Le composite à matrices polymériques renforcées de fibres de carbone (CFRP) est un matériau précieux en raison de ses excellentes propriétés mécaniques, légèreté et durabilité. Un gain important d’efficacité et une réduction des émissions de carbone peuvent être obtenus en remplaçant les pièces métalliques par les CFRPs dans l'industrie du transport. Toutefois, le recyclage de déchets CFRP est problématique, car le renfort de fibres de carbone est chimiquement lié à la matrice de résine réticulée. Néanmoins, la réutilisation de fibres de carbone couteuses rend le recyclage des CFRPs potentiellement viable en termes d’économie. Dans notre laboratoire, une étude multi-échelle d’un procédé de vapo-thermolyse a été réalisée, dont l'objectif est de séparer les fibres de carbone de matrices polymériques en utilisant la vapeur d’eau surchauffée. Afin d’obtenir une meilleure compréhension du comportement de dégradation thermique des matériaux CFRP, de nombreuses analyses thermiques ainsi que les caractérisations physico-chimiques ont été effectuées sur différentes fibres de carbone, résines polymériques (époxyde ou polyphénylène sulfide) et les composites correspondants. Une étude cinétique a été également abordée. Les plans d’expériences réalisées à l'échelle pilote dans un réacteur sophistiqué permettent de déterminer les conditions expérimentales optimales du procédé semi-industriel. Les fibres de carbone récupérées à partir de conditions optimisées apparaissent propres, sans résine et conservent plus de 90% de leur résistance à la traction d’origine. Les phases gazeuse et liquide émises ont également été quantitativement analysées. La modélisation de l’écoulement et des transferts thermiques du réacteur ainsi que la simulation de la dégradation de matrices polymériques montrent les résultats comparables avec les observations expérimentales. L’analyse du cycle de vie indique que le recyclage des CFRPs peut être favorable pour l’environnement par rapport au scénario de mise en décharge. / Carbon fiber reinforced polymer-matrix composite (CFRP) is a highly valued material because of its exceptional strength, rigidity, light weight and durability. Significant fuel efficiency gains and carbon emission reduction can be obtained by replacing metal parts in automotive components with CFRPs. However, the recycling of CFRP waste is problematic because the reinforcement (carbon fiber) is chemically bonded to the cross-linked matrix resin. Nevertheless, the reuse of expensive carbon fibers makes the recycling a potentially economically viable option. A thermal process to separate carbon fibers from polymer matrix by using superheated steam has been studied in our laboratory at both bench and pilot scale. In order to understand the thermal degradation behavior of the CFRP materials, the thermal analyses along with the physicochemical characterizations of various carbon fibers, polymer resins (epoxy or polyphenylene sulfide) as well as the corresponding composites have been carried out. A kinetic study has also been conducted. The experimental design performed in a sophisticated pilot reactor helps to determine the optimal experimental conditions of the process in a semi-industrial scale. Reclaimed carbon fibers from optimized steam-thermolysis appear resin free and exhibit over 90% of their original tensile strength. The gas and liquid phases emitted from the process have also been analyzed quantitatively. The flow modeling of the reactor and the simulation of the polymer thermal degradation are in close agreement with the experimental observations. The life cycle assessment shows that the CFRP recycling can be environmentally beneficial compared to the disposal scenario.

The purpose of this study was to investigate whether a meal supplement fortified with micronutrients would, statistically, significantly improve the intelligence scores of Grade 3 and 4 learners. The data collection procedures in this study took the form of a pre-test – post-test control group design. The Paper and Pencil Games (PPG) Level 3, a standardised psychological test, was administered before and after the respondents were exposed to the meal supplements. For a treatment period of 16 weeks the experimental group received the meal supplement fortified with micronutrients and the control group the meal supplement without any added micronutrients. Data analysis took the form of statistical analysis to determine whether the meal supplements consumed by those in the experimental group could significantly contribute to improving their intelligence scores. The results indicated statistically significant increases in scores, between the pretest and post-test on the various scales of the PPG, of both the experimental and control group on the one hand, but no statistically significant differences between the two treatment groups on the post-test on the other. The null hypothesis that there are no (statistically significant) differences between the average post-test scores (V, NV, and T) of the experimental and control groups could not be rejected. However, the increase between the pre-test and post-test stanine scores of the two treatment groups has led to recommendations for further research. Copyright / Dissertation (MEd)--University of Pretoria, 2011. / Educational Psychology / unrestricted

