Global ETD Search

1	Global Thermospheric Response to Geomagnetic Storms Suresh, Padmashri 01 May 2016 (has links) Geomagnetic storms deposit energy and momentum into the Earth’s magnetosphere which in turn energizes the terrestrial atmosphere through Joule heating and particle precipitation. This storm energy predominantly converges at altitudes of 100 to 150 km, corresponding to the lower thermospheric region, which is then globally redistributed throughout the thermosphere. It is essential that we understand the times and magnitudes of this energy to understand the terrestrial atmospheric response to geomagnetic storms. However, our current knowledge is mostly limited to the studies of orbital altitudes of the thermosphere. We aim to fill this gap by conducting a statistical study of lower thermospheric response to geomagnetic storms. We use neutral temperature data from SABER (Sounding of the Atmosphere Using Broadband Emission Radiometry) instrument onboard the TIMED (Thermosphere, Ionosphere, and Mesosphere Energy Dynamics) satellite for this study. We devise a procedure to extract the storm response from SABER temperature measurements and deduce the magnitudes and times of the global storm energy redistribution in the 100 to 120 km altitude of the thermosphere. We use methods of inferential and descriptive statistics to investigate the lower thermospheric response for 145 storm intervals that occurred between 2002 and 2010. We also investigate the performance of the state-ofart physics and empirical models in replicating the lower thermosphere during geomagnetic storms. Geomagnetic Storms Thermosphere TIMED Machine Learning Statistical Study Electrical and Computer Engineering
2	National Inter-religious Councils and Electoral Violence Restraint in Africa Nakabiito, Joanna January 2022 (has links) A handful of studies have shown that National Inter-religious Councils (NIRCs) contribute to electoral violence prevention. However, no quantitative study has evaluated the impact of their interventions and the conditions under which they lower electoral violence. Using data on African national elections from 1992-2019, I examine whether NIRCs' electoral-related peacebuilding interventions lower the severity of electoral violence and if their ability to do so depends on NIRCs' social power. The results in this thesis indicate that the presence of NIRCs' interventions during electoral rounds lowers the likelihood of severe electoral violence. The findings also reveal a significant disordinal interaction between NIRCs' interventions and their power, where the predicted probability of severe electoral violence reduces by 42% when powerful NIRCs implement peacebuilding interventions and, on the other hand, increases by 20% when less powerful NIRCs intervene. While this thesis fails to explain the disordinal interaction effect, it details this study's methodological tools and limitations and contributes an original dataset of NIRCs' interventions and power for future research. electoral violence prevention political violence social power religious institutions peacebuilding moderation effects religions for peace statistical study quasi-experimental research Social Sciences Interdisciplinary
3	Reverberation Chamber Modeling Using Finite-Difference Time-Domain Method Petit, Frédéric 12 1900 (has links) Since the last few years, the unprecedented growth of communication systems involving the propagation of electromagnetic waves is particularly due to developments in mobile phone technology. The reverberation chamber is a reliable bench-test, enabling the study of the effects of electromagnetic waves on a specific electronic appliance. However, the operating of a reverberation chamber being rather complicated, development of numerical models are of utmost importance to determine the crucial parameters to be considered.This thesis consists in the modelling and the simulation of the operating principles of a reverberation chamber by means of the Finite-Difference Time-Domain method. After a brief study based on field and power measurements performed in a reverberation chamber, the second chapter deals with the different problems encountered during the modelling. The consideration of losses being a very important factor in the operating of the chamber, two methods of implementation of these losses are set out in this chapter. Chapter~3 consists in the analysis of the influence of the stirrer on the first eigenmodes of the chamber; the latter modes can undergo a frequency shift of several MHz. Chapter~4 shows a comparison of results issued from high frequency simulations and theoretical statistical results. The problem of an object placed in the chamber, resulting in a field disturbance is also tackled. Finally, in the fifth chapter, a comparison of statistical results for stirrers having different shapes is set out. reverberation chamber mode-stirred chamber Modeling numerical method FDTD finite difference time domain stirrer numerical error non-uniform mesh FFT modes overlapping frequency shift eigen mode eigen frequency mode density quality factor losses modal study statistical study statistical test statistical criterion correlation angle Chi2 law Rayleigh low Gauss law PDF CDF QC T1
