Verifying shuttle onboard software using expert systems

The Space Shuttle uses a complex set of software to guide, navigate, and control it through all phases of flight. Adding to the complexity is the fact that the software is reconfigured for each flight, i.e., thousands of constants in the software are changed to reflect the unique properties of a given mission. In the last level of tests, the software is flown through end to end nominal and abort scenarios taking the shuttle from liftoff to landing. The analysis of the results of the testing is experience and labor intensive. A set of pass/fail criteria were defined for each test case and in parallel with the knowledge acquisition, tools were developed which allowed the automation of the knowledge being gathered on paper. A prototype of the Analysis Criteria Expert System (ACES) was put into production in the verification of the reconfigured onboard flight software

Fidelity, mismatch extension, and proofreading measurements of apPOL, the Plasmodium falciparum apicoplast-targeted DNA polymerase

Malaria is one of the most common infectious diseases found in developing and tropical regions of the world. It is contracted over 200 million times annually, almost 800,000 of which are fatal. The primary causative agent of malaria is Plasmodium falciparum, a parasite of the phylum Apicomplexa, members of which are characterized by an essential non-photosynthetic organelle called the apicoplast. Like the chloroplast and mitochondria, the apicoplast contains its own genome, which needs to be properly replicated with each cell division for continued survival. To date, the gene PfPREX, a novel polyprotein, encodes for the only known helicase, primase, and polymerase involved in replication of the genome of the apicoplast. In this investigation we characterized the fidelity of the DNA polymerase (apPOL) and examined its ability to extend or remove various base-paring mismatches. This allowed us to determine the relative likelihood of each misincorporation. The purpose of these investigations is to better understand apPOL, which is a vital part of the machinery of Plasmodium falciparum as well as a unique polymerase itself. While the other two products of PfPREX have been shown to be related to those of T7 bacteriophage, the most similar polymerase to apPOL is that of DNA polymerase I of Aquifex aeolicus, a thermophilic bacteria. It is also part of a small group of polymerases that are related to but distinct from prototypical A-family DNA polymerases. For these reasons we have chosen to investigate this important DNA polymerase

Essays on long memory estimation and testing for structural breaks under long-range dependent errors

This thesis contains five essays on estimating the long-memory parameter and testing for structural change under long-range dependent errors

Inhalant Use Among Native American Adolescents: A Comparison of Users and Nonusers at Intemountain Intertribal School

The objective of this study was to investigate a population of identified inhalant users at Intermountain Intertribal School, comparing and contrasting two user groups to a control group of nonusers on a number of selected research variables. The subjects included 42 identified inhalant users. Subjects were further classified into two user groups: one-time users and repeat users, and 20 nonusers. The nonuser group comprised the control group. Each subject was individually interviewed and administered the research and data collection instruments. In addition, other essential information was taken from permanent school records. A one-way analysis of variance was computed to ascertain the relationship between group membership and 11 selected research variables. A discriminant function analysis was computed to determine differences in the 11 research variables as well as to classify and predict group membership. A descriptive analysis of a questionnaire was also reported. Statistically significant differences were found among the three research groups on six of the 11 variables. The discriminant function correctly classified 72% of the subjects, and analysis of the group centroids indicated that the greatest distinctions among the groups were between the nonuser group and the repeat user group. The data present a pattern of inhalant use similar to other populations. The importance of early identification and treatment as well as preventative programs is discussed. Implications of the study and recommendations for further research were made

Social Determinants of Mental Health and Well-Being among Aboriginal Peoples in Canada

