Sharif Digital Repository

In the last decade, magnesium alloy has been developed owing to it’s low density, high specific strength, good castability and damping property. AZ91 alloy is proved to be the most common and most important magnesium casting alloy. It is shown that, rheocasting process is a proper way which increases the mechanical properties of the products. Since 28 years, so many new methods for preparing Semi-Solid alloy slurry and rheoforming process have been suggested. Electromagnetic Stirring ( EMS ) method was used for making globular structures. In this research, the semi-solid slurry of AZ91 magnesium alloy was prepared by electromagnetic stirrer under different conditions of stirring current and... 

Textual news published in the media on a daily basis is a large and valuable source of unstructured data that can be used to analyze and model the financial market by using text mining methods. The purpose of this study is to design a news-reading system for economic analysis and modeling of gold prices using features extracted from textual news and text mining methods; it seeks to enable the machine to read news like financial analysts then analyze and forecast the economic situation and market trends. For this purpose, we collected news from the website of an Iranian economic news agency. To design the economic analyzer, we extracted important economic, political, and social factors from... 

The aim of this project was to design, analyze and fabricate a 4 DOF robotic arm to be used as a slave robot for tool handling in laparoscopic surgery. The mechanism used for this purpose should have a remote center of motion in order to be able to manipulate the tool through the small incision point. The robot should also provide sufficient force to handle endoscopic tools used for large organ manipulation and be capable of measuring these forces. A variety of mechanisms were studied thoroughly, and the best solution was chosen by considering the design parameters such as workspace, manipulability, accuracy, ease of fabrication, etc. The final design consists of a 2 DOF serial spherical... 

In the present dissertation model based grasping of soft tissue with the laparoscopic gripper, tissue deformation under the applied load and control of the tissue-instrument interaction have been studied. As the first step a cantilevered beam under bending and tension has been modeled statically and dynamically using the meshless EFG based method. Results show that an increase in the number of nodes at the displacement boundary and the area of force insertion improves the accuracy of the predicted displacement in the model compared to the analytical solution. In the second step the model is developed for a hemisphere under vertical and lateral compression. Comparison of the deformation of... 

One of the satellite time-critical launch methods is air-launch, which is considered in this research thoroughly. The Large number of important parameters of this method makes the system highly complex. In such complex systems, usual methods of design and development will not be effective. Moreover, based on systemic approaches, interfaces between different elements of a complex system have significant effects on the performance of the whole system. One of the methods for analysis of such systems is “Design Structure Matrix” or DSM. This method is based on system engineering principles and has confirmed capabilities in analysis of highly coupled systems.
In this research, the air launch... 

Security of cryptographic devices lies amongst the most important issues in the field of hardware security. It is frequently seen that in the process of designing cryptographic systems insufficient attention is paid to the physical implementation details. This is happening while a lot of secret information is known to be leaked through side-channels such as power consumption, electromagnetic emission and execution time. Side-channel attacks are able to reveal secret keys by using these side-channel leakages. Additionally, side-channel attacks are one of the most powerful but low-cost attacks that put the security of cryptographic systems in vain. It can be claimed that the most dangerous... 

Public-key cryptography is vital to secure digital communication. The classic instances of these cryptosystems are insecure against large-scale quantum computers. As a result, post-quantum cryptography has emerged as a replacement, which includes different categories. Isogeny-based schemes are one of the promising candidates mainly because of their smaller public key length. Due to high computational cost of such schemes, efficient implementations are significantly important. In this thesis, we have presented various solutions at three different abstraction layers. At the lowest layer, which deals with modular arithmetic, two hardware architectures are presented to perform modular... 

Cerebral palsy is the most common motor disorder among children, resulting from damage to the motor areas of the brain during fetal development or early infancy. Studying motor control changes in individuals with cerebral palsy helps better understand their motor abnormalities. In recent years, various methods for analyzing motor control have evolved, including synergy analysis. The current study aims to thoroughly examine the differences in muscle synergies between children with cerebral palsy and healthy children during walking. In the initial phase of the study, muscle synergies were compared among different groups of children with cerebral palsy (based on Rodda classification) and... 

Knee pain and injuries are very common in athletes. Anterior cruciate ligament (ACL) injury is one of the most important reason of knee acute and chronic pains. As ACL plays a significant role in knee stability and due to amount of reported ACL related injuries, much effort has been placed on finding proper and on time diagnosis and treatment of these injuries. Arthrometric methods are the most non-invasive reliable diagnosis option; however they are not fully capable of separating partial injuries from intact joint. This weakness can be investigated by quantifying the tests using computer simulations; so far few studies have been conducted toward this goal. In this study a two dimensional... 

Motorized intramedullary nails are a viable solution to treat patients with limb-length inequality. These fully implanted devices use external magnetic actuation to extend. This research examines the conceptual design of this type of nails by investigating various ideas and previous designs. The implant mechanism, body and controller are designed in detail. It was then simulated in standard tests to evaluate it. In addition, the implanted nail undergoes a biomechanical analysis and its stiffness is assessed. Finally, the controller design is carried out using dipole magnetic theory and verified by finite element simulations. As a proof of concept, we made a prototype that is twice the size... 

