Spelling suggestions: "subject:"gravity models"" "subject:"ravity models""
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Demographics of dark-matter haloes in standard and non-standard cosmologiesMead, Alexander James January 2014 (has links)
This thesis explores topics related to the formation and development of the large-scale structure in the Universe, with the focus being to compute properties of the evolved non-linear density field in an approximate way. The first three chapters form an introduction: Chapter 1 contains the theoretical basis of modern cosmology, Chapter 2 discusses the role of N-body simulations in the study of structure formation and Chapter 3 considers the phenomenological halo model. In Chapter 4 a novel method of computing the matter power spectrum is developed. This method uses the halo model directly to make accurate predictions for the matter spectrum. This is achieved by fitting parameters of the model to spectra from accurate simulations. The final predictions are good to 5% up to k = 10 hMpc-1 across a range of cosmological models at z = 0, however accuracy degrades at higher redshift and at quasi-linear scales. Chapter 5 is dedicated to a new method of rescaling a halo catalogue that has previously been generated from a simulation of a specific cosmological model to a different model; a gross rescaling of the simulation box size and redshift label takes place, then individual halo positions are modified in accord with the large scale displacement field and their internal structure is altered. The final power spectrum of haloes can be matched at the 5% level up to k = 1 hMpc-1, as can the spectrum of particles within haloes reconstituted directly from the rescaled catalogues. Chapter 6 applies the methods of the previous two chapters to modified gravity models. This is done in as general a way possible but tests are restricted to f(R) type models, which have a scale-dependent linear growth rate as well as having 'chameleon screening' - by which modifications to gravity are screened within some haloes. Taking these effects into account leads to predictions of the matter spectrum at the 5% level and rescaled halo distributions that are accurate to 5% in both real and redshift space. For the spectrum of halo particles it is demonstrated that accurate results may be obtained by taking the enhanced gravity in some haloes into account.
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The social, geographical, and structural environments of minor noble residences in Angus, 1449-1542Buchanan, Katherine Ann January 2014 (has links)
Relying upon two common trends in modern castle studies, this exploratory study works to combine the landscape context and the spatial interaction of the main building to create an assessment of the spatial and social interaction between the main residential structure of a noble’s estate and the landscape features attached to surrounding property features. To explore questions about this kind of interaction this project has taken the sheriffdom of Angus, Scotland, between the year 1450 and 1542, to examine non-royal residences in an area that offered a diverse topography. This project aims to gain a better understanding of the surroundings of late fifteenth and early sixteenth century noble residences in Angus while contributing to the growing discussion of castles and their landscapes, and testing methods for addressing the spatial and social interaction between the main structure and the landscape features. Section A discusses the three source types used for compiling the dataset for this project within the context of three key categories needed to create a GIS dataset: location, object, and attributes. From the landscape features the mills and fishings were the most commonly mentioned and further details regarding the contents of the lordly landscapes were rare. Section B explores three methods of examining the relationships between the main residence and the landscape features: a modified RA and RRA values assessment, which measured levels of segregation within the noble residence site as a whole; a version of the gravity model, which helped identify the draw for interaction within the arrangement of the noble’s landscape; and network analysis questions, which facilitated a clear assessment of any connections between the use of structural terms and landscape features mentioned over both temporal and social contexts. This exploration of spatial and social interaction opens up a discussion about Scottish noble landscape creation and new methods for studying the relationship between the main structure and the wider complex of a noble residence.
