Sharif Digital Repository

The study on new rheoforming technologies of semi-solid alloys has recently been one main subject interesting many researchers and industrials, and so many new methods about preparing semi-solid alloy slurry and rheoforming process have been suggested. Among more than 20 proposed methods, only MHD (Magneto Hydro Dynamics) and EMS (electromagnetic stirring) methods has been industrialized. In this research, the semi-solid slurry of A356 aluminum alloy was fabricated by electromagnetic stirrer under different conditions of stirring current, stirring time and pouring temperatures. Then the semi-solid slurry prepared in optimum conditions was injected into a step-die cavity by a drop device and... 

Bulk metallic glasses (BMGs), in contrast to conventional crystalline materials, are defined as metals with an amorphous and disordered atomic-scale structure. Due to the absence of dislocations and grain boundaries, BMGs have considerably unique mechanical properties such as high strength and elastic strain, high wear resistance and desirable corrosion resistance. However, they generally suffer from poor plasticity caused by an inhomogeneous deformation which leads to catastrophic failure by localization of strain into narrow regions, known as shear bands. This factor has extremely restricted their application as advanced structural materials. Furthermore, the recently discovered phenomenon... 

In drilling oil well with respect to depth of several thousand meters, knowing the physical conditions of down-hole well such as temperature, pressure and stress have particular importance in prevention of possible injuries such as breaking the drill bit or increasing temperature. If these data can transfer from down-hole to bore-hole of the well, the operators can prevent from critical conditions such as intertangle of the drill-string. Currently, because of this lack of information, there are irreparable damages in oil industry annually. Based on researches, because of down-hole conditions of the well, these data can’t transfer with electromagnetic telemetry. Currently one of the data... 

Drilling in oil industry, is an expensive process in produce and extract oil from well. Any mistake in drilling may cause many drawbacks for industry owners. Phisic’s quantities information at downhole like tempreture, pressure and force on bit synchronously can inform user from torrid conditions and prevent undesired events by actions like evoke bit from downhole or change at rotation velocity in drilling and finally stop operations. With attention to a lot of problems in data transport from long distance more than one kilometer from downhole, scientists believe that one of the methods to do this process is converting data gathered at the bottom hole to acoustic waves and transmit them to... 

New development in material fabrication resulted in functionally graded materials (FGM) with properties, can vary continuously based on the desired purpose. Vast applications of these materials attracted scientists to extend the researches in this area. One of the promising applications of these materials is in the optimized spherical and cylindrical pressure vessels. Optimization is usually based on the minimization of heat transfer and maximization of the strength of the vessel under pressure. In the present dissertation, spherical and cylindrical pressure vessels are designed and characteristics of the material distribution for certain pressure and temperature is developed. In this... 

Image classification is one of the most challenging issues in computer vision. One sort of such classifications is Scene Classification. To perform automatic classification reserchers used many aproches.The general approach used features directly extracted from the image, such as color and texture or features extracted by the SIFT algorithmetc. Another method is based on recognizing object of the Scene (espessially indoor scene). This method is based on finding of a limited number of prespecified objects. In the proposed method, first a window surrounding each objects, (regardless of the type of object) founded. Then the SIFT feature is extracted from that window. All features (corresponding... 

Regarding the numerous casualties and financial losses due to intense earthquakes, the ductility is considered of the main importance in addition to stability, stiffness, and strength criteria of the structure’s connections. In order to enhance the seismic behavior of the structures in such severe earthquakes, design codes for steel structures have suggested special types of connections. Among them, bolted end plate connection is considered a conventional type of connection used for creating ductile semi-rigid connection.In this study, in order to simulate the behavior of this joint, a 3-D finite element model is developed in Abaqus software, in which the inelastic behavior of the materials... 

Atomic force microscope (AFM) has a significant capability of imaging surface topography on an atomic scale. It is also widely used for Nanolithography in MEMS/NEMS (micro/nanoelectromechanical systems). Conventional AFMs consist of a cantilever with a sharp conical or pyramidal tip located at the free end of the cantilever that plays an important role in AFM measurements. Scanning across a surface, AFM interacts with the sample surface through its tip. Although the dynamic behavior of the AFM cantilever is complicated, the researchers have been interested in studying AFM dynamic behavior because it has a great influence on the surface imaging process. The imaging rate and contrast of... 

In addition to investigating the overall situation of healthcare information systems (HIS) in Iranian hospitals, in this thesis the goal is to determine the key elements of success and failure in the implementation of HIS. With the advent of the computer systems in Iran and due to the successful and unsuccessful experiences of organizations, the necessity of detecting the influential elements in this field is perceived even more than before. Another importance of this research is because of the essential role of the cultural and social factors in the success of these systems; this claim can be justified by observing different results founded by researchers from different countries. In this... 

Today, with the spread of various videos especially sports video and availability of them, the need for automated methods for search and retrieval of concepts from videos is strongly felt. On the other hand, summarizing video in order to making significant parts of them available is very important. One of the broadest scope that researchers have provided methods for extracting semantic concepts, is soccer videos. Often to extract high-level events, we need a definition and use of intermediate concepts. In this thesis "replay", "audio highlights" and "view type" are used to extract important events in the game. Here, two new methods are introduced for replay detection and view type... 

Gene regulatory network consists of a set of genes; interacting with each other via their protein products. Such interations lead to the regulation of the genes’ production rate. A breakdown in the regulatory process, may lead to some kinds of diseases. Therefore, understanding the gene regulatory process, is beneficial for both diagnosis and treatment. In this thesis, gene regulatory networks are modeled by the means of dynamic Bayesian networks. We have used sampling based methods, in order to learn the network structure. As these methos have a very high computational cost; we have used a correlation test to prune the search space. This way, an undirected network skeleton is obtained; for... 

With respect to the introduction of bio-material into cells (transfection) , microinjection is a highly efficient technique amongst existing methodologies. In cell injection, a manipulator injects the needle into a cellwhich is hold by a pipet mechanism. The moving range for the needle in this operation is of centimeter order and the resolution for the needle tip should be less than the cell’s diameter. In this thesis a Stewart system is used as for the manipulator. Stewart systems are used in flight simulators systems for decades, as mechanisms which are capable of providing multi-axis movements. In high accuracy positioning and multi-axis applications Stewart systems are highly reliable.... 

In accomplishment of knowledge management in real world, organization can be in different processes of awareness about importance of knowledge management and its achievements. Recognition of strength and weakness points of organization helps to logical planning and success in performance of knowledge management. For avoiding from failing in knowledge management projects, it is necessary that before stating for project performance, evaluate development level of organization from viewpoint of knowledge management, and determine some approaches for control of general problems of knowledge management, like abundance of information, work complexities, knowledge Storage.
In literature of... 

Image registration is the process of matching two or more images captured at different times, angles or even sensors. Image registration is finding a transformation between two images. Image registration has many applications in different fields of Image Processing and machine vision. In the field of remote sensing, image registration can be used for environmental monitoring, generating graphical maps and gathering data for geogeraphical information systems, also in the field of medical image processing it can be used to detect tumor growth. Generally whenever there is need to extract information from many images; image registration is considered as an important pre-processing step....