Sharif Digital Repository

In this paper, the effect of two-dimensional electron plasma formed on the surface of a semiconductor on the refraction phase of an optical beam is investigated. Both the density and effective mass of the surface state electrons can be controlled by a transverse electric field. While the surface density of electrons varies slowly with the applied field, their effective mass changes instantaneously. Therefore, a high bandwidth for the phase modulation can be obtained. It is expected that the device operates in the far-infrared region with a semiconductor as the base material. GaAs is one of the best candidates having both large dynamic range, and large ratio of free electron to the crystal... 

The UiO-66 NH2 and ZIF-8 metal organic framework nanoparticles (NMOFs) were incorporated into the polyvinylidene fluoride (PVDF) nanofibrous membrane. Then, the chitosan nanofibers were coated on the PVDF nanofibers to produce the PVDF/chitosan nanofibers. The performance of synthesized PVDF/NMOFs single layer and PVDF/chitosan/NMOFs two layers nanofibrous membranes was investigated for BSA protein molecules and Cr(VI) ions separation via ultrafiltration membrane process. The potential of synthesized nanofibers was also examined for BSA and Cr(VI) adsorption in a batch system. The characteristics of synthesized nanofibrous membranes were determined using SEM, EDX, TGA, BET, porosity and... 

This paper presents a novel method for cooperative educational dissemination systems. Taking into consideration the inherent characteristics of distance learning video streams (existence of a few slow moving objects in a classroom), we have proposed a novel content-based video coding method that is very efficient at low bitrate channels. On the encoding side, we have applied a background subtraction algorithm for motion segmentation using a novel statistical background modeling approach. At each frame, the moving objects are extrapolated with a rectangular model and tracked frame by frame (which forms the only data needed to be sent over the channel). On the decoding side, we have used a new... 

This paper presents a novel video encoding method for cooperative Educational Dissemination Systems. Taking into consideration the inherent characteristics of distance learning video streams, existing a few moving objects in the scene and objects having slow motions, we propose a novel content-based video encoding method which is very efficient on low bandwidth channels. In the encoding process, we apply a background subtraction algorithm for motion segmentation with a novel statistical background modeling. In each frame, the moving objects are extrapolated with rectangular bounding boxes which are the only data send over the low bandwidth channel. In the decoding process, we propose a new... 

This paper presents a multi agent system which can help type 2 diabetic patients. Because of diabetes nature, medical care and lifestyle can both prevent the complications of this illness, so self-managing is very crucial for these patients. Therefore, each effective factor of controlling diabetes and increasing patients' knowledge including: suitable diet and monitoring blood glucose level, is assigned to be an agent which works independently whilst coordinates and cooperates with other agents. The proposed architecture of this multi agent system organizes all the various agents of this system in a way that not only each of them can accomplish their responsibility, but also they can have... 

Photocatalytic reduction of p-nitrochlorobenzene was studied over aluminosilicate-based AgBr and AgBr-TiO2 photocatalysts which were prepared and characterized. The photoreaction was performed in the presence of LiBH4, which is a strong reducing agent, in the solution medium. A new mechanism is proposed for reduction of p-nitrochlorobenzene under photocatalytic conditions. The effect of pH, illumination source, LiBH 4 concentration, temperature, catalyst dosage, and alcoholic scavengers was also studied. The results showed that the best efficiency was obtained over Ag/AgBr/TiO2/aluminosilicates at natural pH under UV light. We observed that the reaction yield was affected by changing the... 

Failure in sheet metal forming can occur by necking, fracture or wrinkling. By using a forming limit diagram (FLD) as a powerful tool to prevent sheets metal failures in the forming process, provides parameters controlling throughout forming. There are different developed methods for predicting FLDs, which estimate sheet metal forming strains limits. Assessment of FLD estimation reveals that there is a dependency between the effect of several factors containing normal stress, shear stress, sheet thickness, mechanical properties, metallurgical properties, yield function, strain path, and bending with formability. In this research, the effects of bending via two finite element models are... 

