Theses and Dissertations
This collection contains the theses and dissertations approved for public release from Texas A&M University.
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Hosking, Edan Robert, 1972- (Texas A&M University, September 17, 2007)[more][less]
Abstract: The MotA and MotB proteins of E. coli form a MotA4MotB2 complex. Proton flow through a transmembrane channel in the complex powers flagellar rotation. Protonation of Asp-32 of MotB within the channel is proposed to cause a conformational change in the large cytoplasmic loop of MotA, which pushes against FliG in the rotor. MotB is believed to anchor the complex to the cell wall via a conserved sequence that is found in many proteins that bind peptidoglycan. The research presented in this dissertation focused primarily on the formation and activation of the MotAB proton channel. A proposed amphipathic α-helical region, extending from residue 52 through 65 of the periplasmic domain of MotB, was discovered to block proton flow through the channel in its inactive state prior to incorporation into a flagellar motor. The plug is thought to lie parallel to the periplasmic face of the cell membrane and to be removed from the membrane by a conformational change triggered by contact with the motor. Negatively charged residues near the cytoplasmic C-terminus of MotA and positively charged residues at the cytoplasmic N-terminus of MotB were identified as being important for motility. A mutational analysis and subsequent suppressor analysis suggest that these residues may align MotA and MotB to form the MotA4MotB2 complex in the proper position relative to FliG and the rotor. The underlying mechanism for producing MotA and MotB in a 2:1 ratio was also investigated and found to be primarily due to translational coupling of motA and motB. The stop codon of motA and the start codon of motB overlap, allowing the ribosome that has just completed translation of motA to reinitiate and translate motB. The efficiency of reinitiation is about 66%; presumably degradation of excess MotB not in the MotA4MotB2 complex produces the final 2:1 ratio. Research was also conducted to determine whether MotB binds directly to the peptidoglycan layer of the cell wall. Although inconclusive, the preliminary results appear to support this notion. The overall work provides insights into several aspects of the assembly and subsequent activation of the stator component of the bacterial flagellar motor. URI: http://handle.tamu.edu/1969.1/6017 Files in this item: 1
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Borders, Stephen Boyce, 1967- (Texas A&M University, September 17, 2007)[more][less]
Abstract: Transportation is frequently cited as a barrier to health care, but rarely have researchers analyzed the problems in depth. The purpose of this study was to assess the role transportation plays in the utilization of preventive health care services among Medicaid recipients ages 0 - 20 in Texas. This preventive care is known as Early Periodic Screening and Diagnostic Testing (EPSDT), a comprehensive prevention and treatment program for Medicaid eligible children. Our computer assisted telephone interviewing based survey was administered to Medicaid recipients selected from a representative sample through a stratified sampling scheme. Binary logistic regression models were used to assess and predict factors associated with utilization of the Texas Medicaid Transportation Program (MTP) and utilization of EPSDT. We also used k-means cluster analysis to identify subgroups of Medicaid clients with particularly acute transportation barriers. Of the 1,214 Medicaid recipients interviewed, the overall odds of a Medicaid recipient being a MTP non-user was 0.94. For clients with automobile access, the probability increases to 0.98. Clients who experienced difficulties paying for gasoline decreased the overall odds to 0.86. When examining utilization of EPSDT, the overall probability of being a low utilizer was 0.59. Two factors, Spanish-speaking patients (0.21) and clients with more than one child at home (0.54) decreased the overall odds of being a low utilizer, while those with difficulty paying for gasoline increased the odds of being a low utilizer to 0.63. Increasing EPSDT utilization among the millions of Texas Medicaid recipients is an important policy objective. Because the Texas Medicaid population is large and diverse, no single approach to increasing utilization is likely to address all needs. The group concept provides a means to understand which Medicaid recipients do not access MTP services and those with low utilization rates. These groupings can be useful in targeting Medicaid clients with specific transportation difficulties. Instead of broad informational campaigns, policy makers should devise targeted strategies to promote the most appropriate types of assistance. In addition to expanding transportation options, policy makers should also examine the locations in which care is delivered, considering telemedicine, mobile health and school-based health clinics as options. URI: http://handle.tamu.edu/1969.1/6016 Files in this item: 1
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Kimball, Jorja Lay, 1962- (Texas A&M University, September 17, 2007)[more][less]
Abstract: For many years, colleges of engineering across the nation have required that a foundational set of courses be completed for entry into upper division coursework or into a specific engineering major. Since 1998, The Dwight Look College of Engineering at Texas A&M University (TAMU) has required that incoming first-time enrolling students complete a Core Body of Knowledge (CBK) with specific cumulative grade points required for specific majors. However, considerations of the time to completion of coursework and other student characteristics and academic factors have not been taken into consideration by TAMU, like most institutions. The purpose of this study is to determine for first year engineering students at TAMU the relationship of gender, ethnicity, engineering major, unmet financial need, cumulative grade point average, and total transfer hours on time to completion of CBK courses. The results of the analysis showed that cumulative grade point average (CGPA) had the strongest relationship to completion of CBK of any independent variable in this study. Statistical significance was found for the following variables in this