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Chinese Physics B 2010年第1期19卷 366-371页

作者： h.Mehdian s.saviz Department of Physics and Institute for Plasma Research Tarbiat Moallem University Plasma Physics Research Center Science and Research CampusIslamic Azad University

A theory of a two-stream flee-electron laser in a combined electromagnetic wiggler （EMW） is developed, in which we use an axial-guide magnetic field and take into account the effects of the self-fields. The electron trajectories and the small signal gain are derived. The stability of the trajectories, the characteristics of the linear-gain, and the normalised maximum gain are studied numerically. The results show that there are nine stable groups of orbits in the presence of self-fields instead of seven groups reported in the absence of the self-field. It is also shown that the normalised gains of four groups of the orbits are decreasing and those for the rest of them are increasing with growing J20. Furthermore, it is found that the two-stream laser with seff-field enhances the maximum gain in comparison with the single stream case.

关键词： free electron laser two-stream

Design of area and power efficient Radix-4 DIT FFT butterfly unit using floating point fused arithmetic

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Journal of Central south University 2016年第7期23卷 1669-1681页

作者： Prabhu E Mangalam h Karthick s Department of Electronics and Communication Engineering Amrita School of EngineeringCoimbatore Amrita Vishwa Vidyapeetham Amrita University Department of Electronics and Communication Engineering Sri Krishna College of Engineering and Technology Department of Electronics and Communication Engineering Bannari Amman Institute of Technology

In this work, power efficient butterfly unit based FFT architecture is presented. The butterfly unit is designed using floating-point fused arithmetic units. The fused arithmetic units include two-term dot product unit and add-subtract unit. In these arithmetic units, operations are performed over complex data values. A modified fused floating-point two-term dot product and an enhanced model for the Radix-4 FFT butterfly unit are proposed. The modified fused two-term dot product is designed using Radix-16 booth multiplier. Radix-16 booth multiplier will reduce the switching activities compared to Radix-8 booth multiplier in existing system and also will reduce the area required. The proposed architecture is implemented efficiently for Radix-4 decimation in time(DIT) FFT butterfly with the two floating-point fused arithmetic units. The proposed enhanced architecture is synthesized, implemented, placed and routed on a FPGA device using Xilinx IsE tool. It is observed that the Radix-4 DIT fused floating-point FFT butterfly requires 50.17% less space and 12.16% reduced power compared to the existing methods and the proposed enhanced model requires 49.82% less space on the FPGA device compared to the proposed design. Also, reduced power consumption is addressed by utilizing the reusability technique, which results in 11.42% of power reduction of the enhanced model compared to the proposed design.

关键词： floating-point arithmetic floating-point fused dot product Radix-16 booth multiplier Radix-4 FFT butterfly fast fouriertransform decimation in time

Nanocrystallization of α-Fe Crystals in Fe_(52)Cr_(18)Mo_7B_(16)C_4Nb_3 Bulk Amorphous Alloy

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Journal of Materials science & Technology 2011年第6期27卷 497-502页

作者： s. Ahmadi h.R. shahverdi s.s. saremi Faculty of Engineering Department of Materials Science Tarbiat Modares University

Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated by X-ray diffraction（XRD）,differential scanning calorimetric（DsC） tests and transmission electron microscopy（TEM） observations in this research *** effect,crystallization and growth mechanism were investigated by using DsC tests at four different heating rates（10,20,30,40 K/min）.Results showed that a two-step crystallization process occurred in the alloy in which α-Fe and Fe3B phases were crystallized,respectively in the structure after heat *** energy for the first step of crystallization,i.e.α-Fe was measured to be 421 and 442 kJ/mol according to Kissinger-starink and Ozawa models,***,Avrami exponent calculated from DsC curves was 1.6 and a two-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was observed in the ***,it was known from the TEM observations that crystalline α-Fe phase nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

关键词： Bulk metallic glasses (BMGs) structural amorphous steels (sAss) Avrami exponent Crystallization and kinetic models

self-propagating high temperature synthesis of Mosi_2 matrix composites

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Rare Metals 2006年第3期25卷 225-230页

作者： Akhtar Farid s.h. Islam Materials science and Engineering school State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

Mosi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. Mosi2 and Mosi2 matrix composites were prepared by self-propagating high temperature synthesis （shs）. Pure Mosi2 was obtained and a compound of Mosi2 and Wsi2was synthesized in the form of predominant solid solution （Mo,W）si2. By adding aluminum of 5.5 at.% to Mo-si, the crystal structure of Mosi2 changed into a mixture of tetragonal Cllb Mosi2and hexagonal C40 Mo（si,Al）2. The （Mo,W）si2-Mo（si,Al）2-W（si,Al）2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-si. however, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. shs is an effective technology for synthesis of Mosi2 and Mosi2 matrix composites.

