As propriedades de superfícies de pós cerâmicos desempenham um papel importante na produção de dispositivos de alta qualidade, elevado desempenho e confiabilidade. Muitas dessas propriedades estão relacionadas a interações com o meio em que o material esta presente. Um exemplo, são materiais cerâmicos utilizados em sensores de gases. A perovisquita BaSnO3 (estanato de bário) é um de material cerâmico promissor a sensor de gás. Neste sentido, a proposta do presente trabalho consistiu em realizar a síntese do composto BaSnO3 por reação no estado sólido e preparar cerâmicas com o objetivo de estudar suas propriedades estruturais, microestruturais e seu comportamento elétrico em função da atmosfera. As amostras foram caracterizadas utilizando-se as técnicas de termogravimetria, calorimetria exploratória diferencial, difratometria de raios x, microscopia eletrônica de varredura, dilatometria e espectroscopia de impedância. Para a produção do BaSnO3 foram utilizadas duas metodologias de síntese. A primeira, chamada de rota 1, a preparação foi realizada a partir da mistura direta dos pós precursores, sem aquecimento prévio. A segunda metodologia, denominada rota 2, os pós precursores foram submetidos a um aquecimento separadamente antes da mistura e síntese. Os resultados obtidos utilizando a rota 1 mostraram a presença de fases secundárias (SnO2 e BaCO3) ao material pretendido, além da formação de fase líquida durante o processo de sinterização das cerâmicas. Contudo, os resultados obtidos com o procedimento adotado na rota 2 mostraram apenas a presença da fase desejada e ausência de fase líquida durante a sinterização. Com o objetivo de assegurar que a presença de fases secundárias na rota 1 e a fase líquida observadas nas microestruturas foram devido a presença de água adsorvida nos pós precursores, corpos cerâmicos `a verde produzidos pela rota 2 foram submetidos a imersão em água por aproximadamente 10 horas antes da sinterização. Este procedimento não resultou no aparecimento de fases secundárias, como era esperado, porém verificou-se a formação de fase líquida durante o processo de sinterização. As cerâmicas assim processadas apresentaram menor densidade relativa e maior tamanho médio de grão. Para a caracterização elétrica das cerâmicas foram utilizados as seguintes atmosferas: ar, em condição de pressão distinta, argônio contendo 5% de hidrogênio e argônio contendo 15% de hidrogênio. Os resultados mostraram que o estanato de bário apresenta significativa sensibilidade relativa da condutividade elétrica para as atmosferas estudadas a temperaturas acima de 100oC. / The surface properties of ceramic powders play an important role in the production of devices of high quality, high performance and reliability. Many of these properties are related to interactions with the environment. One example, ceramics are used in gas sensor devices. A ceramic material that has been reported as promising gas sensor is perovskite BaSnO3 (barium stannate). In this work we performed the synthesis of the BaSnO3 compound by solid state reaction to study its structural properties, microstructure and electrical behavior in function of atmosphere. The samples were characterized by thermogravimetry, differential scanning calorimetry, x-ray diffraction, scanning electron microscopy, dilatometry and impedance spectroscopy. For the production of BaSnO3 used two methods of synthesis. the first method, called route 1, the preparation was performed directly from the mixing of powder precursors. The second, named as route 2, the precursor powders were subjected to heating separately before mixing. The results obtained using the route 1 showed the presence of secondary phases (SnO2 and BaCO3) and the formation of liquid phase during sintering of the ceramics. The results obtained with the procedure adopted in the route 2 showed only the presence of the desired (BaSnO3) phase and no liquid phase during sintering. In order to investigate what the effects caused by the water adsorption by perovskite BaSnO3, the green-ceramic bodies produced by route 2 were submitted to immersion in water prior to sintering. This procedure did not result in the appearance of secondary phases, but was verified the presence of the liquid phase, and the ceramics showed lower density and larger average grain size. For the electrical characterization we used the following atmospheres: vacuum, air, argon containing 5% hydrogen and argon containing 15% hydrogen. The results showed that the barium stannate shows a significant sensitivity to the conductivity in the studied atmospheres at temperatures above 100oC.

