Search for: magnetic-fields
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    Coupled mode theory of waveguides with conducting interfaces

    , Article Scientia Iranica ; Volume 10, Issue 4 , 2003 , Pages 426-435 ; 10263098 (ISSN) Khorasani, S ; Rashidian, B ; Sharif University of Technology
    Sharif University of Technology  2003
    In this paper, the coupling coefficient of two waveguides with conducting interfaces is calculated analytically. It is shown that the control of interface charge densities via a transverse voltage leads to the control of the coupling. To derive the coupling coefficient, the basic Coupled Mode Theory (CMT) with paraxial approximation is improved to include the effect of conducting interfaces. The analysis is performed independently for TE and TM polarizations. Several direct applications of this effect including a multiplexer, a coupler and a modulator/switch and programmable grating are introduced. © Sharif University of Technology, October 2003  

    Considerations of Joule heating and radius reduction in umbral dots

    , Article Astronomy and Astrophysics ; Volume 407, Issue 2 , 2003 , Pages 761-767 ; 00046361 (ISSN) Hamedivafa, H ; Sharif University of Technology
    EDP Sciences  2003
    The physical nature of bright features in sunspot umbra such as umbral dots (UDs) is not fully understood yet. Here, by accepting magnetic field reduction in the UDs, the Joule heating mechanism in the UDs is investigated. In this investigation, a UD model is assumed which is characterized by a) a reduced (possibly zero) magnetic field strength in the UD column relative to its surroundings, b) the electric current generated by magnetic field gradient at the boundary of the UD column can produce some heat, and c) when the radius of the UD - because of pressure reduction inside the column - becomes zero, the death of the UD will occur. The rate of radius reduction is estimated to be nearly 100... 

    Investigation of Io's auroral hiss emissions due to its motion in Jupiter's magnetosphere

    , Article Research in Astronomy and Astrophysics ; Volume 12, Issue 6 , 2012 , Pages 693-702 ; 16744527 (ISSN) Moghimi, M. H ; Sharif University of Technology
    The left-hand side of the auroral hiss emission observed by Galileo has a frequency time profile shaped very similar to the funnel shape observed in the Earth's auroral region. This close similarity indicates that we can use the theory of whistler-mode propagation near the resonance cone to locate the emission source. The general characteristics of the whistler mode are discussed. Then the position of the emission source is investigated using a geometrical method that takes into account the trajectory of Galileo. Initially a point source is assumed. Then the possibility of a sheet source aligned along the magnetic field lines which are tangent to the surface of Io is investigated. Both types... 

    Experimental and numerical investigation of fully developed forced convection of water-based Fe3O4 nanofluid passing through a tube in the presence of an alternating magnetic field

    , Article Advances in Mechanical Engineering ; Volume 7, Issue 2 , February , 2015 , Pages 1-9 ; 16878132 (ISSN) Dibaei Bonab, M. H ; Shafii, M. B ; Nobakhti, M. H ; Sharif University of Technology
    Hindawi Publishing Corporation  2015
    The effect of a magnetic field on the fully developed forced convection of Fe3O4 flow inside a copper tube is experimentally and numerically investigated. The flow is assumed to be under uniform heat flux. This study aims to examine the effects of the nanoparticle volume fraction, as well as alternating magnetic field strength and frequency, on the convective heat transfer for different Reynolds numbers. To ensure accuracy, the numerical results are validated by empirical results with similar geometry and boundary conditions. A satisfying agreement was achieved. The results show that the heat transfer increases with increase in alternating magnetic field frequency but... 

    Simulation of water purification using magnetically ultra-responsive micro- and nanoscavengers

    , Article Journal of Water Process Engineering ; Volume 24 , 2018 , Pages 63-73 ; 22147144 (ISSN) Asghari, E ; Moosavi, A ; Kazemzadeh Hannani, S ; Sharif University of Technology
    Elsevier Ltd  2018
    Access to clean water is one of the challenges of the 21st century. Thus water purification is inevitable. One method of water treatment is purification by magnetic particles in the presence of magnetic field. The contaminants are attached to the magnetic particles and then by applying a magnetic field, magnetic particles and, thus, the pollutants can be collected. For the optimal design of a water treatment system, the effect of important parameters in the design, such as magnetic fields, particle size, and Reynolds number are determined numerically by modeling and simulating the water treatment process. Two methods are used to create the magnetic field: permanent magnet and coils. It is... 

