Sharif Digital Repository

With the recent developments in power electronics and electrical drives, there is a need for precise position sensors today more than ever. Having high precision and high reliability in harsh environments, resolvers are the most preferred position sensors among other types of prevalent position detectors. In order to control linear machines, which are widely used in different industries, linear resolvers are employed. This project aims to propose a structure for tubular variable reluctance resolvers, formulate an analytical model for and optimize the proposed structure. In addition to having an acceptable precision, the proposed model should be less time-consuming compared with finite... 

In Private Equity funds, the manager (known as general partner) collects funds from the investors (known as limited partners) and invests them over a certain time horizon. Assuming that both parties seek to maximize their interests, a situation arises in which the manager does not consider the best interests of the investors. The manager's compensation package is one of the important parts of corporate governance, which consists of four components: management fee, performance based fees (or carried interest), hurdle rate and proceeds distribution method. In this research, first by conducting a semi-structured interview with 15 experts in the PE ecosystem and publishing a questionnaire, the... 

In this study, I examine the role of board composition and ownership structure and trading days on board compensation of 156 Iranian non-financial public firms. Regarding board composition, I find that board size, CEO-Directorship, and the presence of busy directors positively explain board bonus. Concerning ownership structure, results reveal that outside block-holders and the percentage of individual investors negatively influence on board bonus. Also, trading days is proved to have a positive impact on board bonus. Furthermore, I examine the impact of compensation relating to board composition and ownership structure and trading days (predicted compensation) on the future operating... 

There are a wide variety of light-triggered switches. Photoconductive semiconductor switches (PCSSs) have been investigated intensively for many applications owing to their unique advantages over other switches. The advantages of PCSSs make them a perfect choice for many important applications where high switching accuracy and high-power capability are required. Photoconductive switches are fabricated from a variety of semiconductors, including silicon carbide (SiC), gallium arsenide (GaAs) and gallium nitride (GaN). In Photoconductive semiconductor switches (PCSSs) the switching mechanism is initiated by optical illumination and laser source controls the flow of current. In the off or... 

One of the most common problems encountered in multivariable systems is the interactions between the system inputs and outputs. Interaction causes difficulties in control of these systems. Hence reduction of interaction in multivariable systems is an important design objective. One way to do this is to employ a pre-compensator in the open loop systems. Several approaches with different design methods and optimization criterions have been proposed thus far. In this study the problem of interaction reduction for a square stable system is considered and a pre-compensator matrix is designed which reduces interactions in the interacting multivariable system.In this case the purpose is to use... 

By generalizing dictionary learning (DL) algorithms to Multidimensional (MD) mode and using them in applications where signals are inherently multidimensional, such as in three-dimensional (3D) Inverse Synthetic Aperture Radar (ISAR) imaging, it is possible to achieve much higher speed and less computational complexity. In this thesis, the formulation of the Multidimensional Dictionary Learning (MDDL) problem is expressed and six algorithms are proposed to solve it. The first one is based on the method of optimum directions (MOD) algorithm for 1D dictionary learning (1DDL), which uses alternating minimization and gradient projection approach. As the MDDL problem is non-convex, the second... 

In last years, many researches are focoused on improving of suspension systems because of their importance in automotive afavourable performance. One of these advanced suspension systems are Magnetorheological suspension with nonlinear dynamic system and complicated behavior like Hysteresis Loops, so their modeling are notable.
In the first chapter as introduction, suspension systems and their aims are expressed briefly. Then Magnetorheological suspension structure and its function are mentioned. After review of researches that has done about its modeling and control , in the third chapter, different types of classic and generalized Prandtl-Ishlinskii models are introduced and... 

In this study, a practical approach for robotic beating heart surgery was proposed. This approach eliminates lateral movements of the heart and compensates for normal heart movement by using 1 DOF heart stabilizer and 1 DOF heart compensator simultaneously. It is a compromise between complete fixation of the heart, which damages the heart tissue, on one hand and complex and impractical compensation of the free heart movement on the other. One of the core components of the proposed system is the slave robot, which includes a 1 DOF compensator and a 4 DOF tool holder robot. Based on the selected laparoscopic tool, a modified agile-eye mechanism for activating the wrist was introduced,... 

In many industries, including oil and gas industries, power plants, refineries, petrochemicals, steel and cement industries, industrial complexes and consumer industries, there are tanks for storing materials. It is necessary to measure level of products while they are stored in tanks of different sizes. Ultrasonic is one of the non-contact and accurate measurement technologies that can provide a suitable solution for liquid tank monitoring. The purpose of this thesis is to design and build the electronic parts (transmitter and receiver circuits) of an ultrasonic system that is capable of detecting levels at a distance of less than 5 meters with an accuracy of 0.5 % full scale. In this... 

In recent years، one of the most popular and wide areas of research have been focused on Unmanned Aerial Vehicles (UAVs). Among them، Quadrotor which has the capability of Vertical Take-off and Landing (VTOL)، hovering، great agility and maneuverability، simple structure، light weight and reasonable size has particular importance. In the industry، we always deal with plants which there are no precise information about their dynamic model، or their model is too complex to identify. So designing controllers with less dependency to system model and no need to exact knowledge of the system is absolutely vital. The arrangement of motors in a Quadrotor provides six Degree Of Freedoms (DOF) for... 