关键词： powder metallurgy Mosi2 matrix composites self-propagating high temperature synthesis molybdenumtungsten disilicide molybdenum aluminosilicide

Momentum Transport in DIII-D Discharges with and Without Magnetohydrodynamics （MhD） Activity

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Plasma science and Technology 2009年第1期11卷 127-130页

作者：任启龙 M. s. ChU L. L. LAO h. st. JOhN R. LAhAYE Y. M. jeon 张澄周登李国强 J. M. PARK J. s. DEGRAssIE Institute of Plasma Physics Chinese Academy of Sciences Hefei 230031 China General Atomics San Diego CA USA Oak Ridge Institute for science and Education Oak Ridge TN USA Oak Ridge National Laboratory Oak Ridge TN USA

Two phases of a DIII-D discharge with and without magnetohydrodynamics （MhD） activity are analysed using ONETWO code. The toroidal momentum flux is extracted from experimental data and compared with the predictions by neoclassical theory, Gyro-Landau fluid transport model （GLF23） and Multi-Mode model （MMM95）. It is found that without MhD activities GLF23 and MMM95 provide a reasonable description while with MhD activity no model alone can fully describe the experimental momentum flux. For the phase with MhD activity a simple model of resonant magnetic drag is tested and it cannot fully explain the plasma slowing down observed in experiment.

关键词： toroidal rotation MhD activity magnetic drag

Effects of Nb Alloying on Nano-Crystallization Kinetics of Fe_(55-x)Cr_(18)Mo_7B_(16)C_4Nb_x(x=0, 3) Bulk Amorphous Alloys

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Journal of Materials science & Technology 2011年第8期27卷 735-740页

作者： s. Ahmadi h.R. shahverdi s.s. saremi Faculty of Engineering Department of Materials Science Tarbiat Modares University

Crystallization kinetics of Fe55-xCrzsMo7B10C4Nbx（x= 0, 3） bulk amorphous alloys were analyzed using X-ray diffraction and differential scanning; calorimetric （DsC） tests. In practice, crystallization and growth mechanism were evaluated using DsC tests at four different heating rates （10, 20, 30, and 40 K/rain） and kinetic models. Two-step crystallization behavior was observed when Fe55Cr18MOTB16C4 and Fe52Cr18MoTB16C4Nb3 bulk amorphous alloys were annealed, where Fe36Cr12M010 phase was crystallized in the first step of crystallization. Results show that Fe36Cr12Mo10 and Fe3C phases were crystallized in the structures of the alloys after further annealing： process. Activation energy for the crystallization of Fe36Cr12Mozo phase was measured to be 543 kJ/mol in Fe52Cr18MoTB16C4Nb3 alloy and 375 kJ/mol for Fe55Cr18Mo7B16C4 alloy according to Kissinger-starink model. Moreover, a two-dimensiona nucleation rate was found in Fe52Cr18Mo7B16C4Nb3 diffusion controlled growth mechanism with decreasing alloy whereas a three-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in crystallization of Fe36Crz2Mo10 phase during annealing of Fe55Cr18MoTB16C4 alloy. TEM （transmission electron microscopy） observations reveal that crystalline Fe36Cr12M010 phase nucleated in the structures of the alloys in an average size of 10 nm with completely mottled morphology.

关键词： Avrami exponent Crystallization Kinetic models Growth mechanisms Bulk amorphous alloys

Optimal design of V-type ultrasonic motor

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Journal of Central south University 2010年第6期17卷 1247-1250页

作者： jeonG s s PARK C h PARK T G school of Mechatronics Changwon National UniversityChangwon 641773Korea

V-type ultrasonic linear motor fabricated using a simple punching technique was proposed to utilize as an actuator of small precision *** stator of the motor is composed of a thin elastic body and four ceramics attached to the upper and bottom areas of the *** ceramics have each direction of *** two harmonic voltages with a 90° phase difference are applied to the ceramics,symmetric and anti-symmetric displacements will generate at the tip to produce an elliptical motion.A finite element analysis(ATILA) was conducted to simulate the motion pattern for the contact tip of the *** develop a model that generates the maximum displacement at contact tip,the FEM program was used for various *** addition,an optimal model was chosen by considering the magnitude and shape of the displacement according to changes in *** maximum elliptical displacement is shown by W2L11 model,which has a ratio of ceramic width to length of 1:***,the displacement of the contact tip is reduced by the bucking phenomenon if the ratio is larger than 1:6.

