In this work we present an introduction to the theory of point processes in space and time with focus on space--time shot--noise Cox process. Further from theoretical point of view we study its simulation, space--time separability, kernel estimate of intensity function and non--parametric estimation of some summary statistics using edge corrections. For two ambit models and one space--time separable model we do numerical calculations using the presented theory and software Wolfram Mathematica 9.0. For these three models we do simulations, we select the best bandwidth for kernel estimate of the intensity function and we also calculate some theoretical summary statistics including the pair correlation function. Powered by TCPDF (www.tcpdf.org)

Dans cette thèse, nous étudions l’implémentation des contraintes de simplicité dans le nouveau modèle de mousses de spin d’Engle-Pereira-Rovelli-Livine, ainsi que les fonctions de corrélation à deux points de ce modèle. Nous définissons d’une manière simple l’espace de Hilbert limite de la théorie, puis montrons directement que toutes les contraintes s’annulent faiblement sur cet espace. Nous observons que la solution générale a cette contrainte (imposée faiblement) dépend d’un nombre quantique, en plus de ceux de la gravitation quantique a boucles. Nous généralisons également cette construction pour la version de Kaminski-Kisielowski-Lewandowski, ou la mousse n’est pas duale à une triangulation. Nous montrons que cette théorie peut aussi être obtenue comme une théorie BF satisfaisant la contrainte de simplicité, cette fois discrétisée sur un 2-complexe cellulaire oriente. Enfin, nous calculons la fonction de corrélation a deux points du modèle de mousses de spin Engle-Pereira-Rovelli-Livine avec la signature lorentzienne, et nous montrons que la fonction a deux points que nous obtenons correspond dans une certaine limite a celle obtenue a partir du calcul de Regge lorentzien. / In this thesis we study the implementation of simplicity constraints that defines the recent Engle-Pereira-Rovelli-Livine spinfoam model and two-point correlation functions of this model. We define in a simple way the boundary Hilbert space of the theory; then show directly that all constraints vanish on this space in a weak sense. We point out that the general solution to this constraint (imposed weakly) depends on a quantum number in addition to those of loop quantum gravity. We also generalize this construction to Kami´nski-Kisielowski-Lewandowski version where the foam is not dual to a triangulation. We show that this theory can still be obtained as a constrained BF theory satisfying the simplicity constraint, now discretized on a general oriented 2-cell complex. Finally, we calculate the twopoint correlation function of the Engle-Pereira-Rovelli-Livine spinfoam model in the Lorentzian signature, and show the two-point function we obtain exactly matches the one obtained from Lorentzian Regge calculus in some limit.

