Thesis. 1976. B.S.--Massachusetts Institute of Technology. Dept. of Physics. / Microfiche copy available in Archives and Science. / B.S.

Neste trabalho o formalismo semi-clássico convergente sugerido por Cattani é desenvolvido para calcular o alargamento e deslocamento provocado por colisões eletrônicas de linhas espectrais de átomos neutros em plasmas . Para testar o referido formalismo calculamos a largura e o deslocamento de muitas linhas espectrais do hélio neutro em plasmas com temperaturas que vão desde 5000 até 40000K e densidades eletrônicas que variam de 10 POT. -15 até 10 POT. -18cm POT. -3. Efeitos de \"screening\" de Debye e trajetória não retilínea dos elétrons são levados em conta no formalismo. Um estudo sobre a contribuição das colisões iônicas para o alargamento e deslocamento desenvolvido para elétrons e as aproximações quase estática de Griem e adiabática de Barnard, Cooper e Smith, e Griem, Baranger, Kolb e Oertel. Os alargamentos e deslocamentos calculados são comparados com resultados experimentais obtidos por Wulff, Berg e colaboradores, Kelleher e Diatta e teóricos previstos por Griem e Sahal-Bréchot. / n this work the semiclassical convergent formalism suggested by Cattani is developed to calculate the broadening and shift of spectral lines produced by electronic collisions of neutral atoms in plasmas. To test this theory we calculate the widths and shifts of many spectral lines of neutral helium in plasmas with temperatures that goes from 5000 up to 40000 K and electronic densities in the range of 10 POT. -15 até 10 POT. -18cm POT. -3. Effects of Debye screening and non straight line trajectory are taken into account in our approach. To study the ionic collisional contribution to the widths and shifts we use the same convergent treatment developed for electrons and the quasi-static approximation of Griem and adiabatic approximation of Barnard, Cooper and Smith, and Griem, Baranger, Kolb and Oertel. The calculated widths and shifts are compared with experimental results obtained by Wulff, Berg and collaborators, Kelleher and Diatta and theoretical predictions of Griem and Sahal-Bréchot.

<p> This dissertation encompasses experimental and theoretical studies on two cornerstones of modern nonlinear optics: laser filamentation and harmonic generation. Laser filaments are self-guided light structures balanced by Kerr self-focusing and diffraction/plasma defocusing, enabling applications in lightning guiding, long-range spectroscopy, and high-precision laser weapons. Harmonic generation is a nonlinear process that up-converts optical frequencies, and it is a promising source of table-top, ultrashort X-ray/UV radiation. </p><p> The goal of this work is two-fold: control and visualization of nonlinear optical phenomena. First, variable focusing geometries are used to eliminate high-power laser multifilamentation, which is a stochastic process that is notoriously difficult to control. Next, two-color pump-probe experimental schemes are used to enhance third-harmonic generation in air by several orders of magnitude. Our experimental results agree well with calculations based on state-of-the-art unidirectional pulse propagation equations, which give insight into the physical mechanisms underlying our experimental findings. An overarching theme of this work is ultrafast visualization: by combining femtosecond-time-resolved pump-probe methods with advanced quantitative phase microscopy, we can visualize and quantitatively characterize dynamically-evolving micro-structures during various nonlinear laser-matter interactions. Finally, this work will describe some novel properties of mid-infrared and long-wavelength infrared ultrashort pulse propagation, with a focus on the generation of light bullets, which represent a holy grail of nonlinear optics.</p><p>

