Photo reflectance¡]PR¡^ and Contactless electroreflectance¡]CER¡^spectra of Zn and O-faces of a c-plane ZnO bulk have been measured at room temperature, respectively. It was found that the phase of PR is the same as that of CER for the Zn-face and they are inverted for the O-face. This indicates a polarization induced field existing in the c- plane ZnO bulk due to nonzero spontaneous polarization. In addition, a mercury lamp was focused on the ZnO sample in the CER measurements to provide a photovoltaic voltage to reduce electric field in the sample. The CER spectrum with Hg lamp is more blue-shifted and its amplitude is smaller than that without Hg lamp. Hence, the type of transitions was classified as excitonic transition. The A, B, and C excitonic transition energies were obtained by fitting experimental spectra.

In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and CG flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong updrafts and associated large liquid water contents in severe storms lead to enhanced positive charging of graupel and hail via the noninductive charging mechanism, the generation of an inverted charge structure, and increased positive CG lightning production. The corollary is that environmental conditions favoring these kinematic and microphysical characteristics should support severe storms generating an anomalously high (> 25%) percentage of positive CG lightning (i.e., positive storms), while environmental conditions relatively less favorable should sustain storms characterized by a typical (≤ 25%) percentage of positive CG lightning (i.e., negative storms). Forty-eight inflow proximity soundings were analyzed to characterize the environments of nine distinct mesoscale regions of severe storms (four positive and five negative) on six days during May – June 2002 over the central United States. This analysis clearly demonstrated significant and systematic differences in the mesoscale environments of positive and negative storms, which were consistent with the stated hypothesis. When compared to negative storms, positive storms occurred in environments associated with a drier low to midtroposphere, higher cloud base height, smaller warm cloud depth, stronger conditional instability, larger 0-3 km AGL wind shear, stronger 0-2 km AGL storm-relative wind speed, and larger buoyancy in the mixed-phase zone, at a statistically significant level. Differences in the warm cloud depth of positive and negative storms were by far the most dramatic, suggesting an important role for this parameter in controlling CG lightning polarity. Subjective visual inspection of radar imagery revealed no strong relationship between convective mode and CG lightning polarity, and also illustrated that positive and negative severe storms can be equally intense.

In this study, it is hypothesized that the mesoscale environment can indirectly control the cloud-to-ground (CG) lightning polarity of severe storms by directly affecting their structural, dynamical, and microphysical properties, which in turn directly control cloud electrification and CG flash polarity. A more specific hypothesis, which has been supported by past observational and laboratory charging studies, suggests that broad, strong updrafts and associated large liquid water contents in severe storms lead to enhanced positive charging of graupel and hail via the noninductive charging mechanism, the generation of an inverted charge structure, and increased positive CG lightning production. The corollary is that environmental conditions favoring these kinematic and microphysical characteristics should support severe storms generating an anomalously high (> 25%) percentage of positive CG lightning (i.e., positive storms), while environmental conditions relatively less favorable should sustain storms characterized by a typical (≤ 25%) percentage of positive CG lightning (i.e., negative storms). Forty-eight inflow proximity soundings were analyzed to characterize the environments of nine distinct mesoscale regions of severe storms (four positive and five negative) on six days during May - June 2002 over the central United States. This analysis clearly demonstrated significant and systematic differences in the mesoscale environments of positive and negative storms, which were consistent with the stated hypothesis. When compared to negative storms, positive storms occurred in environments associated with a drier low to midtroposphere, higher cloud base height, smaller warm cloud depth, stronger conditional instability, larger 0-3 km AGL wind shear, stronger 0-2 km AGL storm-relative wind speed, and larger buoyancy in the mixed-phase zone, at a statistically significant level. Differences in the warm cloud depth of positive and negative storms were by far the most dramatic, suggesting an important role for this parameter in controlling CG lightning polarity. Subjective visual inspection of radar imagery revealed no strong relationship between convective mode and CG lightning polarity, and also illustrated that positive and negative severe storms can be equally intense.