Suture anchors are implants used for reattaching torn soft tissues to bone. Tilting anchors, a subtype of suture anchors, not only maintain the features of conventional suture anchors but can also be manufactured via 3D printing with a porous surface, enabling bone ingrowth and thus ensuring secure, long-term fixation. Additionally, these anchors can achieve fixation beneath the cortical bone layer, making them effective for secure attachment in areas of low bone density. Despite these advantages, limited research exists on this type of anchor, particularly regarding its performance and strength. One of the most influential factors in suture anchor strength is the method of fixation within... 

The low female labor force participation rate in the Iranian labor market relative to the global average and even to countries that do not differ significantly from the socio-economic characteristics of our country is one of the important questions of the Iranian labor market. In this study, we seek to answer the question of whether the economic participation rate of married women will increase if the gender gaps in wages, job findings and job losses among women and men are eliminated in the Iranian labor market. To answer this question using household expenditure and income data and labor force data, we show that between the two categories of occupations, in terms of the share of women's... 

All humanare subject to a physiligical phenomenon known as tremor, which introduces unintended, relatively high frequency movments into various limbs. This involuntary movment is main reason of human disability in doing of precision tasks. Precision surgery like eye surgery is among them that surgeons must have very ittle tremor to enable them to oprate on the small anatomy of the eye. In this reaearch by emphasizing on reduction of muscle fatigue in precision surgery, weight balancing mechanism designed and analyzed. Fatigue is most important cause of tremor, thus we expected tremor amplitude reduce by reduction of muscle fatigue. Purpose mechanism is passive mechanism that balances the... 

80% of people in all over the world, experience Low Back Pain (LBP) once in their lives. LBP leads to dysfunction of spine. About 25% of LBP relates to the intervertebral disks which in the critical cases, a Posterior Lumbar Surgery (PLS) on the one or more lumbar disks should be done. Due to the some procedure such as retracting, cutting or denervation of muscles, PLS can hurt trunk muscles and spine. Thus, investigation of LBP and postoperative complications of PLS can help us in recognition of causes of LBP and PLS complications and modification of PLS approaches. The objective of this research was investigation of effects of LBP and PLS on the biomechanical function of spine. Pattern of... 

Human joints wear gradually by diseases like arthrosis and will fail. The Pain from joint erode, preventing tracking daily activities, wont disappear by medicines and joint replacement is a common treatment. Hip joint as one of the most important, largest and heaviest joints of the body,is no exception.
Over 600,000 worldwide annual hip replacement surgery is done. The joints are designed in such a way that it can move 15 years without significant wear. Different materials such as ceramics, polymers and metals are used in making it which before in vivo use, itmust succeed many tests like wear test.
Since making artificial joints become increasingly important in recent years and... 

This study aims to provide a multiscale model of traumatic brain injury including the three levels of macro, meso, and microscale information. In order to do this, a macroscale voxel-baed model of human head was constructed. The model was designed and generated to include mesoscale tissue information as well as a voxel-based approach to include voxel-based microscale data and to be coupled in a multiscale framework. Next, three different microscale models were constructed. The variations of fractional anisotropy within one standard deviation in the regions (including 60% to 70% of voxels) can change the stiffness of the tissue by up to the considerable amount of 40%. The microscale models... 

Deformity is one of the common diseases of the spine. For example, in the case of scoliosis, which is a three-dimensional deviation in the spine, the prevalence of 2% to 32% among adults has been reported [1]. In case of severe deformity, surgical methods are usually used to correct it. In surgical methods, rods with appropriate curvature are placed next to the spine and the deviation is completely or partially corrected by connecting the vertebrae to said rods. In general, the curvature of the rods is determined based on the clinical indicators of the patient, the tissue fault strength, the stiffness of the soft tissues, the movement limitation of the vertebrae and the level of spinal cord... 

Fatigue crack growth can have harmful effects on the reliability rotary machine. While an early warning to crack, can be used to extend the life of these expensive machines and increase reliability.Structural Vibration Condition Monitoring as a primary fault detection method, achieved to a lot amazing result and for this reason studies vibration behavior of cracked rotational shaft is a big issue for engineers of dynamic machine.In this research, first check the fault detection methods based on structural vibration condition monitoring, mode shape methods were extracted. Then by modeling rotational shaft in computer and creation of crack on it, fault detection quality of these methods have... 

In the present study, the effects of increasing the value of shale gas production, either due to increased production or price increases, have been studied on economic variables such as employment, wage, property value and the number of births. In this regard, the data for each of these variables was used at the county level in the United States of America between 2000 and 2011. In order to estimate the desired effects, counties are divided into two types of boom and non-boom counties. The findings indicate that increasing natural gas production will lead to more employment and wage growth in boom counties than non-boom counties. Also, during the period of increasing production, the value of...