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mobility of large clusters on a semiconductor surface:Kinetic monte Carlo simulation results

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Chinese Physics B 2016年第1期25卷 580-584页

作者： m Esen A t ttizemen m Ozdemir Vocational School of Adana Cukurova UniversityAdana O1160Turkey Department of Science and mathematics Education Faculty of EducationCumhuriyet UniversitySivas 58140Turkey Department of Physics Cukurova UniversityAdana 01330Turkey

the mobility of clusters on a semiconductor surface for various values of cluster size is studied as a function of temperature by kinetic monte Carlo method. the cluster resides on the surface of a square grid. Kinetic processes such as the diffusion of single particles on the surface, their attachment and detachment to/from clusters, diffusion of particles along cluster edges are considered. the clusters considered in this study consist of 150-6000 atoms per cluster on average. A statistical probability of motion to each direction is assigned to each particle where a particle with four nearest neighbors is assumed to be immobile. the mobility of a cluster is found from the root mean square displacement of the center of mass of the cluster as a function of time. It is found that the diffusion coefficient of clusters goes as D = A（t）Na where N is the average number of particles in the cluster, A（t） is a temperature-dependent constant and a is a parameter with a value of about -0.64 〈 a 〈 -0.75. the value of a is found to be independent of cluster sizes and temperature values （170-220 K） considered in this study. As the diffusion along the perimeter of the cluster becomes prohibitive, the exponent approaches a value of -0.5. the diffusion coefficient is found to change by one order of magnitude as a function of cluster size.

关键词： diffusion constant cluster mobility monte Carlo method

Aphrodisiac potentials of the aqueous extract of Fadogia agrestis(*** Hiern) stem in male albino rats

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Asian Journal of Andrology 2005年第4期7卷 399-404,页

作者： m.t.Yakubu m.A.Akanji A.t.Oladiji medicinal Plants Research Laboratory Department of BiochemistryUniversity of IlorinPMB 1515IlorinNigeria

Aim： to evaluate the phytochemical constituents and the agrestis （Rubiaceae） stem in male albino rats. methods： aphrodisiac potential of the aqueous extract of Fadogia the aqueous stem extract of the plant was screened for phytochemical constituents. male rats were orally dosed with 18 mg/kg, 50 mg/kg and 100 mg/kg body weight, respectively, of the extract at 24 h intervals and their sexual behavior parameters and serum testosterone concentration were evaluated at days 1, 3 and 5. Results： Phytochemical screening revealed the presence of alkaloids and saponins while anthraquinones and flavonoids are weakly present. All the doses resulted in significant increase in mount frequency, intromission frequency and significantly prolonged the ejaculatory latency （P 〈 0.05） and reduced mount and intromission latency （P 〈 0.05）. there was also a significant increase in serum testosterone concentrations in all the groups in a manner suggestive of dose-dependence （P 〈 0.05）. Conclusion： the aqueous extract of Fadogia agrestis stem increased the blood testosterone concentrations and this may be the mechanism responsible for its aphrodisiac effects and various masculine behaviors. It may be used to modify impaired sexual functions in animals, especially those arising from hypotestosteronemia.

关键词： Fadogia agrestis aphrodisiacs sexual behavior testosterone erectile dysfunction

Analytical Determination of Collisionless Sheath Properties for triple Frequency Capacitively Coupled Plasma

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Plasma Science and technology 2015年第2期17卷 141-146页

作者： m.t.RAHmAN m.N.A.DEWAN Department of Electrical and Electronic Engineering Bangladesh University of Engineering and Technology

A triple frequency capacitively coupled plasma （tF-CCP） has been considered to investigate the behavior of the sheath parameters. A self-consistent time-independent collisionless model has been developed. the sheath width and potential are calculated using the present model and compared with those calculated using a single-frequency （SF）, a dual-frequency （DF） and a triple-frequency （tF） model for time independent collisionless cases. the sheath motion and sheath potential are found to be larger compared with those of SF and DF CCPs for an inhomogeneous sheath, and that of tF CCP for a homogeneous sheath. the effects of the source parameters, i.e., current magnitudes, frequencies and phase difference, on the sheath parameters are investigated. the sheath parameters show higher values at higher source currents whereas they decrease with the increase of excitation frequencies. It has also been found that, by the proper choice of source frequencies and phase differences, it is possible to adjust the energy of ions when they hit the electrode.

