Sharif Digital Repository

Due to the high processing capacity of GPGPUs and their requirement to a large and high speed shared memory between thread processors clusters, exploiting Spin-Transfer Torque (STT) RAM as a replacement with SRAM can result in significant reduction in power consumption and linear enhancement of memory capacity in GPGPUs. In the GPGPU (as a many-core) with ability of parallel thread executing, advantages of STT-RAM technology, such as low read latency and high density, could be so effective. However, the usage of STT-RAM will be grantee applications run time reduction and growth threads throughput, when write operations manages and schedules to have least overhead on read operations. The... 

In the framework of the Standard Model of Particle Physics, Quantum Chromodynamics (QCD) is known to be the only theory which describes the strong nuclear force. Because of the property of asymptotic freedom, perturbative methods fail to describe QCD at low energies. Here, mesons and baryons build the main degrees of freedom of QCD. To describe the dynamics of mesons at low energies, nonperturbative methods are used. The Nambu–Jona-Lasinio (NJL) model is one of the most important effective models, which is used to study the nonperturbative phenomena of QCD at low energies. The Lagrangian density of this model includes a local four-fermion term,which descibes the interaction between the... 

Magnetic levitation is an appropriate solution for noncontact 3D manipulation. Workspace of the previously proposed maglev systems is confined to a relatively small cube, which severely limits the application of this technology. In addition, most of the previously given mechanisms require the design and application of a subsystem in order to unify their magnetic field. In this paper, a moving magnet is proposed which results in a horizontally extendable workspace; moreover, the field unifying section is not needed since one electromagnet only is used. Further, details of the mechanism and finite element based design procedure of the magnet are presented. Dynamic equations of the system... 

The precise positioning of magnetic catheters is critical for a range of medical procedures, ensuring efficacy while minimizing potential complications. This research delves into the position control of a magnetic catheter influenced by an external permanent magnet. Due to the intricate and complex equations describing the plant's behavior, a neural network approach was deemed suitable for modeling. Using a 5 degree of freedom manipulator carrying an external permanent magnet, data was gathered from real-world positionings, tracking the coordination of the magnetic catheter's end. These data points served to train the neural network, subsequently allowing for an effective simulation of the... 

Direct Torque Control (DTC) is one of the vector methods to control Permanent Magnet Synchronous Machines (PMSM). In order to achieve an appropriate control in vector control methods, an accurate estimation of flux is indispensable. Flux estimation should be fulfilled in a wide speed range without considerable dependence on motor parameters. Prevalent flux estimation methods are based on integration of stator voltage which is not feasible in low speed, or performed based on assumption of decoupled equations on d and q axis which is not precise for applications with fast dynamic. Different flux estimation methods are investigated in this thesis with the aim of improving the flux estimation in... 

Accurate and fast position controlling is an important issue in today’s industrial needs. Drives used for position control require fast dynamics on speed control. Cascade linear controllers have sluggish response due to bandwidth limitations on speed and current loop. These structures limit the dynamics above all in high power applications where the switching frequency is low. In this thesis, deadbeat direct speed control is proposed, which overcomes limitations by cascade loops resulting in high-speed control dynamics. This approach uses a model of the plant to generate the control signals. According to measured speed and currents, the controller specifies the best voltage vector in order... 

Elastic joints in 2-mass drive systems, because of their limited stiffness, can decrease the performance of the control system and lead to motor and load speed oscillation. Shaft torque ignoring can also stress both mechanical and electrical drive components. Because of low degree of freedom, conventional controllers, such as the PI controllers, cannot improve the performance of the system and keep the system stable at the same time. In this thesis, the dynamic response and stability of the 2-mass systems is improved using state controller. State estimation of 2-mass system is required for state space controller . In the thesis, different state observer is analyzed and compared with each... 

Microrobots have the potential to access small spaces for manipulation or for acting as a sensor. Magnetic microrobots are the most common types of microrobots. Magnetic microrobots have gained particular traction for medical applications due to safety of tissues. For instance, disease diagnosis, minimally invasive surgery and cell manipulation are potential applications of magnetic microrobots. The performance of a single microrobot could be improved by using multiple robots. For example each microrobot could carry a small payload to a goal inside a microfluidic channel, or could assemble fast and in parallel. In order to employ multiple robots, it is necessary to control each microrobot... 

The primary goal of this thesis is to develop a Fault Tolerant Control (FTC) system for a flexible satellite in presence of actuators fault and failure. The actuators of the satellite are including three magnetorquers and three reaction wheels on each principal axis. At first, the three-degree-of-freedom rotational motion of a rigid satellite with two flexible solar panels is modeled. The flexible panels are modeled through the assumed mode approach by a finite set of bending modal motion. The ordinary differential equations of their generalized coordinates are found using the Lagrange’s equation. Then, the dynamic model is validated by comparing the simulation results of the model to the NX... 

In this thesis one of the sensorless methods which exploits the existing anisotropies of the rotor is utilized to estimate rotor position. In order to implement this method, first a high frequency voltage is injected in a specific, time-varying direction and then the corresponding current response would be observed in order to estimate the rotor saliency position. The estimation of rotor position would be more precise as the magnetic anisotropy due to rotor saliency increases and as a result the effect of noise and different disturbances in estimation of rotor position would be decresed. The effect of stator resistence is one of these disturbances which is usually neglected as a result of... 

