The objective of this research project was to simulate the behavior of armor metals at high strain rates and large strains, using the Johnson-Cook visco-plastic model, while incorporating the formation of adiabatic shear bands. The model was then to be applied to three armor metals, namely maraging steel 300, high hardness armor (HHA), and aluminum alloy 5083-H131; supplied by the Canadian Department of National Defense and tested in compression at the University of Manitoba. The Johnson-Cook model can accurately simulate the behavior of BCC metal (steels) up to a point of thermal instability. Conditions for complete shear failure in the model match closely to conditions at which adiabatic shear bands formed in specimens tested experimentally. The Johnson-Cook model is not quite valid for FCC metals, such as aluminum, where strain rate and temperature effects are dependent on the strain while in the Johnson-Cook model, these parameters are separable.

The objective of this research project was to simulate the behavior of armor metals at high strain rates and large strains, using the Johnson-Cook visco-plastic model, while incorporating the formation of adiabatic shear bands. The model was then to be applied to three armor metals, namely maraging steel 300, high hardness armor (HHA), and aluminum alloy 5083-H131; supplied by the Canadian Department of National Defense and tested in compression at the University of Manitoba. The Johnson-Cook model can accurately simulate the behavior of BCC metal (steels) up to a point of thermal instability. Conditions for complete shear failure in the model match closely to conditions at which adiabatic shear bands formed in specimens tested experimentally. The Johnson-Cook model is not quite valid for FCC metals, such as aluminum, where strain rate and temperature effects are dependent on the strain while in the Johnson-Cook model, these parameters are separable.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisor: Herbert L. Berk. Vita. Includes bibliographical references.

Novas seqüências para supressão de contribuições indesejadas em Imagens e Espectroscopia por Ressonância Magnética Nuclear, tais como as provenientes da água, um solvente que sempre resulta num sinal muito intenso em sistemas biológicos, são motivos de estudo e desenvolvimento com diversas aplicações atuais. O método que estamos propondo aqui, uma versão adiabática de MEGA incorporada nas seqüências PRESS e STEAM, visa a supressão do sinal da água presente no espectro de um volume localizado em uma amostra intacta. Para o campo magnético desse estudo (2.0 Tesla) e pelas características do magneto usado nesses experimentos, o pico do solvente tem o inconveniente de apresentar uma linha espectral muito larga quando comparado com a extensão do deslocamento químico das fiações de açúcar. O resultado indesejado é a sobreposição pelas suas vertentes, das diversas outras linhas espectrais, cujo interesse é de extrema importância, como a de alguns sólidos solúveis de açúcares. O principal problema encontrado é que a separação entre os picos da água e dos açúcares próximos é da ordem de 1 ppm. A metodologia proposta consiste na aplicação de pulsos de gradiente de campo magnético intensos em conjunto com uma seqüência de pulsos de RF adiabáticos e convencionais, seletivos em freqüência e espacialmente, para suprimir o pico da água em uma região espectral muito específica, sem nenhum dano a linearidade de fase do espectro restante. Esse procedimento, aliado a uma localização espacial muito eficiente, aumenta ainda mais o poder de análise desta ferramenta, a 1H MRS. Os resultados obtidos em campo de 2.0Tesla (85 Hz/ppm) mostraram que as seqüências híbridas adiabáticas MEGA-PRESS e MEGA-STEAM são bem eficazes na supressão do pico da água, como era esperado. Além disso, sua aplicação no monitoramento do grau de maturação de frutas intactas através do seu teor de açúcar, se mostrou muito bom dadas as condições experimentais extremamente limiares apresentadas pelo espectrômetro / New sequences for suppression of undesirable contributions in Magnetic Resonance Imaging and Spectroscopy, such as water, a solvent that always represent a very strong peak in biological systems, are object of recent development for several different applications. The method proposed here, an adiabatic version of MEGA incorporated within PRESS and STEAM, aims the suppression of the water peak present on volume selected spectra of intact specimens. For the magnetic field of this study (2.0 Tesla) and for the characteristics of the magnet used in the experiments, the solvent peak has the inconvenience of having a large width as compared to the spread in chemical shift of the sugar fractions. The undesirable result is the superposition on its tail with severa1 spectral lines, whose interest is of extreme importance, such as some sugar solid solutes. The main problem encountered is that the separation between the water peak and the nearest sugar peaks is of the order of 1 ppm. The proposed methodology consists on the application of intense gradient pulses along with a sequence of adiabatic and conventional RF pulses, both frequency and spatially selective, to suppress the water peak in a very specific spectral region, without any disturbance of the phase linearity of the remaining part of the spectrum. This procedure, allied to a very efficient spatial localization, enhances the power of the very well-known tool, the 1H MRS. Results obtained at 2.0Tesla (85 Hz/ppm) show that the hybrid adiabatic sequences MEGA-PRESS and MEGA-STEAM are efficient on suppressing the water peak, as expected. Also, their application on monitoring the degree of ripeness of intact fruits through their sugar content, has shown very good results, considering the extremely limiar experimental conditions presented by the spectrometer

