<p>Evidence suggests that a change in the firing rate of dopamine (DA) cells is a major neurobiological correlate of learning. The Temporal Difference (TD) learning algorithm provides a popular account of the DA signal as conveying the error between expected and actual rewards. Other accounts have attempted to code the DA firing pattern as conveying surprise or salience. The DA mediated cells have also been implicated in several neuropsychological disorders such as obsessive compulsive disorder and schizophrenia. Compelling neuropsychological explanations of the DA signal also frame it as conveying salience. A model-based reinforcement learning algorithm using a salience signal analogous to dopamine neurons was built and used to model existing animal behavioral data.</p> <p>Different reinforcement learning models were then compared under conditions of altered DA firing patterns. Several differing predictions of the TD model and the salience model were compared against animal behavioral data in an obsessive compulsive disorder (OCD) model using a dopamine agonist. The results show that the salience model predictions more accurately model actual animal behavior.</p> <p>The role of context in the salience model is different than the standard TD-learning algorithm. Several predictions of the salience model for how people should respond to context shifts of differing salience were tested against known behavioral correlates of endogenous dopamine levels. As predicted, individuals with behavioral traits correlated with higher endogenous dopamine levels are far more sensitive to low salience context shifts than those with correlates to lower endogenous dopamine levels. This is a unique prediction of the salience model for the DA signal which allows for better integration of reinforcement learning models and neuropsychological frameworks for discussing the role of dopamine in learning, memory and behavior.</p> / Doctor of Science (PhD)

Previous research has demonstrated associations between deliberate self-harm (DSH) and perfectionism, although most of that research used retrospective self-report measures of DSH, which are prone to various cognitive biases. Although perfectionism has been associated with alcohol abuse, no research has examined how alcohol intoxication may moderate the relation between perfectionism and DSH. The aims of this experimental study were to determine if perfectionism is associated with a laboratory analogue of DSH (the Self-Aggression Paradigm) and examine the role of alcohol intoxication as a potential moderator. Using archival data, blood alcohol content (BAC) was manipulated by randomly assigning participants to reach one of four target BACs. Results indicated that perfectionism was not associated with DSH (mean self-administered shock or number of “severe” shocks). There was no interaction between perfectionism and BAC. These findings are discussed within the context of the perfectionism measure’s psychometric characteristics and the strength of previous research findings.

Math to Mastery (MTM) is a multi-component math intervention that has demonstrated effective results in building math fluency and skill acquisition. Few studies have explored the use of brief experimental analysis (BEA) procedures to create an individualized, abbreviated MTM intervention to address skill deficits in basic math. The purpose of this current study is to analyze the utility of randomizing BEA procedures to effectively identify necessary mathematic components to create a more efficient intervention that will yield the highest math gains among participants. Researchers used an alternating treatment design with an extended analysis phase to address basic math skills. Participants included three grade school students with difficulty across different core math skills including addition, subtraction, multiplication, and division. Overall, this study yielded mixed results. Results indicated an abbreviated MTM intervention was effective for 1 out of 3 participants. Results, limitations, implications, and future research are also discussed.