关键词： capacitively coupled plasma collisionless sheath triple frequency sheath parameters

multi-segmented nanowires for vortex magnetic domain wall racetrack memory

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Chinese Physics B 2023年第12期32卷 582-588页

作者： m Al Bahri m Al Hinaai t Al Harthy Department of Basic Sciences A'Sharqiyah UniversityPost Box 42PC 400IbraOman

A vortex domain wall's(VW) magnetic racetrack memory's high performance depends on VW structural stability,high speed, low power consumption and high storage density. In this study, these critical parameters were investigated in magnetic multi-segmented nanowires using micromagnetic simulation. thus, an offset magnetic nanowire with a junction at the center was proposed for this purpose. this junction was implemented by shifting one portion of the magnetic nanowire horizontally in the x-direction(l) and vertically(d) in the y-direction. the VW structure became stable by manipulating magnetic properties, such as magnetic saturation(m_(4)) and magnetic anisotropy energy(K_(u)). In this case, increasing the values of m_(4) ≥ 800 kA/m keeps the VW structure stable during its dynamics and pinning and depinning in offset nanowires,which contributes to maintenance of the storage memory's lifetime for a longer period. It was also found that the VW moved with a speed of 500 m/s, which is desirable for VW racetrack memory devices. moreover, it was revealed that the VW velocity could be controlled by adjusting the offset area dimensions(l and d), which helps to drive the VW by using low current densities and reducing the thermal-magnetic spin fluctuations. Further, the depinning current density of the VW(J_(d)) over the offset area increases as d increases and l decreases. In addition, magnetic properties, such as the m_(4) and K_(u),can affect the depinning process of the VW through the offset area. For high storage density, magnetic nanowires(multisegmented) with four junctions were designed. In total, six states were found with high VW stability, which means three bits per cell. Herein, we observed that the depinning current density(J_(d)) for moving the VW from one state to another was highly influenced by the offset area geometry(l and d) and the material's magnetic properties, such as the m_(4) and K_(u).

关键词： micromagnetic simulation vortex domain wall racetrack memory multi-segmented magnetic nanowire spin transfer torque

Algebraic treatment of the mIC-Kepler System in Spherical Coordinates

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Chinese Physics Letters 2007年第8期24卷 2173-2176页

作者： m. t. Chefrour Departement de Physique Institut des Sciences Centre Universitaire de Souk-Ahras Souk-Ahras Algerie

the mIC-Kepler system is studied via the milshtein Strakhovenko variant of the so（2,1） Lie algebra. Green＇s function is constructed in spherical coordinates, with the help of the Kustaanheimo Stiefel variables and the generators of the S0（2,1） group. the energy spectrum and the normalized wavefunctions of the bound states are obtained.

关键词： FIELD

the detrimental effect of autofrettage on externally cracked modern tank gun barrels

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Defence technology（防务技术） 2019年第2期15卷 146-153页

作者： m.Perl t.Saley Pearlstone Center for Aeronautical Engineering Studies Department of Mechanical Engineering Ben-Gurion University of the Negev

Overstraining gun tubes has a twofold advantage. First, it enables the increase of the Safe maximum Pressure(SmP) in the tube, resulting in a higher muzzle velocity which extends the gun's range and its projectile kinetic energy. Second, it reduces the tube's susceptibility to internal cracking which prolongs its fatigue life. Unfortunately, autofrettage also bears an inherent detrimental effect as it considerably increases the tensile hoop stress at the outer portion of the barrel's wall, which enhances external cracking of the tube by increasing the prevailing Stress Intensity Factor(SIF). In order to quantify this disadvantageous effect, 3-D mode I SIFs distributions along the front of a single external radial semielliptical crack initiating from the outer surface of an autofrettaged modern gun barrel, overstrained by either the Swage or the Hydraulic autofrettage processes, are evaluated. the analysis is performed by the finite element(FE) method, using singular elements along the crack front. Innovative residual stress fields(RSFs), incorporating the Bauschinger effect for both types of autofrettage are applied to the ***'s [1] RSF is also applied to the tube for comparison reasons. All three RSFs are incorporated in the FE analysis, using equivalent temperature fields, Values for K_(IA)-the SIF resulting from the tensile residual stresses induced by autofrettage are evaluated for: a typical barrel of radii ratio R_o/R_i = 2, crack depth to wall-thickness ratios(a/t = 0.005-0.1),crack ellipticities(a/c = 0.2-1.0),and five levels of Swage,Hydraulic and Hill's autofrettage(e = 40%,60%,70%,80%,and 100%). In total,375 different 3-D cases are analyzed. the analysis demonstrates undoubtedly the detrimental effect of all types of autofrettage in increasing the prevailing effective stress intensity factor of external cracks, resulting in crack initiation enhancement and crack growth rate acceleration which considerably shortens the total fatigue life of the bar

