Sharif Digital Repository

The paper presents a systematic approach to designing an imaging dish for a concentrator photovoltaic (CPV) system to minimize exergy destruction. The designed CPV system uniformly distributes light rays on the receiver (TPV/multi-junction PV) to enhance the conversion technology efficiency and lifetime. To this end, a parametric dish is designed using imaging optics and the numerical solution of a differential equation. Afterward, a Monte Carlo simulation is used to estimate the output energy and exergy of the CPV system with the parametric dish. Finally, an optimization algorithm finds the optimal design parameters to minimize the system's exergy destruction. The optimal design leads to a... 

In this paper, a novel six-phase outer rotor induction motor equipped with pseudo-concentrated windings is introduced as a robust, reliable, and low-cost solution. Multiple aspects of the proposed motor structure have been investigated such as a design algorithm and an analytical modeling based on the modified winding function considering the skew effect. The effect of using variable number of turns for the coils has been examined on the pseudo-concentrated windings. An appropriate optimization problem has been also defined to maximize the power factor and efficiency and to minimize the output torque ripple. The designed motor has been fabricated to verify the accuracy of the design... 

The present study has been conducted to investigate the effect of inlet flow regimes on vertical velocity and concentration profiles of the turbidity current. Experiments carried out on small scale channel and Kaolin with a density of 2.65 kg/m3 and a mean particle diameter of 4.5 μm, was used to generate the currents. Velocities were obtained at a rate of 10 Hz using an acoustic Doppler velocimeter. Using the siphon sampling approach, the acoustic backscattering intensity was calibrated and concentration was determined using a backscattering analysis. Results showed that the ratio of maximum velocity height to the height of the current was around 0.4-0.5 in sub- and super-critical regimes.... 

Enzymatic decolorization of the monoazo dye, acid orange 7 (AO7) by the fungal peroxidase from Coprinus cinereus NBRC 30628 is a complex system, which is greatly affected by temperature, pH, enzyme activity and the concentrations of H2O2 and dye concentration. The study of these factors and investigating the combined interactions between them by applying one-factor-at-a-time (OFAT) method and two other statistical methods including 2-factorial method and response surface methodology (RSM) were aimed in this work. Through OFAT analysis the optimized conditions were a temperature of 25 °C, pH 9.0 with H2O2 concentration of about 3.9 mM and AO7 concentration of 40 mg/l. A complete... 

Application of immobilized horseradish peroxidase (HRP) in porous calcium alginate (ca-alginate) for the purpose of phenol removal is reported. The optimal conditions for immobilization of HRP in ca-alginate were identified. Gelation (encapsulation) was optimized at 1.0% (w/v) sodium alginate in the presence of 5.5% (w/v) of calcium chloride. Upon immobilization, pH profile of enzyme activity changes as it shows higher value at basic and acidic solution. Increasing initial phenol concentration results in a decrease in % conversion. The highest conversion belongs to phenol concentration of 2 mM. Investigation into time course of phenol removal for both encapsulated and free enzymes showed... 

In past decades, many attempts have been made to use water-soluble polymers as a mobility control agent to improve sweep efficiency of enhanced oil recovery processes. However, sensitivity of the thickening behavior of these polymers to some harsh conditions, such as high salinity, has cast serious doubt on their applicability in reservoir conditions. By expansion of nanotechnology, scientists discovered that nanoparticles can be utilized as thickening and rheology control agents in many polymer solutions. In this study, hydrophilic fumed silica is added to hydrolyzed polyacrylamide and sulfonated polyacrylamide solutions. The effect of the addition of nano silica on the thickening and... 

Herein, we present the large scale fabrication of carbon nanotubes (CNT) electrodes supported on flexible polymeric sheets by subsequent multilayer inkjet printing of a silver layer for electrical connection, CNT layers as active electrode material and an insulation layer to define a stand-alone CNT active electrode area with high accuracy. Optical and electrochemical characterization using several redox mediators demonstrates the reproducibility of the electrode surfaces and their functionality even with a single inkjet printed CNT layer. These electrodes are targeted to the clinical sector for the determination of the antioxidant power (AOP) of biologically relevant fluids by... 

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.... 

Many potential therapies are currently being studied that may promote neural regeneration and guide regenerating axons to form correct connections following injury. It has been shown that adult neurons have some limited regenerative capabilities, and the lack of connection formation between neurons is not an intrinsic inability of these cells to form axons after being damaged, but rather the inhibitory microenvironment of the injured tissue prevents regeneration. In this study, the polarization and chemotaxis of neuronal stem cells (NSC) in response to quantified gradients of nerve growth factor (NGF) was examined. To accomplish this, a microfluidic device was designed and fabricated to... 