Thermal energy storage systems as an integral part of concentrated solar power plants improve the performance of the system by mitigating the mismatch between the energy supply and the energy demand. Using a phase change material (PCM) to store energy increases the energy density, hence, reduces the size and cost of the system. However, the performance is limited by the low thermal conductivity of the PCM, which decreases the heat transfer rate between the heat source and PCM, which therefore prolongs the melting, or solidification process, and results in overheating the interface wall. To address this issue, heat pipes are embedded in the PCM to enhance the heat transfer from the receiver to the PCM, and from the PCM to the heat sink during charging and discharging processes, respectively. In the current study, the thermal-fluid phenomenon inside a heat pipe was investigated. The heat pipe network is specifically configured to be implemented in a thermal energy storage unit for a concentrated solar power system. The configuration allows for simultaneous power generation and energy storage for later use. The network is composed of a main heat pipe and an array of secondary heat pipes. The primary heat pipe has a disk-shaped evaporator and a disk-shaped condenser, which are connected via an adiabatic section. The secondary heat pipes are attached to the condenser of the primary heat pipe and they are surrounded by PCM. The other side of the condenser is connected to a heat engine and serves as its heat acceptor. The applied thermal energy to the disk-shaped evaporator changes the phase of working fluid in the wick structure from liquid to vapor. The vapor pressure drives it through the adiabatic section to the condenser where the vapor condenses and releases its heat to a heat engine. It should be noted that the condensed working fluid is returned to the evaporator by the capillary forces of the wick. The extra heat is then delivered to the phase change material through the secondary heat pipes. During the discharging process, secondary heat pipes serve as evaporators and transfer the stored energy to the heat engine. Due to the different geometry of the heat pipe network, a new numerical procedure was developed. The model is axisymmetric and accounts for the compressible vapor flow in the vapor chamber as well as heat conduction in the wall and wick regions. Because of the large expansion ratio from the adiabatic section to the primary condenser, the vapor flow leaving the adiabatic pipe section of the primary heat pipe to the disk-shaped condenser behaves similarly to a confined jet impingement. Therefore, the condensation is not uniform over the main condenser. The feature that makes the numerical procedure distinguished from other available techniques is its ability to simulate non-uniform condensation of the working fluid in the condenser section. The vapor jet impingement on the condenser surface along with condensation is modeled by attaching a porous layer adjacent to the condenser wall. This porous layer acts as a wall, lets the vapor flow to impinge on it, and spread out radially while it allows mass transfer through it. The heat rejection via the vapor condensation is estimated from the mass flux by energy balance at the vapor-liquid interface. This method of simulating heat pipe is proposed and developed in the current work for the first time. Laboratory cylindrical and complex heat pipes and an experimental test rig were designed and fabricated. The measured data from cylindrical heat pipe were used to evaluate the accuracy of the numerical results. The effects of the operating conditions of the heat pipe, heat input, and portion of heat transferred to the phase change material, main condenser geometry, primary heat pipe adiabatic radius and its location as well as secondary heat pipe configurations have been investigated on heat pipe performance. The results showed that in the case with a tubular adiabatic section in the center, the complex interaction of convective and viscous forces in the main condenser chamber, caused several recirculation zones to form in this region, which made the performance of the heat pipe convoluted. The recirculation zone shapes and locations affected by the geometrical features and the heat input, play an important role in the condenser temperature distributions. The temperature distributions of the primary condenser and secondary heat pipe highly depend on the secondary heat pipe configurations and main condenser spacing, especially for the cases with higher heat inputs and higher percentages of heat transfer to the PCM via secondary heat pipes. It was found that changing the entrance shape of the primary condenser and the secondary heat pipes as well as the location and quantity of the secondary heat pipes does not diminish the recirculation zone effects. It was also concluded that changing the location of the adiabatic section reduces the jetting effect of the vapor flow and curtails the recirculation zones, leading to higher average temperature in the main condenser and secondary heat pipes. The experimental results of the conventional heat pipe are presented, however the data for the heat pipe network is not included in this dissertation. The results obtained from the experimental analyses revealed that for the transient operation, as the heat input to the system increases and the conditions at the condenser remains constant, the heat pipe operating temperature increases until it reaches another steady state condition. In addition, the effects of the working fluid and the inclination angle were studied on the performance of a heat pipe. The results showed that in gravity-assisted orientations, the inclination angle has negligible effect on the performance of the heat pipe. However, for gravity-opposed orientations, as the inclination angle increases, the temperature difference between the evaporator and condensation increases which results in higher thermal resistance. It was also found that if the heat pipe is under-filled with the working fluid, the capillary limit of the heat pipe decreases dramatically. However, overfilling of the heat pipe with working fluid degrades the heat pipe performance due to interfering with the evaporation-condensation mechanism. / Mechanical Engineering

High-speed craft are in high demand in the maritime industry, for example, in maintenance operations for offshore structures, for search and rescue, for patrolling operations, or as leisure craft to deliver speed and excitement. Design and operation of high-speed craft are often governed by the hydrodynamic phenomena of slamming, which occur when the craft impact the wave surface. Slamming loads affect the high-speed craft system; the crew, the structure and various sub-systems and limit the operation. To meet the ever-increasing demands on safety, economy and reduced environmental impact, there is a need to develop more efficient high-speed craft. This progression is however limited by the prevailing semi-empirical design methods for high-speed planing craft structures. These methods provide only a basic description of the involved physics, and their validity has been questioned. This thesis contributes to improving the conditions for designing efficient highspeed craft by focusing on two key topics: evaluation and development of the prevailing design methods for high-speed craft structures, and development towards structural design based on first principles modeling of the slamming process. In particular a methodological framework that enables detailed studies of the slamming phenomena using numerical simulations and experimental measurements is synthesized and evaluated. The methodological framework involves modeling of the wave environment, the craft hydromechanics and structural mechanics, and statistical characterization of the response processes. The framework forms the foundation for an extensive evaluation and development of the prevailing semi-empirical design methods for high-speed planing craft. Through the work presented in this thesis the framework is also shown to be a viable approach in the introduction of simulation-based design methods based on first principles modeling of the involved physics. Summarizing, the presented methods and results provide important steppingstones towards designing more efficient high-speed planing craft. / <p>QC 20160907</p>

