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Total 22 records

    Perpendicular andreev reflection: solid-state signature of black-hole horizon

    , Article Physical Review B ; Volume 10, Issue 24 , 2019 ; 24699950 (ISSN) Faraei, Z ; Jafari, A ; Sharif University of Technology
    American Physical Society  2019
    Abstract
    Beenakker noticed that the peculiar band structure of Dirac fermions in two-dimensional (2D) solids allows for the specular Andreev reflection in these systems, which has no analogue in other 2D electron systems. An interesting deformation of the Dirac equation in the solid state is to tilt it, which has now been realized in materials. In this paper we report another peculiar feature of the Andreev reflection in tilted 2D Dirac cone systems. The tilt deformation of the Dirac equation is characterized by two parameters ζ=ζ(cosθ,sinθ). We show that when the tilt parameter is tuned to its "horizon value" ζ=1, irrespective of the incidence angle of electrons, the Andreev reflected hole is always... 

    Stiffer double-stranded DNA in two-dimensional confinement due to bending anisotropy

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 94, Issue 6 , 2016 ; 15393755 (ISSN) Salari, H ; Eslami Mossallam, B ; Ranjbar, H. F ; Ejtehadi, M. R ; Sharif University of Technology
    American Physical Society  2016
    Abstract
    Using analytical approach and Monte Carlo (MC) simulations, we study the elastic behavior of the intrinsically twisted elastic ribbons with bending anisotropy, such as double-stranded DNA (dsDNA), in two-dimensional (2D) confinement. We show that, due to the bending anisotropy, the persistence length of dsDNA in 2D conformations is always greater than three-dimensional (3D) conformations. This result is in consistence with the measured values for DNA persistence length in 2D and 3D in equal biological conditions. We also show that in two dimensions, an anisotropic, intrinsically twisted polymer exhibits an implicit twist-bend coupling, which leads to the transient curvature increasing with a... 

    New seepage-related design graphs for rock-fill dams

    , Article International Symposium on Dams in the Societies of the 21st Century, ICOLD-SPANCOLD - Dams and Reservoirs, Societies and Environment in the 21st Century, Barcelona, 18 June 2006 through 18 June 2006 ; Volume 1 , 2006 , Pages 971-978 ; 0415404231 (ISBN); 9780415404235 (ISBN) Soleimanbeigi, A ; Jafarzadeh, F ; Sharif University of Technology
    Taylor and Francis/ Balkema  2006
    Abstract
    Seepage analysis serves as one of the most significant stages in the design process of an embankment dam. In two-dimensional (2D) seepage analysis of embankment dams, little or no attention is paid to the widthwise flows from side abutments. Moreover, the role of grout curtain extensions into the side abutments and abutment material properties are inevitably neglected when performing seepage analyses in 2D plane. In this paper, two and three-dimensional (3D) models of a rock-fill dam are generated and several unsteady and steady state seepage analyses are performed using finite element method (FEM). The results obtained from 2D and 3D seepage analyses were compared with measurements from the... 

    A high-order compact finite-difference lattice Boltzmann method for simulation of steady and unsteady incompressible flows

    , Article International Journal for Numerical Methods in Fluids ; Vol. 75, Issue. 10 , 2014 , Pages 713-746 ; ISSN: 02712091 Hejranfar, K ; Ezzatneshan, E ; Sharif University of Technology
    Abstract
    A high-order compact finite-difference lattice Boltzmann method (CFDLBM) is proposed and applied to accurately compute steady and unsteady incompressible flows. Herein, the spatial derivatives in the lattice Boltzmann equation are discretized by using the fourth-order compact FD scheme, and the temporal term is discretized with the fourth-order Runge-Kutta scheme to provide an accurate and efficient incompressible flow solver. A high-order spectral-type low-pass compact filter is used to stabilize the numerical solution. An iterative initialization procedure is presented and applied to generate consistent initial conditions for the simulation of unsteady flows. A sensitivity study is also... 

    Comparing three image processing algorithms to estimate the grain-size distribution of porous rocks from binary 2D images and sensitivity analysis of the grain overlapping degree

    , Article Special Topics and Reviews in Porous Media ; Volume 6, Issue 1 , 2015 , Pages 71-89 ; 21514798 (ISSN) Rabbani, A ; Ayatollahi, S ; Sharif University of Technology
    Begell House Inc  2015
    Abstract
    The grain-size distribution (GSD) of porous rocks is important in order to better understand their hydrodynamic behavior. Clear and precise GSD data can be used to computationally reconstruct rock structure for further analysis. In this study, three main algorithms for image analysis have been examined to estimate the GSD of clastic rocks. The main challenge in GSD determination from images is in detecting overlapping grains and measuring their size separately. In this study, three previously developed image processing algorithms are implemented on two-dimensional (2D) binary images of rocks in order to compare the obtained GSD from each of the methods, i.e., the mean intercept length... 

