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The influence of surface effects on Frederiks transition in nematic liquid crystal doped with ferroelectric nanoparticles

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Chinese Physics B 2018年第4期27卷 357-362页

作者： erfan Kadivar Mojtaba Farrokhbin Department of Physics Shiraz University of Technology Department of Physics Faculty of SciencesYazd University

Motivated by our recent work,in this work,we present the numerical study of the anchoring effect on the Frederiks threshold field in a nematic liquid crystal doped with ferroelectric colloidal *** weak anchoring conditions,we employ the relaxation method and Maxwell construction to numerically solve the Euler–Lagrangian differential equation for the total free energy together the Rapini–Papoular surface energy to take into account anchoring of nematic liquid crystal molecules at the *** this study,we focus our attention on obtaining the phase diagrams of Frederiks transition for different values of anchoring strength which have been not computed in our previous *** this way,the effect of nanoparticle radius,nanoparticle volume fraction,nanoparticle polarization,and cell thickness on the Frederiks transition for different values of anchoring conditions are summarized in the phase *** numerical results show that by increasing the nanoparticles size and nanoparticle volume fraction in the ferronematic system,the Frederiks threshold field is strongly reduced.

关键词： anchoring surface effect ferronematics Frederiks transition Maxwell construction

Leader-following consensus of discrete-time fractional-order multi-agent systems

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Chinese Physics B 2018年第1期27卷 314-321页

作者： erfan Shahamatkhah Mohammad Tabatabaei Department of Electrical Engineering Khomeinishahr Branch Islamic Azad University

Leader-following consensus of fractional order multi-agent systems is investigated. The agents are considered as discrete-time fractional order integrators or fractional order double-integrators. Moreover, the interaction between the agents is described with an undirected communication graph with a fixed topology. It is shown that the leader-following consensus problem for the considered agents could be converted to the asymptotic stability analysis of a discrete-time fractional order system. Based on this idea, sufficient conditions to reach the leader-following consensus in terms of the controller parameters are extracted. This leads to an appropriate region in the controller parameters space. Numerical simulations are provided to show the performance of the proposed leader-following consensus approach.

关键词： multi-agent systems fractional order systems leader-following consensus discrete-time fractionalorder systems

Microstructural Evolution of Nb–V–Mo and V Containing TRIP-assisted Steels during Thermomechanical Processing

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Journal of Materials Science & Technology 2017年第4期33卷 311-320页

作者： erfan Abbasi William Mark Rainforth Department of Materials Science and Engineering The University of Sheffield

The microstructural evolution and precipitation behaviour of Nb–V–Mo and single V containing transformation induced plasticity assisted steels were investigated during thermomechanical processing. A plane strain compression testing machine was used to simulate the thermomechanical processing. Microstructures were characterised by optical microscopy, scanning-transmission electron microscopy and microanalysis, and X-ray diffraction analysis, and Vickers hardness was obtained from the deformed specimens. The resulting microstructure of both Nb–V–Mo and V steels at room temperature primarily consisted of an acicular/bainitic ferrite, retained austenite and martensite surrounded by allotriomorphic *** TEM analysis showed that a significant number of Nb（V,Mo）（C,N） precipitates were formed in the microstructure down to the finishing stage in Nb–V–Mo steel（i.e. 830℃）. It was also found that the V（C,N）precipitation primarily occurred in both ferrite and deformed austenite below the finishing stage. The results suggested that Nb–Mo additions considerably increased the temperature stability of microalloy precipitates and controlled the microstructural evolution of austenite. However, the microalloy precipitation did not cause a significant precipitation strengthening in both Nb–V–Mo and V steels at room temperature.

