Sharif Digital Repository

In this thesis, heterogenous catalysts based on magnetic nanoparticles were synthesized. In these catalysts, magnetic nanoparticles were coated with defferent fuctional groups to produce a catalyst with magnetic properties which is easily separated from the reaction medium. The structure of synthesized catalyst was characterized using techniques such as transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and CHNS elemental analysis. Easy preparation, low cost, biodegradability and high thermal stability are advantages of these catalysts. At the end, the catalytic properties of resulted catalysts were investigated in many... 

In recent years, energy harvesting from ambient sources in order to use for low-powered electronics has been considered by many researchers. Wind energy, solar energy, water energy, mechanical energy from vibrations, etc are common sources of ambient energy. In this thesis, optimization of energy harvesting from ambient vibration using magnetic shape memory alloy is presented. To this end, a clamped-clamped beam coupled with MSMA units is considered. A shock load is applied to a proof mass which is attached to the middle of the beam. As a result of beam vibration a longitudinal strain is produced in the MSMA. This strain changes magnetic flux inside the coil connected to MSMA and as a... 

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... 

A novel thermo responsive decorated system is designed by coating Fe3O4 magnetic nanoparticles with conjugated Pluronic-ATPEG copolymer incorporated into the PEG-PMDA Hydrogel for drug delivery to the cartilage tissue. Grafted copolymer was synthesized by reaction between carboxylated Pluronic and amino terminated Poly ethylene glycol (ATPEG) and confirmed by FTIR and NMR analysis. The magnetic nanoparticles were modified with the produced copolymer and characterized by TEM, HRTEM, XRD, DLS, and VSM. A typical product has 13 nm magnetic core and 105 nm hydrodynamic diameter with narrow size distribution. DLS results showed that there was an increase in size by increasing temperature from 25℃... 

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... 

One of the most useful method in medical imaging is Magnetic Resonance Imaging. Gadolinium base contrast agents used to improve images contrast made by MRI. There are some problems with using these drugs, such as toxicity and lack of targeting. In this research, Silicon nanoparticles were produced by a new fashion of removing template method. Particle size was scanned by Dynamic light scattering (DLS), mesoporous structure was investigated by Brunauer-Emmett-Teller (BET), and amine functionalization was recognized by Fourier transform infrared (FTIR). Functionality was determined by evaluation of signal and relaxation of nanoparticles.T1 was defined by a 1.5 tesla power MRI device. The... 

In this thesis, we study the effect of quantum fluctuations by means of a transverse magnetic field () on the ground state of frustrated antiferromagnetic Ising models on the checkerboard and square lattices with nearest neigbor couplings J1 and next-to-nearest neighbor couplings J2. At zero field, such models have exponentially large degenerate classical ground states at J2 ... J1 for the checkerboard lattice and at J2 = 0:5J1 for the square lattice. Quantum fluctuations can have a major role to lift the degeneracies toward a unique quantum ground states. We consider two types of quantum fluctuations, harmonic ones by using linear spin wave theory (LSWT) with single-spin flip excitations... 

In this thesis, manganese oxide nanoparticles with about 5 nm size were synthesized via solvothermal to maximize surface and active sites for proton relaxation. The synthesized nanoparticles were coated with gentisic acid to acquire suitable colloidal stability and biocompatibility. The nanoparticles showed low cytotoxicity in MTT assay. Electrosteric mechanisim was employed for colloidal stability. This mechanisim doesn’t need high surface charge and thick coat which are vital for particles functionality. Then by cell culture eliminating and adding protamine sulfade, nanoparticles uptake were increased tremendously. In this thesis for first time Prussian blue was utilized for staining... 

1H-MRS thermometry as one of MRI thermometry methods, provides useful information about the distribution of the absolute temperature of tissue that can be used in diagnostic and therapeutic applications. It seems that the magnetic field inhomogeneity and the reduction of spectra resolution also affects the accuracy of MRS thermometry. To our knowledge, effects of magnetic field inhomogeneity on MRS thermometry has never been reported. In this study, we evaluated the effect of susceptibility inhomogeneity on MRS thermometry. In the first stage, MRS thermometry equation was derived in the presence of field inhomogeneity. Then simulation used for estimate the effect of filed inhomogeneity based... 

Magnetic elastomers are smart materials that consist of a combination of elastomeric matrix and magnetic particles. The mechanical and magnetic properties of this materials are changed by Applying an external magnetic field. The presence of an external magnetic field can cause these elastomers deform largely.Significant deformations of the magnetic elastomers, has made them suitable for a wide range of applications. The aim of this project is to solve the governing equations of magnetic elastomers with finite element method. Since there are no suitable models for the behavior of these elastomers in the commercial softwares, magnetic field module and solid mechanics module should be coupled... 