    Input impedance and radiation pattern of a resonant dipole embedded in a two-dimensional periodic leaky-wave structure

    , Article IET Microwaves, Antennas and Propagation ; Volume 9, Issue 14 , 2015 , Pages 1567-1573 ; 17518725 (ISSN) Bakhtafrouz, A ; Borji, A ; Sharif University of Technology
    Institution of Engineering and Technology  2015
    Abstract
    Array scanning method (ASM) is employed to study the input impedance and radiation pattern of a two-dimensional periodic leaky-wave antenna (LWA). The antenna consists of a narrow horizontal strip dipole of arbitrary length underneath a two-dimensional (2D) periodic screen of metallic patches, which acts as a partially reflective surface (PRS), and backed by a ground plane. First, the Green's function in the presence of the 2D array of metallic patches is calculated by means of the ASM and then the current distribution and input impedance of the source dipole are calculated through the electric field integral equation and method of moments. The far-field pattern is computed using the... 

    Application of the adjoint multi-point and the robust optimization of shock control bump for transonic aerofoils and wings

    , Article Engineering Optimization ; Volume 48, Issue 11 , 2016 , Pages 1887-1909 ; 0305215X (ISSN) Mazaheri, K ; Nejati, A ; Chaharlang Kiani, K ; Sharif University of Technology
    Taylor and Francis Ltd 
    Abstract
    A shock control bump (SCB) is a flow control method which uses a local small deformation in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, both equally and variably weighted multi-point optimization and a robust adjoint optimization scheme are used to optimize the SCB. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm are used to find the optimum location and shape of the SCB for two benchmark aerofoils. A multi-point optimization method under a constant-lift-coefficient constraint is... 

    Approach for analytical modelling of axial-flux PM machines

    , Article IET Electric Power Applications ; Volume 10, Issue 6 , 2016 , Pages 441-450 ; 17518660 (ISSN) Taghipour Boroujeni, S ; Abedini Mohammadi, A ; Oraee, A ; Oraee, H ; Sharif University of Technology
    Institution of Engineering and Technology  2016
    Abstract
    In the presented paper, an analytical model is developed for calculation of the air gap magnetic flux density in the axial-flux surface-mounted PM machines. The slotting effect is taken into account in the air gap magnetic flux distribution, accurately. The main novelty of this study is replacing the stator teeth by some surface currents at the border of the removed stator teeth. The uniqueness theorem is applied to find the surface currents. The two-dimensional (2D) field solution in the slotless machine is solved easily by separation of variables method. The multi-slice quasi-3D method is applied for taking 3D nature of field distribution into account. In addition, the back-EMF, armature... 

    Mining DNA sequences based on spatially coded technique using spatial light modulator

    , Article IWCIT 2016 - Iran Workshop on Communication and Information Theory, 3 May 2016 through 4 May 2016 ; 2016 ; 9781509019229 (ISBN) Fazelian, M ; Abdollahramezani, S ; Bahrani, S ; Chizari, A ; Jamali, M. V ; Khorramshahi, P ; Tashakori, A ; Shahsavari, S ; Salehi, J. A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    Abstract
    In this paper, we present an optical computing method for string data alignment applicable to genome information analysis. By applying moire technique to spatial encoding patterns of deoxyribonucleic acid (DNA) sequences, association information of the genome and the expressed phenotypes could more effectively be extracted. Such moire fringes reveal occurrence of matching, deletion and insertion between DNA sequences providing useful visualized information for prediction of gene function and classification of species. Furthermore, by applying a cylindrical lens, a new technique is proposed to map two-dimensional (2D) association information to a one-dimensional (1D) column of pixels, where... 

    Two-dimensional materials for gas sensors: from first discovery to future possibilities

    , Article Surface Innovations ; Volume 6, Issue 4-5 , 2018 , Pages 205-230 ; 20506252 (ISSN) Barzegar, M ; Tudu, B ; Sharif University of Technology
    ICE Publishing  2018
    Abstract
    Semiconductor gas sensors have been developed so far on empirical bases, but now recent innovative materials for advancing gas sensor technology have been made available for further developments. Two-dimensional (2D) materials have gained immense attention since the advent of graphene. This attention inspired researchers to explore a new family of potential 2D materials. The superior structural, mechanical, optical and electrical properties of 2D materials made them attractive for next-generation smart device applications. There are considerable improvements and research studies on graphene, molybdenum disulfide (MoS2), tungsten disulfide (WS2), tin sulfide (SnS2), black phosphorus and other... 

