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 18 of 18 for “"inversion problem"”.
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Magnetic resonance elastography and nonlinear inversion problem in the aging brain
… MR imaging and finite element based nonlinear inversion (NLI) for estimation of viscoelastic material properties have shown NLI-MRE's impressive ability to capture subtle correlations between memory performance and stiffness in grey matter regions. These discoveries are made possible by the …
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On Enhancing Deterministic Sequential ATPG
… Also investigated in this thesis is the Decision Inversion Problem which threatens the completeness of ATPG tools such as HITEC or ATOMS. We propose a technique which can eliminate this problem by forcing the ATPG to consider search space with certain flip-flops untouched. Results show that our …
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Physics Guided Machine Learning algorithm for MAX-DOAS retrieval
… The ill-posed nature of the MAX-DOAS inversion problem makes it almost impossible to design an inversion algorithm providing a definite solution. A possible way to find a low-error inversion algorithm is incorporating the machine learning (ML) technique into the MAX-DOAS retrieval. …
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Design & analysis of a parallel drive spherical rotation mechanism for application in high tech farming robots
… of the mechanism as well as the mathematical inversion problem are analytically solved for. An alpha prototype of the device is designed, constructed, and controlled using the derived equations. Through testing the device demonstrated targeted levels of precision and repeatability.
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Hydrologic Process Parameterization of Electrical Resistivity Imaging of Solute Plumes Using POD MCMC
… computationally intractable in high dimensional problems. This research has developed a MCMC method that operates in the reduced-dimensional space, thereby enabling the estimation of a small number of inversion parameters while incorporating knowledge of the physics of the target process. First, …
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Dynamic reservoir characterization using 4D multicomponent seismic data and rock physics modeling at Delhi field, Louisiana
… of adding more information to the non-unique inversion problem. Combining the inversion results from the monitor surveys of June 2010 and August 2011 provides acoustic impedance and Vp/Vs percentage differences. The time-lapse inverted response enables dynamic characterization of the reservoir …
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Randomization for Efficient Nonlinear Parametric Inversion
Nonlinear parametric inverse problems appear in many applications in science and engineering. We focus on diffuse optical tomography (DOT) in medical imaging. DOT aims to recover an unknown image of interest, such as the absorption coefficient in tissue to locate tumors in the body. Using a …
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Visually adaptive virtual sound imaging using loudspeakers
… three dimensional (3D) sound reproduction. The problem is to update the audio signal processing scheme for a moving listener, so that the listener perceives only the intended virtual sound image. The performance of the audio signal processing scheme is limited by the condition number of the …
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Applied Machine Learning with Latent Space Representation and Manipulation
… accurately located. Second, we solve a seismic inversion problem which is a workflow for deriving the subsurface model from seismic measurements. We propose to utilize autoencoder deep networks with latent space-aligned domain adaptation to migrate the trained model to unexploited data. With the …
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Neural Network Training and Inversion with a Bregman Learning Framework
… other side of the same coin. Early ideas of DNNs inversion trace back to the 1990s, but research interests in more generic network inversion problems have been rekindled and primarily driven due to the rapid advancements in generative modelling in recent years. While several approaches for the …
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Numerical approaches for sequential Bayesian optimal experimental design
… are employed to make solution of the DP problem computationally feasible. First, the optimal policy is sought using a one-step lookahead representation combined with approximate value iteration. This approximate dynamic programming method couples backward induction and regression to …
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Diffusion-weighted MRI of skeletal muscle: Estimation of microstructural parameters
… the full LBM model. Using this meta-model, the inversion problem of estimating microstructural parameters from dMRI measurements is addressed through the development of a Gaussian process regression (GPR) model. The GPR model produces a mean estimate as well as a confidence interval for each …
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Inversion of seismic source parameters for weak mining-induced and natural earthquakes
… of this thesis is to develop an automated inversion scheme to derive point and finite source parameters for weak earthquakes, here intended with the unusual meaning of earthquakes with magnitudes at the limit or below the bottom magnitude threshold of standard source inversion routines. The …
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Advances in Symbolic Regression: From Generalized Formulation to Density Estimation and Inverse Problem
… its potential across diverse domains and problem settings. Initially, we introduce GSR, a Generalized Symbolic Regression method that redefines the traditional SR optimization problem to discover analytical mappings from the input space to a transformed output space. The proposed GSR …
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Near-optimal inversion of incoherent scatter radar measurements: coding schemes, processing techniques, and experiments
… focuses on developing a modern coding scheme and inversion methodology using Arecibo incoherent scatter radar (ISR) to achieve efficient, and near-optimal estimates of the key ionospheric parameters. In particular, this work considers two aspects of the ISR inversion problem: (i) ISR lag estimates …
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Two-dimensional constrained anisotropic inversion of magnetotelluric data
… and realistic Earth models for interpretation, inversion algorithms have to allow for an anisotropic subsurface. Within the framework of this thesis, I analyzed a magnetotelluric (MT) data set taken from the Cape Fold Belt in South Africa. This data set exhibited strong indications for crustal …
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2-D and 3-D tools for electrical imaging in environmental applications
… tomography an ill-posed and under-determined problem, the solution is computed by an over-parameterization of the model element with respect of the available measured data. The need to improve the resolution of resistivity imaging technique without stressing the intrinsic under-determination …
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All-optical photoacoustic and laser-ultrasonic imaging in heterogeneous tissue
… Marchenko imaging developed for two-way imaging problems in seismology to the PA source inversion problem. Iterative convolutions of PA data with nonconfocal LUS predicts reflection artifacts, which we subtract from the PA image. We eliminate dominant artifacts in numerical data using a single …