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    A method for power transformer insulation design improvements through electric field determination

    , Article Scientia Iranica ; Volume 10, Issue 4 , 2003 , Pages 410-418 ; 10263098 (ISSN) Khaligh, A ; Vakilian, M ; Salay Naderi, M ; Sharif University of Technology
    Sharif University of Technology  2003
    Knowledge of potential and field distribution in the insulation system of a transformer during transient excitation is vital to its construction [1]. This paper deals with insulation design improvements of power transformers using electric field analysis. The calculation methods for electric field analysis, inside a power transformer impressed with impulse and power frequency voltages, are presented. Initially, a lumped parameter equivalent model is constructed by dividing transformer windings into several blocks and computing the electric circuit parameters of this model. Next, the electric field is determined by employing the results of the transformer transient model circuit analysis as... 

    Polyelectrolytes polarization in nonuniform electric fields

    , Article International Journal of Modern Physics C ; Volume 25, Issue 12 , 2014 ; ISSN: 17936586 Farahpour, F ; Ejtehadi, M. R ; Varnik, F ; Sharif University of Technology
    Stretching dynamics of polymers in microfluidics is of particular interest for polymer scientists. As a charged polymer, a polyelectrolyte (PE) can be deformed from its coiled equilibrium configuration to an extended chain by applying uniform or nonuniform electric fields. By means of hybrid lattice Boltzmann (LB)-molecular dynamics (MD) simulations, we investigate how the condensed counterions (CIs) around the PE contribute to the polymer stretching in inhomogeneous fields. As an application, we discuss the translocation phenomena and entropic traps, when the driving force is an applied external electric field  

    Shooting at the nanoscale: Collection and acceleration of nanowires with an external electric field

    , Article Applied Physics Letters ; Volume 114, Issue 1 , 2019 ; 00036951 (ISSN) Farain, K ; Esfandiar, A ; Moshfegh, A. Z ; Sharif University of Technology
    American Institute of Physics Inc  2019
    We report an approach for collecting, charging, and exceedingly fast motion of silver nanowires (Ag NWs) using an external static electric field. With a proper choice of suspension medium, dispersed Ag NWs can be efficiently driven to align and accumulate vertically on the edges of two parallel gold microelectrodes on a glass substrate surface by dielectrophoresis. Then, at sufficiently high electric fields (> 2.0 × 10 5 V/m), these NWs break at the electrode contact point while carrying some net charge. Afterwards, they immediately accelerate in the field direction and, despite an extremely low Reynolds number for the motion of NWs in viscous liquids, move with high speeds (> 25 mm/s)... 

    Soap-film flow induced by electric fields in asymmetric frames

    , Article Physical Review E ; Volume 97, Issue 4 , 2018 ; 24700045 (ISSN) Mollaei, S ; Nasiri, M ; Soltanmohammadi, N ; Shirsavar, R ; Ramos, A ; Amjadi, A ; Sharif University of Technology
    American Physical Society  2018
    Net fluid flow of soap films induced by (ac or dc) electric fields in asymmetric frames is presented. Previous experiments of controllable soap film flow required the simultaneous use of an electrical current passing through the film and an external electric field or the use of nonuniform ac electric fields. Here a single voltage difference generates both the electrical current going through the film and the electric field that actuates on the charge induced on the film. The film is set into global motion due to the broken symmetry that appears by the use of asymmetric frames. If symmetric frames are used, the film flow is not steady but time dependent and irregular. Finally, we study... 

    Magnetic and electric field assisted electrospun polyamide nanofibers for on-line μ-solid phase extraction and HPLC

    , Article RSC Advances ; Vol. 4, Issue. 94 , 2014 , pp. 52590-52597 ; ISSN: 20462069 Bagheri, H ; Piri-Moghadam, H ; Rastegar, S ; Sharif University of Technology
    The effects of applied magnetic and electric fields on electrospinning were investigated to produce more efficient nanofibers. Considering the previous extensive studies, polyamide nanofibers were prepared by a conventional approach and under auxiliary electric and magnetic fields. The first sorbent was synthesized by electrospinning of a solution of 18% polyamide in formic acid. The second and third types of polyamide were prepared similarly while the electrospinning processes were assisted by an electric and a magnetic field. The third type of polyamide contained a magnetic ionic liquid (MIL) to induce sufficient magnetic susceptibility in the polymeric solution. The SEM images revealed... 

