Sharif Digital Repository

In this study, mesh-reinforced cellulose acetate (CA)-based membranes were prepared for forward osmosis (FO) by immersion precipitation. Casting composition, preparation conditions, evaporation time, coagulation bath temperature, annealing temperature, CA percent and 1,4-dioxane/acetone ratio were tested for membranes’ performance. Also, the results were compared with commercially CTA membranes. The FO membrane prepared under optimized conditions had a smooth surface similar to commercial ones. The most proper membrane (17.9 % polymer and 1,4-dioxane /acetone ratio 1.89) showed water flux of 9.3 L/m2.hr (LMH) and RSF of 0.536 mol NaCl/m2.hr. Using mesh in the membrane structure, different... 

The use of braced frames has become more popular in seismic design of buildings because of the simplicity in design and construction. The first event that occurs in the earthquake for a concentrically brace frame (CBF), is the buckling of the strut. The inelastic behavior of CBF systems is dominated by brace buckling, yielding and the post buckling behavior. The Inelastic performance of the brace is nonsymmetrical, because of the difference in the tensile and compressive strength of the brace and the deterioration in the resistance after buckling. so we have too complexity in modeling the inelastic performance of brace members. Also the subject of the near fault ground motion and design of... 

Reverse osmosis (RO) is by far the most widely used membrane desalination process worldwide. The RO process depends on the properties of semi-permeable membranes which allow the separation of water from a salt solution by applying external pressure higher than the osmotic pressure on the seawater. The main problem in membrane separation process is the fouling of the membrane walls, which decreases the permeate flux. Having spacer filaments in the feed channel has been proven to dynamically change the concentration boundary layer and preventing fouling. The impact of spacer configurations (cavity, zigzag and submerged) on the alleviation of concentration polarization and the enhancement of... 

Considering the demand for electronic and other products that rare earth elements are one of the necessary materials for their production, recovery of these elements plays an important roll today.The term “rare earth”, represents a group of 17 metalic elements with similar physical and chemical properties such as Sc,Y and lanthanides. Lanthanides are a group of elements with 57 to 71 atomic numbers and all of them except Pr, are present in earth crust.Some of these elements are available in phosphate concentrate(iron ore waste) of chadormalu in bafgh. Base on the analysis performed on apatite concatrate, it was represented that Ce,La and Nd elements are more than the others. So this research... 

In recent years, dust storms have been recognized as one of the most crucial problems for people worldwide. Provided that the dust masses transport mechanisms are properly known, the main dust sources can be identified, and therefore, appropriate actions can be taken. Therefore, the main goals of the present study are estimating dust concentration, determination of dust distribution with an emphasis on Iran (especially Tehran), and finding the main dust sources which will be followed in five steps. In the first step, by analyzing the measured data during dust observations in Tehran through 2013-2016, several simple and multivariate nonlinear regression models have been established in order... 

In this research, modal incremental dynamic analysis (MIDA) has been investigated on three-dimensional structures with irregular plans. The MIDA method is an incremental static analysis that considers higher modes of the structure. In fact, it is a combination of modal pushover (MPO) and incremental dynamic analysis (IDA) methods that incorporate the advantages of both and is much faster than the IDA method. Compared to constant analyses, incremental analysis is more extensive in terms of results and response to earthquakes. Due to the uncertainties in the nature of future earthquakes, engineers use the IDA method to achieve a broader view of the structure's response under potential... 

In this work feasibility of concentrating zinc carbonate ore from Anguran mine by froth flotation process has been studied. Potasium Amyl Xhantate and Oleic Acid have been studied as possible collectors. The initial tests indicate that oleic acid might be a better collector. Experimental were conducted to determined important factors and to optimize the process by careful control of the pulp chemical composition and flotation variables. A concentrate containing 24.9% zinc has been attained. The recovery of zinc in the concentrate is 76.1%.
 

Through our work, we conducted a three-stage solution to effectively reduce the impact of 'concentration polarization' and 'fouling' on ultrafiltration process. The stages were compromise of: 1. the design and selection of appropriate equipment along with outlining the operational parameters, 2. the pretreatment process design, and 3. the cleaning process design. Because of the presence of fat, there are incline both in permeate flux and the quality of the final product. Therefore, we studied the different methods of removing the lipid content, during pretreatment stage. After examining these methods, finally, we found that adding chitosan parallel with employing centrifugal separator is the... 

In this thesis, the application of solar energy in the steam injection as a thermal enhanced oil recovery (TEOR) is evaluated. The motivations of this project are using a renewable energy, suitable solar potential of Iran, successful experience in the world, undeveloped heavy oilfield reservoirs in Iran. This application is investigated by three aspects which are:Reservoir Engineering aspect: the heavy oilfield are determined and then screening for selection good candidate of steam injection are done. One of the reservoirs is analyzed by simulation and optimization the steam injection to determine how much it’s production will be improved by using steam injection (contionous and cyclic)... 

gas injection method is one of the common methods of EOR, which has a long history. In gas injection, molecular entry gas mixing is the controlling factor of oil play. Therefore, the exact value of this coefficient becomes an important requirement for the simulation and modeling of oil reservoirs, which can only be determined by laboratory consumption methods. In this research, the pressure decay method is used as a common laboratory method to determine the penetration coefficient of methane, nitrogen and gas enriched with intermediate compounds in crude oil of one of Iran's oil reservoirs. In most of the available records in the investigation of the mentioned gas diffusion coefficient in... 

