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Sellner, Richard, Manfred M. Fischer y Matthias Koch. "A Spatial Autoregressive Poisson Gravity Model". Wiley-Blackwell, 2013. http://dx.doi.org/10.1111/gean.12007.
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In this article, a Poisson gravity model is introduced that incorporates spatial dependence
of the explained variable without relying on restrictive distributional assumptions of the
underlying data-generating process. The model comprises a spatially filtered component
including the origin-, destination-, and origin-destination-specific variables and a spatial
residual variable that captures origin- and destination-based spatial autocorrelation. We
derive a two-stage nonlinear least-squares (NLS) estimator (2NLS) that is heteroscedasticity-
robust and, thus, controls for the problem of over- or underdispersion that often
is present in the empirical analysis of discrete data or, in the case of overdispersion, if
spatial autocorrelation is present. This estimator can be shown to have desirable properties
for different distributional assumptions, like the observed flows or (spatially) filtered component
being either Poisson or negative binomial. In our spatial autoregressive (SAR)
model specification, the resulting parameter estimates can be interpreted as the implied
total impact effects defined as the sum of direct and indirect spatial feedback effects. Monte
Carlo results indicate marginal finite sample biases in the mean and standard deviation of
the parameter estimates and convergence to the true parameter values as the sample size
increases. In addition, this article illustrates the model by analyzing patent citation flows
data across European regions. (authors' abstract)
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Wu, Wei Trindade Vitor. "Three essays on trade gravity model". Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6156.
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Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 17, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Vitor Trindade. Vita. Includes bibliographical references.
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Kalasin, Thaveechai. "Dynamic macroelement model for gravity retaining walls". Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404085.
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Karl, Joanna Robin. "Gravity Sedimentation: A One-Dimensional Numerical Model". PDXScholar, 1993. https://pdxscholar.library.pdx.edu/open_access_etds/4594.
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A large fraction of the current cost of wastewater treatment is from the treatment and disposal of wastewater sludge. Improved design, energy efficiency, and performance of dewatering facilities could significantly decrease transport and disposal costs. Dewatering facilities are designed based on field experience, trial and error, pilot plant testing, and/or full scale testing. Design is generally time-consuming and expensive. A full-scale test typically consists_ of side-by-side operation of 4 to 5 full-scale dewatering units for several weeks to more than 6 months. Theoretical modeling of the physics of dewatering units such as the belt filter press, based on laboratory determined sludge properties, would better predict dewatering performance. This research developed a numerical computer model of the physics of gravity sedimentation. The model simulated the gravity sedimentation portion of the belt filter press. The model was developed from a physically-based numerical computer model of cake filtration by Wells (1990). As opposed to the cake filtration model, the inertial and gravity terms were retained in the gravity sedimentation model. Although in the cake filtration model, the inertial terms were shown to be negligible, according to Dixon, Souter, and Buchanan (1985), inertial effects in gravity sedimentation cannot generally be ignored. The region where inertia is important is the narrow interface between suspension and sediment. In the cake filtration model the gravity term was negligible due to the relatively large magnitude of the applied pressure; but in the gravity sedimentation model, since there was no applied pressure, it was necessary to consider the effect of gravity. _ Two final governing equations were developed - solid continuity and total momentum with continuity ("momentum"). ·The finite difference equations used a "space-staggered" mesh. The solid continuity equation was solved using an explicit formulation, with a forward difference in time and central difference in space. The "momentum" equation used a fully implicit formulation with a forward difference in time. The modeler could choose either a central difference or forward difference in space. Non-linear terms were linearized. Boundary Conditions and constitutive relationships were determined. Numerical errors in the numerical model were analyzed. The model was calibrated to known data and verified with additional data. The model was extremely sensitive to the constitutive relationships used, but relatively unaffected by the At or the use of central difference or forward difference for the spatial derivative term in the "momentum" equation. Correlations of the calibrated model to data with a low initial concentration show that the constitutive parameters approximate the data, but not very well. Model runs with low initial concentration required the addition of artificial viscosity to remain stable. The gravity term was always significant, whereas the inertial terms were many orders of magnitude less than gravity. However, the lower the initial concentration, the larger the inertial terms. In addition to the belt filter press, the model can also be applied to cake filtration and design of gravity sedimentation tanks as well.
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Ahmed, Dhafar Ibrahim. "Experimental and numerical study of model gravity currents in coastal environment : bottom gravity currents". Thesis, Brest, 2017. http://www.theses.fr/2017BRES0060/document.
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Le but de ce travail de recherche est de contribuer à une meilleure compréhension de la dynamique de propagation et de la miscibilité de jets gravitaires au-dessous d’un liquide ambiant. Des expériences ont été réalisées en laboratoire à l’aide d’une plateforme expérimentale constituée d’un bassin parallélépipédique contenant de l’eau douce et d’un canal d’injection de section rectangulaire de jets gravitaires de concentration constante initiale fixée. Les calculs mathématiques et numériques sont basés sur les modèles RANS (Reynolds-Averaged Navier Stokes equations), k-ε (K-epsilon) et DCE (Diffusion-Convective Equation) de la fraction volumique de l’eau salée pour décrire la propagation et le mélange du jet gravitaire. L’évolution du front du jet obtenue expérimentalement est utilisée pour valider le modèle numérique. Par ailleurs, la comparaison des résultats obtenus sur l’écoulement moyen (z⁄z0.5 =U/Umax) avec ceux des études 2D expérimentales et numériques antérieures ont montré des similarités. La simulation numérique des champs hydrodynamiques montre que la vitesse maximale est atteinte à la position 0.18 z0.5, où z0.5 est la hauteur d’eau pour laquelle la vitesse moyenne u est égale à la moitié de la vitesse maximale UmaxThe aim of this investigation is to contribute to a better understanding of the propagation dynamics and the mixing process of dense gravity currents. The Laboratory experiments proceeded with a fixed initial gravity current concentration in one experimental set-up. The gravity currents are injected using a rectangular injection channel into a rectangular basin containing the ambient lighter liquid. The injection studied is said in unsteady state volume, as the Reynolds number lies in the range 1111 - 3889. The experiments provided the evolution of the boundary interface of the jet, and it is used to validate the numerical model. The numerical model depends on the Reynolds-Averaged Navier Stokes equations (RANS). The k-ε (K-epsilon) and the Diffusion-Convective Equation (DCE) of the saline water volume fraction were used to model the mixing and the propagation of the gravity current jet. On the other hand, comparison of the mean flow (z⁄z0.5 =U/Umax) with previous two-dimensional numerical simulations and experimental measurements have shown similarities. The numerical simulations of the hydrodynamic fields indicate that the velocity maximum at 0.18 z0.5, where z0.5 is the height at which the mean velocity u is the half of the maximum velocity Umax
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Buchanan, Katherine Ann. "The social, geographical, and structural environments of minor noble residences in Angus, 1449-1542". Thesis, University of Stirling, 2014. http://hdl.handle.net/1893/21135.
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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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Chattopadhyay, Mohar. "Gravity wave parameterization in the general circulation model". Thesis, University of Canterbury. Physics and Astronomy, 2003. http://hdl.handle.net/10092/6065.
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Although there is a rich literature on modelling the effects of broad spectrum gravity waves (GW) in General circulation Models (GCM), the effect of a coupled interactive broad spectrum and monochromatic GW has not been studied in detail. Such a study is of paramount importance as it could conclusively demonstrate that the coupled interactive broad spectrum and monochromatic GW can be parameterized in a GCM and its effects on atmospheric circulations can be studied.
