A Formal Preparation for Object-Oriented Query Optimisation

This paper describes work that is in progress on a formalised preparation to object-oriented query optimisation. Such preparation is conducive to the development of optimisation strategies. As an example of a formal preparation, this paper presents a formalised object algebra, a suggested optimisation method and an implementation of an algebraic converter suitable for DAPLEX

The Interactions of Small Molecules on Astrochemically Relevant Surfaces

The known Universe is composed of 99.9% hydrogen and helium. The remaining 0.1 % constitutes the abundance of the rest of the elements. Despite their low abundance relative to the lighter elements, the reactions of these heavier elements account for the complexity of species found in space. In particular, more than 200 complex organic species have been detected in the interstellar medium. They, along with carbonaceous and silicate dust grains, accumulate together in interstellar clouds. This thesis focusses on the reactions taking place within dense interstellar dust clouds, where the inner core is shielded from radiation emitted by nearby stellar objects by a dense, opaque outer layer of gas and dust. Within the cores of these dense clouds, molecular lifetimes are extended which allows for the formation of complex molecules through further reactions. The species observed within the interstellar medium can be formed via ion-neutral reactions in the gas-phase. However, for many molecules, the observed abundance cannot be accounted for by gas-phase chemistry alone. Therefore, reactions must also be occurring on the cold surfaces of the interstellar dust grains. This thesis will focus on the reactions taking place on these grains, presenting investigations into the interactions with, and reactions of, various species upon astrochemically relevant surfaces. The investigation into the reaction of acrolein with atomic oxygen on a graphitic surface is discussed in Chapter 4. Multilayer doses of both species were co-dosed onto a graphite substrate held at temperatures ranging from 20 K to 140 K. A product with m/z 72 is observed for this reaction, suggesting the addition of oxygen across the double bond of the organic molecule: C3H4O2. The kinetics of this reaction were modelled to gain a deeper understanding of the mechanisms occurring on the cold surface. Specifically, the contribution of the two prototypical surface mechanisms, Langmuir-Hinshelwood and Eley-Rideal mechanisms, was assessed at each surface temperature. Additionally, the desorption characteristics of various astrochemically relevant molecules are outlined in Chapter 5. The behaviour of each species on a graphite surface was investigated and compared to the desorption characteristics previously investigated in the literature. The behaviour of the species observed in our desorption experiments is in good agreement with the behaviour observed in previous studies. The cohesion between our data and interactions observed previously, validates our experimental technique as a method to model the interactions of molecules under conditions similar to those in the ISM. In Chapter 6 the desorption characteristics of molecular oxygen, acrolein and carbon dioxide from an amorphous carbonaceous surface are investigated. The amorphous surface is composed of porous, broken fullerene-like cage structures. Through analysis of the desorption spectra of the gases, it was found that each molecule had significantly larger binding energies to this amorphous surface than previously observed on graphite. This is consistent with previous studies into the desorption characteristics of various gases from the surface of single walled carbon nanotubes (SWCNTs) by Ulbricht et al. where the gas molecules showed enhanced binding to the SWCNTs compared to graphite surfaces. The implications of the discovery of these higher energy binding sites to astrochemistry is discussed. Finally, in Chapter 7, results concerning the reaction of atomic oxygen with propene on a different amorphous carbonaceous surface are presented. The new surface is hydrogenated and consists of a large proportion of sp3 hybridised carbon. Interestingly, the expected product, showing the addition of oxygen across the double bond of the propene was not observed for the reaction on this surface. On the other hand, a product with m/z 90 was detected, suggesting the addition of ozone across the double bond to form a product with the general formula C3H6O3. The ozonolysis of an alkene is a well-known reaction in gas-phase chemistry but has not yet been observed under astrochemically relevant conditions. Additionally, in the gas phase, the C3H6O3 product is known to undergo a rearrangement via the Criegee mechanism before breaking down into various oxygen-containing molecules, such as aldehydes, ketones, carboxylic acids and alcohols. If this mechanism can occur on the surfaces of interstellar dust grains it could help to account for the rich variety of complex organic molecules observed in the ISM

The Design and Evaluation of an Educational Software Development Process for First Year Computing Undergraduates

