Browsing by Subject "Accommodation"
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Item Biomechanics of the lens capsule(Texas A&M University, 2005-11-01) Heistand, Mark RichardKnowledge of the mechanics of the lens capsule is crucial for improving cataract surgery as well as understanding better the physiological role of the lens capsule in the process of accommodation. Previous research on the mechanical properties of the lens capsule contains many gaps and contradictions due to experimental limitations and inappropriate assumptions. Thus, the goal of this work is to quantify fully the regional, multiaxial mechanical behavior of the lens capsule and to calculate the change in stress and strain fields as a result of cataract surgery. Determining in situ the multiaxial mechanical behavior of the lens capsule required the design and construction of an experimental device capable of altering stresses in the capsule while measuring localized surface deformations. Tests performed on this device reveal that the meridional and circumferential strains align with the principal directions and are equivalent through most of the anterior lens capsule, except close to the equator where the meridional strain is greater. Furthermore, preconditioning effects were also found to be significant. Most importantly, however, these tests provide the data necessary for calculating material properties. This experimental system is advantageous in that it allows reconstruction of 3D geometry of the lens capsule and thereby quantification of curvature changes, as well as measurement of surface deformations that result from various surgical interventions. For instance, a continuous circular capsulorhexis (CCC) is commonly used during cataract surgery to create a hole in the anterior lens capsule (typically with a diameter of 5 mm). After the introduction of a CCC, strain was found to redistribute evenly from the meridional direction (retractional strain) to the circumferential direction (extensional strain), where both directional components of strain reached magnitudes up to 20% near the edge of the CCC. Furthermore, the curvature was found to increase at the edge of the CCC and remain the same near the equator, indicating that the mere introduction of a hole in the lens capsule will alter the focal characteristics of the lens and must therefore be considered in the design of an accommodative intraocular lens.Item Essays on the Relationship of Competition and Firms' Price Responses(2012-02-14) Lee, SungbokThis dissertation investigates the relationship of competition and firms' price responses, by analyzing: i) whether new entry reduces price discrimination, ii) when incumbents reduce price discrimination preemptively in response to the threat of entry, and iii) how competition increases prices. The dissertation consists of three independent essays addressing each of the above questions. The first two essays present an empirical analysis of the airline industry and the third essay presents a theoretical analysis of the credit card industry. In the empirical study of the relationship between competition and firms' pricing in the airline industry, I emphasize the importance of distinguishing the equilibrium behaviors with respect to different market characteristics. Major airlines can price discriminate differently in a market where they compete with low-cost carriers comparing to in another market where they don't, and also they can respond dfferently to the threat of entry depending on whether they are certain about the rival's future entry. The study reveals that competition has a positive effect on price discrimination in the routes where major airlines compete against one anther. In these routes, competition reduces lower-end prices to a greater extent than upper-end prices. In contrast, an entry by low-cost carriers results in a significant negative relationship between competition and price discrimination. Thus, the opposite results in the literature are both evident in the airline industry, and it is very important to identify the different forces of competition on price discrimination. Firms can respond to potential competition as well as actual competition. So, I extend the study to the relationship of potential competition and price discrimination, specially in cases where major airlines compete against one another while facing Southwest's threat of entry. I also attempt to suggest major airlines' motives of reducing price discrimination preemptively. The results of the study suggest that incumbents reduce price dispersion when it is possible to deter the rival's entry and that the potential rival discourages incumbents from deterring entry by announcing before its beginning service. Finally, I examine when competition can increase prices in a market, by analyzing the issuing side of the credit card industry. This industry is characterized by a two-sided market with a platform. Under the no-surcharge rule that restricts merchants to set the same price for cash and card purchases, the equilibrium interchange fee increases with competition. This occurs because issuers can compensate losses from competing on the issuing side by collectively increasing the interchange fee. As a result, limiting competition may improve social welfare when the interchange fee is higher than the social optimal level. In contrast, in the absence of the no-surcharge rule, the analysis shows that competition always improves social welfare by lowering the price of the market.Item Information technology and corporate acquisitions(2013-08) Du, Kui, active 2013; Tanriverdi, HüseyinThis dissertation examines how information technology can help acquirers to improve the performance of their acquisition targets. An acquisition creates value when the acquirer can generate more returns from the acquired business than its former owner can, a condition we call the acquirer's parenting advantage. Then, we introduce two IT-related sources of parenting advantage. Acquirers with more extensive process digitization can provide richer digitized resource to serve their newly acquired businesses, and acquirers with more related process digitization can unlock more synergies between the newly acquired and existing business units. So, as we argue, digitization extensiveness enables a digitization-revitalization mechanism for acquisition value creation, and digitization relatedness enables an integration-synergy-creation mechanism. Both mechanisms can be carried out through digital accommodation activities after acquisitions. Furthermore, the digitization gap between acquirers and targets is a major contingency for digital accommodation, with the second mechanism functioning mostly when the target has already had advanced digitization achievements. We empirically validated these hypothesized relationships by tracking the IT and performance changes in 109 U.S. hospitals before and after they were acquired, using a 7 year study timeframe.Item Voseo to Tuteo Accommodation among Two Salvadoran Communities in the United States(2011-08-08) Sorenson, Travis DougThis study documents and accounts for maintenance and change in dialectal features of Salvadoran Spanish in the United States, especially voseo, as opposed to tuteo, terms signifying the use of the second person singular familiar pronouns vos and tu, with their corresponding verb forms. It compares two distinct Salvadoran populations, one in Washington, D.C., and the other in Houston, Texas. Salvadorans constitute the largest Hispanic group in the nation's capital, while in Houston they are outnumbered by other Hispanics, particularly Mexicans. It was predicted that Salvadorans in Washington, D.C. would maintain voseo more and employ tuteo less than those in Houston. This sociolinguistic phenomenon is accounted for by Accommodation Theory. Based on previous studies, it was also predicted that male participants would maintain voseo more than females due to the covert prestige of this form. To test these hypotheses, data were gathered using three protocols. The first was a questionnaire, with over 100 respondents in each city, on second person singular address forms and social variables. In the second protocol, 10 pairs of subjects in each city engaged in different verbal activities aimed at eliciting direct forms of address. The third protocol involved unstructured home visits with two married couples to observe spontaneous speech. The results supported the hypotheses in some regards more than others. When considering all the protocols, the levels of voseo were much lower and those of tuteo much higher in both cities than what had been predicted. As expected, voseo usage rates in Washington, D.C., were higher than in Houston in the second and third protocols, but voseo claiming rates in the first protocol were slightly higher in Houston. Also as expected, in both the first and second protocols there was a significantly higher rate of accommodation to tuteo among women than men. The most salient finding from the home visit participant observations was that while there was voseo use in Washington, D.C., there was none in Houston, even among those who had previously used it.