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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
151

Study and application of methods of fractal processes monitoring in computer networks / Fraktalinių procesų kompiuterių tinkluose stebėsenos ir valdymo metodų tyrimas

Kaklauskas, Liudvikas 09 August 2012 (has links)
The field of the dissertation research is features of computer network packet traffic, the impact of network node features on traffic service, methods of real-time analysis of network traffic features and their application for dynamic prognostication of computer network packet traffic variance. The object of the research is the features of computer network packet traffic, the impact of network node features on computer network traffic service, methods of real-time network traffic features analysis and their application for dynamic prognostication of network traffic variances. The aim of work is to investigate fractal processes in computer networks, grounding on the results obtained to select methods suitable for real-time analysis of network traffic and to work out methods for real-time measurement of self-similarity as well as to apply it for perfection of computer networks service quality. Possibilities for mathematical modelling of network components, computer network packet traffic models and models using service theory instruments have been analysed. The package of network traffic features analysis has been worked out; it was used for analysis, assessment and comparison of methods for computer networks fractality and self-similarity research. For assessment of self-similarity of the network traffic time lines analysis, frequency/wave feature estimates, self-similarity analysis methods based on time line stability parameters estimators and assessed by the chaos theory... [to full text] / Disertacijos tyrimų sritis – kompiuterių tinklo paketinio srauto savybės, tinklo mazgo savybių įtaka srauto aptarnavimui, tinklo srauto savybių realaus laiku analizės metodai ir jų taikymas kompiuterių tinklo srauto kaitos dinaminiam prognozavimui. Tyrimų objektas – kompiuterių tinklo paketinio srauto savybės, tinklo mazgo savybių įtaka paketinio kompiuterių tinklo srauto aptarnavimui, realaus laiko tinklo srauto savybių analizės metodai ir jų taikymas tinklo srauto kaitos dinaminiam prognozavimui. Darbo tikslas – ištirti fraktalinius procesus kompiuterių tinkluose, remiantis gautais rezultatais parinkti metodus, tinkamus tinklo srauto analizei realiu laiku, ir sukurti savastingumo matavimo realiu laiku metodiką bei ją pritaikyti kompiuterių tinklų aptarnavimo kokybei gerinti. Išanalizuotos tinklo komponentų matematinio modeliavimo galimybės, kompiuterių tinklo paketinio srauto modeliai ir modeliai, naudojantys aptarnavimo teorijos instrumentus. Parengtas tinklo srauto savybių analizės paketas, panaudotas kompiuterių tinklų fraktališkumo ir savastingumo tyrimo metodams analizuoti, vertinti ir palyginti. Ištirti paketinio kompiuterių tinklo srauto laiko eilučių analizės, dažninių/banginių savybių įvertinimo, laiko eilutės stabilumo parametrų įverčiais grindžiami bei chaoso teorijos priemonėmis įvertinami savastingumo analizės metodai. Sudarytas tinklo srauto savastingumo realiu laiku analizės paketas, kurį naudojant savastingumo matavimui realiu laiku atrinktas robastinis... [toliau žr. visą tekstą]
152

Microfabrication of Plasmonic Biosensors in CYTOP Integrating a Thin SiO2 Diffusion and Etch-barrier Layer

Hanif, Raza 18 April 2011 (has links)
A novel process for the fabrication of Long Range Surface Plasmon Polariton (LRSPP) waveguide based biosensors is presented herein. The structure of the biosensor is comprised of Au stripe waveguide devices embedded in thick CYTOP claddings with a SiO2 solvent diffusion barrier and etch-stop layer. The SiO2 layer is introduced to improve the end quality of Au waveguide structures, which previously deformed during the deposit of the upper cladding process and to limit the over-etching of CYTOP to create micro-fluidic channels. The E-beam evaporation method is adapted to deposit a thin SiO2 on the bottom cladding of CYTOP. A new micro-fluidic design pattern is introduced. Micro-fluidic channels were created on selective Au waveguides through O2 plasma etching. The presented data and figures are refractive index measurements of different materials, thickness measurements, microscope images, and AFM images. Optical power cutback measurements were performed on fully CYTOP-cladded symmetric LRSPP waveguides. The end-fire coupling method was used to excite LRSPP modes with cleaved polarization maintaining (PM) fibre. The measured mode power attenuation (MPA) was 6.7 dB/mm after using index-matched liquid at input and output fibre-waveguide interfaces. The results were compared with the theoretical calculations and simulations. Poor coupling efficiency and scattering due to the SiO2 are suspected for off-target measurements.
153