    Exposure of the human brain to an electromagnetic plane wave in the 100-1000 MHz frequency range for potential treatment of neurodegenerative diseases

    , Article IET Microwaves, Antennas and Propagation ; Volume 6, Issue 14 , 2012 , Pages 1565-1572 ; 17518725 (ISSN) Khaleghi, A ; Eslampanah Sendi, M.S ; Chávez Santiago, R ; Mesiti, F ; Balasingham, I ; Sharif University of Technology
    Radio signals can induce an electric field inside the brain, which might be potentially beneficial in the treatment of neurodegenerative diseases. For instance, a new method for the treatment of Alzheimer's disease in mice through the exposure to the radiation of mobile phones has been successfully demonstrated. In the light of these results, studying the induction of an electric field in the human brain through the controlled exposure to radio signals is of paramount importance for the eventual development of similar treatment techniques in humans. In this study, the authors study the radio signals in 100-1000 MHz as a means for inducing an electric field into the human brain in a... 

    Dielectrophoretic interaction of two particles in a uniform electric field

    , Article Microsystem Technologies ; Volume 25, Issue 7 , 2019 , Pages 2699-2711 ; 09467076 (ISSN) Javidi, R ; Moghimi Zand, M ; Dastani, K ; Sharif University of Technology
    Springer Verlag  2019
    The local electric field distorsion induced by a dielectric particle leads to particle–particle interactions and assembly which is very interesting for their useful applications on microfluidic devices. Particles behavior becomes more complicated if several particles interact at the same time. This paper presents a comprehensive numerical analysis of the assembly and particle–particle interactions for two similar and dissimilar dielectric particles immersed in a dielectric fluid using the immersed interface method based on two-dimensional direct-current dielectrophoresis. The immersed interface method is a finite-difference (or finite element) based numerical method which its key advantage... 

    Study on different dimensions of C-type corona rings in 400 kV insulator strings based on fem analysis of electric field distribution

    , Article 27th Iranian Conference on Electrical Engineering, ICEE 2019, 30 April 2019 through 2 May 2019 ; 2019 , Pages 673-678 ; 9781728115085 (ISBN) Sardast, R ; Faghihi, F ; Vakilian, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    This paper presents analysis of electric field distribution and optimization of C-type corona rings for 400 kV V-insulator strings composed of ceramic insulator units which are the most common configuration of overhead transmission lines. These strings are equipped with corona rings to enhance the insulation performance regarding to the effect of these rings on the insulation function and potential and electric field distribution. 3D field simulations are performed for the C-type of corona rings with different dimensions by software based on FEM analysis  

    Optical modulation by surface states

    , Article Semiconductor Science and Technology ; Volume 18, Issue 1 , 2003 , Pages 60-67 ; 02681242 (ISSN) Darabi, E ; Khorasani, S ; Rashidian, B ; Sharif University of Technology
    In this paper, the effect of two-dimensional electron plasma formed on the surface of a semiconductor on the refraction phase of an optical beam is investigated. Both the density and effective mass of the surface state electrons can be controlled by a transverse electric field. While the surface density of electrons varies slowly with the applied field, their effective mass changes instantaneously. Therefore, a high bandwidth for the phase modulation can be obtained. It is expected that the device operates in the far-infrared region with a semiconductor as the base material. GaAs is one of the best candidates having both large dynamic range, and large ratio of free electron to the crystal... 

    Induced soap-film flow by non-uniform alternating electric field

    , Article Journal of Electrostatics ; Volume 73 , February , 2015 , Pages 112-116 ; 03043886 (ISSN) Shirsavar, R ; Ramos, A ; Amjadi, A ; Taherinia, J ; Mashhadi, M ; Nejati, A ; Sharif University of Technology
    Elsevier  2015
    Fluid flows generated on soap films by non-uniform alternating electric fields are studied. Two parallel metal rods subjected to an AC voltage are placed perpendicular to the soap film, which is anchored in a dielectric frame. The fluid flow is generated by electrohydrodynamic induction. At very low signal frequencies there is induced surface charge, but there is no tangential electric field at the surface, so there is no force and no flow. Fluid flow is observed increasing the frequency, when there are both surface charge and tangential electric field. The flow velocity increases with decreasing thickness of the soap film  