First year, undergraduate computing students experience a series of well-known challenges when learning how to design and develop software solutions. These challenges, which include a failure to engage effectively with planning solutions prior to implementation ultimately impact upon the students’ competency and their retention beyond the first year of their studies. In the software industry, software development processes systematically guide the development of software solutions through iterations of analysis, design, implementation and testing. Industry-standard processes are, however, unsuitable for novice programmers as they require prior programming knowledge. This study investigates how a researcher-designed educational software development process could be created for novice undergraduate learners, and the impact of this process on their competence in learning how to develop software solutions. Based on an Action Research methodology that ran over three cycles, this research demonstrates how an educational software development methodology (termed FRESH) and its operationalised process (termed CADET which is a concrete implementation of the FRESH methodology), was designed and implemented as an educational tool for enhancing student engagement and competency in software development. Through CADET, students were reframed as software developers who understand the value in planning and developing software solutions, and not as programmers who prematurely try to implement solutions. While there remain opportunities to further enhance the technical sophistication of the process as it is implemented in practice, CADET enabled the software development steps of analysis and design to be explicit elements of developing software solutions, rather than their more typically implicit inclusion in introductory CS courses. The research contributes to the field of computing education by exploring the possibilities of – and by concretely generating – an appropriate scaffolded methodology and process; by illustrating the use of computational thinking and threshold concepts in software development; and by providing a novel evaluation framework (termed AKM-SOLO) to aid in the continuous improvement of educational processes and courses by measuring student learning experiences and competencies

Association of Mothers' Perception of Neighborhood Quality and Maternal Resilience with Risk of Preterm Birth.

We examined the associations of mothers' perception of neighborhood quality and maternal resilience with risk of preterm birth and whether maternal resilience moderated the effect of neighborhood quality perception. We analyzed data from 10,758 women with singleton births who participated in 2010-2012 Los Angeles Mommy and Baby surveys. Multilevel logistic regression models assessed the effects of mothers' perception of neighborhood quality and maternal resilience on preterm birth (yes/no), controlling for potential confounders and economic hardship index, a city-level measure of neighborhood quality. Interaction terms were assessed for moderation. Mothers' perception of neighborhood quality and maternal resilience were each uniquely associated with preterm birth, independent of potential confounders (p-values < 0.05). The risk of preterm birth among mothers who perceived their neighborhood as of poor quality was about 30% greater compared to mothers who perceived their neighborhood as of good quality; the risk was 12% greater among mothers with low resilience compared to those with high resilience. Effects of neighborhood quality were not modified by maternal resilience. The findings suggest that mothers' perception of neighborhood quality and resilience are associated with the risk of preterm birth. Further research should explore whether initiatives aimed at improving neighborhood quality and women's self-esteem may improve birth outcomes

Prevalence and Trends of Depression among Cyberbullied Adolescents - Youth Risk Behavior Survey, United States, 2011 – 2019

The difference in depression between non-cyberbullied and cyberbullied youth is not well understood. To describe the prevalence and trends in depression among cyberbullied adolescents. Using cross-sectional, nationally-representative data from the YRBS 2011 - 2019, we estimated the prevalence and trends of depression across the total years and within cyberbullied groups that include biological sex and race and ethnicity among adolescents. The results indicated the prevalence of depression was higher among those that were cyberbullied. Within the cyberbullied groups the total trend was higher than the non-cyberbullied, females had a higher prevalence of depression than males, and Hispanics had a higher prevalence of depression than blacks. Further, the results showed the trends for cyberbullied, males, females, whites, and blacks had significant linear increases, but Hispanics remained stable. Further, the non-cyberbullied trend was quadratic where there was no change from 2011-2015, but an increase occurred between 2015-2019. Depression is high among adolescents. It appears to be increasing among individuals that are cyberbullied, with the exception of Hispanics. These results are discussed with programming recommendations

Metal Inert Gas (MIG) Welding of ASTM A500 Grade B Steel Pipes: Infrared Thermal Imaging and Analysis

In this investigation, welding of circular pipes is undertaken. An experimental setup was designed and built to observe the welding process and gather temperature isotherms under different welding conditions. Thermal images of welding of ASTM A500 Grade B steel pipes are collected using an infrared camera. An analytical solution is used to calculate the temperature isotherms for comparison with the experimental data. The analytical approach, developed by Komanduri and Hou, uses Jaegers moving heat source method, is extended to calculate spot temperature data in pipe welding to determine the temperature profiles under various welding conditions. The analytical and experimental temperature isotherms were compared. Some differences in the temperature distributions produced by the analytical and experimental results were observed. They include the geometry and magnitude of the temperature distributions. An attempt has been made to explain for these differences.Engineering and Technology Managemen