Doctor of Philosophy

dissertationThe chemical composition of cosmic rays is critically important to understanding cosmic ray sources as well as a cosmic ray's propagation through the Galaxy and Universe. Theories explaining the features seen in the cosmic ray spectrum depend strongly on the chemical composition of cosmic rays. Composition has implications for anisotropy studies as atomic nuclei with large atomic number are more susceptible to deflection by Galactic and extragalactic magnetic fields. This work presents a composition analysis using data from the Telescope Array (TA) experiment and uses the point of shower maximum, Xmax, as the marker of a cosmic ray's chemical composition. TA is the largest cosmic ray detector in the Northern Hemisphere and makes use of both ground array as well as nitrogen fluorescence methods for detecting cosmic rays. This analysis combines both ground array and fluorescence data in a hybrid analysis to obtain resolutions of 0.5◦ in reconstructed pointing directions and 20 g/cm2 in reconstructed Xmax. Above 1018.5 eV, measured Xmax distributions using hybrid TA data are compatible with proton MC and exclude iron. However, above 1019.3 eV, the statistical power is limited and the data is compatible either proton or iron MCs. The shapes of the Xmax distributions independent of their means are compared, showing again that the data is compatible with protons and incompatible with iron. However, the statistical power for this measurement is limited above 1018.8 eV

Investigation of Power Using F Approximations for the Hotelling-Lawley Trace and Pillai\u27s Trace

Differences among treatment groups in terms of which variable or linear combination of variables causes a significant multivariate analysis of variance (MANOVA) are often difficult to determine. This study is an attempt to develop a means by which a significant MANOVA can be followed by a discriminant analysis for the purpose of finding a significant contrast which can determine which variable or linear combination of variables is causing differences in which treatment groups. Significance of the contrast was tested using Roy-Bose simultaneous confidence intervals. These intervals traditionally have been considered conservative as a hypothesis-testing procedure. Of concern in any hypothesis-testing procedure is type I error and power. This study investigated type I error and power of the procedure in numerous situations which used many combinations of number of groups, number of variables, nominal alpha, and group size. Included are situations which involved no violation of MANOVA assumptions, as well as situations involving a violation of normality or a violation of the assumption of a homogeneous covariance structure. Results show that the proposed procedure needs great improvement when the assumptions of MANOVA are not met. When the assumptions are met, the procedure works fairly well in terms of power and type I error for a small number of groups or variables. As the number of groups or variables reaches six, the procedure begins to lose power, but type I error is acceptable

Hypervelocity Stars: Predicting the Spectrum of Ejection Velocities

The disruption of binary stars by the tidal field of the black hole in the Galactic Center can produce the hypervelocity stars observed in the halo. We use numerical models to simulate the full spectrum of observable velocities of stars ejected into the halo by this binary disruption process. Our model includes a range of parameters for binaries with 3-4 M_Solar primaries, consideration of radial orbits of the ejected stars through an approximate mass distribution for the Galaxy, and the impact of stellar lifetimes. We calculate the spectrum of ejection velocities and reproduce previous results for the mean ejection velocity at the Galactic center. The model predicts that the full population of ejected stars includes both the hypervelocity stars with velocities large enough to escape from the Galaxy and a comparable number of ejected, but bound, stars of the same stellar type. The predicted median speeds of the population of ejected stars as a function of distance in the halo are consistent with current observations. Combining the model with the data also shows that interesting constraints on the properties of binaries in the Galactic Center and on the mass distribution in the Galaxy can be obtained even with modest samples of ejected stars.Comment: 26 pages, including 6 figures, accepted for publication in the Astrophysical Journa

Hopefulness predicts resilience after hereditary colorectal cancer genetic testing: a prospective outcome trajectories study

<p>Abstract</p> <p>Background -</p> <p>Genetic testing for hereditary colorectal cancer (HCRC) had significant psychological consequences for test recipients. This prospective longitudinal study investigated the factors that predict psychological resilience in adults undergoing genetic testing for HCRC.</p> <p>Methods -</p> <p>A longitudinal study was carried out from April 2003 to August 2006 on Hong Kong Chinese HCRC family members who were recruited and offered genetic testing by the Hereditary Gastrointestinal Cancer Registry to determine psychological outcomes after genetic testing. Self-completed questionnaires were administered immediately before (pre-disclosure baseline) and 2 weeks, 4 months and 1 year after result disclosure. Using validated psychological inventories, the cognitive style of hope was measured at baseline, and the psychological distress of depression and anxiety was measured at all time points.</p> <p>Results -</p> <p>Of the 76 participating subjects, 71 individuals (43 men and 28 women; mean age 38.9 ± 9.2 years) from nine FAP and 24 HNPCC families completed the study, including 39 mutated gene carriers. Four patterns of outcome trajectories were created using established norms for the specified outcome measures of depression and anxiety. These included chronic dysfunction (13% and 8.7%), recovery (0% and 4.3%), delayed dysfunction (13% and 15.9%) and resilience (76.8% and 66.7%). Two logistic regression analyses were conducted using hope at baseline to predict resilience, with depression and anxiety employed as outcome indicators. Because of the small number of participants, the chronic dysfunction and delayed dysfunction groups were combined into a non-resilient group for comparison with the resilient group in all subsequent analysis. Because of low frequencies, participants exhibiting a recovery trajectory (n = 3 for anxiety and n = 0 for depression) were excluded from further analysis. Both regression equations were significant. Baseline hope was a significant predictor of a resilience outcome trajectory for depression (<it>B </it>= -0.24, <it>p </it>< 0.01 for depression); and anxiety (<it>B </it>= -0.11, <it>p </it>= 0.05 for anxiety).</p> <p>Conclusions -</p> <p>The current findings suggest that hopefulness may predict resilience after HCRC genetic testing in Hong Kong Chinese. Interventions to increase the level of hope may be beneficial to the psychological adjustment of CRC genetic testing recipients.</p

Taking it personally: the effect of ethnic attachment on preferences for regionalism

This article presents three related findings on regional decentralization. We use an original dataset collected in Uganda to establish, for the first time in a developing country context, that individuals have meaningful preferences over the degree of regional decentralization they desire, ranging from centralism to secessionism. Second, multilevel models suggest that a small share of this variation is explained at the district and ethnic group levels. The preference for regional decentralization monotonically increases with an ethnic group or a district’s average ethnic attachment. However, the relationship with an ethnic group or district’s income is U-shaped: both the richest and the poorest groups desire more regionalism, reconciling interest-based and identity-based explanations for regionalism. Finally, we show that higher individual ethnic attachment increases preferences for regionalism using fixed effects and a new matching method

Portable Take-Home System Enables Proportional Control and High-Resolution Data Logging With a Multi-Degree-of-Freedom Bionic Arm

This paper describes a portable, prosthetic control system and the first at-home use of a multi-degree-of-freedom, proportionally controlled bionic arm. The system uses a modified Kalman filter to provide 6 degree-of-freedom, real-time, proportional control. We describe (a) how the system trains motor control algorithms for use with an advanced bionic arm, and (b) the system\u27s ability to record an unprecedented and comprehensive dataset of EMG, hand positions and force sensor values. Intact participants and a transradial amputee used the system to perform activities-of-daily-living, including bi-manual tasks, in the lab and at home. This technology enables at-home dexterous bionic arm use, and provides a high-temporal resolution description of daily use—essential information to determine clinical relevance and improve future research for advanced bionic arms