Sharif Digital Repository

A promising electrochemical sensor was developed based on a layer by layer process by electro-polymerization of pyrrole in the presence of new coccine (NC) as dopant anion on the surface of the multi-walled carbon nanotubes (MWCNTs) pre-coated glassy carbon electrode (GCE). The modified electrode was used as a new and sensitive electrochemical sensor for voltammetric determination of sumatriptan (SUM). The electrochemical behavior of SUM was investigated on the surface of the modified electrode using linear sweep voltammetry (LSV). The results showed a remarkable increase (∼12 times) in the anodic peak current of SUM in comparison to the bare GCE. The effect of experimental variables such... 

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 presents an event based scheme for uncompressed video watermarking. The video signal is assumed to be a sequence of overlapping visual components - called events. We address this overlapping structure of video contents and present an event based approach through employing a block based Temporal Decomposition (TD) scheme. The TD describes a set of spectral parameters of the video as a linear combination of a set of temporally overlapping compact event functions. We have applied the decomposition results to digital video watermarking. To construct the matrix of parameters in the TD, Multiresolution Singular Value Decomposition (MR-SVD) is utilized and singular values of a set of... 

Differential pulse polarography (DPP) was applied for the determination of the herbicide Tribenuron-methyl (TBM). This is a first study for various parameters affecting the reduction peak current were simultaneously optimized using experimental design and these results are different from other reports. The effect of factors such as voltage step, voltage step time, pulse amplitude, pulse time, sample pH, concentration of the supporting electrolyte and the mercury drop size were assessed by means of a (27-2) fractional factorial design. It was found that the effects and interactions of four out of seven factors were significant. Consequently, a central composite design (CCD) with four factors,... 

The condition known as a water-hammer problem is a transient condition that may occur as a result of worst-case loadings, such as pump failures, valve closures, etc. in pipeline systems. The pressure in the water hammer can vary in such a way that in some cases it may increase and cause destruction to the hydraulic systems. The pressure in the water hammer can also be decreased to the extent that it can fall under the saturation pressure, where cavitation appears. Therefore, the liquid is vaporized, thus, making a two-phase flow. This pressure decrease can be as dangerous as the pressure rise. As a result of the pressure drop and vaporization of the liquid, two liquid regions are separated,... 

Surface tension driven passive micro-pumping relies mainly on the surface tension properties. To have control over surface tension driven passive micro-pumps (STD-PMPs), it is essential to understand the physical background of the fluid flow in these pumps. Hence, the purpose of this work is to give an exploration of the flow physics of a STD-PMP. In this regard, computer simulation is used to give detailed information about the flow pattern and physical phenomena at different conditions. To this end, a droplet of water, with a specified diameter, is placed onto an entry port connected to another droplet at the exit port via a microchannel. The results indicate that the pumping process, in... 

The unsteady flow of blood through stenosed artery, driven by an oscillatory pressure gradient, is studied. An appropriate shape of the time-dependent stenoses which are overlapped in the realm of the formation of arterial narrowing is constructed mathematically. A msathematical model is developed by treating blood as a non-Newtonian fluid characterized by the Oldroyd-B and Cross models. A numerical scheme has been used to solve the unsteady nonlinear Navier-stokes equations in cylindrical coordinate system governing flow, assuming axial symmetry under laminar flow condition so that the problem effectively becomes two-dimensional. Finite difference technique was used to investigate the... 

Piping systems commonly experience the transient-state situation as the result of changes to flow conditions during pump failures, valve closures or turbine load rejection. This paper addresses transients as a consequence of the load rejection of a Francis hydropower plant (Karun 4, Ahwaz, Iran). To control the turbine system and related equipment during load rejection, the valve closing law of wicket gates is of paramount importance. The pressure rise at the end of the pressure shaft, the pressure drop in the draft tube and the speed rise while the electromagnetic braking torque disappears are solely dependent on the closing curve. Thus, an optimum closing law can eliminate the probable... 

Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented... 

This paper aims at the investigation of acoustic streaming produced by surface acoustic waves (SAWs) in a drop. Computational simulation of acoustofluidic phenomenon, using lattice Boltzmann method (LBM), presenting acoustic applications in flow control, and a relatively complete parametric study are the motivations of this work. For this purpose, a computational fluid dynamics modeling based on multi-relaxation time multi-component multiphase color gradient lattice Boltzmann method was used. The simulations were carried out at wave frequencies ranging from 20 MHz to 271 MHz and wave amplitudes ranging from 0.5 nm to about 350 nm. First, the non-dimensional form of Navier-Stokes equations... 

A mobile ad hoc network is a collection of mobile hosts forming a temporary network on the fly, without using any fixed infrastructure. Characteristics of mobile ad hoc networks such as lack of central coordination, mobility of hosts, dynamically varying network topology, and limited availability of resources make QoS provisioning very challenging in such networks. In this paper, we introduce a fuzzy QoS traffic conditioner for mobile ad hoc networks. The proposed traffic conditioner consists of fuzzy admission control (FAC), fuzzy traffic rate controller (FTRC), and fuzzy scheduler (FS). The proposed FAC monitors the delay and available bandwidth and decides whether to accept or reject the... 

