Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.

A Low-fat Diet Containing Heated Soybean Oil Promotes Hyperglycemia in C57BL/6J Mice Introduction: The metabolic effects of consuming mildly oxidized lipids as compared to highly oxidized lipids are not well documented. Consumption of highly oxidized polyunsaturated fatty acids, even in a low-fat diet, may be a threat to one’s health. Previous studies in our lab have shown that mice consuming soybean oil heated for 3 hours, compared to unheated, gain less body weight, but more fat pad mass, and 3T3-L1 adipocytes treated with soybean oil heated for ≥ 6 hours have abrogated triglyceride accumulation. Another study showed that rats fed highly oxidized oil (heated > 24 hrs), as compared to fresh soybean oil and fish oil, had lower fat pad mass and weight gain but developed glucose intolerance. This suggested that the extent of lipid oxidation determined the subsequent metabolic risk. Objective: Our aim, in the current study, is to investigate if a low-fat diet with soybean oil heated for increasing time points (3h, 6h and 9h) alter fat mass and glucose tolerance. Methods: Six week old, male, C57BL/6J mice were randomly divided into six groups (n=8/group). Three groups were fed a low fat diet with soybean oil heated for 3 (3hr-HO), 6 (6hr-HO), or 9 (9hr-HO) hours for 16 weeks. Another three groups were pair-fed to each of the 3hr-HO, 6hr-HO and 9hr-HO groups with a low-fat diet containing unheated oil (PF-UHO). Food consumption was recorded every 3-4 days, and body weights were recorded weekly. Soy oil in the diets was analyzed for products of oxidation. At 16 weeks, blood glucose levels were measured after a 6 hour fast; fat pad and liver weights were recorded, and blood was collected by cardiac puncture for serum insulin analysis. Results: Final weight gain was not significantly different between all HO groups as a percent of their respective PF groups (p >0.05). The feeding efficiency for 3hr, 6hr, and 9hr-HO groups as a percent of PF was 92.75, 113.02, and 111.28, respectively. Mean weights of all fat pads for HO groups decreased with heating time as a percent of PF, although these differences were not statistically significant. Blood glucose was lowest in the 3hr-HO group and significantly increased from 3hr-HO group to 6hr-HO group (p=0.021) as a percent of PF. Serum insulin levels decreased for the HO groups as heating time increased, although these differences were not statistically significant. Conclusion: Consuming a diet with increasing amounts of oxidized lipids decreased fat pad mass and insulin levels, while increasing fasting glucose levels. This paradoxical relationship between increased glucose in the presence of decreased insulin in c57BL/6J mice could be due to either reduced insulin secretion or increased insulin resistance. Further research in our lab will aim to analyze triglyceride accumulation in the liver and muscle cells of these mice to determine if oxidized lipids promote ectopic fat deposition.

Hot microelectrodes are very small electrodes (usually 1 100 µm in diameter), which have a surface temperature much higher than the temperature in the bulk solution. In this work, the heating is achieved by applying an alternating potential of very high frequency (100 MHz 2 GHz) and of high amplitude (up to 2.8 Vrms) to the microelectrode. As a result, very fast (on the order of milliseconds) changes in the temperature of the electrolyte solution surrounding the electrode can be achieved. Due to the size of the heated microelectrodes, the hot zone in solution is small. Therefore, the solution can be easily overheated and temperatures above the boiling point can be reached.<p> The purpose of this research was to investigate and understand the phenomena occurring at ac polarized microelectrodes and to propose new applications of these electrodes. Using both steady-state and fast-scan (10 V/s) cyclic voltammetry measurements, mass transport of redox species has been studied at ac heated microelectrodes. It has been established that the convection at hot-disk microelectrodes is driven primarily by the electrothermal flow of an electrolyte solution. In addition, other effects such as ac dielectrophoresis and Soret (nonisothermal) diffusion are also observed. Numerical simulations have been employed to predict the distribution of temperature in the hot zone, the direction and magnitude of the electrothermal force and the solution flow rate, as well as the voltammetric response of hot-disk microelectrodes. The results of the simulations agree well with the experimental observations. Theoretical findings of this PhD work are very important for the understanding of the fundamentals of high temperature electrochemistry, particularly mass transport. The proposed explanation of the convection mechanism is most likely applicable not only to ac polarized microelectrodes, but also to the microwave heated microelectrodes, since the only difference between these two heating methods is in the way of delivering electrical energy (wired vs. wireless). The results of the studies of Soret diffusion indicate that it contributes significantly to mass transfer of redox species at hot microelectrodes. Taking into account that the magnitude of the Soret effect has been considered negligible by other electrochemists, the results obtained in this work prove the opposite and show that Soret diffusion affects both the faradaic current and the half-wave potential of the redox reaction. Therefore, the Soret effect can not be ignored if working with hot microelectrodes.<p> Hot microelectrodes can have a number of interesting applications. The results of the initial investigations indicate that these electrodes can be successfully used in the arrangement for Scanning Electrochemical Microscopy (such a novel technique is termed Hot-Tip SECM). In addition, the observed dielectrophoretic and electrothermal convection effects can enhance the performance of the electrochemical sensors based on hot microelectrodes. This can lead to the improvement of the detection limits of many biologically important analytes, such as proteins, bacteria and viruses.

Recently, with the escalating demands for optical communications, the need for bandwidth in optical communication network has increased. The technology breakthrough indry fiber fabrication opens the possibility for fiber bandwidth form 1.3 to 1.6 £gm. Cr4+:YAG double-clad crystal fiber (DCF) grown by the co-drawing laser-heated pedestal growth method has a strong spontaneous emission spectum form 1.3 to 1.6 £gm. Such fiber is therefore, eminently suitable for optical coherence tomography (OCT), broadband optical amplifier, amplifier spontaneous emission (ASE) light source, and tunable solid-state laser applications. In this thesis, multilayer dielectric thin films were directly deposited by E-gun coating onto the end faces of the Cr4+:YAG DCF. To improve the thin-film quality, to increase transmittance of laser output, and to design for the high power laser. For broadband optical amplifier in dual-pump and double-pass scheme, a 3.0-dB gross gain, a 3.0-dB insertion loss, and a 0-dB net gain at 1.4-£gm signal wavelength have been successfully developed with HR coating onto one of the Cr4+:YAG DCF end faces. In addition, we have successfully developed the Cr4+:YAG DCF laser by direct HR coatings onto fiber end faces and increase transmittance of laser output. A record-low threshold of 31.2 mW with a slope efficiency of 7.5% was achieved at room temperature.

Cr4+ doped Yttrium aluminum garnet (YAG) has a strong spontaneous emission that can generate near-infrared emission from 1.2 to 1.6 £gm. This broadband emission have aroused great interest in developing tunable wavelength lasers and amplified spontaneous emitter (ASE).In this dissertation, The valence states of Cr ions in Ca or Ca/Mg co-doped Cr:YAG single-crystal fibers are studied. The fibers were grown using the laser-heated pedestal growth (LHPG) method, followed by annealing treatments up to 1500 oC. The concentrations of the Cr3+ and Cr4+ ions in octahedral and tetrahedral sites in oxygen or nitrogen environments were characterized for the first time to our knowledge. Above 700 oC, migration of Cr4+ between octahedral and tetrahedral sites takes place, the ratio is about 4%; its relative stabilization energy was estimated. For Ca,Cr:YAG annealed in an oxygen or nitrogen environment, it was 0.25 and 0.3 eV, respectively. For Mg,Ca,Cr:YAG annealed in oxygen or nitrogen, it was 0.47 and 0.49 eV, respectively. For the Ca,Cr:YAG crystal fiber (Ca/Cr=113.1%) with oxygen annealing, about 35% and 2.5% of Ca ions took part in charge compensation for Cr4+ in the octahedral and tetrahedral sites, respectively. The density of oxygen vacancies depends on the concentration of Ca ions. The estimated ratios of the unreacted oxygen vacancies to total oxygen vacancies were about 63% and 88% for oxygen and nitrogen annealing, respectively. The main limitation on the concentration of Cr4+ in the tetrahedral site of YAG is the presence of unreacted oxygen vacancies. Furthermore, chromium ions tend to diffuse outward during the LHPG of YAG crystal fiber, in which the average Cr4+ ion concentration decreases significantly after each diameter-reduction step. The Cr4+ ions are replenished using an electron gun to deposit Cr2O3 and divalent-ion oxide (CaO or MgO) on the source rod circumference before growth. It was observed that Ca2+ has better efficiency to diffuse into the source rod more efficiently than Mg2+generating fewer defects and stacking faults. By CaO deposition and post growth annealing at 1350 oC under an oxygen environment, a 110% increase in Cr4+ concentration was obtained. The achieved Cr4+ concentration and the ratio of Cr4+ to total Cr were 1.76 10^18 cm^-3 and 5.5, respectively.

As forensic techniques employed in homicide investigation are refined, so are the methods by which perpetrators of these crimes attempt to eliminate evidence that could lead to their prosecution. Acid submersion is an increasingly popular method of body disposal due to its highly destructive effects upon organic tissues and their suitability for macroscopic analyses that could enable positive identification. Sixteen fleshed pig (Sus scrofa) forelimbs were submerged in hydrochloric acid, sulfuric acid, and sodium hydroxide (n = 2 per trial) under control conditions and heated to 40˚C or 100˚C, to determine whether dissolution of all tissues was possible quickly enough to ensure a practical method of disposal, and whether heating would accelerate this process. Hydrochloric acid (31-35%) under control conditions failed to dissolve all soft tissues, but destroyed all bones within 68 hours; at 40˚C the soft tissues still were not entirely dissolved, but all bones were destroyed within 24 hours. Sulfuric acid (93%) under control conditions destroyed all soft tissue within 52 hours and all bones within 28 days. Sulfuric acid at 40˚C destroyed all soft tissue in 2.75 hours and all bones within nine days; at 100˚C all soft tissues were destroyed within 0.75 hour and all bones within nine hours. Sodium hydroxide (20-30%) failed to dissolve the soft and hard tissues in all trials, but the rapidity of alterations observed was positively correlated to temperature. The present research indicates that these chemicals can destroy large, fleshed body parts and that this destruction can be accelerated through heating.

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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Tooling design is crucial for the production of cost-effective and durable composite products. As part of the current search for cost reduction (by reducing capital investment, energy use and cycle time), integrally-heated tooling is one of the technologies available for ‘out-of-autoclave’ processing of advanced thermoset polymer composites. Despite their advantages, integrally-heated tools can suffer from uneven distribution of temperature, variability in heat flow rate and inconsistency in heating/cooling time. This research, therefore, investigates a number of design variables such as shape and layout of heating channels in order to improve the heating performance of an integrally-heated tool. Design of Experiments (DoE) has been carried out using Taguchi’s Orthogonal Array (OA) method to set several combinations of design parameters. Each of these design combinations has been evaluated through numerical simulation to investigate heating time and mould surface temperature variation. The simulation results suggest that the layout of the channels and their separation play a vital role in the heating performance. Signal-to-Noise (S/N) ratio and analysis of variance (ANOVA) have been applied to the results obtained to identify the optimal design combination of the integrally-heated tool. Statistical analysis reveals that the heating performance of an integrally-heated tool can be significantly improved when the channels’ layout is parallel. The shape of the channels has negligible effect and the distance between the channels should be determined based on the production requirement. According to the predicted optimal design, a developed integrally water-heated tool is manufactured. The actual thermal properties of the constituent materials of the produced tool are also measured. Then a numerical model of the experimental tool model is simulated in ANSYS software, with setting the actual material properties and boundary condition to define the temperature uniformity and heating rate of the experimental tool. Comparison of the experimental and numerical results of the experimental tool confirmed the well assigning of the boundary conditions and material properties during simulation the heated tool. The experimental results also confirmed the predicted optimal design of the integrally heated tool. Finally, in order to define its thermomechanical behaviour under the effective (in service) thermal loads, a tool model is simulated. Numerical results presented that the produced extremes of thermal deformation, elastic strain, normal and plane shear stresses, under the effective thermal loading, are within the allowable elastic limits of the participated materials.

In the light of extreme events of natural disasters (earthquakes or hurricanes) and accidents (fire or explosion), repairing and strengthening of existing concrete structures has become more common during the last decade due to the increasing knowledge and confidence in the use of composite advanced repairing materials. The past experience from real fires shows that it is exceptional for a concrete building to collapse as a result of fire and most fire-damaged concrete structures can be repaired economically rather than completely replacing or demolishing them. In this connection an experimental study was conducted to investigate the effectiveness of fibre reinforced polymer jackets for axial compressive and seismic shear performance of post-heated columns. This study also investigates the effectiveness of ferrocement laminate for the repairing of post-heated reinforced concrete columns.A total of thirty-five reinforced concrete columns were constructed and then tested after categorising them into three main groups: un-heated, post-heated and post-heated repaired. The post-heated columns were initially damaged by heating (to a uniform temperature of 500°C). The concrete cubes were also heated to various temperatures to develop the relation between compressive strength and ultrasonic pulse velocity. The residual compressive strength of the concrete cubes and reinforced concrete columns were determined by ultrasonic testing. The post-heated columns were subsequently repaired with unidirectional glass or carbon fibre reinforced polymer and ferrocement jackets. The experimental programme was divided into two parts. The columns of experimental part-1 were tested under axial compressive loading. The columns of experimental part-2 with a shear span to depth ratio of 2.5 were tested under constant axial and reversed lateral cyclic loading. The results indicated that the trend of reduction in ultrasonic pulse velocity values and in residual compressive strength of concrete was similar with increasing temperature. The reduction in residual stiffness of both post-heated square and circular columns was greater than the reduction in ultimate load. The circular sections benefited more compared to the square cross-sections with fibre reinforced polymers for improving the performance of post-heated columns in terms of compressive strength and ductility tested under axial compression. GFRP and CFRP jackets performed in an excellent way for increasing the shear capacity, lateral strength, ductility, energy dissipation and slowed the rate of strength and stiffness degradation of fire damaged reinforced concrete square and circular columns tested under combined constant axial and reversed lateral cycle loading. However, the effect of a single layer of glass or carbon fibre reinforced polymer on the axial stiffness of post-heated square and circular columns was negligible. The use of a ferrocement jacket for the repairing of post-heated square and circular columns enhanced the axial stiffness and ultimate load carrying capacity of columns significantly.