Statistical inference in continuous-time models with short-range and/or long-range dependence

Casas Villalba, Isabel January 2006 (has links)
The aim of this thesis is to estimate the volatility function of continuoustime stochastic models. The estimation of the volatility of the following wellknown international stock market indexes is presented as an application: Dow Jones Industrial Average, Standard and Poor’s 500, NIKKEI 225, CAC 40, DAX 30, FTSE 100 and IBEX 35. This estimation is studied from two different perspectives: a) assuming that the volatility of the stock market indexes displays shortrange dependence (SRD), and b) extending the previous model for processes with longrange dependence (LRD), intermediaterange dependence (IRD) or SRD. Under the efficient market hypothesis (EMH), the compatibility of the Vasicek, the CIR, the Anh and Gao, and the CKLS models with the stock market indexes is being tested. Nonparametric techniques are presented to test the affinity of these parametric volatility functions with the volatility observed from the data. Under the assumption of possible statistical patterns in the volatility process, a new estimation procedure based on the Whittle estimation is proposed. This procedure is theoretically and empirically proven. In addition, its application to the stock market indexes provides interesting results.
154

Phases classiques et quantiques des systèmes dipolaires de basse dimensionnalité / Classical and quantum phases of low-dimensional dipolar systems

Cartarius, Florian 22 September 2016 (has links)
Cette thèse étudie les phases classiques et quantiques des systèmes atomiques ou moléculaires de basse dimension en mettant un accent particulier sur le crossover dimensionnel de une à deux dimensions.La première partie de la thèse est consacrée à la description d'un système d'atomes froids interagissants avec un potentiel de contact. Plus précisément, nous étudions le dé-piégeage dynamique qui, suite à l'extinction rapide d'un réseau optique, s'opère dans un gaz composé de bosons impénétrables dans un guide d'onde atomique linéaire.  Nous employons une solution exacte, basée sur une  correspondance entre bosons en forte interaction et fermions sans interaction pour déduire l'évolution dynamique quantique exacte. Dans la limite thermodynamique, nous observons l'approche vers un état stationnaire hors équilibre, caractérisé par l'absence d'ordre hors diagonal à longue distance et une visibilité réduite de la distribution en impulsions. Des caractéristiques similaires sont observées dans un système de taille finie pour des temps  correspondant à la moitié du temps de récurrence, lors desquels nous observons que le système approche un état  quasi-stationnaire auquel le système s'approche avec une dépendance temporelle en loi de puissance.La deuxième partie de la thèse analyse l'effet des interactions dipolaires sur l'état fondamental du système. L'inclusion de l'interaction dipôle-dipôle donne lieu à de nouvelles phases quantiques du système unidimensionnel, mais peut également entraîner une instabilité transverse.Cette instabilité est tout d'abord analysée dans le régime classique. Nous considérons des particules classiques  avec interactions dipolaires, confinés sur un anneau par un potentiel harmonique radiale.  Les dipôles sont polarisés perpendiculairement au plan de confinement. En diminuant le confinement dans la direction radiale, les particules classique montrent une transition entre une chaîne simple et une chaîne double (en zigzag).  Nous montrons que cette transition est faiblement du premier ordre. Nous expliquons que la nature de cette transition est déterminée par le couplage entre les modes d'excitation transversaux et axiaux de la chaîne des dipôles.  Ce résultat est très différent du  comportement observé dans les systèmes Coulombiens, où la transition entre la chaîne linéaire et la chaîne en zigzag est continue et appartient à la classe d'universalité de la transition ferromagnétique. Nos résultats s'appliquent aux systèmes dipolaires classiques et aux atomes Rydberg, qui peuvent constituer un banc d'essai pour simuler le comportement critique des aimants couplés à des grilles.Dans le régime quantique, nous considérons un système des bosons dipolaires sur un réseaux optique, confinés par un potentiel harmonique anisotrope. Dans le régime favorisant l'instabilité d'une chaîne simple, nous démontrons que le système peut être  décrit  par