The use of inflatable, rigidizable structures in solar arrays and other space structures has the potential to drastically reduce the weight, volume, and cost of placing payloads into orbit. Inflatable components consist of ultra-lightweight, flexible materials that enable compact packaging prior to launch. These structures are then transformed from their initially flexible state to one that offers permanent shape-holding and structural integrity through a tailored rigidization process. Inflatable spacecraft must be impervious to the environmental conditions in space--such as ionizing radiation, UV and particle radiation, atomic oxygen, and impacts from space debris and meteoroids. They must also exhibit stable operation over a useful storage and mission life. Methods for causing rigidization in inflatable spacecraft include both passive and active techniques. Passive techniques rely on an uncontrolled, unprovoked reaction between the rigidizable materials in the structure and the surrounding space environment. The benefits of a passive system are offset by their inherent lack of control, which can lead to long curing times and weak spots due to uneven curing. This work presents internal resistive heating as an alternative approach for inducing matrix consolidation and curing of thermoset-coated carbon fiber tows. The ability to dictate this physical transformation through temperature-controlled resistive heating highlights the responsive nature of thermoset polymer composites and demonstrates the advantages of active rigidization. Feedback temperature control is implemented so as to provide a reliable, robust heating method for prescribing material-specific curing profiles. Resistive heating curing schedules developed from previous thermal analysis on two resins, U-Nyte Set 201A and 201B, are prescribed for samples of carbon fiber tow coated with each resin. The rigidization success of each curing profile is then evaluated with respect to both the increase in mechanical stiffness and the cure completion. These experiments indicate that rigidizing the coated fiber tow results in a composite material that is 20 times stronger in bending than prior to curing. The stiffening process requires roughly 1W-hr of energy with 5W peak power over the course of a 24-minute curing schedule. Curing temperature, curing time, and heating rate are also individually varied to determine their effect on rigidization as well as develop methods for reducing curing time and energy. The rigidization of an inflatable structure culminates this work and demonstrates the ability to achieve real strengthening through temperature-controlled internal resistive heating. / Master of Science

Current research has developed a fully predictive model of an electrically heated common residential oven. This system was modeled using a fully explicit approach and, where applicable, considered natural convective correlations, various radiation networks, and conduction relations. Two oven configurations were modeled, a conventional (unmodified) residential oven and a modified design. By comparing the theoretical results obtained through modeling with experimental results, verification of the modeling assumptions and results has been achieved. This research has produced an analytical design tool for predictive modeling of time dependant surface temperatures, maximum expected temperatures, and the baking performance of various oven designs. Thus this software package can be used to predict the overall feasibility of an oven design prior to fabrication.

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<p>An active optical shutter for infrared light (3-5 μm) has been designed, exploiting the phase transition in thermochromic vanadium dioxide (VO₂). A spin coating processing route for VO₂ films has been adapted to manufacture reproducible depositions onto sapphire (Al₂O₃) substrates. The VO₂ films have been characterized by X-ray powder diffraction (XRPD) and infrared spectroscopy (FTIR), showing 55 % transmittance in the open mode and 0.1 % in the closed mode.</p><p>The VO₂ film temperature determines the operating mode of the shutter, and a resistive circuit of gold was deposited on top of the film for heating purposes. Switching times from the open to the closed mode down to 15 ms have been measured.</p><p>This work is a part of a comprehensive project at the Swedish Defence Research Agency (FOI), aiming to improve active components for protection against lasers. The shutter within this work is at this stage an early prototype, and needs further development and complementary systems such as a control unit to be implemented in an optical system.</p>

An active optical shutter for infrared light (3-5 μm) has been designed, exploiting the phase transition in thermochromic vanadium dioxide (VO2). A spin coating processing route for VO2 films has been adapted to manufacture reproducible depositions onto sapphire (Al2O3) substrates. The VO2 films have been characterized by X-ray powder diffraction (XRPD) and infrared spectroscopy (FTIR), showing 55 % transmittance in the open mode and 0.1 % in the closed mode. The VO2 film temperature determines the operating mode of the shutter, and a resistive circuit of gold was deposited on top of the film for heating purposes. Switching times from the open to the closed mode down to 15 ms have been measured. This work is a part of a comprehensive project at the Swedish Defence Research Agency (FOI), aiming to improve active components for protection against lasers. The shutter within this work is at this stage an early prototype, and needs further development and complementary systems such as a control unit to be implemented in an optical system.