The main objective of this thesis is to investigate how the climate simulated by the Unified Model (UM), a state-of-the-art GCM, responds to more physically realistic gravity wave parameterizations, beginning with the addition of a spectral gravity wave scheme, and then progressing to a scheme which couples both orographic and spectral gravity waves.
Behaviour of the schemes are analyzed using a set of four idealized experiments in a single column test-bed based on the architecture of the UM. Results from these experiments are discussed before implementing the schemes in the UM. These findings provide the necessary backdrop around which more complex interactions modelled by the UM are discussed.
The UM is run for six years with the two GW schemes. Monthly means of a range of diagnostic fields results are compared qualitatively with the U.K. Met. Office global assimilated data. Both schemes simulate the overall structure of the atmospheric circulation. The simulations based on the two GW schemes are also compared against each other to observe any potential effect on the climatology of the UM due to their different underlying assumptions. The results show sensitivity of the model in the dynamics of middle atmosphere. Some degree of variability is also exhibited in tropospheric circulation. A major conclusion that emerges from the extension of the spectral gravity wave scheme to the coupled interactive scheme is that the latter is equivalent to a change in the global mean gravity wave strength.
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Hall, David. "A mathematical model for rapid gravity filter backwashing". Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272201.
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Raizner, Carina. "GOCE data and gravity field model filter comparison". Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2007. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-34036.
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Driver, David. "BREXIT: The Swedish Perspective : A Gravity Model Approach". Thesis, KTH, Skolan för industriell teknik och management (ITM), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-264219.
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The subject of trade negotiations has been a highly publicised debate in the context of Brexit. The term ‘no deal’ has come to represent the United Kingdom leaving with no specific or comprehensive preferential trade agreement, whereas the potentially most far-reaching deal would resemble something along the lines of an EFTA membership. By using bilateral trade data between 2005 and 2017 for Sweden and their top 60 trading partners, an elaborated gravity model for trade suggests a significant long-run decline in the magnitude of trade between Sweden and the United Kingdom. For trade in goods, the results suggest an impact between 21.4%-25.7% in reduced bilateral trade between the UK and Sweden, if the UK leave under WTO terms. The findings also indicate that the impact on trade in services, for which the United Kingdom is Sweden’s second largest trading partner, will be significantly more pronounced between 45.7%-70.0% under a ‘no deal’ scenario. Whilst the model is such that no robust conclusions can be made about the EFTA-type deal for goods, they suggest that terms similar to EFTA would have a significant mitigating effect on any reduction in trade in services. However, a less comprehensive free trade agreement would do little to replace lost service trade when compared to the ‘no deal’ impact.
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Rodriguez, Ameal Carlos <1997>. "A Bayesian Gravity Model for Italian domestic tourism". Master's Degree Thesis, Università Ca' Foscari Venezia, 2021. http://hdl.handle.net/10579/20003.
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The gravity model has been used extensively to model trade flows among countries with proven succcess, and when applied to tourism flows it have provided even better results. In this paper I propose a Bayesian approach based on a MCMC algorithm to estimate the coefficients of the model. Then I apply this method to a Panel Data dataframe with the monthly number of tourists travelling from every Italian region to every Italian province between 2008 and 2018. Then I use it to predict the flows for 2019 and I compare the results.
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Lilienthal, Friederike, P. Sácha y Christoph Jacobi. "Gravity wave effects on a modeled mean circulation". Universität Leipzig, 2015. https://ul.qucosa.de/id/qucosa%3A16646.
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Using a global circulation model of the middle atmosphere we analyze the influence of different tropospheric gravity wave amplitude distributions in the gravity wave parameterization on the mean circulation. Thereby we compare the standard configuration, which includes a simple zonal mean weighting of gravity wave amplitudes with a more realistic zonal mean weighting obtained from measurements using GPS radio occultations and a GW distribution in both latitude and longitude. The results show a stronger polar vortex and a descent of the meridional wind jet in the mesopause. Furthermore, two-dimensional weightings from the measurements are considered in order to analyze nonzonal effects resulting especially in stationary planetary waves. In this case we obtain a stronger stationary planetary wave and find enhanced equatorward wave motions in the lower stratosphere. These results give reason for further investigations about the impact of gravity waves on the Brewer-Dobson circulation.Mit Hilfe eines globalen Zirkulationsmodells für die mittlere Atmosphäre untersuchen wir den Einfluss verschiedener in der Troposphäre festgelegter Verteilungen der Schwerewellenamplitude in der Schwerewellenparametrisierung des Modells auf die mittlere Zirkulation. Dazu vergleichen wir den Standardfall zonal gemittelter künstlicher Wichtungen der Schwerewellenamplituden mit sowohl zonal gemittelten als auch längen-breitenabhängigen Wichtungen aus GPS-Radiookkultationensmessungen. Die Ergebnisse zeigen einen stärkeren Polarwirbel und ein Absinken des meridionalen Windjets in der Mesopause. Zusätzlich wurden zweidimensionale Wichtungen aus den GPS-Radiookkultationen ausgwertet, um den Einfluss planetarer Wellen zu analysieren. In diesem Fall lässt sich eine äquatorwärts gerichtete Verstärkung der Wellenbewegung in der unteren Stratosphäre feststellen. Diese Ergebnisse geben Anlass für weitere Nachforschungen über den Einfluss von Schwerewellen auf die Brewer-Dobson-Zirkulation.
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Da, Silva Caroline Dos Santos. "Cosmic strings and scalar tensor gravity". Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4577/.
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This thesis is concerned with the study of cosmic strings. We studied the values for the Higgs mass and string coupling for which the gravitational effect of an infinite cosmic string in the context of the Einstein theory is not only locally but also globally weak. We conclude this happens for strings formed at scales less or equal to the Planck one with Higgs mass being less or equal to the boson vectorial mass. Then we examined the metric of an isolated self-gravitating abelian-Higgs vortex in dilatonic gravity for arbitrary coupling of the vortex fields to the dilaton. We looked for solutions in both massless and massive dilaton gravity. We compared our results to existing metrics for strings in Einstein and .Jordan-Brans-Dicke theories. We explored the generalisation of Bogomolnyi arguments for our vortices and commented on the effects on test particles. We then included the presence of an axion field and examined the metric of an isolated self-gravitating axionic-dilatonic string. Finally we studied dilatonic strings through black hole solutions in string theory. We concluded that the horizon of non-extreme charged black holes supports the long-range fields of the Nielsen-Olesen string that can be considered as black hole hair and whose gravitational effect is in general the production of a conical deficit into the metric of the black hole background. We also concluded that the effect of the dilaton on the horizon of these black holes is to generate an additional charge.
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Pearl, Jason. "Quadrature-Based Gravity Models for the Homogeneous Polyhedron". ScholarWorks @ UVM, 2019. https://scholarworks.uvm.edu/graddis/1166.
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A number of missions to comets and asteroids have been undertaken by major space organizations driving a need to accurately characterize their gravitational fields. This is complicated however by their irregular shapes. To accurately and safely navigate spacecraft in these environments, a simple point-mass gravity model is insufficient and instead higher-fidelity models are required. Several such models exist for this purpose but all posess drawbacks. Moreover, there are some applications for which the currently available models are not particular well suited.
In this dissertation, numerical quadrature and curvilinear meshing techniques are applied to the small body gravity problem. The goal of this work is to to create a gravitational model suitable for integating large numbers of low altitude trajectories and rapidly characterizing the near-surface potential field. In total three new models are developed. The first applies two-dimensional quadrature formulas to calculate the gravitational field of an arbitrary triangular surface mesh. The second extends this result to curvilinear surface meshes that more accurately approximate the surface topology. The third applies three-dimensional quadrature to curvilinear tetrahedral meshes to generate accurate distributions of point-masses. The accuracy of the new models is fully characterized and simple relations are presented for predicting the error of integrated trajectories. The efficiency of the models is then compared to other high-fidelity models currently in use. The new models perform well between the body's circumsphere and a thin layer that surrounds the surface.