Os padrões de atividade de muitas espécies de morcegos têm sido frequentemente associados à disponibilidade de alimento, à estrutura da vegetação e ao clima. Usualmente há maior atividade em áreas com maior disponibilidade de recursos alimentares e em ambientes que permitem maior facilidade de deslocamento. Em geral, a atividade de morcegos reduz em períodos com temperaturas extremas, sabendo-se que a redução da atividade de morcegos durante períodos frios está relacionada tanto com questões fisiológicas associadas ao balanço entre produção e perda de calor, quanto com ciclos reprodutivos das espécies. Sendo assim, o objetivo geral deste trabalho é avaliar a influência de variáveis meteorológicas e do habitat sobre os padrões de atividade de morcegos em uma região de clima temperado do Brasil. A avaliação da atividade dos morcegos foi realizada entre janeiro e maio de 2016, por meio de monitoramento acústico. Para relacionar a atividade dos morcegos com as condições meteorológicas locais, sensores de temperatura e umidade conectados a data loggers foram instalados perto de cada detector de ultrassom. O número de passagens de morcegos e o número de chamados de alimentação foram comparados entre guildas de uso do espaço – morcegos forrageadores de áreas abertas e morcegos forrageadores de bordas – e entre tamanhos – morcegos pequenos (entre 4g e 8g) e morcegos grandes (entre 30g e 35g). O local onde se registrou maior atividade de morcegos foi uma área aberta em meio a um contínuo de Floresta Ombrófila Densa, localizado em baixa altitude e maiores níveis de atividade de alimentação foram registrados em locais próximos a fontes de água. O padrão de atividade diferiu significativamente entre as guildas: morcegos forrageadores de espaço aberto apresentaram os maiores níveis de atividade concentrados nas primeiras horas da noite e em temperaturas entre 12°C e 16°C, enquanto os forrageadores de borda mantiveram atividade razoavelmente constante ao longo da noite e entre 16°C e 20°C. Um possível aumento da densidade de insetos em estratos altos ao anoitecer pode otimizar o sucesso de captura dos forrageadores de espaços abertos de tal forma que possibilitaria a concentração da atividade neste período. O padrão de atividade de morcegos grandes e pequenos também diferiu significativamente: a atividade de morcegos grandes ocorreu em temperaturas mais baixas do que a de morcegos pequenos. Como esperado, a temperatura de atividade de morcegos grandes foi mais baixa do que a de morcegos pequenos. Estimou-se, que a temperatura que limita a atividade de morcegos grandes é mais baixa do que a temperatura que limita a atividade dos morcegos pequenos. Isto é uma consequência esperada em razão da maior inércia térmica de animais de maior tamanho corporal, desse modo a temperatura crítica mínima dos morcegos grandes deve ser sempre menor do que a dos morcegos pequenos. A temperatura e o habitat parecem explicar os padrões de atividade tanto de morcegos forrageadores de espaço aberto e de borda, quanto de diferentes tamanhos corporais em um clima temperado mesotérmico no Brasil. / The activity patterns of many bat species have often been associated with food availability, vegetation structure and climate. There is usually more activity in areas with higher availability of food resources, and in landscapes that allow greater ease of commuting. The activity is generally reduced in periods with more extreme temperatures, and it is known that the reduction of bat activity during cold periods is related both to physiological issues associated to the balance between production and heat loss, and to the reproductive cycles of the species’. Therefore, the general objective of this work is to evaluate the influence of meteorological and habitat variables on the pattern of bat activity in a temperate region of Brazil. The evaluation of bat activity was carried out between January and May 2016, through acoustic monitoring. To relate bat activity to local weather conditions, temperature and humidity sensors connected to data loggers were installed near each ultrasound detector. The number of bat passes and the number of feeding buzzes were compared between guilds of space use – open and edge foragers bats – and between different body sizes – small bats (between 4g and 8g) and large bats (between 30g and 35g). The area where the largest bat activity was recorded was a continuous area of Dense Ombrophylous Forest, located at low altitude, and the highest feeding activity was recorded in sites near water sources. The activity pattern differed significantly among guilds: open-space foraging bats registered the highest activity levels concentrated in the early hours of the night and were active at lower temperatures, while edge-space foragers maintained activity reasonably constant throughout the night, though focusing their activity at higher temperatures. A