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Choosing a course of action in our daily lives requires an accurate assessment of the associated risks as well as the potential rewards. The present two studies investigated the mechanism of how reward and risk level influence the motor decisions of speeded actions (Chapter 2) and its neural dynamics (Chapter 3) by focusing on the beta band (15-30 Hz) oscillation patterns reflected in the EEG signals. Participants performed a modified version of the Go-NoGo task, in which they earned reward points based on the speed and accuracy of response. On each trial, the reward points at stake (120 vs. 6) and the probability that a Go signal would follow (Go-probability) were presented prior to a Go/NoGo signal (Trial Information Period). The behavioral results (from both Chapters 2 and 3) showed that larger amount of rewards can motivate people to respond faster, and this effect was modulated by the assessed risk, suggesting that decisions for actions are based on a systematic trade-off between rewards and risks. The EEG data showed that motor beta oscillations from the two studied brain regions reflected different levels of motivation towards a motor response across different reward and risk levels. Specifically, the lower beta power associated with higher reward and lower risk level. Collectively, the results provide a mechanistic understanding of how motivational cues are translated into action outcomes via modulating patterns of brain oscillations.

Air contamination strongly decreases the efficiency of fluid power systems and when the allowable limits are exceeded, the performance of the system deteriorates. The hydraulic reservoir performs the function of releasing the entrained air of the hydraulic system to the surroundings. In recent years, the reservoir design has become an important task in the design of the hydraulic system due to space restrictions forcing the use of small sized reservoirs. Despite this fact, experimental results on an air release are not available. In this paper, an experimental investigation of the air release in hydraulic reservoirs is presented. A test apparatus using an optical method as well as the post-processing of the results is described. These are given in terms of an air release rate for different reservoir designs over a wide range of oil flow rates and air loads. The current study is a significant step forward in the design of fluid power systems, as it provides an experimental procedure to measure the air release in the hydraulic reservoir as well as its quantitative analysis.

Sub-Saharan Africa has an underutilised solar resource that is available to provide distributed-scale power to rural communities that are not reached by the current grid systems that are in place. Renewable power generation systems are typically infeasible for this purpose due to their high manufacturing and maintenance costs. This research proposes to address this by experimentally investigating the performance of a micro-scale, solar thermal Rankine cycle with direct steam generation using an affordable solar collector design. The intended power generation range is between 0.1 and 1 kW, which can be used for the direct mechanical pumping of rural irrigation systems or municipal water supplies. The study focuses on the performance of the solar collector (the solar reflector and the solar receiver) under realistic solar thermal conditions in sub-Saharan Africa, as it is considered to be one of the most important components in the solar thermal Rankine cycle. The performance of the solar collector was first characterised in an optical analysis of the new faceted dish reflector design, which comprised six Mylar membranes stretched over the elliptical rims of television satellite dishes. The optical analysis was conducted with the main goal of determining how much concentrated solar radiation would intercept the experimental receiver aperture during solar testing. This was determined by measuring the reflectivity of the reflector facets through ultraviolet and visible light (UV-VIS) spectroscopy and producing an intercept factor trend as a function of receiver aperture size through photographic lunar flux mapping. Based on the spectroscopy analysis, the spectral reflectivity of the clean Mylar facets was determined to be 97% for the visible light spectrum. The intercept factor was determined to be 87% for the designed receiver aperture diameter of 135 mm. The thermal testing took place on a clear, sunny day with low wind velocities. The solar collector followed the arc of the sun throughout the day with a 1° tracking error. During the testing, municipal water was passed through the receiver at 0.284 g/s and the temperature and pressure within the receiver were recorded. A 91-minute testing period occurred, where the inlet and outlet process flows obtained relatively constant operating temperatures with the inlet temperature at 54 °C and the outlet temperature at 343 °C. The total solar irradiance dropped from 801 to 705 W/m2 during this testing period. Using a reflector with a total incident area of 2.73 m2, the total radiation intercepted at the aperture dropped from 1 845 to 1 625 W during this period. The total power capture by the working fluid averaged at approximately 861 W and the total rate of heat loss was determined to be between 1 000 and 750 W. An average collector efficiency of 42% and an average receiver efficiency of 49% were determined for the testing period. An analysis of the heat loss showed that approximately 84% of the heat was lost through the aperture, of which, 31% was from reflected radiation. The second-law analysis showed that most of the irreversibility in the solar collector was caused by absorption of the concentrated radiation at the coil surface. This was because of the large temperature difference between the sun and the receiver coils. The experimental thermal analysis highlighted the design challenges of the micro-scale thermal Rankine cycle. However, the analysis showed that a solar collector can be constructed using locally sourced, affordable materials and can be used to produce power at a micro-scale. With appropriate attention given to optimising the collector design and determining the optimum operating conditions of the solar receiver, the power cycle would be able to compete with current technologies to provide decentralised power to communities in need. / Dissertation (MEng)--University of Pretoria, 2019. / Technology Innovation Agency (TIA); National Research Foundation (NRF); Department of Science and Innovation (DSI) / Mechanical and Aeronautical Engineering / MEng (Mechanical) / Unrestricted