关键词： Microalloyed TRiP-assisted steel Thermomechanical processing Precipitation behaviour Microstructural evolution

Molecular dynamics simulation of structure H clathrate-hydrates of binary guest molecules

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Journal of Natural Gas Chemistry 2011年第6期20卷 577-584页

作者： Hamid erfan-Niya Hamid Modarress Department of Chemical Engineering Amirkabir University of Technology

Molecular dynamics （MD） simulations are performed to study the stability of structure H clathrate-hydrates of methane＋large-molecule guest substance （LMGS） at temperatures of 270, 273, 278 and 280 K under canonical （NVT-） ensemble condition in a 3×3×3 structure H unit cell replica with 918 TIP4P water molecules. The studied LMGS are 2-methylbutane （2-MB）, 2,3-dimethylbutane （2,3-DMB）, neohexane （NH）, methylcyclohexane （MCH）, adamantane and tert-butyl methyl ether （TBME）. In the process of MD simulation, achieving equilibrium of the studied system is recognized by stability in calculated pressure for NVT-ensemble. So, for the accuracy of MD simulations, the obtained pressures are compared with the experimental phase diagrams. Therefore, the obtained equilibrium pressures by MD simulations are presented for studying the structure H clathrate-hydrates. The results show that the calculated temperature and pressure conditions by MD simulations are consistent with the experimental phase diagrams. Also, the radial distribution functions （RDFs） of host-host, host-guest and guest-guest molecules are used to analysis the characteristic configurations of the structure H clathrate-hydrate.

关键词： structure H clathrate-hydrate methane+large-molecule guest substance molecular dynamics stability radial distribution function

Comprehensive analysis of pulsed plasma nitriding preconditions on the fatigue behavior of AISI 304 austenitic stainless steel

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International Journal of Minerals,Metallurgy and Materials 2021年第4期28卷 657-664页

作者： Okan Unal erfan Maleki Remzi Varol Mechanical Engineering Department Karabuk UniversityKarabuk 78050Turkey Modern Surface Engineering Laboratory(MSELAB) Karabuk UniversityKarabuk 78050Turkey Mechanical Engineering Department Sharif University of Technology-International CampusKish Island 79417-76655Iran Mechanical Engineering Department Suleyman Demirel UniversityIsparta 32200Turkey

This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding *** pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and *** reveal that nitriding depth increased as process temperature and duration *** nitriding depth remarkably increased at 475℃for 8 h and at 550℃for 4 *** austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite(S-phase)during low-temperature plasma *** S-phase was converted to CrN precipitation at 475℃for 8 h and at 550℃for 4 *** hardness and fatigue limit increased through plasma nitriding regardless of process *** best surface hardness and fatigue limit were obtained at 550℃for 4 h because of the occurrence of CrN precipitation.

关键词： pulsed plasma nitriding S-phase fatigue nitrided layer

A Semi-analytical Method for Vibrational and Buckling Analysis of Functionally Graded Nanobeams Considering the Physical Neutral Axis Position

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Computer Modeling in Engineering & Sciences 2015年第6期105卷 151-181页

作者： Farzad Ebrahimi erfan Salari Department of Mechanical Engineering Faculty of EngineeringImam Khomeini International UniversityQazvinIran

In this paper,a semi-analytical method is presented for free vibration and buckling analysis of functionally graded(FG)size-dependent nanobeams based on the physical neutral axis *** is the first time that a semi-analytical differential transform method(DTM)solution is developed for the FG nanobeams vibration and buckling *** properties of FG nanobeam are supposed to vary continuously along the thickness according to the power-law *** physical neutral axis position for mentioned FG nanobeams is *** small scale effect is taken into consideration based on nonlocal elasticity theory of *** nonlocal equations of motion are derived through Hamilton’s principle and they are solved applying *** is demonstrated that the DTM has high precision and computational efficiency in the vibration analysis of FG *** good agreement between the results of this article and those available in literature validated the presented *** detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as neutral axis position,small scale effects,the material distribution profile,mode number,thickness ratio and boundary conditions on the normalized natural frequencies and dimensionless buckling load of the FG nanobeams in *** is explicitly shown that the vibration and buckling behaviour of a FG nanobeams is significantly influenced by these effects.

