986 resultados para Gravity model


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The pharmaceutical industry is one of the most competitive sectors in the European Union. With its substantial investments in research and development, this industry represents a key asset for the European economy and a major source of growth and employment. However, despite the importance of the pharmaceutical sector for the European Union, few researchers have attempted to assess the determinants of the EU exports of pharmaceuticals. This paper aims at filling the aforementioned gap by examining what drives EU exports of pharmaceuticals. In order to tackle this question, this paper has derived hypotheses from the Gravity Model of Trade and the relevant academic literature on pharmaceuticals. Based on an econometric analysis, the research sheds light on the complex interaction of factors influencing the EU exports of pharmaceuticals. The paper finds that the protection of intellectual property in the receiving countries, their economic size, the importance of their health sector, and the quality of infrastructures constitute major drivers to the EU exports of pharmaceuticals. On the contrary, the research shows that transports costs as well as tariff barriers and non-tariff barriers tend to hinder the EU exports of pharmaceuticals.

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The themes of this thesis are that international trade and foreign direct investment (FDI) are closely related and that they have varying impacts on economic growth in countries at different stages of development. The thesis consists of three empirical studies. The first one examines the causal relationship between FDI and trade in China. The empirical study is based on a panel of bilateral data for China and 19 home countries/regions over the period 1984-98. The specific feature of the study is that econometric techniques designed specially for panel data are applied to test for unit roots and causality. The results indicate a virtuous procedure of development for China. The growth of China’s imports causes growth in inward FDI from a home country/region, which in turn causes the growth of exports from China to the home country/region. The growth of exports causes the growth of imports. This virtuous procedure is the result of China’s policy of opening to the outside world. China has been encouraging export-oriented FDI and reducing trade barriers. Such policy instruments should be further encouraged in order to enhance economic growth. In the second study, an extended gravity model is constructed to identify the main causes of recent trade growth in OECD countries. The specific features include (a) the explicit introduction of R&D and FDI as two important explanatory variables into an augmented gravity equation; (b) the adoption of a panel data approach, and (c) the careful treatment of endogeneity. The main findings are that the levels and similarities of market size, domestic R&D stock and inward FDI stock are positively related to the volume of bilateral trade, while the geographical distance, exchange rate and relative factor endowments, has a negative impact. These findings lend support to new trade, FDI and economic growth theories. The third study evaluates the impact of openness on growth in different country groups. This research distinguishes itself from many existing studies in three aspects: first, both trade and FDI are included in the measurement of openness. Second, countries are divided' into three groups according to their development stages to compare the roles of FDI and trade in different groups. Third, the possible problems of endogeneity and multicollinearity of FDI and trade are carefully dealt with in a panel data setting. The main findings are that FDI and trade are both beneficial to a country's development. However, trade has positive effects on growth in all country groups but FDI has positive effects on growth only in the country groups which have had moderate development. The findings suggest FDI and trade may affect growth under different conditions.

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This paper analyzes the relationship between freight accessibility and logistics employment in the US. It develops an accessibility measure relevant for logistics companies based on a gravity model. This allows for an analysis of the accessibility of US counties focusing on four different modes of transportation: road, rail, air, and maritime. Using a Partial Least Squares model, these four different freight accessibility measures are combined into two constructs, continental and intercontinental freight accessibility, and related to logistics employment. Results show that highly accessible counties attract more logistics employment than other counties. The analyses show that it is very important to control for the effect of the county population on both freight accessibility and logistics employment. While county population explains the most variation in the logistics employment per county, there is a significant relationship between freight accessibility and logistics employment, when controlling for this effect.

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Wine is a very special product from an economic, cultural, and sociological point of view. Wine culture and wine trade play an important role in Hungary. The effect of cultural and geographical proximity on international trade has already been proven in the international trade literature. The size of bilateral trade flows between any two countries can be approximated by the gravity theory of trade. The gravity model provides empirical evidence of the relationship between the size of the economies, the distances between them, and their trade. This paper seeks to analyse the effect of cultural and geographical proximity on Hungary’s bilateral wine trade between 2000 and 2012, employing the gravity equation. The analysis is based on data from the World Bank WITS, WDI, as well as CEPII, and WTO databases. I apply OLS, Random Effects, Poisson, Pseudo-Poisson-Maximum-Likelihood and Heckman two stage estimators to calculate the gravity regression. The results show that in the case of Hungary, cultural similarity and trade liberalisation have a positive impact, while geographical distance, landlockedness, and contiguity have a negative impact on Hungarian wine exports.

