Several Arctic council reports conclude that oil spills are the most significant threat to the Arctic ecosystem. Some studies have shown that in-situ burning (ISB) of oil spills over water can remove more than 90% of the oil, and is the most promising technology for an efficient response to oil spills in the Arctic region. The definition of "In situ" is intentional, controlled burning of oil in place (i.e., without extracting or removing the oil first). Earlier studies [Bellino (WPI 2012), Farahani, (WPI 2014)] have investigated burning behavior of crude oil on ice, similar to what one would expect in sea-ice or bare lake ice conditions. The focus of the current study is to investigate the burning behavior of crude oil in snow, similar to oil spills in snow-covered land, or in snow covered sea ice in the Arctic. Understandably, due to the difference in packing density between ice/water and snow, the parameters that influence burning behavior of oil in snow are different compared to burning oil in the sea or ice conditions. The current experimental study shows that the snow behaves as a porous medium, and depending on the porosity and volume of the oil spill, two extreme behaviors are exhibited. In the case of an oil spill on snow with low porosity, the oil sinks easily to the bottom, and the burning involves, significant thermo capillary effects enabling the oil to rise up and burn. On the other hand, if the snow is less porous, most of the oil layer remains on the surface, approaching the case of an ice bed. However, the melting of snow due to flame heat flux causes a circulating flow pattern of the oil, whereby the hot layer at the surface moves down and comes back up due to capillary action. These processes, which have not been observed in the earlier studies, are physically explained in this study. The implications to overall efficiency of the burning process, which represents the amount of crude oil left in the snow after the burning process is discussed. The results will ultimately improve the strategies and the net environmental benefit of, and by it the success of, oil clean-up after an accidental spill on snow.

O presente trabalho envolve a análise experimental do efeito da deposição de nanopartículas por meio da ebulição em piscina na molhabilidade e na textura da superfície. Inicialmente, este estudo apresenta uma análise da literatura sobre métodos de avaliação do ângulo de contato, preparo de nanofluidos, procedimentos de avaliação da rugosidade e possíveis efeitos que a deposição de nanopartículas tem sobre a textura da superfície. Verificou-se para as superfícies recobertas com nanopartículas ângulos de contato próximos a zero e comportamento dinâmico para gotas de água depositadas sobre elas. Desta forma, optou-se por avaliar a molhabilidade qualitativamente através da análise da velocidade de espalhamento de uma gota depositada sobre a superfície recoberta. Caracterizou-se também a massa de nanopartículas depositadas, a morfologia e a rugosidade das superfícies. Efetuou-se o recobrimento das superfícies por meio da ebulição em piscina de nanofluidos a base de água deionizada contendo nanopartículas de Al2O3 (10, 20-30 e 40-80 nm), Cu (25 nm) e SiO2 (15 e 80 nm) para concentrações volumétricas de 0,001, 0,01, 0,1 e 0,5%, submetidos a tempos de ebulição de 15, 30, 45 e 180 minutos em superfícies de alumínio e aço inoxidável. Como resultado final deste estudo concluiu-se que a rugosidade superficial e a molhabilidade se elevam com a deposição das nanopartículas. Além disso, a molhabilidade aumenta com o incremento da área da superfície recoberta com aglomerados. / The present study concerns an investigation on the wettability and the surface texture behavior of flat aluminum and stainless steel plates covered with porous thin-films of nanoparticles obtained through pool boiling of nanofluids. Since the contact angle of the obtained surfaces is small and in many cases the deposited droplet exhibits a dynamic behavior, dynamic top-down analyses of spreading droplets were performed. Evaluations were performed of nanoparticles mass deposition on the sample, surface roughness and micro-structural with an SEM (Scanning Electron Microscopy). Experiments were performed for nanofluids containing nanoparticles of Al2O3 (10, 20-30 and 40-80 nm), Cu (25nm) and SiO2 (15 and 80 nm) for volumetric concentrations of 0.001, 0.01, 0.1 and 0.5% for pool boiling time set to 15, 30, 45 and 180 minutes over aluminum and stainless steel plates. As a final result of this study it was found that surface roughness and wettability increase with the deposition of the nanoparticles. In addition, the wettability increases with increasing of the surface area covered with clusters.