possible increase in insect density in high strata at dusk can optimize the success of capture of open space foragers in such a way that would allow the concentration of activity in this period. The pattern of activity of large and small bats also differed significantly: large bats were more frequently recorded at lower temperatures than small bats. As expected, the activity of large bats occurred at lower temperatures than that of small bats. It was estimated that the limiting temperature to the activity of the large bats is lower than that to small bats. This is an expected consequence because of the greater thermal inertia of animals of larger body size, thus the minimum critical temperature of large bats should always be smaller than that of small bats. Temperature and habitat seem to explain the activity patterns of both foraging bats of open space and border, and of different body sizes in a temperate mesothermic climate in Brazil.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Climate change has already increased the frequency, intensity, and duration of heat waves around the world. In the coming decades, this trend will continue and likely accelerate, exposing much of the world’s population to historically unprecedented conditions. In some regions, extreme temperatures (as indexed by the annual maximum temperature) are projected to increase at a faster rate than mean daily maximum temperatures. This dissertation shows that under a high emissions scenario, by 2060 – 2080 models project that the most extreme temperatures could warm by 1 – 2°C more than the warm season average in some regions. This amplified warming of the most extreme temperatures is most pronounced in the eastern U.S., Europe, eastern China, and parts of the Amazon rainforest, and may have substantial implications for heat risk in these regions. This dissertation explores the physical mechanisms driving the projected amplified warming of extremes in climate models and assesses the associated uncertainty. It shows that the amplification is linked to reductions in cloud cover, increased net surface shortwave radiation, and general surface drying as represented by declines in the evaporative fraction. In addition to rising temperatures, atmospheric humidity has been observed to increase in recent decades and models project this trend to continue. As a result, joint heat-humidity metrics indicating heat stress are likely to rapidly increase in the future. This dissertation explores how extreme wet bulb temperatures may change throughout the century and assesses the risk of exceeding a fundamental human heat tolerance limit that has been proposed in prior research. It then combines climate data with spatially explicit population projections to estimate the future population exposure to unprecedented wet bulb temperatures. Several regions stand out as being at particular risk: India, the coastal Middle East, and parts of West Africa are likely to experience extremely high wet bulb temperatures in the future, and rapidly growing populations in these regions will result in large increases in exposure to dangerous heat stress. In some areas, it is possible that wet bulb temperatures could occasionally exceed the proposed human tolerance limit by 2080 under a high emissions scenario, but limiting emissions to a moderate trajectory eliminates this risk. Nevertheless, even with emissions reductions, large portions of the world’s population are projected to experience unprecedented heat and humidity in the future. The projected changes in extreme temperatures will have a variety of impacts on infrastructure and other human systems. This dissertation explores how more frequent and severe hot conditions will impact aircraft takeoff performance by reducing air density and limiting the payload capacity of commercial aircraft. It uses performance models constructed for a variety of aircraft types and projected temperatures to assess the payload reductions that may be required in the future. These payload limits, along with sea level rise, changes in storm patterns, increased atmospheric turbulence, and other effects of climate change, stand to have significant economic and operational impacts on the aviation industry. Finally, this dissertation discusses evidence-based adaptation strategies to reduce the impacts of extreme heat in urban areas. It reviews a body of literature showing that effective strategies exist to both lower urban temperatures on a large scale and drastically reduce heat-related mortality during heat waves. Many adaptation techniques are not costly, but have yet to be widely implemented. Given the rapid increases in climate impacts that are projected in the coming decades, it will be essential to rigorously assess the cost-effectiveness of adaptation techniques and implement the most efficient strategies in both high- and low-income areas.