    Intensification of heat transfer rate in a rectangular channel equipped with pins, using non-uniform magnetic field

    , Article Journal of Nanofluids ; Volume 8, Issue 5 , 2019 , Pages 1041-1050 ; 2169432X (ISSN) Mokhtari, M ; Hariri, S ; Sharif University of Technology
    American Scientific Publishers  2019
    In the present study, numerical simulation is used to evaluate the influence of the non-uniform magnetic field on the heat transfer of magnetic nanofluids inside a pinned channel. This article focused on the flow pattern and heat transfer of water-based nanofluids in the presence of a wire in a three-dimensional geometry. In this work, the fluid flow is laminar and constant heat flux is applied on the wall of the channel. A wire in various orientations, in comparison with the axis of the channel, generates the magnetic field. The base fluid is water and Nano-particles (Fe3O4 and Fe) add to base fluid with different volume concentrations (0, 0.5, 1%). The computational fluids dynamic is used... 

    The influence of conductor sag on spatial distribution of transmission line magnetic field

    , Article 5th IFAC Symposium on Power Plants and Power Systems Control 2003, 15 September 2003 through 19 September 2003 ; Volume 36, Issue 20 , 2003 , Pages 1145-1149 ; 14746670 (ISSN) Kumleh, B. P ; Varahram, M. H ; Kumieh, S. P ; Sharif University of Technology
    IFAC Secretariat  2003
    Common methods for the calculation of electric fields created by power transmission lines assume straight lines parallel to a flat ground and the influence of the sag due to the line weight is neglected. In this paper the magnetic fields of a catenary 3Phase line that has a change in direction was calculated and discussed. It is believed that this work has not been published before. © 2003 IFAC  

    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... 

    Experimental study of internal forced convection of ferrofluid flow in porous media

    , Article Defect and Diffusion Forum ; Vol. 348 , April , 2014 , pp. 139-146 ; ISSN: 10120386 ; ISBN: 9783038350002 Sehat, A ; Sadrhosseini, H ; Shafii, M. B ; Sharif University of Technology
    This work presents an experimental study of the effect of a magnetic field on laminar forced convection of a ferrofluid flowing in a tube filled with permeable material. The walls of the tube are subjected to a uniform heat flux and the permeable bed consists of uniform spheres of 3-mm diameter. The ferrofluid synthesis is based on reacting iron (II) and iron (III) in an aqueous ammonia solution to form magnetite, Fe3O4. The magnetite is mixed with aqueous tetra methyl ammonium hydroxide, (CH3) 4NOH, solution. The dependency of the pressure drop on the volume fraction, and comparison of the pressure drop and the temperature distribution of the tube wall is studied. Also comparison of the... 

    Superparamagnetic nanoparticles for epilepsy detection

    , Article World Congress on Medical Physics and Biomedical Engineering, 2015, 7 June 2015 through 12 June 2015 ; Volume 51 , June , 2015 , Pages 1237-1240 ; 16800737 (ISSN) ; 9783319193878 (ISBN) Pedram, M. Z ; Shamloo, A ; Alasty, A ; Ghafar Zadeh, E ; Jaffray D. A ; Sharif University of Technology
    Springer Verlag  2015
    Epilepsy is the most common neurological disorder that is known with uncontrolled seizure. Around 30% of patients with epilepsy resist to all forms of medical treatments and therefore, the removal of epileptic brain tissue is the only solution to get these patients free from chronical seizures. The precise detection of an epileptic zone is key to its treatment. In this paper, we propose a method of epilepsy detection using brain magnetic field. The possibility of superparamagnetic nanoparticle (SPMN) as sensors for the detection of the epileptic area inside the brain is investigated. The aggregation of nanoparticles in the weak magnetic field of epileptic brain is modeled using potential... 

    Experimental study of internal forced convection of ferrofluid flow in non-magnetizable/magnetizable porous media

    , Article Experimental Thermal and Fluid Science ; Volume 96 , 2018 , Pages 441-450 ; 08941777 (ISSN) Shafii, M. B ; Keshavarz, M ; Sharif University of Technology
    Elsevier Inc  2018
    In this work, the thermal and hydrodynamic performance of ferromagnetic fluid, which flows through a copper tube in thermal entrance region, has been studied. The flow in the tube is laminar and subjected to constant heat flux. A part of the tube contains a porous medium with paramagnetic properties and porosity of 0.46. Ferrofluid is composed of Fe3o4 and water with (CH3)4NOH as a surfactant that is prepared in three different volume fractions. The effects of constant and oscillating magnetic fields on convective heat transfer coefficient were examined for various Reynolds numbers, frequencies and volume fractions. The results show that the maximum enhancements of average heat transfer... 