The stochastic behavior of a point reactor is modeled with a system of Ito stochastic differential equations. This new approach does not require computing the square root of a matrix which is a great computational advantage. Moreover, the derivation procedure clearly demonstrates the mathematical approximations involved in the final formulation. Three numerical benchmarks show the accuracy of this model in predicting the mean and variance of the neutron and precursor population in a point reactor  

Functionally-graded NiO-8. mol % YSZ composite films were prepared by a controlled voltage-decay electophoretic deposition (EPD) process. The films consisted of three layers with varying NiO concentrations and porosities. Effects of different parameters including the type of the organic media, solid concentration, NiO:YSZ ratio, and iodine on the stability of EPD suspensions and deposition kinetics were studied. A stable NiO-YSZ suspension was attained in isopropanol with NiO-YSZ ratio of 60:40 and iodine concentration of 0.5. mM. The composite film contained varying NiO concentration from 46. wt.% near the substrate to 32. wt.% close to the electrolyte with 42. wt% NiO in the intermediate... 

In this study, crosslinked and non-crosslinked carboxymethylcellulose (CMC) membranes were prepared with different concentrations of polymer. Then, the permeability of pure CO2, N2, and CH4 was measured through these membranes in dry state to investigate the influence of polymer concentration and applied feed pressure on permeability and permselectivity. The permeability of CO2 through membranes was higher than the other gases. A comparison of permeabilities revealed that the permeability of N2, CO2, and CH4 increased on an average of 33, 40 and 20 percent, respectivly, by increasing the feed pressure from 6 to 10... 

The current study was carried out to investigate the kinetics of reactions for the pressure oxidative leaching of a molybdenite concentrate in less than one hour. The effects of oxygen pressure, stirring speed, pulp density, acid concentration and temperature on the leaching rate of the molybdenum were studied. It was found that about 85% of molybdenite was oxidized to molybdic oxide precipitate with remaining molybdenum dissolved in the leaching liquor. Analysis of experimental data showed that the reaction is chemically controlled with activation energy of 68.8 kJ/mol. Furthermore SEM images showed no significant boundary diffusion layer and it was noted that the molybdic oxide... 

This study is concerned with investigation of pressure oxidative leaching of entire molybdenum of a molybdenite concentrate. Effects of oxygen pressure, stirring speed, pulp density, acid concentration, and temperature on the leaching rate of molybdenum were studied. A three-layer feed-forward artificial neural network was applied to model the effect of the abovementioned parameters on the leaching ability. The leaching efficiency was considered as a target value for modeling. The quantified leaching efficiencies obtained by applying different parameters demonstrated a good agreement with neural network predictions  

Models play an important role in fuel cell design and development. One of the critical problems to overcome in the proton exchange membrane (PEM) fuel cells is the water management. In this work a steady state, two dimensional, isothermal model in a single PEM fuel cell using individual computational fluid dynamics code was presented. Special attention was devoted to the water transport through the membrane which is assumed to be combined effect of diffusion, electro osmotic drag and convection. The effect of current density variation distribution on the Water content (λ) in membrane/electrode assembly (MEA) was determined. After that detailed distribution of oxygen concentration, water... 

Calendula alata plants were tested for their potential to remove stable cesium and lead from solutions in a 15-day period. The plants were grown hydroponically and placed in solutions containing CsCl and Pb(C 2H 3O 2)2 at different concentrations (0.6, 2 and 5 mg l-1). When plants were incubated in CsCl solutions 46.84 ± 2.12%, 41.35 ± 1.59%, and 52.06 ± 1.02% cesium was found to be remediated after 15 days. Moreover, more than 99% lead was removed from the Pb(C 2H 3O 2)2solution in all three concentrations after 15 days during the same period. When both CsCl and Pb(C 2H 3O 2)2were supplemented together in the solution, 9.92 ± 1.22%, 45.56 ± 3.52%, and 46.16 ± 1.48% cesium and 95.30 ± 0.72%,... 

The optimization of leaching parameters for the Ni recovery of the used catalyst was developed using response surface methodology. The relationship between the Ni recoveries, and four main leaching parameters, temperature, acid concentration, leaching time and particle size were presented as empirical model equations. The predicted values of nickel recoveries were found to be in a reasonable agreement with the experimental values, with R2 as correlation factor being 0.9669 and 0.9869 for sulfuric and nitric acids, respectively. The model equations were then optimized using the quadratic programming method to maximize nickel recovery. The optimum conditions were found to be 103.4°C... 

In this study, the inverse emulsion polymerization modeling of polyacrylamide with population balance equations (PBEs) was performed. The PBEs were derived on the basis of the zero-one kinetic model. The effects of the surfactant steric barrier and surfactant reaction with radicals, including monomeric radicals, on the radical entry rate into the particle were taken into account. In the modified model, the coagulation phenomenon was included through consideration of the effects of forces not included in the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory; these include hydration and steric forces in addition to DLVO forces. The effects of the surfactant and initiator concentrations on... 

A model to predict air pollutants' concentrations was developed by implementing spectral decomposition of time series data, obtained by Kolmogorov-Zurbenko filter, in Artificial Neural Networks (ANN). This model was utilized to separate and individually predict three spectral components of air pollutants' time series of short, seasonal, and long-term. The best set of input variable was selected by evaluating the significance of different input variables while modeling different time series components. Moreover, different possible approaches for constructing such models were examined. Performance of the constructed model to predict air pollutants' level at a central location in Tehran, Iran,...