Thesis (Ph. D.)--Duke University, 2007.

Thesis (M. Sc.)--Carleton University, 2001. / Includes bibliographical references (p. 108-110). Also available in electronic format on the Internet.

This thesis describes the results of an investigation of the physical properties of the Gum Nebula. For this investigation a radio continuum map of the region was made at 2326 MHz and resolution ⅓° with the HartRAO antenna. This map was used to generate spectral index images and an infrared to radio flux density ratio (IRR) image. The latter image shows that the IRR of the nebula is in the range 20 to 250, identifying it as an old SNR. Several spectral index images of this region were generated using two different methods, one based on the isolation of the nebula from its background radiation, the other based on TT-plots (Turtle et al., 1962). The two methods yield similar results, which show that the nebula has a thermal shell with a non-thermal region in its interior. Below the galactic plane the thermal region dominates and above the plane the nonthermal region. These results suggest a model of an old SNR with an H II region shell. Spectral line observations of hydrogen recombination lines and hydroxyl (OH) were made with the HartRAO and the Mopra telescopes. The detection of hydrogen recombination lines at four positions in the thermal regions of the nebula give electron temperatures and emission measures in the ranges 4000 to 6000 K and 220 to 460 pc.cm⁻⁶ respectively. The turbulent velocities are of the order of 20 km/s. A search for shocked OH lines at 1667 MHz and 1720 MHz in the Gum Nebula gave results that were negative, but numerous unshocked 1667 MHz OH lines were detected. The latter were used in a test for an expansion of the nebula. The most plausible fit to the data gives an expansion centre at l = 260.5°, b = -2.5° and at a distance of 0.7 kpc from us. The front face angular radius and expansion velocity are 10.5° and 16 km/s respectively. The back face angular radius and expansion velocity are 8.50 and 7 km/s respectively.

In this work we introduce a fast Bayesian algorithm designed for detecting compact objects immersed in a diffuse background. A general methodology is presented in terms of formal correctness and optimal use of all the available information in a consistent unified framework, where no distinction is made between point sources (unresolved objects), SZ clusters, single or multi-channel detection. An emphasis is placed on the necessity of a multi-frequency, multi-model detection algorithm in order to achieve optimality. We have chosen to use the Bayes/Laplace probability theory as it grants a fully consistent extension of formal deductive logic to a more general inferential system with optimal inclusion of all ancillary information [Jaynes, 2004]. Nonetheless, probability theory only informs us about the plausibility, a ‘degree-of-belief ’, of a proposition given the data, the model that describes it and all ancillary (prior) information. However, detection or classification is mostly about making educated choices and a wrong decision always carries a cost/loss. Only resorting to ‘Decision Theory’, supported by probability theory, one can take the best decisions in terms of maximum yield at minimal cost. Despite the rigorous and formal approach employed, practical efficiency and applicability have always been kept as primary design goals. We have attempted to select and employ the relevant tools to explore a likelihood form and its manifold symmetries to achieve the very high computational performance required not only by our ‘decision machine’ but mostly to tackle large realistic contemporary cosmological data sets. As an illustration, we successfully applied the methodology to ESA’s (European Space Agency) Planck satellite data [Planck Collaboration et al., 2011d]. This data set is large, complex and typical of the contemporary precision observational cosmology state-of-the-art. Two catalogue products are already released: (i) A point sources catalogue [Planck Collaboration et al., 2011e], (ii) A catalogue of galaxy clusters [Planck Collaboration et al., 2011f]. Many other contributions, in science products, as an estimation device, have recently been issued [Planck et al., 2012; Planck Collaboration et al., 2011g,i, 2012a,b,c]. This new method is called ‘PowellSnakes’ (PwS).