High speed and high accuracy are two of the major trends for many systems in the 21st century, such as machine tools and semiconductor equipment. For the purpose of high speed, it is well known that active magnetic bearing (AMB) is an inevitable substitute for conventional bearings. The noncontact nature of AMB brings up many advantages over the conventional bearing, including energy efficiency, low wearing, long life span, and absence of lubrication. Hence, AMBs are especially essential for high-speed rotating devices nowadays.
While the 3-pole AMB has been proposed for many years, it received little attention due to the magnetic coupling between poles that makes the 3-pole AMB system... 

One of the most challengeable topic in the field of green chemistry is the synthesis of organic structure in water. In this project immobilized glucose on Fe3O4 was prepared as a nano heterogeneous dispersive catalyst in water. The catalyst was fully characterized by FT-IR, TGA, CHN, SEM, EDX and atomic absorption spectroscopy. The synthesized catalyst was used in the synthesis of different derivatives of 1,2,3-triazole via one-pot three component reaction of alkynes, alkyl halides, sodium azides; And to the best of our knowledge this novel catalyst coin sides to the principles of green chemistry. This nano catalyst can be recycled and reused for several runs without significant loss of its... 

In this study, polyelectrolyte-coated magnetic silica nanocomposites were prepared via the covalent attachment of polyelectrolytes onto the as-prepared magnetite-silica particles with core-shell structures and average diameter of 210±50 nm, and subsequently applied for the immobilization of lipase molecules. In this regard, polyethyleneimine (PEI) with two molecular weights of 10000 and 750000 and polyacrylic acid (PAA) with two molecular weights of 1800 and 100000 were utilized. The type and molecular weight of the polyelectrolyte molecules greatly impacted the concentration of binding sites on the particles surface and consequently on the lipase immobilization efficiency and loading... 

In the presented dissertation an analytical model is developed for the air gap flux density and the cogging torque in the axial flux surface-mounted PM machines. The slotting effect is taken into account in the magnetic flux distribution.The model is derived from solving the 2D Poisson' equation in the slotted air gap. To simplify the solution process, the concept of the uniqueness theorem is used to replace the slotted air gap by a slotless one and some surface current distribution. In addition, the separation of variables method is applied to the analytical solution of the Poisson equation. However, the proposed 2D analytical model is developed for the quasi 3D model by the well-known... 

Among different mechanisems for ambient energy harvesters, energy harvesting systems by means of magnetic shape memory alloys are noted due to their long life time, large strain amplitudes and the ability to operate at low frequencies. Strain change in these systems, changes the MSMA magnetization resulting change in the magnetic flux leading to inducing voltage by means of pickup coil. in the commercial systems, magnetic flux path is created by inserting an MSMA specimen in the air gap of ferromagnetic core and generation of bias magnetic field by means of the permanent magnet or electromagnet. In this proposed research, a thermodynamic based constitutive model is selected for the mdeling... 

The project aims to design and build a device that is capable of manipulation and control of micro-scale objects in dry and fluid medium. Among all the micro-manipulation methods, the use of magnetic fields has many applications. Because it has the ability to work without direct contact and also within a specified range for living tissue, is safe. To achieve this goal,manipulation systems ever made, were studied. Then, by presenting a conceptual design and the use of appropriate dynamic models for describing the behavior of micro-robot, the system performance was simulated. After this stage, The detailed design of the closed-loop system which must controls the position of the micro-robot... 

This thesis completely introduses ferromagnetic single electron transistor while that identifies the application and types of the transistor.Master equation is used for simulationing of the transistor. This simulation is divided to two general sections.In the first section proposed thermal equilibrium the normal island and The two spin subsystems , however, are in thermal equilibrium and quantized nature of energy spectrum of a small central electrode and fluctuations in the spin accumulation were ignored , however, we simplify the problem and assume that the charging energy are independent of the electron distribution, and number of electrons in the normal island. ،hat tunnel rates can be... 

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... 

In this project, Fe3O4 nanoparticles were synthesized and coated with different polymeric materials for drug delivery application. For this purpose, water dispersible oleic acid(OA)- pluronic block copolymer coated magnetite iron oxide nanoparticles were synthesized that can be loaded with proper doses of cephalexin. Our data indicated that formulation of iron oxide nanoparticles was developed by optimizing the amount of oleic acid required to coat iron oxide nanoparticles and then by optimizing the amount of pluronic required to form an aqueous dispersion of oleic acid coated nanoparticles. Synthesis of magnetite nanoparticles was done by the addition of a strong base (NH4OH) to ferrous... 

Molecular nanomagnets, also known as Single Molecule Magnets (SMMs) are a class of molecules that at low temperature exhibit magnetic hysteresis of pure molecular origin and not related to a cooperative effect. In the past fifteen years they have attracted great interest for their potentiality to act as magnetic memory units and for the many quantum effects in the dynamics of their magnetization. Organization of SMM on surfaces is the first step in order to address the magnetic state of a single molecule or to connect the molecule to a conducting substrate. The complex nature of SMMs and the peculiar origin of their magnetic bistability have been representing for half a decade an obstacle to...