Loading...
Search for:
electric-fields
0.017 seconds
Total 227 records
Rotational and Translational Dynamics of Silver and Titanium Dioxide Nanowires Suspended in Dielectric Media in Electric Fields
, Ph.D. Dissertation Sharif University of Technology ; Moshfegh, Alireza (Supervisor) ; Esfandiar, Ali (Co-Supervisor)
Abstract
Wide utilization of nanomanipulation as a promising approach in microorganisms, nanoelectromechanical systems (NEMS) and assembly of nanostructures remarks the importance of nanostructures’ motion in electric fields. Despite of many reports on manipulation and assembly of nanowires (NWs) in non-uniform and alternating electric fields by dielectrophoresis, and also rotation of NWs in rotating electric fields, there is still a lack of knowledge on rotational and translational dynamics of metallic and dielectric NWs in uniform static electric fields. In this dissertation, we study the dynamics of silver (Ag) and titanium dioxide (TiO2) NWs, with diameters and lengths in the range of 40 to 100...
Numerical Simulation of Non-Newtonian Droplet Formation under External Electric Field in a Microfluidic Device
, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor) ; Kazemzadeh Hannani, Siamak (Supervisor)
Abstract
Droplet formation and breakup processes are one of the important steps in many microfluidic devices with a wide range of biological and chemical applications. The purpose of this study is numerical simulation of non-Newtonian droplet formation under the influence of electric field in a microfluidic system. The innovation aspect of this project is the use of non-Newtonian fluid in this process, which, despite many applications in real issues, has been less studied, and in most of the previous researches, Newtonian fluid assumption has been used to simplify the solving. Also, simultaneously, the effects of an external electric field on this process were also studied. Carboxymethyl cellulose...
Eigenfield Theory for Grade Two Flexoelectric Composites with Periodic or Arbitrary Nanostructure and General Anisotropy
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
Studying the behavior of electromechanical systems containing nanostructures, because of their widespread applications in the nanoscience and technology is of great interest. For this purpose, this work is devoted to analytical and exact determination of the electroelastic fields associated with periodic and arbitrary distributions of electromechanical nano inclusions and nano inhomogeneities of various shapes within electroelastic mediums of general anisotropy. Since classical continuum Theories are inadequate in accounting for size affects in nanostructures, a first strain gradient - first electric field gradient theory is applied. The present work considers Piezoelectric and Flexoelectric...
Investigating the Effect of Electric Fields on the Efficiency of Phase Micro Separator Using Simulation
, M.Sc. Thesis Sharif University of Technology ; Mohammadi, Ali Asghar (Supervisor)
Abstract
In this study, the performance of electrocoalescence in a microfluidic device was investigated through numerical simulations. The microfluidic device consisted of two immiscible fluids, a continuous phase, and a dispersed phase, which were modeled as incompressible Newtonian fluids. The interface between the two phases was tracked using a phase-field model. A flow-focusing geometry was employed to crate water droplets in oil. The dispersed droplets were then pass over a set of electrodes. The merging of two adjacent droplets in the microfluidic device was observed by applying a constant electric field. The voltage of 60 V is the lowest voltage at which the regular merging of pairs of drops...
Numerical simulation of high voltage electric pulse comminution of phosphate ore
, Article International Journal of Mining Science and Technology ; Volume 25, Issue 3 , 2015 , Pages 473-478 ; ISSN: 20952686 ; Rezai, B ; Irannajad, M ; Ravanji, M. H ; Sharif University of Technology
Abstract
Numerical simulation of the electrical field distribution helps in-depth understanding of the mechanisms behind the responses and the benefits of the high voltage pulse comminution. The COMSOL Multiphysics package was used to numerically simulate the effect of ore compositions in this study. Regarding phosphate ore particles shape and composition, the effects of mineral composition, particle size, particle shape and electrodes distance were investigated on the electrical field intensity and distribution. The results show that the induced electrical field is significantly dependent on the electrical properties of minerals, the feed particle size and the location of conductive minerals in...
A novel field ionization gas sensor based on self-organized CuO nanowire arrays
, Article Sensors and Actuators, A: Physical ; Vol. 216 , 2014 , pp. 202-206 ; ISSN: 09244247 ; Ahmadvand, H ; Iraji Zad, A ; Sharif University of Technology
Abstract
In this study, we present fabrication and characterization of a gas ionization sensor based on high aspect ratio one-dimensional CuO nanowires as the field enhancing medium. Self-organized arrays of CuO nanowires have been synthesized based on a low-cost thermal oxidation method and integrated into a gas ionization sensor (GIS). The self-organized arrays of CuO nanowires have been employed to detect the identity of several gas species such as He, Ar and CO at ambient temperature and pressure. The sharp nanoscale size of CuO tips provide very high electric fields at moderate voltages (less than 100 V) and provoke the breakdown of different gases. The reduced breakdown current of the metal...
