Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xii, 146 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 134-146).

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Rebecca Richards-Kortum. Vita. Includes bibliographical references. Also available from UMI.

Thesis (M.E.E.)--University of Delaware, 2005. / Principal faculty advisor: Balaji Panchapakesan, Dept. of Electrical & Computer Engineering. Includes bibliographical references.

Not available / text

Dynamical heterogeneity (DH) has been observed in many systems approaching the glass or jamming transition. Whether DH has a structural origin is under heated debate. To provide a deeper understanding, in this thesis I investigate the microscopic dynamics in weakly attractive colloidal systems by confocal fluorescence microscopy. The van Hove density-density correlation function is applied to our systems. Separable fast and slow populations emerge in the self part (svH), while the distinct part shows a strong signature of DH close to the gel transition. At intermediate time, svH shows a purely exponential tail, mainly arising from the fast population. I show that this broad tail is a direct consequence of the occurrence of rare large jumps that are statistically distributed. The slow population tends to form a space-spanning backbone, and its mean squared displacement close to the gel transition exhibits a plateau, whose height is consistent with the range of attraction, suggesting a bonding mechanism for the dynamical arrest. I further examine various quantities characterizing local structure and local dynamics and a strong correlation is identified between them. Subsequently, I develop order parameters for quantifying amorphous structure and apply them to our systems. I find that attractive colloidal systems exhibit higher order under higher attraction tension, while hard spheres become more ordered under higher compression. Finally, I investigate the effect of the range of attraction on the structure and dynamics of attractive colloidal systems. I observe that the system with shorter range of attraction forms a denser and more heterogeneous structure. Meanwhile, I observe an even stronger dynamical heterogeneity. These observations provide further evidence of a connection between structural heterogeneity and dynamical heterogeneity in these systems, providing guidance for a theoretical description of the dynamical arrest as well as the relaxation mechanisms upon gelation and its relation to solidification in glasses. / In order to do all of this, I first implemented full 3D subpixel resolution localization of particles and improved particle tracking algorithms tailored for the sorts of heterogenous dynamics these systems exhibit, that otherwise confounds existing methods such that the very relaxation mechanisms would be missed. This allows us to obtain unprecedented precision in positions of all of the particles and complete tracking, both of which are essential for correctly determining system properties that depend on measured particle dynamics.

The object of this thesis is to present two novel applications of Spatiotemporal Image Correlation Spectroscopy (STICS) to biological systems. STICS is a technique which uses the correlations in pixel intensity fluctuations of an image time series, captured under fluorescence microscopy, to measure the speed and direction of a flowing population of fluorescently labeled molecules. The method was first applied to measure the dynamics of transport vesicles inside growing pollen tubes of lily flowers. The measured vector maps allowed to confirm the presence of actin filaments along the periphery of the tubes, as well as the presence of a reverse-fountain pattern in the apical region. In a second set of experiments, STICS was used to measure the retrograde flow of filamentous actin in migrating chick DRG neuronal growth cones. These results serve as proof of principle that STICS can be used to probe the response of the growth cone cytoskeleton to external chemical cues.

abstract: In this work, atomic force microscopy (AFM) and time resolved confocal fluorescence microscopy are combined to create a microscopy technique which allows for nanometer resolution topographic and fluorescence imaging. This technique can be applied to any sample which can be immobilized on a surface and which can be observed by fluorescence microscopy. Biological problems include small molecular systems, such as membrane receptor clusters, where very high optical resolutions need to be achieved. In materials science, fluorescent nanoparticles or other optically active nanostructures can be investigated using this technique. In the past decades, multiple techniques have been developed that yield high resolution optical images. Multiple far-field techniques have overcome the diffraction limit and allow fluorescence imaging with resolutions of few tens of nanometers. On the other hand, near-field microscopy, that makes use of optically active structures much smaller than the diffraction limit can give resolutions around ten nanometers with the possibility to collect topographic information from flat samples. The technique presented in this work reaches resolutions in the nanometer range along with topographic information from the sample. DNA origami with fluorophores attached to it was used to show this high resolution. The fluorophores with 21 nm distance could be resolved and their position on the origami determined within 10 nm. Not only did this work reach a new record in optical resolution in near-field microscopy (5 nm resolution in air and in water), it also gave an insight into the physics that happens between a fluorescent molecule and a dielectric nanostructure, which the AFM tip is. The experiments with silicon tips made a detailed comparison with models possible on the single molecule level, highly resolved in space and time. On the other hand, using silicon nitride and quartz as tip materials showed that effects beyond the established models play a role when the molecule is directly under the AFM tip, where quenching of up to 5 times more efficient than predicted by the model was found. / Dissertation/Thesis / Ph.D. Physics 2012

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Thesis (Ph. D.)--University of Western Australia, 2007.