Theses and Dissertations from UMD
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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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Item MULTISCALE MEASUREMENTS OF ELECTRICAL & MECHANICAL CELLULAR DYNAMICS(2023) Alvarez, Phillip; Losert, Wolfgang; Biophysics (BIPH); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation focuses on the study and measurement of coupled electrical and mechanical responses in mammalian cells, tissues, and organs. Cellular biophysics often studies forces and their impact on biochemical pathways. These forces can be electrical, resulting in neuronal action potentials or cardiac cell contractions, or mechanical, driving e.g., a cell’s ability to recognize physical probing or surface texture. These forces and their responses, though, are frequently coupled through interlinked cellular mechanisms which result in emergent responses that take both electrical and mechanical signals into account. One challenge in capturing these emergent responses is that they occur on multiple scales, from the intracellular scale to the organ scale, limiting the ability of commercial microscopes to image these responses simultaneously. In this work I use surface texture, optical imaging, and multiscale-capable image analysis algorithms across these scales to elicit and measure electrical and mechanical responses. To image emergent responses from electrical and mechanical coupling, I developed two custom microscopes that can image at multiple length scales and timescales simultaneously. The Multiscale Microscope can capture slow intracellular mechanical dynamics concurrently with fast tissue scale electrical dynamics, while the BEAMM microscope links fast tissue scale electrical dynamics with both intracellular mechanical dynamics and slower organ-scale mechanical and electrical responses. Finally, I describe ongoing and future studies which exploit these new capabilities for multiscale measurements of electrical and mechanical dynamics.Item Investigation of nanophotonic structures for imaging and sensing(2017) ZHANG, ZHIJIAN; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to image micro/nano scale objectives with miniaturized optical components has always been of great interest due to its great potential in applications such as microscopy, nanofabrication, and biomedical monitoring. However, in traditional practice using dielectric lenses, the focal size is inevitably limited by the Abbe’s diffraction limit (0.51fλ/ρ). Here, λ is the wavelength in vacuum, and f and ρ are the focal length and the radius of the lens, respectively. Moreover, the performance of conventional spherical lenses deteriorates as their sizes approach the wavelength. On the other hand, owing to the recent advances in micro/nano fabrication techniques, miniature sensors have received much attention, which are highly desirable in many sensing applications for physical, chemical, and biomedical parameter measurements. However, the performance of miniature sensors usually suffers from the similar difficulty as miniaturized imaging systems. Recently nanophotonic structures have been explored for the development of miniaturizing imaging and sensing systems due to their capability of confining and manipulating light at a subwavelength scale. In this dissertation work, several different mechanisms that nanophotonic structures can be used to help enhance the performance of imaging and sensing in miniaturized systems are investigated. First, plasmonic lens utilizing the nanophotonic structure to achieve the subwavelength focusing ability is studied. Three different regions in the plasmonic lens design are defined. Furthermore, a plasmonic lens in the Fresnel’s region is designed and k.ed to achieve a sub-diffraction limit focus. Second, radially polarized light generated by the TEM mode in the annular aperture in metal is investigated, which can further enhance the focusing ability. Third, in terms of sensing, an ultra-thin plasmonic interferometer constructed with a nano-hole array is fabricated on a fiber facet. By using this structure, the multi-parameter sensing capability of this interferometer is demonstrated; high sensitivity refractive index and temperature sensing are achieved. Finally, a novel sensor design based on the cladding modes and buffer modes generated by the planar grating on the fiber facet is proposed. Experimental studies of this sensor demonstrate its superior temperature sensitivity and the potential of multi-parameter sensing.Item PARTIAL-TRANSFER ABSORPTION IMAGING OF 87Rb BOSE-EINSTEIN CONDENSATES(2016) Marshall, Erin; Spielman, Ian B; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)We present the design, testing, and implementation of a minimally-destructive, partial- transfer absorption imaging system. Partial-transfer absorption imaging in 87Rb utilizes a microwave transition to transfer a fraction of the atoms in a Bose-Einstein condensate (BEC) prepared in the F = 1 hyperfine state into the F = 2 hyperfine state, where they can be imaged on a cycling transition. The F = 1 and F = 2 hyperfine states are far apart enough in frequency that the F = 1 BEC is essentially unaffected by the imaging probe beam. The modulation transfer function, spot diagram, and point spread function for the imaging optics are simulated and measured on a bench model. We demonstrate the use of the imaging system, and we characterize the atom number and decay rate in a series of images of a repeatedly imaged BEC as a function of one of the imaging parameters, the microwave pulse time.Item Detection of Fecal Contamination on Cantaloupes and Strawberries Using Hyperspectral Fluorescence Imagery(2006-05-08) Vargas, Angela Maria; Tao, Yang; Kim, Moon; Biological Resources Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fluorescence methods are widely used for investigation of biological materials, and in recent years have also been used to monitor food quality and safety. In this research, fluorescence imaging techniques for detecting fecal contamination on cantaloupes and strawberries were evaluated. Fluorescence images at emission peaks were examined for fecal classification. These images were subjected to further analysis utilizing band ratios and principal component analysis. Two-band ratio images and principal component images, compared to the single-band images, enhanced the contrast between the feces-contaminated spots and untreated sample surfaces. The images exhibited useful results for contamination detection, however, false positives resulting from natural color variation on strawberry surfaces present a problem throughout the methods. This study confirmed the capability of hyperspectral fluorescence imaging in detecting fecal matter on cantaloupes and strawberries and the potential for this method to be used for developing on-line applications.