<p>Space and water heating contribute over 50% of all the residential building energy consumption and are especially major energy consumers in the cold climates. Meanwhile, conventional furnaces and boilers with energy efficiency limited to below 100% dominate the residential heating in the cold climate, and the electric vapor-compression heat pump capacity and efficiency decline drastically at low ambient temperatures. Thermally driven ammonia-based chemical adsorption (chemisorption) heat pump (CSHP) systems utilize the reversible chemical reaction between the ammonia vapor and solid sorbent to generate heat pumping effect, which can provide heating with much higher energy efficiency than existing cold-climate heating technologies. Despite the significant potential of energy efficiency improvement from existing technologies, most studies in the literature on chemisorption heat pump systems focus on adopting the technology for refrigeration and energy storage applications, with very limited investigations available for using the technology for producing heating in cold climates. </p> This thesis study is thus conducted to characterize the operation behavior and performance of a CSHP system under cold ambient conditions and further identify optimal design and control for such systems to achieve high performance. In this study, both experimental and modelling approaches are pursued to investigate a CSHP heating system from the perspective of the sorption material using the multiple-stage LiCl-ammonia reactions, to the novel adsorber component with hybrid heat pipe heat exchanger, and finally to the performance of the complete heat pump system. The experimental studies are based on a prototype CSHP system tested to identify the chemical kinetics of the sorption material, as well as the transient performance of the adsorber and the system. The calibrated chemical kinetics are then used in the development of a transient adsorber model to analyze the operation and improve design of the adsorber. The heating COP of the prototype system was measured to be 0.75-1.16 under ambient temperatures of 8-20 C. Finally, a dynamic system model is developed based on the dynamic models of the adsorber and other components in the system. The system model is validated against the experimental data and used to analyze the detailed energy flow and operation dynamic. Based on the inefficiencies revealed by the simulation of the current prototype system, an improved system design with reduced thermal mass and heat loss is introduced. Simulation of the improved system results in heating COP of 1.17 to 1.23 under -13.9 C to 8.3 C ambient, respectively.

Sexual minorities experience mental and physical health disparities in comparison to heterosexual individuals due to minority stress (Branstrom et al., 2016; Kerridge et al., 2017; Meyer, 2003). Positive psychology interventions have improved mental and physical health (Antoine et al., 2018; Lambert D'raven et al., 2015), and therefore these interventions have potential to address health disparities. The current study tested an identity-specific intervention (n = 30) to a general positive psychology intervention (n = 30) and a control group (n = 30) among sexual minorities. This built on a recent pilot study which tested the efficacy of an identity-specific intervention designed for sexual minorities and showed significant improvements in depressive and anxiety symptoms. Thus, I hypothesized that individuals in intervention conditions would have better mental health, physical health, and substance use outcomes than the control group. Additionally, outcomes of the identity-specific condition were compared to those of the general positive psychology intervention. Participants included 91 sexual minority adults that completed three surveys (baseline, one week after the intervention, one month follow-up) including outcomes measures (depressive symptoms, anxiety symptoms, problematic drinking, problems associated with drug use, well-being, and self-rated health), potential covariates (anticipated stigma, internalized stigma, concealment) and manipulation checks (self-compassion, forgiveness, optimism, coping using humor, social support seeking). Fifty-three participants completed interventions featuring five intervention tasks eliciting self-compassion, optimism, forgiveness, humor, and social support seeking. Analyses included descriptive statistics, bivariate correlations, and multilevel modeling. Compared to the control condition, results showed significantly greater improvements in well-being (b = .40, p = .013), self-rated health (b = -.42, p = .006), and problems associated with drug use (b = -.97, p = .004) among participants in the intervention conditions. No significant differences emerged for depressive symptoms, anxiety symptoms, or problematic drinking. Limitations include lack of power for analyses examining extended follow-up and comparing intervention types, as well as a number of history effects. Despite these limitations, the current study has potential to improve health outcomes and aid clinical practices. More research on positive psychology interventions with sexual minorities is needed.

That each is born with differing capacities and potentials is self-evident. Both students and teachers should accept as their right and duty the task of bringing to full fruition these latent potentialities. It is a cause of concern in the nation, among parents and teachers, and in later years among students themselves, that many of our youth fail to achieve that of which they are capable. This is a loss to society and a disappointment to the individual. The purpose of this study is to add to the growing fund of knowledge concerning factors related to this important area of education and the relationship of these factors to life's fulfillment

The current study was designed: (1) to develop an educational tool on female masturbation capable of reaching a wide audience of women with accurate and complete information on female masturbation; (2) to provide initial validation for the further educational usefulness of this tool and (3) to assess its potential ability for improving overall sexual functioning in women by possibly altering negative attitudes toward masturbation and/or by dis-inhibiting masturbatory behavior.

Recent research has shown that outcome favorability (Ryan & Ployhart, 2000) and perceived performance (Chan, Schmitt, Jennings, Clause, & Delbridge, 1998a) are key determinates of justice judgments, suggesting that self-serving bias is a critical mechanism in the formation of applicant reactions. However, organizational justice theory continues to be the dominant paradigm for understanding applicant reactions. Chan and Schmitt (2004) have suggested a far ranging agenda for research into reactions, which includes considering reactions in a longitudinal framework and considering the natural effect of time on reactions. The current study incorporates these theoretical approaches and addresses these gaps in the research by examining applicant reactions at four time points during and after a selection procedure. This study also uses a multi-dimensional measure of test taking motivation (TTM) based on expectancy theory which enables me to explicate the effect of test performance, expectations, and outcome feedback on each motivational component. Using a sample of 227 student participants, this study provides evidence that an applicant's expectations regarding the selection outcome and the selection outcome itself have strong effects on fairness perceptions and TTM. Some key findings are the following: I) negative selection decisions and negative expectations tend to reduce fairness perceptions and TTM in applicants, while for the most part, positive expectations and positive selection decisions do little to increase these reactions and 2) valence, or the desire for the job, seems to be the motivational component most affected by the selection procedure. These findings have important implications for future research into applicant reactions.