Decentralized control is a typical method for the design of industrial MIMO control systems. However, in most multivariable systems, the existence of large interactions limit the achievable performance of such controllers. In the Nyquist Array design method proposed by Rosenbrock, the system interactions can be reduced using a precompensator, such that a decentralized controller may be used with acceptable performance. A well designed pre-compensator will effectively decouple the system and the multivariable systems may be considered as a set of SISO systems. It is therefore obvious that the key element in the Nyquist Array design method is the design of the pre-compensator. There are two... 

Nowadays, with the increasing need of various industries and applications to directly create linear motion, linear resolvers are attracting more attention than ever. Achieving high accuracy as well as measuring absolute position leads to the introduction of a new generation of resolvers, called multi-turn resolvers. Usually, a multi-turn resolver consisted of two individual resolvers in one frame, while using a common core for both resolvers can help to make the multi-turn sensor smaller, cheaper, and lighter. Nevertheless, the studies conducted on linear and multi-turn resolvers are very limited. Therefore, this research proposes an integrated core linear variable reluctance multi-turn... 

Due to the simplicity and generality, design of feedback control systems in the frequency domain is among the most prominent topics in the control systems engineering. The problem of compensation means properly adjusting the loop frequency response at critical frequencies. Considering the point that the traditional methods usually use trial and error procedures for compensation, analytical design of fixed-structure controllers for exactly adjusting such values has great importance. Benefitting from the capability of fractional-order dynamics, the compensation problem is studied from three aspects in this thesis. At first according to the importance of adjusting the system frequency response... 

In this work, an analytical model has been proposed for rectifiers used in RFID & WSN applications. Body effect has been considered in this model, as well as the effect of transistor size and number of stages on the output voltage of the rectifier. Using proposed equations for both rectifier circuit and the matching network, the power harvesting system is optimized by means of co-designing the rectifier and the matching network. The results of the proposed model are in good agreement with the simulation results.
Finally, A Rectifier circuit which is designed to generate 1-V dc across a capacitive load is presented. Simulation results show that the sensitivity of this power harvesting... 

n this article, we find necessary conditions for the existence of Ito Integral in a Banach space with respect to compensated Poisson random measure (cPrm). Ito integrals with values on M-type 2 Banach spaces F of the above form exist for all measurable, adapted functions f square integrable w.r.t. β ⊗ d t (f ∈ M2T;_(E/F)),with β being Lévy measure associated with cPrm, and have strong second moments. We show that, for general separable Banach spaces F, an inequality of the type resulting for M-type 2 Banach spaces with constant depending on cPrm is necessary and sufficient for the existence of Ito integral having second moment finite for all f ∈ M2 T;_(E/F). It is shown that M2 T;_(E/F) is... 

SRAM has a very wide application in different platforms including Cache Memory in Microcontrollers, etc. also SRAM is the first candidate for memory usage in every application needing High speed or static memory circuits. SRAM Cells are constructed by Minimum size transistors in each technology node and usually the newest technology nodes are used for building SRAM blocks for accommodating maximum number of SRAM Cells in a specific area. Going through smaller technology nodes, Leakage current and Process variations problem, creates serious difficulties in designing Low Power or High speed SRAM Memories and many academic and industrial works are done wishing for improvement in SRAM power... 

One of the important problems in fulfilling the consumers' power demand that has been especially intensified after restructuring is transmission line congestion. To solve this problem, either new transmission lines should be constructed or the existing transmission lines should be better utilized. Construction of new transmission lines is both expensive and time consuming. Therefore, it is usually better to enhance the utilization of the existing transmission assets. FACTS devices have been introduced over the past decades to enhance power systems operation. However, wide scale deployment of them has not occurred yet due to their high initial investment cost and some other problems. In order... 

Magnetic bearings have been used in industry to achieve an acceptable performance, high precision and vibration suppression of rotating machinery in recent decades.The absence of physical contact between the bearing and rotating components provides access to high rotational speeds which is a problem in conventional bearings.In addition, capabilities such as stiffness and damping adjustment can be used to reduce the harmonic vibrations caused by mass unbalance. The unbalance compensation is one of the main topicswhich has attracted the attention of many researchers in the field of rotordynamics. The aim of this thesis is to design and fabricatea three-pole active magnetic bearing test rig and... 

Refractory metals (W,Re,Ta,Mo,Nb) and their alloys can exhibit exceptional properties at elevated temperatures. However, refectory metals tend to be relatively heavy and, in some cases, can be relatively difficult to form in complex shapes at low cost. Light composites of refractory metals with high-melting ceramics, which can be fabricated into dense, near net shapes at low temperatures, would be particularly attractive for advanced aerospace applications. In this project, WC powders have been pressed and shaped to cylindrical preforms. Secondly, these performs have been sintered slightly(presintered) into porous, rigid ones with about 50% open porosity. Finally, in order to reach dense... 

In cases with excessive anteversion even after adolescence, surgeons have to choose osteotomy surgery to modify this abnormality. This surgery and modifying the anatomical problem does not necessarily lead to modify the patients’ gait cycle abnormalities; the authors’ hypothesis is the probable reason may be the persistence of the implement of the patients’ kinematics compensation mechanism even after the surgery. This mechanism is used to almost correct the gait of those with excessive anteversion. First, by using gait analysis text books, a patient’s gait cycle is analyzed; this analysis is consist of 3DGA with EMG and observational gait. Then, by using OpenSim, the patient’s patterns of...