Over the past twenty years, the geographical bases of state legislative parties have shifted substantially. In statehouses across the country, legislators from densely-populated districts with large racial minority populations have become a larger presence inside Democratic caucuses while legislators from exurban and sparsely-populated districts have become a larger presence inside Republican caucuses. These changes have had important consequences for roll-call voting and policy outcomes inside legislatures, as new coalitional configurations formed by the intersection of party and geography have replaced older ones. In this dissertation, I examine the causes and consequences of these changes in a new way, one that more closely approximates a legislator's relationship to her "geographical constituency" (to use Richard Fenno's famous term). Unlike traditional studies of the social origins of legislative conflict, which have focused on how the constituency bases of legislative parties can be distinguished by reference to a small set of district-level demographic variables examined independently of each other, my approach views district demographic variables as the empirical manifestations of a wide variety of distinct, if latent, geographical contexts. My efforts to model the geographical constituency are centered upon a technique called Latent Profile Analysis (LPA), which estimates a latent categorical variable (in this case, legislative district categories indicative of distinct socioeconomic contexts) that captures covariation among a set of observed continuous variables (in this case, district-level demographic and geographical variables). The LPA analysis, which incorporates over 3,500 districts from seventeen chambers in the 1990s and 2000s, yields a nine-fold district categorization scheme that serves as the basis for subsequent inquiries of the dissertation. These inquiries examine how demographic and electoral change have interacted to influence trends in partisan representation of the district categories, how party and district category come together to explain patterns of roll-call ideology among state legislators, and how social cleavages over public policy within state electorates are translated into particular voting alignments involving the district categories. The dissertation speaks to a large literature in political science on the constituency-legislator relationship, as well to current debates about geographical sorting, legislative polarization, and the role of policy content in shaping voting coalitions. / text

This dissertation seeks to improve our understanding of the process by which citizens' selective exposure contributes to attitudinal polarization and engagement in political activities. In this dissertation, I test two models that explicate the relationship between selective exposure and political polarization and participation. The knowledge model suggests that the effects of selective exposure on individuals' attitudinal polarization and political engagement are mediated by knowledge of candidate issue stances. The stereotype model proposes that selective exposure indirectly influences polarized attitudes and political participation via stereotypical perceptions of candidates (i.e., McCain's age and the prospect of a Black presidency). By posing issue knowledge and stereotypical perceptions as potential mediators, this study extends current literature to analyze why and how selective exposure leads to polarization and political participation. The results provide evidence that selective exposure influences individuals' stereotypical perceptions of the candidates' age and race, and these stereotypic perceptions influence attitudinal polarization and participation in campaign activities. There was no support for the knowledge model; selective exposure did not have a significant relationship with citizens' issue knowledge nor did it play a mediating role in the relationship between selective exposure and political polarization and participation. This dissertation thus challenges the argument that selective exposure is normatively desirable due to its contribution to citizens' greater levels of political participation. The findings of this study call into question such a contention because the results show that individuals who engage in selective exposure are motivated to participate in political activities by forming stereotypic perceptions of candidates rather than by gaining factual issue knowledge, which is in contrast to democratic theories' assumptions of informed citizenship. Turning to the role of exposure to dissonant media outlets, two contrasting roles were found. On one hand, results offer some evidence that dissonant media use contributes to gaining issue knowledge and inspiring citizen participation. On the other hand, some findings suggest that it reinforces, rather than attenuates, citizens' attitudinal polarization and stereotypical perceptions of candidates. Thus the findings from this study offer mixed support for encouraging citizen exposure to dissimilar viewpoints. / text

Severe corrosion damage and even complete failure was recently discovered in external post-tensioned (PT) tendons of three Florida's pre-cast, segmental bridges over seawater. A key deterioration factor was the formation of large bleed water grout voids at or near the anchorages. Steel corrosion may occur at the grout-void interface or in the air space of the void itself. Since the tendons are critical to the structural integrity of the bridges, reliable and non-intrusive damage detection methods are desirable to manage or prevent future occurrences. In recent years several indirect non-destructive methods have been developed or improved to evaluate the conditions of the tendons. One of those methods is vibration-based tension measurements, consisting of detecting tendon tension loss by analyzing the tendon's natural frequencies. Until recently, vibration-based tension measurements were costly and laborious since they required several operators to conduct the tests and complicated analysis through different programs. The first objective of this research is to provide a practical, simplified, user-friendly testing and analysis method for screening tendons by vibration measurements. Electrochemical Impedance Spectroscopy, Linear Polarization, and Electrical Resistance are alternative methods that could nondestructively detect or monitor corrosion before strand failures occur. The reliability and sensitivity of these conventional monitoring methods in solid or liquid media are well proven. However, few investigations exist on applying these methods to air-space corrosion as it may occur in tendon anchors. The second objective of this research is to establish the feasibility of using the above conventional monitoring methods for detecting air-space corrosion. In this investigation, two different types of Electrical Resistance probes were designed and evaluated. Also, electrochemical probes were constructed simulating strands conditions in the grout-void interface. Electrochemical Impedance Spectroscopy and Linear Polarization measurements were conducted in the electrochemical probes to calculate their instantaneous corrosion rates. Electrical Resistance and Electrochemical probes results indicate that both methods provide sufficient sensibility to determine the ongoing damage.

