Sharif Digital Repository

A new method for fluorescent microscopy has been proposed. Proposed method uses indirect excitation of fluorophores with nanometer localized illuminating source. Localized source is created at corners of gold nanotriangles which are deposited on glass substrate. Actually the combination of gold nanotriangle (deposited on glass) acts as active substrate (where species will be placed) for our proposed method. The structure will be scanned with a focused beam of laser (or combination of beams). Due to electric field enhancement in corners and edges of nanotringle (because of surface plasmons), third order nonlinear effect will be enhanced accordingly. Enhancement in third order nonlinearity... 

Controlled rotation of a suspended soap water film, simply generated by applying an electric field, has been reported recently. The film rotates when the applied electric field exceeds a certain threshold. In this study, we investigate the phenomenon in films made of a number of other liquids with various physical and chemical properties. Our measurements show that the intrinsic electrical dipole moments of the liquid molecules seems to be vital for the corresponding film rotation. All the investigated rotating liquids have a molecular electric dipole moment of above 1 Debye, while weakly polar liquids do not rotate. However, the liquids investigated here cover a wide range of physical... 

Electrophoretic technique was used to deposit micro- and nano-sized aluminum nitride coatings on stainless steel surfaces by using a well-dispersed stable suspension produced by addition of AlN powder plus a small amount of iodine to ethanol. Parabolic regime governed the deposition. Electrophoretic deposition for 240 s at 100 V resulted in formation of a uniformly dense film on the top, but a porous inhomogeneous layer at the bottom. This was attributed to fast deposition of coarse particles and/or agglomerates at large electric fields. After drying, micro-sized particles led to a uniform crack-free interface while nano-particles resulted in fragmented non-cohesive layers. Weight loss... 

The axisymmetric problem of a concentric set of energetically consistent annular and penny-shaped cracks in an infinite piezoelectric body subjected to uniform far-field electromechanical loading is addressed. With the aid of a robust innovated technique, the pertinent four-part mixed boundary value problem (MBVP) is reduced to a decoupled Fredholm integral equation of the second kind. The results of two limiting cases of a single penny-shaped crack and a single annular crack are recovered. The contour plots of dimensionless intensity factors (IFs) at each crack front provide the stress and electric displacement intensity factors (SIFs and EDIFs, respectively) for all combination of crack... 

Abstract: In this study, chitosan–Laponite nanocomposite coatings with bone regenerative potential and controlled drug-release capacity are prepared by electrophoretic deposition technique. The controlled release of a glycopeptide drug, i.e. vancomycin, is attained by the intercalation of the polymer and drug macromolecules into silicate galleries. Fourier-transform infrared spectrometry reveals electrostatic interactions between the charged structure of clay and the amine and hydroxyl groups of chitosan and vancomycin, leading to a complex positively-charged system with high electrophoretic mobility. By applying electric field the charged particles are deposited on the surface of titanium... 

Some of electrokinetic-based biomicrofluidic devices work at zeta potentials that are sufficiently high for ionic size (steric) effects to show up. In the present effort, consideration is given to the steric effects on the hydrodynamics of electroosmotic flow in a rectangular microchannel. The distinction between this research and the previous ones is that we account for non-linear rheology of the fluids encountered in biomicrofluidic systems by means of the power-law viscosity model. The method of analysis consists of a finite-difference-based numerical procedure for a non-uniform distribution of grid points, which is applied to the dimensionless form of the governing equations including... 

Transformers are known as one of the most important equipment in power system transmission and distribution network. Safety of transformer insulation is determined mainly by its insulating oil dielectric strength. A major concern which threaten the withstand strength of a liquid insulation is the presence of particle contamination. One of the best methods to detect any abnormality and insulation weakness inside the transformer insulation is based on partial discharge (PD) measurement. Here, to identify the presence of conducting particles inside the transformer insulating oil, the general routine used for PD recognition is employed. This process involves the following steps: current signal... 

Partial Discharge (PD) measurements in Ultra High Frequency (UHF) band requires modern techniques for monitoring of power transformer. This is a topic of interest investigated in this field, especially in recent years. Different experimental models, such as: defect models, and winding models are used in PD studies of power transformer. The purpose in application of these models is to represent and simulate the real transformer performance using a simple model. The proposed model needs to be a simplified one which can be implemented of them. However, the applied simplifications may result in some changes (inaccuracy) into the recorded PD current signals captured by UHF sensors. These changes... 