The aim of this study was to examine associations between biases in decision-making (delay discounting [DD], opportunity cost neglect [OCN], status quo bias [SQB]), educational attainment, and use of cigarettes and other tobacco and nicotine delivery products among women of reproductive age. Women of reproductive age are of special interest because of the additional risks that cigarette smoking or use of these other products represents should they become pregnant. Data were collected anonymously online in survey format using Amazon Mechanical Turk [AMT]. Participants were 800 women of reproductive age (24-44 years) from across the US. Half (n = 400) were smokers who reported current, daily smoking and half (n = 400) were never smokers who reported smoking less than 100 cigarettes in their lifetime. Participants reported smoking characteristics, plans to quit smoking, use of nicotine replacement therapies, use of other tobacco and nicotine delivery products, alcohol and drug use histories, and the Fagerström Test for Nicotine Dependence. Participants completed two measures for each of the three biases in decision-making, the Barratt Impulsiveness Scale [BIS-11], and two scales measuring short- and long-term propensity to plan for money expenditures [PPMS and PPML]. Educational attainment analyses compared three education groups: high school or less vs. some college (e.g. some college/A.A.) vs. B.A. or higher. DD was steeper among current vs. never smokers and for women with lower vs. higher levels of education, with no significant interaction between smoking and education. Modifying the instructions of the DD measure to make the zero option explicit reduced DD similarly across levels of smoking status and education. OCN was worse at lower vs. higher educational attainment on one OCN measure, with no significant effect of smoking status or interaction between opportunity cost neglect and educational attainment on either measure. No evidence was found for stronger SQB by smoking status or education. Smoking status was related to BIS Total, BIS Motor and Nonplanning subscales and to PPML in initial models but remained significant after adjusting for baseline differences in participant characteristics only for BIS Motor subscale and educational attainment was related only to BIS Nonplanning subscale. Preliminary comparisons of e-cigarette users to non-users suggest smokers using e-cigarettes only differ from smokers not using e-cigarettes on measures related to quitting smoking whereas within never smokers e-cigarette users demonstrated a pattern of riskier decision-making compared to non-users. Results confirm that DD and education are important to understanding the use of tobacco and nicotine products in women of reproductive age, and suggest that smoking and educational attainment are independently related to discounting rates. The observed explicit-zero framing effect suggests making alternatives more explicit when presenting choices may help reduce DD and lead to better decision-making, which has possible treatment implications. Results identify OCN as an additional decision-making bias to consider in understanding how low educational attainment might relate to smoking vulnerabilities. The preliminary examination of e-cigarette use suggests for women of reproductive age above age 24 years, e-cigarette use among current smokers may reflect desire or attempts to quit or cut back on smoking whereas e-cigarette use among non-smokers may be a marker of a more impulsive, riskier repertoire, although additional study of this question is needed.

