Physics
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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 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.