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A água, conhecida como solvente universal, participa da maioria das reações químicas e composições biológicas, tem importância vital em nosso planeta, tornando a vida como conhecemos inconcebível sem a sua presença. Tais propriedades advêm da forma como as moléculas interagem entre si, e a principal ligação química existente é a ligação de hidrogênio. Portanto, compreender como ela acontece e ser capaz de manipulá-la pode ser considerada uma importante técnica na busca de novos comportamentos. Esta dissertação visa compreender como o campo elétrico nas suas variantes: direção, sentido e intensidade podem afetar a água. Sendo tal estudo realizado através de cálculos utilizando métodos de química quântica: Teoria do Funcional da Densidade e a Teoria de Perturbação Moller-Plesset de segunda ordem. Como resultado obteve-se que quando o campo elétrico é aplicado em uma direção e sentido fora do plano da ligação de hidrogênio, a estrutura inicial tende a se rearranjar produzindo uma estrutura mais fracamente ligada do que a ordinária. Quando aplicamos o campo no plano da ligação de hidrogênio, temos resultados mais pronunciados, sendo que, se o sentido for : Doador -> Receptor a estrutura resultante estará mais fracamente ligada e se o sentido for Receptor -> Doador a estrutura produzida estará mais fortemente ligada. Os resultados obtidos mostram também que tais mudanças acontecem principalmente devido a alterações eletrostáticas, como mudança na densidade de carga da ligação de hidrogênio. Também confirmou-se um ponto crítico no campo 0,15 V/Å, como sugerido na literatura. Esta singularidade foi atribuída neste trabalho à uma transição estrutural. O campo também modificou a importância das interações secundárias, principalmente entre os átomos de oxigênio, e ao desligá-lo, o sistema tende a voltar ao estado inicial. / The water is know as the universal solvent, part of most chemical reactions and biological compositions, it is vitally important to our planet, making life as we know it inconceivable without its presence. These properties arise from how the molecules interact, and the main existing chemical link is the hydrogen bond. Therefore, to understand how this happens and be able to manipulate it can be considered an important technique in the search for new behaviors. Thus, this paper aims to understand how the electric field in its variants: direction, sense and intensity can affect the water. This study is undertaken through calculations using quantum chemistry methods: Density Functional Theory and Moller-Plesset Perturbation Theory to Second Order. As a result was found that when the electric field is applied in direction and sense out of the plane of the hydrogen bond, the initial structure tends to rearrange itself to produce a more loosely bound than the ordinary. When the electric field is applied in the hydrogen bond plane, the have results obtained are more pronounced. Sense is: Donor -> Receiver initial structure will be more loosely connected and that when the sense is Receiver -> Donor initial structure will be tightly linked. Our results also show that such changes occur mainly due to electrostatic changes, mainly in the change in the charge density of hydrogen bond. It was also confirmed a critical point in the field 0, 15 V / Å, as suggested by Vegiri. This was attributed to a structural transition. The field also changed the importance of secondary interactions, especially between the oxygen atoms. And when the field is shutdown the system tends back to its to initial structure.