A computação quântica adiabática tem sua pedra angular no teorema adiabático, cuja eficiência está relacionada tradicionalmente à proporção da variação temporal do Hamiltoniano que descreve o sistema e o gap mínimo entre o estado fundamental e o primeiro excitado. Normalmente, esse gap tende a diminuir quando aumenta o número de recursos (bit quântico: qubit) de um processador quântico, exigindo dessa maneira variações lentas do Hamiltoniano para assim garantir uma dinâmica adiabática. Entre os candidatos para a sua implementação física, estão os qubits baseados em circuitos supercondutores os quais têm um grande potencial, por causa de seu alto controle e escalabilidade promissora. No entanto, quando esses qubits são implementados, eles têm uma fonte intrínseca de ruído devido a erros de fabricação, que não podem ser desprezados. Por isso, nesta tese nós estudamos como os efeitos causados pelas flutuações dos parâmetros físicos do qubit afetam o comportamento da fidelidade da computação, realizando com esse propósito a simulação da dinâmica de cadeias de spin pequenas desordenadas. A partir do análise exaustivo desse estúdio foi possível propor uma estratégia que permite aumentar a fidelidade considerando um sistema ruidoso. Por outro lado, motivados pelo interesse de obter critérios suficientes e necessários para satisfazer uma computação quântica adiabática e pelo fato que ainda não existe uma condição de adiabaticidade geral apesar de existir inúmeras propostas, nós apresentamos um novo critério que manifesta suficiência para sistemas mais gerais e finalmente apresentamos evidências de que tal condição seria um quantificador consistente. / Adiabatic quantum computation has its cornerstone in the adiabatic theorem, whose efficiency is traditionally related to the ratio of the Hamiltonian temporal variation that describes the system and the minimum gap between the ground state and the first excited state. Usually, this gap tends to decrease when the number of quantum resources (quantum bit: qubit) of a quantum processor increases, thus it requires slow variations of the Hamiltonian to ensure an adiabatic dynamic. Among the candidates for its physical implementation are the qubits superconducting circuit-based which have great potential because of their high control and promising scalability. However, when these qubits are implemented, they have an intrinsic source of noise due to manufacturing errors that can not be despised. Therefore, in this thesis we study how the effects caused by the fluctuations of the physical parameters of the qubit affect the behavior of the fidelity of the computation, accomplishing with this purpose the simulation of the dynamics of small disordered spin chains. From the exhaustive analysis of this studio, it was possible to propose a strategy that allows to increase the fidelity considering a noisy system. On the other hand, motivated by the interest of obtaining sufficient and necessary criteria to satisfy an adiabatic quantum computation and the fact that there is still no general adiabaticity condition despite there being numerous proposals, we present a new criterion that manifests sufficiency for more general systems and we finally presented evidence that such a condition would be a consistent quantifier.