关键词： Buckling Vibration Functionally graded nanobeam Neutral axis Differential transformation method Nonlocal elasticity

Microstructural Characteristics and Mechanical Properties of Low-Alloy, Medium-Carbon Steels After Multiple Tempering

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Acta Metallurgica Sinica(English Letters) 2019年第1期32卷 74-88页

作者： erfan Abbasi Quanshun Luo Dave Owens Materials and Engineering Research Institute Sheffield Hallam University Tyzack Machine Knives Ltd

The microstructure and mechanical properties of NiCrMoV-and NiCrSi-alloyed medium-carbon steels were investigated after multiple tempering. After austenitising, the steels were hardened by oil quenching and subsequently double or triple tempered at temperatures from 250 to 500 °C. The samples were characterised using scanning electron microscopy and X-ray diffraction, while the mechanical properties were evaluated by Vickers hardness testing, V-notched Charpy impact testing and tensile testing. The results showed that the retained austenite was stable up to 400 °C and the applied multiple tempering below this temperature did not lead to a complete decomposition of retained austenite in both steels. It was also found that the microstructure, hardness and impact toughness varied mainly as a function of tempering temperature,regardless of the number of tempering stages. Moreover, the impact toughness of NiCrMoV steel was rather similar after single/triple tempering at different temperatures, while NiCrSi steel exhibited tempered martensite embrittlement after single/double tempering at 400 °C. The observed difference was mainly attributed to the effect of precipitation behaviour due to the effect of alloying additions in the studied steels.

关键词： Medium-carbon steels Multiple tempering Alloying addition Mechanical properties Retained austenite Precipitation behaviour

Simultaneous Employment of Generation Rescheduling and Incentive-based Demand Response Programs for Congestion Management in Case of Contingency

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Journal of Modern Power Systems and Clean Energy 2022年第4期10卷 902-912页

作者： Seyed erfan Hosseini Alimorad Khajehzadeh Mahdiyeh Eslami Department of Electrical Engineering Kerman branchIslamic Azad UniversityKermanIran

Relieving congestion significantly influences the operation and security of the transmission ***,the congestion alleviation of transmission network in all power systems is ***,it could prevent price spikes and/or involuntary load shedding and impose high expenses on the transimission network,especially in case of ***,the increasing or decreasing generation rescheduling has been used as one of the most imperative approaches for correctional congestion management when a contingency ***,demand response programs(DRPs)could also be a vital tool for managing the ***,the simultaneous employment of generation rescheduling and DRPs is proposed for congestion management in case of *** objective is to reschedule the generation of power plants and to employ DRPs in such a way so as to lessen the cost of *** crow search algorithm is employed to determine the *** accuracy and efficiency of the proposed approach are assessed through the tests conducted on IEEE 30-bus and 57-bus test *** results of various case studies indicate the better performance of the proposed approach in comparison with different approaches presented in the literature.

关键词： Congestion management demand response generation rescheduling transmission economy transmission lines

Effects of Zr additions on structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti(wt.%) alloy

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China Foundry 2022年第1期19卷 9-16页

作者： Hamed Kamali erfan Kamali Massoud Emamy School of Metallurgy and Materials Engineering College of EngineeringUniversity of TehranP.O.Box 11155-4563TehranIran Faculty of Materials Engineering Sahand University of TechnologyP.O.Box 51335-1996TabrizIran

The effects of different Zr additions(0.05wt.%-0.5wt.%)on the structure and tensile properties of an Al-4.5Cu-0.3Mg-0.05Ti(wt.%)alloy solidified under a high cooling rate(18℃·s^(-1)),in as-cast and T6 heat-treated conditions were *** as-cast structure of the alloy consists of equiaxed grains ofα-Al with an average size of 64μm which is unaffected by the Zr additions,indicating the ineffectiveness of Zr in the grain refinement of the *** electron microscopy,along with X-ray diffraction analysis revealed the presence of elongatedθ-Al2Cu at the grain boundaries;in addition,coarse Al3Zr particles exist in the intergranular regions of the 0.5wt.%Zr-containing *** the T6 heat treatment,the elongatedθparticles were fragmented;however,the coarse Al3Zr particles remained unchanged in the ***,the formation of fineβ’-Al3Zr andθ’’-Al3Cu/θ’-Al2Cu phases during T6 heat treatment was revealed by transmission electron *** results of the tensile tests showed that the Zr additions increase the strength of the alloy in both as-cast and T6 heat-treated conditions,but reduce its elongation,especially with 0.5wt.%Zr *** 0.3wt.%Zr-added alloy in the T6 heat-treated condition has the highest quality index value(249 MPa).Fractography of the fracture surfaces of the alloys revealed ductile fracture mode including dimples and cracked intermetallic phases in both conditions.

关键词： Al-Cu-Mg alloys casting T6 heat treatment structure precipitation hardening tensile properties fractography