<p>Focusing of strong shock waves in a gas-filled thin test section with various forms of the reflector boundary is investigated. The test section is mounted at the end of the horizontal co-axial shock tube. Two different methods to produce shock waves of various forms are implemented. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamic interaction between the shape of the shock and the propagation velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method cylindrical obstacles are placed in the test section at various positions and in various patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way by means of obstacles. The influence of the supports of the inner body of the co-axial shock tube on the form of the shock is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflector boundaries but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body. The production of light, as a result of shock convergence, has been preliminary investigated. Flashes of light have been observed during the focusing and reflection process.</p>

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 69-75).

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 133-156).

Sol-gel capillary microextraction (CME) is a new direction in solvent-free extraction and preconcentration of trace analytes. CME presents significant interest in environmental, pharmaceutical, petrochemical, biomedical, agricultural, food, flavor, and a host of other important areas. Sol-gel CME utilizes advanced material properties of organic-inorganic hybrid sol-gel polymers to perform efficient extraction and enrichment of target analytes from a variety of matrices. In this dissertation, two novel sol-gel coatings were developed for CME: (a) sol-gel benzyl-terminated dendrimer coating, and (b) sol-gel polytetrahydrofuran (poly-THF) coating. A detailed investigation was conducted to evaluate the performance of the newly developed sol-gel coatings in solvent-free extraction of a wide range of polar and nonpolar analytes. Sol-gel chemistry was used to chemically immobilize dendrimer- and poly-THF-based hybrid organic-inorganic coatings on fused silica capillary inner surface. The sol-gel coatings were created using a coating solution containing a sol-gel active organic component (dendrimer or poly-THF), a sol-gel precursor (methyltrimethoxysilane, MTMOS), a sol-gel catalyst (trifluoroacetic acid, TFA, 5% water) and a deactivating reagent (hexamethyldisilazane, HMDS). Sol-gel reactions were conducted inside a hydrothermally treated fused silica capillary for 60 min. A wall-bonded sol-gel coating was formed via condensation of silanol groups residing on the capillary inner surface with those on the sol-gel network fragments evolving in close vicinity of the capillary walls. Due to the strong chemical bonding with capillary inner walls, these sol-gel coatings showed excellent thermal and solvent stability in CME in hyphenation with gas chromatography (GC).

Two highly polar sol-gel coatings were developed for capillary microextraction (CME). One of the coatings contained cyanopropyl-polydimethylsiloxane (CN-PDMS) and the other low molecular weight polyethylene glycol. These highly polar coatings were immobilized via sol-gel chemistry allowing for direct chemical bonding to the inner surface of fused silica capillaries. These sol-gel coated microextraction capillaries were employed in CME for solvent-free microextraction and preconcentration of trace analytes (polar, moderately polar, and nonpolar) from aqueous matrices. CN-PDMS and short chain PEG extraction phases exhibit both polar and polarizable characteristics. Therefore, both sol-gel CN-PDMS and short chain sol-gel PEG coatings were able to extract analytes of different polarity from aqueous media. Both sol-gel CN-PDMS and sol-gel PEG coatings provided effective extraction of polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures commonly used in SPME experiments with conventional coatings. For each of these coatings, detection limits on the order of nanogram/liter (ng/L) were achieved for both polar and nonpolar analytes extracted simultaneously from aqueous media followed by GC-FID analysis. Both sol-gel CN-PDMS and short chain sol-gel PEG coated microextraction capillaries showed excellent run-to-run and capillary-to-capillary extraction reproducibility (GC peak area RSD < 6% & 5%, respectively) for nonpolar as well as polar analytes. For the sol-gel CN-PDMS coatings, the upper allowable conditioning temperatures were 330 degrees C and 350 degrees C, for the extraction of polar and nonpolar organic analytes, respectively. Similarly, the sol-gel PEG coatings used for the extraction of polar organic analytes survived a conditioning temperature of 340 degrees C. Both sol-gel CN-PDMS and sol-gel PEG coated microextraction capillaries showed no significant changes in the peak areas of the extracted analytes even after being washed with organic solvents (dichloromethane and methanol (1:1), v/v) for 24 hours. The excellent thermal and solvent stabilities can be attributed to the presence of chemical bonds between the sol-gel coatings and the fused silica surface.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(農学) / 甲第19043号 / 農博第2121号 / 新制||農||1032 / 31994 / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 縄田 栄治, 教授 田中 千尋, 教授 北島 宣 / 学位規則第4条第1項該当