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Bayesian Emulation for Sequential Modeling, Inference and Decision AnalysisIrie, Kaoru January 2016 (has links)
<p>The advances in three related areas of state-space modeling, sequential Bayesian learning, and decision analysis are addressed, with the statistical challenges of scalability and associated dynamic sparsity. The key theme that ties the three areas is Bayesian model emulation: solving challenging analysis/computational problems using creative model emulators. This idea defines theoretical and applied advances in non-linear, non-Gaussian state-space modeling, dynamic sparsity, decision analysis and statistical computation, across linked contexts of multivariate time series and dynamic networks studies. Examples and applications in financial time series and portfolio analysis, macroeconomics and internet studies from computational advertising demonstrate the utility of the core methodological innovations.</p><p>Chapter 1 summarizes the three areas/problems and the key idea of emulating in those areas. Chapter 2 discusses the sequential analysis of latent threshold models with use of emulating models that allows for analytical filtering to enhance the efficiency of posterior sampling. Chapter 3 examines the emulator model in decision analysis, or the synthetic model, that is equivalent to the loss function in the original minimization problem, and shows its performance in the context of sequential portfolio optimization. Chapter 4 describes the method for modeling the steaming data of counts observed on a large network that relies on emulating the whole, dependent network model by independent, conjugate sub-models customized to each set of flow. Chapter 5 reviews those advances and makes the concluding remarks.</p> / Dissertation
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Regional Geoid Determination Methods for the Era of Satellite Gravimetry : Numerical Investigations Using Synthetic Earth Gravity ModelsÅgren, Jonas January 2004 (has links)
It is the purpose of this thesis to investigate different regional geoid determination methods with respect to their feasibility for use with a future GOCE satellite-only Earth Gravity Model (EGM). This includes investigations of various techniques, which involve different approximations, as well as the expected accuracy. Many, but not all, of these tasks are tested by means of Synthetic Earth Gravity Models (SEGMs). The study is limited to remove-compute-restore methods using Helmert condensation and to Sjöberg's combined approach (method with additive corrections). First, a number of modifications of Stokes' formula are tested with respect to their compatibility with a GOCE EGM having negligible commission error. It is concluded that the least squares modification method should be preferred. Next, two new point-mass SEGMs are constructed in such a way that the resulting models have degree variances representative for the full and topographically reduced gravity fields, respectively. These SEGMs are then used to test different methods for modified Stokes' integration and downward continuation. It is concluded that the combined method requires dense observations, obtained from the given surface anomalies by interpolation using a reduction for all known density anomalies, most notably the topography. Examples of other conclusions are that the downward continuation method of Sjöberg (2003a) performs well numerically. To be able to test topographic corrections, another SEGM is constructed starting from the reduced point-mass model, to which the topography, bathymetry and isostatic compensation are added. This model, which is called the Nordic SEGM, is then applied to test one strict and one more approximate approach to Helmert's condensation. One conclusion here is that Helmert's 1st method with the condensation layer 21 km below sea level should be preferred to Helmert's 2nd condensation strategy. The thesis ends with a number of investigations of Sjöberg's combined approach to geoid determination, which include tests using the Nordic SEGM. It is concluded that the method works well in practice for a region like Scandinavia. It is finally shown how the combined strategy may preferably be used to estimate height anomalies directly.
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Factors Determining Czech Export on Different Aggregations with Focus on Electrical Engineering: Gravity Model ApproachTachovská, Tereza January 2015 (has links)
The thesis provides a quantitative analysis of the Czech export with a further focus on the electrical engineering and on the electric motors and generators. The tool used for the analysis is the gravity model of the international trade, and the estimation method employed is the PPML estimator. The novelty of the research lies in a one country export analysis, and in a comparison of the export functions on three different aggregations and for two states (the Czech Republic and France). The panel data analysis of the period between 1995 and 2013 reveals that the Czech Republic was more export-driven than France, an unanticipated fact about a dissimilarity of the total and the machinery and transport equipment export functions of the Czech Republic, and a statistically nonsignificant influence of the euro on the Czech export. The one year analyses of 1995 and 2013 reveal an increasing importance of the distance and the partner's GDP on both countries' exports, and a nonimportance of the partner's EU membership and of the geographic location in the CEE on the Czech export. JEL Classification C13, C23, F10, F12, F14 Keywords determining factors of export, gravity models of trade, Czech Republic, electrical engineering Author's e-mail t.tachovska@seznam.cz Supervisor's e-mail benacekv@fsv.cuni.cz
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Commerce et migrations internationales dans le bassin méditerranéen : cas de la France / International trade and migrations : the french caseMillogo, Doslalo Albert 26 November 2015 (has links)
Les échanges dans la zone euro-méditerranéenne ont été caractérisés par une intensification des flux commerciaux au début des années 2000. A cette même période, la question migratoire a été mise en avant en raison d’une explosion de l’immigration clandestine dans les pays du sud de l’Europe. L’objectif de cette thèse est d’étudier certaines conséquences économiques actuelles de ces migrations dans le cas de France. Dans cette optique nous abordons les questions liées à la relation commerce-migrations, à la politique migratoire, et à la localisation spatiale des immigrés en France. En utilisant des données récentes et en intégrant des paramètres jusque là peu utilisés, nous mettons en évidence des caractéristiques particulières de l’immigration en France. Nous apportons également des réponses quant a` la contribution des immigrés a` la production nationale, de même qu’a` l’accroissement du commerce bilatéral avec les pays d’origine. Les implications en termes de politiques économiques se situent d’une part dans la mise en œuvre d’une facilitation des opportunités d’aaires entre la France et les pays d’origine. Cela s’impose au regard de l’impact positif de l’immigration sur le commerce bilatéral. D’autre part, les difficultés relevées au niveau des politiques migratoires appellent a` une nécessaire harmonie de ces dernières, au plan européen, pour une gestion plus efficace. Cela passe encore par une implication des pays d’origine afin de faciliter l’immigration légale, et limiter les entrées clandestines. Enfin, la localisation spatiale des immigrés indique que leur concentration dans les pôles régionaux a un impact négatif sur leur contribution `a la production. La réponse peut se situer dans une analyse détaillée de la structure et du processus d’intégration des populations immigrés / The Euro-Mediterranean trade has grown up a lot in the early 2000. At the same time, the migration issue has been highlighted due to an explosion of illegal immigration in the Southern Europe countries. The aim of this thesis is to study some current economic impact this immigration in the French case. We address the issues of trade and migration relationship, migration policy, and spatial location of immigrants in France. Using recent data and shaping factors little used empirically, we highlight the specific characteristics of immigration in France. We also provide explanations to the contribution of immigrants to the domestic, as well as increasing bilateral trade with the country. In terms of economic policies, it lies firstly in the implementation of facilitating business opportunities between France and the countries of origin. This is necessary to take more profit from the positive impact of immigration on bilateral trade. On the other hand, problems identified in migration policies call for a necessary harmony of policies, at European level, for more effective management. Such objectives require the involvement of countries of origin to facilitate legal migration, and limit illegal entries. Finally, the spatial location of immigrants indicates that their concentration at regional level has a negative impact on their contribution to production. The solution may lie in a detailed analysis of the structure, and the integration of immigrant populations’ process.
