Sharif Digital Repository

AZ91 is the most applicable alloy of magnesium alloys.Semisolid stir welding of AZ91 magnesium alloy was investigated due to its welding problem such oxide formation, hot cracking in weld metal, and high residual stress through solidification with special focus on the effect of the welding temperatures, stirring rates, and tool shape. The interlayer with thickness of 2mm was located between two AZ91 pieces with 7.5mm thickness. Then, they were heated to the desired temperatures (515C, 530C and 540C), the semisolid temperature of both base metal and interlayer. A grooved stirrer with six rotational speeds from 0rpm to 2000rpm was introduced into the stir weld seam and the welded coupons... 

In this research, a general model is proposed aiming at establishment of optimized application of Methane gas with maximum added value. That is, maximum added value of methane for different applications of methane including consumption as fuel, export and injection-to-wells are calculated and compared. Accordingly, results of this study are used for decision making regarding Iran’s most important gas reservoirs. In this study, maximum present net value of investment concerning comparison of petrochemical industry input and export to a number of selected countries in addition to injection in 20 years is calculated based on a specific discount rate. It is noteworthy that the scope of this... 

Passenger cars (PCs) are of particular importance among mobile air pollutants emissions sources due to their population and significant share in air pollutants emissions and gasoline consumption. Moreover, ownership and use intensity of PCs are affected by socio-economic situation. The present study projects the future trends of air pollutants emissions and fuel consumption from PCs in Tehran by 1415 and assesses the effect of economic situation on the emission trends and effectiveness of emission reduction polices. Accordingly, the present study develops an interdisciplinary modeling framework, which combines econometric models with a bottom-up emission estimation model to simulate the... 

In the current digital era, the large number of mobile developers and android applications has led to intense competition. Users can easily access many android applications to meet their needs. This abundance of available software makes it difficult for developers to attract and retain users, as they can easily switch from one application to another. This switch can happen if the current application does not meet the user’s needs, has issues, or if a better alternative is available. Therefore, developers must focus on keeping their users satisfied. To ensure user satisfaction, developers need to address user needs effectively. This includes fixing reported issues, adding new features, and... 

In this study, membrane distillation was used for desalination of high saline water. Recently, the synthesis of nanoparticles for the synthesis of membranes for membrane distillation has shown incredible improvement in the morphological properties, flux, and rejection. In this study, by incorporating UiO-66 functionalized with Palmitic acid into PVDF/PEG polymer solution we could improve membranes properties. Functionalization of UiO-66 with Palmitic acid was confirmed with FTIR, XRD, BET, SEM. In the membrane containing 3% Palmitic acid-UiO-66, the flux was increased by 46.5%, resulting in a flux of 12.6 LMH, and the salt rejection was improved from 99.5% to 99.9%. These results confirmed... 

Many aroma compounds of fruit juice recovered by thermal evaporation and distillation processes can lead to undesirable chemical changes and even their loss. Pervaporation is a promising process for the recovery of volatile organic compounds from their aqueous solutions. In the present work, pervaporation recovery of Ethyl acetate as a model solution of apple juice’s aroma compound was evaluated with polyvinylidene fluoride (PVDF) and ethylvinylacetate (EVA) membranes. For PVDF and PES membranes in the feed concentration of 250-1000 ppm and the operating temperature of 30 ºC, separating factor , respectively, was obtained in the range of 67-70 and 49-53, and also total permeation flux was... 

With the advancement of GPUs and the availability of massive datasets, the main reasons behind the emergence of large language models, human life has been profoundly impacted. Large language models, due to their numerous applications and their increasing development, have influenced various aspects of human life, and this influence continues to grow. As a result, large language models are being used to solve a wide range of problems. However, using these models for problem-solving requires appropriate training data and significant computational resources. Because deep models can be attacked, leading to the extraction of their training data, preserving the privacy of training data in the... 

The growing use of the Internet has led to the creation of new businesses around it. Traditional businesses have to use the Internet in order to maintain their competitive conditions. One of the most important strategies for developing sales on the Internet is the proper use of recommendation systems.With the advent of businesses in cyberspace, the way has been paved for the use of recommendation systems in this space.Recommendation systems should exploit their knowledge about users’ preferences and explore their new preferences simultaneously. Establish a balance between exploring users’ new interests and exploiting known interests is key to build a good recommendation system. Existing data... 

In this study, membrane distillation process was used for treatment of high salinity waters. The focus of this study is to simulate and build a setup of membrane distillation process. Since the membrane distillation process is based on the driving force of the temperature difference, the required temperature is provided by both the use of heaters and the use of solar energy. To increase the feed temperature by solar energy, a black polymer coating on the main membrane is used. The main membrane used in this process is PVDF polymer and the polymer coated on the surface is the PAN polymer. After simulating and constructing the laboratory setup, the influence of a variety of parameters on the... 

FGM sheets with component or grain size gradient in their thickness direction provide mechanical and physical gradient properties through ND direction. FGMs are fabricated by various methods including centrifugal casting, powder metallurgy, PVD and CVD,all of which suffer from some shortcomings such as porosity of the products, low rate and high cost of production and restrictions on mass production. In this study, 2 and 4 layered Al matrix FGM sheets containing SiC and Al2O3 powders were fabricated by laminating method of Accumulative Roll Bonding(ARB). Two approaches of stacking were chosen as accumulative coupled roll bonding (ACRB) and (ASRB) for initial roll bonding and subsequent... 