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Bonacorsi, Laura. "Essays in International Trade". Thesis, Boston College, 2016. http://hdl.handle.net/2345/bc-ir:107278.
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Thesis advisor: James E. AndersonThe gravity model proved to to be one of the most successful framework for analyzing international trade flows, being referred to as the “workhorse” in the international trade literature (Head and Mayer (2014)). Microfoundations to this model has been provided in Anderson (1979) and it has often been employed to estimate the effects of a variety of trade policies (see Cipollina and Salvatici (2010) for a meta-analysis on reciprocal trade agreements, Rose (2000) for the effects of currency unions). The two chapters of this dissertation, which are independent empirical pieces, both make use of gravity equations for the estimation of trade flows, although with different purposes. The first chapter focuses on the specification of the gravity equation. In the second chapter, instead, gravity equations are employed for assessing the relationship between trade and growth: in fact, their estimation represents the first step for the creation of an instrumental variable for export flows. In the first chapter, a solo-authored work titled Scale Economies in European Trade, I show that European data support the existence of economies of scale in trade flows. The impact of trade costs on trade flows, in fact, is assumed to be constant by almost all empirical studies employing the gravity framework. Anderson et al. (2016) are the first to depart from this assumption, allowing trade costs to vary as a function of trade volumes. Their model nests the more traditional one and hence can be used to test for the existence of these scale economies, which are shown to be in place for trade between US and Canada. For my analysis I construct a comprehensive dataset for European trade in manufacturing over a long time span (from 1980 to 2013), on which I employ the same methodology. My results show that scale economies in trade costs are indeed a strong empirical fact outside of the American continent, and this holds for all the 26 manufacturing sectors considered, with an estimated average of 0.64% decrease in trade costs given by a 10% increase in trade volume. The focus on Europe allows me to test whether the EU expansion affected these economies of scale. While this is not true on average, it seems to be the case for some industries: trade with a EU partner entails scale elasticities 50% lower than trade with a non-EU member for 11 sectors out of the 26 considered. I also investigate whether scale elasticities can be rationalized by the existence of informational asymmetries. Using detailed product-level data, I do not find evidence that the degree of product homogeneity can account for the observed cross-sectoral variation. The scale coefficients are instead linked to country-specific institutional variables, such as the level of corruption: exporting to the country whose level of corruption is the lowest in the sample entails half the scale elasticity than exporting to the most corrupted one. In other words, corruption depresses trade to an higher extent on longer distances. In the second chapter, joint with Carlo Altomonte and Italo Colantone and titled Trade and Growth in the Age of Global Value Chains, we revisit the relationship between trade and income, taking into account the recent surge of global value chains (GVCs). First, we develop a new geography-based, time-varying instrument for export, exploiting the sharp increase (almost tripling) in the maximum size of container ships between 1995 and 2007. This global shock has an asymmetric impact on bilateral trade flows across countries, affecting disproportionately more countries endowed with a larger number of deep-water ports, which are needed to accommodate the new, much larger ships. We exploit this heterogeneity for identification, building up the instrument for export in a gravity framework. Our result show that export has a positive effect on GDP per capita, with a 0.6 elasticity. Evidence at the country-level shows that this effect works through capital accumulation. Exploiting the decomposition methodology by Wang et al. (2013), we show that differences in the value added composition of exports matter for trade-growth nexus. We find evidence in favor of an income premium for countries that upgrade their positioning in GVCs, whereas the degree of participation to GVCs does not seem to play a role. Consistent with this finding, we show that countries whose average level of upstreamness (a’ la Antras and Chor (2013)) increases the most over time exhibit a higher trade elasticity of income. Both papers indirectly deal with the effect of geographical distance on international trade flows. One of the strongest regularities in economics is certainly the negative role played on trade flows by the distance between origin and destination. Disdier and Head (2004), comparing 1,467 different studies, compute an average distance elasticity of trade of about -0.9. Hummels (2007) shows that the distance elasticity of trade does not seem to diminish over time, as it would do should distance be capturing only transportation costs, thanks to the technological developments witnessed in the transportation sector. Distance seems then to refer to trade costs in general, including institutional, policy and regulatory barriers that, also for historical reasons, often increase the further away countries are located. In the first paper, I show that the impact of distance on trade flows is not constant but varies with trade volumes. This corresponds with having a component of the composite friction described before, hidden in the distance term, being fixed and is consistent with micro-evidence on the export behavior obtained from firm-level data (Roberts and Tybout (1997)). It seems natural, then, to test whether some characteristics, either at the product-level or at the country-level, have a prominent role in explaining the non-linear effect that distance has on trade. My results find in level of corruption of the destination country an important determinant. In the second paper, we test whether the distance elasticity of trade varies as a function of the number of deep water ports on both the importer’s and the exporter’s shores, capturing the extent to which countries can trade via container vessels. The data support this claim for all the manufacturing sectors considered, showing that geographical distance, even though non-exclusively, captures the incidence of transportation costs on export flows
Thesis (PhD) — Boston College, 2016
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Economics
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Nicotra, Alessandro. "Analytical map between EPRL spin foam models in loop quantum gravity". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23179/.
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Loop Quantum Gravity (LQG) is one of the theoretical frameworks attempting to build a quantum theory of gravitation.
Spin Foam theory provides a regularized, background-independent, and Lorentz covariant path integral for the transition amplitudes between LQG kinematical states.
The state of the art of the theory is the EPRL model, formulated with the Euclidean and the Lorentzian signatures. They differ by their gauge group structures, which are respectively SO(4,R) and SO(1,3).
The first is a compact group: it has finite-dimensional unitary irreducible representations, and the integral on the group manifold is simple. The second is non-compact. Therefore, the computations in the Lorentzian EPRL model are more complicated than in the Euclidean one. The Euclidean model is the preferred choice for physical calculations. Given their similarities it has been so far assumed, as a strong hypothesis, that the results obtained in the Euclidean model also hold for the Lorentzian one.
This work's primary goal is to present the main characteristics of the models and a set of prescriptions to map the structure and, at least in a qualitative way, the results obtained in the Euclidean model into the Lorentzian one.
Chapter 1 provides an overview of the basic ingredients of the discussion: General Relativity, BF theories and LQG transition amplitudes between quantum states of spacetime.
Chapters 2 and 3 are respectively a description of the Euclidean and Lorentzian EPRL models, from the representation theory of their gauge groups to the construction of the EPRL transition amplitudes.
Chapter 4 portrays the current state of research in EPRL Spin Foam theory, with a qualitative description of the main results achieved in both models.
The main topic of the thesis and my original work is contained in Chapter 5, in which, from a set of prescriptions, the group structure of the Euclidean model is mapped into the Lorentzian one, allowing a comparison between the transition amplitudes.
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Radzevičiūtė, Eglė. "Assessment of foreign direct investment by gravity model approach". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130129_192400-56972.