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Um método de utilização de dados de pesquisa embarque/desembarque na calibração de modelos do tipo gravitacional. / A method of use of data of research embarque/desembarque in the calibration of models of distribution of the gravitational type.Ferreira, Eric Amaral 26 August 1999 (has links)
O objetivo deste trabalho é testar um modelo de distribuição de viagens do tipo gravitacional para a calibração de matrizes origem/destino (O/D) em linhas de transporte público por ônibus a partir de dados de pesquisa de contagem de embarque/desembarque (E/D). A metodologia proposta possibilita a obtenção de matrizes O/D de forma rápida e barata, pois combina um método de pesquisa simples e de baixo custo (pesquisa de contagem de usuários) com um modelo de distribuição de viagens. O modelo associa a cada ponto de origem um valor de parâmetro. A utilização de um valor de parâmetro associado a cada origem busca neste caso reproduzir o custo médio de distribuição de viagens de uma origem em relação aos seus diferentes destinos. O modelo incorpora ainda como restrição a probabilidade de um passageiro desembarcar no ponto seguinte ao seu ponto de embarque. Os dados de pesquisa foram cedidos pelo Departamento de Transportes da Universidade Federal do Paraná. O teste de desempenho do modelo foi realizado através da comparação entre matrizes O/D observadas e simuladas para as cidades de Curitiba e Paranaguá. / The aim of this work is to test a gravity model for trip distribution designed to estimate bus routes origin/destination (O/D) matrices based on boarding and alighting data. The proposed method combines a simple and low-cost survey method (on/off passenger counting) with a mathematical model for trip distribution, which enables the estimation of an O/D matrix in a fast and inexpensive manner. The model assumption that each origin point is associated to a parameter value tries to reproduce the average costs of the actual trip distribution from each origin to every single destination along the bus route. The model brings also as a built-in restriction an expected (usually low) probability of passengers getting off the vehicle in the bus stop following the boarding point. The survey data used in this work have been collected by researchers of the Transportation Department at the Federal University of Paraná. The model performance has been tested by the comparison of observed and simulated O/D matrices in the cities of Curitiba and Paranaguá. The results found in most of the simulations showed that for an estimated trip frequencies did not statistically differ from the actual values for a required level of significance.
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Essays on Foreign Direct Investment, Economic Vulnerability and Uncertainty / Essais sur les investissements directs étrangers, la vulnérabilité économique et l'incertitudeRazafindravaosolonirina, Romain 10 December 2018 (has links)
L'objet de la thèse est d'étudier le lien entre les différents volets de la vulnérabilité économique, définie selon les termes de Guillaumont, et le niveau d'Investissement Direct Etranger (IDE). Plus précisément, l'objectif des papiers présentés dans la thèse s'articule selon la logique suivante. Tout d'abord, il s'agit de déceler dans le cadre du premier papier les différentes formes de vulnérabilité qui affectent le niveau d'IDE. Dans un second temps, notre analyse se focalise sur le lien avec les traités d'investissements et étudie comment ces traités modifient la relation IDE - Vulnérabilité. Dans un troisième temps, notre focus concerne l'étroite relation qui existe entre l'aide au développement et les IDE, afin de préciser dans quelles mesures l'Aide et les IDE sont intimement liés. Finalement, nous abordons un spectre plus large en étudiant non plus seulement l'investissement mais aussi l'économie en général, avec un travail sur l'influence de l'incertitude de la politique économique sur les variables macroéconomiques. / The aim of the thesis is to analyze to what extent Economic Vulnerability, defined by Guillaumont, affects Foreign Direct Investment (FDI). More precisely, various papers in the thesis follow the current logic. First, It is important to unveil the relationship between various components of economic vulnerability affecting the level of FDI. Second, our analysis focus on how investment treaties modify the link FDI-Vulnerability. Third, focus on the close link between FDI and Official Development Assistance. Finally, We assess a larger spectrum by taking into account how uncertainty resulting from economic policy could affect macroeconomic aggregates.