Electrospinning produces submicron fibers from a wide range of polymer/solvent systems that enable a variety of different applications. In electrospinning process, a straight polymer/solvent charged jet is initially formed, followed by a circular moving jet in the shape of a cone, called the bending region. The process physics in the bending region are difficult to study since the jet diameter cannot be measured directly due to its rapid motion and small size (~microns and smaller), and due to complex coupling of multiple forces, mass transport, and changing jet geometry. Since the solutions studied are hydrophilic, they readily absorb ambient moisture. This thesis explores the role of the bending region in determining the resulting electrospun fiber diameter through a combined experimental and modeling analysis for a variety of hydrophilic polymer/solvent solutions. Electrospinning experiments were conducted over a broad range of operating conditions for 4 different polymer/solvent systems. Comparison of the final straight jet diameters to fiber diameters reveals that between 30% to 60% jet thinning occurs in the bending region. These experiments also reveal that relative humidity significantly affects the electrospinning process and final fiber diameter, even for non-aqueous solutions. A model is developed to obtain insight into the bending region process physics. Important ones include understanding the mass transport for non-aqueous hydrophilic jets (including solvent evaporation and water absorption on the jet surface, radial diffusion, and axial advection), and the coupling between the mass and force balances that determines the final fiber diameter. The absorption and evaporation physics is validated by evaporation experiments. The developed model predicts fiber diameter to within of 8%, even though the solution properties and operating conditions that determines net stretching forces and net evaporation rates vary over a large range. Model analysis reveals how the net evaporation rate affects the jet length and net stretching force, both of which ultimately determine the fiber diameter. It is also shown that the primary impact of RH on the process is through occupation of the surface states that limits solvent evaporation rate, rather than the amount of water absorbed. Correlation functions between process conditions, solution properties and the resulting fiber diameters are discussed.

This study looked at the effect relative humidity had on respirator performance.

Indoor Air Quality is an increasing concern in the world today. The mere presence of people in a building or residence can significantly alter indoor air quality. Relative humidity over the range of normal indoor temperatures (66 - 80 degrees Farenheit) has been linked both directly and indirectly to various health and structural problems. The purpose of this project was to discover whether residential dwellings might benefit from an indoor humidification system. The project consisted of the deployment of three separate sensor networks consisting of 12 tmote sky modules manufactured by the Moteiv corporation, each equipped with a temperature and humidity sensor manufactured by Sensirion. Each tmote sky module continuously transmitted the raw data readings to a base station to be processed. The lifetime of each network was approximately four days of continuous data transmission. The results verified the hypothesis that relative humidity levels have a significant affect on the indoor environment and can be linked to the health and structural problems reported by the occupants of each monitored residence. Based on the project findings residential dwellings would benefit from an indoor humidification system, given the symptoms associated with relative humidity level problems exist.

The hygroscopic and electrical resistance characteristics of lithium chloride are investigated. Then an evaluation is made of the lithium chloride characteristics that would be suitable in development of a dew point hygrometer with measurement accuracy of + 0. 3 c. The development of a 12 volt battery-powered hygrometer is presented with circuit details and performance characteristics. Lithium chloride phase transition hygrometers tend to oscillate under certain conditions. A damping control is presented as part of the circuit details and recordings of the response characteristics and effectiveness of damping are presented showing effective control of the oscillations with a wide range of humidity transients.

Growth chamber studies showed that a relationship exists between transpiration and dry matter production of spring wheat (Tritiaum Aestivum L. var . Thatcher). A temperature of 27 C for a 16-hour day,and 21 C at night were used throughout the experiment. Relative humidities (RH) of 12, 25, 71, and 83 percent and matric suctions of 1, 3, and 9 bars were used a l ong with six fertility levels and a 20-day growing period. An equation was developed from previous equations by De Wit and Arkley to describe the transpiration ratio (Tr = mass of water transpired/mass of dry matter produced) as it relates to evaporative demand conditions measured by humidity and pan evaporation. Time and fertility effects were not included because of insufficient data. As humidity both increases and decreases from 25 percent, the transpiration ratio decreases. Increasing levels of matric suction had an effect on Tr only at 25 percent RH. As fertility increased, Tr decreased toward some minimum level. Tr seems to reach a stable maximum as plants mature under steady state conditions.