No description available.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 181-188).

Free volume and free volume distribution have long been used to explain differences in the gas transport properties of polymeric materials. However, only a few experimental techniques allow a comprehensive evaluation of polymeric void space. Through the use of computer simulations, the free volume was characterized of two polyester systems used for beverage packaging and polynorbornene, a unique polymer with possible applications in both microelectronic fabrication and membrane separations. Delaunay Tessellation was used to calculate the fractional free volume (FFV) of both polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) molecular models. It was hypothesized that differences in the FFV distributions could be used to explain the higher experimental O2 solubility in PEN relative to PET. The analysis showed that there was no statistical difference between the FFV distributions for O2 sized penetrants. Clustering analysis was performed based upon the tetrahedra formed by Delaunay Tessellation to examine the connectivity of free volume pockets. These results show that there is a statistically larger number of small (containing less than 10 tetrahedra/cluster and between 20-30 and #506;3 in volume) clusters in PEN. It is this difference in small clusters which provides for the 30% higher O2 solubility in PEN. The free volume of a representative high molecular weight amorphous model of Hexafluroalcohol Subsituted Polynorbornene (HFA-PNB) was also characterized in to examine the shape of the free volume cavities and to draw correlations with the mean lifetime of ortho-positronium (o-Ps) from Positron Annihilation Lifetime Spectroscopy (PALS). Delaunay Tessellation and clustering analysis indicated that the free volume clusters in high molecular weight HFA-PNB are slightly non-spherical. Correcting lifetimes for the somewhat non-spherical shape of these free volume clusters was insufficient to reproduce experimentally measured positron annihilation lifetimes because the clusters contained many tortuous connections within the clusters. Inclusion of this connectivity information does produce a more accurate estimate of the measured life times. This indicates that the o-Ps does sample many tetrahedra in these static clusters, but does not freely sample every section of these clusters.

The lymphatic system returns interstitial fluid back to the blood circulation. They have a network of vessels with numerous lymphangions, the segment of lymphatic vessel between two unidirectional valves. The valves aid in transporting lymph against a pressure gradient, in addition to the lymphangion pump which exhibit cyclical variations in diameter. Like blood vessels, baseline lymphatic tone is regulated with changes in transmural pressure; however, the transient response of lymphatic diastolic diameter following changes in transmural pressure has not been studied. The lymphangion pump is often described using cardiac analogies. However, since an active system empties into another active system in a lymphatic vessel, the analogy cannot characterize the principles governing optimal lymphatic vessel function. Furthermore, to optimize lymph flow there is also a need to characterize the lymphatic network structure. To characterize the transient diameter response of lymphatic segment, we used post-nodal bovine mesenteric lymphangions in an isobaric preparation and measured the diameter response to a step change in pressure. An immediate active reduction in enddiastolic diameter with each incremental increase in pressure was observed. To identify the principles governing optimal lymphatic vessel function, we applied the result obtained from optimizing the interaction of the heart-arterial system to measured lymphangion pressure-volume relationships. We assumed that the slope of end systolic pressure-volume relationship (Emax) is equal to the slope of end-diastolic relationship (Emin) above a cutoff pressure and Emax>Emin below the cutoff pressure. Unlike the heart, we found that stroke work is not optimized when Emax = Emin. However, there is a region where lymph flow is insensitive to changes in transmural pressure. To characterize the lymphatic network structure, we used an approximation of time-varying elastance model. We found there is an optimal length for the lymphangion when it produces maximal flow. To develop a fractal network model, we determined the ratio of radius and ratio of length of lymphangion at a confluence. Using conservation of mass and certain simplifying assumptions, we showed that the ratio of radius, as well as ratio of length of upstream lymphangion, to the downstream lymphangion at confluences is 1.26.

No description available.