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The Shroom family of proteins is currently comprised of four members, Shroom1, 2, 3 and 4. Since Shroom3 was shown to be a critical protein for neural tube closure, the other three proteins are also expected to play an important role for proper development. However, their functions during development were not clear. To address this, my study started with Shroom3 function in the neural plate. Shroom3 had been previously known to induce apical constriction by controlling actin filaments in neuroepithelial cells. My studies show that Shroom3 induces apico-basal cell heightening by controlling parallel microtubule assembly. Shroom3 is able to change the distribution of γ-tubulin, suggesting that Shroom3 controls apical constriction and apico-basal cell elongation via both actin filaments and microtubules. The ability to control γ-tubulin distribution is possessed not only by Shroom3, but also by all other Shroom proteins, although they can not induce apical constriction. In addition, they are expressed in tissues which contain apico-basally elongated cells. Data from functional assays with Shroom2 show that it induces cell elongation and is required for proper cell shape in deep layer neuroepithelial cells in Xenopus. These data suggest that Shroom family proteins control cell architecture during morphogenetic development. I have discovered another role for Shroom2. By comparative analysis with Xenopus and Physalaemus, which have different pigment patterns in eggs, I show that a high level of maternal Shroom2 mRNA is important for pigment polarity in Xenopus. Furthermore, Shroom2 controls the distribution of spectrin which plays a role in pigment granule movement. Thus, Shroom2 is suggested to be a key molecule to control the pigment polarity in amphibian eggs. Together all these data suggest that Shroom family proteins play a role in cell morphogenesis and polarization via controlling the cytoskeleton during Xenopus development. / text

This dissertation studies social incentives in pro-social behavior and its various implications, including but not limited to disclosure policies, fundraising strategies and geographic polarization. / Economics

Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3×3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for anisotropic ray tracing. This P matrix has the following characteristics: (1) Multiple P matrices are calculated to describe the polarization of the multiple eigenmodes at an anisotropic intercept. (2) Each P matrix maps the orthogonal incident basis vectors (Ê_m, Ê_n, Ŝ) before the optical interface into three orthogonal exiting vectors (a_m Ê'_m, a_n Ê'_n, Ŝ') after the interface, where a_m and a_n are the complex amplitude coefficients induced at the intercept. The ray tracing algorithms described in this dissertation handle three types of uncoated anisotropic interfaces isotropic/anisotropic, anisotropic/isotropic and anisotropic/anisotropic interfaces. (3) The cumulative P matrix associated with multiple surface interactions is calculated by multiplying individual P matrices in the order along the ray path. Many optical components utilize anisotropic materials to induce desired retardance. This important mechanism is modeled as the optical phase associated with propagation. (4) The optical path length OPL of an eigenpolarization along an anisotropic ray path is incorporated into the calculation of each P matrix. Chapter 4 presents the data reduction of the P matrix of a crystal waveplate. The diattenuation is embedded in the singular values of P. The retardance is divided into two parts: (A) The physical retardance induced by OPLs and surface interactions, and (B) the geometrical transformation induced by geometry of a ray path, which is calculated by the geometrical transform Q matrix. The Q matrix of an anisotropic intercept is derived from the generalization of s- and p-bases at the anisotropic intercept; the p basis is not confined to the plane of incidence due to the anisotropic refraction or reflection. Chapter 5 shows how the multiple P matrices associated with the eigenmodes resulting from propagation through multiple anisotropic surfaces can be combined into one P matrix when the multiple modes interfere in their overlapping regions. The resultant P matrix contains diattenuation induced at each surface interaction as well as the retardance due to ray propagation and total internal reflections. The polarization aberrations of crystal waveplates and crystal polarizers are studied in Chapter 6 and Chapter 7. A wavefront simulated by a grid of rays is traced through the anisotropic system and the resultant grid of rays is analyzed. The analysis is complicated by the ray doubling effects and the partially overlapping eigen-wavefronts propagating in various directions. The wavefront and polarization aberrations of each eigenmode can be evaluated from the electric field distributions. The overall polarization at the plane of interest or the image quality at the image plane are affected by each of these eigen-wavefronts. Isotropic materials become anisotropic due to stress, strain, or applied electric or magnetic fields. In Chapter 8, the P matrix for anisotropic materials is extended to ray tracing in stress birefringent materials which are treated as spatially varying anisotropic materials. Such simulations can predict the spatial retardance variation throughout the stressed optical component and its effects on the point spread function and modulation transfer function for different incident polarizations. The anisotropic extension of the P matrix also applies to other anisotropic optical components, such as anisotropic diffractive optical elements and anisotropic thin films. It systematically keeps track of polarization transformation in 3D global Cartesian coordinates of a ray propagating through series of anisotropic and isotropic optical components with arbitrary orientations. The polarization ray tracing calculus with this generalized P matrix provides a powerful tool for optical ray trace and allows comprehensive analysis of complex optical system.

Στην παρούσα διπλωματική εργασία προσομοιώνεται η διασπορά τρόπων πόλωσης σε συστήματα οπτικών επικοινωνιών. Ο στόχος μας είναι να προσεγγίσουμε τη θεωρητική συνάρτηση πυκνότητας πιθανότητας που ακολουθεί η διασπορά τρόπων πόλωσης, η οποία αποδεικνύεται ότι είναι η μαξγουελιανή. / In this thesis we discuss the problem of simulation of the polarization dispersion mode in lightwave systems. Our purpose is to approach the theoretical probability density function of the polarization dispersion mode, which is proved to be maxwellian.