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In the thesis foreign direct investment in the Baltic countries using gravity model have been analysed. The first part of the thesis consists of foreign direct investment definition, the positive and negative influencing factors of foreign direct investment evaluation criteria analysis of the scientific literature and the authors different approaches to them. It is also made a critical evaluation of literature, authors usually distinguishing factors mentioned in different sources that affect foreign direct investment. Also in the first part of the paper theoretically gravity model and its application in practice of direct foreign investment assessment has been described. In the practical, analytical part the analysis of the chosen 7 most popular parameters from has been performed using the graphical methods. Also analyzed the market size, average wages, education levels, tax burden, economic openness index , GDP per capita and the average disposable income per household member on foreign direct investment in the Baltic countries, using multiple regression and correlation analysis and using a gravity model. The thesis ends with conclusions and recommendations. Structure: introduction, theoretical part, practical part, conclusions and suggestions, references. Thesis consist of: 77 p. text without appendixes, 19 pictures, 34 tables, 55 bibliographical entries.Baigiamajame magistro darbe nagrinėjamos tiesioginės užsienio investicijos Baltijos šalyse taikant gravitacinį modelį. Pirmoje darbo dalyje pateikiama tiesioginių užsienio investicijų sąvokos, teigiamą ir neigiamą įtaką darančių veiksnių, tiesioginių užsienio investicijų vertinimo kriterijų analizė mokslinėje literatūroje bei skirtingas autorių požiūris į juos. Taip pat atliktas kritinis literatūros vertinimas, išskiriant dažniausiai autorių minimus veiksnius skirtinguose šaltiniuose, kurie daro įtaką tiesioginėms užsienio investicijoms. Taip pat pirmoje darbo dalyje teoriniu požiūriu išanalizuotas gravitacinis modelis bei jo taikymas praktikoje tiesioginėse užsienio investicijoms įvertinti. Praktinėje, analitinėje darbo dalyje pagal pasirinktus 7 parametrus iš dažniausiai pasitaikančių literatūros apžvalgose išanalizuotas Baltijos šalių tiesioginių užsienio investicijų atvejis naudojant grafinę analizę. Taip pat nagrinėjamas rinkos dydžio, vidutinio darbo užmokesčio, išsilavinimo lygio, mokesčių naštos, ekonominio atvirumo indekso BVP vienam gyventojui bei vidutinių disponuojamų pajamų vienam namų ūkio nariui įtaka tiesioginėms užsienio investicijoms Baltijos šalyse naudojant daugianarę koreliacinę regresinę analizę bei pritaikant gravitacinį modelį. Darbo pabaigoje pateikiamos išvados ir siūlymai. Darbą sudaro 2 dalys: įvadas, teorinė dalis, praktinė dalis išvados ir siūlymai, literatūros sąrašas. Darbo apimtis – 77 p. teksto be priedų, 19 iliustr., 34 lent., 55... [toliau žr. visą tekstą]
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Tang, Hon Cheong 1980. "Gravity-based trust model for web-based social networks". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112366.
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Web-based social networks have become one of the most popular applications on the Internet in recent years. However, most of the social networks rely on some simplistic trust models to manage trust information of the users, which can cause problems ranging from unsatisfied user experience to exposure to malicious users. This thesis proposes a gravity-based trust model to enhance the aggregation of personal trust information into a subjective reputation system. This new model maps all users on the social network into n-dimensional Euclidean spaces based on their direct trust information, and creates a trust social neighborhood for each user. The reputation of a target user is determined by applying gravity model to the information from both target's and observer's trust social neighborhood. A prototype of this trust model is implemented in order to evaluate the effects of varying different parameters of the gravity-based trust model.
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LeSage, James P. y Manfred M. Fischer. "Conventional versus network dependence panel data gravity model specifications". WU Vienna University of Economics and Business, 2019. http://epub.wu.ac.at/6828/1/2019%2D2%2D11_v12_panel_gravity_model.pdf.
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Past focus in the panel gravity literature has been on multidimensional fixed effects specifications
in an effort to accommodate heterogeneity. After introducing conventional multidimensional fixed effects, we find evidence of cross-sectional dependence in
flows.
We propose a simultaneous dependence gravity model that allows for network dependence
in flows, along with computationally efficient Markov Chain Monte Carlo estimation methods
that produce a Monte Carlo integration estimate of log-marginal likelihood useful for model
comparison. Application of the model to a panel of trade
flows points to network spillover
effects, suggesting the presence of network dependence and biased estimates from conventional
trade flow specifications. The most important sources of network dependence were found to
be membership in trade organizations, historical colonial ties, common currency and spatial
proximity of countries.Series: Working Papers in Regional Science
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Skopovi, Ivan 1976. "A model for nonlinear gravity waves in stratified flows". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/91372.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, September 2002."August 2002."
Includes bibliographical references (leaves 77-78).
by Ivan Skopovi.
S.M.
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Romero, Jose Renato Sanchez. "Topics in gauge/gravity dualities". Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-13012015-121829/.
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This thesis consists in a self-contained study of gauge/gravity dualities in the line of the Klebanov-Witten model. Here we explore first the known Maldacena duality that relates N=4 SYM theory in four dimensions to type IIB supergravity on AdS_5×S^5 in reasonable detail, after some necessary preliminaries on supersymmetric gauge theories, where we display in detail the supersymmetry algebra and representations for N 1 supersymmetry. There we also construct the so-called superfields that will be helpful to write invariant lagrangians for gauge theoriesmreadily, and then useful to construct the gauge theory side of the Klebanov-Witten model. In the original AdS/CFT correspondence and its phenomenologically interesting extensions, Dp-branes as solutions of supergravity and nonperturbative objects in string theory where gauge theory lives are crucial. So, to preserve the self-contained nature of this work, we include a brief review of superstring theory addressed to understand the need to include this higher-dimensional objects by T-duality and, at low-energy limit of the string theory, as solutions of the Einstein equations. The first climax of this work occurs when we use all we learned to establish the Maldacena conjecture, N=4 SU(Nc) SYM theory we study in the supersymmetry chapter, living on the four-dimensional worldvolume of a stack of Nc D3-branes in a flat-space, corresponds exactly to type IIB supergravity on AdS_5×S^5 .In order to prove it, we match symmetries and operators with states in both sides. But actually this corresponds to the weak form of the correspondence, because it is not possible to handle neither string theory or gauge theory at strong coupling. The focus and main motive to have to learn the first hundred of pages here will be to extend the dual gauge theory we studied in AdS/CFT towards more realistic gauge theories as duals of some supergravity theory. The Klebanov-Witten model, consists in replacing the five-sphere in the gravity background of type IIB for a more interesting Einstein manifold X5 , a coset space called T^1,1 .The resulting dual gauge theory is expected to be less supersymmetric, and it is indeed N = 1 superconformal field theory with matter content in the bifundamental representation of the gauge group SU(N)×SU(N), and a quartic superpotential that exhibits SU(2)×SU(2)×U(1) global symmetry, which is precisely the symmetry of the coset space in the gravity side. This is not the end of the story, the Klebanov-Witten model extended the Maldacena correspondence and found as a dual gauge theory a less supersymmetric but still conformal theory. Breaking of the conformal theory, proposed by Klebanov, Nekrasov and Tseytlin, is achieved by introducing fractional M D3-branes in addition to the N regular D3-branes. The resulting theory is an SU(N+M)×SU(N) gauge theory with N = 1 supersymmetry, no longer conformal and then a little more interesting as a part of the crusade to find a QCD-like theory. This is still not the end, the last model suffers from a singularity in the deep IR, rendering the gravitational description invalid in that regime. It was conjectured that the strong dynamics of the gauge theory should somehow resolve this problem. Klebanov, again, and Strassler showed that this conjecture was correct, and argue that the RG flow is in fact an infinite series of Seiberg duality transformations- a cascade - in which the number of colors repeatedly drops from N NM , so the gaugegroup changes from SU(N+M)×SU(N) to