Les forces de contact dans un milieu granulaire se répartissent de façon très inhomogène en un réseau de "chaînes de forces" qui supporte la plus grosse partie des contraintes. Il est primordial de bien comprendre l'influence du désordre des forces à l'échelle du grain sur les propriétés d'équilibre mécanique d'un milieu granulaire à l'échelle macroscopique.<br /><br />La mesure de forces dans un milieu granulaire est délicate à cause d'un couplage fondamental entre les déformations du capteur et la mobilisation des forces de friction entre grains ou entre grains et paroi. Cependant, en définissant proprement le protocole de mesure, nous avons pu améliorer de façon très significative la reproductibilité des résultats en comparaison des mesures que l'on trouve dans la littérature.<br /><br />Nous nous sommes intéressé aux liens qui existent entre la structure de l'empilement granulaire et la répartition des contraintes. Sous l'effet d'un cisaillement ou de vibrations, l'équilibre d'une colonne granulaire dans un silo évolue considérablement ainsi que la structure de l'empilement comme le révèlent des mesures de densité moyenne et locale. Sous le sommet d'un tas de sable formé par écoulement des grains en avalanches, j'ai observé très clairement un minimum ou "trou" de pression, alors que la pression est maximum si les grains sont déposés en couches horizontales. Nous avons aussi mesuré les fluctuations résiduelles de la pression en fonction de la taille des grains ou de la hauteur de remplissage du silo et ai observé que leur dépendance avec la taille des grains montrent une régression statistique anormale en comparaison de celle déduite de la distribution des forces à l'échelle du grain.<br /><br />La plupart des observations sont qualitativement et quantitativement bien reproduites par le modèle OSL dans lequel les contraintes se propagent selon deux directions dont l'une s'identifie à la direction moyenne des chaînes de forces. La notion de propagation anisotrope de forces permet de comprendre la distribution de pression sous un tas ou la forme de la courbe de saturation de la pression dans un silo, y compris les oscillations de la pression en présence d'une surcharge.<br /><br />Nous avons proposé en outre un modèle de durcissement d'arches qui permet d'expliquer l'existence d'un mode d'écoulement fragmentaire après renversement d'un tube rempli de grains et met en évidence le rôle non négligeable de l'élasticité des parois.

The Modifiable Areal Unit Phenomenon (MAUP) has traditionally been regarded as a problem in the analysis of spatial data organised in areal units. However, the approach adopted here is that the MAUP provides an opportunity to gain information about the data under investigation. Crucially, attempts to remove the MAUP from spatial data are regarded as an attempt to remove the geography. Therefore, the work seeks to provide an insight to the causes of, and information behind, the MAUP. The data used is from the 1991 Census of Great Britain. This was chosen over 2001 data due to the availability of individual level data. These data are of key importance to the methods employed. The methods seek to provide evidence of the magnitude of the MAUP, and more specifically the scale effect in the GB Census. This evidence is built on using correlation analysis to demonstrate the statistical significance of the MAUP. Having established the relevance of the MAUP in the context of current geographical research, the factors that contribute to the incidence of the MAUP are considered, and it is noted that a wide range of influences are important. These include the population size and density of an area, along with proportion of a variable. This discussion also recognises the importance of homogeneity as an influential factor, something that is referenced throughout the work. Finally, a search is made for spatial processes. This uses spatial autocorrelation and multilevel modelling to investigate the impact spatial processes have in a range of SAR Districts, like Glasgow, Reigate and Huntingdonshire, on the scale effect. The research is brought together, not to solve the MAUP but to provide an insight into the factors that cause the MAUP, and demonstrate the usefulness of the MAUP as a concept rather than a problem.

