous circular plate made up of porous metamaterial resting on an auxetic material *** mechanical properties of the main plate,as well as moisture concentration,vary as an exponential function in the transverse ***’s ratio is *** elastic supporting medium is developed by considering the structurestructure *** on the linear hygroelasticity theory,the governing state equations in terms of displacements and moisture concentration are *** first,the Fickian equation is solved to compute the nonlinear distribution of moisture through the plate thickness,and then the state equations are semi-analytically solved using the statespace(SS)method and the differential quadrature(DQ)rule to predict the elastic field quantities.A comprehensive parametric analysis is accomplished to elucidate the effects of key parameters on the steady-state response of the plate under the mechanical and hygral loads.

关键词： metamaterial hygroelasticity auxeticity hygral interaction

Comparison between the methods of Determining the Critical Stress for Initiation of Dynamic Recrystallization in 316 Stainless Steel

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Journal of materials Science & Technology 2008年第6期24卷 840-844页

作者： m.jafari A.Najafizadeh Department of materials Engineering Isfahan University of TechnologyIsfahanIran

Several methods have been proposed to calculate the critical stress for initiation of dynamic recrystallization （σc） on the basis of mathematical methods. One＇ of them is proposed by Stewart et al. in which this critical point appears as a distinct minimum in the （-dθ/dσ vs σ） through differentiating from θ vs σ. Another one is presented by Najafizadeh and Jonas by modifying the Poliak and Jonas method. According to this method, the strain hardening rate was plotted against flow stress, and the value of σc was attained numerically from the coefficients of the third-order equation that was the best fit from the experimental θ-σ data. Hot compression tests were used in the range of 1000 to 1100℃ with strain rates of 0.01^-1 s^-1 and strain of I on 316 stainless steel. The result shows that Najafizadeh and Jonas method is simpler than the previous one, and has a good agreement with microstructures. Furthermore, the value of normalized critical stress for this steel was obtained uc=σc/σp=0.92.

关键词： Dynamic recrystallization Critical stress Strain hardening rate

INVESTIGATION OF THE THICkNESS VARIABILITY AND mATERIAL HETEROGENEITY EFFECTS ON FREE VIBRATION OF THE VISCOELASTIC CIRCULAR PLATES

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Acta mechanica Solida Sinica 2013年第1期26卷 83-98页

作者： m.Shariyat A.A.jafari m.m.Alipour Faculty of mechanical Engineering K.N.Toosi University of Technology

The present study deals with free vibration analysis of variable thickness viscoelastic circular plates made of heterogeneous materials and resting on two-parameter elastic foundations in addition to their edge conditions. It is assumed that the viscoelastic material properties vary in the transverse and radial directions simultaneously. The complex modulus approach is employed in conjunction with the elastic-viscoelastic correspondence principle to obtain the solution. The governing equations are solved by means of a power series solution. Finally, a sensitivity analysis including evaluation of effects of various edge conditions, thickness variations, coefficients of the elastic foundation, and material loss factor and heterogeneity on the natural frequencies and modal loss factors is accomplished.

关键词： viscoelastic variable thickness circular plate natural frequencies elastic foundation material heterogeneity power series solution

Laser-Plasma Interaction in Presence of an Obliquely External magnetic Field:Application to Laser Fusion without Radioactivity

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Communications in Theoretical Physics 2016年第8期65卷 237-243页

作者： m.mobaraki S.jafari Department of Physics University of Guilan

In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic field has been studied. Imposing an external magnetic field on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen–Boron(HB) fuel,the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle(from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.

关键词： laser-plasma interaction external magnetic field laser fusion HB fuel

Novel Nanostructured mnO_2 Prepared by Pulse Electrodeposition:Characterization and Electrokinetics

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Journal of materials Science & Technology 2008年第6期24卷 857-862页

作者： H.Adelkhani m.Ghaemi S.m.jafari Department of Chemistry School of SciencesTarbiat Modares UniversityP.O.Box 14115-175TehranIran Department of Chemistry Science FacultyGolestan UniversityP.O.Box 49138-15739GorganIran Department of mathematics Science FacultyGolestan UniversityGorganIran