SU(NM) ×SU(N). This process can be repeated until the IR limit where the gauge group simply becomes SU(M). So, at the end we get a N=1 SU(M) gauge theory, a QCD-like theory. We say that the standard model itself may lie at the base of a duality cascade.Essa tese consiste num estudo autocontido das dualidades calibre/gravidade na linha do modelo do Klebanov-Witten. Aqui nos exploramos primeiro de um jeito razoavelmente detalhado,a conhecida dualidade do Maldacena que relaciona a teoria N=4 SYM em quatro dimensões com as supercordas tipo IIB no espaço AdS_5×S^5, depois de alguns preliminares necessários sobre teorias supersimétricas de calibre, onde nós mostramos em detalhe à algebra supersimétrica e as representações para N 1 supersimetria. Nós também construímos os conhecidos supercampos que são úteis para escrever lagrangianas invariantes para teorias de calibre facilmente, e então serão úteis para construir a teoría de calibre do modelo de Klebanov-Witten. Na correspondência AdS/CFT original e as suas extensões fenomenologicamente interessantes, as Dp-branas, como soluções de supergravidade e objetos não perturbativos na teoria de cordas onde as teorias de calibre moram, são essenciais. Assim ,a fim de preservar a natureza autocontida desse trabalho, nós incluímos uma breve revisão sobre teoria de supercordas dirigida a entender a necessidade de incluir esses objetos extra-dimensionais usando dualidade-T e, no limite de baixa-energia da teoria de cordas, como soluções das equações de Einstein. O primeiro clímax desse trabalho ocorre quando nós usamos tudo o que aprendemos para estabelecer a conjectura do Maldacena, a teoria de calibre N=4 SYM que nós estudamos no capítulo de supersimetria, morando no volume de mundo quadridimensional de uma pilha de Nc D3-branas (sim, o subscrito c significa cor!) em espaço plano, corresponde exatamente à teoria de supergravidade tipo IIB no espaço AdS_5×S^5 . A fim de testar ela, nós identificamos simetrias e operadores com estados em ambos lados da dualidade. Mas na verdade isto corresponde à forma fraca da correspondência, porque não é possível lidar nem com a teoria de cordas nem com a teoria de calibre no limite de acoplamento forte. O foco e motivo principal de porque nós temos que aprender as primeiras cem páginas aqui, será estender a teoria de calibre dual que estudamos em AdS/CFT, para teorias de calibre mais realisticas como duais de alguma teoria de supergravidade. O modelo do Klebanov-Witten, consiste em substituir a esfera de cinco dimensões no fundo de supergravidade da teoria de supercordas tipo IIB por um espaço que é mais interessante X5, um espaço coset chamado T^1,1. Nós esperamos que a teoria de calibre dual que resulta é menos supersimetrica, e na verdade é N =1 superconforme com um conteúdo de matéria na representação bifundamental do grupo de calibre SU(N)×SU(N), e um superpotencial quártico que tem simetria global SU(2)×SU(2)×U(1), que é precisamente a simetria do espaço coset no lado da gravidade. Mas isso não é tudo, o modelo do Klebanov-Witten estendeu a correspondência do Maldacena e encontrou como teoria dual uma teoria menos supersimetrica mas ainda conforme. A quebra da simetria conforme, proposta pelo Klebanov, Nekrasov e Tseytlin, é obtida introduzindo M D3-branas fracionais além das N D3-branas regulares. A teoria resultante é uma teoria de calibre SU(N+M)×SU(N) com N = 1 supersimetria, não mais conforme e então um pouco mais interessante como parte da nossa cruzada para encontrar uma teoria tipo-QCD. Isso ainda não é o final, o modelo anterior sofre de uma singularidade no IR profundo, tornando inválido a descrição gravitacional. Foi conjeturado então que a dinâmica do acoplamento forte na teoria de gauge deveria de algum jeito resolver esse problema. Klebanov, de novo, e Strassler mostraram que essa conjetura foi correta, e argumentaram que o fluxo do GR é de fato uma serie infinita de transformações de dualidade de Seiberg - uma cascata - onde o numero de cores cai repetidamente de NNM, e o grupo de calibre muda de SU(N+M)×SU(N) a SU(NM)×SU(N). O processo pode ser repetido até o limite IV onde o grupo de calibre simplesmente torna-se SU(M). Então, no final nós obtemos uma N = 1 teoria de calibre SU (M ), ou seja uma teoria tipo-QCD. Então, nós dissemos que o modelo padrão mesmo pode se situar na base da cascata de dualidade.
22
Eshagh, Mehdi. "On Satellite Gravity Gradiometry". Doctoral thesis, Stockholm : Skolan för arkitektur och samhällsbyggnad, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10429.
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Yamashita, Yasuho. "Embedding Ghost-free Bigravity into Higher-Dimensional Gravity". 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225402.
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Heliani, Leni Sophia. "Determination of the Indonesian gravity fields from combination of surface gravity, satellite altimeter and digital terrain model data". 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149084.
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Olsson, Agneta. "Sweden´s Affinity towards Czech Republic : - A Gravity Model Approach". Thesis, Internationella Handelshögskolan, Högskolan i Jönköping, IHH, Nationalekonomi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-15266.
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Abstract It is well known that geographical distances between nations cause differences in cul-tural resemblances as well as affinity. Defined, affinity is inheriting similarities between nations in familiarity, language and mutual understanding. It cause variations in the uni-lateral trade volume flowing towards the destination countries and can be estimated by a traditional gravity model (GM). So far Swedish affinity towards Czech Republic (CZ) has remained unexplored. Hence, this paper investigates Swedish firm´s export perfor-mance and affinity towards CZ, both through the aggregate export and the extensive margin (average number of exporters). The investigation aims to seek clarification of what particular factors influence unilateral export towards CZ as well as stronger affini-ty in contrast to similar markets. To answer those questions, a one sided GM is re-gressed on two gravity equations, covering panel data for 177 destination countries from year 1997 to 2006. Results are in line with the expected behavior of the GM and show evidently; distance as well as land lock features have negative effects on unilateral ex-ports to CZ. Additionally, evidence of positive influence on unilateral export is found for GDP and familiarity to the nation. Both regressions for the gravity equations are showing high goodness of fit for the panel data. Findings of positive residuals in both the equations conclude that Swedish export have stronger affinity to CZ and solider country characteristics than its resembling countries Slovenia and Slovakia. However, positive residuals also indicate larger export flows to CZ than motivated by the tradi-tional GM coefficients. Various explanations are suggested as origins for those, such as differences in purchasing power and regions, were Prague was found to be the most suitable option for export and other regions rather for outsourcing possibilities.
26
Davids, Stefan. "A state sum model for (2+1) Lorentzian quantum gravity". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391393.
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Cain, Donneil. "The gravity model of international trade : econometric properties and applications". Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/43400/.
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This thesis reviews the literature, simulates and applies the Gravity Model of International Trade. The gravity model is widely used in international trade to examine trade flows within a network of exporters and importers. It describes the push and pull factors of trade flows and is fast becoming the most favoured tool when estimating the welfare effects of a trade policy. Therefore, estimating an accurate baseline equation is critical to correctly identify the welfare effects of trade and accompanying trade policies. Recent developments in the literature on the gravity model have helped in this regard. Chapter 1 presents a summary. The literature identifies several estimation issues and prescribes several actions that could be taken to best estimate the gravity model and minimize potential bias in the coefficient(s) of interest. With the objective of minimizing the bias on the coefficient(s) of interest, this thesis, in Chapter 2, builds on the literature by simulating and estimating the gravity model using varying assumptions about the data generating process (dgp) of the errors, conditional mean and sample. The findings from these simulations are then used to guide the application (Chapter 3) of the gravity model to trade among Caribbean Community (CARICOM) members and trade between CARICOM members and the rest of the world (ROW). Subsequently, in Chapter 4, the gravity model is used as the basis for a general equilibrium framework to investigate the importance of international borders, regional trade agreements (RTAs) and the potential impact of deeper integration in the form of a currency union among CARICOM members. The welfare implications for CARICOM members, associated with being a member of the RTA and adapting a common currency, are presented in Chapter 4 along with several recommended trade policies and areas for future research.