    Effect of magnetic field treatment on interfacial tension of CTAB nano-emulsion: developing a novel agent for enhanced oil recovery

    , Article Journal of Molecular Liquids ; Volume 261 , July , 2018 , Pages 107-114 ; 01677322 (ISSN) Saeedi Dehaghani, A. H ; Badizad, M. H ; Sharif University of Technology
    Elsevier B.V  2018
    Nanoemulsion is a novel type of emulsified solutions holding great promises for utilizing in industrial applications. Although microemulsions have been the subject of numerous studies in past decades, however, nanoemulsions are quite virgin and merit detailed investigation to scrutinize their characteristics specific to reservoir engineering, in particular, Enhanced Oil Recovery (EOR). To this end, the present study is an attempt to evaluate the effectiveness of a specific nanoemulsion for oil displacement through porous media. In this regard, flooding experiments were designed and Hexa decyl trimethylammonium bromide (CTAB), which is a cationic surfactant, was used as the emulsifying agent.... 

    Ferrofluid droplet formation from a nozzle using alternating magnetic field with different magnetic coil positions

    , Article Journal of Magnetism and Magnetic Materials ; Volume 498 , 2020 Favakeh, A ; Bijarchi, M. A ; Shafii, M. B ; Sharif University of Technology
    Elsevier B.V  2020
    Ferrofluid has been used in many fields, such as microfluidics, droplet formation, and heat transfer, due to its potential to be attracted in the presence of a magnetic field. Droplet formation, itself, has many applications such as emulsions, 3D micro-printers, MEMS, and electro-sprays. In this study, the mechanism of ferrofluid droplet formation from the nozzle in the presence of an alternating magnetic field was investigated. The magnetic coil was fixed at different angles with respect to gravity and the effect of the alternating magnetic field and the angle of the magnetic coil axis with respect to gravity on the produced droplet volume, satellite droplet, and droplet formation frequency... 

    Methods of reducing magnetic field near the transmission lines

    , Article Amirkabir (Journal of Science and Technology) ; Volume 14, Issue 55 A , 2003 , Pages 610-630 ; 10150951 (ISSN) Porkar, B ; Porkar, S ; Vahidi, B ; Sharif University of Technology
    Due to biological effects of magnetic fields of high voltage transmission lines and induceed effects on gas pipe line, telecommunication system and inteference with sensitive electronic equipment, many effort have been done to reduce transmission lines magnetic fields and several ideas have been introduced. In this paper we review three methods: phase split, shielded and compacted line methods. With aid of a developed software programme these methods are then applied to transmission lines and the results are analyzed  

    Itinerant electron transport in microscopically inhomogeneous magnetic fields

    , Article Journal of Magnetism and Magnetic Materials ; Volume 299, Issue 2 , 2006 , Pages 356-361 ; 03048853 (ISSN) Nasirpouri, F ; Nogaret, A ; Atkinson, D ; Ghorbani, M ; Iraji Zad, A ; Sharif University of Technology
    We report on magnetoresistance measurements in thin nickel films modulated by a periodic magnetic field emanating from micromagnetic arrays fabricated at the film surface. By increasing the strength of the magnetic potential using nickel and dysprosium micromagnets, we are able to quench the anisotropic magnetoresistance (AMR) in the film. © 2005 Elsevier B.V. All rights reserved  

    Convective-heat transfer of magnetic-sensitive nanofluids in the presence of rotating magnetic field

    , Article Applied Thermal Engineering ; Volume 116 , 2017 , Pages 329-343 ; 13594311 (ISSN) Fadaei, F ; Molaei Dehkordi, A ; Shahrokhi, M ; Abbasi, Z ; Sharif University of Technology
    Elsevier Ltd  2017
    In this work, forced-convection heat transfer of magnetic-sensitive nanofluids has been investigated in the presence of rotating magnetic field. In this regard, the laminar, Newtonian, incompressible, and two-dimensional (2D) fluid flow in a horizontal duct subject to constant wall temperature boundary condition was modeled. Moreover, the fluid was supposed to be non-electrical conductive and the magnetic field source comprised of two time varying components perpendicular to each other. Influences of magnetic field intensity and frequency, inlet fluid velocity, and spin viscosity on the forced-convection heat transfer of the magnetic nanofluids were investigated. It was found that the... 