Neste trabalho apresentamos um procedimento para o cálculo da contribuição eletrônica para o gradiente de campo elétrico no núcleo (GCE), baseado no método de recorrência e no método de arbitais \"muffin-tin\" linearizados (LMTO) na representação forteme~ te ligada (\"tlght-binding\"). Este esquema é desenvolvido no esp~ ço real e pode ser aplicado em sistemas sem simetria, tais como metais amorfos, onde métodos de espaço-k não podem ser utilizados. A contribuição eletrônica é a dominante em sistemas metálicos e requer para sua avaliação o conhecimento das funções de onda eletrônicas do sistema. O esquema sugerido aqui, possui duas etapas principais: a es colha da Hamiltoniana do sistema, que neste caso foi a LMTO na aproximação de esfera atômica fortemente ligada (LMTO-ASA-TB), e o desenvolvimento dos termos do tensor GCE em uma abordagem de orbl tais fortemente ligados. Para o cálculo deste último, sugerimos a utilização do método de recorrência na obtenção dos elementos diagonais e não diagonais da função de Green, que compõem as expressões dos termos do tensor GGE em cada sitio. Como teste para nosso procedimento de espaço real, calculamos o GCE para o ao longo do eixo Zr hcp com o eixo /1. z do sistema de /1. c do cristal e também ao longo de coordenadas uma direção arbitrária. Os resultados se mostraram independentes da escolha do sistema, mostrando que o procedimento funciona na ausência de simetria. FinaJ.mente, como iLustração, calcuLamos a distribuição de GCE\'s para um agJ.omerado de Zt amorfo construído segundo o mode- Io de empacotamento denso e aleatório de esferas rígidas (DRPHS). / We present here a new method to cal-culate the el-ectronic contrlbution to the electric field gradient (GCE), which is based on the recursion method and in the recently developed tight-binding representation of the LMI0 method. This is a real-space scheme and can be applied to systems which lack symmetry, as amorphous metal.s where R-space methods can not be used. The electronic contribution is dominant Ín metalLÍc systems and requÍres for its evaluation the knowledge of the electronic wave functions of the system. The scheme I¡/e suggest here has two main steps: the choice of the Hamiltonian which in this case was the tight-binding LMT0 i\'n the atomÍc sþhere approxÍmation ( t-Uf O-ASA-TB ) and the deveJ.opment of the GCE tensor\'s components in a tight-binding approach. In the last step we suggest to use the recursion method to caLculate the diagonal and the off-diagonal Greenrs function eLements which build the GCE tensot\'s components in each site. As a test of our real space method we calculate the GCE for hcp zr with the c axis parall-eL to the crystaI\' s z axis and also in an arbitrary direction. The resuLts have shown to be independent of the choice of the system, showing that the procedure works in the abcense ofl symmetry. FinaJ.ly, as an iliustration we cal-cuLate the GCErs distribution for an amorphous Zr cluster buÍ1t in the model of dense random packing of hard spheres (DRPHS).

Estudamos as propriedades eletrônicas, estruturais e hiperfinas, nos sítios de nitrogênio, para o composto imidazol nas fases gasosa e sólida. Utilizamos o método PAW que é um método ab initio all-electron, dentro da Teoria do Funcional da Densidade, através do código computacional CP-PAW. Nossos valores, tanto para a fase gasosa quanto para a fase cristalina do gradiente de campo elétrico no núcleo, de freqüência de acoplamento quadrupolar (ν) e parâmetro de assimetria (η) estão em ótima concordância com os resultados experimentais da literatura e são os primeiros resultados obtidos, por método ab initio no espaço recíproco, para os átomos de nitrogênio no imidazol cristalino. Utilizamos resultados da literatura e também aqui calculados para estudar a tendência de comportamento tanto de ν quanto de η para diferentes meros (um, dois, três, cadeia infinita) e cristal investigando, assim, a estreita influência das ligações de hidrogênio sobre os valores do Gradiente de Campo Elétrico nos núcleos de nitrogênio. / Here we study structural, electronic and hyperfine properties at the Nitrogen sites in imidazole in the gas and the crystal phases. We use the PAW method which is an ab initio all electron method in the framework of the Density Functional Theory, as embodied in the computer code CP-PAW. The results for quadrupole coupling (ν) and asymmetry parameter (η) at the gas and at the crystal phases are in excellent agreement with the experimental values in the literature. This is the first time that such calculations are performed for the crystalline imidazole through a reciprocal space approach. We also study the behavior of both ν and η trends studing diferent meres (one, two, three and infinite chain) and cristal to investigate the influence of hydrogen bonding on the Electric Field Gradient at the nucleus.