Decision on the location of new wells through infill drilling projects is a complex problem that depends on the reservoir rock and fluid properties, well and surface facilities specifications, and economic measures. Conventional approach to address this is a direct optimization that uses the numerical flow simulation. However, this is computationally very extensive. In this study the authors use a hybrid genetic algorithm (HGA) optimization technique based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. This hybridization introduces hill-climbing into the stochastic search and makes use of proxies created and calibrated iteratively... 

Decision on the location of new wells through infill drilling projects is a complex problem that depends on the reservoir rock and fluid properties, well and surface facilities specifications, and economic measures. Conventional approach to address this is a direct optimization that uses the numerical flow simulation. However, this is computationally very extensive. In this study the authors use a hybrid genetic algorithm (HGA) optimization technique based on the genetic algorithm (GA) with helper functions based on the polytope algorithm and the neural network. This hybridization introduces hill-climbing into the stochastic search and makes use of proxies created and calibrated iteratively... 

Transaction cost theory is largely used to investigate the formal domain of land and housing. In the informal domain, however, this perspective has been employed largely as a supplement in addressing the other fundamental notion in new institutional economics—property rights—despite the possibility that informality in land development can emerge regardless of the informality or formality of such rights. To cover this gap, this study developed a theoretical framework based on transaction cost theory to explain the formal–informal dichotomy in land development. The proposed framework maintains that land development depends on engaging in transactions that involve total or partial ownership of... 

In this study, the robust sliding mode attitude control of a tethered satellite system using optimal tether offset in the presence of perturbations and uncertainties is investigated. The three main goals of this study are: (1) comprehensive modeling of two satellites connected by a tether considering the coupling between their attitude and position, (2) finding a robust attitude control for both satellites, and (3) reducing the reaction wheels’ power consumption for attitude control utilizing the tether tension. In this regard, the 6 DOF governing equations of the coupled nonlinear rotational and translational dynamics of a two-satellite tethered system in the presence of perturbing forces... 

Transaction cost theory is largely used to investigate the formal domain of land and housing. In the informal domain, however, this perspective has been employed largely as a supplement in addressing the other fundamental notion in new institutional economics—property rights—despite the possibility that informality in land development can emerge regardless of the informality or formality of such rights. To cover this gap, this study developed a theoretical framework based on transaction cost theory to explain the formal–informal dichotomy in land development. The proposed framework maintains that land development depends on engaging in transactions that involve total or partial ownership of... 

The chitosan-grafted-poly(N-vinylcaprolactam) (chitosan-g-PNVCL) nanofibers were synthesized via electrospinning method. ZIF-8 metal-organic frameworks nanoparticles were incorporated into the nanofibers for adsorption of Cr(VI), As(V) and phenol from water. The BET, FTIR, XRD and SEM analysis were carrfried out to obtain the characteristics of nanofibers. The optimum parameters of ZIF-8 content, pH, contact time, adsorbent dosage, and initial concentration of adsorbates on the Cr(VI), As(V) and phenol removal were studied. The reusability of synthesized nanofibers for five sorption-desorption cycles was also examined. The maximum experimental adsorption capacity of the... 

ZSM-5 (Seolite Sconoy Mobil) aluminosilicate zeolites synthesized by the hydrothermal method were incorporated into the hydrophobic ethyl cellulose (EC) nanofibrous membrane. The performance of synthesized nanofibers was investigated for a gravity driven oil–water separation. The synthesized ZSM-5 nanozeolites and EC/ZSM-5 composite nanofibers were characterized using XRD, FESEM, XPS, FTIR and AFM analysis. The permeability of EC/ZSM-5 5 wt% for oil in water mixture was in order of n-hexane (5170 ± 60 L/m2 h) > n-heptane (4600 ± 50 L/m2 h) > cyclohexane (4350 ± 35 L/m2 h) > pump oil (3780 ± 28 L/m2 h) > lubricating oil (3200 ± 25 L/m2 h) > motor oil (2980 ± 20 L/m2 h) with a separation...