Previous psychological literature has shown mathematics anxiety in older populations to have an association with many factors, including an adverse effect on task performance. However, the origins of mathematics anxiety have, until recently, received limited attention. It is now accepted that this anxiety is rooted within the early educational years, but research has not explored the associated factors in the first formal years of schooling. Based on previous focus groups with children aged 4-7 years, ‘numeracy apprehension’ is suggested in this body of work, as the foundation phase of negative emotions and experiences, in which mathematics anxiety can develop. Building on this research, the first piece of research utilized 2 interviews and 5 focus groups to obtain insight from parents (n=7), teachers (n=9) and mathematics experts (n=2), to explore how children experience numeracy and their observations of children’s attitudes and responses. Thematic and content analysis uncovered a range of factors that characterised children’s numeracy experiences. These included: stigma and peer comparisons; the difficulty of numeracy and persistent failure; a low sense of ability; feelings of inadequacy; peer evaluation; transference of teacher anxieties; the right or wrong nature of numeracy; parental influences; dependence on peers; avoidance and children being aware of a hierarchy based on numeracy performance. Key themes reflected the focus group findings of children aged 4-7 years. This contributed to an item pool for study 2, to produce a first iteration of the Numeracy Apprehension Scale (NAS) that described day-to-day numeracy lesson situations. This 44-item measure was implemented with 307 children aged 4-7 years, across 4 schools in the U.K. Exploratory factor analysis led to a 26-item iteration of the NAS, with a 2-factor structure of Prospective Numeracy Task Apprehension and On-line Number Apprehension, which related to, for example, observation and evaluation anxiety, worry and teacher anxiety. The results suggested that mathematics anxiety may stem from the initial development of numeracy apprehension and is based on consistent negative experiences throughout an educational career. The 26-item iteration of the NAS was further validated in study 3 with 163 children aged 4-7 years, across 2 schools in the U.K. The construct validity of the scale was tested by comparing scale scores against numeracy performance on a numeracy task to determine whether a relationship between scale and numeracy task scores was evident. Exploratory factor analysis was again conducted and resulted in the current 19-item iteration of the NAS that related to a single factor of On-line Number Apprehension. This related to the experience of an entire numeracy lesson, from first walking in to completing a task and was associated with, for example, explaining an answer to the teacher, making mistakes and getting work wrong. A significant negative correlation was observed between the NAS and numeracy performance scores, suggesting that apprehensive children demonstrate a performance deficit early in education and that the NAS has the potential to be a reliable assessment of children’s numeracy apprehension. This empirical reinforces that the early years of education are the origins of mathematics anxiety, in the form of numeracy apprehension.

Amebas de vida livre (AVL) são distribuídas mundialmente no solo e na água. Um número pequeno delas é considerado importante para a saúde dos seres humanos: Acanthamoeba spp., Naegleria fowleri, Balamuthia mandrillaris e Sappinia diploidea. Algumas das infecções são oportunistas, ocorrendo em indivíduos imunocomprometidos, enquanto outras são não oportunistas. Amostras de água foram coletadas de banheira de hidromassagens e piscinas térmicas na cidade de Porto Alegre, RS, Brasil, com o objetivo de determinar a presença de Acanthamoeba, bem como realizar a caracterização fenotípica e genotípica dos isolados. Amebas foram isoladas em cultivo monoxênico com Escherichia coli. A identificação dos isolados foi baseada na morfologia dos cistos e na amplificação por PCR com oligonucleotídeos gênero-específico. De 72 amostras analisadas, 20 (27,77%) foram positivas para amebas de vida livre, e identificadas morfologicamente como pertencentes ao gênero Acanthamoeba. Destas, 11 possuíam características compatíveis com o grupo morfológico II e 9 com o grupo III. Entre os isolados, 11(55%) foram considerados potencialmente patogênicos a partir de testes de osmotolerância e termotolerância. Somente 9 isolados quando submetidos à Reação da PCR, confirmaram pertencer ao gênero Acanthamoeba. A análise do sequenciamento através da comparação das sequências dispostas no GenBank, demonstrou a distribuição nos grupos genotípicos T3 (11,1%), T5 (11,1%), T4 (33,3%) e T15 (44,4%).Os resultados obtidos com este confirmam a presença de isolados potencialmente patogênicos que podem representar um risco à saúde humana nos ambientes de banheiras de hidromassagem e piscinas térmicas. / Free-living amoebae (FLA) are widely distributed in soil and water. A few number of them are implicated in human disease: Acanthamoeba spp., Naegleria fowleri, Balamuthia mandrillaris and Sappinia diploidea. Some of the infections were opportunistic, occurring mainly in immunocompromised hosts, while others are non opportunistic. Water samples were collecyed from both hot tubs and thermal swimming pools in the city of Porto Alegre, RS, Brazil, to determine the presence of Acanthamoeba in the water as well as perform the phenotypic and genotypic characterization of the isolates. Amoebae were isolated in monoxenic culture with Eschererichia coli. The identification of the isolates was based on the cysts morphology and PCR amplification using genus-specific oligonucleotides. From 72 samples analyzed, 20 (27,77%) were positive for free-living amoebae, and the isolates were morphologically identified as belonging to the genus Acanthamoeba. Out of these, 11 presented morphological characteristics compatible with group II, and 9 with group III. Among the isolates, 11 (55%) were considered potentially pathogenic according to osmotolerance and temperature assays. The isolates when submitted to PCR reaction only 9 were confirmed as belonging to the genus Acanthamoeba. The sequences analysis when compare to the sequences in the GenBank, showed that genotype distribution in group T3 (11,1%), T5 (11,1%), T4 (33,3%) and T15 (44,4%). The results of this study confirmed the presence of potentially pathogenic isolates of free living amoebae in hot swimming pool and spas which can present risks to human health.