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Beiki, Majid. "New Techniques for Estimation of Source Parameters : Applications to Airborne Gravity and Pseudo-Gravity Gradient Tensors". Doctoral thesis, Uppsala universitet, Geofysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-143015.
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Gravity gradient tensor (GGT) data contains the second derivatives of the Earth’s gravitational potential in three orthogonal directions. GGT data can be measured either using land, airborne, marine or space platforms. In the last two decades, the applications of GGT data in hydrocarbon exploration, mineral exploration and structural geology have increased considerably. This work focuses on developing new interpretation techniques for GGT data as well as pseudo-gravity gradient tensor (PGGT) derived from measured magnetic field. The applications of developed methods are demonstrated on a GGT data set from the Vredefort impact structure, South Africa and a magnetic data set from the Särna area, west central Sweden. The eigenvectors of the symmetric GGT can be used to estimate the position of the causative body as well as its strike direction. For a given measurement point, the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the source body. For quasi 2D structures, the strike direction of the source can be estimated from the direction of the eigenvectors corresponding to the smallest eigenvalues. The same properties of GGT are valid for the pseudo-gravity gradient tensor (PGGT) derived from magnetic field data assuming that the magnetization direction is known. The analytic signal concept is applied to GGT data in three dimensions. Three analytic signal functions are introduced along x-, y- and z-directions which are called directional analytic signals. The directional analytic signals are homogenous and satisfy Euler’s homogeneity equation. Euler deconvolution of directional analytic signals can be used to locate causative bodies. The structural index of the gravity field is automatically identified from solving three Euler equations derived from the GGT for a set of data points located within a square window with adjustable size. For 2D causative bodies with geometry striking in the y-direction, the measured gxz and gzz components of GGT can be jointly inverted for estimating the parameters of infinite dike and geological contact models. Once the strike direction of 2D causative body is estimated, the measured components can be transformed into the strike coordinate system. The GGT data within a set of square windows for both infinite dike and geological contact models are deconvolved and the best model is chosen based on the smallest data fit error.Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 730
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Probst, Jonas. "Applications of the gauge/gravity duality". Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:970c6e71-371f-442f-94c9-8f1fffc8a4f7.
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This thesis investigates applications of the gauge/gravity duality to strongly coupled quantum field theories. After a review of the duality and of correlators and transport in quantum systems, we present our results on second-order non-conformal hydrodynamics. We derive new Kubo formulae for five second-order transport coefficients in non-conformal relativistic fluids. We then apply these Kubo formulae to a class of non-conformal holographic fluids at infinite coupling. We find strong evidence that the Haack-Yarom identity, known to relate second-order coefficients in conformal holographic fluids at infinite coupling, continues to hold in holographic fluids without conformal symmetry: Within our class of models, we prove that it still holds when leading non-conformal corrections are taken into account, and we show numerically that it is also obeyed beyond leading order. This provides further evidence that the identity may be a universal feature of strongly coupled fluids. Next, we present our results on magnetic spin impurities in strongly correlated systems. We build a holographic two-impurity Kondo model, identifying the inter-impurity interaction as double-trace deformation. Our numerical results for the phase diagram suggest a quantum phase transition between a trivial phase with uncorrelated spins and no Kondo screening, and a non-trivial phase with anti-ferromagnetic correlations and simultaneous Kondo screening. Computing the spectrum in the single-impurity case, we observe Fano resonances, which at low temperatures we identify with the Kondo resonance.
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Marchildon, Miguel. "An Application of the Gravity Model to International Trade in Narcotics". Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37258.
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The transnational traffic of narcotics has had undeniable impacts on international development, for instance, stagnant economic growth in Myanmar (Chin, 2009), unsustainable agricultural practices in Yemen (Robins, 2016), and human security threats in Columbia (Thoumi, 2013). Furthermore, globalization is a catalyst for the transnational narcotics traffic (Robins, 2016; Aas, 2007; Kelly, Maghan & Serio, 2005). Several qualitative studies exist on the transnational narcotics traffic, yet few quantitative studies examine the issue. There is thus an opportunity for novel quantitative studies on the general question: “what are the main economic factors that influence the transnational traffic of narcotics between countries?” This study looked at the specific question: “are distance and economic size correlated with the volume of narcotics traffic between countries?” This study chose the gravity model as it centres on bilateral trade (Tinbergen, 1962), accounts for trade barriers (Kalirajan, 2008) and is empirically robust (Anderson 2011). This study defined a basic functional gravity model relating a proxy of the narcotics traffic to distance and economic size. Four augmented functional gravity models were also advanced to address omitted variable bias. The research was limited conceptually to cross sectional and pooled time series data. In addition, the data was also limited practically to a convenience sample of secondary data drawn from: the United Nations Office on Drugs and Crime’s (UNODC) (2016a) Individual Drug Seizures (IDS); the World Bank’s (2016) World Development Indicators; and the CEPII’s GeoDist (2016) datasets. This study used a novel “dosage” approach to unit standardization to overcome the challenge posed by the many measures and forms of narcotics. The study used the Poisson pseudo maximum likelihood (PPML) estimator as its estimations of the gravity model are consistent (Gourieroux et al., 1984), allow heteroscedasticity (Silva & Tenreyro, 2006) and avoid back transformation bias (Cox et al., 2008). The evidence analyzed in this study seem to indicate that the gravity model may not be applicable in its current form to the transnational narcotics traffic among countries that report drug seizures to the UNODC. However, the sampling method and the choice of proxy are likely to influence these findings. Moreover, the low explanatory power of the gravity model for the narcotics traffic, reflected in the values of the pseudo-R-squared coefficient of determination, indicates that other factors are at play. For instance, authors such as Asad and Harris (2003) and Thoumi (2003) argue that institutions could be a key factor in the narcotics traffic. Future empirical research into this topic could build on the theses findings to introduce new proxies and to explore alternate theoretical frameworks.
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Fonte, Daniel John. "Implementing a 50x50 gravity field model in an orbit determination system". Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/49587.
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So, Tat-man. "Internal migration in Hong Kong, 1971-1981 : a gravity model analysis /". [Hong Kong : University of Hong Kong], 1985. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12318358.
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Fellner, Johannes Josef. "Numerical study on orthometric heights using a synthetic Earth gravity model". Thesis, Curtin University, 2011. http://hdl.handle.net/20.500.11937/1047.
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The fundamental problem of orthometric heights is that the mean gravity value cannot be determined due to the lack of precise topographical mass information. This thesis employs a global synthetic Earth gravity model, based on known and simulated global masses, in order to circumvent this problem. Applying forward gravity modelling techniques, the behaviour of gravity inside the topography as well as orthometric heights are studied in detail.
34
Sugishita, Sotaro. "Construction of a new model generating three-dimensional random volumes:Towards a formulation of membrane theory". 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215308.
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Drottz, Per y David Lantz. "Sweden’s Commodity Export Potential - A Gravity Approach : South-Korea". Thesis, Jönköping University, JIBS, Economics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-6832.
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This bachelor thesis aims to estimate Sweden’s export potential towards South-Korea since initial data indicates that Sweden has from 1997 up until 2005 been exporting less to South-Korea when compared to, in general, OECD. Furthermore, South-Korea seems to be a low prioritized market for Swedish firms in the East-Asian region. As many before us, we have used a basic gravity model, including GDP and distance in kilometer has been used as explanatory variables for the observed trade value. The dummy variable land-locked, to estimate trade potential for 15 commodity groups. Sweden was set to be the exporting country, South-Korea the importing country together with all the other OECD members, which were used as points of reference.