In this thesis, functionalized Fe3O4 nanoparticles have been utilized as a support for immobilization of homogeneous catalysts. The catalytic activity of the supported heterogeneous nanocatalysts was investigated in hydrocarbon and sulfide oxidation reactions. In the first part of this research, imidazole functionalized Fe3O4 nanoparticles (Fe3O4@SiO2-Im) were used as a support to anchor manganese porphyrin complex, [MnT(4-OMeP)P]OAc; via axial ligation. Catalytic application of the immobilized manganese porphyrin was studied in oxidation of alkenes and sulfides. To find suitable reaction conditions, the effect of different parameters such as solvent and temperature on immobilization process... 

Magnetic resonance imaging (MRI) is a highly efficient method that can provide acceptable contrast between soft tissues. But the big disadvantage of this method is that its acquisition is slow. To find the reason of being time-consuming should the procedure be surveyed. In the magnetic resonance imaging, location information obtained using phase and frequency encoding gradients. So the output is matrix of image data in the frequency domain, which is called k space. For the formation of the k space phase, need to apply gradients several times and this is the main reason of dullness of the system. Therefore, in this project using software methods try to reduce the scan time as possible. Among... 

There are many industries in the world that produce colorized wastewater. Because of the complex structure and good solubility of dyes, such industries have problem treating this wastewaters. On the other hand, because of the toxicity of these materials for water living, dye removal from discharged wastewater of these industries is very important. In recent years, researchers have become interested in the synthesis of dye Nano adsorbents and they have published many works on this subject. The important parameters in the synthesis of such adsorbent include; non-toxicity, high adsorption capacity and easy separation. In this project, cellulose was extracted from bagasse and then CMC was... 

Synchronous machines is one of the most popular machines in industry and in power plants. Because the dynamic of this machine is nonlinear, it can exhibit complex behaviors. In this project we have studied a special case in Permanent Magnet Synchronous Machines. A case in which speed of rotor, frequency, currents amplitude and voltages amplitude change in an irregular manner. This special case is called chaos. Chaos occurs for some specific values of parameters and inputs. In this study in the first step, we have tried to find the chaotic area of parameters of system (Prediction of chaos). Then in the next step, we have designed some controllers which can eliminate chaos in the system. The... 

The optimum wave functions and calculation method were obtained using a 24 factorial design. Based on preliminary experiences, the following four factors at two level was selected: electron correlation, triple-ξ valence shell, diffuse function and polarization function.
The wave functions for calculating gas phase 1H chemical shifts of primary and secondary alcohols were optimized using factorial design as multivariate technique. Gas-phase experimental 1H chemical shifts of 18 alcohols were used to establish the best levels of theory for obtaining 1H chemical shift, among them the new experimental values of 1H chemical shifts of 10 alcohols were obtained in our laboratory. HF/6-31G(d,p)... 

This research work deals with application of poly-saccharide to improve coating process of bioactive ceramic composite on aNd-Fe-B magnetic alloy substrate. Bioactive glass particles were synthesized through a sol-gel process and coated in the form of composite with poly-saccharide onto a magnetic substrate by electrophoretic deposition technique. Stable suspensions of 0.5 gr/lit polysaccharide polymer-ceramic were prepared using bioactive glass particles (<1µm), acetic acid 1%. The influence of added water to ethanol, pH and tri-ethanol-amine (TEA) additive on suspension stability, deposition rate and coating’s structure was investigated. It was shown that by increasing the water to ethanol... 

This thesis cantain two section. In the first section a novel extracting medium based on magnetic molecularly imprinted polymers (MIPs) nanoparticles was synthesized by chemical polymerization for micro-solid phase extraction. In this work, the modified chitosan magnetite nanoparticles (MNP-CS) was synthesized by co-precipitating Fe2+ and Fe3+ in the chitosan solution [1,2]. The characteristic properties of Fe3O4@MIPs nanoparticles were determined using Fourier transform infrared spectrometer. Extraction efficiency of the novel extracting medium was compared with MNP-CS sorbents for the determination of RhB in aqueous samples, via quantification by spectrofluorimetry. The obtained results... 

In this thesis a novel non-rotating space tethered configuration is introduced which its relative positions are controlled using electromagnetic forces. The attitude dynamics is controlled by three reaction wheels in the body axes. The nonlinear coupled orbital dynamics of a dumbbell tethered satellite formation flight are derived through a constrained Lagrangian approach. These equations are presented in the leader satellite orbital frame. The advantage of using equations in the Cartesian coordinate system over presenting the equations of satellite formation plane angles is the appearance of gravity gradient and Earth’s magnetic field effects. The tether is assumed to be mass-less and... 

Quantum Information Processing (QIP) is one of the active areas of research in both theoretical and experimental physics. Any experimental technique that is used for a scalable implementation of QIP must satisfy DiVincenzo’s criteria [17]. Nuclear Magnetic Resonance (NMR) satisfies many of these conditions, but it is not scalable and cannot initialize the qubits to pure state [28]. NMR can be a great platform for studying the fundamentals of QIP. In this project, for a two­qubit system, we prepare pseudo pure states from the initial mixed states by using unitary operations and implement CNOT gates. According to the results of our experiments, we can apply all the gates with high fidelity.... 

The goal of this thesis is to understand the physical properties of lanthanum based manganites and barium based ruthenates. In order to obtain negative colossal magnetoresistance in manganites and fabrication of barium ruthenate in ordinary condition, the effects of variables such as ionic radii, chemical composition, temperature, magnetic field and processing in manganites and ruthenates systems are investigated. In the first part, the effects of potassium doping on structure, metalinsulator transition and magnetoresistance in )La1-yKy)0.7 Ca0.3 MnO3 and)La1-yKy)0.7 Ba0.3 MnO3 manganites systems are studied. Polycrystalline samples of manganites are synthesized by the sol‐gel method. In the...