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A globalizálódó világgazdaságban a vezető bortermelő országok egyre jelentősebb borkereskedelmet bonyolítanak le egymás között. Míg Európában a fogyasztók egyre kevesebb bort vásárolnak, addig Amerikában és Ázsiában a bor iránti kereslet folyamatosan bővül: a borkereskedelem földrajzi átrendeződése zajlik. A kulturális hasonlóság és a földrajzi távolság kereskedelemre gyakorolt hatását gyakran a kereskedelemelméletek gravitációs modelljével elemzik. E tanulmány azt vizsgálja, hogy a fő borexportáló országok közötti földrajzi távolság, kulturális hasonlóság és szabadkereskedelem milyen hatással van a nemzetközi borkereskedelemre, annak költségeire. A regressziós becslés eredményei alátámasztják, hogy a borkereskedelem költségei alacsonyabbak, ha a kereskedelmi partnerek kulturálisan hasonlók, földrajzilag közel helyezkednek el egymáshoz, vagy van tengeri kikötőjük, tagjai a WTO-nak, illetve ha kötöttek egymással regionális kereskedelmi megállapodást. Ezenkívül megállapítható, hogy az angolszász, a latin-amerikai és az európai kulturális klaszterek elsősorban egymással kereskednek. A kutatás számos kulturális változó alkalmazásával és több ökonometriai modell, illetve becslési eljárás nagymintás tesztelésével gazdagítja a szakirodalmat. ____ In a globalizing world, major wine-producing countries export considerable quantities to the global wine market and turn over a notable trade, but in what happens European wine regions differ markedly from the New World. Here major wine producers suffered a remarkable fall in domestic wine consumption in recent decades, while New World wine producers increased their production potential and generated new foreign demand. The changes have been joined by geographical relocation of wine consumption and exports. The gravity equation can be derived from demand-side or supply-side theory-consistent estimation methods that suggest relationships between the size of the economies, geographical distances, cultural similarities, and size of their trade. The paper analyses the effects of cultural and geographical proximity, free trade, and linguistic similarity on bilateral trade in the main wine-producing countries, using a cross-section gravity model for 2012. The results suggest that larger countries export more wine, while transport costs rise in line with geographical distance and are higher for landlocked trading partners. Wine export costs are lower if trading partners are culturally similar, share a dominant religion, or are both WTO members with regional trade agreements. Anglo-Saxon, Germanic, Latin American and Latin European countries mainly trade wines within their groups. The paper looks to extend the number of trading partners, investigate the effect of language clusters, and confirm that the results are robust by different econometric methodologies.

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Annual Average Daily Traffic (AADT) is a critical input to many transportation analyses. By definition, AADT is the average 24-hour volume at a highway location over a full year. Traditionally, AADT is estimated using a mix of permanent and temporary traffic counts. Because field collection of traffic counts is expensive, it is usually done for only the major roads, thus leaving most of the local roads without any AADT information. However, AADTs are needed for local roads for many applications. For example, AADTs are used by state Departments of Transportation (DOTs) to calculate the crash rates of all local roads in order to identify the top five percent of hazardous locations for annual reporting to the U.S. DOT. ^ This dissertation develops a new method for estimating AADTs for local roads using travel demand modeling. A major component of the new method involves a parcel-level trip generation model that estimates the trips generated by each parcel. The model uses the tax parcel data together with the trip generation rates and equations provided by the ITE Trip Generation Report. The generated trips are then distributed to existing traffic count sites using a parcel-level trip distribution gravity model. The all-or-nothing assignment method is then used to assign the trips onto the roadway network to estimate the final AADTs. The entire process was implemented in the Cube demand modeling system with extensive spatial data processing using ArcGIS. ^ To evaluate the performance of the new method, data from several study areas in Broward County in Florida were used. The estimated AADTs were compared with those from two existing methods using actual traffic counts as the ground truths. The results show that the new method performs better than both existing methods. One limitation with the new method is that it relies on Cube which limits the number of zones to 32,000. Accordingly, a study area exceeding this limit must be partitioned into smaller areas. Because AADT estimates for roads near the boundary areas were found to be less accurate, further research could examine the best way to partition a study area to minimize the impact.^

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The discussion about rift evolution in the Brazilian Equatorial margin during the South America-Africa breakup in the Jurassic/Cretaceous has been focused in many researches. But rift evolution based on development and growth of faults has not been well explored. In this sense, we investigated the Cretaceous Potiguar Basin in the Equatorial margin of Brazil to understand the geometry of major faults and the influence of crustal heterogeneity and preexisting structural fabric in the evolution of the basin internal architecture. Previous studies pointed out that the rift is an asymmetrical half-graben elongated along the NE-SW direction. We used 2D seismic, well logs and 3D gravity modeling to analyze four major border fault segments and determine their maximum displacement (Dmax) and length (L) ratio in the Potiguar Rift. We constrained the 3D gravity modeling with well data and the interpretation of seismic sections. The difference of the fault displacement measured in the gravity model is in the order of 10% compared to seismic and well data. The fault-growth curves allowed us to divide the faulted rift border into four main fault segments, which provide roughly similar Dmax/L ratios. Fault-growth curves suggest that a regional uniform tectonic mechanism influenced growth of the rift fault segments. The variation of the displacements along the fault segments indicates that the fault segments were formed independently during rift initiation and were linked by hard and soft linkages. The latter formed relay ramps. In the interconnection zones the Dmax/L ratios are highest due to interference of fault segment motions. We divided the evolution of the Potiguar Rift into five stages based on these ratios and correlated them with the major tectonic stages of the breakup between South America and Africa in Early Cretaceous.

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The discussion about rift evolution in the Brazilian Equatorial margin during the South America-Africa breakup in the Jurassic/Cretaceous has been focused in many researches. But rift evolution based on development and growth of faults has not been well explored. In this sense, we investigated the Cretaceous Potiguar Basin in the Equatorial margin of Brazil to understand the geometry of major faults and the influence of crustal heterogeneity and preexisting structural fabric in the evolution of the basin internal architecture. Previous studies pointed out that the rift is an asymmetrical half-graben elongated along the NE-SW direction. We used 2D seismic, well logs and 3D gravity modeling to analyze four major border fault segments and determine their maximum displacement (Dmax) and length (L) ratio in the Potiguar Rift. We constrained the 3D gravity modeling with well data and the interpretation of seismic sections. The difference of the fault displacement measured in the gravity model is in the order of 10% compared to seismic and well data. The fault-growth curves allowed us to divide the faulted rift border into four main fault segments, which provide roughly similar Dmax/L ratios. Fault-growth curves suggest that a regional uniform tectonic mechanism influenced growth of the rift fault segments. The variation of the displacements along the fault segments indicates that the fault segments were formed independently during rift initiation and were linked by hard and soft linkages. The latter formed relay ramps. In the interconnection zones the Dmax/L ratios are highest due to interference of fault segment motions. We divided the evolution of the Potiguar Rift into five stages based on these ratios and correlated them with the major tectonic stages of the breakup between South America and Africa in Early Cretaceous.

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The characteristics of convectively-generated gravity waves during an episode of deep convection near the coast of Wales are examined in both high resolution mesoscale simulations [with the (UK) Met Oce Unified Model] and in observations from a Mesosphere-Stratosphere-Troposphere (MST) wind profiling Doppler radar. Deep convection reached the tropopause and generated vertically propagating, high frequency waves in the lower stratosphere that produced vertical velocity perturbations O(1 m/s). Wavelet analysis is applied in order to determine the characteristic periods and wavelengths of the waves. In both the simulations and observations, the wavelet spectra contain several distinct preferred scales indicated by multiple spectral peaks. The peaks are most pronounced in the horizontal spectra at several wavelengths less than 50 km. Although these peaks are most clear and of largest amplitude in the highest resolution simulations (with 1 km horizontal grid length), they are also evident in coarser simulations (with 4 km horizontal grid length). Peaks also exist in the vertical and temporal spectra (between approximately 2.5 and 4.5 km, and 10 to 30 minutes, respectively) with good agreement between simulation and observation. Two-dimensional (wavenumber-frequency) spectra demonstrate that each of the selected horizontal scales contains peaks at each of preferred temporal scales revealed by the one- dimensional spectra alone.

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We report on a numerical study of the impact of short, fast inertia-gravity waves on the large-scale, slowly-evolving flow with which they co-exist. A nonlinear quasi-geostrophic numerical model of a stratified shear flow is used to simulate, at reasonably high resolution, the evolution of a large-scale mode which grows due to baroclinic instability and equilibrates at finite amplitude. Ageostrophic inertia-gravity modes are filtered out of the model by construction, but their effects on the balanced flow are incorporated using a simple stochastic parameterization of the potential vorticity anomalies which they induce. The model simulates a rotating, two-layer annulus laboratory experiment, in which we recently observed systematic inertia-gravity wave generation by an evolving, large-scale flow. We find that the impact of the small-amplitude stochastic contribution to the potential vorticity tendency, on the model balanced flow, is generally small, as expected. In certain circumstances, however, the parameterized fast waves can exert a dominant influence. In a flow which is baroclinically-unstable to a range of zonal wavenumbers, and in which there is a close match between the growth rates of the multiple modes, the stochastic waves can strongly affect wavenumber selection. This is illustrated by a flow in which the parameterized fast modes dramatically re-partition the probability-density function for equilibrated large-scale zonal wavenumber. In a second case study, the stochastic perturbations are shown to force spontaneous wavenumber transitions in the large-scale flow, which do not occur in their absence. These phenomena are due to a stochastic resonance effect. They add to the evidence that deterministic parameterizations in general circulation models, of subgrid-scale processes such as gravity wave drag, cannot always adequately capture the full details of the nonlinear interaction.

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An analytical model of orographic gravity wave drag due to sheared flow past elliptical mountains is developed. The model extends the domain of applicability of the well-known Phillips model to wind profiles that vary relatively slowly in the vertical, so that they may be treated using a WKB approximation. The model illustrates how linear processes associated with wind profile shear and curvature affect the drag force exerted by the airflow on mountains, and how it is crucial to extend the WKB approximation to second order in the small perturbation parameter for these effects to be taken into account. For the simplest wind profiles, the normalized drag depends only on the Richardson number, Ri, of the flow at the surface and on the aspect ratio, γ, of the mountain. For a linear wind profile, the drag decreases as Ri decreases, and this variation is faster when the wind is across the mountain than when it is along the mountain. For a wind that rotates with height maintaining its magnitude, the drag generally increases as Ri decreases, by an amount depending on γ and on the incidence angle. The results from WKB theory are compared with exact linear results and also with results from a non-hydrostatic nonlinear numerical model, showing in general encouraging agreement, down to values of Ri of order one.

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The behavior of the ensemble Kalman filter (EnKF) is examined in the context of a model that exhibits a nonlinear chaotic (slow) vortical mode coupled to a linear (fast) gravity wave of a given amplitude and frequency. It is shown that accurate recovery of both modes is enhanced when covariances between fast and slow normal-mode variables (which reflect the slaving relations inherent in balanced dynamics) are modeled correctly. More ensemble members are needed to recover the fast, linear gravity wave than the slow, vortical motion. Although the EnKF tends to diverge in the analysis of the gravity wave, the filter divergence is stable and does not lead to a great loss of accuracy. Consequently, provided the ensemble is large enough and observations are made that reflect both time scales, the EnKF is able to recover both time scales more accurately than optimal interpolation (OI), which uses a static error covariance matrix. For OI it is also found to be problematic to observe the state at a frequency that is a subharmonic of the gravity wave frequency, a problem that is in part overcome by the EnKF.However, error in themodeled gravity wave parameters can be detrimental to the performance of the EnKF and remove its implied advantages, suggesting that a modified algorithm or a method for accounting for model error is needed.