Pulse current technique was applied for the preparation of novel electroactive manganese dioxide and possible influences of different electrokinetic phenomena on material characteristics were discussed. The characterizations of pulse deposited sample （pcmD） were carried out by different techniques： Fourier transform infrared spectroscopy （FTIR）, scanning electron microscopy （SEm）, X-ray diffraction （XRD）, Brunauer-Emmett-Teller （BET） method, Raman spectroscopy, and atomic force microscopy （AFm）. SEm image revealed that pulse current could improve the current distribution. This was confirmed by AFm images showing a decrease in surface roughness of pcmDs in comparison to amorphous samples, which were deposited by direct current （dcmD）. Higher distortion of mnO6 octahedral environment of dcmD was detected by FTJR and Raman spectroscopy. Cyclic voltammetric （CV） measurements showed a generally higher energy level drained from the second electron discharge of pcmD. This is mainly attributed to a higher surface area and a lower diffusion pass of electrons and protons arisen via a rather unique nanostructural arrangement of pcmD grains. Results indicate a higher surface area available for the non homogenous second electron discharge of pcmD grains.

关键词： manganese dioxide Pulse electrodeposition Nano-structures Electrocrystallization

Characterization and magnetic Properties of Nickel Ferrite Nanoparticles Prepared by Ball milling Technique

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Chinese Physics Letters 2010年第12期27卷 150-153页

作者： G. Nabiyouni m. jafari Fesharaki m. mozafari J. Amighian Department of Physics Faculty of Science Arak University Arak 38156-8-8349 Iran Department of Physics Faculty of Science Isfahan University Isfahan Iran

Nickel ferrite nanoparicles with various grain sizes are synthesized using annealing treatment followed by ball milling of its bulk component materials. Commercially available nickel and iron oxide powders are first mixed, and then annealed at 1100~C in an oxygen environment furnace and for 3h. The samples are then milled for different times in an SPEX mill. X-ray diffraction pattern indicates that in this stage the sample is single phase. The average grain size is estimated by scanning electron microscopy （SEm） and x-ray diffraction techniques. magnetic behavior of the sample at room temperatm＇e is studied using a superconducting quantum interference device （SQUID）. The Curie temperature of the powders is measured by an LCR meter unit. The x-ray diffraction patterns clearly indicate that increasing the milling time leads to a decrease in the grain size and consequently leads to a decrease in the saturation magnetization as well as the Curie temperatures. This result is attributed to the spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core.

关键词： Condensed matter: structural, mechanical & thermal Nanoscale science and low-D systems

Lattice Boltzmann method and RANS approach for simulation of turbulent flows and particle transport and deposition

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Particuology 2017年第1期15卷 62-72页

作者： H. Sajjadi m. Salmanzadeh G. Ahmadi S. jafari Department of mechanical Engineering Shahid Bahonar University ofKerman Kerrnan lran Department of mechanical and Aeronautical Engineering Clarkson University Potsdam NY USA Department of Petroleum Engineering Shahid Bahonar University ofKerrnan Kerman lran

Using the lattice-Boltzmann computational approach in conjunction with the Reynolds averaged Navier-Stokes （RANS） model, several turbulent flows and the transport and deposition of particles in different passages were studied. The new lattice Boltzmann method （LBm） solved the RANS equations coupled with the standard and renormalization group k-E turbulence models. In particular, the LBm formulation was augmented by the addition of two transport equations for the probability distribution function of populations of k and 8. The discrete random walk model was used to generate the instanta- neous turbulence fluctuations. For turbulent channel flows, the analytical fits to the root mean-square velocity fluctuations obtained by the direct numerical simulation of the turbulent flow were used in the analysis. Attention was given to the proper evaluation of the wall normal turbulent velocity fluctuations particularly near the wall. The simulation results were compared with the available numerical simulation and experimental data. The new LBm-RANS model is shown to provide a reasonably accurate description of turbulent flows and particle transport and deposition at modest computational cost.

关键词： Lattice Boltzmann method Reynolds averaged Navier-Stokes Renormalization group model k-ε model Particle transport and deposition

Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy

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Acta metallurgica Sinica(English Letters) 2009年第6期22卷 401-407页

作者： H. jafari m.H. Idris A. Ourdjini G. Payganeh Department of materials Engineering Faculty of Mechanical EngineeringUniversiti Teknologi Malaysia Department of materials Engineering Faculty of Mechanical EngineeringShahid Rajaee Teacher Training University Department of materials Engineering Faculty of Mechanical Engineering Shahid Rajaee Teacher Training University

Due to their high specific strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two different thermomechanical treatments （TmTs）. For the first TmT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃and 250 ℃ for 3, 9 and 25 h. In the second TmT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of fine β-phase （mglTA112） in the alloy matrix. The results also reveal that, the best hardness from the first TmT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TmT, aging at 250 ℃ exhibited the best hardness values.

关键词： Thermomechanical treatment magnesium alloys Cold work Aging AZ63