Nesta tese realizamos um estudo de campo médio dos efeitos da desordem do campo cristalino sobre os diagramas de fases do modelo ANNNI com spin 1. Resultados de campo médio anteriores obtidos para o modelo com campo cristalino constante mostraram fases parcialmente desordenada em seus diagramas de fases. No entanto, a existência de tais fases não é garantida, devido às flutuações não levadas em conta na aproximação de campo médio. Sendo assim, estudamos o modelo com campo cristalino constante por meio de simulações de Monte Carlo. Nosso objetivo foi fornecer maior credibilidade aos resultados de campo médio obtidos anteriormente, e com isso adquirirmos maior confiança nos resultados de campo médio apresentados nesta tese para um campo cristalino aleatório. Os resultados das simulações mostraram evidências de que a configuração com planos desordenados da fase comensurável de período 6, observada em baixas temperaturas, pode sofrer uma transição interna para uma configuração na qual tais planos estão ausentes. Esse resultado está em concordância com os estudos de campo médio. Para o caso de um campo cristalino aleatório, investigamos os diagramas de fases do modelo na aproximação de campo médio. Para uma distribuição de probabilidades genérica do campo cristalino, obtivemos o funcional da energia livre e as equações de campo médio, assim como as expressões das linhas críticas e dos pontos tricríticos do modelo. Para investigarmos os efeitos da desordem sobre os diagramas de fases, consideramos as distribuições de probabilidade do campo cristalino delta-bimodal e gaussiana. / In this thesis we present a mean-field study of the effects of the disorder of the single-ion anisotropy on the phase diagrams of the spin-l ANNNI model. Previous mean-field results for the model with constant single-ion anisotropy showed partially disordered phases in the phase diagrams of the model. H owever , the existence of such phases cannot be taken as granted, due to the fiuctuations not taken into account in the mean-field approximation. Thus, we studied the model with constant single-ion anisotropy by means of Monte Carlo simulations. Qur aim was to give credit to previous mean-field results and to get more confidence in the mean-field results showed in this thesis obtained for a random single-ion anisotropy. The results obtained from the simulations showed evidences that the configuration of the commensurate phase with period 6 displaying disordered planes, found at low temperatures, may undergo an internaI phase transition to a phase in which such planes are absent. This result is in agreement with previous mean-field studies. For a random single-ion anisotropy, we investigated the phase diagrams of the model within mean-field approximation. For a generic probability distribution of the anisotropy, we obtained the free-energy functional and the mean-field equations, as well as the expressions for the criticallines and tricritical points of the model. In order to investigate disorder effects, we obtained phase diagrams of the model by considering a double-delta and a Gaussian probability distribution of the single-ion anisotropy.

Profissionais da área aeronáutica, como pilotos e comissários de bordo, são submetidos a doses de radiação de origem cósmica, que podem ser maiores do que as doses médias dos trabalhadores da indústria nuclear. A diversidade de partículas de altas energias presentes no campo de radiação a bordo das aeronaves torna complexa a mensuração da dose e requer cuidados especiais em relação aos sistemas de dosimetria a serem empregados nesta área. A Força Aérea Brasileira, por meio de seu Instituto de Estudos Avançados (IEAv /DCTA), em conjunto com o Instituto de Pesquisas Energéticas e Nucleares (IPEN / CNEN -SP) vem estudando o assunto desde 2008. Um protótipo de detector de radiação passivo para medições em aeronaves foi previamente construído e testado em condições de voo e de laboratório. O detector é capaz de medir a grandeza dosimétrica conhecida como dose absorvida (usando dosímetros passivos), que serão posteriormente correlacionados ao equivalente de dose ambiente e à dose efetiva recebidos por profissionais da área aeronáutica. Neste contexto, uma abordagem teórica por meio de simulações Monte Carlo com os códigos computacionais MCNP5 e MCNPX, foi usada para modelar e caracterizar a resposta do detector em determinadas condições experimentais. Este trabalho apresenta os resultados preliminares da modelagem computacional, com ênfase especial na comparação entre a grandeza fundamental dose absorvida (mensurada e simulada) e sua relação com o equivalente de dose ambiente e dose efetiva para este detector. / Aircrews, as pilots and flight attendants, are subjected to cosmic ray doses which can be higher than the average doses on workers from the nuclear industry. The diversity of particles of high energies present in the radiation field on board of aircrafts, turns the determination of the incident dose and requires special care regarding dosimetric systems to be used in this kind of field. The Brazilian Air Force, through the Institute for Advanced Studies (Instituto de Estudos Avançados, IEAv/DCTA) in conjunction with the Institute of Energetic and Nuclear Research (Instituto de Pesquisas Energéticas e Nucleares IPEN/CNEN-SP) are working on this subject since 2008. A prototype of a radiation detector for aircraft measurements was previously built and tested in flight and laboratory conditions. The detector is able of measuring a quantity known as absorbed dose (using passive dosimeters), which will subsequently be correlated to the ambient dose equivalent and the effective dose received by aircrews. In this context, a theoretical approach through Monte Carlo simulations with the computational codes MCNP5 and MCNPX was used to model and characterize the detector response at such experimental conditions. This work presents the preliminary results of the computational modeling, with special emphasis on the comparison between the absorbed dose quantity (measured and simulated) and its relationship with the ambient dose equivalent and the effective Dose for this detector.