Landscape is about the relationship between people and place and in 2000 was defined by the European Landscape Commission (ELC) as "an area as perceived by people whose character is the result of natural and human actions and interactions”. In the 70s the reason for studying the landscape was because of the necessity of attributing a value to it. Nowadays the motivations behind managing, conserving and enhancing the landscape is because the landscape is the place where people belong to and, consciously or not, recognise themselves. In addition, people identify different landscapes on the basis of the particular combinations of the elements in the landscape. As a consequence a landscape can be distinguished from another on the basis of its character which, according to the Landscape Character Assessment (LCA) guidance for England and Scotland (C. Swanwick and Land Use Consultant, 2002), is defined as “a distinct, recognisable and consistent pattern of elements in the landscape that makes one landscape different from the other rather than better or worse”. This definition was the starting point of a PhD research project aimed at developing and implementing a methodology able to identify and quantify the character of the Scottish landscape through the application of GIS and statistics. The reason for doing this research was to provide the landscape architects and practitioners with a tool that could help them to define the landscape character types in a more consistent, objective, and scientifically robust way. One of the objectives of the research was to identify the spatial patterns formed by the landscape elements by taking into account the influence of the spatial location. The first law of geography, which states that "everything is related to everything else but near things are more related than distant ones" (W Tobler, 1970), was transposed in the assumption of the presence of spatial autocorrelation amongst the data which contributes to form spatial patterns within the data. Since landscape comprises of many elements, data were also multivariate, thus the analysis required a method of calculation able to deal simultaneously with multivariate and spatial autocorrelation issues. MULTISPATI-PCA, a spatially constrained Principal Component Analysis, was the statistical technique applied for the analysis of the data whose results showed that it was possible to detect the spatial structure of the data and that each spatial pattern corresponded to a distinct landscape. Despite their importance in forming the character of the landscape, aesthetic and perceptual aspects were not inlcuded in MULTISPATI-PCA analysis. It was preferred to test the technique only on data that were quantifiable in a more objective way. Perhaps taking into account the human perception of the landscape can be the starting point for future investigation.

Deterministic and stochastic weighting methods are commonly used methods for estimating missing precipitation rain gauge data based on values recorded at neighboring gauges. However, these spatial interpolation methods seldom check for their ability to preserve site and regional statistics. Such statistics and primarily defined by spatial correlations and other site-to-site statistics in a region. Preservation of site and regional statistics represents a means of assessing the validity of missing precipitation estimates at a site. This study evaluates the efficacy of traditional interpolation methods for estimation of missing data in preserving site and regional statistics. New optimal spatial interpolation methods intended to preserve these statistics are also proposed and evaluated in this study. Rain gauge sites in the state of Kentucky are used as a case study, and several error and performance measures are used to evaluate the trade-offs in accuracy of estimation and preservation of site and regional statistics. / by Husayn El Sharif. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Spatial and temporal interpolation methods are commonly used methods for estimating missing precipitation rain gauge data based on values recorded at neighboring gauges. However, these interpolation methods have not been comprehensively checked for their ability to preserve time series characteristics. Assessing the preservation of time series characteristics helps achieving a threshold criteria of length of gaps in a data set that is acceptable to be filled. This study evaluates the efficacy of optimal weighting interpolation for estimation of missing data in preserving time series characteristics. Rain gauges in the state of Kentucky are used as a case study. Several model performance measures are also evaluated to validate the filling model; followed by time series characteristics to evaluate the accuracy of estimation and preservation of precipitation data characteristics. This study resulted in a definition of region-specific threshold of the maximum length of gaps allowed in a data set at five percent. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