A abóbora se destaca como uma hortaliça de grande potencial nutritivo e tecnológico. Para que se possa aumentar a variabilidade dos produtos de origem vegetal disponíveis no mercado, a abóbora deve ser submetida a processos térmicos que visam prolongar a sua vida de prateleira, além de realizar as modificações necessárias para a sua comercialização. Neste contexto, o objetivo principal da presente pesquisa foi avaliar a aplicação da tecnologia de aquecimento ôhmico em diferentes etapas a serem realizadas durante o processamento da abóbora híbrida Tetsukabuto. Na primeira etapa do trabalho, objetivou-se investigar os efeitos do branqueamento convencional e ôhmico (realizados a 80 ºC durante 4 minutos e 163 V no aquecimento ôhmico) sobre a inativação da enzima peroxidase e sobre a cor das abóboras. Para o ajuste dos dados relativos à inativação enzimática, diferentes modelos cinéticos foram avaliados, sendo o modelo de distribuição de Weibull o escolhido para descrever a cinética de inativação da peroxidase. Com este estudo, foi possível observar que o branqueamento com campo elétrico afetou significativamente os parâmetros cinéticos de inativação enzimática, tornando esse processo mais rápido. A aplicação de ambas as tecnologias não causou modificações significativas dos parâmetros de cor da abóbora. Na segunda etapa do trabalho, creme de abóbora foi pasteurizado via tratamento térmico convencional e ôhmico realizados a 90 ºC por 2 horas e 47 V no aquecimento ôhmico. O objetivo dessa etapa foi avaliar os efeitos de ambas as tecnologias sobre a variação de cor, degradação de carotenoides totais e mudanças nos parâmetros reológicos do creme. Foi possível observar que a cor do creme foi levemente afetada durante a aplicação dos processos, tornando-se ligeiramente mais escura e perdendo o tom amarelado. Além disso, foi verificada perda no teor de carotenoides totais presentes no creme. Ainda, não foi observado um efeito não-térmico adicional do campo elétrico sobre a cor e os carotenoides presentes no produto. O creme de abóbora apresentou comportamento pseudoplástico e que se ajustou satisfatoriamente ao Modelo da Lei da Potência. Com a aplicação dos tratamentos, foi observado um aumento significativo no índice de consistência do creme, sendo que ambas as tecnologias não apresentaram diferenças representativas entre si. O conjunto de resultados obtidos pelo presente trabalho sugere que o aquecimento ôhmico é uma tecnologia promissora a ser aplicada em diferentes operações envolvidas durante o processamento de alimentos. / Pumpkins stand out as vegetable of great nutritional and technological potential. In order to increase the variability of vegetal products available on the market, pumpkins must be subjected to thermal process which can prolong its shelf life, and imposing also the necessary modifications for its commercialization. In this context, the main objective of the present research was to evaluate the application of ohmic heating technology in different stages carried out during the processing of the hybrid pumpkin Tetsukabuto. In the first part of the work, the objective was to investigate the effects of conventional and ohmic blanching (performed at 80 ºC during 4 minutes and 163 V in the ohmic heating) on the inactivation of peroxidase enzyme and on the color of the pumpkins. In order to adjust the data related to enzyme inactivation, different kinetic models were evaluated, being the Weibull distribution model chosen to describe the inactivation kinetics of peroxidase. With this study, it was possible to observe that the electric field blanching significantly affected the kinetic parameters of enzymatic inactivation, turning this process faster. The application of both technologies did not cause significant modifications of pumpkins color parameters. In the second part of the work, pumpkin cream was pasteurized via conventional and ohmic thermal treatment carried out at 90 ºC for 2 hours and 47 V in the ohmic heating. The objective of this stage was to evaluate the effects of both technologies on the color variation, the degradation of total carotenoids and the changes in rheological parameters of the cream. It was possible to observe that the color of the cream was slightly affected during the application of the processes, becoming slightly darker and losing its yellowish tone. In addition, it was verified loss of total carotenoid content in the cream. Furthermore, no additional non-thermal effect of the electric field on the color and on carotenoids present in the product was observed. The pumpkin cream presented a shear thinning behavior and was satisfactorily adjusted to the Power Law Model. It was observed a significant increase in the consistency index of the cream after the application of both treatments, and both technologies did not present significative differences between them. The overall results obtained in the present work suggests that ohmic heating is a promising technology to be applied in different operations involved during food processing.