O sistema de três elétrons é tratado pelo Método Adiabático Hiperesférico (HAA) impondo uma separação adiabática angular entre as coordenadas do core de dois elétrons e do elétron mais externo. Esta abordagem possibilita a substituição das equações diferenciais parciais, inerentes ao sistema de três elétrons, por dois sis¬temas de equações diferenciais ordinárias. Com a finalidade de investigar a origem das instabilidades numéricas do problema, obtivemos propriedades analíticas das funções de onda analisando a estrutura das singularidades regulares das equações diferenciais. Apresentamos curvas de potencial suportando estados ligados, dupla e triplamente excitados, calculadas na aproximação adiabática, para o dubleto e o quadrupleto de spins do átomo de lítio nas configurações de momentum angular s3 e sp2. Estes resultados abrem uma nova perspectiva, ao estabelecer uma metodologia fundamentada nas propriedades analíticas em contra-posição à técnicas puramente numéricas, para o estudo de sistemas de quatro corpos em geral, tais como excitons, sistemas bi-dimensionais em semi-condutores e sistemas positrônicos (Ps-H, PS2) / The three-electron system is treated in the hyperspherical adiabatic approach (HAA), imposing a angular adiabatic separation of the two-electron core and the outermost electron coordinates. This approach allow the substitution of the par-tial differential equations, inerent to the three-electron systems, by two systems of ordinary equation. To investigate the origin of the numerical instabilities, analyt¬ical properties for the wave functions are obtained analysing the regular singular structure of the differential equations. Potential curves supporting singly, doubly and triply excited states, calculated in the adiabatic approximation, are obtained for the doublet and quartet symmetry in the 53 and 5p2 angular momentum configuration. These results open a new insight, establishing a analytical approach in contraposi¬tion to purely numerical techniques, to the learning of general four-body systems, like excitons, bi-dimentional systems in semi-conductors and positronic systems (Ps-H, Ps2)

Energias de ligação para excitons ligados por impurezas doadoras no ZnSe e CdS são calculadas pelo Método Adiabático Hiperesférico. Os acoplamentos não adiabáticos são incluídos na equação radial levando a valores de energias menores que os valores variacionais encontrados na literatura. Estados ressonantes, similares a estados autoionizantes em átomos de dois elétrons, são obtidos acima do primeiro limiar de ionização elétron-impureza. / Binding energy for excitons trapped by impurities in ZnSe and CdS are calculated withing the hyperspherical adiabatic approach. The non adiabatic couplings are included in the radial equations leading to energies lower than the variational values available in the literature. Resonant states similar to autoionizing lines in atoms are predicted to lie above the first electron-impurity ionization threshold.

Este trabalho apresenta os resultados de um estudo experimental sobre a ocorrência do atraso de vaporização no escoamento de misturas de fluidos refrigerantes em tubos capilares adiabáticos, com o intuito de aprimorar modelos de simulação do desempenho desse componente do ciclo de refrigeração previamente desenvolvidos. Foi realizada uma série de levantamentos experimentais para o R410A, uma mistura quase azeotrópica composta de 50% de HFC 32 e 50% de HFC 125 em base mássica, utilizando a unidade laboratorial para estudo de tubos capilares do Laboratório de Máquinas Térmicas do PMEEPUSP. Os sensores de temperatura foram posicionados adequadamente ao longo do tubo capilar, com maior concentração na região onde o atraso de vaporização tende a ocorrer, de forma a permitir uma determinação acurada do ponto onde se inicia a mudança de fase para diversas condições operacionais e geométricas. Primeiramente foram realizados estudos para caracterização de alguns parâmetros geométricos, como a medição dos diâmetros dos tubos capilares e a determinação das curvas de fator de atrito em função do n° de Reynolds para cada tubo capilar. A seguir foram realizados 27 ensaios, nos quais se obteve um total de 44 pontos experimentais, caracterizando o efeito de vários parâmetros geométricos e operacionais na diferença de pressão de saturação e no comprimento do trecho metaestável. Os dados obtidos foram correlacionados com os parâmetros experimentais no intuito de obter uma correlação para previsão da diferença de pressão de saturação no escoamento do R 410A em tubos capilares adiabáticos. A correlação obtida prevê 67% dos valores experimentais dentro da faixa de ± 26,4%, com um erro médio de 3,2%, resultado semelhante a outros trabalhos existentes na literatura. / This work presents the results of an experimental study on the occurrence of the delay of vaporization in the flow of refrigerant blends in adiabatic capillary tubes in order to improve previously developed models that simulate this component of refrigeration cycle. Experiments were carried out for R410A, a near azeotropic mixture composed of 50% of HFC 32 and 50% of HFC 125 on mass basis, using the capillary tubes laboratorial unit of the Mechanical Engineering Department of University of São Paulo. The temperature sensors was properly positioned along the capillary tubes, concentrated in the region where the delay of vaporization is expected to happen, to allow an accurate determination of the flashing point inception for a several operational conditions and geometries. Preliminary studies for characterization of some geometric parameters like capillary tubes diameters and determination of friction factor curves as function of the Reynolds number were performed. A total of 44 experimental points, collected from 27 runs, allowed the characterization of the effect of geometric and operational parameters on the underpressure of vaporization and metastable length. A correlation was developed for predicting the underpressure of vaporization as function of operational parameters and capillary tube geometry. The obtained correlation predicts 67% of experimental data within a ± 26,4% range, with an average error of 3,2%. This result is similar to other works in the literature.