Wh-indefinites in Chinese have received great attention and discussion in the literature. This thesis investigates the status of Chinese wh-indefinites and their behaviors in the so-called donkey sentence. A typical example of wh-indefinite will be like the following: (4) Ta bu xiang zai shuo shenme le he not want again say what LE ¡¥He does not want to say anything again.¡¦ ¥L¤£·Q¦A»¡¤°»ò¤F¡C In this thesis, accounts of wh-indefinites as variables, polarity items and quantifiers from Huang (1982), Li (1992), Cheng (1991, 1994) and Lin (1996, 1998) are provided and this thesis discusses the problems each account presents. Countering Li¡¦s (1992) work, this work argue that wh-indefinite like zenmeyang ¡¦how¡¦ and weishenme ¡¥why¡¦ cannot be directly treated as variables since they feature variables only if they appear after an auxiliary (under which situation they will express purpose or method) in a donkey sentence according to Tsai (1999, 2000), see the following examples: (5) a. Akiu hui wei (le) shenme cizhi wo jiu hui wei (le) shenme cizhi¡@ Akiu will for LE what resign I then will for LE what resign ¡¥If Akiu will resign for the purpose x, I will then also resign for the purpose x.¡¦ ªüQ·|¬°¡]¤F¡^¤°»òÃ㾡A§Ú´N·|¬°¡]¤F¡^¤°»òÃ㾡C b. *Akiu wei (le) shenme hui cizhi wo jiu wei (le) shenme hui cizhi Akiu for LE what will resign I then will LE what will resign Intended ¡¥If Akiu will resign because of the reason x, I will then also resign because of the reason x. *ªüQ¬°¤F¤°»ò·|Ã㾡A§Ú´N¬°¤F¤°»ò·|Ã㾡C (Tsai¡¦s 2000, 15 glossed and translated by the author) Avoiding treating wh-indefinites as variables, we may treat them as quantifiers according to Huang¡¦s observation. But Huang¡¦s (1982) quantifier account of wh-indefinites is also rejected because I observe that wh-indefinites do not exhibit island sensitivity. Then we are led to another treatment: treating wh-indefinites as polarity items because they are sensitive to polarity environment. Aside from the sensitivity to polarity environment, Lin¡¦s (1996) work argues that wh-indefinites are licensed as polarity items if the sentence is subject to NEEC- non-entailment of existence condition. NEEC tells us that if (part of) a sentence does not have the existential import of object; wh-words can be licensed as wh-indefinites. This faces challenge because there are cases presupposing existential import yet the wh-indefinite is licensed. In chapter 3, two types of donkey sentences are identified in Cheng and Huang¡¦s (1996) work and are accounted with different approaches-Unselective Binding and E-type analysis. Though accepting their viewpoint generally, Lin (1996) makes a distinction between one-case and multi-case reading and opens the possibility of universal interpretation in ruguo-conditionals. Later I introduce Indirect binding approach to account both types of donkey sentences. Indirect Binding argues that some quantified expression plays the role as associating the indefinite with the anaphoric element in donkey sentences: (6) [Everyone who ti keeps a dogj]i like itj. The example here captures the very basic idea of Indirect Binding: the chunk of expression, which has the indefinite a dog in its scope, c-commands the pronoun it and hence relates it to the indefinite. I extend it to the analysis of Chinese donkey sentences and discover that although Indirect Binding does not target at a particular status, the condition that the indirect binder must c-command the indefinite seems to suggest that c-commanding is the way of licensing a wh-indefinite, which echoes Li¡¦s and Cheng¡¦s analyses. In Chapter 4, I introduce wh-indefinites in Japanese and Korean respectively and conclude that quantificational force comes from the environment but not from wh-indefinites themselves, countering Huang (1982). Finally, I suggest that licensing a wh-word as a wh-indefinite is through being c-commanded by the relevant operators. It is so because of Li¡¦s and Cheng¡¦s observation of wh-indefinites licensing and also of a condition in Indirect Binding that indirect binders must c-command the indefinite in order to have it as in its scope, as I have mentioned. This thesis then provides a viewpoint that perhaps, wh-indefinites can be treated uniformly as polarity items considering that Indirect Binding approach explains their behavior in donkey sentences. This thesis also opens the door for analyzing wh-indefinites in donkey sentences under Indirect Binding in other languages. Keywords¡G Wh-indefinite, polarity item, variable, quantifier, donkey phenomenon, Indirect Binding

Thesis (Ph. D.)--University of Oregon, 2000. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 76-79). Also available for download via the World Wide Web; free to University of Oregon users.

Thesis (Ph. D.)--University of Oregon, 2002. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 90-98). Also available for download via the World Wide Web; free to University of Oregon users.