study: CGPA, gender, ethnicity, and unmet financial need. For the study's variable of major, statistical significance was found for Chemical, Electrical, and Computer Engineering majors. The one variable in this study that did not show statistical significance in relation to time to completion of CBK was transfer credit. Findings with implications for recruitment and retention of underrepresented in engineering is a statistical significance indicating that on average females are taking less time than males to complete CBK. The conclusion from the study is that efforts to attract more women into engineering have merit as do programs to support underrepresented students in order that they may complete CBK at a faster pace. Further study to determine profiles of those majors where statistical significance was found for students taking a greater or lesser amount of time for CBK completion than the mean is recommended, as is ongoing data collection and comparison for current cohorts of engineering majors at TAMU. URI: http://handle.tamu.edu/1969.1/6015 Files in this item: 1
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Lavin, Tucker Alan, 1981- (Texas A&M University, September 17, 2007)[more][less]
Abstract: Compressible ideal-gas turbulence subjected to homogeneous shear is investigated at the rapid distortion limit. Specific issues addressed are (i) the interaction between kinetic and internal energies and role of pressure-dilatation; (ii) the modifications to pressure-strain correlation and Reynolds stress anisotropy and (iii) the effect of the composition of velocity fluctuations (solenoidal vs. dilatational). Turbulence evolution is found to be strongly influenced by gradient Mach number, the initial solenoidal-to-dilatational ratio of the velocity field and the initial intensity of the thermodynamic fluctuations. The balance between the initial fluctuations in velocity and thermodynamic variables is also found to be very important. Any imbalance in the two fluctuating fields leads to high levels of pressure-dilatation and intense exchange. For a given initial condition, it is found that the interaction via the pressuredilatation term between the momentum and energy equations reaches a peak at an intermediate gradient Mach number. The energy exchange between internal and kinetic modes is negligible at very high or very low Mach number values due to lack of pressure dilatation. When present, the exchange exhibits oscillations even as the sum of the two energies evolves smoothly. The interaction between shear and solenoidal initial velocity field generates dilatational fluctuations; for some intermediate levels of shear Mach number dilatational fluctuations account for 20% of the total fluctuations. Similarly, the interaction between shear and initial dilatation produces solenoidal oscillations. Somewhat surprisingly, the generation of solenoidal fluctuations increases with gradient Mach number. Larger levels of pressure-strain correlation are seen with dilatational rather than solenoidal initial conditions. Anisotropies of solenoidal and dilatational components are investigated individually. The most interesting observation is that solenoidal and dilatational turbulence tend toward a one componential state but the energetic component is different in each case. As in incompressible shear flows, with solenoidal fluctuations, the streamwise (1,1) component of Reynolds stress is dominant. With dilatational fluctuations, the stream-normal (2,2) component is the strongest. Overall, the study yields valuable insight into the linear processes in high Mach number shear flows and identifies important closure modeling issues. URI: http://handle.tamu.edu/1969.1/6014 Files in this item: 1
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Roberts-Walter, Patricia Fay, 1961- (Texas A&M University, September 17, 2007)[more][less]
Abstract: The purpose of this study was to examine the validity and reliability of the Cultural Awareness and Beliefs Inventory (CABI). The CABI consist of forty-six items that measures urban teachers’ cultural awareness and beliefs on a Likert-type four-point scale. In addition, this study also examined the extent the CABI determined statistically significant differences by demographic characteristics, such as teachers’ ethnicity or years of teaching experience. During the 2005–2006 academic year, data for this study was collected from the Cultural Awareness and Beliefs Inventory (CABI). Approximately 1873 Prekindergarten through Grade 12 teachers, employed by an urban public school district located in southeastern Texas, completed the survey. Construct validity was determined by internal consistency, content validity, convergent and divergent validity. To investigate the internal structure, an exploratory factor analysis, EFA, yielded an eight-factor, 36-item inventory. The eight factors, Factor I: Teachers’ Beliefs, Factor II: School Climate, Factor III: Culturally Responsive Classroom Management, Factor IV: Home Community School, Factor V: Cultural Awareness, Factor VI: Curriculum and Instruction, Factor VII: Cultural Sensitivity, and Factor VIII: Teacher Efficacy were examined by a jury of experts to establish the content validity of the eight-factor, 36-item inventory. Convergent and divergent validity was established for six of the eight constructs by conducting a Pearson product moment correlation. Cronbach’s alpha coefficient was conducted to measure the internal consistency reliability of the 36-item CABI. The reliability was established at .83. Further, the alpha for the eight factors, or scales, ranged from 46 percent for TE to 88 percent for CRCM. Differences in the teachers’ perceptions by teachers’ ethnicity were determined for TB, CRCM, CS and TE. Follow-up Scheffe post hoc analyses indicated that African American teachers had significantly more positive perceptions of TB, CRCM, and CS. Hispanic American teachers had significantly more positive perceptions of TE. Differences in the teachers’ perceptions by years of experience were determined for CRCM and HCS. Follow-up Scheffe post hoc analyses indicated that teachers with more years of experience had significantly more positive perceptions of CRCM than first year teachers. First year teachers had significantly more positive perceptions of HCS. URI: http://handle.tamu.edu/1969.1/6013 Files in this item: 1
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