Les Oscillations Baryoniques Acoustiques (BAOs) correspondent au phénomène d'ondes acoustiques dans le plasma baryon-photon avant la recombinaison. Ces oscillations impriment une échelle standard, correspondant à l'horizon sonique, qui peut être observée dans les grandes structures de l'Univers. De par cette propriété d'étalon standard, les BAOs permettent d'étudier la relation distance-redshift dans les catalogues de galaxies et fournissent un outil très prometteur pour étudier les propriétés de l'énergie sombre. Les BAOs peuvent être étudiés à partir des statistiques du second ordre (la fonction de corrélation ou le spectre de puissance) dans la distribution des galaxies. Dans cette thèse, on se restreint au cas de la fonction de corrélation. Les BAOs apparaissent dans la fonction de corrélation comme un faible pic à l'échelle de l'horizon sonique. Il y a deux applications principales des BAOs: la détection des BAOs et la contraintes des paramètres cosmologiques grâce à la propriété d'étalon standard. La détection du pic BAO à une échelle proche de l'échelle attendue permet de confirmer le modèle cosmologique actuel. Quant à la contrainte des paramètres cosmologiques, permettant d'étudier l'énergie sombre, il s'agit d'un objectif majeur de la cosmologie moderne. Dans cette thèse, on s'intéresse à différents problèmes statistiques concernant l'étude de la fonction de corrélation dans la distribution des galaxies, avec un accent particulier sur l'étude des BAOs. Dans la première partie, on fait une étude à la fois théorique et pratique du biais dû à la contrainte intégrale dans les estimateurs de la fonction de corrélation. On montre que ce biais est très faible pour les relevés de galaxies actuels. Dans la seconde partie, on s'intéresse à la détection des BAOs. On montre les limitations de la méthode de détection classique, et on propose une nouvelle méthode plus rigoureuse. Notre méthode permet notamment de prendre en compte la dépendance de la matrice de la covariance de l'estimateur en fonction du modèle. Enfin dans la troisième partie, on étudie à nouveau la question la dépendance de la matrice de la covariance, cette fois pour la contrainte des paramètres cosmologiques. On estime une matrice de covariance dépendant du modèle et l'on compare nos contraintes avec les contraintes obtenues en faisant l'approximation habituelle d'une matrice de covariance constante. On montre que l'effet de cette approximation est relativement faible et diminue lorsque les relevés de galaxies grandissent. / Baryon Acoustic Oscillations (BAOs) correspond to the acoustic phenomenon in the baryon-photon plasma before recombination. BAOs imprint a particular scale, corresponding to the sound horizon, that can be observed in large-scale structures of the Universe. Using this standard ruler property, BAOs can be used to probe the distance-redshift relation in galaxy catalogues, thus providing a very promising tool to study dark energy properties. BAOs can be studied from the second order statistics (the correlation function or the power spectrum) in the distribution of galaxies. In this thesis we restrict to the case of the correlation function. BAOs appear in the correlation function as a small localized bump at the scale of the sound horizon in comoving coordinates. There are two major applications of BAO study: BAO detection and cosmological parameter constraints using the standard ruler property. The detection of BAOs at the expected scale enables to confirm the current cosmological model. As for cosmological parameter constraints, enabling the study of dark energy, it is a major goal of modern cosmology. In this thesis we tackle different statistical problems concerning the correlation function analysis in the galaxy distribution, with a focus on the study of BAOs. In the first part, we make both a theoretical and practical study of the bias due to the integral constraints in correlation function estimators. We show that this bias is very small for current galaxy surveys. In the second part we study the BAO detection. We show the limitations of the classical detection method and propose a new method, which is more rigorous. In particular our method enables to take into account the model-dependence of the covariance matrix of the estimators. In the third part, we focus again on the model-dependence of the covariance matrix, but this time for parameter constraints. We estimate a model-dependent covariance matrix and compare our constraints with constraints obtained by making the usual approximation of a constant covariance matrix. We show that the effect of this approximation is quite small for current galaxy surveys and decreases with the survey size.

The charge and spin density correlations in a one dimensional electron gas (1DEG) confined in a semiconductor quantum wire structure at zero temperature are studied. The dielectric formulation of the many--body problem is employed and the longitudinal dielectric function, local-field correction, static structure factor, pair correlation function, ground state energy, compressibility, spin-dependent effective interaction potentials, paramagnon dispersion and static spin response function of the 1DEG are computed within the self-consistent field approximations of Singwi et al., known as the STLS and SSTL. The results are compared with those of other groups, and those obtained for two-dimensional electron gas systems whenever it is possible. It is observed that the SSTL satisfies the compressibility sum rule better than the STLS. Calculating the ground state energy of the 1DEG in unpolarized and fully polarized states, it is shown that both STLS and SSTL predict a Bloch transition for 1DEG systems at low electron densities. Finally, the coupled plasmon-phonon modes in semiconductor quantum wires are calculated within the Fermi and Luttinger liquid theories. The coupling of electrons to bulk longitudinal optical phonons without dispersion and to acoustic phonons via deformation potential with a linear dispersion are considered. Using the dielectric formalism, a unified picture of the collective coupled plasmon-phonon modes is presented. Considerable differences between the predictions of the Fermi and Luttinger liquid approaches at large wave vector values, which may be observed experimentally, are found.