Abstract The purpose of the present research was (I-II) to evaluate the effects of clinical, hand-held Doppler (HHD) and duplex ultrasonographic examinations on the planning of operative procedure for primary varicose veins, (III) to assess the feasibility, safety and efficacy of endovenous saphenous vein obliteration with radiofrequency-resistive heating and (IV) to compare endovenous saphenous vein obliteration with conventional stripping operation in terms of short-term recovery and costs. Sixty-two legs (in 49 consecutive patients) and 142 legs (in 111 consecutive patients) with primary uncomplicated varicose veins were examined clinically and with HHD and duplex ultrasonography for planning the subsequent treatment. At the saphenous-femoral junction (SFJ) and at the saphenous-popliteal junction (SPJ), sensitivity was 56-64% and 23%, specificity 93-97% and 96%, positive predictive value 97-98% and 43% and negative predictive value 44-45% and 91%, respectively. In 9% of the cases, the treatment plan was modified on the basis of the duplex ultrasound findings. The present study showed that, in primary uncomplicated varicose veins, the accuracy of HHD is unsatisfactory. Thirty legs of 27 patients with varicose veins were treated using an endovenous catheter (Closure® System, VNUS Medical Technologies, Inc., Sunnyvale, CA), which was inserted under ultrasound guidance via a percutaneous puncture or a skin incision. The persistence of vein occlusion and complications potentially attributable to the endovenous treatment were assessed at 1-week, 6-week, 3-month, 6-month and 1-year follow-up visits. By the time of the last follow-up visit, occlusion of the treated segment of the LSV had been achieved in 22 (73.3%) legs. Persisting patency or recanalization of LSV was detected in 8 legs (26.7%). Postoperative complications included saphenous nerve paresthesia in 3 legs (10%) and thermal skin injury in one limb (3.3%). Twenty-eight selected patients admitted for operative treatment of varicose veins in the tributaries of the primary long saphenous were randomly assigned to endovenous obliteration (n = 15) or stripping operation (n = 13). The patients were followed up for 7-8 weeks postoperatively and examined by duplex ultrasonography. The comparison of costs included both direct medical costs and costs due to lost of productivity. All operations were successful, and the complication rates were similar in the two groups. The sick leaves were significantly shorter in the endovenous obliteration group [6.5 (SD 3.3) vs. 15.6 (SD 6.0), 95 % CI 5.4 to 12.9, p &lt; 0.001, t-test]. When the value of the lost working days was included, the endovenous obliteration was societally cost-saving.

The easiest and most effective way to influence the separation process in gas chromatography (GC) is achieved by controlling the temperature of the chromatographic column. In conventional GC, the temperature along the length of the column is constant at any given time, T(t). In my research, I investigated the effects of temperature gradients on GC separations as a function of time and position, T(t,x), along the column. This separation mode is called thermal gradient GC (TGGC). The research reported in this dissertation highlights the fundamental principles of axial temperature gradients and the separation potential of the TGGC technique. These goals were achieved through the development of mathematical models and instrumentation that allowed study of the effects of axial temperature gradients. The use of mathematical models and computer simulation facilitated evaluation of different gradient profiles and separation strategies prior to development of the instrumentation, providing theoretical proof of concept. Three instruments capable of generating axial temperature gradients, based on convective cooling and resistive heating, were developed and evaluated. Unique axial temperature gradients, such as nonlinear and moving sawtooth temperature gradients with custom profiles were generated and evaluated. The results showed that moving sawtooth temperature gradients allowed continuous analysis and were well-suited for comprehensive GCxGC separations. The use of custom temperature profiles allowed unique control over the separation power of the system, improving separations, as well as selectively increasing the peak capacity and signal-to-noise. A direct comparison of TGGC with conventional GC methods showed that TGGC produces equivalent separations to temperature programmed GC. This technology holds great promise for performing smart separations in which the column volume is most efficiently utilized and optimum separations can be quickly achieved. Moreover, precise control of the elution of compounds can be used to greatly reduce method development time in GC. This feature can be automated using feedback to develop efficient separations with minimum user intervention. This technology is of special interest in micro-GC systems, which allows relatively easy incorporation of resistive heating elements in the micro-column design.

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Submitted by Sandro Camargo (sandro.camargo@unipampa.edu.br) on 2015-05-09T22:33:43Z No. of bitstreams: 1 126110043.pdf: 2117805 bytes, checksum: f107c883cc20c40fff355188fc0e7df6 (MD5) / Made available in DSpace on 2015-05-09T22:33:44Z (GMT). No. of bitstreams: 1 126110043.pdf: 2117805 bytes, checksum: f107c883cc20c40fff355188fc0e7df6 (MD5) Previous issue date: 2014-08-20 / Atualmente as técnicas não lineares de modulação de potência aplicadas ao aquecimento resistivo de água, principalmente em redes elétricas mal projetadas, podem gerar vários problemas no ambiente onde estão instaladas. É o caso dos chuveiros eletrônicos que, dependendo da técnica utilizada para executar o processo de modulação de potência, podem ocasionar efeitos indesejáveis na rede elétrica e ambiente. Um exemplo típico é o Controle por Ciclos Inteiros, foco deste trabalho, que apresenta baixa probabilidade de geração de harmônicas e interferência eletromagnética (IEM). Em contrapartida, é praticamente inevitável o surgimento de flicker na rede elétrica decorrente de sua utilização, principalmente devido às altas potências dos equipamentos de aquecimento resistivo, agravadas pelos longos intervalos entre condução e não condução de corrente. Considerando que a geração de flicker é a principal desvantagem proveniente do Controle por Ciclos Inteiros, o presente trabalho tem por objetivo propor outras técnicas a fim de atenuar este efeito indesejável e, ao mesmo tempo, possibilitar a utilização de vários níveis de potência. / Currently the non-linear power modulation techniques applied to resistive water heating, mainly on not properly designed electric installations, can generate various problems in the environment where they are present. This is the case of electronic showers that depending on the power modulation technique may result in undesirable effects in the power grid and environment. A typical example is the zero-crossing AC power control, focus of this work, which has low probability of generating harmonics and electromagnetic interference (EMI). On the other hand, it is almost inevitable the emergence of Flicker on the power grid resulting from its use, mainly due to high electrical power consumed by heating equipment, compounded by long conducting and non-conducting power intervals. Whereas the flicker generated is the main drawback from the zero-crossing power control, this work aims to propose other techniques to reduce this undesirable effect allowing several output power levels.