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 247 for “"Inhomogeneity"”.
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Detecting surface inhomogeneity of asteroids
… the detection of surface composition inhomogeneity on asteroids using time-series spectroscopy and photometry. Observations were conducted on three test cases—Pluto, asteroid 2005 EK70, and the weather satellite Meteosat-11 using the Mookodi instrument on the Lesedi telescope. For …
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Inherent insensitivity to RF inhomogeneity in FLASH imaging
… 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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Investigation of surface inhomogeneity and estimation of the GOES skin temperature assimilation errors of the MM5 implied by the inhomogeneity over Houston metropolitan area
… the 1-d PBL model was used to investigate the inhomogeneity-caused model errors in applying the GOES satellite skin temperature assimilation technique into the MM5 over the Houston metropolitan area (HOU). In order to investigate the surface inhomogeneity impacts on the surface fluxes and PBL …
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The impact of inhomogeneity on the analysis of cosmological data
We consider the Lemaˆıtre metric, which is the inhomogeneous, spherically symmetric metric, containing a non-static, comoving, perfect fluid with non-zero pressure. We use it to generalise the metric of the cosmos algorithm, first derived for the zero-pressure Lemaˆıtre-Tolman (LT) metric, to the …
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Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows
… importance will exhibit unsteadiness and strong inhomogeneity. To date, investigations of unsteadiness and inhomogeneity in high-speed flows are rare. The goal of this dissertation is to study and understand these non-ideal effects when pertinent to shear flows. Towards this goal, we perform …
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LUNG CLEARANCE INDEX: a new biomarker of ventilation inhomogeneity in pediatric respiratory diseases.
… methods permit the identification of ventilatory inhomogeneity in the lungs by analyzing the clearance of an inert gas used as a tracer. The equipment consists of a mass spectrometer combined with a flow meter. For all tests, the lung clearance index (LCI) is the parameter that is most often used …
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The effect of flow and mixture inhomogeneity on the dynamics of strained flames
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.
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Off-resonance and detuned surface coils for B₁ inhomogeneity in 7-Tesla MRI
A problem with high-field MRI is the lack of B1 homogeneity, particularly signal cancellation in the outer parts of the head. Here we attempt to correct this by adding surface coils. To adjust the mutual coupling, we vary the resonance properties of the added coil. A new agar-based head phantom was …
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Bilateral Ortohogonality Generative Acquisitions Method for Transmit Field Inhomogeneity Correction in Magnetic Resonance Imaging
… and reducing scan time. However, transmit field inhomogeneity of ultra-high field systems, present an obstacle for widespread clinical utilization. In literature, radiofrequency pulse design and multi-acquisition methods with and without parallel transmission systems have been demonstrated for …
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Mitigating Inhomogeneity in High-Field MRI Excitations: Arbitrary Waveform Optimization and Multiphoton Parallel Transmission (MP-pTx)
… While pTx effectively addresses flip angle inhomogeneity, it remains costly and introduces challenges in SAR management. We address the SAR management and cost problems of pTx by introducing and characterizing the MP-pTx method, which leverages the multiphoton phenomenon to improve …
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Influence of Fuel Inhomogeneity and Stratification Length Scales on Detonation Wave Propagation in a Rotating Detonation Combustor (RDC)
… is a measure of the degree of fuel-oxidizer inhomogeneity. To model the effect of unmixedness in a 2-D domain, a lognormal distribution of the fuel mass fraction is generated with a mean equivalence ratio of 1 and varying standard deviations at the inlet boundary as a numerical source term. …
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Investigation of opto-electronical properties of DC magnetron sputtered ZnO:Al films with respect to the layer thickness, annealing temperature and resistance inhomogeneity
… thickness, annealing temperature and resistance inhomogeneity
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Study on corrosion protection of organic coatings using electrochemical techniques: developing electrochemical noise method, effective of surface preparation and inhomogeneity of organic coatings
… conduction through organic coatings and their inhomogeneity which are normally formed in crosslinking systems was extensively studied with the aim of finding the cause of formation of the more permeable areas and the ways by which they can be prevented. Several structural and environmental …
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Magnetic structures and proximity effects in rare-earth / transition metal ferromagnetic and superconductor systems
… percurrents. This was possible due to magnetic inhomogeneity present in the devices, however the precise nature of the inhomogeneity was not understood. Here we present a comprehensive study of the Ni/Gd/Ni system using a powerful element-specific measurement technique: x-ray magnetic circular …
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FAR-END CROSSTALK MODELING AND PREDICTION FOR HIGH-SPEED PCB DESIGN WITH INHOMOGENEOUS DIELECTRIC LAYERS (IDLS)
… systems. The FEXT level is sensitive to the inhomogeneity of the dielectric layers in fabricated printed circuit boards (PCB). The stripline is laminated by multiple inhomogeneous dielectric layers (IDL). The dielectric layers of the stripline are laminated with epoxy resin and glass bundles. …
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The atmospheric boundary layer above the Agulhas current
… characteristics demonstrate high horizontal inhomogeneity. The results suggest that this inhomogeneity is permanent. The spatial heat flux gradient is reflected in the overlying atmosphere by a transition in stability of the boundary layer and potential cumulus formation from the cool shelf …
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Methods for chemical exchange saturation transfer magnetic resonance imaging
… imaging is extremely sensitive to magnetic field inhomogeneity. Images suffer from large susceptibility artifacts unless specialized BO inhomogeneity correction methods are employed that tremendously increase scan time. Second, the CEST contrast cannot be separated from the intrinsic …
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Numerical field simulation for parallel transmission in MRI at 7 tesla
… that has been demonstrated to mitigate B1* inhomogeneity, manifest as center brightening, for high-field magnetic resonance imaging (MRI). Parallel transmission achieves spatially-tailored pulses through multiple radiofrequency (RF) excitation coils that can be activated independently. In …
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Examination of susceptibility effects on functional and dynamic magnetic resonance imaging
… and brain function. However, magnetic field inhomogeneity also drives certain contrast mechanisms including blood oxygenation level dependent fMRI. The two projects in this work look at the effects of inhomogeneity on functional and dynamic MRI. We simultaneously acquired functional and …
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Foliage Echoes and Sensing in Natural Environments
… patterns of L-system. The evaluation of inhomogeneity in echoes produced with two distributions shows that there is always inhomogeneity in echoes, and L-system model does bring more inhomogeneity but not to the same extent as changes in the relative orientation between sonar beam and …
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