Our thesis tackles the many-electronic problem considering a non-relativistic and a relativistic orbital approach. Using the suites of programs ATSP and GRASP, we are able to approximate many-electron wave functions beyond the independent particle model by considering a superposition of CSFs. The optimization process, based on the variational principle, provides the best possible mixing coefficients fixing the linear combination of CSFs and spin-orbital basis on which we impose the orthonormality condition between functions of the same l or kappa subspace. Using this conventional approach within the relativistic framework, we estimate different properties of the triply ionized antimony atom (Sb IV), namely transition energies, transition probabilities, isotope shifts and a hyperfine-induced transition.<p><p>In the aim of partially relaxing the orthogonality constraints between correlation orbitals, we use the variational principle for targeting specific correlation effects by tailoring the configuration space. Independent sets of correlation orbitals, embedded in PCF, are produced from MCHF calculations. These non-orthogonal functions span CSF spaces that are coupled to each other by solving the associated generalized eigenvalue problem. The Hamiltonian and overlap matrix elements are evaluated using the biorthonormal orbital transformations and the efficient counter-transformations of the configuration interaction eigenvectors. This original method is successfully applied for describing different light atomic systems such as Li I, Be I, B I, C II and Ne I. An unwanted effect, called the ``constraint effect', is described and studied for these particular atomic systems. Even if this constraint can be completely relaxed through the DPCFI method, the computational resources required by such an approach lead us to study some simple strategies relaxing partially this constraint. This study takes it place in the context of neutral beryllium for which we test two particular strategies: one based on a weight criterion and one based on the type of excitations. Before concluding, we expose some developments combining the SCF process and the biorthonormal condition to relax the orthogonality constraints that are presently applied to the optimization process of the spin-orbital basis.<p>/<p>Dans notre thèse, nous abordons le problème polyélectronique dans un contexte non-relativiste et relativiste en adoptant une approche orbitalaire. En utilisant les suites de programmes reconnues ATSP et GRASP, nous sommes aptes à approcher des fonctions d'ondes polyélectroniques au-delà du modèle des particules indépendantes en utilisant une superposition de CSFs. Le processus d'optimisation, basé sur le principe des variations, fournit la meilleure estimation possible des coefficients de mélange, fixant la combinaison linéaire de CSFs et la meilleure base de spin-orbitales sur laquelle on impose la condition d'orthonormalité entre les fonctions appartenant au même sous-espace l ou kappa. En adoptant cette approche dans un cadre relativiste, nous évaluons des énergies de transition, des probabilités de transition, des déplacements isotopiques ainsi qu'une transition induite par mélange hyperfin pour l'atome d'antimoine trois fois ionisé (Sb IV).<p><p>Dans le but de relâcher partiellement les contraintes d'orthogonalité entre les orbitales de corrélation, nous utilisons le principe des variations afin de cibler des effets précis de la corrélation en taillant l'espace des configurations. Les ensembles indépendants d'orbitales de corrélation sont obtenus via la méthode MCHF. Les espaces de CSFs, exprimés sur ces fonctions mono-électronique non-orthogonales, sont couplés en résolvant le problème aux valeurs propres généralisé associé. Les matrices Hamiltonienne et de recouvrement sont déterminées au moyen de la technique des transformations biorthonormales et de la contre-transformation des vecteurs propres associés. Cette méthode originale est utilisée avec succès pour décrire des systèmes atomiques légers comme Li I, Be I, B I, C II et Ne I. Un effet indésirable, appelé ``effet de contrainte', est déecrit et étudié pour ces derniers systèmes atomiques. Même si ces contraintes peuvent-être en principe totalement levées au travers de la méthode DPCFI, les ressources nécessaires à l'application de cette dernière approche nous ont conduit à la recherche de stratégies simples et efficaces autorisant leur levée partielle. Pour ce faire, dans le cadre de nos calculs réalisés sur l'atome de béryllium, nous avons envisagé deux stratégies particulières: l'une basée sur les coefficients de mélange et l'autre basée sur le type d'excitation. Avant de conclure, nous proposons quelques développements combinant le processus auto-cohérent et la condition de biorthonormalité dans le but de relâcher les contraintes d'orthogonalité appliquées lors du processus d'optimisation de la base de spin-orbitales. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Silné prostorové omezení materiálů způsobuje jejich nové vlastnosti, které mohou najit uplatnění v mnoha vědeckých i technických odvětvích. Snaha zmenšit velikosti součástek, zvětšit hustotu zápisu a zefektivnit procesy je současným trendem elektronického průmyslu. V této práci je studován vliv prostorového omezení na vlastnosti metamagnetického železo-rhodia (FeRh) během fázové přeměny. FeRh je materiál vykazující fázovou přeměnu prvního druhu mezi antiferomagnetickou a feromagnetickou fází. Metodou mikroskopie magnetických sil v magnetickém poli kolmém na rovinu vzorku je zobrazeni a analyzována struktura fázových domén behem fázové přeměny. Kvantitativní analýza naměřených dat je provedena užitím výškové korelační funkce a její výsledky jsou porovnány pro různé velikosti struktur a tloušťky tenkých vrstev.