    Deciphering the electric field changes in the channel of an open quantum system to detect DNA nucleobases

    , Article Journal of Computational Electronics ; Volume 16, Issue 2 , 2017 , Pages 411-418 ; 15698025 (ISSN) Khadempar, N ; Berahman, M ; Yazdanpanah Goharrizi, A ; Sharif University of Technology
    DNA nucleobases strongly absorbed onto a graphene sheet placed between two gold electrodes in a contact–channel–contact configuration were distinguished. We analyzed the system using the nonequilibrium Green’s function method combined with density functional theory. The changes of the electric field in the middle of the vacuum gap (channel) were investigated. The Mulliken population was deciphered for graphene and the nucleobases. We also extracted the image plane, which was found to lie very close to the position of peak induced density. The projection of the electron difference density and electrostatic difference potential of the nucleobases are also presented. The nucleobases were... 

    Stability and breakup of liquid jets: Effect of slight gaseous crossflows and electric fields

    , Article Chemical Engineering Science ; Volume 165 , 2017 , Pages 89-95 ; 00092509 (ISSN) Rajabi, A ; Morad, M. R ; Rahbari, N ; Sharif University of Technology
    Elsevier Ltd  2017
    Instability and breakup of a liquid jet under the influence of a gaseous crossflow in the presence of an electric field is investigated. A dispersion relation for disturbances on the jet surface is derived for the combined effects based on pioneer linear stability analysis for low speed limits. Effects of Weber, Bond and Ohnesorge numbers on the growth rate of disturbances are studied. The theoretical analysis developed for breakup length is used for comparisons with experimentally obtained breakup lengths. Measured breakup lengths were predicted satisfactorily by the linear theory in the region of low crossflow velocities (0–4 m/s) and electric field intensities (0–3×105 V/m). © 2017... 

    Fine-grained SnO2 varistors prepared by microwave sintering for ultra-high voltage applications

    , Article Materials Letters ; Volume 230 , 2018 , Pages 9-11 ; 0167577X (ISSN) Maleki Shahraki, M ; Mahmoudi, P ; Abdollahi, M ; Ebadzadeh, T ; Sharif University of Technology
    Elsevier B.V  2018
    In this research, fine-grained SnO2-based varistors with a simple microstructure and the mean grain size of 0.8 µm were obtained by the microwave sintering method. The breakdown electric field measured for these varistors was 12 kV/cm that is 3 times higher than the conventional-sintered varistors. The high nonlinear coefficient (60) and low leakage current density (9 µA/cm2) were achieved in fine-grained SnO2 varistors. The fine-grained SnO2 varistors appropriately clamped pulse current surges and the calculated value of the clamping voltage ratio of these varistors was 2. The excellent electrical properties and protective effect of fine-grained SnO2 varistors showed that these varistors... 

    Universal rotation of nanowires in static uniform electric fields in viscous dielectric liquids

    , Article Applied Physics Letters ; Volume 113, Issue 6 , 2018 ; 00036951 (ISSN) Farain, K ; Esfandiar, A ; Moshfegh, A. Z ; Sharif University of Technology
    American Institute of Physics Inc  2018
    The wide utilization of nanomanipulation as a promising approach in microorganisms, nanoelectromechanical systems, and assembly of nanostructures remarks the importance of nanostructures' motion in electric fields. Here, we study the rotational dynamics of metallic and non-metallic nanowires (NWs) in a static uniform electric field in viscous dielectric liquids. For metallic NWs, it has been theoretically shown that the electric field-induced rotation is practically independent of the geometrical dimensions and the electrical properties of NWs. Our experimental results for suspended silver (Ag) NWs in microscope oil are perfectly in agreement with this model. However, in the case of TiO2... 

    Chain deformation in translocation phenomena

    , Article Soft Matter ; Volume 9, Issue 9 , 2013 , Pages 2750-2759 ; 1744683X (ISSN) Farahpour, F ; Maleknejad, A ; Varnik, F ; Ejtehadi, M. R ; Sharif University of Technology
    Deformation of single stranded DNA in a translocation process before reaching the pore is investigated. By solving the Laplace equation in a suitable coordinate system and with appropriate boundary conditions, an approximate solution for the electric field inside and outside a narrow pore is obtained. With an analysis based on the "electrohydrodynamic equivalence" we determine the possibility of the extension of a charged polymer due to the presence of an electric field gradient in the vicinity of the pore entrance. With a multi-scale hybrid simulation (LB-MD), it is shown that an effective deformation before reaching the pore occurs, which facilitates the process of finding the entrance for... 