un modèle de  Bose-Hubbard étendu à plusieurs modes couplés entre eux, dont les coefficients peuvent être déterminés en utilisant une théorie de basse énergie. La méthode d'intégrale de chemin Monte Carlo, la diagonalisation exacte et TEBD sont utilisés pour déterminer l'état fondamental de modèle de Bose-Hubbard étendu et démontrent que ce modèle capture la transition entre la chaîne linéaire et la chaîne en zigzag. / In this work, the classical and quantum phases of low-dimensional atomic or molecular systems is studied with a particular focus on the regime where a system goes over from a strictly one-dimensional to a two dimensional system.The first part of the thesis is dedicated to atoms interacting via contact interactions. In particular, we study the dynamical depinning following a sudden turn off of an optical lattice for a gas of impenetrable bosons in a tight atomic waveguide. We use an exact solution, which is based on an equivalence between strongly interacting bosons and noninteraction fermions, in order to derive the exact quantum dynamical evolution. At long times, in the thermodynamic limit, we observe the approach to a nonequilibrium steady state, characterized by the absence of quasi-long-range order and a reduced visibility in the momentum distribution. Similar features are found in a finite-size system at times corresponding to half the revival time, where we find that the system approaches a quasisteady state with a power-law behavior.In the second part, we study the effect of additional dipolar interactions on the ground state of the system. The inclusion of dipole-dipole interaction leads to new quantum phases of the one-dimensional system, but can also lead to a transverse instability.This instability is first analyzed in the classical regime. We study classical particles with dipolar interactions, that are confined on a chain by a harmonic potential. The dipoles are polarised perpendicular to the plane of confinement. Classical particles with repulsive power-law interactions undergo a transition from a single to a double chain (zigzag) by decreasing the confinement in the transverse direction. We theoretically characterize this transition when the particles are classical dipoles, polarized perpendicularly to the plane in which the motion occurs, and argue that this transition is of first order, even though weakly. The nature of the transition is determined by the coupling between transverse and axial modes of the chain and contrasts with the behavior found in Coulomb systems, where the linear-zigzag transition is continuous and belongs to the universality class of the ferromagnetic transition. Our results hold for classical dipolar systems and Rydberg atoms, which can offer a test bed for simulating the critical behavior of magnets with lattice coupling.In the quantum regime, we consider dipolar bosons in an optical lattice, tightly confined by an anisotropic harmonic potential. In the regime where a single chain becomes unstable, we show that the system can be mapped onto an extended multi-mode Bose-Hubbard model, where the coefficients can be determined by means of a low energy theory. A path integral Monte Carlo method, exact diagonalization and TEBD are used to determine the ground state of the extended Bose-Hubbard models. and show that the model captures the linear to zigzag transition.
155

Towards Long-Range Backscatter Communication with Tunnel Diode Reflection Amplifiers

Eriksson, Gustav January 2018 (has links)
Backscatter communication enables wireless communication at a power consumption orders of magnitude lower than conventional wireless communication. Instead of generating new RF-signals backscatter communication leverages ambient signals, such as WiFi-, Bluetooth- or TV-signals, and reflects them by changing the impedance of the antenna. Backscatter communication is known as a short-range communication technique achieving ranges in the order of meters. To improve the communication range, we explore the use of a tunnel diode as an amplifier of the backscattered RF-signal. We developed the amplifier on a PCB-board together with a matching network tuned to give maximum gain at 868 MHz. Our work demonstrates that the 1N3712 tunnel diode can achieve gains up to 35 dB compared to a tag without amplification while having a peak power consumption of 48 μW. With this amplifier the communication distance can be increased by up to two orders of magnitude.
156