A novel method for extraction and analysis of volatile compounds of Artemisia haussknechtii Boiss., using simultaneous hydro-distillation and static headspace liquid microextraction followed by gas chromatography-mass spectrometry (SHD-SHLPME-GCMS) is developed. SHLPME parameters including nature of extracting solvent, headspace volume and design, extraction time, sample weight and microdrop volume were optimized. Comparison of hydro-distillation gas chromatography-mass spectrometry and HD-SHLPME-GCMS showed that the latter method is fast, simple, inexpensive and effective for the analysis of volatile compounds of aromatic plants. By using this method, 56 compounds were extracted and... 

With modified measuring procedure and measuring cell design in the drop profile tensiometer PAT, it became possible to study the rate of water evaporation through adsorbed or spread surface layers. This method was employed to measure the rate of water evaporation from drops covered by adsorbed layers of some proteins and surfactants, in particular n-dodecanol. It was shown that the formation of dense (double or condensed) adsorbed layers of protein and the formation of 2D-condensed n-dodecanol layer decrease the water evaporation rate by 20-25% as compared with pure water. At the same time, the adsorbed layers of ordinary surfactants (sodium dodecyl sulfate and nonionic ethoxylated... 

The effects of leachate recycling and bed mixing on the removal rate of H 2S from waste gas stream were investigated. The experimental setup consisted of an epoxy-coated three-section biofilter with an ID of 8cm and effective bed height of 120cm. Bed material consisted of municipal solid waste compost and PVC bits with an overall porosity of 54% and dry bulk density of 0.456gcm -3. Leachate recycling had a positive effect of increasing elimination capacity (EC) up to 21gSm -3 bedh -1 at recycling rates of 75mld -1, but in the bed mixing period EC declined to 8g Sm -3bedh -1. Pressure drop had a range of zero to 18mm H 2Om -1 in the course of leachate recycling. Accumulation of sulfur reduced... 

In the present work, a thermal modeling is conducted for optimal design of compact heat exchangers in order to minimize cost and entropy generation. In this regard, an εNTU method is applied for estimation of the heat exchanger pressure drop, as well as effectiveness. Fin pitch, fin height, fin offset length, cold stream flow length, no-flow length, and hot stream flow length are considered as six decision variables. Fast and elitist nondominated sorting genetic algorithm (i.e., nondominated sorting genetic algorithm II) is applied to minimize the entropy generation units and the total annual cost (sum of initial investment and operating and maintenance costs) simultaneously. The results for... 

This paper deals with the coordinated control of rotor- and grid-side converters in wind turbines with doubly fed induction generators (DFIGs) to improve the low-voltage ride-through capability. The rotor-side converter control and additional equipment, called stator damping resistor, are used to limit the rotor inrush current and to reduce the oscillations and settling time of DFIG transient response during the voltage dip. Also, the grid-side converter is controlled to limit the dc-link overvoltage during the voltage drop. It is found that the dynamics of the grid-side converter and dc-link voltage exhibit nonminimum phase behavior, and thus there is an inherent limitation on the... 

A sensitive and selective electrochemical sensor was fabricated via the drop-casting of carbon nanoparticles (CNPs) suspension onto a glassy carbon electrode (GCE). The application of this sensor was investigated in simultaneous determination of acetaminophen (ACE) and tramadol (TRA) drugs in pharmaceutical dosage form and ACE determination in human plasma. In order to study the electrochemical behaviors of the drugs, cyclic and differential pulse voltammetric studies of ACE and TRA were carried out at the surfaces of the modified GCE (MGCE) and the bare GCE. The dependence of peak currents and potentials on pH, concentration and the potential scan rate were investigated for these compounds... 

Commercial purity aluminum sheets are subjected to a severe plastic deformation technique called constrained groove pressing. In this study for the first time by using some technical optimizations, a strain magnitude of 6.9 is imposed to the sheets. The grain size evolution during severe plastic deformation is studied using Williamson-Hall analysis on X-ray diffraction pattern of the deformed samples. These results and transmission electron microscopy observations show that constrained groove pressing process can effectively refine the coarse-grained structure to an ultrafine grain range. The results of mechanical tests show that imposing strain in range of 0-5.75 causes to strengthening of... 

There are high attractions in the development of conducting polymer (CP) coatings to improve the electrochemical properties and biocompatibility of electrodes in the area of biosensors. A new type of the modified electrodes is prepared in a layer-by-layer process by using multi-walled carbon nanotube (MWCNT) and poly-pyrrole. In this procedure, the glassy carbon electrode is casted by a drop suspension of MWCNT, which leads to form a thin film of nanotube on its surface. In the second step, electrochemical polymerization of pyrrole in the presence of tiron (used as doping anion) is performed on the surface of the MWCNT pre-coated electrode. The modification procedure led to fabrication of a... 

Aiming at improving efficiency in combustion systems, the study on droplet behavior and its trajectory is of crucial importance. Vortex engine is a kind of internal combustion engine which uses swirl flow to achieve higher combustion efficiency. One of the important advantages of designing vortex engine is to reduce the temperature of walls by confining the combustion products in the inner vortex. The scopes of this investigation are to study vortex engine flow field as well as effective parameters on fuel droplet behavior such as droplet diameter, droplet initial velocity and inlet velocity of the flow field. The flow field is simulated using Reynolds Stress Transport Model (RSM). The...