    Proper measurement of pure dielectrophoresis force acting on a RBC using optical tweezers

    , Article Biomedical Optics Express ; Volume 10, Issue 11 , 2019 , Pages 5639-5649 ; 21567085 (ISSN) Sasanpour, M ; Azadbakht, A ; Mollaei, P ; S. Reihani, N. S ; Sharif University of Technology
    OSA - The Optical Society  2019
    The force experienced by a neutral dielectric object in the presence of a spatially non-uniform electric field is referred to as dielectrophoresis (DEP). The proper quantification of DEP force in the single-cell level could be of great importance for the design of high-efficiency micro-fluidic systems for the separation of biological cells. In this report we show how optical tweezers can be properly utilized for proper quantification of DEP force experienced by a human RBC. By tuning the temporal frequency of the applied electric field and also performing control experiments and comparing our experimental results with that of theoretically calculated, we show that the measured force is a... 

    Electric field assisted amplification of magnetic fields in tilted Dirac cone systems

    , Article Physical Review B ; Volume 100, Issue 4 , 2019 ; 24699950 (ISSN) Jafari, S. A ; Sharif University of Technology
    American Physical Society  2019
    We show that the continuum limit of the tilted Dirac cone in materials such as 8-Pmmn borophene and layered organic conductor α-(BEDT-TTF)2I3 corresponds to deformation of the Minkowski space-time of Dirac materials. From its Killing vectors we construct an emergent tilted-Lorentz (t-Lorentz) symmetry group for such systems. As an example of the t-Lorentz transformations we obtain the exact solution of the Landau bands for a crossed configuration of electric and magnetic fields. For any given tilt parameter 0≤ζ<1, if the ratio χ=vFBz/Ey of the crossed magnetic and electric fields satisfies χ≥1+ζ, one can always find appropriate t-boosts in both valleys labeled by τ=±1 in such a way that the... 

    Second Harmonic Generation (SHG) measurement affected by electric field

    , Article Scientia Iranica ; Volume 14, Issue 3 , 2007 , Pages 236-239 ; 10263098 (ISSN) Amjadi, A ; Rajai, P ; Latifi, H ; Sharif University of Technology
    Sharif University of Technology  2007
    A type II (eoe: extraordinary-ordinary-extraordinary) phase matching condition in a 2nd Harmonic Generation of Nd-YAG laser under a high electric field in a uniaxial KDP crystal has been measured. Type II phase matching takes place when the two mixing waves are of orthogonal polarizations (extraordinary-ordinary) and the 2nd harmonic radiation corresponds to an extraordinary wave. By applying an electric field along the X(Y) axes of the crystal, a new phase-matching angle was measured under the influence of different electric fields. The deflection angle of the SHG beam was measured as a function of the applied voltage. An optical collector will focus the 1st harmonic and a fraction of its... 

    TED Large Signal Modeling in the Dominant Mode

    , M.Sc. Thesis Sharif University of Technology Sadeghi, Amir Hossein (Author) ; Farzaneh, Forouhar (Supervisor)
    Transferred Electron Device is a semiconductor device being capable of generating oscillation in microwave frequencies. Applying a bias voltage to the device and putting it in a resonant circuit, a periodic waveform in the output current is observed. The cause of the generation of oscillation in the device is related to the characteristics of velocity-field in the device. In some part of the characteristics, it is observed that increasing the field inside the device causes the velocity of electrons to be reduced. This causes the generation of the negative conductance and the oscillation of the output current under some conditions. The purpose of this thesis is to represent an equivalent... 

    Theory of the liquid film motor

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 92, Issue 3 , September , 2015 ; 15393755 (ISSN) Feiz, M. S ; Namin, R. M ; Amjadi, A ; Sharif University of Technology
    American Physical Society  2015
    The liquid film motor is a freely suspended liquid film placed between two capacitively coupled plates that rotates when an electric current is passed through it. Here we propose a theory for its rotation mechanism based on thin film electroconvection. The capacitively coupled plates induce free charges on the surfaces of the film, and the electric field on the film exerts a force that induces rotation. Results of the proposed theory and simulation are in good agreement with the experiments in different properties of the liquid film motor