This master's thesis is focused on localization static (entering semester project) and moving acoustic sources (entering master's thesis) by the help of microphonic arrays. In the first part deal with common problems of localization. Further are here described types of microphonic arrays, simplifying possibilities which delimited this problems and general information about room acoustics. In the next part of this master's thesis are step by step mentioned methods localization of acoustic sources. In practical part were used algorithms: Steered-Beamformer-Based Locators and TDOA-Based Locators. Last part of this master's work includes results of these algorithms.

The global effort to rehabilitate and restore destroyed mangrove forests is unable to keep up with the high mangrove deforestation rates which exceed the average pace of global deforestation by three to five times. Our knowledge of the underlying processes of mangrove forest regeneration is too limited in order to find suitable techniques for the restoration of degraded mangrove areas. The general objective of my dissertation was to improve mangrove restoration by understanding regeneration processes and local plant-plant interaction in a regenerating Avicennia germinans forest. The study was conducted in a high-shore mangrove forest area on the Ajuruteua peninsula, State of Para, Northern Brazil. The dwarf forest consisting of shrub-like trees is recovering from a stand-replacing event caused by a road construction in 1974 which interrupted the tidal inundation of the study area. Consequently, infrequent inundation and high porewater salinity limit tree growth and canopy closure. All trees and seedlings were stem-mapped in six 20 m x 20 m plots which were located along a tree density gradient. Moreover, height, crown extent, basal stem diameter of trees were measured. The area of herbaceous ground vegetation and wood debris were mapped as well. The mapped spatial distribution of trees, seedlings and covariates was studied using point pattern analysis and point process models, such as Gibbs and Thomas point process, in order to infer underlying ecological processes, such as seed dispersal, seedling establishment, tree recruitment and tree interaction. In the first study (chapter 2), I analyzed the influence of abiotic and biotic factors on the seedling establishment and tree recruitment of A. germinans during the recolonization of severely degraded mangrove sites using point process modeling. Most seedlings established adjacent to adult trees especially under their crown cover. Moreover, seedling density was higher within patches of the herbaceous salt-marsh plants Blutaparon portulacoides and Sesuvium portulacastrum than in uncovered areas. The higher density of recruited A. germinans trees in herb patches indicated that ground vegetation did not negatively influence tree development of A. germinans. In addition, tree recruitment occurred in clusters. Coarse wood debris had no apparent effect on either life stage. These results confirm that salt-marsh vegetation acts as the starting point for mangrove recolonization and indicate that the positive interaction among trees accelerates forest regeneration. In the second study (chapter 3), I analyzed how intraspecific interaction among A. germinans trees determines their growth and size under harsh environmental conditions. Interaction among a higher number of neighboring trees was positively related to the development of a focal tree. However, tree height, internode length and basal stem diameter were only positively associated in low-density forest stands (1.2 trees m-2) and not in forest stands of higher tree density (2.7 trees m-2). These results indicated a shift from facilitation, i.e. a positive effect of tree interaction, towards a balance between facilitation and competition. In the third study (chapter 4), I used point process modeling and the individual-based model mesoFON to disentangle the impact of regeneration and interaction processes on the spatial distribution of seedlings and trees. In this infrequently inundated area, propagules of A. germinans are only dispersed at a maximum distance of 3 m from their parent tree. Furthermore, there is no evidence that the following seedling establishment is influenced by trees. I was able to differentiate positive and negative tree interactions simulated by the mangrove model mesoFON regardless of dispersal processes based on static tree size information using the mark-correlation function. The results of this dissertation suggest that mangrove forest regeneration in degraded areas is a result of facilitative and not competitive interactions among mangrove trees, seedling and herbaceous vegetation. This has important implications for the restoration of degraded mangrove forest. Degraded mangrove areas are usually restored by planting a high number of evenly spaced seedlings. However, high costs constrain this approach to small areas. Assisting natural regeneration could be a less costly alternative. Herbaceous vegetation plays a crucial role in forest recolonization by entrapping propagules and possibly ameliorating harsh environmental conditions. So far only competition among mangrove trees has been considered during restoration. However, facilitative tree interactions could be utilized by planting seedling clusters in order to assist natural regeneration instead of planting seedlings evenly-spaced over large areas. This dissertation also showed that point pattern analysis and point process modeling can enable forest ecologists to describe the spatial distribution of trees as well as to infer underlying ecological processes.

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