Light field remote vision / Algorithmes de traitement et de visualisation pour la vision plénoptique à grande distance

Nieto, Grégoire 03 October 2017 (has links)
Les champs de lumière ont attisé la curiosité durant ces dernières décennies. Capturés par une caméra plénoptique ou un ensemble de caméras, ils échantillonnent la fonction plénoptique qui informe sur la radiance de n'importe quel rayon lumineux traversant la scène observée. Les champs lumineux offrent de nombreuses applications en vision par ordinateur comme en infographie, de la reconstruction 3D à la segmentation, en passant par la synthèse de vue, l'inpainting ou encore le matting par exemple.Dans ce travail nous nous attelons au problème de reconstruction du champ de lumière dans le but de synthétiser une image, comme si elle avait été prise par une caméra plus proche du sujet de la scène que l'appareil de capture plénoptique. Notre approche consiste à formuler la reconstruction du champ lumineux comme un problème de rendu basé image (IBR). La plupart des algorithmes de rendu basé image s'appuient dans un premier temps sur une reconstruction 3D approximative de la scène, appelée proxy géométrique, afin d'établir des correspondances entre les points image des vues sources et ceux de la vue cible. Une nouvelle vue est générée par l'utilisation conjointe des images sources et du proxy géométrique, bien souvent par la projection des images sources sur le point de vue cible et leur fusion en intensité.Un simple mélange des couleurs des images sources ne garantit pas la cohérence de l'image synthétisée. Nous proposons donc une méthode de rendu direct multi-échelles basée sur les pyramides de laplaciens afin de fusionner les images sources à toutes les fréquences, prévenant ainsi l'apparition d'artefacts de rendu.Mais l'imperfection du proxy géométrique est aussi la cause d'artefacts de rendu, qui se traduisent par du bruit en haute fréquence dans l'image synthétisée. Nous introduisons une nouvelle méthode de rendu variationnelle avec des contraintes sur les gradients de l'image cible dans le but de mieux conditionner le système d'équation linéaire à résoudre et supprimer les artefacts de rendu dus au proxy.Certaines scènes posent de grandes difficultés de reconstruction du fait du caractère non-lambertien éventuel de certaines surfaces~; d'autre part même un bon proxy ne suffit pas, lorsque des réflexions, transparences et spécularités remettent en cause les règles de la parallaxe. Nous proposons méthode originale basée sur l'approximation locale de l'espace plénoptique à partir d'un échantillonnage épars afin de synthétiser n'importe quel point de vue sans avoir recours à la reconstruction explicite d'un proxy géométrique. Nous évaluons notre méthode à la fois qualitativement et quantitativement sur des scènes non-triviales contenant des matériaux non-lambertiens.Enfin nous ouvrons une discussion sur le problème du placement optimal de caméras contraintes pour le rendu basé image, et sur l'utilisation de nos algorithmes pour la vision d'objets dissimulés derrière des camouflages.Les différents algorithmes proposés sont illustrés par des résultats sur des jeux de données plénoptiques structurés (de type grilles de caméras) ou non-structurés. / Light fields have gathered much interest during the past few years. Captured from a plenoptic camera or a camera array, they sample the plenoptic function that provides rich information about the radiance of any ray passing through the observed scene. They offer a pletora of computer vision and graphics applications: 3D reconstruction, segmentation, novel view synthesis, inpainting or matting for instance.Reconstructing the light field consists in recovering the missing rays given the captured samples. In this work we cope with the problem of reconstructing the light field in order to synthesize an image, as if it was taken by a camera closer to the scene than the input plenoptic device or set of cameras. Our approach is to formulate the light field reconstruction challenge as an image-based rendering (IBR) problem. Most of IBR algorithms first estimate the geometry of the scene, known as a geometric proxy, to make correspondences between the input views and the target view. A new image is generated by the joint use of both the input images and the geometric proxy, often projecting the input images on the target point of view and blending them in intensity.A naive color blending of the input images do not guaranty the coherence of the synthesized image. Therefore we propose a direct multi-scale approach based on Laplacian rendering to blend the source images at all the frequencies, thus preventing rendering artifacts.However, the imperfection of the geometric proxy is also a main cause of rendering artifacts, that are displayed as a high-frequency noise in the synthesized image. We introduce a novel variational rendering method with gradient constraints on the target image for a better-conditioned linear system to solve, removing the high-frequency noise due to the geometric proxy.Some scene reconstructions are very challenging because of the presence of non-Lambertian materials; moreover, even a perfect geometric proxy is not sufficient when reflections, transparencies and specularities question the rules of parallax. We propose an original method based on the local approximation of the sparse light field in the plenoptic space to generate a new viewpoint without the need for any explicit geometric proxy reconstruction. We evaluate our method both quantitatively and qualitatively on non-trivial scenes that contain non-Lambertian surfaces.Lastly we discuss the question of the optimal placement of constrained cameras for IBR, and the use of our algorithms to recover objects that are hidden behind a camouflage.The proposed algorithms are illustrated by results on both structured (camera arrays) and unstructured plenoptic datasets.
157