Avian influenza H5N1 is one kind of important bird flu. Unfortunately, this virus has swiftly evolved and become highly pathogenic to humans and poultry, resulting in 100% of death in infected poultry and over 60% of mortality among infected human population. Moreover, the virus tends to reassort with other influenza viruses, such as the current swine flu H1N1, to establish themselves in environments and further this epidemic all over the world. The World Health Organization (WHO) has in fact warned that highly pathogenic avian influenza H5N1 poses a graver risk of a global human pandemic than at any time since the Hong Kong outbreak (H3N2) in the 1960s. / Finally, avian influenza is an inter-disciplinary issue across virology, medical geography, and spatial epidemiology. How to quantify and integrate knowledge from different disciplines remains a challenge in fully understanding the disease. We propose a method to formally integrate genetic analysis that identifies the evolution of the H5N1 virus in space and time, epidemiological analysis that determines socio-environmental factors associated with H5N1 occurrence and statistical analysis that identifies outbreak dusters. Our integrated results show a significant advance in findings over reports in, for instance, Gilbert et al. (2008) and we believe our findings are more precise and informative in representing the occurrence and the space-time dynamics of H5N1 spread. Overall, unlike traditional influenza studies, our work sets up a solid foundation for the inter-disciplinary study of this and other spatial infectious diseases. / First, we apply multifractal detrended fluctuation analysis to determine the temporal scaling behavior of outbreaks in Asia, Europe, Africa, and the whole of the world between December 2003 to March 2009. Long-range correlation and multifractality, two important properties characterizing the scaling behavior of complex dynamics, are first detected in the outbreak time series. In addition, this study identifies different temporal scaling behaviors of outbreaks of these continents 8,nd specific seasonal patterns in Asia. These findings confirm our perspective that avian-influenza outbreak behaviors are self-similar over time and are spatially heterogeneous. / One key to preventing such a calamity is to obtain a thorough understanding of the mechanisms of avian influenza transmission and its spatio-temporal patterns of dispersal. The issues at stake are outbreaks' spatial and temporal patterns, the interrelationship of these with the evolution of influenza viruses in such a way that geography is understood as a dimension of the disease's virology, and the human and avian behaviors and socio-ecological environments associated with H5Nl spread. This thesis sets out to study these problems in detail and propose solutions. / Second, we conduct a spatial analysis for global trends and local clusters of H5N1 outbreaks at multiple geographical scales. Currently, the local K function used in a point pattern analysis searches outbreak clusters, assuming the disease is spatially homogeneous. The thesis proposes a much more efficient method to measure the degree of clusters accurately. The modified function works by weighting outbreaks through distances, counting the number of the weighted outbreaks for each lattice point no matter whether the disease emerges in a grid. This weighted local K function extends cluster analysis from a point pattern to lattice data. Spatial representation in these terms then seeks to explore local patterns of H5N1 over a continuous space. / Third, we study a set of socio-environmental factors, which are plausibly associated with the occurrence of H5N1. Spatial epidemiological models are built for predicting the disease at both continental and national levels, covering Indonesia, China, and the whole of East-Southeast Asia. We evaluate the statistical models using 1,000 bootstrap replicates, showing a consistently high rate of prediction, assessed by statistics: AUC, Kappa Index, and pseudo R square. / Ge, Erjia. / Advisers: Yee Leung; Tung Fung. / Source: Dissertation Abstracts International, Volume: 73-06, Section: A, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 169-197). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The aim of the research project that is the subject of this thesis is to apply mathematical techniques, especially those in the area of operations research, to the problem of maritime minefield transit. We develop several minefield models applicable to different aspects of the minefield problem. These include optimal mine clearance, shortest time traversal and time constrained traversal. We hope the suite of models and tools developed will help make mine field clearance and traversal both safer and more efficient and that exposition of the models will bring a clearer understanding of the mine problem from a mathematical perspective. In developing the solutions to mine field models, extensive use is made of network path planning algorithms, particularly the Weight Constrained Shortest Path Problem (WCSPP) for which the current state-of-the-art algorithm is extended. This is done by closer integration of Lagrangean relaxation and preprocessing to reduce the size of the network. This is then integrated with gap-closing algorithms based on enumeration to provide optimal or near optimal solutions to the path planning problem. We provide extensive computational evidence on the performance of our algorithm and compare it to other algorithms found in the literature. This tool then became fundamental in solving various separate minefield models. Our models can be broadly separated into obstacle models in which mine affected regions are treated as obstacles to be avoided and continuous threat in which each point of space has an associated risk. In the later case, we wish to find a path that minimizes the integral of the risk along the path while constraining the length of the path. We call this the Continuous Euclidean Length Constrained Minimum Cost Path Problem (C-LCMCPP), for which we present a novel network approach to solving this continuous problem. This approach results in being able to calculate a global lower bound on a non-convex optimization problem.