    Experimental investigation into laminar forced convective heat transfer of ferrofluids under constant and oscillating magnetic field with different magnetic field arrangements and oscillation modes

    , Article Experimental Thermal and Fluid Science ; Volume 68 , November , 2015 , Pages 601-611 ; 08941777 (ISSN) Yarahmadi, M ; Moazami Goudarzi, H ; Shafii, M. B ; Sharif University of Technology
    Elsevier Inc  2015
    In this study, the effects of ferrofluids on the forced convective heat transfer in a tube with a round cross section under constant heat flux in the laminar flow regime are investigated experimentally. For this purpose, an experimental setup was designed and built. Furthermore, the effects of an external magnetic field on the forced convective heat transfer were examined for various Reynolds numbers and volume concentrations. The parameters of magnetic field strength, magnetic field arrangement, the constancy or oscillation of the magnetic field and also its oscillatory mode were examined. As a result of the experimental studies, in the absence of a magnetic field enhancement in convective... 

    Experimental investigation on laminar forced convective heat transfer of ferrofluid loaded with carbon nanotubes under constant and alternating magnetic fields

    , Article Experimental Thermal and Fluid Science ; Volume 76 , 2016 , Pages 1-11 ; 08941777 (ISSN) Shahsavar, A ; Saghafian, M ; Salimpour, M. R ; Shafii, M. B ; Sharif University of Technology
    Elsevier Inc 
    In this paper, the effects of both constant and alternating magnetic fields on the laminar forced convective heat transfer of a hybrid nanofluid containing tetramethylammonium hydroxide (TMAH) coated Fe3O4 nanoparticles and gum arabic (GA) coated carbon nanotubes (CNTs) flowing through a heated tube were investigated experimentally. The experiments were carried out over wide range of parameters such as Reynolds number (548-2190), volume concentrations of Fe3O4 (0.5-0.9%) and carbon nanotube (0.25-1.35%) nanoparticles, magnetic field strength (300-700 Gauss) and alternating magnetic field frequency (10-50 Hz). In present study, the experimental observations in the case without magnetic field... 

    A SPH solver for simulating paramagnetic solid fluid interaction in the presence of an external magnetic field

    , Article Applied Mathematical Modelling ; Volume 40, Issue 7-8 , 2016 , Pages 4341-4369 ; 0307904X (ISSN) Hashemi, M. R ; Manzari, M. T ; Fatehi, R ; Sharif University of Technology
    Elsevier Inc  2016
    The Smoothed Particle Hydrodynamics (SPH) method is extended to solve magnetostatic problems involving magnetically interacting solid bodies. In order to deal with the jump in the magnetic permeability at a fluid-solid interface, a consistent SPH scheme is utilized and a modified formulation is proposed to calculate the magnetic force density along the interface. The results of the magnetostatic solver are verified against those of the finite element method. The governing fluid flow equations are discretized using the same SPH scheme, developing an efficient method for simulating the motion of paramagnetic solid bodies in a fluid flow. The proposed algorithm is applied to a benchmark problem... 

    Numerical investigation of effects of uniform magnetic field on heat transfer around a sphere

    , Article International Journal of Heat and Mass Transfer ; Volume 114 , 2017 , Pages 703-714 ; 00179310 (ISSN) Abbasi, Z ; Molaei Dehkordi, A ; Abbasi, F ; Sharif University of Technology
    Elsevier Ltd  2017
    In this article, ferrohydrodynamic forced-convection heat transfer from a heated sphere embedded in a ferrofluid in the presence of the uniform external magnetic field has been studied numerically for the first time over a wide range of Reynolds number value, nanoparticle diameter, particle volume fraction, and magnetic field intensity. Despite the uniform external magnetic field applied, the internal magnetic field near the sphere could be nonuniform due to the considerable difference between the relative magnetic permeability of the sphere and the surrounding medium. Kelvin body force arises from this nonuniformity and induces vortexes near the sphere. These vortexes disturb the boundary...