In recent years, application of silica nanoparticles for wettability alteration of reservoir rocks as an effective approach in enhancing oil recovery from petroleum reservoirs is introduced. However, in this area, lack of fundamental studies to provide a clear understanding about the interaction between these nanoparticles and carbonate rocks (as the predominant reservoir rocks in the world and Iran), which is of particular importance, is sensed. Therefore, the main purpose of this dissertation is to present a mechanistic investigation about the interaction of silica nanoparticles (the most used nanoparticles) with carbonate rock from theoretical and experimental viewpoints. To better... 

Particle reinforced aluminum matrix composites have considerable attraction in automotive and aerospace industries due to their special properties as light weight, high ratio of strength/density, improved elastic modulus, low coefficient of thermal expansion and high wear and corrosion resistance. Among the production processes of metal matrix composites, accumulative roll bonding process has particular importance due to producing ultrafine grained composite sheets. However, uncontrolled and undesired agglomeration of particles is the main problem in producing these composites. In this research, the Al2O3 and SiC nanoparticles were electrostatically stabilized against agglomeration by... 

This project examines four alternatives such as pipelines, oil injection wells, LNG & GTL in the purpose of Iran gas utilization. In this Project four strategies using cost/benefit analysis are examined. For this purpose, at first the cost of inlet feed gas per Mmbtu are calculated. Then regarding various scenarios of average world gas prices for the following thirty years, the cost & benefit of any way will be counted. Then with the use of energy security, the project will make energy policy. For this purpose, Shannon indicator will be used as one of the most reliable indicators. Due to the of use this indicator, the popular project will be chosen accordingly as a certain amount of gas the... 

Lipid membranes are fundamental constituents of cell membranes and are now used in lap-on-a-chip technology. Membranes in living cells contain a significant fraction of proteins, which undergo lateral random movements due to thermal fluctuations and shear forces imposed by the solvent fluid. Prominent natural and biotechnological systems where membranes are highly sheared include the plasma membrane of endothelial cells, and membranes used in biosensors for high throughput screening of drug candidates, and in water purification devices. In these systems membrane is in direct contact with the mainstream suspension flow, which is driven by pressure gradients. The efficiency and function of... 

Splitting in ingot cast structures and transverse cracks in continuous cast structures are the main problems of hot rolling of low carbon resulfurized free-cutting (LCRF) steels. Presence of high volume fraction of manganese sulfide inclusions in cast structure increases the risk of alligatoring in hot rolling. Because of high sulfur content of these steels and probability of formation of low melting point phases, minimum level of manganese and maximum level of copper and tin is necessary. Morphology of manganese sulfide is another important factor in hot forming of these steels, which can be controlled by level of deoxidation in steel making. In fact, MnS2 is present in fully killed... 

Based on International Energy Agency studies, achievement of 450 ppm CO2-equivalent emission target in global emission means that the CO2 emissions in 2050 must be reduced to %50 of 2005 level, and this implies that a portfolio of emission reduction policies and strategies need to be exploited through current century.
At the present time, Carbon Capture and Storage (CCS) Technology is a dominant strategy among all the long-term carbon abatement strategies in many countries. Nevertheless, its potential as a climate mitigating option will be proved, only if it is implemented in the countries which are developing at a great pace and taking advantage of fossil fuels in order to afford their... 

Climate change and energy security are key drivers for future energy policy. While energy security has been a pillar of energy policy for about a century, concern about climate change is more recent and is bound to radically change the landscape of energy policy. Policy makers are now under increasing pressure to address these twin challenges: to develop cost-effective policies that will both ensure the security of our energy system and reduce greenhouse gas emissions.
Main Effort in this Project is to construct an integrated model of Iran’s energy system to serve as a policy analysis tool, by which policymakers are able to identify the future effects of a wide range of policies in... 

Dependence of some magnetic properties such as core loss and permeability on temper rolling was studied in this thesis. It is shown that with a proper temper rolling sharper textures are obtained in the electrical steel and the magnetic properties in the longitudinal and traverse directions are improved. By texture analysis, it is shown that because of temper rolling, shear strain on the surface of the sheet is the main factor for abnormal grain growth and shear texture formation on the surface. The result of formation of this texture is enhancement of the {100} intensity and reduction of the {111} intensity, leading to the improvement of the permeability. Temper rolling is always... 

Distributed generation (DG) and its utilization have some benefits and risks for its owner and power network. From owner perspective, benefits of DG include selling energy, reducing costs related to fuel, and other economic benefits. However, there are some risk factors for the owner including risk of supplying fuel, risk of selling generated power, and other risk factors related to establishment of the DG unit. Utilizing risk-reduction tools such as signing agreements for selling power, purchasing fuel, and related economic tools are necessary for risk management of the owners of DG units. The purpose of this thesis is to investigate the economic situation of the DG units and optimize the... 

In software programs, most of the time, there is a chance of error, even though they are tested carefully. Finding error-related pieces of code is one of the most complicated tasks and it can make incorrect results if done manually. Semi-automated and fully-automated methods have been introduced to overcome this issue. The rapid growth of developing smart mobile applications (SMAs) in recent years, competition among the development teams and many other factors have increased the chance of errors and hence, the quality of these applications have reduced. There are two approaches to test SMAs in order to reach a high degree of quality: (1) using existing traditional methods and adapting them...