Efeitos de superfície nas propriedades térmicas e dinâmicas de filmes de cristais líquidos esméticos. / Surface effects on the thermal and dynamical proprieties of smectic liquid crystal filmes.

Oliveira, Italo Marcos Nunes de 03 August 2007 (has links)
The thermal and dynamical properties of free-standing films are strongly dependent on the boundary conditions and the presence of an external field. Using distinct theoretical models and the dynamic light scattering experimental setup, we study the surface and external field effects on the relaxation dynamics, fluctuation-induced interaction energy, and phase transitions of smectic films. Using an extended McMillan model, we study as a homeotropic anchoring stabilizes the smetic order above the bulk transition temperature of the system. In particular, we determine as the transition temperature depends on the surface ordering and film thickness. We identify a characteristic anchoring for which the transition temperature does not depend on the film thickness. For strong surface ordering, we observe that the transition temperature presents a power law scaling behavior with the film thickness, in agreement with a series of existing experimental results in the literature. Within a Gaussian functional approximation, we also investigate how the fluctuationinduced interaction force depends on the nematic and smectic order parameter profiles. Close to nematic-smectic phase transition, our results indicate that the thermal Casimir force has a significant enhancement which reinforces the predominance of the fluctuationinduced interaction as compared to standard van der Waals interaction in thin smectic films. In temperatures where the smectic phase is well established, we investigate how the interplay of the surface order and the external field induced order affect the Casimirlike force. For asymmetrically anchored films, the fluctuation-induced interaction energy obeys a law of corresponding states and can change its nature from attractive to repulsive through variations of an external field. We discuss the possible relevance of this field effect in smectic wetting transitions. With concern to the dynamical properties, we investigate how surface operators modify the relaxation dynamics of hexatic-B liquid crystal films. In particular, we study how a surface ordering field modifies the damping rate of the orientational modes in the system. In a purely diffusive regime, we demonstrate that a surface tilted order drives the slowest relaxation mode from hydrodynamical to non-hydrodynamical character. In the viscous regime, the hydrodynamical character of the slowest relaxation mode persists even for a surface tilted order. However, the normal modes develop an oscillatory-exponential relaxation. Finally, we use the photon correlation spectroscopy technique to investigate the dynamic properties of free-standing films close to smectic-A - crystal-B transition. We observe that the experimental data indicate the existence of a non-hydrodynamic mode and measure the temperature dependence of the damping rate. We considered a simplified model that incorporates the gradient velocity field effects which reproduces qualitatively the experimental measurements. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As propriedades térmicas e dinâmicas de filmes de cristais líquidos na fase esmética são extremamente dependentes das condições de contorno e da presença de campos externos. Utilizando diferentes modelagens teóricas e a técnica de espectroscopia de fotocorrelação, estudamos como as condiçõoes de contorno e a presença de um campo externo afetam a dinâmica de relaxação, a energia de interação induzida por flutuações e as transições de fase envolvendo a fase esmética. Utilizando uma extensão para o modelo de McMillan, estudamos como o ancoramento homeotrópico estabiliza a ordem esmética acima da temperatura de transição do sistema. Em particular, determinamos como a temperatura de transição depende da intensidade do ancoramento superficial e da espessura do filme. Identificamos um ancoramento característico para o qual a temperatura de transição independe da espessura. Para ancoramentos fortes, observamos que a depend encia da temperatura de transição com a espessura do filme segue aproximadamente uma lei de potência, em concordância com uma série de resultados experimentais existentes na literatura. Baseado em uma teoria funcional Gaussiana para o funcional energia livre, investigamos tamb´em como a força induzida por flutuações esméticas depende do perfil dos parâmetros de ordem nemático e esmético. Nas proximidades da transição nemática esmética, nossos resultados indicam que a força de Casimir térmica cresce significativamente, podendo ser mais relevante que a força de van der Waals usual. Em temperaturas onde a fase esmética é bem estabelecida, investigamos como a competição entre a ordem superficial e a ordem induzida por um campo externo se reflete nas características da força de Casimir. Obtivemos que, para filmes com ancoramentos superficiais assimétricos, a força de Casimir térmica obedece a uma lei de estados correspondentes e pode mudar sua natureza de atrativa para repulsiva através de variações de um campo externo. Discutimos como este comportamento pode influenciar as transições de umedecimento da fase esmética. No que diz respeito às propriedades dinâmicas, investigamos como operadores de superfície modificam a dinâmica de relaxação de filmes na fase hexática-B. Em particular estudamos como um campo de ordenamento superficial modifica a taxa de amortecimento dos modos orientacionais do sistema. Num regime puramente difusivo, nós demonstramos que uma ordem superficial com o vetor diretor não paralelo à direção normal das camadas faz com que os modos de relaxação tornem-se não-hidrodinâmicos. No regime viscoso, sempre existirão modos hidrodinâmicos e a dinâmica de relaxação é sempre lenta. Entretanto, os modos normais podem apresentar um decaimento oscilatório. Por fim, usamos a técnica de espectroscopia de fotocorrelação para investigar as propriedades dinâmicas de filmes livremente suspensos nas proximidades da transição esmética-A - cristal-B. Observamos que os dados experimentais indicam a existência de um modo não-hidrodinâmico e medimos a dependência da taxa de relaxação com a temperatura. Propusemos um modelo que incorpora a influência do gradiente do campo de velocidades que reproduz qualitativamente as observações experimentais.
158