关键词： ultrasonic motor piezo-actuator finite element method optimal design elliptical motion

Electrical features of radio-frequency atmospheric pressure helium discharge with and without dielectric electrodes

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Plasma science and Technology 2019年第2期21卷 60-67页

作者： h AshRAF s Z A shAh h I A QAZI M A KhAN s hUssAIN M A BADAR s NIAZ M shAFIQ Department of Physics University of Sargodha Department of Physics Quaid-i-Azam University

A comparative study of radio-frequency atmospheric pressure glow discharge(rf APGD)generated in helium with and without dielectric electrodes to investigate the effect of electrodes insulation on electrical features of APGD is presented. In the α mode, both the rf APGDs remain volumetric, stable and uniform. In the γ mode, the APGD without dielectric electrodes shrinks into a constricted plasma column whereas APGD with dielectric electrodes remains stable and retains the same volume without plasma constriction even at higher densities of discharge current. A comparison of electrical features of both rf APGDs in normal and abnormal glow discharge regimes is presented. In both APGDs with and without dielectric electrodes,impedance measurements have been performed and compared with equivalent circuit *** measured impedance data is found to be in good agreement with simulated data.

关键词： radiofrequency atmospheric pressure glow discharge dielectric electrodes plasma stability control

Thermal vibration of functionally graded porous nanocomposite beams reinforced by graphene platelets

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Applied Mathematics and Mechanics(English Edition) 2020年第8期41卷 1209-1226页

作者： M.h.YAs s.RAhIMI Department of Mechanical Engineering Razi UniversityKermanshah 67346-67149Iran

The thermal vibration of functionally graded(FG)porous nanocomposite beams reinforced by graphene platelets(GPLs)is *** beams are exposed to the thermal gradient with a multilayer *** temperature varies linearly across the thickness *** different types of dispersion patterns of GPLs as well as porosity distributions are *** material properties vary along the thickness *** using the mechanical parameters of closed-cell cellular solid,the variation of Poisson’s ratio and the relation between the porosity coefficient and the mass density under the Gaussian random field(GRF)model are *** using the halpin-Tsai micromechanics model,the elastic modulus of the nanocomposite is *** equations of motion based on the Timoshenko beam theory are obtained by using hamilton’s *** equations are discretized and solved by using the generalized differential quadrature method(GDQM)to obtain the fundamental *** effects of the weight fraction,the dispersion model,the geometry,and the size of GPLs,as well as the porosity distribution,the porosity coefficient,the boundary condition,the metal matrix,the slenderness ratio,and the thermal gradient are presented.

关键词： thermal vibration functionally graded(FG) porous material graphene platelet(GPL) Timoshenko beam

Flexural-wave-generation using a phononic crystal with a piezoelectric defect

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Applied Mathematics and Mechanics(English Edition) 2023年第8期44卷 1241-1262页

作者： s.h.JO D.LEE Department of Mechanical Roboticsand Energy EngineeringDongguk UniversitySeoul 04620Republic of Korea Department of Mechanical Engineering Seoul National UniversitySeoul 08826Republic of Korea

This paper proposes a method to amplify the performance of a flexural-wave-generation system by utilizing the energy-localization characteristics of a phononic crystal(PnC)with a piezoelectric defect and an analytical approach that accelerates the predictions of such wave-generation *** proposed analytical model is based on the Euler-Bernoulli beam *** proposed analytical approach,inspired by the transfer matrix and s-parameter methods,is used to perform band-structure and time-harmonic analyses.A comparison of the results of the proposed approach with those of the finite element method validates the high predictive capability and time efficiency of the proposed model.A case study is explored;the results demonstrate an almost ten-fold amplification of the velocity amplitudes of flexural waves leaving at a defect-band frequency,compared with a system without the ***,design guidelines for piezoelectric-defect-introduced PnCs are provided by analyzing the changes in wave-generation performance that arise depending on the defect location.

关键词： phononic crystal(PnC) defect wave-generation fexural wave analytical model