Neste trabalho apresentamos um procedimento para o cálculo da contribuição eletrônica para o gradiente de campo elétrico no núcleo (GCE), baseado no método de recorrência e no método de arbitais \"muffin-tin\" linearizados (LMTO) na representação forteme~ te ligada (\"tlght-binding\"). Este esquema é desenvolvido no esp~ ço real e pode ser aplicado em sistemas sem simetria, tais como metais amorfos, onde métodos de espaço-k não podem ser utilizados. A contribuição eletrônica é a dominante em sistemas metálicos e requer para sua avaliação o conhecimento das funções de onda eletrônicas do sistema. O esquema sugerido aqui, possui duas etapas principais: a es colha da Hamiltoniana do sistema, que neste caso foi a LMTO na aproximação de esfera atômica fortemente ligada (LMTO-ASA-TB), e o desenvolvimento dos termos do tensor GCE em uma abordagem de orbl tais fortemente ligados. Para o cálculo deste último, sugerimos a utilização do método de recorrência na obtenção dos elementos diagonais e não diagonais da função de Green, que compõem as expressões dos termos do tensor GGE em cada sitio. Como teste para nosso procedimento de espaço real, calculamos o GCE para o ao longo do eixo Zr hcp com o eixo /1. z do sistema de /1. c do cristal e também ao longo de coordenadas uma direção arbitrária. Os resultados se mostraram independentes da escolha do sistema, mostrando que o procedimento funciona na ausência de simetria. FinaJ.mente, como iLustração, calcuLamos a distribuição de GCE\'s para um agJ.omerado de Zt amorfo construído segundo o mode- Io de empacotamento denso e aleatório de esferas rígidas (DRPHS). / We present here a new method to cal-culate the el-ectronic contrlbution to the electric field gradient (GCE), which is based on the recursion method and in the recently developed tight-binding representation of the LMI0 method. This is a real-space scheme and can be applied to systems which lack symmetry, as amorphous metal.s where R-space methods can not be used. The electronic contribution is dominant Ín metalLÍc systems and requÍres for its evaluation the knowledge of the electronic wave functions of the system. The scheme I¡/e suggest here has two main steps: the choice of the Hamiltonian which in this case was the tight-binding LMT0 i\'n the atomÍc sþhere approxÍmation ( t-Uf O-ASA-TB ) and the deveJ.opment of the GCE tensor\'s components in a tight-binding approach. In the last step we suggest to use the recursion method to caLculate the diagonal and the off-diagonal Greenrs function eLements which build the GCE tensot\'s components in each site. As a test of our real space method we calculate the GCE for hcp zr with the c axis parall-eL to the crystaI\' s z axis and also in an arbitrary direction. The resuLts have shown to be independent of the choice of the system, showing that the procedure works in the abcense ofl symmetry. FinaJ.ly, as an iliustration we cal-cuLate the GCErs distribution for an amorphous Zr cluster buÍ1t in the model of dense random packing of hard spheres (DRPHS).