Ng, Siu Fai = 溫暖稠密物質及高能量密度物理的研究 / 吳肇輝. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 126-133). / Abstracts also in Chinese. / Ng, Siu Fai = Wen nuan chou mi wu zhi ji gao neng liang mi du wu li de yan jiu / Wu Zhaohui. / Chapter 1 --- Introduction --- p.16 / Chapter 1.1 --- General review of high energy density physics --- p.16 / Chapter 1.2 --- General review of warm dense matter --- p.20 / Chapter 1.2.1 --- Physics of warm dense matter --- p.20 / Chapter 1.2.2 --- Uncertainties of warm dense matter --- p.23 / Chapter 1.2.3 --- Challenges of warm dense matter studies --- p.25 / Chapter 1.3 --- Use of intense heavy ion beam --- p.27 / Chapter 1.4 --- Motivation and structure of this thesis --- p.32 / Chapter 2 --- Hydrodynamic simulations --- p.34 / Chapter 2.1 --- Lagrangian hydrodynamic code --- p.34 / Chapter 2.2 --- Hydrodynamic equations --- p.35 / Chapter 2.3 --- Artificial viscosity --- p.36 / Chapter 3 --- Equations of state --- p.38 / Chapter 3.1 --- Van der Waals' equation of state --- p.39 / Chapter 3.2 --- Quotidian equation of state --- p.41 / Chapter 3.3 --- Saha-based equation of state --- p.41 / Chapter 3.4 --- Inverse power potentials equation of state --- p.48 / Chapter 3.5 --- Gruneisen-type equation of state --- p.53 / Chapter 3.6 --- Discussion --- p.59 / Chapter 4 --- Single bubble sonoluminescence --- p.63 / Chapter 4.1 --- Introduction --- p.63 / Chapter 4.2 --- Theory of sonoluminescence --- p.65 / Chapter 4.2.1 --- Bubble wall dynamics --- p.66 / Chapter 4.2.2 --- Radiation transport --- p.67 / Chapter 4.2.3 --- Diffusive stability --- p.68 / Chapter 4.3 --- Numerical simulation --- p.68 / Chapter 4.3.1 --- Determination of the ambient radius --- p.69 / Chapter 4.3.2 --- Simulations using SEOS --- p.70 / Chapter 4.3.3 --- Simulations using QEOS --- p.77 / Chapter 4.4 --- Conclusion --- p.82 / Chapter 5 --- Collapsing bubble in ion-beam-heated metal --- p.83 / Chapter 5.1 --- Introduction --- p.83 / Chapter 5.2 --- Bubble collapse --- p.86 / Chapter 5.2.1 --- First step of collapse --- p.88 / Chapter 5.2.2 --- Stagnation point and bubble size --- p.89 / Chapter 5.2.3 --- Outer boundary and metal thickness --- p.91 / Chapter 5.2.4 --- Metal layer just outside bubble --- p.93 / Chapter 5.3 --- Effect of equation of state used --- p.95 / Chapter 5.3.1 --- Inverse power potentials equation of state --- p.95 / Chapter 5.3.2 --- Effect of ionization --- p.97 / Chapter 5.3.3 --- Effect of hard core --- p.97 / Chapter 5.3.4 --- Effect of EOS for metal --- p.97 / Chapter 5.4 --- Effect of proposed experimental parameters --- p.102 / Chapter 5.4.1 --- Initial gas density --- p.102 / Chapter 5.4.2 --- Energy deposition rate --- p.102 / Chapter 5.5 --- Conclusion and discussion --- p.105 / Chapter 6 --- High coupling efficiency compression by intense ion beams --- p.108 / Chapter 6.1 --- Introduction --- p.108 / Chapter 6.2 --- Ion stopping formulation --- p.111 / Chapter 6.3 --- Numerical simulation --- p.112 / Chapter 6.3.1 --- Lithium hydride target --- p.112 / Chapter 6.3.2 --- Underdense aluminum foam --- p.118 / Chapter 6.4 --- Conclusion --- p.119 / Chapter 7 --- Conclusion --- p.121 / Chapter 7.1 --- Summary --- p.121 / Chapter 7.2 --- Suggestions for future work --- p.123 / Bibliography --- p.126

Este trabalho procura caracterizar uma cavidade eletromagnetica ressonante toroidal teorica e experimentalmente. Do ponto de vista teorico, foi obtida a relacao de dispersao para as autofrequencias da cavidade, resolvendo as equacoes de maxwell usando teoria de perturbacao. Duas solucoes em ordem zero foram obtidas: uma em termos de funcoes hipergeometricas e outra em termos de uma serie de frobenius. Os resultados foram comparados com a literatura. Baseados nestes autovalores calculados, foi projetado e construido um toroide em cobre, com seccao transversal circular e razao de aspecto 1,25 (\'R IND.0\'=0.125m e \'R IND.0\'=0.100m). As medidas experimentais realizadas incluem as autofrequencias e seus respectivos indices de merito. Pelo que se sabe, estas medidas foram as primeiras feitas num toroide. Os dados experimentais tambem foram comparados com os resultados teoricos, permitindo estabelecer qual dos tratamentos e mais compativel com a realidade e fornecendo elementos para um aprimoramento da teoria / Electromagnetic resonance in toroidal cavities - theory and experience

