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... 

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 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... 

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... 

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... 

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... 

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... 

In present research, a new system of energy extraction from water flow has been studied and optimized. This semi-active energy harvesting system consists of an airfoil that is connected to the generator by an arm. The passage of water causes the airfoil to move, so the hydrodynamic forces on the airfoil will cause the arm to move and finally the generator. In this research, complete dynamic modeling of this energy extraction system including generator, airfoil, controller and actuator modeling is presented and the governing dynamic equations are extracted using this modeling for dynamic simulation. Two dimensional fluid simulations have also been performed using fluent software. Finally, in... 

The Oil and gas industry is one of the most important industries in the world. It has great role in Iran’s economy also. Regarding complexities of new companies, there is room for more cooperation and coordination within the industry and with other actors. Oil and gas niches have close interdependency with financial sector. The new encrypted currencies play great role in new financial models. Blockchain technology can help the oil and gas industry by using its appropriate features. Blockchain is a system of recording information in a way that makes it difficult or impossible to change, hack, or cheat the system. The supply chain of oil and gas industry in Iran includes upstream, midstream... 

Nowadays, the tendency to use Al/SiC composites with FGM structure has increased in the automotive and aerospace industries, because in this type of composite, the properties can be gradually changed in the direction of thickness. For example, one composite surface is used as a wear-resistant or high-temperature-resistant coating, and the other surface can be welded, has high thermal conductivity, or has a good toughness. In recent years, methods have been used to make surface composites, most of which are in the molten state and at high temperatures. In this case, the reactions between the compounds can not be easily controlled and the possibility of the formation of undesirable or... 

Proper documentation plays an important role in successful software management and maintenance. Software repositories such as GitHub host an enormous number of software entities with various features. Developers collaboratively implement, use, and share these repositories in the community. Software repositories use issue tracking systems to keep track of issue reports, both to manage workload and document the highlight of teams’ effort. An issue report can contain a request for new features, a reported problem, or simply a question by users of a software product. As the number of these issues increases, it becomes harder to manage them. Github provides labels for tagging issues, however,... 

Developers often seek to find projects that match their topics of interest in version control systems with the goal of reusing code, extracting similar requirements, learning, and more. However, due to the widespread use of these systems, the number of projects maintained on them is huge and ever-increasing. This has made it difficult to identify projects based on their topics. GitHub, as a prominent version control system, with the aim of facilitating access to projects based on their topics, has provided the possibility of assigning software topics to projects in the form of free-text tags for users. Assigning a correct and complete set of topics to software projects allows programmers to... 

As one of the most important software artifacts, release reports include most essential changes of software systems in each release. These reports are useful for documenting team activities, improving communication between team members and facilitating decision makings. They are often generated manually by a team member, which can be a tedious and time-consuming task. For each release, one should go through hundreds of issue reports, changed files, source code, and other related documents to determine what has changed and why. Then they need to identify the most important and relevant changes. Therefore, automated generation of release reports can be highly desirable. Despite the... 

In this study, the physic of an unsteady flow surrounding two oscillating airfoils in tandem configuration at low Reynolds-numbers has been simulated in a 2D manner by utilizing the Sliding-mesh approach and K-ω-SST turbulent model in Ansys-Fluent application. The first step in this study is selecting the decent numerical grid and flow solution scheme. After choosing the proper solution for this problem, next is to verify the methodology with respect to the references. In the next step, The tandem configuration and pitching motion of the airfoils is being implemented with existing tools and the flow structure, leading-edge and trailing-edge vortex shedding and blade-vortex interactions is... 

Software requirements are changing continuously and hence during software evolution and maintenance, source codes changes are being committed in the software repositories. Reading source codes to understand the changes is a very time consuming and tedious activity. Commit messages contain information about code changes that let developers be aware of the essence of the changes without reading the source codes. Unfortunately, due to the pressure of deadlines and lack of time, developers neglect to write these messages. Commit messages can speed up the process of software understanding for developers and also play an important role in software documentation. Therefore, an automated method for... 

Iran has the second largest natural gas resources in the world and these rich resources provide Iran with good potential for exporting natural gas but so far this potential has not been used well. In contrast, India is a major importer of these energy carriers due to high energy consumption and low level of energy production, especially oil and natural gas production, and continues to increase its imports so that its natural gas imports in 2018 equals 30 billion cubic meters, the IEA expects to reach 85 billion cubic meters by 2040. So the two countries can complement each other in the field of natural gas, such as crude oil and have close relations.In this study, using AHP, Iran's gas...