The submitted thesis is focused on the development, optimization, testing and practical application of the new microextraction method called Bell Shaped Extraction Device assisted Liquid-Liquid Microextraction (BSED-LLME). The method is based on the application of a miniature bell-shaped extraction tool in which the extraction takes place, so that only minimal solvent losses can occur, and which allows a reproducible dosing and collection of a small volume of the extraction solvent. The BSED- LLME method was used to preconcentrate selected volatile and less volatile analytes from aqueous samples into organic solvents of a density lower than water. After the extraction, the analytes were determined by fast gas chromatography with flame ionization detection and gas chromatography with mass spectrometry. The statistical methods known as Design of Experiment (DOE) were used for determination of the optimal extraction conditions for BSED-LLME procedure. DOE is based on a mathematical description of the system and the prediction of the optimal setting of experimental parameters that may influence extraction efficiency. Factors such as extraction time, volume of extraction solvent, addition of sodium chloride (ionic strength), stirring rate and the diameter of the extraction vessel ect., have been tested....

This study was intended to evaluate the impact of socioeconomically disadvantaged children's participation in the Texas Home Instruction for Parents of Preschool Youngsters (TX HIPPY) Program on their school readiness and academic achievement. The study used a quasi-experimental design and applied full and optimal propensity score matching (PSM) to address the evaluation concern of the impact of the TX HIPPY program on HIPPY participants' academic achievement compared to non-HIPPY participants. This evaluation targeted former HIPPY participants and tracked them in the Dallas ISD database through Grade Levels K-8. Data were obtained by administering Istation's Indicators of Progress (ISIP) for kindergarten, TerraNova/SUPERA for Grades K-2, and State of Texas Assessments of Academic Readiness for math and reading (STAAR) for Grades 3-8. HIPPY and non-HIPPY groups were matched using propensity score analysis procedures. The evaluation findings show that the TX HIPPY program positively influences kindergarten students to start school ready to learn. The findings of math and reading achievements suggest that HIPPY children scored at the same level or higher than non-HIPPY children did on math and reading achievement, indicating that TX HIPPY program has achieved its goal of helping children maintain long-term academic success. However, the evaluation findings also indicated that the impact evaluation framework must be designed with attention to higher-level factors beyond academic achievement that influence children's academic success.

<p>Driven by various benefits, such as authenticity, enjoyment, sustainability, socialization, and uniqueness, peer-to-peer (P2P) accommodation has become an increasingly important socio-economic phenomenon. To study this emerging hospitality consumption format systematically and to enhance the understanding of consumers’ motivations, perceptions, and behavioral intentions in the P2P accommodation context, three projects were proposed and completed in this dissertation. These focused on the mechanisms underlying consumers’ perceptions and participation in the world of P2P accommodation. Project I provided a comprehensive overview of how diverse motivators can influence consumers’ satisfaction and loyalty toward P2P accommodation services, following the push and pull theoretical framework. By conducting a meta analysis, Project I revealed that improving push motivators (i.e., psychological and intrinsic motivators) is more important than pull motivators (i.e., cognitive and extrinsic motivators) in enhancing consumers’ satisfaction, re-patronage intentions, and the spreading of positive word-of-mouth interactions. Next, by employing the dual-process theory, Project II comprised a series of three studies to investigate how various types of online reviews (i.e., fact-based versus emotion-based; property-focused versus host-focused) can affect consumers’ consumption decisions pertaining to P2P accommodation. The findings revealed that fact-based reviews result in higher booking intentions due to enhanced trust in the P2P property/host. Moreover, it was found that female consumers exhibit higher booking intentions when they read host-focused reviews. Finally, drawing on the norm activation theory, Project III comprised an investigation into how consumers’ altruistic value versus egoistic value orientations impacted their consumption intentions of sustainable P2P accommodation. Furthermore, by employing both survey and experimental design studies, the underlying mechanism explaining the impacts of various consumption value orientations on behavioral intentions was explored, focusing on booking intentions and willingness-to-pay-more for sustainable green P2P accommodation. Bringing these findings together, this dissertation provides theoretical and practical implications from various perspectives with regard to how consumers’ motivators and perceptions lead to their participation in the P2P accommodation world.</p>

