Made available in DSpace on 2016-05-17T16:51:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-22. Added 1 bitstream(s) on 2016-05-17T16:54:32Z : No. of bitstreams: 1 000857245.pdf: 574030 bytes, checksum: 8966f79c533ef00580f3bb1b8e5482f6 (MD5) / Este trabalho é uma revisão do método de integração em dimensão negativa como uma ferramenta poderosa no cálculo das correções radiativas presentes na teoria quântica de campos perturbativa. Este método é aplicável no contexto da regularização dimensional e permite obter soluções exatas de integrais de Feynman onde tanto o parâmetro de dimensão como os expoentes dos propagadores estão generalizados. As soluções apresentam-se na forma de combinações lineares de funções hipergeométricas cujos domínios de convergência estãoo relacionados com a estrutura analíica da integral de Feynman. Cada solução definida por seu domínio de convergência está conectada com as outras através de continuações analíticas. Além de apresentar e discutir o algoritmo geral do método com detalhe, mostram-se aplicações concretas a integrais escalares de um e dois loops e à renormalização da eletrodinâmica quântica (QED) a um loop / This work is a review of the Negative Dimension Integration Method as a powerful tool for the computation of the radiative corrections present in Quantum Field Perturbation Theory. This method is applicable in the context of Dimensional Regularization and it provides exact solutions for Feynman integrals with both dimensional parameter and propagator exponents generalized. These solutions are presentedintheformoflinearcombinationsofhypergeometricfunctionswhosedomains of convergence are related to the analytic structure of the Feynman Integral. Each solution is connected to the others trough analytic continuations. Besides presenting and discussing the general algorithm of the method in a detailed way, we offer concrete applications to scalar one-loop and two-loop integrals as well as to the one-loop renormalizationofQuantumElectrodynamics (QED)

Orientador: Alfedo Takashi Suzuki / Banca: Bruto Max Pimentel Escobar / Banca: Jorge Henrique de Oliveira Sales / Resumo: Este trabalho é uma revisão do método de integração em dimensão negativa como uma ferramenta poderosa no cálculo das correções radiativas presentes na teoria quântica de campos perturbativa. Este método é aplicável no contexto da regularização dimensional e permite obter soluções exatas de integrais de Feynman onde tanto o parâmetro de dimensão como os expoentes dos propagadores estão generalizados. As soluções apresentam-se na forma de combinações lineares de funções hipergeométricas cujos domínios de convergência estãoo relacionados com a estrutura analíica da integral de Feynman. Cada solução definida por seu domínio de convergência está conectada com as outras através de continuações analíticas. Além de apresentar e discutir o algoritmo geral do método com detalhe, mostram-se aplicações concretas a integrais escalares de um e dois loops e à renormalização da eletrodinâmica quântica (QED) a um loop / Abstract: This work is a review of the Negative Dimension Integration Method as a powerful tool for the computation of the radiative corrections present in Quantum Field Perturbation Theory. This method is applicable in the context of Dimensional Regularization and it provides exact solutions for Feynman integrals with both dimensional parameter and propagator exponents generalized. These solutions are presentedintheformoflinearcombinationsofhypergeometricfunctionswhosedomains of convergence are related to the analytic structure of the Feynman Integral. Each solution is connected to the others trough analytic continuations. Besides presenting and discussing the general algorithm of the method in a detailed way, we offer concrete applications to scalar one-loop and two-loop integrals as well as to the one-loop renormalizationofQuantumElectrodynamics (QED) / Mestre