Polyelectrolytes polarization in nonuniform electric fields
, Article International Journal of Modern Physics C ; Volume 25, Issue 12 , 2014 ; ISSN: 17936586 ; Ejtehadi, M. R ; Varnik, F ; Sharif University of Technology
Abstract
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
High-performance/low-temperature-processed dye solar cell counter electrodes based on chromium substrates with cube-like morphology
, Article Journal of Power Sources ; Vol. 260 , 2014 , Pages 299-306 ; ISSN: 03787753 ; Taghavinia, N ; Sharif University of Technology
Abstract
There is still an open question of how to prepare high-performance counter electrodes for dye solar cells (DSCs) at room temperature; a requirement for flexible DSCs. Here, we introduce Pt deposited cube-like chromium coating as a low-temperature highly-efficient counter electrode for DSCs. Cr is a chemically stable metal and can be easily electroplated on conductive substrates with high roughness (here ∼160 nm) and cube-like appearance. A cyclic electrochemical deposition method with optimized temperature and number of cycles is used to grow Pt nanoparticles on this surface and charge transfer resistance as low as 0.54 Ω cm2 and 0.27 Ω cm2 were obtained at 40 °C and 55 °C solution...
Effects of electrophoretic deposition parameters on the photocatalytic activity of TiO2 films: Optimization by response surface methodology
, Article Colloids and Surfaces A: Physicochemical and Engineering Aspects ; Vol. 452, Issue. 1 , 2014 , pp. 1-8 ; ISSN: 09277757 ; Vossoughi, M ; Feilizadeh, M ; Rashtchian, D ; Moradi, S ; Alemzadeh, I ; Sharif University of Technology
Abstract
In this work, the electrophoretic deposition method was utilized to immobilize TiO2 particles on stainless steel substrates. In addition, for the first time, statistics-based experimental design using response surface methodology was employed to investigate the effect of four key coating parameters (i.e. applied voltage, calcination temperature, photocatalyst weight percentage, and deposition time) on the photocatalytic degradation. Analysis of variance revealed that the proposed model was adequate. X-ray diffraction and scanning electron microscope were used to evaluate the effects of the parameters on degradation efficiency. The optimum applied voltage, calcination temperature, catalyst...
Critical study and discrimination of different formulations of electromagnetic force density and consequent stress tensors inside matter
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Vol. 89, issue. 4 , April , 2014 ; ISSN: 10502947 ; Mehrany, K ; Sharif University of Technology
Abstract
By examination of the exerted electromagnetic (EM) force on boundary of an object in a few examples, we look into the compatibility of the stress tensors corresponding to different formulas of the EM force density with special relativity. Ampere-Lorentz's formula of the EM force density is physically justifiable in that the electric field and the magnetic flux density act on the densities of the total charges and the total currents, unlike Minkowski's formula which completely excludes the densities of the bounded charges and the bounded currents inside homogeneous media. Abraham's formula is fanciful and devoid of physical meaning. Einstein-Laub's formula seems to include the densities of...
Nanofluidic transport inside carbon nanotubes
, Article Journal of Physics D: Applied Physics ; Volume 47, Issue 6 , 12 February , 2014 ; ISSN: 00223727 ; Moosavi, A ; Akbarzadeh, A. M ; Sharif University of Technology
Abstract
Using non-equilibrium molecular dynamics simulations, we investigate the effects of nanotube size, mean flow velocity, ion concentration and temperature of an electrolyte water solution on shearing stress and nominal viscosity. It is shown that the distributed electric field arising from the electrolyte water solution has significant influences on fluid properties. Also, the temperature of the solution, which causes thermal movement, affects nanofluidic transport in nanoenvironments. The nominal viscosity and shearing stress increases as the tube diameter increases. When the temperature of solution increases or ion concentration decreases, the shearing stress and nominal viscosity increase....
Liquid soap film generates electricity: a suspended liquid film rotating in an external electric field as an electric generator
, Article Microfluidics and Nanofluidics ; Vol. 18, issue. 1 , Apr , 2014 , pp. 141-147 ; ISSN:16134982 ; Feiz, M. S ; Namin, R. M ; Sharif University of Technology
Abstract
We have observed that a rotating liquid soap film generates electricity when placed between two non-contact electrodes with a sufficiently large potential difference. In our experiments, suspended liquid film (water + soap film) is formed on the surface of a circular frame, which is forced to rotate in the x−y horizontal plane by a motor. This system is located at the center of two capacitor-like vertical plates to apply an external electric voltage difference in the x-direction. The produced electric current is collected from the liquid film using two conducting electrodes that are separated in the y-direction. We previously reported that a liquid film in an external electric field rotates...
LBM simulation of electro-osmotic flow (EOF) in nano/micro scales porous media with an inclusive parameters study
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Vol. 7 , November , 2014 ; ISBN: 9780791849545 ; Lee, E. S ; Salimi, M. R ; Sharif University of Technology
Abstract
In this paper, we present our results about simulation of 2D-EOF in Nano/Micro scales porous media using lattice Boltzmann method (LBM) in micro-channel for EOF. The high efficient numerical code use strongly high nonlinear Poisson Boltzmann equation to predicate behavior of EOF in complex geometry. The results are developed with precisely investigation of several effective parameters on permeability of EOF, such as geometry (channel height and number and location of charge), external electric field, thickness of Debye length (ionic concentration), and zeta potential. Our results are in excellent agreement with available analytical results. Our results show that for certain external electric...