The outcome of the gravity regression shows that distance and the dummy variable landlocked (if a country does not have access to open water) have a very strong relationship to the observed export data. However, GDP was proven to have a very weak relationship to the observed export data thus making the estimation process of trade potential for all, except one, commodity group biased.
The gravity model has been widely criticized for inflating export potential due to misspecification a problem that we experienced when running our regression. Thus, from this study no strong conclusions can be drawn concerning the trade potential from Sweden to South-Korea.
36
Wu, Lichuan. "Introducing Surface Gravity Waves into Earth System Models". Doctoral thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-314760.
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Surface gravity waves alter the turbulence of the bottom atmosphere and the upper ocean. Accordingly, they can affect momentum flux, heat fluxes, gas exchange and atmospheric mixing. However, in most state-of-the-art Earth System Models (ESMs), surface wave influences are not fully considered or even included. Here, applying surface wave influences into ESMs is investigated from different aspects. Tuning parameterisations for including instantaneous wave influences has difficulties to capture wave influences. Increasing the horizontal resolution of models intensifies storm simulations for both atmosphere-wave coupled (considering the influence of instantaneous wave-induced stress) and stand-alone atmospheric models. However, coupled models are more sensitive to the horizontal resolution than stand-alone atmospheric models. Under high winds, wave states have a big impact on the sea spray generation. Introducing a wave-state-dependent sea spray generation function and Charnock coefficient into a wind stress parameterisation improves the model performance concerning wind speed (intensifies storms). Adding sea spray impact on heat fluxes improves the simulation results of air temperature. Adding sea spray impact both on the wind stress and heat fluxes results in better model performance on wind speed and air temperature while compared to adding only one wave influence. Swell impact on atmospheric turbulence closure schemes should be taken into account through three terms: the atmospheric mixing length scale, the swell-induced momentum flux at the surface, and the profile of swell-induced momentum flux. Introducing the swell impact on the three terms into turbulence closure schemes shows a better performance than introducing only one of the influences. Considering all surface wave impacts on the upper-ocean turbulence (wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves), rather than just one effect, significantly improves model performance. The non-breaking-wave-induced mixing and Langmuir circulation are the most important terms when considering the impact of waves on upper-ocean mixing. Accurate climate simulations from ESMs are very important references for social and biological systems to adapt the climate change. Comparing simulation results with measurements shows that adding surface wave influences improves model performance. Thus, an accurate description of all important wave impact processes should be correctly represented in ESMs, which are important tools to describe climate and weather. Reducing the uncertainties of simulation results from ESMs through introducing surface gravity wave influences is necessary.
37
Zhao, Yang y Min Zhang. "The Ising Model on a Heavy Gravity Portfolio Applied to Default Contagion". Thesis, Högskolan i Halmstad, Tillämpad matematik och fysik (MPE-lab), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-16459.
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In this paper we introduce a model of default contagion in the financail market. The structure of the companies are represented by a Heavy Gravity Portfolio, where we assume there are N sectors in the market and in each sector i, there is one big trader and ni supply companies.The supply companies in each sector are directly inuenced by the bigtrader and the big traders are also pairwise interacting with each other.This development of the Ising model is called Heavy gravity portfolioand according to this, the relation between expectation and correlationof the default of companies are derived by means of simulations utilisingthe Gibbs sampler. Finally methods for maximum likelihood estimationand for a likelihood ratio test of the interaction parameter in the modelare derived.
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Thai, Tri Do. "A gravity model for trade between Vietnam and twenty-three European countries". Thesis, Högskolan Dalarna, Nationalekonomi, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:du-2160.
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This thesis examines the bilateral trade between Vietnam and twenty three European countries based on a gravity model and panel data for years 1993 to 2004. Estimates indicate that economic size, market size and real exchange rate of Vietnam and twenty three European countries play major role in bilateral trade between Vietnam and these countries. Distance and history, however, do not seem to drive the bilateral trade. The results of gravity model are also applied to calculate the trade potential between Vietnam and twenty three European countries. It shows that Vietnam’s trade with twenty three European countries has considerable room for growth.
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Bai, Lu. "Effects of global financial crisis on Chinese export: a gravity model study". Thesis, Internationella Handelshögskolan, Högskolan i Jönköping, IHH, Economics, Finance and Statistics, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-18297.
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Barazanji, Deleer. "Model Based Estimation of Height of Center of Gravity in Heavy Vehicles". Thesis, KTH, Matematik (Inst.), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-92571.
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Abstract The center of gravity height in a vehicle a ects its dynamic driving properties but there is no accurate way of measuring the height of center of gravity today. One example of vehicle stabilizing systems is vehicle rollover warning and assist system which has to rely on a relatively accurate height of center of gravity estimate in order to be implemented in vehicles e_ciently and would otherwise be considered useless. In this thesis a literature study on the height of center of gravity in heavy vehicles in general and semitrailers in particular is conducted at Scania CV and emphasis is towards a model relying as little as possible on data from outside the tractor. A partly new model for detecting the vehicle's axle loads at di_erent acceleration values is developed and compared to other models, pros and cons are examined, furthermore an estimation tool is developed for the new model in a realistically applicable manner with regards to normal driving situations and solution limitations.The estimation tool is tested on Scania semitrailers with di_erent suspension con_gurations and the result shows that the height of center of gravity can be estimated as close as 4.1 (cm) from the real value for 4x2 Gen 2 Scania tractor and 3.3 (cm) for 4x2 Gen 3 Scania tractor.
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Thanyakhan, Sutana. "The Determinants of FDI and FPI in Thailand: a Gravity Model Analysis". Phd thesis, Lincoln University. Commerce Division, 2008. http://theses.lincoln.ac.nz/public/adt-NZLIU20080429.102238/.
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Thailand has been one of significant recipients of foreign direct investment (FDI) among
developing countries over the last 30 years, and has recorded rapid and sustained growth
rates in a number of different industrial categories. Thailand has shown a clear policy
transition for foreign investment over time from an import-substitution regime to an
export-oriented regime. Before the 1997 Asian Financial Crisis (1985-1996), Thailand had
the fastest growing level of exports in manufactured goods among Asian economies. FDI
plays a significant role in the Thai economy. Thailand has been pursuing different foreign
investment policies at different times depending on the development objectives and
economic situation in the country.
The main objective of this research is to evaluate the determinants of FDI and foreign
portfolio investment (FPI) in Thailand using the extended Gravity Model. Panel data is
used to estimate and evaluate the empirical results based on the data for the years 1980 to
2004. It also examines the FDI flows between different locations and their geographical
distances in Thailand. The primary research question addresses what factors motivate,
attract, and sustain the FDI and FPI in Thailand. In addition, this study also examines the
effects of the 1997 Asian Financial Crisis on the inflows of FDI and FPI into Thailand.
The results show that the inflows of FDI in Thailand, which are supply-driven, are
significantly influenced by its 21 largest investing partners. The 1997 Asian Financial
Crisis has no impact on the determinants of the inflows of FDI into Thailand, but positively
influences the inflows of FPI into Thailand. Our results also show that increases in GDP
and trade between investing partners and Thailand potentially attract more FDI and FPI
into Thailand. Investing partners closer to Thailand draw more portfolio investment into Thailand than distant partners emphasising that distance has a negative impact on the
portfolio investment but a negligible impact on the FDI.
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Tajmar, Martin. "Derivation of the Planck and Fine-Structure Constant from Assis’s Gravity Model". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-173411.
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Presently, Planck’s constant is a fundamental constant that can not be derived from other onstants. Assis developed a model based on an extended Weber-type potential energy, that allows calculating gravitational-type forces from neutral oscillating electric dipoles. Here we show that the maximum possible point-mass in his model equals the Planck mass which allows us to derive Planck’s constant and the fine-structure constant. We match the exact order of magnitude only requiring a pre-factor that is present in all Weber-type theories and has to be determined empirically. This classical model allows to link electromagnetic, gravitational and quantum properties with one approach.
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Xu, Albert. "Investigating the Effects of Cultural Distance on the Gravity Model of Trade". Scholarship @ Claremont, 2017. http://scholarship.claremont.edu/cmc_theses/1568.
Texto completoResumen
The gravity model of trade is the workhorse model for international trade. In its most basic form, it stipulates that bilateral trade flow between two countries is proportional to the countries’ Gross Domestic Product (GDP) and the distance between them. According to the gravity model, the elasticity of trade flows to distance, or the “distance effect,” has increased since the early 1970s, a confounding empirical result known as the “distance puzzle.” This paper investigates the distance effect more closely by decomposing it. More specifically, it aims to isolate the effects from culture, constructing measures of cultural distance and examining their effects on bilateral trade levels and the distance effect. The results show that cultural differences do not account for the distance puzzle. However, it also finds that cultural distance has both a substantial and statistically significant effect on bilateral trade.
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Mead, Alexander James. "Demographics of dark-matter haloes in standard and non-standard cosmologies". Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/9951.
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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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Exner, Andreas. "The European Union and the Euro : A Gravity Approach on Bilateral Trade". Thesis, Internationella Handelshögskolan, Högskolan i Jönköping, IHH, Nationalekonomi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-21662.
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In the year of 1999 a new monetary experiment commenced – the birth of the euro. Over the years more countries have joined the new currency and it was expected to be a continuously growing community. The purpose of this paper is to measure the effect of European membership, the currency of euro and the financial crisis on trade between the countries located in Europe. For the task of this paper the gravity model is used to study the bilateral trade flows in the European Union from 1995-2011. It additionally investigates, besides the correlation between GDP and distance, the effect of shared border, shared language and coastal access. The results showed that the euro did indeed have a positive impact on trade in the introduction year to later significantly have a negative impact on trade. Moreover, a membership in the European Union results showed to promote intra-European Union trade at the cost of extra-European Union trade and have its largest impact in the beginning and end of the study years. The conclusion is that other factors than increased trade were the main reasons to join the European Union, such as enhancing the role of Europe in the world market and to turn into a unified market. Finally, the effect of the financial crisis was found to have a negative impact on trade, concluded that it exposed the failures and lack of coordination between and within countries. It was also shown that the physical distance, and not specifically distances in i.e. social culture and languages, boosted the trade between countries.
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Dev, Abha, Deepak Jain, S. Jhingan, S. Nojiri, M. Sami y I. Thongkool. "Delicate f(R) gravity models with a disappearing cosmological constant and observational constraints on the model parameters". American Physical Society, 2008. http://hdl.handle.net/2237/11278.
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Santos, Ignacio. "Simulation and Study of Gravity Assist Maneuvers". Thesis, KTH, Rymdteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-276462.
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This thesis takes a closer look at the complex maneuver known as gravity assist, a popular method of interplanetary travel. The maneuver is used to gain or lose momentum by flying by planets, which induces a speed and direction change. A simulation model is created using the General Mission Analysis Tool (GMAT), which is intended to be easily reproduced and altered to match any desired gravity assist maneuver. The validity of its results is analyzed, comparing them to available data from real missions. Some parameters, including speed and trajectory, are found to be extremely reliable. The model is then used as a tool to investigate the way that different parameters impact this complex environment, and the advantages of performing thrusting burns at different points during the maneuver are explored. According to theory, thrusting at the point of closest approach to the planet is thought to be the most efficient method for changing speed and direction of flight. However, the results from this study show that thrusting before this point can have some major advantages, depending on the desired outcome. The reason behind this is concluded to be the high sensitivity of the gravity assist maneuver to the altitude and location of the point of closest approach.Detta examensarbete tittar närmare på den komplexa manöver inom banmekanik som kallas gravitationsassisterad manöver, vilken är vanligt förekommande vid interplanetära rymduppdrag. Manövern används för att öka eller minska farkostens rörelsemängd genom att flyga förbi nära planeter, vilket ger upphov till en förändring i fart och riktning. En simuleringsmodell är skapad i NASAs mjukvara GMAT med syftena att den ska vara reproducerbar samt möjlig att ändra för olika gravitationsassisterade manövrar. Resultaten från simuleringarna är validerade mot tillgängliga data från riktigt rymduppdrag. Vissa parametrar, som fart och position, har en väldigt bra överenstämmelse. Modellen används sedan för att noggrannare undersöka hur olika parametrar påverkar det komplexa beteendet vid en graviationsassisterad manöver, genom att specifikt titta på effekterna av en pålagd dragkraft från motorn under den gravitationsassisterade manövern. Teoretiskt fås mest effekt på fart och riktning om dragkraften från motorn läggs på vid punkten närmast planeten. Resultaten från denna studie visar att beroende på vilken parameter man vill ändra så kan man erhålla mer effekt genom att lägga på dragkraften innan den närmsta punkten. Förklaringen till detta är att den gravitationsassisterade manövern är väldigt icke-linjär, så en tidigare pålagd dragkraft kan kraftigt förändra farkostens bana nära planeten, så att farkosten t.ex. kommer närmare och då påverkas mer.
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Gao, Shen. "The Predictive Capacity of the Gravity Model of Trade on Foreign Direct Investment". Thesis, Uppsala University, Department of Economics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-102534.
Texto completoResumen
The link between foreign direct investments (FDI) and trade is firmly established in economic literature. Yet despite the vast amount of literature on this subject, very few have tried to look at FDI through the lens of trade theory, choosing rather to approach the subject on either a macroeconomic-level or on firm-level. The purpose and scope of this paper is to explore FDI through the lens of trade-theory. The central questions in this thesis are whether the gravity model of trade can serve as a reliable model for FDI value as well? Are there certain variables in the gravity model that are distinctively powerful determinants of FDI? Two econometric models are used to determine the gravitational impact on FDI, one ordinary OLS model and one fixed-effect model. The findings when using OLS regressions are that the components of the gravity model of trade are indeed key determinants of FDI value, and the two most significant positive determinants were home country GDP as well as home country per-capita GDP. In the fixed-effect model however, several variables were found to have no significant effect on FDI value and only home country GDP and host country per-capita GDP were consistent positive determinants of FDI.
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Yokokura, Yuki. "A Self-consistent Model of the Black Hole Evaporation and Entropy in Gravity". 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188488.
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Wang, Daoyan. "On c=1 matrix model and 2D gravity - with emphasis on chiral formalism". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/5526.
Texto completoResumen
In this thesis, we study the relationship between the effective spacetime
theory of Liouville string theory in two spacetime dimensions and the collective
field of the c=1 matrix model by finding exact solutions on both sides. The
correspondence between the matrix model and the effective spacetime theory
turns out to be nonlinear in their fields. By comparing the exact solutions
on both side, we show the nonlinearity begins to appear at the second order
in terms of the incoming tachyon field.
In particular, we employ the chiral formalism in the matrix model the
formalism allowing to write down solutions to equations of motion explicitly
— to find out exact solutions. We show the chiral formalism is much simpler
than the more traditional classical field method. Also it is more powerful
as it enables us to study the behavior around the singular point in the
background of the matrix model.