Thermoplastics reinforced with continuous fibers are very promising building materials for the auto industry and consumer electronics to reduce the weight of vehicles and portable devices, and to deliver a high impact tolerance at the same time. Polypropylene is an abundant thermoplastic, and its glass fibers composites make a valuable solution that is suitable for mass production. But the adoption of such composites requires a deep understanding of their mechanical behavior under the relevant loading conditions. In this Ph.D. work, we aim to understand the damage process in continuous glass fiberreinforced polypropylene in detail. We will focus in particular on developing an approach for microscale observation of damage during the out-of-plane loading process and will use these observations for both qualitative and quantitative evaluation of the composite. We will apply our approach to two kinds of polypropylene composites, one of them is specially designed to withstand impact. The comparison between the two types of composites at slow and fast loading cases will shed some light on the effect of the polymer properties on the behavior of composites under out-of-plane loading.

Philosophiae Doctor - PhD / The faint radio population consisting of star forming galaxies (SFG) and radio-quiet active galactic nuclei (AGN) is important in the study of galaxy evolution. However, the bulk of the faint population is below the detection threshold of the current radio surveys. I study this population through a Bayesian-stacking technique that I have adapted to probe the radio luminosity function (RLF) below the typical 5σ detection threshold. The technique works by fitting RLF models to radio flux densities extracted at the position of galaxies selected from an auxiliary catalogue. I test the technique by adding Gaussian noise (σ) to simulated data and the RLF models are in agreement with the simulated data for up to three orders of magnitude (3 dex) below the detection threshold (5σ). The source of radio emission from radio quiet quasars (subset of AGN) is widely debated. I apply the technique to 1.4-GHz flux densities from the Faint Images of the Radio Sky at Twenty-cm survey (FIRST) at the positions of the optical quasars from the Sloan Digital Sky Survey (SDSS). The RLF models are constrained to 2 dex below the FIRST detection threshold. I found that the radio luminosity where radio-quiet quasars emerge coincides with the luminosity where SFGs are expected to start to dominate the RLF. This Implies that the radio emission of radio-quiet quasars and radio-quiet AGN, in general, could have a significant contribution from star formation in the host galaxies.

Intervention programs providing support for father parenting skills need a practical but psychometrically strong observational measure of fathers’ early positive parenting interactions with children. The primary purpose of this project was to develop a valid, reliable observational measure of father-child interaction, based on research and theory, that predicts child outcomes, identifies fathers’ strengths, and will be useful for home visiting practitioners. This study sought to fulfill this need by developing a new measure called Dads’ Parenting Interactions with Children—Checklist of Observations Linked to Outcomes (PICCOLO-D) for home visitors to use to identify fathering strengths. Developed with extant video observations of over 400 ethnically diverse, lowincome fathers, 73 positive observable behavioral items of early positive father-child interaction were tested for variability, reliability, and validity. The final measure of 21 items representing four domains of positive parenting, affection, responsiveness, encouragement, and teaching, demonstrated good reliability and validity, including associations with children’s language, cognitive, and social emotional outcomes into prekindergarten. Contextual influences were examined within father ethnicity and child gender groups and in a second observational setting. European and Latino American fathers had higher scores than African American fathers. Fathers had higher scores with daughters than sons. Fathers had higher scores in a semistructured play setting than in a father-choice setting. The new measure is intended for use as part of an individualized strengths-based approach for home visiting practitioners.

No description available.

The effectiveness of seven methods of handling missing data was investigated in a factorial design using random samples selected from the National Education Longitudinal Study of 1988 (NELS-88). Methods evaluated were listwise deletion, pairwise deletion, mean substitution, Buck's procedure, mean regression, one iteration regression, and iterative regression. Factors controlled were number of variables (4 and 8), average intercorrelation (0.2 and 0.4), sample size (200 and 2000), and proportion of incomplete cases (10%, 20%, and 40%). The pattern of missing values was determined by the pattern existing in the variables selected from NELS-88 data base. Covariance matrices resulting from the use of each missing data method were compared to the 'true' covariance matrix using multi-sample analysis in LISREL 7. Variable means were compared to the 'true' means using the MANOVA procedure in SPSS/PC+. Statistically significant differences (p≤.05) were detected in both comparisons. The most surprising result of this study was the effectiveness (p>.05) of pairwise deletion whenever the sample size was large thus supporting the contention that the error term disappears as sample size approaches infinity (Glasser, 1964). Listwise deletion was also effective (p>.05) whenever there were four variables or the sample size was small. Almost as surprising was the relative ineffectiveness (p<.05) of the regression methods. This is explained by the difference in proportion of incomplete cases versus the proportion of missing values, and by the distribution of the missing values within the incomplete cases. / Ph. D.