O estudo da polarização eletrostática em líquidos homogêneos é crucial para compreender as propriedades termodinâmicas e de solvatação. Estes efeitos de polarização são também importantes para estudar a dinâmica molecular de reações químicas, conformações (tais como proteínas), e do meio solvente (solvatocromismo e RMN). Nesta dissertação, estudou-se a variação do momento de dipolo da fase gasosa para a fase líquida das moléculas: acetona, acetonitrila, amônia e água. Os momentos de dipolo em fase gasosa foram obtidos com cálculos quânticos ab initio para a molécula isolada. Para a fase líquida, cálculos equivalentes foram feitos sobre estruturas geradas de simulação computacional clássica (Monte Carlo). Tal procedimento foi feito segundo a metodologia \"Monte Carlo / Mecânica Quântica - Seqüencial\". Este método foi aplicado iterativamente, tornando possível estudar a variação do momento de dipolo e das propriedades termodinâmicas devido à mútua polarização das moléculas do solvente. Usando os resultados calculados, uma discussão foi realizada sobre a polarização eletrostática e o dipolo induzido em fase líquida. / The study of the electrostatic polarization in homogeneous liquids is crucial to the understanding of thermodynamic and solvation properties. These polarization effects are also important to study molecular dynamics of chemical reactions, conformations (such as proteins), and solvent environment (solvatocromism and NMR). In this dissertation, the variation of dipole moments from the gas phase to the liquid phase of acetone, acetonitrile, ammonia and water, were studied. The dipole moments in the gas phase were obtained with quantum mechanical ab initio calculation on the isolated molecule. For the liquid phase, equivalent quantum mechanical calculations were made on structures generated from classical computer simulations (Monte Carlo). Such procedure was made according to the methodology \"Sequential - Monte Carlo/Quantum Mechanics\". This method was applied iteratively, becoming possible to study the variation of the dipole moment and the thermodynamic properties due to the mutual polarization of the solvent molecules. Using the calculated results, a discussion was made of the electrostatic polarization and the induced dipole moment in the liquid phase.