4	Metapopulation dynamics of dengue epidemics in French Polynesia / Dynamique métapopulationelle des épidémies de dengue en Polynésie française Teissier, Yoann 22 May 2017 (has links) La dengue circule en Polynésie française sur un mode épidémique depuis plus de 35 ans. Néanmoins, en dépit de la taille relativement faible de la population de Polynésie française, la circulation de la dengue peut persister à de faibles niveaux pendant de nombreuses années. L’objectif de ce travail de thèse est de déterminer si l'épidémiologie de la dengue dans le système insulaire de la Polynésie française répond aux critères d’un contexte de métapopulation. Après avoir constitué une base de données regroupant les cas de dengue répertoriés sur les 35 dernières années, nous avons réalisé des analyses épidémiologiques descriptives et statistiques. Celles-ci ont révélé des disparités spatio-temporelles distinctes pour l’incidence de la dengue des archipels et des îles, mais la structure de l'épidémie globale à l’échelle de la Polynésie française pour un même sérotype ne semble pas être affectée. Les analyses de la métapopulation ont révélé l'incidence asynchrone de la dengue dans un grand nombre d’îles. Celle-ci s’observe plus particulièrement par la différence de dynamique de l’incidence entre les îles plus peuplées et celles ayant une population plus faible. La taille critique de la communauté nécessaire à la persistance de la dengue n’est même pas atteinte par la plus grande île de Polynésie Française, Tahiti. Ce résultat suggère que la dengue peut uniquement persister grâce à sa propagation d’île en île. L'incorporation de la connectivité des îles à travers des modèles de migration humaine dans un modèle mathématique a produit une dynamique de la dengue davantage en adéquation avec les données observées, que les tentatives de modélisation traitant la population dans son ensemble. Le modèle de la métapopulation a été capable de simuler la même dynamique que les cas de dengue observés pour l'épidémie et la transmission endémique qui a suivi pour la période de 2001 à 2008. Des analyses complémentaires sur la différenciation de l'incidence de la maladie et de l'infection seront probablement instructives pour affiner le modèle de métapopulation de l'épidémiologie de la dengue en Polynésie française. / Dengue has been epidemic in French Polynesia for the past 35 years. Despite the relatively small population size in French Polynesia, dengue does not disappear and can persist at low levels for many years. In light of the large number of islands comprising French Polynesia, this thesis addresses the extent to which a metapopulation context may be the most appropriate to describe the epidemiology and persistence of dengue in this case. After compiling a database of dengue cases over the last 35 years, we used a number of descriptive and statistical epidemiological analyses that revealed distinct spatio-temporal disparity in dengue incidence for archipelago and islands. But the global structure of the epidemics of the same serotype were not affected. Metapopulation analyses revealed asynchronous dengue incidence among many of the islands and most notably larger islands lagged behind the smaller islands. The critical community size, which determines dengue persistence, was found to exceed even the largest island of Tahiti, suggesting that dengue can only exist by island-hopping. Incorporation of island connectedness through patterns of human migration into a mathematical model enabled a much better fit to the observed data than treating the population as a whole. The metapopulation model was able to capture to some extent the epidemic and low level transmission dynamics observed for the period of 2001-2008. Further analyses on differentiating incidence of disease and infection will likely prove informative for the metapopulation model of dengue epidemiology in French Polynesia. Dengue Épidémies Métapopulation Polynésie française Modélisation SEIR Transmission endémique Persistance Infection Migration Population Circulation insulaire Population critique Connections insulaires Modèle Logiciel R Études statistiques Identification des facteurs de risques Densité de la population Vecteur Aedes aegypti Géographie insulaire Milieu tropical Distance de vol du vecteur Immunité de la population Densité vectorielle Taux de récupération de l’hôte Mortalité du vecteur Cycle de transmission des virus Arbovirus Dynamique de la dengue Simulations Dynamique épidémique Dengue Epidemics Metapopulation French Polynesia Modeling SEIR Endemic transmission Persistence Infection Migration Population Insular circulation Critical population Insular connections Model Ordinary differential equation (ODE) R software Statistical study Risk factor identification Population density Vector Aedes aegypti Insular geography Tropical environment Vector flight distance Population immunity Vector density Host recovery rate Vector mortality Virus transmission cycle Arbovirus Dengue dynamic Simulations Epidemic dynamics 614.4

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