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Um método de utilização de dados de pesquisa embarque/desembarque na calibração de modelos do tipo gravitacional. / A method of use of data of research embarque/desembarque in the calibration of models of distribution of the gravitational type.Eric Amaral Ferreira 26 August 1999 (has links)
O objetivo deste trabalho é testar um modelo de distribuição de viagens do tipo gravitacional para a calibração de matrizes origem/destino (O/D) em linhas de transporte público por ônibus a partir de dados de pesquisa de contagem de embarque/desembarque (E/D). A metodologia proposta possibilita a obtenção de matrizes O/D de forma rápida e barata, pois combina um método de pesquisa simples e de baixo custo (pesquisa de contagem de usuários) com um modelo de distribuição de viagens. O modelo associa a cada ponto de origem um valor de parâmetro. A utilização de um valor de parâmetro associado a cada origem busca neste caso reproduzir o custo médio de distribuição de viagens de uma origem em relação aos seus diferentes destinos. O modelo incorpora ainda como restrição a probabilidade de um passageiro desembarcar no ponto seguinte ao seu ponto de embarque. Os dados de pesquisa foram cedidos pelo Departamento de Transportes da Universidade Federal do Paraná. O teste de desempenho do modelo foi realizado através da comparação entre matrizes O/D observadas e simuladas para as cidades de Curitiba e Paranaguá. / The aim of this work is to test a gravity model for trip distribution designed to estimate bus routes origin/destination (O/D) matrices based on boarding and alighting data. The proposed method combines a simple and low-cost survey method (on/off passenger counting) with a mathematical model for trip distribution, which enables the estimation of an O/D matrix in a fast and inexpensive manner. The model assumption that each origin point is associated to a parameter value tries to reproduce the average costs of the actual trip distribution from each origin to every single destination along the bus route. The model brings also as a built-in restriction an expected (usually low) probability of passengers getting off the vehicle in the bus stop following the boarding point. The survey data used in this work have been collected by researchers of the Transportation Department at the Federal University of Paraná. The model performance has been tested by the comparison of observed and simulated O/D matrices in the cities of Curitiba and Paranaguá. The results found in most of the simulations showed that for an estimated trip frequencies did not statistically differ from the actual values for a required level of significance.
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Regional Geoid Determination Methods for the Era of Satellite Gravimetry : Numerical Investigations Using Synthetic Earth Gravity ModelsÅgren, Jonas January 2004 (has links)
<p>It is the purpose of this thesis to investigate different regional geoid determination methods with respect to their feasibility for use with a future GOCE satellite-only Earth Gravity Model (EGM). This includes investigations of various techniques, which involve different approximations, as well as the expected accuracy. Many, but not all, of these tasks are tested by means of Synthetic Earth Gravity Models (SEGMs). The study is limited to remove-compute-restore methods using Helmert condensation and to Sjöberg's combined approach (method with additive corrections).</p><p>First, a number of modifications of Stokes' formula are tested with respect to their compatibility with a GOCE EGM having negligible commission error. It is concluded that the least squares modification method should be preferred.</p><p>Next, two new point-mass SEGMs are constructed in such a way that the resulting models have degree variances representative for the full and topographically reduced gravity fields, respectively. These SEGMs are then used to test different methods for modified Stokes' integration and downward continuation. It is concluded that the combined method requires dense observations, obtained from the given surface anomalies by interpolation using a reduction for all known density anomalies, most notably the topography. Examples of other conclusions are that the downward continuation method of Sjöberg (2003a) performs well numerically.</p><p>To be able to test topographic corrections, another SEGM is constructed starting from the reduced point-mass model, to which the topography, bathymetry and isostatic compensation are added. This model, which is called the Nordic SEGM, is then applied to test one strict and one more approximate approach to Helmert's condensation. One conclusion here is that Helmert's 1st method with the condensation layer 21 km below sea level should be preferred to Helmert's 2nd condensation strategy.</p><p>The thesis ends with a number of investigations of Sjöberg's combined approach to geoid determination, which include tests using the Nordic SEGM. It is concluded that the method works well in practice for a region like Scandinavia. It is finally shown how the combined strategy may preferably be used to estimate height anomalies directly.</p>
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