The latest edition of the Food and Drug Administration's Model Food Code provides the definition of an acceptable donated food item but does not specify any safe storage or handling standards for these items. Virginia has not adopted this edition, but its own food handling regulations provide liability protections to food donors and exempt food pantries from any relevant retail food handling regulations. This means that food pantries must provide their own oversight over implementation of safe food handling requirements. Some pantries only accept nonperishables, but others accept both perishable and nonperishable food, or prepare/repurpose food on site. Therefore, pantries have varying needs in terms of safe food handling and preparation oversight and guidance. This project aims to observe food safety practices at food pantries within Virginia, and to establish a set of recommendations based on these observations for food pantries to consider implementing. Twenty pantries throughout the Commonwealth of Virginia were observed when distributing food using a standardized rubric. This rubric allowed the observer to collect detail on food storage, handling, and preparation at the pantry. Each pantry was visited once and observed for about two hours. The manager of the pantry completed a survey to determine basic food safety knowledge. Generally, pantries successfully followed basic food safety guidelines, however there were some clear risky practices observed. These included improper handwashing, improper storage of perishable items, and improper volunteer personal hygiene. There were only two handwashing attempts observed between all 20 pantries and neither of these attempts was correct. In addition, 8 of 20 (40%) of the pantries did not keep up to date records of their refrigerator and freezer temperatures. Lack of personal hygiene, especially the use of personal items while handling food and lack of glove usage, was a concern. 9 of 20 (45%) of pantries had someone on site using a personal item while handling food, and 4 of 6 (67%) of pantries that prepared or cooked food on site had volunteers improperly wearing gloves during these activities. Managers at seventeen of twenty (85%) pantries reported completing some type of food safety training while only volunteers at six of twenty (30%) pantries reported the same. This demonstrates gaps in knowledge between volunteers and managers. The results of this study demonstrate the need for standard operating procedures (SOPs) to be made available for food pantries, as well as a food safety training created specifically for food pantry volunteers that is applicable to their scope of work. / Master of Science in Life Sciences / The latest edition of the Food and Drug Administration's Model Food Code provides the definition of an acceptable donated food item but does not specify any safe storage or handling standards for these items. Virginia has not adopted this edition, but its own food handling regulations provide liability to food donors and exempt food pantries from any relevant retail food handling regulations. This means that food pantries must provide their own oversight over implementation of safe food handling requirements. Some pantries only accept nonperishable food items, but others accept both perishable and nonperishable food, or prepare/repurpose food on site. Therefore, pantries have varying needs in terms of safe food handling and preparation oversight and guidance. This project aims to observe food safety practices at food pantries within Virginia, and to establish a set of recommendations based on these observations for food pantries to consider. Twenty pantries throughout the state of Virginia were observed during distribution using a standardized rubric. This rubric allowed the observer to collect detail on food storage, handling, and preparation at the pantry. Each pantry was visited once and observed for two hours. The manager of the pantry completed a survey on general basic food safety knowledge. Generally, pantries successfully followed basic food safety guidelines, however there were some clear risky practices observed. Consistently, these included risky practices around handwashing, proper storage of perishable items, and personal hygiene of volunteers. The results of this study show a pointed need for standard operating procedures (SOPs) to be created for food pantries, as well as a food safety training created specifically for food pantry volunteers that is applicable to their scope of work.