Le transfert radiatif joue un rôle important en combustion turbulente et doit donc êtrepris en compte dans les simulations numériques. Toutefois, à cause du fait que la combustionet le rayonnement sont deux phénomènes physiques très différents caractérisés par deséchelles de temps et d’espace également différentes, et la complexité des écoulements turbulents,l’effet du rayonnement est souvent négligé ou modélisé par des modèles très simples.Le couplage entre la combustion (LES) et le rayonnement avec l’environnement CORBAa été étudié. Dans le présent travail, quatre formulations de la méthode de Monte Carlo(méthode classique et méthode réciproque) dédiées à la résolution de l’équation de transfertradiatif ont été comparées sur un cas test de flamme 1D où l’on tient compte de l’absorptionet de l’émission du milieu en utilisant un maillage 3D. Le but de ce cas test est de valider lesolveur Monte Carlo et de choisir la méthode la plus efficace pour réaliser le couplage. Afind’améliorer la performance du code de Monte Carlo, deux techniques ont été développées.De plus, un nouveau code dédié au couplage a été proposé. Ensuite, deux solveurs radiatifs(Emission Reciprocity Monte Carlo Method et Discrete Ordinate Method), appliquésà une flamme turbulente stabilisée en aval d’un dièdre avec un modèle CK de propriétésradiatives, sont comparés non seulement en termes de description physique de la flamme,mais aussi en terme de performances de calcul (stockage, temps CPU et efficacité de laparallélisation). Enfin, l’impact de la condition limite a été discuté en prenant en comptel’émissivité et la température de paroi. / Radiative transfer plays an important role in turbulent combustion and should be incorporatedin numerical simulations. However, as combustion and radiation are characterized bydifferent time scales and different spatial and chemical treatments, and the complexity of theturbulent combustion flow, radiation effect is often neglected or roughly modelled. Couplinga large eddy simulation combustion solver and a radiation solver through a dedicated languageCORBA is investigated. Four formulations of Monte Carlo method (Forward Method,Emission Reciprocity Method, Absorption Reciprocity Method and Optimized ReciprocityMethod) employed to resolve RTE have been compared in a one-dimensional flame testcase using three-dimensional calculation grids with absorbing and emitting medium in orderto validate the Monte Carlo radiative solver and to choose the most efficient model forcoupling. In order to improve the performance of Monte Carlo solver, two techniques havebeen developed. After that, a new code dedicated to adapt the coupling work has beenproposed. Then results obtained using two different RTE solvers (Reciprocity Monte Carlomethod and Discrete Ordinate Method) applied to a three-dimensional turbulent reactingflow stabilized downstream of a triangular flame holder with a correlated-k distributionmodel describing the real gas medium spectral radiative properties are compared not onlyin terms of physical behavior of the flame but also in computational performance (storagerequirement, CPU time and parallelization efficiency). Finally, the impact of boundary conditionstaking into account the actual wall emissivity and temperature has been discussed.

Observations of exoplanet transit spectra are essential to understanding the physics and chemistry of distant worlds. The effects of opacity sources and many physical processes combine to set the shape of a transit spectrum. Two such key processes-refraction and cloud and/or haze forward-scattering-have seen substantial recent study. However, models of these processes are typically complex, which prevents their incorporation into observational analyses and standard transit spectrum tools. In this work, we develop analytic expressions that allow for the efficient parameterization of forward-scattering and refraction effects in transit spectra. We derive an effective slant optical depth that includes a correction for forward-scattered light, and present an analytic form of this correction. We validate our correction against a full-physics transit spectrum model that includes scattering, and we explore the extent to which the omission of forward-scattering effects may bias models. Also, we verify a common analytic expression for the location of a refractive boundary, which we express in terms of the maximum pressure probed in a transit spectrum. This expression is designed to be easily incorporated into existing tools, and we discuss how the detection of a refractive boundary could help indicate the background atmospheric composition by constraining the bulk refractivity of the atmosphere. Finally, we show that opacity from Rayleigh scattering and collision-induced absorption will outweigh the effects of refraction for Jupiter-like atmospheres whose equilibrium temperatures are above 400-500 K.

The gas kinetic temperature (T-K) of various interstellar environments is often inferred from observations that can deduce level populations of atoms, ions, or molecules using spectral line observations; H I 21 cm is perhaps the most widely used, and has a long history. Usually the H I 21 cm line is assumed to be in thermal equilibrium. and the populations are given by the Boltzmann distribution. A variety of processes, many involving Ly alpha, can affect the 21 cm line. Here we show how this is treated in the spectral simulation code Cloudy, and present numerical simulations of environments where this temperature indicator is used, with a detailed treatment of the physical processes that determine level populations within H-0. We discuss situations where this temperature indicator traces TK, cases where it fails, as well as the effects of Lya pumping on the 21 cm spin temperature. We also show that the Lya excitation temperature rarely traces the gas kinetic temperature.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21573号 / 理博第4480号 / 新制||理||1643(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 前田 啓一, 准教授 上田 佳宏, 教授 嶺重 慎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