The No Child Left Behind Act of 2001 demanded that public schools demonstrate adequate yearly progress by increasing student educational achievements. In 2014, the local high school at this study enrolled 62.7% socioeconomically disadvantaged students and implemented a precollege intervention program; however, little is known about its efficacy due to a lack of a formal evaluation, prohibiting an informed approach to continual improvement. The purpose of this program evaluation was to determine if program participation resulted in the higher academic outcomes. Guided by the theory of change, the program evaluation was used to assess the efficacy of the local high school's year-long precollege intervention program in a convenience sample of 112 Grade 9 students. The research questions examined the difference between the program participants and non-participants' academic outcomes including grade point average and semester course grades in math, English, science, and social science from Semester 1 to Semester 2 in the 2014-2015 school year. Independent samples t tests were used to identify whether there was a significance difference between the mean-scores of the intervention and control groups. The results indicated that the program did not significantly impact the participants' academic outcomes, and the program goals were not met. The evaluation report included the results, provided recommendations to increase understanding of the intervention program and students' needs, inform and engage stakeholders, redesign program goals, allocate resources, and streamline program activities. The improved program model could enhance students' academic outcomes and lead to higher high school graduation and college enrollment rates for students.

Statistical research can be more difficult to plan than other kinds of projects, since the research must adapt as knowledge is gained. This dissertation establishes a formal language and methodology for designing experimental research strategies with limited resources. It is a mathematically rigorous extension of a sequential and adaptive form of statistical research called response surface methodology. It uses sponsor-given information, conditions, and resource constraints to decompose an overall project into individual stages. At each stage, a "parent" decision-maker determines what design of experimentation to do for its stage of research, and adapts to the feedback from that research's potential "children", each of whom deal with a different possible state of knowledge resulting from the experimentation of the "parent". The research of this dissertation extends the real-world rigor of the statistical field of design of experiments to develop an deterministic, adaptive algorithm that produces deterministically generated, reproducible, testable, defendable, adaptive, resource-constrained multi-stage experimental schedules without having to spend physical resource.

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Printed circuit boards (PCBs) are essential components in various electronic devices, playing a vital role in their functionality. Over time, PCBs have evolved significantly, becoming smaller, more complex, and multi-layered to meet the demands of advancing technology and consumer preferences. The quality of solder paste deposits is measured by circularity, volume, positioning, and the number of satellites. Mycronic is a supplier of jet printing machines for PCB manufacturers and needs to investigate and counteract an unwanted variation in volume and positioning within the first dot of the solder paste strip, and its so-called “sea saw” effect for the following three dots.  This master’s thesis has two aims. The first aim is to develop and evaluate an experimental method to reduce variation between the dots in the strip. The second aim is to reduce the variation between the 1st dot and the following three dots by finding a combination of pre-feed, first, second, and third waveforms to obtain improved precision, volume, circularity, and reduced volume variation. Using an experimental design a full factorial design was used, examining six experimental factors. The design was further augmented with a central composite design to describe the second-order model. The knowledge from the experiment was used to optimize and improve the quality factors of jet printing, which were verified with an additional experiment. The results of the study provided compelling evidence that only the selected experimental factors had a significant impact on improving the volume metric. It was observed that the presence or absence of satellites during the experiment did not have any effect on the results, and neither did the positioning and circularity factors contribute to any improvement or deterioration. Specifically, the most significant difference in volume between 1st and following three dots for the optimized solution is 0.5 nl, and the currently used settings have a difference of 2.65 nl. The experimental approach employed in this master's thesis holds excellent promise for Mycronic, as it paves the way for the future development of piezo-actuation profiles (i.e. specific settings for the jet printer). The potential contributions to the industry are significant, particularly in terms of advancing the methodology for investigating and enhancing the quality metrics of piezo-actuation profiles through experimental means. This research opens up new avenues for Mycronic to refine its printing processes and improve overall print quality, ultimately leading to better outcomes for their customers.