O presente trabalho tem como objetivo principal avaliar o efeito da nitretação e da carbonetação por plasma na liga Ti-6Al-4V sob condições de fluência na faixa de 500 a 600°C. Os resultados permitiram concluir que a microestrutura da liga Ti-6Al-4V é constituída pela configuração de Widmanstätten, com uma dureza média de 300 ± 17 HV para a condição como recebida e 334±18 HV para a amostra tratada termicamente. Após os tratamentos termoquímicos por plasma observou-se para a nitretação a plasma a formação de uma camada nitretada de espessura média de 4?m e dureza de 1539 ± 157 HV. A dureza está relacionada com a espessura e a presença das fases Ti2N e TiN identificadas por difratometria de raios X. Para a carbonetação a plasma verificou-se a formação de uma camada constituída pelo carboneto TiC0,66, de espessura média igual a 1,5 ?m e dureza de 809 ± 79 HV. A nitretação a plasma reduziu os valores de rugosidade média de 1,29?m do material como recebido para 1,18?m e a carbonetação aumentou esse valor de 1,28 ?m da amostra tratada termicamente para 2,02 ?m. Os testes demonstraram que a nitretação reduziu a taxa de fluência e aumentou a vida em fluência a 600 °C. A carbonetação contribuiu para reduzir a taxa estacionária. Com base nos valores de energia de ativação na faixa de 272 a 309 kJ/mol e nos valores do expoente de tensão de 4,82 a 7,28, estima-se que o mecanismo dominante de deformação por fluência está associado à escalagem de discordâncias para todas as condições experimentais. A análise fractográfica revelou que os mecanismos de fratura estão associados principalmente à nucleação e coalescência de microcavidades e decoesão intergranular. / This work aims to evaluate the effect of plasma nitriding and carburizing on the Ti-6Al-4V alloy subjected to creep in the range 500-600 °C. The results showed that the microstructure of Ti-6Al-4V consists of Widmanstätten morphologie, with a hardness of 300 ± 17 HV for the as received condition and 334 ± 18 HV for the sample heat-treated. After treatments thermochemical by plasma was observed for plasma nitriding the formation of a nitrided layer of hardness of 1539 ± 157 HV and of average thickness of 4 ?m. The hardness is due to the thickness and the presence of Ti2N and TiN phases identified by X-ray diffraction. For plasma carburizing was observed the formation of a carbide layer composed of TiC0,66, of average thickness equal to 1.5 ?m and hardness of 809 ± 79 HV. The treatment of plasma nitriding reduced the values of average roughness of 1.29 ?m of the as received condition to 1.18 ?m and the plasma carburizing increased this value of 1.28 ?m of the sample heat-treated to 2.02 ?m. The tests showed that the plasma nitriding reduced the rate of creep and increased the creep life at 600 °C. Based on the values of activation energy in the range 272-309 kJ / mol and the values of stress exponent from 4.82 to 7.28, it was estimated that the dominant mechanism of creep deformation is associated with the climb of dislocations for all experimental conditions. The fractographic analysis revealed that the fracture mechanisms are mainly associated with the nucleation and coalescence of microvoids and decoehasion intergranular.

Neste trabalho o formalismo semi-clássico convergente sugerido por Cattani é desenvolvido para calcular o alargamento e deslocamento provocado por colisões eletrônicas de linhas espectrais de átomos neutros em plasmas . Para testar o referido formalismo calculamos a largura e o deslocamento de muitas linhas espectrais do hélio neutro em plasmas com temperaturas que vão desde 5000 até 40000K e densidades eletrônicas que variam de 10 POT. -15 até 10 POT. -18cm POT. -3. Efeitos de \"screening\" de Debye e trajetória não retilínea dos elétrons são levados em conta no formalismo. Um estudo sobre a contribuição das colisões iônicas para o alargamento e deslocamento desenvolvido para elétrons e as aproximações quase estática de Griem e adiabática de Barnard, Cooper e Smith, e Griem, Baranger, Kolb e Oertel. Os alargamentos e deslocamentos calculados são comparados com resultados experimentais obtidos por Wulff, Berg e colaboradores, Kelleher e Diatta e teóricos previstos por Griem e Sahal-Bréchot. / n this work the semiclassical convergent formalism suggested by Cattani is developed to calculate the broadening and shift of spectral lines produced by electronic collisions of neutral atoms in plasmas. To test this theory we calculate the widths and shifts of many spectral lines of neutral helium in plasmas with temperatures that goes from 5000 up to 40000 K and electronic densities in the range of 10 POT. -15 até 10 POT. -18cm POT. -3. Effects of Debye screening and non straight line trajectory are taken into account in our approach. To study the ionic collisional contribution to the widths and shifts we use the same convergent treatment developed for electrons and the quasi-static approximation of Griem and adiabatic approximation of Barnard, Cooper and Smith, and Griem, Baranger, Kolb and Oertel. The calculated widths and shifts are compared with experimental results obtained by Wulff, Berg and collaborators, Kelleher and Diatta and theoretical predictions of Griem and Sahal-Bréchot.