Electrokinetic mixing and displacement of charged droplets in hydrogels
, Article Transport in Porous Media ; Vol. 104, Issue. 3 , Jun , 2014 , pp. 469-499 ; ISSN: 01693913 ; Sharif University of Technology
Abstract
Mixing in droplets is an essential task in a variety of microfluidic systems. Inspired by electrokinetic mixing, electric field-induced hydrodynamic flow inside a charged droplet embedded in an unbounded polyelectrolyte hydrogel is investigated theoretically. In this study, the polyelectrolyte hydrogel is modeled as a soft, and electrically charged porous solid saturated with a salted Newtonian fluid, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which is located at the plane of shear, with the electrostatic potential ζ. The fluid inside the droplet attains a finite velocity owing to hydrodynamic coupling with the...
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 ; Piri-Moghadam, H ; Rastegar, S ; Sharif University of Technology
Abstract
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...
Thermal conductivity of anisotropic spin-1/2 two leg ladder: Green's function approach
, Article European Physical Journal B ; Vol. 87, issue. 8 , Oct , 2014 ; Langari, A ; Van Loosdrecht, P. H. M ; Zotos, X ; Sharif University of Technology
Abstract
We study the thermal transport of a spin-1/2 two leg antiferromagnetic ladder in the direction of legs. The possible effect of spin-orbit coupling and crystalline electric field are investigated in terms of anisotropies in the Heisenberg interactions on both leg and rung couplings. The original spin ladder is mapped to a bosonic model via a bond-operator transformation, where an infinite hard-core repulsion is imposed to constrain one boson occupation per site. The Green's function approach is applied to obtain the energy spectrum of quasi-particle excitations responsible for thermal transport. The thermal conductivity is found to be monotonically decreasing with temperature due to increased...
Numerical analysis of ciliary beat in Paramecium: Increasing ciliary spacing as a low energy cost method for maneuvering
, Article Recent Patents on Mechanical Engineering ; Volume 6, Issue 3 , September , 2013 , Pages 227-237 ; 1874477X (ISSN) ; Zand, M. M ; Sharif University of Technology
2013
Abstract
In recent years, a number of patents have been devoted to designing micro robots for minimally invasive therapies inspired by Paramecium. Paramecium changes its swimming direction due to application of an external magnetic or electric field. Changing ciliary beat direction and frequency have been identified as possible methods for maneuvering through water; however, effects of variations in ciliary spacing on swimming trajectory have been poorly studied. In this work, it is aimed to analyze the effects of adjusting the ciliary spacing on swimming trajectory. For determining the swimming trajectory, Paramecium membrane is discretized to boundary elements with length of 15μm on which there are...
Experimental investigation of the stability of the floating water bridge
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 88, Issue 3 , 2013 ; 15393755 (ISSN) ; Azizpour Lindi, S ; Amjadi, A ; Jafari, N ; Irajizad, P ; Sharif University of Technology
2013
Abstract
When a high voltage is applied between two beakers filled with deionized water, a floating bridge of water is formed in between exceeding the length of 2 cm when the beakers are pulled apart. Currently two theories regarding the stability of the floating water bridge exist, one suggesting that the tension caused by electric field in the dielectric medium is holding the bridge and the other suggesting surface tension to be responsible for the vertical equilibrium. We construct experiments in which the electric field and the geometry of the bridge are measured and compared with predictions of theories of the floating water bridge stability. We use a numerical simulation for estimation of the...
Semi-conducting carbon nanotube as variable capacitor
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 54 , 2013 , Pages 9-14 ; 13869477 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2013
Abstract
This paper proposes a novel, one-part, variable capacitor, using semi-conducting carbon nanotube (CNT). This variable capacitor works based on the change in the electronic structure of CNTs under applied voltage and deformations. Positive and negative charges are stored at both ends of a non-zero band gap nanotube which works as metallic electrodes in parallel plate capacitors. Also the neutral strip in the middle acts as the dielectric part of a conventional capacitor under the influence of an external electric field. Mechanical strains on carbon nanotube change its band gap energy and thus the length of neutral strip and charged regions. The lengths of these parts are primarily dependent...
Continuous size-based focusing and bifurcating microparticle streams using a negative dielectrophoretic system
, Article Microfluidics and Nanofluidics ; Volume 14, Issue 1-2 , 2013 , Pages 265-276 ; 16134982 (ISSN) ; Saidi, M. S ; Sadeghi, A ; Sani, M
2013
Abstract
Dielectrophoresis (DEP) is an electrokinetic phenomenon which is used for manipulating micro- and nanoparticles in micron-sized devices with high sensitivity. In recent years, electrode-based DEP by patterning narrow oblique electrodes in microchannels has been used for particle manipulation. In this theoretic study, a microchannel with triangular electrodes is presented and a detailed comparison with oblique electrodes is made. For each shape, the behavior of particles is compared for three different configurations of applied voltages. Electric field, resultant DEP force, and particle trajectories for configurations are computed by means of Rayan native code. The separation efficiency of...