With the rise of modern infrastructure and systems, testing and evaluation of specific components such as structural health monitoring is becoming increasingly important. Fiber optic sensors are ideal for testing and evaluating these systems due many advantages such as their lightweight, compact, and dielectric nature. This thesis presents a novel method for detecting electric fields in harsh environments with slab coupled optical sensors (SCOS) as well as a novel method for detecting strain gradients on a Hopkinson bar specimen using fiber Bragg gratings (FBG). Fiber optic electric field sensors are ideal for characterizing the electric field in many different systems. Unfortunately many of these systems such as railguns or plasma discharge systems produce one or more noise types such as vibrational noise that contribute to a harsh environment on the fiber optic sensor. When fiber optic sensors are placed in a harsh environment, multiple noise types can overwhelm the measurement from the fiber optic sensor. To make the fiber optic sensor suitable for a harsh environment it must be able to overcome all these noise types simultaneously to operate in a harsh environment rather than just overcome a single noise type. This work shows how to eliminate three different noise types in a fiber optic sensor induced by a harsh environment simultaneously. Specifically, non-localized vibration induced interferometric noise is up converted to higher frequency bands by single tone phase modulation. Then localized vibrational noise, and radio frequency (RF) noise are all eliminated using a push-pull SCOS configuration to allow for an optical measurement of an electric field in a harsh environment. The development and validation of a high-speed, full-spectrum measurement technique is described for fiber Bragg grating sensors in this work. A fiber Bragg grating is surface mounted to a split Hopkinson tensile bar specimen to induce high strain rates. The high strain gradients and large strains which indicate material failure are analyzed under high strain rates up to 500 s-1. The fiber Bragg grating is interrogated using a high-speed full-spectrum solid state interrogator with a repetition rate of 100 kHz. The captured deformed spectra are analyzed for strain gradients using a default interior point algorithm in combination with the modified transfer matrix approach. This work shows that by using high-speed full-spectrum interrogation of a fiber Bragg grating and the modified transfer matrix method, highly localized strain gradients and discontinuities can be measured without a direct line of sight.

Having a net dipole moment, water molecules tend to align with an external electric field. The re-orientation of water molecules to align with the field direction can result in structural and dynamic changes in liquid water. Studying these changes can help us to understand the role of an E-field in many biological systems, chemical reactions, and many technological advancements. In short, the application of static electric fields causes molecules to stay aligned with the field, so, fewer hydrogen bonds break, and molecules have slower dynamics. This type of field can be used when the mobility of water molecules needs to be reduced, like in electroporation. Alternating electric fields, on the other hand, cause continuous re-orientation of dipole moments, which results in more H bond breaking, water is less structured, and molecules have faster motion. Water under static and alternating electric fields have several applications in science and technology. Although many of the interesting usages of the application of electric fields to water happen at surfaces, the response of hydrogen bonding of water molecules to an E-field is still not fully understood even in bulk. For instance, the rate of hydrogen bond breaking, the re-orientation of water molecules, and the random walk of water molecules under the restrictions of the static electric field have not been thoroughly assessed. The static electric field limits the re-orientation of water molecules, but the translation reduces at the same time, this is clear evidence of roto-translational coupling, and the static electric field is a great groundwork for studying this coupling which is generated by the hydrogen bonds. For studying the effects of an E-field on H-bonding dynamics in depth, we need a model of hydrogen bonding. There are a few models for dynamics of H-bonding and reorientation of water molecules, including Luzar and Chandler model, published in 1996, and the Laage and Hynes jump model, published in 2006, which are described in the introduction chapter. The two models are related but have different perspectives, so it would be very interesting to look for a more general framework of hydrogen bonding by combining these two models, with the help of the influence of external electric fields. We also explain the relation of the random walk diffusion of water molecules and the hydrogen bonding. Since the external electric field can change the dipole moment of water molecules, for a more realistic picture, we need do the simulations with sophisticated polarizable water models to obtain a better estimate of the behavior of experimental water in an electric field. In this thesis, we introduce our generalized hydrogen bond framework; then we assess this framework, as well as other static and dynamic properties of water under static and alternating electric fields.

Rational magnetic flux surfaces in fusion (toroidal plasma confinement) devices can break the magnetic field lines and reconnect them in the form of magnetic islands. Formation of these magnetic islands can have a serious impact on the plasma confinement properties of the device. Islands can in general degrade the confinement by mixing up different regions of the plasma. However there has been experimental evidence of confinement improvement by island induced transport barriers, under certain conditions. Even though there are a large number of theoretical and experimental works on magnetic islands to date, there is clearly a paucity of convincing experimental understanding on the nature of behaviour of islands in plasma. This thesis reports detailed experimental studies conducted on the H-1NF heliac stellarator, to gain an in-depth understanding of magnetic islands and their influence in plasma confinement.¶ Work reported in this thesis can be mainly divided into three parts: (a) high resolution imaging of vacuum magnetic islands and flux surfaces of H-1NF, (b) accurate computer modeling of H-1NF magnetic geometry and (c) detailed experiments on magnetic islands in plasma configurations.¶ Electron-beam wire-tomography in the H-1NF has been used for the high resolution mapping of vacuum magnetic flux surfaces and islands. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, has enabled systematic exploration of magnetic islands and surfaces of interest. A fast mapping technique has been developed, which significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields.¶ Flux surface mapping has been carried out at various magnetic configurations and field strengths. The extreme accuracy of this technique has been exploited to understand the nature of error fields, by point-by-point matching with computer tracing results. This has helped in developing a best-fit computer model for H-1NF magnetic configurations, which can predict rotational transform correct to three decimal places. Results from plasma experiments on magnetic configuration studies are best explained by the new model.¶ Experiments with low order magnetic islands in plasma configurations yielded some new results. It has been observed that the low order magnetic islands (m = 2) near the core of the plasma serve as pockets of improved confinement region under favourable conditions. This results in significant profile modifications including enhancement of the radial electric field near the core to a large positive value. The characteristics of islands are found to be dependent on the plasma collisionality and the island width.¶ Experiments with a magnetic configuration which exhibits no vacuum islands, but the core rotational transform very close to low order rational value, show a spontaneous transition of the radial electric field near the core to a large positive value (nearly 5 kV/m), with a strong electric field shear (nearly 700 kV/m2) and localised improvement in confinement, during the discharge. Evidence indicates that the transition is driven by the excitation of low order magnetic islands near the axis during the plasma discharge, due to the modification of rotational transform profile by toroidal plasma currents. The situation is similar to the Core Electron-Root Confinement (CERC) observed during high temperature ECH plasma discharges on other helical devices. This result provides an experimental evidence for the hypothesis that the threshold conditions for observing CERC can be reduced by exciting magnetic islands near the core of the plasma.

Cellulose whiskers (CWs) obtained from naturally occuring cellulose are nano-inclusions which show a lot of promise as mechanical reinforcements in polymers. Typically, a relatively high content is added to realize improvement in effective mechanical behavior. This enhancement in modulus is usually followed by a modest increase in strength but generally the ductility and toughness decrease. Our approach is to use small concentrations of CWs so as not to detrimentally affect processability, toughness and ductility. By aligning the small concentrations, we target the same kind of improvement in modulus and strength as reported in the literature, but at much smaller volume contents. In this work, we investigate the effect of AC electric field on the alignment of dispersed nanoscale CW in a polymer. Polyvinyl acetate (PVAc) is used as the model polymer because of the good interaction between CWs and PVAc. A low concentration of 0.4wt% was used for the study. Two dispersion methods, namely basic and modified, were developed. The basic method led to micron scale dispersion. Using the modified method, CWs were individually dispersed in PVAc with average lengths and diameters of 260 nm and 8 nm respectively yielding an aspect ratio of approximately 30. The behavior of CWs (alignment and chain formation) under an applied electric field was found to be a function of applied electric field magnitude, frequency and duration. Following alignment, the CW/PVAc nanocomposites are thermally dried in the presence of electric field to maintain the aligned microstructure. Improvements in dielectric constant and mechanical properties were observed for the aligned cases as compared to random case and pure PVAc. The optimal electric field magnitude, frequency and duration for the alignment and chain formation were found to be 200Vpp/mm, 50 KHz for duration of 20 minutes for the microcomposite and 250Vpp/mm, 10KHz for a duration of 1hr for the nanocomposite. At 0.4wt% concentration, 21% increase in dielectric constant for the optimal nanocomposite case. Above Tg, a 680% improvement in elastic modulus at 0.4wt% concentration for the optimal nanocomposite case. The reason for the significant reinforcement is attributed to alignment (rotation and chain formation) and chain-chain interaction (3D network formation and hydrogen bonding).