Fire is one of the main hazards associated with storage tanks containing flammable liquids. These tanks are usually closely spaced and in large groups, so where a petroleum fire occurs, adjacent tanks are susceptible to damage leading to further development of the fire. The structural behaviour such as thermal stability and failure modes of the tanks under such fire scenario are very important to the safety design and assessment of oil depots. However, no previous studies on this problem are known to the best knowledge of the author. This thesis presents a systematic exploration of the potential thermal and structural behaviours of an oil tank when one of its neighbour tanks is on fire. Under such scenario, the oil tanks are found to easily buckle under rather moderate temperature rises. The causes of such buckling failures are the reduced modulus of steel at elevated temperatures, coupled with thermally-induced stresses due to the restraint of thermal expansion. Since the temperatures reached in such structures can be several hundred Centigrade degrees, any restraint to thermal expansion can lead to the development of compressive stresses. The high susceptibility of thin shell structures to elastic buckling under low compressive stresses means that this type of failure can be easily provoked. The main objectives of this thesis were to reveal the thermal distribution patterns developed in an oil tank under the heating from an adjacent tank fire, to understand the underlying mechanism responsible for the buckling of tank structure, and to explore the influences of various thermal and geometrical parameters on the buckling temperature of the tanks. The study began with analytical solutions for stresses and deformations in a partially filled roofless cylindrical tank under an idealised axisymmetrical heating regime involving thermal discontinuity at the liquid level. The results demonstrate that large compressive circumferential membrane stresses occur near the bottom boundary for an empty tank and near the liquid level for a partially-filled tank. Heat transfer analysis was conducted to explore the temperature distribution developed in the tank when the fire reaches a steady state. Parameters and assumptions used in the adopted pool fire model were carefully examined. The results show that a rather non-uniform distribution of temperature is developed in the tank especially around the tank circumference. A simple model was then proposed to describe the temperature distribution based on the numerical heat transfer analysis. The accuracy of the proposed temperature distribution model for predicting the structure behaviour was evaluated by comparing its predictions with those using directly the temperature distribution obtained from the numerical heat transfer analysis. Extensive geometric and material nonlinear analyses were carried out to capture the buckling behaviour of the tank using both the proposed temperature distribution and that from heat transfer analysis. It was found large vertical compressive membrane stresses are induced in the tank, causing buckling. The influence of fire diameter, location, liquid filling level and tank geometry were investigated.