[Truncated abstract] The malleefowl (Leipoa ocellata) is a large, ground-dwelling bird that is listed as threatened in all states of Australia in which it occurs. Its range encompasses much of southern Australia; however, much of it has been cleared for agriculture. Malleefowl are thought to have suffered substantial decline owing to multiple threats that include habitat loss, predation from exotic predators, grazing of habitat by introduced herbivores and fire - common threats in the decline of many Australian vertebrate species. The malleefowl has an unmistakeable appearance, unique biology, and widespread distribution across Australia. Consequently, it has been the focus of much scientific and community interest. In the Western Australian wheatbelt, community groups are working to conserve the species and have been actively collecting data on its distribution for over 15 years. The vast majority of these data are presence-only and have been collected in an opportunistic manner but, combined with long-term data from government agencies and museums spanning over 150 years, they present a significant opportunity to inform ecological questions relevant to the conservation of the species. The purpose of this study was to answer key ecological questions regarding the distribution, status and habitat preferences of malleefowl using unstructured occurrence records supplemented by reliable absences derived from Bird Atlas data sets and targeted surveys. Malleefowl in the Western Australian wheatbelt were used as a case study to illustrate: 1) how the decline of a species can be quantified and causes of that decline identified; and 2) how threats can be identified and responses to threats explored. I used bioclimatic modelling to define and explore variation within the climatic niche of the Malleefowl across Australia. '...' This thesis provides substantial additional knowledge about the ecology, distribution and status of malleefowl in Western Australia. It also illustrates how opportunistic and unstructured data can be augmented to investigate key aspects of a species' ecology. Despite the limitations of these data, which primarily relate to variation in observer effort across time and space, they can provide important outcomes that may not be achieved using standard survey and data collection techniques. The utility of opportunistic data is greatest in situations where the species: is recognisable and easily observed; is relatively sedentary; and occurs within a landscape containing consistent land use and habitat types. The approaches used in this study could be applied by researchers to situations where community interest exists for species with these attributes. At a national scale, the malleefowl is predicted to decline by at least 20% over the next three generations. The findings of this thesis suggest that the future for the species in the Western Australian wheatbelt may not be as dire as predicted elsewhere within its range, owing largely to the easing and cessation of threatening processes (e.g. land clearing, grazing of habitat by livestock) and the ability of the species to occupy a variety of habitat types. Despite this perceived security, some caution must be exercised until there is a more complete knowledge of the impact of fox predation and reduced rainfall due to climate change on malleefowl populations. Furthermore, the status of the species beyond the agricultural landscapes in Western Australia requires closer examination.

La transition vitreuse se caractérise par un ralentissement dramatique de la dynamique, soit lorsqu'on refroidit un liquide soit lorsque l'on compacifie une assemblée de particules dans un état amorphe. Dans cette thèse nous explorons deux situations distinctes liées à cette phénoménologie, principalement dans le cas de matériaux granulaires. Dans une première partie nous étudions la réponse fortement non-linéaire d'un système de particules frottantes vibrées à très haute densité soumis à une contrainte locale. Pour cela nous tirons une particule "intrus" à force constante dans le milieu en suivant le mouvement des particules alentour. Nous mettons en évidence deux transitions distinctes : la première est l'analogue d'une transition de fluidification et se manifeste par le passage d'un mouvement continu de l'intrus à un mouvement fortement intermittent ainsi que par l'apparition d'une contrainte seuil dans la réponse ; la deuxième est identifiée à la transition de blocage qui intervient de manière générique dans de nombreux systèmes. Nous montrons que les réorganisations induites par l'intrus ont un comportement critique à la transition, venant conforter le caractère critique de la transition de blocage mis en évidence en l'absence d'intrus, et établissant d'intéressantes connections avec des simulations récentes de systèmes athermiques de particules non-frottantes. Dans une deuxième partie nous étudions les relations entre la dynamique à très court terme - essentiellement vibratoire - et à plus longue échelle de temps, où de fortes hétérogénéités dynamiques sont responsables du ralentissement des relaxations structurales à l'approche de la transition vitreuse. La dynamique des états métastables est analysée dans plusieurs systèmes granulaires (cellule de cisaillement cyclique et lit fluidisé) ainsi que dans une simulation d'un liquide de Lennard-Jones répulsif ; nous mettons en évidence le rôle de mouvements coopératifs quasi-instantanés qui construisent à long terme par un mécanisme de facilitation de larges motifs de décorrélation intermittents. Ce mécanisme de facilitation diminue lorsque le matériau se densifie, menant à des évènements dynamiques de plus en plus séparés et concentrés dans l'espace et le temps. La dynamique vibratoire aboutissant aux mouvements coopératifs est elle aussi étudiée, et nous montrons que ces derniers sont déterminés pour une large part par la structure du matériau à un niveau mésoscopique.