Esse trabalho avalia a metodologia utilizada pelo Laboratório de Monitoração in vivo (LMIV) do IPEN na calibração dos detectores de NaI(Tl) pelo código PENELOPE- penEasy, baseado no Método de Monte Carlo. Inicialmente, foram realizadas simulações sem o simulador antropomórfico com o objetivo de encontrar uma geometria que representasse adequadamente os detectores para exames de corpo inteiro e de tireoide. A aquisição dos dados experimentais foi realizada pelo software GENIE, que é utilizado na rotina do laboratório e as áreas dos fotopicos foram calculadas pelos softwares GENIE e GNUPLOT e pelo método descrito no Ciemat Technical Report, que também fornece os valores de eficiência de fotopico. Fontes de 60Co, 137Cs, 152Eu, 207Bi e 241Am calibradas foram utilizadas nas medições. Os resultados mostraram que o software GENIE é apropriado para ser utilizado nas calibrações de rotina e fontes que possuam picos isolados e definidos pelo detector de NaI(Tl), são ideais para serem utilizadas nas calibrações em eficiência. A simulação MC indica que é possível substituir calibrações experimentais por simulações utilizando uma geometria simplificada do detector de NaI(Tl), mas as grandezas relevantes como a fonte, o detector e o sistema eletrônico devem ser conhecidos com detalhes para que as fontes de erros sistemáticos sejam as menores possíveis. / The calibration methods of NaI(Tl) detectors of the in vivo Monitoring Laboratory (LMIV) of IPEN were analyzed by comparing experimental results with simulations performed with the PENELOPE- penEasy Monte Carlo radiation program. The first simulations were performed without the anthropomorphic simulator aiming to find a simplified detector geometry that could represent the whole body and thyroid detectors. The data acquisition was performed with the GENIE software, which is used in the laboratory routine, and the photopeak areas were calculated with the GENIE and GNUPLOT softwares as well as using the method described on the Ciemat Technical Report. Standard sources of 60Co, 137Cs, 152Eu, 207Bi and 241Am were used in the measurements. The results show that GENIE is a suitable software to be used in the laboratory routine and ideal sources are those that present isolated and well-defined photopeaks in the spectra measured with NaI(Tl) detectors. The Monte Carlo study reveals that the simplified models of the NaI detectors are able to provide a full- energy peak efficiency curve but it is necessary to know all details of the significant quantities as the source, the detector and the electronics in order to minimize sources of systematic errors.

Há diversas enfermidades radiossensíveis epidermotrópicas, como a micose fungóide e a síndrome de Sézary, neoplasias cutâneas originadas de linfócitos do tipo T, que apresentam grande possibilidade de erradicação quando tratadas com feixes de elétrons com energia entre 4 e 10 MeV, conforme apontam diversos estudos. No entanto, esta técnica de tratamento apresenta inúmeras dificuldades práticas, pois a doença dissemina-se por todo o corpo do paciente tornando necessário um grande campo de radiação e deposição de energia limitada à profundidade da pele. A fim de obter uma distribuição de dose uniforme, muitas técnicas já foram desenvolvidas. Com base em estudos anteriores e guiados pelo protocolo n. 23 da American Association of Physicists in Medicine (AAPM), o presente trabalho desenvolveu placas espalhadoras e degradadoras de energia e realizou toda a dosimetria (computacional e experimental), a fim de fornecer subsídios para a implementação da técnica de tratamento Total Skin Electron Therapy (TSET) no Serviço de Radioterapia do Hospital das Clínicas de São Paulo. O programa MCNP4C baseado no método de Monte Carlo foi utilizado para reconstruir o espectro energético do acelerador Varian Clinac 2100C, por meio de medidas experimentais de percentual de dose em profundidade (PDP) e perfis radiais de dose. Com estes dados, foi possível efetuar simulações computacionais para a seleção de materiais, mediante análise da distribuição radial e axial de dose, produção de raios-X e a atenuação do feixe, além da simulação de placas espalhadoras e degradadoras de energia, a serem posicionadas na saída do acelerador. Os resultados das simulações foram validados por meio de medidas experimentais a fim de obter um grande campo de radiação com 200 cm x 80 cm que atendesse as especificações do protocolo da AAPM. / There are many radiosensitive epidermotropics diseases such as mycosis fungoids and the syndrome of Sézary, coetaneous neoplasics originated from type T lymphocytes. Several studies indicate the eradication of the disease when treated with linear accelerators emitting electron beams with energies between 4 to 10 MeV. However, this treatment technique presents innumerable technical challenges since the disease in general reaches all patient´s body, becoming necessary not only a very large field size radiation beam, but also deliver superficial doses limited to the skin depth. To reach the uniformity in the dose distribution, many techniques had already been developed. Based on these previous studies and guided by the report n. 23 of the American Association of Physicists in Medi-cine (AAPM), the present study developed an energy scattering and degrading plates and made dosimetry (computational and experimental), supplying subsidies for a future installation of Total Skin Electron Therapy (TSET) at the Serviço de Radioterapia do Hospital das Clínicas de São Paulo. As part of the plates design, first of all, the energy spectrum of the 6 MeV electron beam of the VARIAN 2100C accelerator was reconstructed through Monte Carlo simulations using the MCNP4C code and based on experimental data. Once the spectrum is built, several materials were analyzed for the plates design based on radial and axial dose distribution, production of rays-x and dose attenuation. The simulation results were validated by experimental measurements in order to obtain a large field of radiation with 200 cm x 80 cm that meets the specifications of the AAPM protocol.