This dissertation focuses on the effects of superhydrophobic (SHPo) surfaces on thermal transport. The work is divided into two main categories: thermal transport without phase change and thermal transport with phase change. Thermal transport without phase change is the topic of four stand-alone chapters. Three address jet impingement at SHPo surfaces and the fourth considers natural convection at a vertical, SHPo wall. Thermal transport with phase change is the topic of a single stand-alone chapter exploring pool boiling at SHPo surfaces. Two chapters examining jet impingement present analytical models for thermal transport; one considered an isothermal wall and the other considered an isoflux wall. The chapter considering the isothermal scenario has been archivally published. Conclusions are presented for both models. The models indicated that the Nusselt number decreased dramatically as the temperature jump length increased. Further, the influence of radial position, jet Reynolds number, Prandtl number and isoflux versus isothermal heating become negligible as temperature jump length increased. The final chapter concerning jet impingement reports an experimental exploration of jet impingement at post patterned SHPo surfaces with varying microfeature pitch and cavity fraction. The empirical results show a decrease in Nusselt number relative to smooth hydrophobic surfaces for small pitch and cavity fraction and the isoflux model agrees well with this data when the ratio of temperature jump length to slip length is 3.1. At larger pitch and cavity fractions, the empirical results have higher Nusselt numbers than the SHPo surfaces with small pitch and cavity fraction but remain smaller than the smooth hydrophobic surface. We attribute this to the influence of small wetting regions. The chapter addressing natural convection presents an analytical model for buoyant flow at a vertical SHPo surface. The Nusselt number decreased dramatically as temperature jump length increased, with greater decrease occurring near the lower edge and at higher Rayleigh number. Thermal transport with phase change is the topic of the final stand-alone chapter concerning pool boiling, which has been archivally published. Surface heat flux as a function of surface superheat was reported for SHPo surfaces with rib and post patterning at varying microfeature pitch, cavity fraction, and microfeature height. Nucleate boiling is more suppressed on post patterned surfaces than rib patterned surfaces. At rib patterned surfaces, transition superheat decreases as cavity fraction increases. Increasing microfeature height modestly increases the transition superheat. Once stable film boiling is achieved, changes in surface microstructure negligibly influence thermal transport.

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This dissertation explores how property rights to a natural resource affect economic decisions for investment or sale, and how these decisions may in turn impact other areas of the economy. The first essay focuses on how incomplete land ownership on Indian Reservations in the United States affects landowner incentives to engage in agricultural production. The second essay explores how the transfer of water in arid regions via water right sales affects local labor markets and environmental outcomes. The third essay seeks to understand how shale-gas drilling has affected organic food production. This dissertation provides several policy implications. First, the findings suggest that the key to improving lagging agricultural development on American Indian land is to improve tribal farmers’ access to capital, so they can invest in agricultural systems (including irrigation) at the level of their neighbors enjoying fee-simple title. Second, while a potentially effective solution to reduce costly water shortfalls among high-value urban users, water sales from agricultural to urban users appear to simultaneously decrease employment and environmental quality in the water exporting region. Third, Drilling activities appear to discourage organic farming in Colorado. While farmers with mineral ownership benefit, identifying the direct causes of lost organic certification can inform policy that regulates negative externalities on organic farms caused by drilling.

Nucleate boiling is widely used as a means of heat transfer in thermal management systems because of its high heat transfer rates. This study explored the effects of heat flux and surface geometry on heat transfer behavior and bubble dynamics of nucleate pool boiling in microgravity. A single platinum wire, a twist of three platinum wires, and a twist of four platinum wires were used as boiling surfaces for two separate experiments performed in microgravity on board NASA’s parabolic flight aircraft. Wire temperature, thermocouple, and video measurements were taken during a total of 44 microgravity parabolas. Results show that the crevices formed by wire twisting provide regions of localized superheating and are able to reduce the heat flux necessary for boiling onset to occur. This localized heating results in a lower average heater temperature and shortened superheating periods, but this effect decreases when more wires are present in the twist. This behavior was investigated and confirmed with a finite volume, transient conduction model. This model also showed that the water temperature profile at the bubble onset indicates that water at a certain distance from the wire surface, in this experiment 50 μm, needs to be heated to above saturation temperature in order to initiate and generate a burst of bubbles. A relative bubble area analysis method was able to quantify vapor production and bubble behavior across multiple frames of video. Application of this method revealed a transition of bubble behavior from large isolated bubbles to jet flows of small bubbles, and this method allowed the heat flux contribution of jet flows to be approximated. Additionally, a new mode of jet flows was observed. Particle image velocimetry was used to provide approximate velocities of small bubble jet flows and their influence on heat transfer to the bulk fluid.

acase@tulane.edu