    On coarse grids simulation of compressible mixing layer flows using vorticity confinement

    , Article Journal of Fluids Engineering, Transactions of the ASME ; Volume 140, Issue 3 , 2018 ; 00982202 (ISSN) Hejranfar, K ; Ebrahimi, M ; Sadri, M ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2018
    Abstract
    In this work, the capability and performance of the vorticity confinement (VC) implemented in a high-order accurate flow solver in predicting two-dimensional (2D) compressible mixing layer flows on coarse grids are investigated. Here, the system of governing equations with incorporation of the VC in the formulation is numerically solved by the fourth-order compact finite difference scheme. To stabilize the numerical solution, a low-pass high-order filter is applied, and the nonreflective boundary conditions are used at the farfield and outflow boundaries to minimize the reflections. At first, the numerical results without applying the VC are validated by available direct numerical... 

    Real-space exciton distribution in strained-siligraphene g-SiC7

    , Article Journal of Applied Physics ; Volume 126, Issue 6 , 2019 ; 00218979 (ISSN) Le, P. T. T ; Ebrahimi, M. R ; Davoudiniya, M ; Yarmohammadi, M ; Sharif University of Technology
    American Institute of Physics Inc  2019
    Abstract
    Siligraphene belonging to the family of two-dimensional (2D) materials has great potential in optoelectronics due to its considerable excitonic effects. In this study, the strain effects on the electronic structure and the real-space exciton wave functions of g - SiC 7 are investigated using the first-principles calculations based on the ab initio many-body perturbation theory. Alongside the increase (decrease) of the bandgap with compressive (tensile) strain, our results show that the exciton in the siligraphene monolayer under in-plane biaxial compressive strains is much more localized than that in the case of tensile one, leading to the higher and lower exciton binding energies,... 

    Proposed 2D and 3D geometries intended for smart antenna applications, including direction finding and beamforming implementation

    , Article IET Radar, Sonar and Navigation ; Volume 13, Issue 5 , 2019 , Pages 673-681 ; 17518784 (ISSN) Poormohammad, S ; Farzaneh, F ; Sharif University of Technology
    Institution of Engineering and Technology  2019
    Abstract
    Novel two-dimensional (2D) and three-dimensional (3D) antenna array geometries for smart antenna application are introduced. Minimum mean square error beamforming algorithm, using these arrays, in presence of signal, noise and interferences is implemented. Beamforming approach is used for every type of array assuming uniform and log-normal distributions for the interference amplitudes. Equal volume cylindrical or prism type arrays with circular, hexagonal, triangular, square and star cross-sections with equal number of elements are considered. Novel geometries consisting of rotated cross-sections are studied as well. In each case, the relative signal-to-interference ratios (SIRs) are... 

    Proposed 2D and 3D geometries intended for smart antenna applications, including direction finding and beamforming implementation

    , Article IET Radar, Sonar and Navigation ; Volume 13, Issue 5 , 2019 , Pages 673-681 ; 17518784 (ISSN) Poormohammad, S ; Farzaneh, F ; Sharif University of Technology
    Institution of Engineering and Technology  2019
    Abstract
    Novel two-dimensional (2D) and three-dimensional (3D) antenna array geometries for smart antenna application are introduced. Minimum mean square error beamforming algorithm, using these arrays, in presence of signal, noise and interferences is implemented. Beamforming approach is used for every type of array assuming uniform and log-normal distributions for the interference amplitudes. Equal volume cylindrical or prism type arrays with circular, hexagonal, triangular, square and star cross-sections with equal number of elements are considered. Novel geometries consisting of rotated cross-sections are studied as well. In each case, the relative signal-to-interference ratios (SIRs) are... 

    HTS transformer’s partial discharges raised by floating particles and nitrogen bubbles

    , Article Journal of Superconductivity and Novel Magnetism ; Volume 33, Issue 10 , 6 July , 2020 , Pages 3027-3034 Moradnouri, A ; Vakilian, M ; Hekmati, A ; Fardmanesh, M ; Sharif University of Technology
    Springer  2020
    Abstract
    Presence of defects, conducting particles, nonconducting particles, and nitrogen gas bubbles in the insulation system of high-temperature superconducting (HTS) transformers, mainly inside the liquid nitrogen as its major insulation, can create local field enhancement and consequently partial discharges which eventually lead to the catastrophic failure of the transformer. In this paper, two-dimensional (2D) axisymmetric finite element method (FEM) modeling via COMSOL Multiphysics software has been utilized for the investigation of the impact of size and shape of conducting particles and nitrogen gas bubbles on partial discharge (PD) activities in liquid nitrogen. Conducting particles of... 