Inhalants are a loosely defined diverse group of volatile substances which people abuse. Despite widespread misuse of inhalants, there are limited preclinical methods available to study the reinforcement-like properties of inhalants. One procedure which has demonstrated substantial promise as a tool to investigate inhalant pharmacology is the intracranial self-stimulation (ICSS) procedure. ICSS utilizes pulses of electrical stimulation to the mesolimbic reward pathway to serve as a temporally defined and controlled operant reinforcer with a highly adjustable efficacy. The first aim of the project was to characterize the effects of commonly abused inhalants: including toluene, trichloroethane, nitrous oxide, isoflurane and R134a in ICSS. The second aim was to attenuate inhalant-facilitated ICSS by utilization of compounds which would attenuate the pharmacological actions of toluene on GABAA receptors. The low efficacy benzodiazepine negative modulator Ro15-4513 significantly attenuated the ability of toluene to facilitate ICSS without itself significantly altering baseline ICSS responding. Pretreatment with Ro15-4513 also attenuated methamphetamine ICSS even though there is no evidence of methamphetamine interacting with GABAA receptors. Given these unexpected results, I employed a microdialysis procedure to examine the effect of Ro15-4513 on methamphetamine stimulated dopamine release in the nucleus accumbens. Pretreatment with Ro15-4513 significantly attenuated methamphetamine stimulated dopamine release while having a negligible effect on dopamine release when administered alone. These results suggest that a modest level of benzodiazepine-site negative modulation can reduce the reinforcement enhancing effects of abused drugs regardless of their primary mechanism of action through allosteric modulation of GABAergic neurons within the mesolimbic pathway. Further, these results may have implications for expanding the examination of GABAA negative modulator medications beyond those trials currently being conducted with alcohol. Finally, the effects of chronic intermittent toluene exposure on ICSS and nesting behaviors were examined. Subjects were systemically exposed to air, chronic intermittent toluene (CIT), or escalating chronic intermittent (ECIT) toluene for 15 min at 3300 PPM toluene vapor per exposure. The results show that ECIT resulted in decreased overall responding in ICSS relative to air control and showed a tolerance-like effect to facilitatory effects of 3300 ppm toluene during ICSS compared to CIT group. These results indicate that escalating use of toluene produces reductions in its reward-like effects and may contribute to escalation to other drugs of abuse.

A proposta central desta tese é o desenvolvimento de estratégias de modelagem computacional de estruturas de concreto reforçadas com CFRP (Carbon Fiber Reinforced Polymer). Foram utilizados neste estudo os programas computacionais DIANA (plataforma comercial), QUEBRA2D e FEMOOP (plataformas acadêmicas de desenvolvimento). Em cada um dos programas foram implementados ou utilizados modelos constitutivos existentes apropriados para cada fase do sistema estrutural. Implementaram-se modelos constitutivos apropriados para o concreto, para as armaduras de aço, para os polímeros FRP e suas interfaces, a fim de representar o sistema estrutural reforçado com os compósitos. Elementos finitos de interface e de barras de treliça foram implementados (formulações discreta e incorporada) para a representação numérica das armaduras e dos compósitos, bem como de suas interfaces com o concreto. Em complementação às análises numéricas desenvolveram-se ensaios experimentais de vigas de concreto armado reforçadas com fibras de carbono - flexão e cisalhamento - de seção transversal retangular e \"T\". Esses ensaios, assim como outros disponíveis na literatura, são essenciais para uma melhor interpretação sobre a eficiência do reforço e também para a validação da capacidade de modelagem numérica desenvolvida. Foram avaliadas as eficiências dos sistemas de compósitos de fibra de carbono aplicados em reforços de vigas submetidas à flexão e ao cisalhamento, bem como os seus mecanismos de colapso mediante a aplicação de carregamentos monotônicos. Complementarmente, efetuaram-se análises comparativas com os modelos de dimensionamento sugeridos por diferentes normas técnicas ou disponíveis na literatura técnica. / The purpose of this thesis is the development of strategies for computational modeling of reinforced concrete structures strengthened with CFRP (Carbon Fiber Reinforced Polymer). The software systems DIANA (commercial system), QUEBRA2D and FEMOOP (academic systems) have been utilized. In each program appropriate constitutive models have been implemented or existing ones used for representing each phase of the structural system. Appropriate constitutive models for concrete, rebars, CFRP reinforcement and bond-slip interfaces have been implemented and adjusted to represent the behavior of the composite system. Interface and truss finite elements have been implemented (discrete and embedded approaches) to represent rebars and CFRP\'s, as well their interfaces with concrete. An experimental study of reinforced concrete beams with rectangular and \"T\" cross sections strengthened with CFRP - under bending and shear - have been realized to complement the numerical study. These tests, as well as others available in the literature, are very useful for a better understanding of the strengthening capacity of the CFRP\'s and also for the validation of the proposed computational modeling. The efficiency of CFRP systems for bending and shear strengthening has been evaluated, as well as the collapse mechanisms observed under monotonic loads. In addition comparative analyses with design models prescribed by different codes of practice and others proposed in the literature have been carried out.