The articles in this volume address the question: How do social determinants structure the health and well-being of the Aboriginal population in Canada? The first article uses bivariate statistical tests to assess whether First Nations residents’ subjective assessments of personal and community well-being correspond to scores from the Community Well-Being (CWB) Index, which is a measure of socioeconomic conditions in the community. The second article uses path analysis to test the extent to which the stress process model explains the social distribution of psychological distress and well-being in the off-reserve Aboriginal population. Specifically, it investigates whether stress, mastery, and social support mediate the pathways between social status and mental health outcomes. The results of these two chapters suggest that education is an important determinant of well-being. The final two chapters explore potential barriers to higher educational attainment. The third article uses multinomial logistic regression to assess whether intergenerational exposure to residential schools patterns educational attainment across three cohorts of First Nations adults. The fourth chapter uses churn theory to examine whether mobility patterns affect educational attainment among Aboriginal adolescents and young adults living off-reserve. Collectively, the articles presented here support the contention that the health and well-being of the Aboriginal population is tied to, although not solely determined by, their social and economic positions. CWB scores were significantly associated with residents’ perceptions of their own and community’s well-being. Stress, mastery, and social support are mediators between social status and mental health; however, it appears that specific social statuses are more strongly associated with specific mediators. In terms of educational attainment, there was no clear patterning based on intergenerational proximity or density of residenial school exposure. The results suggest that exposure alone is a poor predictor. Patterns of migration were associated with educational attainment in both cohorts. Generally, it appears that frequent moves are associated with higher odds of dropping out or falling behind in high school. However, having never moved is associated with lower odds of attending post-secondary

Specification and Morphogenesis of the Drosophila Testis Niche

Adult stem cells have the unique ability to either self-renew or differentiate, thus giving them tremendous therapeutic potential. These tissue-specific stem cells are directed to self-renew by signals from the local microenvironment termed the stem cell niche. While reconstitution assays have demonstrated the existence of stem cell niches in many adult organs, unambiguous identification of the resident stem cells and their niche cells continues to be a challenge. Accordingly, the mechanisms that direct specification and formation of a stem cell niche in vivo remain unclear. The Drosophila testis has emerged as a powerful system in which to study stem cell-niche interactions. The niche cells, called hub cells, form a small aggregate at the apical tip of the testis. Hub cells promote attachment and self-renewal in the germline stem cells and cyst stem cells, which are organized in a radial array around the hub. The signaling pathways that direct the maintenance and differentiation of these lineages have been well characterized; however, the initial specification and organization of the niche is still being elucidated. It was previously shown that Notch activation in a subset of somatic gonadal precursors specifies them as hub cells in the embryonic gonad. Here we use genetic analysis to show that Notch signaling activates a branched pathway for hub cell differentiation. Along one arm of the pathway, the Maf factor Traffic jam is downregulated to allow for niche signaling and adhesion. Along a separate arm, the transcription factor Bowl, promotes the assembly of hub cells at the anterior of the gonad where they recruit and organize stem cells. We also use live imaging to reveal two phases of niche morphogenesis; 1) a sorting and guidance phase in which hub cells are directed to the anterior by an extra-gonadal cue and 2) a compaction phase characterized by the formation of an acto-myosin cable around the compacting hub concomitant with the onset of oriented GSC divisions. These observations suggest a model in which the germ cells shape their own niche by driving hub compaction. These findings greatly advance our understanding of how a stem cell niche develops within a tissue

Exploration of an oculometer-based model of pilot workload

Potential relationships between eye behavior and pilot workload are discussed. A Honeywell Mark IIA oculometer was used to obtain the eye data in a fixed base transport aircraft simulation facility. The data were analyzed to determine those parameters of eye behavior which were related to changes in level of task difficulty of the simulated manual approach and landing on instruments. A number of trends and relationships between eye variables and pilot ratings were found. A preliminary equation was written based on the results of a stepwise linear regression. High variability in time spent on various instruments was related to differences in scanning strategy among pilots. A more detailed analysis of individual runs by individual pilots was performed to investigate the source of this variability more closely. Results indicated a high degree of intra-pilot variability in instrument scanning. No consistent workload related trends were found. Pupil diameter which had demonstrated a strong relationship to task difficulty was extensively re-exmained