Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    A Search for the Neutrinoless Double Beta Decay of Xenon-136 with Improved Sensitivity from Denoising
    (2014) Davis, Clayton G.; Hall, Carter; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The EXO-200 detector is designed to search for the neutrinoless double beta decay of 136Xe. ββ0ν decay, if it occurs in nature, would demonstrate the fundamental nature of neutrino mass; set the mass scale of the neutrino sector; and demonstrate lepton number non-conservation. Since the ββ0ν decay produces a monoenergetic peak, the energy resolution of the detector is of fundamental importance for the sensitivity of the experiment. The present work describes a new analysis technique which improves the energy resolution of EXO-200 through a combination of waveform denoising and weighting of waveform components based on their expected signal-to-noise ratio. With this method, the energy resolution of the detector is improved by 21% and the expected background in the 2σ region of interest is reduced by 32%. Applying this technique to 99.8 kg*years of exposure collected by EXO-200 between October 5, 2011 and September 1, 2013, we find no statistically significant evidence for the presence of ββ0ν in the data. We set a half-life limit T1/2 > 1.1 × 1025 years at 90% confidence. We also describe further improvements which could impact the energy resolution of EXO-200, and consider implications for the planned nEXO experiment.
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    Novel integro-differential schemes for multiscale image representation
    (2009) Athavale, Prashant Vinayak; Tadmor, Eitan; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Multiscale representation of a given image is the problem of constructing a family of images, where each image in this family represents a scaled version of the given image. This finds its motivation from biological vision studies. Using the hierarchical multiscale image representation proposed by Tadmor et. al. [32], an image is decomposed into sums of simpler `slices', which extract more refined information from the previous scales. This approach motivates us to propose a novel integro-differential equation (IDE), for a multiscale image representation. We examine various properties of this IDE. The advantage of formulating the IDE this way is that, although this IDE is motivated by variational approach, we no longer need to be associated with any minimization problem and can modify the IDE, suitable to our image processing needs. For example, we may need to find different scales in the image, while retaining or enhancing prominent edges, which may define boundaries of objects. We propose some edge preserving modifications to our IDE. One of the important problems in image processing is deblurring a blurred image. Images get blurred due to various reasons, such as unfocused camera lens, relative motion between the camera and the object pictured, etc. The blurring can be modeled with a continuous, linear operator. Recovering a clean image from a blurry image, is an ill-posed problem, which is solved using Tikhonov-like regularization. We propose a different IDE to solve the deblurring problem. We propose hierarchical multiscale scheme based on (BV; L1) decomposition, proposed by Chan, Esedoglu, Nikolova and Alliney [12, 25, 3]. We finally propose another hierarchical multiscale representation based on a novel weighted (BV;L1) decomposition.