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From the simplest unicellular organisms to complex metazoans, cell polarity is a widespread characteristic that is essential for almost every aspect of biology. Proper polarization of cells is crucial for the establishment and maintenance of higher order structures such as tissue and organs. Cell polarity refers to the asymmetric distribution of various macromolecules and cellular structures, resulting in polarized architecture and function of the cell. Defects in cell polarity lead to various phenotypes, ranging from aberrant signaling, proliferation, cell adhesion and migration, cell fate determination and pluripotency, as well as embryonic lethality, neoplasia and cancer. Given the various roles for cell polarity in development and disease, the characterization of the components involved in polarity and their mechanisms of function is of great importance. My thesis work has encompassed three major projects, each of which is focused on understanding the role of cell polarity in development and disease. Although genetic screens in invertebrates have led to the identification of a number of cell-polarity proteins, similar systematic approach have not been undertaken in mammalian systems. The goal of my first project was to design and implement a high-throughput screen to systematically knockdown individual genes using siRNA, and then assess cell junction integrity as a measure of cell polarity. Given the importance of cell polarity to signaling pathways, I next sought to determine the mechanism by which cell polarity affects TGFβ and Hippo pathways, two important signaling pathways involved in development and disease. Lastly, by studying the acquisition of pluripotency by somatic cells, I uncovered a central role for cell polarity in the establishment and maintenance of pluripotency. Here I will present and discuss our discovery pertaining to the role of cell polarity in cell signaling and pluripotency.

From the simplest unicellular organisms to complex metazoans, cell polarity is a widespread characteristic that is essential for almost every aspect of biology. Proper polarization of cells is crucial for the establishment and maintenance of higher order structures such as tissue and organs. Cell polarity refers to the asymmetric distribution of various macromolecules and cellular structures, resulting in polarized architecture and function of the cell. Defects in cell polarity lead to various phenotypes, ranging from aberrant signaling, proliferation, cell adhesion and migration, cell fate determination and pluripotency, as well as embryonic lethality, neoplasia and cancer. Given the various roles for cell polarity in development and disease, the characterization of the components involved in polarity and their mechanisms of function is of great importance. My thesis work has encompassed three major projects, each of which is focused on understanding the role of cell polarity in development and disease. Although genetic screens in invertebrates have led to the identification of a number of cell-polarity proteins, similar systematic approach have not been undertaken in mammalian systems. The goal of my first project was to design and implement a high-throughput screen to systematically knockdown individual genes using siRNA, and then assess cell junction integrity as a measure of cell polarity. Given the importance of cell polarity to signaling pathways, I next sought to determine the mechanism by which cell polarity affects TGFβ and Hippo pathways, two important signaling pathways involved in development and disease. Lastly, by studying the acquisition of pluripotency by somatic cells, I uncovered a central role for cell polarity in the establishment and maintenance of pluripotency. Here I will present and discuss our discovery pertaining to the role of cell polarity in cell signaling and pluripotency.

<p>Many cells are remarkably proficient at tracking even shallow chemical gradients, despite tiny differences in receptor occupancy across the cell. Stochastic receptor-ligand interactions introduce considerable noise in instantaneous receptor occupancy, so it is thought that spatial information must be integrated over time to allow noise filtering. The mechanism of temporal integration is unknown. We used the mating response of the budding yeast, <italic>Saccharomyces cerevisiae</italic>, as a model to study eukaryotic gradient tracking. </p><p>During mating, yeast cells polarize and grow up a gradient of pheromone to find and fuse with opposite-sex partners. Exposure to pheromone causes polarity regulators to cluster into a tight "patch" at the cortex, directing growth toward that site. Timelapse microscopy of fluorescently-labeled polarity proteins revealed that the patch wandered around the cortex during gradient tracking. Mathematical modeling and genetic analysis suggested that fusion of vesicles near the polarization site could perturb the polarity patch and promote wandering. Wandering is decreased due to global effects from pheromone signaling as well as interactions between receptor-activated G&beta; and the exchange factor for the polarity regulator Cdc42. We found that artificially stabilizing patch wandering impaired accurate gradient tracking.</p><p>We suggest that ongoing polarized vesicle traffic causes patch wandering, which is locally reduced by pheromone-bound receptors. Thus, over time, spatial information from the pheromone gradient biases the random wandering of the polarity patch so that growth occurs predominantly up-gradient. Such temporal integration may enable sorting the low signal from stochastic noise when tracking shallow gradients.</p> / Dissertation