<p>Radiative cooling is an approach that utilizes the material reflectance in solar spectrum to reflect solar irradiation and emit the energy to deep space (2.7K) through the transparent portion in atmosphere (8-13μm). Therefore, radiative cooling is a passive cooling method that can generate a large reduction in energy consumption in the cooling sector. Scientists have been researching on the best solution for passive radiative cooling, including the utilization of multi-layer techniques with a metallic base layer. However, the current solutions are usually not cost effective and thus limited in the commercial applications. We initially started with the experiment on single-layer cooling paints embedded with TiO₂nanoparticles, and we were able to achieve a partial daytime radiative cooling effect of 60Wm^-2 Built upon our lab’s success of full-daytime sub-ambient cooling based on BaSO₄-acrylic paints, we experiment with colored cooling paints based on BaSO₄ nanoparticles instead of TiO₂ nanoparticles. Our results show much enhanced solar reflectance while matching the color, indicating the potential for colored cooling paints, although outdoor tests have not shown significant temperature drop compared to commercial colored paints yet. At the same time, we also explore creatures with shells in nature for possible solutions. Seashells are collected and the microstructures and radiative properties are characterized. The results provide insights into bio-inspired radiative cooling solutions.</p>

Synchrotron radiation and inverse Compton (IC) scattering are the two most essential radiation mechanisms in high energy astrophysics. Synchrotron radiation typically dominates lower energy emission, up to GeV, and IC scattering dominates higher energy gamma-ray emission. In this work, radiation codes are developed to calculate broadband synchrotron and IC spectra for relativistic astrophysical sources: Pulsar Wind Nebulae (PWNe) and Gamma-Ray Bursts (GRBs). Our robust radiation code takes into account varying intrinsic plasma properties (e.g., magnetic field evolution), various inverse Compton processes (synchrotron self-Compton and external Compton) while accounting for Klein-Nishina effects, as well as relativistic bulk motion of the emitting plasma.

Thin-film silicon nitride (SiN) membranes mechanical resonators have been widely used for many fundamental opto-mechanical studies and sensing technologies due to their extremely low mechanical dissipation (high mechanical Q-factor). In this work, we experimentally demonstrate an opto-mechanical approach to perform thermal radiation sensing, using a SiN membrane resonator. An important aspect of this work is to develop a closed-form analytical heat transfer model for assessing the thermal coupling conditionbetween free-standing membranes and their environment. We also derive analytical expressions for other important intrinsic thermal quantities of the membrane, such as thethermal conductance, the heat capacity and the thermal time constant. Experimental results show good agreement with our theoretical prediction. Of central importance, we show that membranes of realistic dimensions can be coupled to their environment more strongly via radiation than by solid-state conduction. For example, membranes with 100nm thickness (frequently encountered size) are predicted to be radiation dominated when their side length exceeds 6 mm. Having radiation dominated thermal coupling is a key ingredient for reaching the fundamental detectivity limit of thermal detectors. Hence, our work proves that SiN membranes are attractive candidates for reaching the fundamental limit. We also experimentally exhibit the high temperature responsivity of the SiN membranes resonance, in which we shift a 88.7 KHz resonance by over 1 KHz when temperature increment on the membrane is approximately 2 K.

Research on the propagation of acoustic waves in ocean bottom sediment is of interest for active sonar applications such as target detection and remote sensing. Currently, all seabed scattering models available in the literature are based on the full solution of the wave equation, which sometimes leads to mathematically intractable problems. In the electromagnetics community, an alternative formulation that overcomes some of this complexity is radiative transfer theory, which has established itself as an important technique for remote sensing. In this work, radiative transfer (RT) theory is proposed for the first time as a tool for the study of seabed acoustic scattering. The focus of this work is the development of a complete model for the interaction of acoustic energy with water-saturated sediments. The general geometry considered in this study consists of multiple elastic layers containing random distributions of inhomogeneities. The accuracy of the proposed model is assessed by rigorous experimental work, with data collected from random media in which acoustic properties such as the concentration and size of scatterers, background material, and the presence of elastic boundaries are controlled parameters. First, the ultrasound RT model is implemented for layers of finite thickness. The range of applicability of the proposed model is then illustrated using scaled experiments conducted at the Northwest Electromagnetics and Acoustics Research Laboratory (NEAR-Lab). Next, the model is applied to field data collected in a region with gassy sediments and compared to the formulation originally used to explain these data. Finally, insight into the emerging area of study of the time-dependent RT formulation is presented, and its role in the representation of finite broadband pulses is discussed.