Two-phase flow in small tubes and channels is becoming a common phenomenon in industrial processes. However, the study of two-phase flow regimes in small tubes is still at its infancy. The previous studies are reviewed and discussed in the literature section. The problems and inconsistencies encountered in the earlier studies are presented and discussed. The experimental facility is introduced in the chapters that follow. They include a section on the design of the experimental system and the test sections, the selection of the experimental parameters and the introduction of the purposely-developed programs to control the experiments and collect and process the data. The methodology of the calibration and the uncertainty analysis, the problems encountered and their solutions and the single-phase validation experiments are also described. In this project we studied the effect of tube diameter and fluid flow parameters on flow patterns in small tubes using R134a as the working fluid. The tested tube diameters were 1.10, 2.01, 2.88 and 4.26 mm; the fluid pressures were 6, 10 and 14 bar; the liquid and gas superficial velocities covered a range of 0.04-5.0 m/s and 0.01-10.0 m/s respectively. The observed flow patterns included bubbly, dispersed bubble, confined bubble, slug, chum, annular and mist flow. Twelve integrated flow maps are sketched in this report. The obtained results were compared with earlier experiments by other workers and with existing models, with obvious differences in the prediction of the transition boundaries. A set of new models and correlations were developed, based on the new data for boiling R134a presented in this thesis, to predict the effect of tube diameter and fluid properties on the transition boundaries. Some also agreed with the limited data available from earlier studies for adiabatic air-water flow in small to normal size tubes.

In this thesis, we present a theoretical investigation of reactive processes involving the HeH$^+$ molecular ion, with applications in laboratory and astrophysical plasma physics. We consider in particular two processes, which are the charge transfer in H + He$^+$ collisions at low energy from a molecular approach and the photodissociation of HeH$^+$.<p><p>At the molecular level, the cross section is the basic quantity that has to be determined in order to achieve an understanding of reactive processes. Its calculation will be based on the description of the reactions using an emph{ab initio}, quantum mechanical approach. In this work, we will rely on the Born-Oppenheimer approximation, which allows the molecular motion to be separated into an electronic and a nuclear motion. The evaluation of cross sections then follows two steps.<p>The first is the determination of the electronic structure of the molecule. We will calculate the adiabatic potential energy curves of the excited electronic states as well as the dipole matrix elements between these states. The non-adiabatic radial and rotational couplings, which result from the breakdown of the Born-Oppenheimer approximation, are also estimated. The second step is to solve the nuclear motion, which we achieve using a time-dependent method based on the propagation of wave packets on the coupled electronic states. <p><p>A particular emphasis will be put on the importance of the excited states and of the non-adiabatic couplings in the description of reactive processes. <p>In the treatment of the charge transfer reaction between H and He$^+$ in excited states, it is well known that the non-adiabatic radial couplings cannot be neglected. However, we will show that the inclusion of the non-adiabatic rotational couplings is also necessary in order to obtain accurate state-to-state cross sections.<p>In the description of the photodissociation of HeH$^+$ from its ground state, we will show the influence of the excited states on the rate constant and the role of the non-adiabatic radial couplings in the determination of partial cross sections.<p>We will also consider the possible astrophysical applications of the first triplet state of HeH$^+$. We will show that this state is metastable by evaluating its lifetime, and calculate the cross sections and rate constants for the photodissociation and radiative association of HeH$^+$ in this state.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished