Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"rf field"”.
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Theoretical studies of the VASIMR plasma propulsion concept
… plasma source, which creates cold plasma via rf-discharge; an ion cyclotron-resonance heating (ICRH) section, which is used to deposit rf-power into the plasma; and a magnetic nozzle, which forms highly directed superalfvenic outgoing plasma flow. The dissertation is focused on fundamental …
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High resolution NMR scattering : the first measurement of spin diffusion rates in a homogeneous solid
… diffusion through a homogeneous sample was performed as an incoherent NMR scattering experiment. The experiment consists of a combination of pulsed gradient spin echo methods with multiple pulse/ pulsed gradient spatial encoding met.hods. The NMR scattering experiment involves the creation of …
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Diagnostics and modelling of an inductively coupled RF low-pressure low-temperature plasma
… in the experimental work. Given fixed external RF coil current and voltage and the measured plasma density profile, Maxwell's equations and magnetohydrodynamical (MHD) fluid equations are used to calculate the self-consistent electromagnetic field. A number of predictions are presented and …
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Inherent insensitivity to RF inhomogeneity in FLASH imaging
… the past three decades. In MRI, radiofrequency (RF) field inhomogeneity is an unavoidable problem in practice and becomes severe at high magnetic fields due to the dependence of B1 on the sample. It leads to nonuniformities in image intensity and contrast, causing difficulties in quantitative …
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A fundamental investigation of the gas phase polymerization of styrene and vinyl type monomers in a low power inductively coupled 4 MHz RF plasma
… in a cold, low power, inductively-coupled RF plasma. All vinyl type monomers yielded an insoluble, crosslinked film which was slightly colored. A kinetic study is reported for styrene. The effects of power level, bleed rate of monomer, pressure and reactor geometry on the rate of polymer …
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Implantable electrode structures and their RF effects in MRI machines
… Imaging (MRI) scan. Under the high-power RF field from an MRI machine, the conductors can behave as antennas and concentrate energy into small regions of body tissue, leading to excessive joule heating. Neurostimulator implants that employ long electrode leads such as those for Deep Brain …
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The sensitivity of nuclear magnetic double resonance
… to the impurity concentration when an rf field at the resonance frequency of the quadrupole shifted transitions was applied. Using a new method, intermittent search field irradiation, evidence was found that the finite spin diffusion rate caused a double resonance energy transfer rate …
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Modulation and cross-relaxation effects on the lineshape of strongly saturated nuclear magnetic resonance in solids
… condition of slow passage with magnetic field modulation, while applying an rf field, HI' intense enough to produce saturation, and have found that the lineshape does not agree with the very weak HI theory of Bloembergen, Purcell, and Pound, or with Redfield's strong HI theory. We have …
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Magnetic resonance imaging via radio frequency gradient with examples from NMR and pure NQR
In this thesis, we explore the use of RF gradients in NMR imaging. RF gradients have advantages over gradients of the static magnetic field in that they are non-secular and offer more experimental freedom (for example they permit amplitude, phase and frequency variations). In the case of pure NQR …
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Electro-Mechanical Interactions in Superconducting Spoke -Loaded Cavities
… and proton linear accelerators. We present a powerful method for characterizing arbitrary time-dependent Lorentz force induced detuning of superconducting cavities; the convolution of the Lorentz transfer function and the cavity accelerating gradient. Using the beta = 0.5 triple-spoke-loaded …
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Integral Equation-Based Inverse Scattering and Coil Optimization in Magnetic Resonance Imaging
… been to steadily increase the static magnetic field strength and hence the frequency of operation, resulting in higher available signal-to-noise ratio that could be traded for shorter scan times and increased image quality. In the ultra-high field regime (≥7T), since the radiofrequency …
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Measurement of Radiofrequency Induced Heating in Patients with Retained Post-Surgical Epicardial Leads During MRI
… the lead to interact with the radiofrequency (RF) field produced in the MRI scanner, causing a significant amount of heating in the patient. While there are numerous studies on transvenous leads, there is insufficient data to comment on the safety of patients with retained post-surgical …
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Nonlinear Dynamics of Vortices in Different Types of Grain Boundaries
… accelerators, superconducting radio-frequency (SRF) resonator cavities are required to operate with lowest energy dissipation and highest accelerating gradient. SRF cavities are made of polycrystalline materials in which grain boundaries can limit maximum RF currents and produce additional power …
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Accurate monitoring of x, y, and z magnetization for analysis of hardware and pulse sequence performance in NMR spectroscopy
… imaging pulse-train technique to obtain RF-field (B<sub>1</sub>) and resonance-offset (ΔB<sub>0</sub>) dependent profiles for each Cartesian component in the rotating magnetic coordinate system. The proposed protocol was used to analyze the distribution of the sample as a function of the …
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The Development and Application of Nuclear Magnetic Cross Relaxation Spectroscopy to Model and Retrograding Starch Systems
… aqueous waxy corn starch suspension to better perform and interpret the results obtained using CRS. The CRS data collection properties evaluated were the time to achieve steady state saturation, the direct saturation of liquid protons, generation of transverse magnetization, and the dependence of …
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Investigation of the Superconducting Properties of Niobium Radio-Frequency Cavities
<p>Radio-frequency (rf) superconducting cavities are widely used to increase the energy of a charged particle beam in particle accelerators. The maximum gradients of cavities made of bulk niobium have constantly improved over the last ten years and they are approaching the theoretical limit of the …
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RF-induced Heating Assessment and Heating Reduction Techniques for Partially-In and Partially-Out Medical Implants in MRI
… strong static, gradient, and radio frequency (RF) fields to produce detailed images of internal body structures. However, patients with partially-in and partially-out (PIPO) medical implants who require MRI scans are continually growing and often excluded from examinations or subjected to scans …
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Design and Verification of a LabVIEW Automated Antenna Radiation Pattern Measurement System
… so that accurate measurement of radio frequency (RF) systems such as wireless radios and antennas can take place. Despite the fact that Cal Poly already has a larger anechoic chamber, primarily used for antenna characterization, it is the purpose of this project to design, code, and equip the new …
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Experimental studies of novel accelerator structures at 11 GHz and 17 GHz
… operation without structure damage due to rf-field-induced breakdowns. This thesis reports theoretical results on the design of PBG structures and the generation of wakefields in such structures. It also reports experimental results on PBG structure breakdown testing at high power at both …
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Study of the thermal effects induced by magnetic resonance on endocardial leads: numerical models and experimental validation
… increase caused by the radiofrequency (RF) field generated during MRI procedures in the tissues surrounding thin metallic implants. On the other side, the technical evolution of MRI scanners and of AIMDs together with published data on the lack of adverse events have reopened the …
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