Método variacional dependente do tempo para a equação de Schrödinger não linear e não-local em condensados de Bose-Einstein / Time-dependent variational method for the non-linear and non-local Schrödinger equation in Bose-Einstein condensates

Soares, Luiz Gustavo Ferreira January 2016 (has links)
Condensação de Bose-Einstein é um fenômeno quântico que pode ser observado macroscopicamente. Para a sua obtenção são necessários aprisionamentos externos, porém a presença desses leva ao colapso da função de onda. As interações de longo alcance são propostas como uma forma alternativa ao confinamento externo, um vez que podem prevenir o colapso da função de onda. Neste trabalho será apresentada uma revisão sobre os estudos de condensados de Bose-Einstein. Também, será buscada a solução aproximada da equação de Schrödinger não linear e não-local, a qual descreve condensados de Bose-Einstein com auto-interações de longo alcance. Para isso, será suposta uma forma espacial da função de onda, permitindo o tratamento analítico do sistema dinâmico resultante. Ao fim, por meio do método variacional dependente do tempo, será demonstrado que existem soluções estáveis para a função de onda sujeito a interações de longo alcance na forma gaussiana e gravitacional. / Bose-Einstein condensation is a quantum phenomenon that can be observed macroscopically. External trappings are required to obtain them, however the presence of these leads to the collapse of the wave function. Long-range interactions are proposed as an alternative to external confinement, since they can prevent the collapse of the wave function. In this work a review will be presented on the Bose-Einstein condensate studies. Also, we review the approximate solution of the non-linear and non-local Schrödinger equation, which describes Bose-Einstein condensates with long-range auto-interactions. For this, a spatial form of the wave function will be assumed, allowing the analytical treatment of the system. Finally, through the time-dependent variational method, it will be demonstrated that there are stable solutions for the wave function subject to long-range interactions in gaussian and gravitational form.
159