Este trabalho descreve uma pesquisa experimental de lajes cogumelo de concreto armado com armadura de cisalhamento, sem envolver a armadura de flexão. Onze lajes cogumelo quadradas de concreto com 200 mm de espessura e 3000 mm de lado, com uma área central carregada de 200 mm de lado, foram testadas até a ruptura. O principal objetivo dos ensaios foi investigar a eficiência de se utilizar esse tipo de armadura de cisalhamento sem envolver a armadura de flexão. Todas as lajes romperam por punção, com cargas de ruptura superiores em até 110%, em relação às cargas de ruptura em lajes similares sem armadura de cisalhamento, demostrando a eficiência da armadura. Foram realizadas também simulações numéricas utilizando modelos axissimétricos e tridimensionais, de lajes cogumelo de concreto armado, com o objetivo de reproduzir numericamente alguns resultados obtidos por pesquisadores e documentados na literatura, validando a parte experimental e a modelagem numérica. As simulações numéricas nãolineares foram realizadas com programa DIANA, e o modelo de fissuração do concreto adotado foi o distribuído (smeared crack). Foram analisados os resultados de cargas últimas e tipos de ruptura, fissuração, deformações nas armaduras e no concreto e as curvas carga x deslocamento. / This work reports experimental research of reinforced concrete flat slabs with use of shear reinforcement not embracing the flexural reinforcement. Eleven square reinforced concrete flat slabs with 200 mm thickness and 3000 mm side lengths, with a square central column of 200mm of side, were tested up to failure. The main objective was to investigate the efficiency of using the mentioned shear reinforcement. All slabs failed by punching and the ultimate loads were superior in up to 110% in relation to slabs without shear reinforcement, demonstrating the efficiency of the reinforcement. The numerical simulations using axisymmetric and three dimensional analyses, of reinforced concrete flats slabs, were carried out with the objective of reproducing some experimental results reported by different investigators, validating the experimental part and also the numerical modelling . The numerical simulations were performed with the software package DIANA, adopting the smeared crack approach to reproduce the concrete behaviour under shear and tension. The evaluated results were mode of failure, strain in steel and loaddeflections curves.

Com o crescente uso de estruturas de membrana tensionada, as relações tensãodeformação do tecido utilizado em sua fabricação devem ser bem entendidas. Deste modo, esta dissertação apresenta um estudo sobre o comportamento mecânico de um tecido arquitetônico PTFE-vidro, ressaltando seu complexo mecanismo de deformação que engloba efeitos de anisotropia, não-linearidade física, troca de ondulações, histerese, remoção do espaçamento entre os fios e variação de temperatura. Diferentes métodos para modelagem do material foram estudados, com ênfase no modelo de material ortótropo representado por um funcional energia de deformação hiperelástico. Além disso, vários protocolos para ensaios de tração em tecidos recobertos foram analisados e uma série de ensaios biaxiais com amostras cruciformes foram realizados no Centro de Pesquisa e Desenvolvimento da Birdair, Inc. Um determinado funcional energia de deformação foi então ajustado aos dados de campo obtidos nestes testes, cujos resultados foram então comparados diretamente aos dados obtidos em campo e a um ajuste direto de uma superfície suave tensão-deformação. A performance do modelo ajustado não se encontra ainda em um patamar de aplicação industrial, entretanto este estudo permite um entendimento global dos mecanismos de deformação do tecido PTFEvidro, fornecendo também uma massa de dados consistentes que podem ser utilizados em situações práticas. / Considering the growing use of tensioned membrane structures, the stress-strain relation of the fabric used on its construction must be well understood. This dissertation presents a study of the mechanical behavior of a PTFE coated fiberglass fabric, emphasizing its complex strain mechanism which is influenced by the material anisotropy, physical non-linearity, crimp interchange, hysteresis, removal of yarn spacing and changes in temperature. Different material models were studied, focusing on an orthotropic material model represented by a hyperelastic strain energy function. Also, different test protocols were reviewed and a series of biaxial tests on cruciform samples were performed at the Birdair, Inc.s Research and Development Center. A strain energy function was adjusted to the collected data and than its results compared to the data itself and to another stress-strain function directly adjusted to the data. The performance of the strain-energy function chosen is not on a level of industrial application; however this study gives a global understanding of the PTFE coated fiberglass strain mechanism and also provides a consistent database that may be used on real situations.