The formation of a continuous tubular network in the mammalian urinary system requires the interconnection of two epithelial populations with distinct cellular origins. The proximal component of the renal network is the nephron--a complex tubule responsible for much of the physiological action of the kidney. Nephrons connect to a collecting duct network to transport urine from the kidney to the bladder, via the ureter. I have used high-resolution image analysis of genetically labeled nephron and collecting duct networks together with apical and luminal markers to characterize the epithelial interconnection process in the developing kidney. Morphological protrusions at the distal end of the nephron precursor, adjacent to the tip of the collecting duct epithelium, precede luminal interconnection at the S-shaped body stage. Distal cells in the nephron precursor do not display clear epithelial junction complexes and show upregulation of phospho-myosin light chain, suggestive of a quasi-mesenchymal cell behavior. The close apposition of this group of cells with the collecting duct epithelium is facilitated by the absence on an intervening basal lamina. Live imaging of explanted kidneys suggests that distal cells break through into the lumen of the collecting duct epithelium and undergo cell death. No interconnection is observed upon Notch-mediated proximalization of distal cell fates. Furthermore, distal factor bone morphogenetic protein 2 (Bmp2) expression is lost in proximalized nephron precursor derivatives. Finally, I demonstrate that mice with specific loss of Bmp2 in nephron precursors and their derivatives results in a fraction of disconnected mature nephrons that later results in nephron atrophy and compromised renal function at juvenile stage compared to control mice. These data support a model in which the establishment of distal identity in nephron precursor cells closest to the nascent collecting duct epithelium leads to an active cell invasion that establishes a patent tubular interconnection between the nephron and collecting duct.

The basis of developmental biology lies in the idea of when and how cells decide to divide or to differentiate. Previous studies have established several signaling pathways that determine cell fate decisions, including Notch, Wingless, Hedgehog, Bone morphogenetic protein, and Fibroblast growth factor. Signaling converges on transcriptional factors that regulate gene expression. In mouse embryonic stem cells, I explored how pluripotency and differentiation are regulated through opposing actions of beta-catenin-mediated canonical Wnt signaling, and the mechanisms underlying Sonic hedgehog signaling in generating progenitor cells in the ventral neural tube.

Patterning, morphogenesis, and cell divisions are distinct processes during development yet are concurrent and likely highly integrated. However, it has been challenging to investigate them as a whole. Recent advances in imaging and labeling tools make it possible to observe live tissues with high coverage and resolution. In this dissertation work, we developed a novel imaging platform that allowed us to fully capture the early neural tube formation process in live zebrafish embryos at cellular resolution. Importantly, these datasets allow us to reliably track single neural progenitors. These tracks carry information on the history of cell movement, shape change, division, and gene expression all together. By comparing tracks of different progenitor fates, we found they show a spatially noisy response to Sonic hedgehog (Shh) and become specified in a positionally mixed manner, in surprising contrast to the "French Flag" morphogen patterning model. Both cell movement and division contribute to cell mixing. In addition, we decoupled the temporal and genetic regulatory network (GRN) noises in Shh interpretation using tracks that carry both Shh signaling and cell fate reporters. Our tracks suggest that, after specification, progenitors undergo sorting to self-assemble a sharp pattern. Consistent with this hypothesis, we found ectopically induced progenitors move to correct locations. Furthermore, we show that proper adhesion is required for cell sorting to happen (Chapters 2 and 3). In the cleavage stage embryos, the cells on the surface undergo shape changes followed by lineage separation and differentiation. We quantitatively measured this morphogenesis process and tracked cell divisions. By applying a mathematical model we uncover a predictive, and perhaps general link between cell division orientation, mechanical interaction, and the morphogenetic behavior of the whole surface layer (Chapter 4). Finally, we discuss the concepts and tools of cell tracking including a multi-color cell labeling method we developed by modifying the "Brainbow" system (Chapter 5). Together this dissertation showcases the importance and promise of live observation based, quantitative and integrated analysis in our understanding of complex multi-cellular developmental processes.

<p>Neural tube defects (NTDs) are a common class of human birth defects with a complex, multifactorial etiology. Although many contributing factors have been identified, an estimated 60% of human population risk remains unexplained. A portion of that risk is likely attributable to gene-gene and gene-environment interactions which have yet to be fully elucidated. In one project, we used whole-exome sequencing to identify candidate genetic factors in a multiplex anencephaly family, revealing an aggregation of rare and common variants in planar cell polarity genes among the affecteds. In the second project, we profiled the methylomes of a pair of monozygotic twins discordant for anencephaly and identified several differentially methylated sites which could contribute to NTD risk, particularly the <italic>mir-886</italic> locus. Finally, we performed whole-exome and whole-methylome sequencing of mouse strains with differential susceptibility to fumonisin-induced NTDs, in combination with a human SNP association study. We identified epigenetic changes and variant associations which implicate Wnt and Hippo signaling genes as modifiers of the metabolic impacts of fumonisin exposure. These findings underscore the complexity of NTD pathogenesis and highlight the need to elucidate gene-gene and gene-environment interactions contributing to NTD etiology.</p> / Dissertation