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  

Abstract This article studies a submerged membrane electro-bioreactor (SMEBR), an integrated system embracing biological treatment, electrical coagulation, and membrane filtration, all in one individual reactor, by applying an alternating electric field to a membrane bioreactor (MBR). The alternating electric field has been applied with current densities ranging from 5 to 23 A/m2 under eight different electrical exposure modes. The results indicate that under the optimum condition with a current density of 12.5 A/m2 and an exposure mode of (415 s OFF-185 s ON), the COD and phosphate removals would be respectively 4% and 43% more compared to an unmodified MBR system. Also at the same current... 

Abstract A visible-light-active Ag3PO4/BiPO4 nanocomposite with a p-n heterojunction structure was fabricated via a co-precipitation hydrothermal process using 2-hydroxylethylammonium formate (RTIL) as a room-temperature ionic liquid. The resulting catalysts were characterized by various techniques. The photocatalytic activity of the photocatalysts was evaluated by the photodegradation of phthalocyanine Reactive Blue 21 (RB21) under both visible and UV light irradiations. The results reveal that the heterojunction composite prepared in RTIL noticeably exhibited an improvement in both efficiency and rate of RB21 photodegradation in comparison with pure Ag3PO4 and BiPO4. The enhanced... 

In this paper, the effect of radial structure on the performance of a linear-lateral GaAs high power photoconductive semiconductor switch (PCSS) is investigated. For this purpose a three-dimensional device modeling is used to model the optically initiated GaAs switch. In this simulation a p-type device with carbon as shallow acceptor is compensated by deep donor EL2 level as a trap level. The PCSS device is designed in a back-triggered, radially symmetric switch structure which extends the blocking voltage by reducing the peak electric field near the electrodes. Device modeling was performed and the effect of different trap concentrations on dark I-V characteristics has been investigated. In... 

The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In the present work, attention is given to the influences of finite ionic size on the cross stream diffusion process in an electrokinetically actuated Y-shaped micromixer. The method consists of a finite difference based numerical approach for non-uniform grid which is applied to the dimensionless form of the governing equations, including the modified Poisson-Boltzmann equation. The results reveal that, neglecting the ionic size at high zeta potentials gives... 

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  

Determination of effective transport properties of droplet-hydrogel composites is essential for various applications. The transport of ions through a droplet-hydrogel composite subjected to an electric field is theoretically studied as an initial step toward quantifying the effective transport properties of droplet-hydrogel composites. A three-phase electrokinetic model is used to derive the microscale characteristics of the polyelectrolyte hydrogel, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which encloses the interior fluid. The surface has the thickness of zero and the electrostatic potential ζ. Standard... 

This paper has investigated the performance of a linear, 6H-SiC high power photoconductive semiconductor switch. A three-dimensional device modeling with SILVACO ATLAS tools was used to model the optically initiated 6H-SiC switch. The 6H-SiC PCSS device is designed in a rear-illuminated, radial switch structure. The material properties of vanadium compensated 6H-SiC PSCC have been analyzed for breakdown, photocurrent profile such as rise and fall time in terms of their applications as a photoconductive switch at high bias conditions. This structure and also new type of illumination extends the blocking voltage by reducing the peak electric field near electrodes. In this presentation the... 

Micro actuators are an irreplaceable part of motion control in miniaturized systems and are intended to have a high range of deformation, high accuracy, large force, and quick response. In this article, an analytical model for a hybrid thermopiezoelectric micro actuator is developed in which a double lead-zirconnate-titanate piezoceramic (PZT) beam structure consisting of two arms with different lengths are used. Governing differential equation of motion and electrical field are derived and solved. Out of parametric studies it was observed that, under application of temperature and voltage gradients, the deflection of the actuator shows different trends depending on the geometry of the micro... 

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... 

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... 

We present here a simulator that solves the main semiconductor charge and transport equations coupled to Maxwell equations to study receivers based on photoconductive antennas (R-PCAs). Making use of this tool we were able to correctly characterize the operation of these antennas. In doing so, we compared simulations with the results of the semi-empirical expression ITHz(r) ∝σc(t)∗ ETHz(t) employed to evaluate the detected photocurrent by means of the convolution between the photoconductivity in the receiver and the electric field linked to the emitter antenna. We were able to accurately reproduce experimental data with our simulation tool. These kinds of...