by Wai-chuen Tso. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 90-94). / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Prior Information --- p.5 / Chapter 2.1 --- Prior Distribution --- p.6 / Chapter 2.2 --- Quantification of Prior Belief --- p.10 / Chapter 2.2.1 --- Prior Belief --- p.10 / Chapter 2.2.2 --- Some Basic Concepts of Fuzzy Set Theory --- p.12 / Chapter 2.2.3 --- Quantification --- p.16 / Chapter 2.3 --- Specification and Determination of Model Parameters --- p.20 / Chapter 2.3.1 --- A Questionnaire --- p.21 / Chapter 2.3.2 --- Parameter Value --- p.22 / Chapter 2.3.3 --- Determination of Degree of Fuzziness --- p.23 / Chapter 2.4 --- Comments --- p.26 / Chapter 2.4.1 --- Interpretation of Time Length of Poisson Process --- p.26 / Chapter 2.4.2 --- Likelihood Interpretation of Membership Value --- p.28 / Chapter 2.4.3 --- Comparison with Existing Modeling --- p.30 / Chapter 2.4.4 --- Conclusion of Prior Information --- p.31 / Chapter 3 --- Posterior Analysis --- p.33 / Chapter 3.1 --- Posterior Analysis by Monte Carlo Method --- p.34 / Chapter 3.1.1 --- Monte Carlo Method --- p.34 / Chapter 3.1.2 --- Estimation of Posterior Mean and Posterior Variance of Log-odds Ratio --- p.35 / Chapter 3.1.3 --- Construction of Credible Region of Log-odds Ratio --- p.38 / Chapter 3.1.4 --- Estimation of Posterior Mean of Cell Probability --- p.41 / Chapter 3.2 --- Sampling of Prior Cell Frequency Vector by Gibbs Sampler --- p.42 / Chapter 3.2.1 --- Gibbs Sampler --- p.42 / Chapter 3.2.2 --- Two Sampling Algorithms --- p.45 / Chapter 3.2.3 --- Acceptance-Rejection Algorithm --- p.50 / Chapter 3.3 --- Some Practical Problems --- p.51 / Chapter 3.3.1 --- Number of Iterations in Gibbs Sampler --- p.51 / Chapter 3.3.2 --- Sample Size of Gibbs Sample --- p.53 / Chapter 4 --- Simulation Study --- p.58 / Chapter 4.1 --- Multinomial Model --- p.59 / Chapter 4.1.1 --- Determination of Number of Iterations --- p.61 / Chapter 4.1.2 --- Determination of Sample Size --- p.62 / Chapter 4.1.3 --- Posterior Estimation --- p.63 / Chapter 4.1.4 --- Sensitivity Analysis --- p.64 / Chapter 4.2 --- Poisson Model --- p.71 / Chapter 4.2.1 --- Determination of Number of Iterations --- p.72 / Chapter 4.2.2 --- Determination of Sample Size --- p.73 / Chapter 4.2.3 --- Posterior Estimation --- p.74 / Chapter 4.2.4 --- Sensitivity Analysis --- p.75 / Chapter 4.3 --- Conclusion --- p.82 / Chapter 5 --- Conclusions and Discussions --- p.85 / References --- p.90

Liu Guoxin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 24-25). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.2 / Chapter 2 --- The Model --- p.4 / Chapter 3 --- "Estimation of μ1 ,μ2 ,α and β" --- p.7 / Chapter 4 --- Extension --- p.9 / Chapter 5 --- Monte Carlo Simulation --- p.11 / Chapter 5.1 --- "Case 1. a < 1, β < 1" --- p.12 / Chapter 5.2 --- "Case 2. a > 1, β < 1" --- p.12 / Chapter 5.3 --- "Case 3. a < 1,β > 1" --- p.13 / Chapter 5.4 --- "Case 4. a > 1, β> 1" --- p.13 / Chapter 6 --- Empirical Application --- p.15 / Chapter 6.1 --- Model Construction --- p.15 / Chapter 6.2 --- Estimation Results --- p.15 / Chapter 6.2.1 --- 1973Oil Crisis --- p.16 / Chapter 6.2.2 --- 1981 Oil Crisis --- p.18 / Chapter 6.2.3 --- 1991 Oil Crisis --- p.20 / Chapter 7 --- Conclusion --- p.23 / Chapter 8 --- Bibliography --- p.24

