Thesis (M.S.)--University of Wisconsin--Madison, 1985. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 61-63).

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It is known that a thermistor displays inductive reactance and negative resistance at low frequencies when biased with a current greater than turnover current. Thus when shunted by a capacitance in this condition sustained oscillations are possible. These oscillations range from a sinusoidal small - amplitude character, when the system is just above the threshold for oscillation, to a strongly relaxational type when a large shunt capacitance is employed. The investigation described in this thesis involved a study of the dynamic properties of these oscillations and their relation to the static properties of the thermistor. The relevant thermistor parameters which were measured included the dependence of resistance on temperature, the thermal conductance and the thermal time constant. For the determination of the latter, special very low frequency techniques were developed. Thermistors of high resistance and low thermal time constant were selected in order to avoid the necessity for very large capacitances in the study of relaxation oscillations. The oscillations were studied over a wide range of capacitances covering the transition from sinusoidal to relaxation type. The voltage extrema and period were measured as functions of capacitance, voltage supply resistance and operating point. Also, in order to elucidate the dynamic processes involved, the transient phenomena produced by abrupt pertubations were investigated. In parallel with the experimental program, an investigation was made of the features of the differential equations describing the behaviour of the system, especially for the limit cycles corresponding to relaxation oscillations. The asymptotic form of the cycles were derived for the case where the circuital time constant greatly exceeds the thermal time constant of the thermistor. The complicated nature of the equations precluded a solution in a closed form and approximational methods were found to be necessary. However, in the case of sinusoidal oscillations of small amplitude, the period can be exactly expressed in terms of the system parameters (Burgess, Nov. 1955) and this result was confirmed experimentally. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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The purpose of this study was: (1) to find the effect of temperature on the wet oxidation of chalcopyrite, pyrite, and copper sulfide over the biological and nonbiological range; (2) to determine the influence of ferrous and ferric iron and free oxygen(air) on the oxidation. The sulfide minerals studied were oxidized over a range of temperatures between 25° to 75° C. The optimum biological oxidation occurred near 35° C. The nonbiological oxidation was very slow at low temperatures but increased with increasing temperature. The effect of solutions used in leaching the various sulfides over the temperature range differred. A synthetic nutrient solution, containing only a source of phosphate and nitrogen, was more effective on the biological oxidation of pyrite than on copper sulfide at the optimum temperature. Tailings water, obtained from Bingham Canyon, Utah, was more effective on chalcopyrite over a long period of time than the synthetic nutrient. Ten times more chalcopyrite was oxidized at 70° C. than at 55° C. in a dilute solution of sulfuric acid. A dilute solution of ferrous sulfate had very little effect on the oxidation of the sulfides. Oxygen and ferric iron in oxidized tailings water were shown to affect the oxidation of chalcopyrite at 65° C. The ferric iron was reduced. In an atmosphere of nitrogen, ferrous iron in fresh tailings water was inactive on the oxidation of chalcopyrite. Oxygen is the primary oxidizing agent in the biological and nonbiological oxidation of sulfide minerals in the leaching process.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Graham, Samuel; Committee Member: Das, Suman; Committee Member: Joshi, Yogendra. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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The ultimate goal of this research was to determine the feasibility of measuring thermal conductivity of food materials using the bead thermistor with particular reference to high temperature. Feasibility was established by examining the effects of the input parameters and the measurement error associated with them on the ability to estimate the test medium thermal conductivity test medium. This study showed that estimation of effective radius and bead thermal conductivity, the probe parameters, had the most significant impact on the ability to estimate the thermal conductivity of food materials. The probe parameters were determined by standardizing the thermistor probe against materials of known thermal conductivity. The current lack of well defined thermal reference materials in the range of water and most food products is a primary source of error associated with the method. The accuracy and coefficient of variation of the Bead Thermistor Method were statistically documented in 10° increments over the temperature range of 25°C to 125°C. These results showed the method to have better than 10% accuracy across the entire temperature range. Distinct differences in accuracy between probes at a given temperature were also discovered. Standardization with water and castor oil resulted in a more accurate method than was achieved using water, castor oil, and glycerin. The minimum particle diameter necessary to maintain the infinite boundary condition assumption required by heat transfer theory was found to be >5 mm. The methodology was evaluated by examining the effects of temperature on the thermal conductivity of milk of different fat contents. A prediction equation for each product was attempted from the experimental data, but the data appear best fit by assuming a constant value across temperature. Heat altered the product physically which likely affected temperature dependence. Based on the results of this study, the bead thermistor method can be considered a practical method for determining thermal conductivity of food materials over the temperature range considered in this study. / Ph. D.

Orientador: Fabiano Fruett / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-17T21:03:29Z (GMT). No. of bitstreams: 1 CostaJunior_JuvenilSeverinoda_M.pdf: 3663986 bytes, checksum: 04fada688bb589e761d7e3d0f1bc7715 (MD5) Previous issue date: 2011 / Resumo: Sensores de umidade relativa do ar estão sendo cada vez mais utilizados em sistemas de controle e aquisição de dados. Estes sensores são facilmente encontrados em estufas, automóveis, refrigeradores, equipamentos médicos, eletrodomésticos, instrumentos de precisão e outros. Mais recentemente, com o crescimento do mercado agrícola no Brasil, a demanda por sensores de umidade vem crescendo substancialmente. Este trabalho e dedicado ao estudo de um sistema sensor de umidade por detecção de ponto de orvalho utilizando uma ponte de impedância. A ponte de impedância foi microfabricada diretamente sobre um substrato de alumina que compõe uma pastilha Peltier. Um termistor também micro fabricado no mesmo substrato fornece o sinal necessário para a detecção do ponto de orvalho. A face fria da pastilha Peltier e resfriada ate alcançar a temperatura do ponto de orvalho do ar ao seu redor. Este resfriamento resulta na saturação do vapor de d'água presente no ar, fazendo com que gotículas de água condensem sobre o substrato de alumina. A condensação de água sobre os eletrodos da ponte de impedância causa um desbalanceamento que gera um sinal de controle para a pastilha Peltier. As temperaturas no limiar de condensação e ambiente são utilizadas no calculo da umidade relativa. Este sensor de umidade foi projetado para que alguns requisitos com relação a resistência contra contaminantes e baixa histerese fossem alcançados / Abstract: Sensors for relative humidity are being increasingly used in control systems and data acquisition. These sensors are easily found in greenhouses, cars, weather equipment, medical equipment, appliances, etc.. More recently, with the growth of the agricultural market in Brazil, the demand for humidity sensors has been growing substantially. This work is dedicated to the study of a humidity sensor for dew point detection using an impedance bridge. The impedance bridge was microfabricated directly on an alumina substrate that comprises a Peltier device. A thermistor also microfabricated on the same substrate control the temperature of the Peltier device to the threshold where the dew point produces the saturation of water vapor in the air. The cold face of the Peltier device is cooled until it reaches the dew point temperature. This cooling results in saturation of water vapor in the air, around the side of the Peltier device causing water droplets to condense on the alumina substrate. Water condensation on the electrodes of the impedance bridge causes an imbalance that generates a control signal to the Peltier device. The temperatures measured at the threshold of condensation along with ambient temperature are used to calculate the relative humidity. This sensor was designed to fulfill some requirements related to resistence to contaminants and low hysteresis / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica