Ethylene propylene rubber (EPR) cable has been extensively used for distribution of power. The insulation of cable should withstand electrical, thermal, mechanical, and chemical stresses during its operation. It is imperative to measure the data providing dielectric strength of EPR cable for these stresses. Significant improvements on the quality of insulation have been progressing for better performance of cable under these stresses. This study deals with ac voltage stress imposed on the cable. The electrical breakdown strength of 5kV EPR cable under ac voltage has been measured by constructing a suitable test set in Mississippi State University High Voltage Lab.

O amido é o mais abundante dos polissacarídeos de armazenamento de energia de plantas, usualmente depositado na forma de grânulos no citoplasma das células. Também é a principal fonte de energia para o homem, compondo 80-90% dos polissacarídeos da dieta humana, e é o principal responsável pelas propriedades tecnológicas que caracterizam grande parte dos produtos processados. O presente trabalho teve como objetivo a aplicação da ressonância paramagnética eletrônica (RPE) e espectroscopia de Infravermelho por transformada de Fourier (FTIR) ao estudo de amidos irradiados. Amostras em pó de dois amidos naturais, batata (bulbo) e milho (cereal) e farinha de mandioca fermentada ou polvilho azedo (raiz) foram submetidos à ação da radiação ionizante de fonte de 60Co Gammacell 220 com doses de 10, 20 e 30 kGy, taxa de dose de 1kGy h-1. Foram registrados e comparados os espectros de RPE dos três tipos de amidos irradiados e não irradiados. Os amidos apresentaram espectros de RPE semelhantes variando apenas na intensidade do sinal de radicais livres que acompanhou o incremento da dose. Foram estabelecidas as curvas de decaimento para cada um dos amidos ensaiados. No caso de amido de batata o decaimento do sinal apresentou excepcionalmente um comportamento linear quando a dose utilizada foi de 20 kGy. Foi obtido de maneira experimental o valor do fator g, que variou de 2,06062 a 1,94661, sendo o valor teórico g = 2,0023. Foram também estabelecidas as modificações radioinduzidas na estrutura molecular das amostras através da análise dos espectros de absorção no infravermelho por FTIR. / Starch is the most abundant plant energy storage polysaccharide, usually deposited in the form of granules in the cytoplasm of cells. It is also the main source of energy for man, making up 80-90% of polysaccharides in the human diet, and is mainly responsible for the technological properties that characterize most processed products. The present work aimed to the application of electronic paramagnetic resonance and Fourier Transform Infrared Spectroscopy to the study of irradiated starches. Powdered samples of two natural starches, potato (bulb) and corn (cereal) and fermented cassava flour or sour cassava (root) were subjected to the action of ionizing radiation from a 60Co Gammacell 220 at doses of 10, 20 and 30 kGy, dose rate of 1kGy h-1. The electronic paramagnetic resonance spectra of the three types of irradiated and non-irradiated starches were recorded and compared. The starches showed similar electronic paramagnetic resonance spectra varying only in the intensity of the free radical signal that accompanied the dose increase. The decay curves were established for each of the tested starches. In the case of potato starch, signal decay showed an exceptionally linear behavior when the dose used was 20 kGy. The value of factor g was obtained experimentally, ranging from 2.06062 to 1.94661, with the theoretical value g = 2.0023. The radioinduced modifications in the molecular structure of the samples were also established by the analysis of the infrared absorption spectra by Fourier Transform Infrared Spectroscopy.

O amido é o mais abundante dos polissacarídeos de armazenamento de energia de plantas, usualmente depositado na forma de grânulos no citoplasma das células. Também é a principal fonte de energia para o homem, compondo 80-90% dos polissacarídeos da dieta humana, e é o principal responsável pelas propriedades tecnológicas que caracterizam grande parte dos produtos processados. O presente trabalho teve como objetivo a aplicação da ressonância paramagnética eletrônica (RPE) e espectroscopia de Infravermelho por transformada de Fourier (FTIR) ao estudo de amidos irradiados. Amostras em pó de dois amidos naturais, batata (bulbo) e milho (cereal) e farinha de mandioca fermentada ou polvilho azedo (raiz) foram submetidos à ação da radiação ionizante de fonte de 60Co Gammacell 220 com doses de 10, 20 e 30 kGy, taxa de dose de 1kGy h-1. Foram registrados e comparados os espectros de RPE dos três tipos de amidos irradiados e não irradiados. Os amidos apresentaram espectros de RPE semelhantes variando apenas na intensidade do sinal de radicais livres que acompanhou o incremento da dose. Foram estabelecidas as curvas de decaimento para cada um dos amidos ensaiados. No caso de amido de batata o decaimento do sinal apresentou excepcionalmente um comportamento linear quando a dose utilizada foi de 20 kGy. Foi obtido de maneira experimental o valor do fator g, que variou de 2,06062 a 1,94661, sendo o valor teórico g = 2,0023. Foram também estabelecidas as modificações radioinduzidas na estrutura molecular das amostras através da análise dos espectros de absorção no infravermelho por FTIR. / Starch is the most abundant plant energy storage polysaccharide, usually deposited in the form of granules in the cytoplasm of cells. It is also the main source of energy for man, making up 80-90% of polysaccharides in the human diet, and is mainly responsible for the technological properties that characterize most processed products. The present work aimed to the application of electronic paramagnetic resonance and Fourier Transform Infrared Spectroscopy to the study of irradiated starches. Powdered samples of two natural starches, potato (bulb) and corn (cereal) and fermented cassava flour or sour cassava (root) were subjected to the action of ionizing radiation from a 60Co Gammacell 220 at doses of 10, 20 and 30 kGy, dose rate of 1kGy h-1. The electronic paramagnetic resonance spectra of the three types of irradiated and non-irradiated starches were recorded and compared. The starches showed similar electronic paramagnetic resonance spectra varying only in the intensity of the free radical signal that accompanied the dose increase. The decay curves were established for each of the tested starches. In the case of potato starch, signal decay showed an exceptionally linear behavior when the dose used was 20 kGy. The value of factor g was obtained experimentally, ranging from 2.06062 to 1.94661, with the theoretical value g = 2.0023. The radioinduced modifications in the molecular structure of the samples were also established by the analysis of the infrared absorption spectra by Fourier Transform Infrared Spectroscopy.

In the framework of Ph.D. thesis the evaluation of radical reactions of four groups of secondary amines R1–NH–R2 in the presence of some selected types of agents was performed using EPR spectroscopy. First group was represented by peroxoagents (3-chloroperbenzoic acid, tBuO2 radicals), the second group involved compounds of PbIV+ (PbO2, Pb(OAc)4) functioning as hydrogen-abstracting agents. In the presence of peroxyagents the formation of corresponding aminoxyl radicals R1–NO–R2 was demonstrated. In the case of surplus of tBuO2 radicals these radicals enter the consecutive reactions which products are new types of secondary aminoxyls. By the interpretation of reaction mechanism the intermediary formation of nitrones was assumed. These function in later steps of the reaction as spin traps for tBuO2 radicals. By the study of radical mechanism of amines R1–NH–R2 initiated by PbIV+ agents was proved, that these compounds hydrogen atom not only from –NH– group under formation of aminyl radicals, but also from C–H bonds in substituents R1, R2 (the formation of C-radicals). Because both groups of the radicals formed are characterized by high reactivity, their identification was possible only using spin-trapping method. In the course of the investigation of radical reactions of secondary amines the big amount of experimental EPR spectra was obtained. These exhibited in many cases very high hyperfine structure. Due to this fact it was necessary to perform the detailed evaluation on the basis of spectral simulation. Except of some special cases using this approach the interpretation of majority of registered EPR spectra was interpreted and EPR parameters were summarized in tables.

This thesis presents the results of a combined cathodoluminescence (CL) and electron paramagnetic resonance (EPR) spectroscopic study of quartz from the uranium-mineralized Athabasca Basin. CL imaging not only distinguishes detrital quartz grains from their secondary overgrowths but also is able to differentiate two generations of overgrowths in the Athabasca sandstones. Moreover, the Athabasca quartz samples are characterized by three types of bright CL: 1) haloes around U- and Th-bearing mineral inclusions, 2) patches associated with U-bearing minerals in matrices or pores and 3) continuous rims in samples with or without any visible U-bearing minerals. These three types of bright CL are all of constant widths of ~35-45 Ým, indicative of bombardments of alpha particles emitted from the 238U, 235U and 232Th decay series. CL spectral analyses show that the radiation damaged areas, relative to their undamaged hosts, are characterized by intense but broad emission bands at ~350 nm and 620-650 nm. <p>Detailed EPR measurements of the Athabasca quartz samples revealed six paramagnetic defects: one oxygen vacancy center (E1'), three silicon vacancy hole centers (O23¡V/H+(I), O23¡V/H+(II) and O23¡V/M+) and two O2¡V peroxy centers. Moreover, dissolution experiments using concentrated HF showed that that the silicon vacancy hole centers and the peroxy centers are concentrated in the radiation-damaged rims/fractures, whereas the oxygen vacancy center (E1') is evenly distributed in quartz grains. CL and EPR data of quartz samples after isochronal annealing experiments suggest that the silicon vacancy hole centers and the peroxy centers are most likely responsible for the characteristic ultraviolet CL and the red CL, respectively. <p>CL haloes in detrital quartz grains are ubiquitous in the Athabasca sandstones. CL patches are also widespread but are best developed in altered sandstones close to the unconformity or faults/fractures. Continuous CL rims, however, are more restricted in occurrences and are best developed at the high-grade Cigar Lake and McArthur River deposits, where they are restricted to lithological boundaries and faults and are pervasively developed in mineralized samples and associated alteration haloes close to the unconformity. At the Key Lake deposit, continuous rims occur only in mineralized samples close to the unconformity. Continuous CL rims are absent in basement rocks below mineralization, including those at the Cigar Lake and McArthur River deposits. The occurrence of radiation damages in Athabasca quartz have also been confirmed by detailed EPR measurements, which are significantly more sensitive than CL imaging. <p>Continuous CL rims on Athabasca quartz grains most likely record bombardments of alpha particles emitted from U-bearing mineralization fluids. Therefore, their associations with the unconformity, lithological boundaries and faults provide direct evidence for those structures being the pathways for mineralization fluids. The exclusive occurrence of continuous CL rims on detrital quartz grains and the abundance of U-bearing minerals in both generations of overgrowths suggest that U mineralization must have commenced during early diagenesis and continued during the formation of overgrowths. The absence of significant radiation damages in altered basement rocks supports the hypothesis that the basement was not a major source for uranium mineralization in the Athabasca basin. The common occurrence of CL haloes in euhedral quartz grains and CL patches associated with U-bearing minerals in faults, fractures and voids provide further (visual) evidence for late remobilization of uranium.

This thesis presents the results of a combined cathodoluminescence (CL) and electron paramagnetic resonance (EPR) spectroscopic study of quartz from the uranium-mineralized Athabasca Basin. CL imaging not only distinguishes detrital quartz grains from their secondary overgrowths but also is able to differentiate two generations of overgrowths in the Athabasca sandstones. Moreover, the Athabasca quartz samples are characterized by three types of bright CL: 1) haloes around U- and Th-bearing mineral inclusions, 2) patches associated with U-bearing minerals in matrices or pores and 3) continuous rims in samples with or without any visible U-bearing minerals. These three types of bright CL are all of constant widths of ~35-45 Ým, indicative of bombardments of alpha particles emitted from the 238U, 235U and 232Th decay series. CL spectral analyses show that the radiation damaged areas, relative to their undamaged hosts, are characterized by intense but broad emission bands at ~350 nm and 620-650 nm. <p>Detailed EPR measurements of the Athabasca quartz samples revealed six paramagnetic defects: one oxygen vacancy center (E1'), three silicon vacancy hole centers (O23¡V/H+(I), O23¡V/H+(II) and O23¡V/M+) and two O2¡V peroxy centers. Moreover, dissolution experiments using concentrated HF showed that that the silicon vacancy hole centers and the peroxy centers are concentrated in the radiation-damaged rims/fractures, whereas the oxygen vacancy center (E1') is evenly distributed in quartz grains. CL and EPR data of quartz samples after isochronal annealing experiments suggest that the silicon vacancy hole centers and the peroxy centers are most likely responsible for the characteristic ultraviolet CL and the red CL, respectively. <p>CL haloes in detrital quartz grains are ubiquitous in the Athabasca sandstones. CL patches are also widespread but are best developed in altered sandstones close to the unconformity or faults/fractures. Continuous CL rims, however, are more restricted in occurrences and are best developed at the high-grade Cigar Lake and McArthur River deposits, where they are restricted to lithological boundaries and faults and are pervasively developed in mineralized samples and associated alteration haloes close to the unconformity. At the Key Lake deposit, continuous rims occur only in mineralized samples close to the unconformity. Continuous CL rims are absent in basement rocks below mineralization, including those at the Cigar Lake and McArthur River deposits. The occurrence of radiation damages in Athabasca quartz have also been confirmed by detailed EPR measurements, which are significantly more sensitive than CL imaging. <p>Continuous CL rims on Athabasca quartz grains most likely record bombardments of alpha particles emitted from U-bearing mineralization fluids. Therefore, their associations with the unconformity, lithological boundaries and faults provide direct evidence for those structures being the pathways for mineralization fluids. The exclusive occurrence of continuous CL rims on detrital quartz grains and the abundance of U-bearing minerals in both generations of overgrowths suggest that U mineralization must have commenced during early diagenesis and continued during the formation of overgrowths. The absence of significant radiation damages in altered basement rocks supports the hypothesis that the basement was not a major source for uranium mineralization in the Athabasca basin. The common occurrence of CL haloes in euhedral quartz grains and CL patches associated with U-bearing minerals in faults, fractures and voids provide further (visual) evidence for late remobilization of uranium.

Metal-RNA interactions are important to neutralize the negative charge and aid in correctly folding the RNA. Spectroscopically active metal ions, especially Mn2+, have been used to probe the type of interaction the metal has with RNA. In previous studies, the hammerhead ribozyme, an RNA motif that catalyzes a site-specific phosphodiester bond cleavage reaction, was determined by room temperature EPR (electron paramagnetic resonance) studies to have a set of tightly and weakly bound metal ions. Under high salt concentrations, the hammerhead was found to bind a single Mn2+ ion with high affinity and with a characteristic low temperature EPR signal. Using site specific 15N labeling of a guanine residue in conjunction with ESEEM (electron spin echo envelope modulation) spectroscopy, the high affinity Mn2+ ion was conclusively determined coordinated to G10.1 of the proposed A9/G10.1 site with four water molecules coordinated to the Mn2+ ion. EPR power saturation studies determined that under low salt conditions the hammerhead coordinates up to four Mn2+ ions in relatively close proximity compared to an RNA duplex. EXAFS (extended X-ray absorption fine structure) spectroscopy was used to determine that a Cd2+ ion coordinates to both the Rp and Sp sulfur atoms of a phosphorothioate modification at the A9 phosphate of the hammerhead. Previous EXAFS results for the Mn2+ substituted A9 phosphorothioate suggested that the Mn2+ ion coordinates to the oxygen atom for both isomers. Molecular modeling suggested that the A9/G10.1 metal site will twist the phosphate group in order to accommodate this coordination. A Mn-GMP and Mn-phosphate model complexes were prepared and characterized by EXAFS to assign the origin of the features observed for the hammerhead sample. A series of RNA sequences with internal loops containing the sheared G-A metal ion binding motif showed greater thermal stabilization of the RNA structure in the presence of Mn2+ ions compared to sequences without the motif. The EPR binding isotherms also showed a set of moderately tight metal ion interaction while circular dichroism spectroscopy was used to investigate structural differences between the sequences. These results suggest a mostly electrostatic, not structural role, for the Mn2+ ion interactions with these sequences.

This thesis describes the synthesis of a range of novel dithiadiazolyl radicals. The structures of these compounds are discussed. The physical properties of several compounds have been investigated using EPR spectroscopy and magnetic susceptibility studies. Chapter one begins with an overview of the chemistry of 1,2,3,5-dithiadiazolyl radicals. A general discussion of the history of organic conductors and magnets, and the terms involved in some of the techniques used is given in order to provide a background to the work presented. The second chapter outlines the synthesis and general characterisation of all the dithiadiazolyl radicals discussed in this thesis. A proposed mechanism for the conversion of parent nitriles into dithiadiazolyl radicals has been included. The third chapter describes the solid state structures of three dichlorophenyl dithiadiazolyl derivatives (2,4-, 2,5- and 3,5-dichlorophenyl-l,2,3,5-dithiadiazolyl). A further polymorph of 3,5-dichlorophenyl-1,2,3,5-dithiadiazolyl has also been included. The magnetic susceptibility of 2,4- and 3,5-dichlorophenyl-1,2,3,5-dithiadiazolyl has been investigated and the EPR analysis of all three compounds has been performed. These compounds are the first examples of neutral dithiadiazolyl radicals that form evenly spaced, segregated stacks in the solid state. Chapter four describes the dimer stacking structures of two further dichlorophenyl dithiadiazolyl derivatives (2,3- and 3,4-dichlorophenyl-1,2,3,5-dithiadiazolyl). The fifth chapter discusses the association of 3,5-dibromphenyl-1,2,3,5-dithiadiazolyl in the solid state. An investigation of this compound by EPR spectroscopy is also presented. Chapter six describes the trans cofacial association of p-iodophenyl-1,2,3,5-dithiadiazolyl in the solid state, only the second published example of this mode of dimerisation. The synthesis of o- and p-iodobenzonitrile are also described. An investigation of the EPR signal of this compound has also been included. Chapter seven describes the specialised techniques used in the synthesis of all the compounds. A list of the instruments used for analysis is also included.

Accelerated aging of 15 kV Cross-linked Polyethylene (XLPE) and Ethylene Propylene Rubber (EPR) power cables was carried out in the experiments set for the study of this thesis. The degradation of cable insulation under different aging conditions was studied and compared. The study helped to understand the effects of different factors on the aging of XLPE and EPR cable insulation. In the study, degradation of XLPE cable insulation caused by switching impulses was investigated. The deterioration of EPR cable insulation initiated by elevated ac voltage and switching impulses were also studied. Measurements of partial discharge parameters, capacitance, and dissipation factor were analyzed to evaluate the condition of cable insulation during accelerated aging process. Measurement of ac breakdown voltage provided evidence of the cables’ remaining dielectric strength after accelerated aging.

No description available.