The problem of coherent reflecton of an acoustic plane wave from a random seabed consisting of a randomly inhomogeneous sediment layer overlying a uniform elastic sea floor is considered in this analysis. The random perturbation in the sediment layer is attributable to the sound-speed variations, resulting in volume scattering due to medium inhomogenieties. An approach based upon perturbation theory, combining with a derived Green's function for a slab bounded above and below respectively by a fluid and an elastic half space ,is employed to obtain an analytic solution for the coherent field in the sediment layer. A linear system is then constructed to facilitate the analysis of the coherent reflection field. The results of the coherent reflection coefficient for various sediment randomness, frequency , sediment thickness, and sea floor elasticity have been numerically generated and analyzed. It was found that the higher/larger size of randomness , frequency, thickness, and shear-wave speed, the lower the coherent reflection. Physical interpretation for the characteristics of various results were provided.

This thesis presents an expressive (non-photorealistic) rendering approach created by combining volumetric rendering techniques with the Line Integral Convolution (LIC) in 3D space. Although some techniques that combine volume rendering with the LIC have been introduced in computer graphics, they are mainly used for the scientific visualization fields, such as the visualization of 3D fluid fields. Unlike earlier research, we will focus on artistic representation, which is significantly different than scientific visualization research. We will implement a brush-stroke effect on the implicit surfaces by using the LIC. The implicit surfaces are described as volume datasets that are created by the voxelization of triangular meshes. To acquire smearing effects on the surface we convolve along the vector fields with the densities of the voxels of the datasets. These vector fields are defined by users as texture maps. The final images are rendered with volume ray casting, integrating colors and densities of voxels with Perlin noise along vector fields. The Perlin noise provides randomness and allows us to generate scratches. Smearing effects on the surface of an object create the illusion of 3D brush-strokes as if a painter had created brush strokes on a canvas. The rendering system is implemented using standard C and C++ programming languages. 3D models are then created using Alias MayaTM and TopmodTM.

Advancement in high-throughput microscopy technology such as the Knife-Edge Scanning Microscopy (KESM) is enabling the production of massive amounts of high-resolution and high-quality volumetric data of biological microstructures. To fully utilize these data, they should be efficiently distributed to the scientific research community through the Internet and should be easily visualized, annotated, and analyzed. Given the volumetric nature of the data, visualizing them in 3D is important. However, since we cannot assume that every end user has high-end hardware, an approach that has minimal hardware and software requirements will be necessary, such as a standard web browser running on a typical personal computer. There are several web applications that facilitate the viewing of large collections of images. Google Maps and Google Maps-like interfaces such as Brainmaps.org allow users to pan and zoom 2D images efficiently. However, they do not yet support the rendering of volumetric data in their standard web interface. The goal of this thesis is to develop a light-weight volumetric image viewer using existing web technologies such as HTML, CSS and JavaScript while exploiting the properties of stereo vision to facilitate the viewing and annotations of volumetric data. The choice of stereogram over other techniques was made since it allows the usage of raw image stacks produced by the 3D microscope without any extra computation on the data at all. Operations to generate stereo images using 2D image stacks include distance attenuation and binocular disparity. By using HTML and JavaScript that are computationally cheap, we can accomplish both tasks dynamically in a standard web browser, by overlaying the images with intervening semi-opaque layers. The annotation framework has also been implemented and tested. In order for annotation to work in this environment, it should also be in the form of stereogram and should aid the merging of stereo pairs. The current technique allows users to place a mark (dot) on one image stack, and its projected position onto the other image stack is calculated dynamically on the client side. Other extra metadata such as textual descriptions can be entered by the user as well. To cope with the occlusion problem caused by changes in the z direction, the structure traced by the user will be displayed on the side, together with the data stacks. Using the same stereo-gram creation techniques, the traces made by the user is dynamically generated and shown as stereogram. We expect the approach presented in this thesis to be applicable to a broader scientific domain, including geology and meteorology.

Thesis--M. Phil., University of Hong Kong.

No description available.