关键词： Gun barrel Swage and hydraulic autofrettage External crack 3-D Finite element

New methodological Approach to Investigation of Kinetics of REE Extraction in Nonstationary Conditions

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Journal of Rare Earths 2007年第4期25卷 385-391页

作者： Kopyrin A A Fomichev A A Afonin m A todd t A Saint-Petersburg Institute of technology Idaho National Laboratory

the influence of periodical oscillations of the temperature on extraction and stripping processes in the extraction systems was studied. two extraction systems were investigated：（1） 6 mol · L^-1 NaNO3-Nd（NO3）3-Pr（NO3）3-tBP kerosene and （2） [Nd（NO3）3 · 3tBP] -[ Pr（NO3）3 · 3tBP] -kerosene - 0.1 mol · L^-1 HNO3. mathematical modeling of the nonstationary membrane extraction has been enhanced by including the dependence of the extraction rate constants on temperature. the values of activation energy for direct and reverse extraction and stripping reactions of Pr and Nd were calculated from experimental temporal dependencies of metal concentration and temperature by solving the reverse kinetics problem using the proposed mathematical model, A series of experiments with periodical oscillations of the temperature on the extraction system for the separation of rare earth elements （REE） using bulk liquid membrane between two extractors were performed. the mathematical model adequately describes the experimental data. the optimization of the extraction process for separation of REE by liquid membrane, under the influence of periodical oscillation of the temperature, was made based on the extraction rate constants and activation energies. the optimal conditions of separation by liquid membrane were found： frequency and amplitude of thermal oscillations, liquid membrane flow rate, and optimal ratio between organic and aqueous phase in extractors.

关键词： kinetics extraction non-stationary rare earths

Influence of residual stresses on failure pressure of cylindrical pressure vessels

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Chinese Journal of Aeronautics 2013年第6期26卷 1415-1421页

作者： m.Jeyakumar t.Christopher Department of mechanical Engineering Sardar Raja College of EngineeringAlangulamTirunelveli 627 808India Department of mechanical Engineering Government College of EngineeringTirunelveli 627 007India

the utilization of pressure vessels in aerospace applications is *** this work,fnite element analysis（FEA）has been carried out using ANSYS software package with 2D axisymmetric model to access the failure pressure of cylindrical pressure vessel made of AStm A36 carbon steel having weld-induced residual *** fnd out the effect of residual stresses on failure pressure,frst an elasto-plastic analysis is performed to fnd out the failure pressure of pressure vessel not having residual *** a thermo-mechanical fnite element analysis is performed to assess the residual stresses developed in the pressure vessel during *** one more elasto-plastic analysis is performed to assess the effect of residual stresses on failure pressure of the pressure vessel having residual *** analysis indicates reduction in the failure pressure due to unfavorable residual stresses.

关键词： Aerospace engineering AStm A36 Finite element analysis Pressure vessels Welding residual stress

A Flexible Fin with Bio-Inspired Stiffness Profile and Geometry

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Journal of Bionic Engineering 2011年第4期8卷 418-428页

作者： t. Salumae m. Kruusmaa Centre for Biorobotics Tallinn University of Technology Akadeemia tee 15A-111 12618 Tallinn Estonia

Biological evidence suggests that fish use mostly anterior muscles for steady swimming while the caudal part of the body is passive and, acting as a carrier of energy, transfers the momentum to the surrounding water. Inspired by those findings we hypothesize that certain swimming patterns can be achieved without copying the distributed actuation mechanism of fish but rather using a single actuator at the anterior part to create the travelling wave. to test the hypothesis a pitching flexible fin made of silicone rubber and silicone foam was designed by copying the stiffness distribution profile and geometry of a rainbow trout. the kinematics of the fin was compared to that of a steadily swimming trout. Fin＇s propulsive wave length and tail-beat am- plitude were determined while it was actuated by a single servo motor. Results showed that the propulsive wave length and tail-beat amplitude of a steadily swimming 50 cm rainbow trout was achieved with our biomimetic fin while stimulated using certain actuation parameters （frequency 2.31 Hz and amplitude 6.6 degrees）. the study concluded that fish-like swimming can be achieved by mimicking the stiffness and geometry of a rainbow trout and disregarding the details of the actuation mechanism.

关键词： biomimetics stiffness profile fin robotics fish