In this study, in the base case using a modeling system WRF=CAMx Distribution concentration of all pollutants from mobile sources in an episode of 60 days (November and December 2015) is calculated in Tehran. In this context, the emissions inventory related to mobile sources outputs the code in Fortran and WRF meteorological model to model air quality prepared and then using the CAMx, Tehran’s air quality is simulated. In order to verification in this case, the results of pollutant concentration NO2, CO, PM2٫5, with concentrations of air pollution monitoring stations compared. Given that in this study the concentration of pollutants from mobile sources is modeled, predicted by the model,... 

In this study the behavior of steel bracings under cyclic loading, is modeled with finite element method. Analysis have shown that after local buckling in plastic mid-span position, due to the severe geometry change, the strain grows rapidly, The sharp growth of plastic strains is entitled as strain rises. Geometry change created will cause the collapse brace speeding up. In fact, the main local buckling can be used as a determinative factor in performance base design for steel braces. So the thesis has been investigated, using the parameters fracture life to quantify local buckling and fracture. Also with using the CVGM model, the fracture of the brace could be predicted. The analytical... 

Heart attack is considered as one of the most common reasons of morality all over the world. Coronary Atherosclerosis is known as the major causes of heart attack. The commence and proceed of this disease is related to cross of Low Density Lipoprotein. In this project, based on numerical simulation using ANSYS Fluent, hemodynamic variables and the rate of LDL particles penetration to porous wall of coronary artery is investgated. The geometry is the first bifurcation of Left Anterior Descending and is located on the supposed sphere that represents heart configuration. Sinsuidal variations of shere radii, simulates pulsating movement of heart. Heart diameter is supposed to remain constant... 

In this Thesis, the behaviour of stell brace was studied in finite element models. In this section, a comparison between the results of these models and the results of experimental models which were done in past years, was carried out. It shows that these result is in good agreement with each other, Moreover it has been found that the primary cause of failure in the sample is local bucking and then change in the geometry of sample which will be followed by strain jumping in next cycles which shows the importance of local buckling due to the proximity of this event to strain jumps and can be accepted as braces limit state design.Finally, we try to predict the time of failure of samples with... 

In this research, we answer that whether trade liberalization increase market competition. First, we discuss this problem using inter-temporal comparison. To do this, we set a control variable group and a test variable group. The control variable group includes the industries that did not report trading and non-tradable industry in 1379 and 1386 (non-trading industries) and the test variable group includes industries that have entered the the trade in recent two years and are named trading industries. In this research, we study the effect of Herfindahl Index and markup on industry Openness,controlling for some factors. Using abovementioned influences, the relation between trade... 

Although financial theory recommends investors to diversify their portfolios to reduce their overall unsystematic risk, some fund managers hold their portfolios concentrated in specific industries. This thesis study the relation between the industry concentration and the performance of Iranian equity funds in the period from 1392 to mid-1397. This relationship has been investigated in two approaches of dividing funds into portfolios by their industry concentration index and multivariate regression model approach by considering some characteristics of funds. To measure the performance of funds, two sets of measures based on the analysis of information of fund holdings and time series of fund... 

Steel Concentrically Braced Frames are common lateral load resisting frames. Poor design of this system can lead it to premature failure of braces. This failure may be due to non-elastic buckling of brace members or their connections. Design Codes divide Concentrically Braced frames into two groups: Ordinary Concentrically Braced Frames and Special Concentrically Braced Frames and for each, specific limitations have been determined for width to thickness ration and slenderness. Many of these limitation have been obtained on the basis of experimental tests. In this thesis steel braces behavior under cyclic loading is studied. For parametric investigation, Finite Element Method is used. Abaqus... 

The spherical ensemble is a well-studied determinantal process with a fixed number of points on the sphere. The points of this process correspond to the generalized eigenvalues of two appropriately chosen random matrices, mapped to the surface of the sphere by stereographic projection. This model can be considered as a spherical analogue for other random matrix models on the unit circle and complex plane such as the circular unitary ensemble or the Ginibre ensemble, and is one of the most natural constructions of a (statistically) rotation invariant point process with repelling property on the sphere. In this dissertation we study the spherical ensemble and its local repelling property by... 

To obtain solutions containing Titanium, leaching of Ilmenite Concentrate of Kahnooj and its Slag by Sulfuric Acid 98% in various Conditions are Studied. Screening tests by Fractional Factorial method were designed, at this step effects of Temperature, Acid Concentration, Particle Size, Solid to liquid Ratio, Time and Stirring Speed were investigated and It was Concluded that Temperature, Time, Acid Concentration and Particle Size were the effective Parameters in both leaching process of Ilmenite and Slag. The Temperature, Time and Acid concentration had positive effect, whereas the Particle Size had negative effect. After screening step, effective parameters were optimized by Rotatable... 

Finding suitable locations for installing conventional concentric bracings such as X and V, without interfering with building architecture and its openings, is a routine challenge in building design. One of the less known forms of concentric bracings which can be used to solve this issue, is the y-shaped bracing composed of three braces. In the current thesis, results of analytical studies, computer modeling and experimental tests are presented to extend the knowledge of structural behavior of y-bracings. As the first step, effective buckling lengths of braces with rigid connections were found from equilibrium equations incorporating the effect of axial force on rotational stiffness of...