Ce document est une synthèse de mes travaux de recherche en Physique qui s'articule selon trois axes: turbulence hydrodynamique, magnétohydrodynamique et turbulence d'onde. J'ai développé des techniques de mesure originales destinées à l'analyse lagrangienne de la turbulence hydrodynamique: il s'agit de suivre le mouvement de particules entraînées par un écoulement à haut nombre de Reynolds. Malgré le fait que la statistique de vitesse Lagrangienne soit gaussienne avec une décorrélation exponentielle, la modélisation de l'écoulement par une équation de Langevin est insuffisante à cause la très forte intermittence de la vitesse Lagrangienne. Celle-ci se traduit en particulier par un distribution fortement non gaussienne de l'accélération. En comparant les données expérimentales avec un modèle de marche aléatoire multifractale, nous avons mis en évidence le lien entre corrélations temporelles longues de l'amplitude de l'accélération et les propriétés statistiques d'intermittence. Une description multifractale suggère par ailleurs une certaine universalité de l'intermittence Lagrangienne entre différents écoulements expérimentaux ou numériques. Les mêmes techniques expérimentales sont appliquées à l'étude de la dynamique de particules inertielles. Cela permet en particulier d'améliorer la modélisation des effets d'inertie et de taille finie dans les simulations numériques. Finalement, j'analyse le lien entre le mouvement des particules de fluide et les propriétés de transport de scalaire passif. Je participe également à la collaboration VKS dont le but est l'étude expérimentale de l'effet dynamo, c'est-à-dire la génération d'un champ magnétique par le mouvement d'un fluide conducteur (du sodium liquide dans notre cas). Nous avons mis en évidence cet effet en 2006 et montré l'existence de régimes dynamiques du champ magnétique qui, pour certains, ressemblent fortement aux renversements du champ magnétique terrestre. Nous avons montré que les conditions aux limites jouent un rôle crucial. Les régimes dynamiques correspondent au comportement attendu par des systèmes dynamiques de basse dimension malgré le fait que l'écoulement est fortement turbulent et fait donc intervenir un grand nombre de degrés de liberté. Pour étudier la saturation de la croissance du champ dynamo, nous avons mis en oeuvre à l'ENS Paris, une expérience dans le gallium dans laquelle nous étudions l'effet d'un champ magnétique élevé sur un écoulement turbulent. Les effets de freinage magnétique ont été mis en évidence. Finalement, j'ai développé récemment une expérience de turbulence d'onde. La turbulence d'onde présente des ressemblances phénoménologiques avec la turbulence hydrodynamique, avec l'avantage d'une théorie statistique: la turbulence faible. Nous étudions expérimentalement les vibrations d'une tôle mince en acier inoxydable. Une technique de profilométrie par transformée de Fourier à haute vitesse permet de mesurer l'évolution temporelle de la déformation de la plaque résolue à la fois en temps et en espace. Les propriétés statistiques de ces vibrations sont en désaccord quantitatif avec la théorie mais la phénoménologie semble similaire. Ces nouvelles mesures ouvrent de nombreuses perspectives d'interaction avec les théoriciens de la turbulence d'onde.