by Wong Chi Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 38-39). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Monte Carlo Method --- p.2 / Chapter 1.3 --- Outline of Thesis --- p.5 / Chapter 2 --- The Random Number Generators --- p.7 / Chapter 2.1 --- Built-in Random Number Generating Functions --- p.7 / Chapter 2.2 --- Linear Congruential Generators --- p.8 / Chapter 3 --- Memory Reduction Methods --- p.10 / Chapter 3.1 --- The Full-Storage Method --- p.10 / Chapter 3.2 --- The Forward-Path Method --- p.12 / Chapter 3.3 --- The Backward-Path Method --- p.14 / Chapter 4 --- The Least-Squares Method --- p.17 / Chapter 5 --- Numerical Examples --- p.28 / Chapter 6 --- Concluding Remarks --- p.34 / Appendix --- p.36 / Bibliography --- p.38

Tam Ka Ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 142-145). / Text in English; abstracts in English and Chinese. / Tam Ka Ming. / Acknowledgement --- p.ii / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Models for Many Body Systems --- p.1 / Chapter 1.2 --- High Temperature Superconductor --- p.5 / Chapter 1.3 --- Reasons of Study Double Layers --- p.9 / Chapter 1.4 --- "Incommensurate Magnetic Excitation, Order Parameters" --- p.10 / Chapter 1.5 --- Thesis Organization --- p.10 / Chapter 2 --- Monte Carlo Methods --- p.12 / Chapter 2.1 --- General Aspects of Monte Carlo Simulation --- p.12 / Chapter 2.2 --- "Markov Chain, Metropolis Algorithm, Heat-Bath Algorithm" --- p.18 / Chapter 2.3 --- Quantum Monte Carlo --- p.21 / Chapter 2.4 --- Variational Quantum Monte Carlo --- p.22 / Chapter 2.5 --- Green Function Monte Carlo --- p.27 / Chapter 2.6 --- Auxiliary Field Monte Carlo --- p.35 / Chapter 2.7 --- Summary of Quantum Monte Carlo --- p.38 / Chapter 3 --- Constrained Path Monte Carlo --- p.40 / Chapter 3.1 --- Various Formulas Used in Constrained Path Monte Carlo --- p.40 / Chapter 3.2 --- Constrained Path Monte Carlo --- p.47 / Chapter 3.3 --- Constrained Path Approximation --- p.51 / Chapter 3.4 --- Measurements --- p.52 / Chapter 3.5 --- Method of Avoiding Numerical Instability --- p.55 / Chapter 4 --- Parallelisation of CPMC Program --- p.57 / Chapter 4.1 --- Architecture of Parallel Machine --- p.57 / Chapter 4.2 --- Communication Methods in Parallel Program --- p.65 / Chapter 4.3 --- Comparison of Parallel and Serial Program --- p.74 / Chapter 4.4 --- Measure of Parallel Program --- p.85 / Chapter 4.5 --- Analysis of Serial CPMC Program --- p.89 / Chapter 4.6 --- Analysis of the Parallel CPMC Program --- p.93 / Chapter 5 --- Results from CPMC --- p.101 / Chapter 5.1 --- Hubbard Model with Next Nearest Neighbour Hopping --- p.101 / Chapter 5.2 --- Spin and Charge Correlations --- p.104 / Chapter 5.3 --- Vertex Contributions --- p.111 / Chapter 6 --- Mean Field Calculations of bilayer --- p.119 / Chapter 6.1 --- Objective --- p.119 / Chapter 6.2 --- Theoretical Model --- p.121 / Chapter 6.3 --- Method of Solving the Model --- p.122 / Chapter 6.4 --- Finding Susceptibility by RPA --- p.131 / Chapter 6.5 --- Results --- p.136 / Chapter 6.6 --- Summary --- p.140 / Chapter 7 --- Summary --- p.141 / Bibliography --- p.142

Cheung, Yu Hin Ray. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 59-66). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.