Neste trabalho foi desenvolvida a t¶ecnica de Espectroscopia de Plasma Induzido por Laser aplicada µa an¶alise de patrim^onio hist¶orico atrav¶es do estudo das moedas de Um Cruzeiro de 1945 e Mil R¶eis de 1939, utilizando um laser de Nd:YAG operando em modo de chaveamento Q. Foram determinadas as melhores condi»c~oes de energia do pulso laser e tempos de atraso entre o pulso e a aquisi»c~ao dos espectros e de integra»c~ao do sinal espectrosc¶opico para aplica»c~ao da t¶ecnica em patrim^onio hist¶orico. Para garantir a reprodutibilidade da t¶ecnica, a temperatura de excita»c~ao eletr^onica, a temperatura de ioniza»c~ao e a densidade eletr^onica do plasma foram determinadas. O dano causado µas moedas foi avaliado utilizando a t¶ecnica de Tomogra¯a por Coer^encia ¶ Optica. Utilizando o m¶etodo livre de calibra»c~ao, as concentra»c~oes elementares foram determinadas, por¶em a concentra»c~ao determinada para o Alum¶³nio, presente no material de forja, estava abaixo de seu valor nominal e do valor determinado atrav¶es da t¶ecnica de An¶alise por Ativa»c~ao Neutr^onica. Uma investiga»c~ao da fra»c~ao de ioniza»c~ao revelou que a fra»c~ao de ioniza»c~ao presente no plasma estava acima do valor esperado por ioniza»c~ao t¶ermica para as temperaturas atingidas, indicando a presen»ca de processos de ioniza»c~ao n~ao t¶ermicos, que in°uenciavam nas medidas do Alum¶³nio. Foi realizada uma corre»c~ao na concentra»c~ao do elemento, utilizando a fra»c~ao de ioniza»c~ao devido aos processos de ioniza»c~ao n~ao t¶ermicos, e os novos valores de concentra»c~ao determinados obtiveram uma grande concord^ancia com os valores nominal e determinados por An¶alise por Ativa»c~ao Neutr^onica. ii / In this work, the technique of laser induced breakdown spectroscopy was developed for application in cultural heritage analysis in order to study coins of one \\Cruzeiro\" from 1945 and a thousand \\R¶eis\" from 1939, using a Nd:YAG laser operating in Q-switched mode. It had been determined the best conditions of laser and detection features such as pulse energy, delay time between the pulse and the acquisition of spectra and integration time of the spectroscopic signal for the technique applied to cultural heritage. The electronic excitation temperature, the ionization temperature and the electronic density of the plasma had been determined in order to assure the technique reproductivity. The actual damage to the coins was evaluated using the technique of Optical Coherence Tomography. Using the calibration free method, elemental composition had been determined, however the concentration for Aluminum, forge material element , was below of its nominal value and the Neutron Activation Analysis value. An investigation of the ionization fraction disclosed that the ionization fraction of present ionization in the plasma was above of the expected value for thermal ionization at measured temperatures, indicating the presence of non thermal ionization processes, in°uencing the values for Aluminum concentration. A correction in the ionic concentration of the element was performed using the ionization fraction for non thermal processes and the new concentration values had an agreement with the nominal values and the ones determined by Neutron Activation Analysis. i

No description available.

This dissertation reports research about the phase space perspective for solving wave problems, with particular emphasis on the phenomenon of mode conversion in multicomponent wave systems, and the mathematics which underlie the phase space perspective. Part I of this dissertation gives a review of the phase space theory of resonant mode conversion. We describe how the WKB approximation is related to geometrical structures in phase space, and how in particular ray-tracing algorithms can be used to construct the WKB solution. We further review how to analyze the phenomena of mode conversion from the phase space perspective. By making an expansion of the dispersion matrix about the mode conversion point in phase space, a local coupled wave equation is obtained. The solution of this local problem then provides a way to asymptotically match the WKB solutions on either side of the mode conversion region. We describe this theory in the context of a pedagogical example; that of a pair of coupled harmonic oscillators undergoing resonant conversion. Lastly, we present new higher order corrections to the local solution for the mode conversion problem which allow better asymptotic matching to the WKB solutions. The phase space tools used in Part I rely on the Weyl symbol calculus, which gives a way to relate operators to functions on phase space. In Part II of this dissertation, we explore the mathematical foundations of the theory of symbols. We first review the theory of representations of groups, and the concept of a group Fourier transform. The Fourier transform for commutative groups gives the ordinary transform, while the Fourier transform for non-commutative groups relates operators to functions on the group. We go on to present the group theoretical formulation of symbols, as developed recently by Zobin. This defines the symbol of an operator in terms of a double Fourier transform on a non-commutative group. We give examples of this new type of symbol, using the discrete Beisenberg-Wey1 group to construct the symbol of a matrix. We then go on to show how the path integral arises when calculating the symbol of a function of an operator. We also show how the phase space and configuration space path integrals arise when considering reductions of the regular representation of the Heisenberg-Wey1 group to the primary representations and irreducible representations, respectively. We also show how the path integral can be interpreted as a Fourier transform on the space of measures, opening up the possibility of using tools from statistical mechanics (such as maximum entropy techniques) to analyze the path integral. We conclude with a survey of ideas for future research and describe several potential applications of this group theoretical perspective to problems in mode conversion.