    Two-dimensional model of melt flows and interface instability in aluminum reduction cells

    , Article Light Metals 2008, New Orleans, LA, 9 March 2008 through 13 March 2008 ; 2008 , Pages 443-448 ; 01470809 (ISSN); 9780873397100 (ISBN) Kadkhodabeigi, M ; Sharif University of Technology
    2008
    Abstract
    We derive a new non-linear two dimensional model for melt flows and interface instability in aluminum reduction cells. This model is based on non-linear de St. Venant shallow water equations and contains the main features of an aluminum reduction cell. In this model we consider linear friction terms but in a new way that has not been considered in previous works. Our results are in good agreement with the results of simulation of viscous flow. This model is applicable both in determination of melt flows in molten aluminum and cryolite layers and also in finding the extreme limit for stability of interfacial waves in an aluminum reduction cell  

    Minimization of Non-repeatable Runout (NRRO) in High-Speed Spindle Bearings

    , Article SAE 2021 Automotive Technical Papers, WONLYAUTO 2021, 1 January 2021 ; Issue 2021 , 2021 ; 01487191 (ISSN) Farahani, M. R ; Khodaygan, S ; Sharif University of Technology
    SAE International  2021
    Abstract
    The production with high quality at the lowest production time can be a key means to success in the competitive environment of manufacturing companies. Therefore, in recent years, the need for extra precise and high-speed machine tools has been impressively increased in manufacturing applications. One of the main sources of errors in the motion of high-speed spindles is the occurrence of non-repetitive runouts (NRRO) in the bearing. The NRRO can be caused by some factors such as the form of balls, the waviness of rings, the number of balls, and the permutation of one or two balls in the ball bearing. In this paper, a Taguchi-based approach is proposed for the optimal design of high-speed... 

    Seedless growth of two-dimensional disc-shaped WS2 layers by chemical vapor deposition

    , Article Materials Chemistry and Physics ; Volume 257 , 2021 ; 02540584 (ISSN) Rahmani Taji Boyuk, M.R ; Ghanbari, H ; Simchi, A ; Maghsoumi, A ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    Chemical processing of two-dimensional (2D) transition metal dichalcogenides has attracted immense attention due to their unique optical, electrical, and catalytic properties. In this paper, we show that under special conditions during seedless chemical vapor deposition (CVD), it is possible to grow large-area 2D WS2 layers with disc-shaped morphology, which has been scarcely reported. Detailed characterizations of the CVD-grown layers by Raman spectroscopy, atomic force microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy have revealed that a gradient in the precursor concentration in the gas phase and strain energy in the deposited hexagonal clusters favor... 

    Mechanistic study of the effects of dynamic fluid/fluid and fluid/rock interactions during immiscible displacement of oil in porous media by low salinity water: Direct numerical simulation

    , Article Journal of Molecular Liquids ; Volume 322 , 2021 ; 01677322 (ISSN) Alizadeh, M ; Fatemi, M ; Sharif University of Technology
    Elsevier B.V  2021
    Abstract
    Low salinity waterflooding (LSWF) is a process in which by lowering the ionic strength and/or manipulation of the composition of the injection water, the long term equilibrium in oil/brine/rock system is disturbed to reach a new state of equilibrium through which the oil production will be enhanced due to fluid/fluid and/or rock/fluid interactions. In spite of recent advances in the simulation of the LSWF at core scale and beyond, there are very few works that have modelled and simulated this process at the pore scale specially using direct numerical simulation (DNS). As a result the effects of wettability alteration and/or Interfacial Tension (IFT) change on the distribution of the phases... 

    Mechanistic study of the effects of dynamic fluid/fluid and fluid/rock interactions during immiscible displacement of oil in porous media by low salinity water: Direct numerical simulation

    , Article Journal of Molecular Liquids ; 2020 Alizadeh, M. R ; Fatemi, M ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    Low salinity waterflooding (LSWF) is a process in which by lowering the ionic strength and/or manipulation of the composition of the injection water, the long term equilibrium in oil/brine/rock system is disturbed to reach a new state of equilibrium through which the oil production will be enhanced due to fluid/fluid and/or rock/fluid interactions. In spite of recent advances in the simulation of the LSWF at core scale and beyond, there are very few works that have modelled and simulated this process at the pore scale specially using direct numerical simulation (DNS). As a result the effects of wettability alteration and/or Interfacial Tension (IFT) change on the distribution of the phases...