Relaxation and quasi-stationary states in systems with long-range interactions / Relaxação e estados quasi-estacionários em sistemas com in- terações de longo alcance

Benetti, Fernanda Pereira da Cruz January 2016 (has links)
Sistemas cujos componentes interagem por meio de forças de longo alcance não-blindadas por exemplo, sistemas estelares e plasmas não-neutros têm algumas características anô- malas em relação a sistemas com forças blindadas ou de curto alcance. Além de apresentarem características termodinâmicas peculiares como calor especí co negativo e inequivalência de ensembles, sua dinâmica é predominantemente não-colisional e leva à estados quasiestacion ários fora de equilíbrio. Esses estados são notoriamente difíceis de prever dada uma condição inicial qualquer, e ainda não existe uma teoria uni cada para tratá-los. O equilíbrio termodinâmico é atingido somente após tempos longos que escalam com o tamanho do sistema, muitas vezes excedendo o tempo de vida do universo. A relaxação para o equilíbrio, portanto, tem duas escalas de tempo: uma, curta, que leva a estados quasi-estacionários fora de equilíbrio, e a segunda, longa, que leva ao equilíbrio termodinâmico. Nesta tese de doutorado, examinamos esses fenômenos aplicando modelos teóricos e simulação numérica para diferentes sistemas de interação de longo-alcance, incluindo um modelo de spins clássicos tipo XY com longo alcance, e o sistema auto-gravitante em três dimensões. Em uma segunda etapa, estudamos a relaxação para o equilíbrio termodinâmico, a relaxação colisional, através de equações cinéticas e simulação numérica. Desta forma, buscamos esclarecer os mecanismos por trás dos estados quasi-estacionários e da relaxação colisional. / Systems whose components interact by unscreened long-range forces for example, stellar systems and non-neutral plasmas have characteristics that are anomalous with respect to systems with shielded or short-range forces. Besides presenting unique thermodynamic properties such as negative speci c heat and inequivalence of ensembles, their dynamics is predominantly collisionless and leads to out-of-equilibrium quasi-stationary states. These states are notoriously di cult to predict given an arbitrary initial condition, and there is still no uni ed theory to treat them. Thermodynamic equilibrium is reached only after long timescales that increase with the system size and often exceed the lifetime of the universe. Relaxation to equilibrium, therefore, has two timescales: one short, leading to outof- equilibrium quasi-stationary states, and a second, longer, which leads to thermodynamic equilibrium. In this thesis, we examine these phenomena by applying theoretical models and numerical simulation for di erent long-range interacting systems, including a model of classical XY-type spins with long-range interactions, and the self-gravitating system in three dimensions. In a second stage we study the collisional relaxation to thermodynamic equilibrium through kinetic equations and numerical simulation. We thus seek to clarify the mechanisms behind the quasi-stationary states and collisional relaxation.
160

A Study of the Louisiana Learning Resources System Focusing on Projections for 1985

Brooks, William Kelly 08 1900 (has links)
The problem addressed in this study was the lack of long-range projections resulting from an absence of data in terms of functions, funding, administrative staffing, and collection of materials for the Louisiana Learning Resources System (LLRS) network of 1985. The purpose of this study was to make long-range projections in these areas. Based upon the findings and conclusions of this study, the following projections were made. 1. The LLRS of 1985 should be a local unit which would be specialized in function and operate on the same academic calendar as that of the local education agency. 2. The role of the LLRS Director of 1985 should continue to be that of a materials/media specialist. 3. The primary funding source of the LLRS of 1985 should be that of federal dollars. 4. The Ideal Collection of Materials for the LLRS of 1985 should include teacher oriented materials, student oriented materials, and hardware for use with special education materials.

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