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It is well established that maximizing the information extracted from upcoming and ongoing stage-IV weak-lensing surveys requires higher order summary statistics that complement the standard two-point statistics. In this work, we focus on weak-lensing peak statistics to test two popular modified gravity models, |$f(R)$| and nDGP, using the forge and bridge weak-lensing simulations, respectively. From these simulations, we measure the peak statistics as a function of both cosmological and modified gravity parameters simultaneously. Our findings indicate that the peak abundance is sensitive to the strength of modified gravity, while the peak two-point correlation function is sensitive to the nature of the screening mechanism in a modified gravity model. We combine these simulated statistics with a Gaussian Process Regression emulator and a Gaussian likelihood to generate stage-IV forecast posterior distributions for the modified gravity models. We demonstrate that, assuming small scales can be correctly modelled, peak statistics can be used to distinguish general relativity from |$f(R)$| and nDGP models at the 2σ level with a stage-IV survey area of |$300$| and |$1000 \, \rm {deg}^2$|⁠ , respectively. Finally, we show that peak statistics can constrain |$\log _{10}\left(|f_{R0}|\right) = -6$|  per cent to 2 per cent precision, and |$\log _{10}(H_0 r_c) = 0.5$| per cent to 25 per cent precision. [ABSTRACT FROM AUTHOR]

We consider the canonical trade model with heterogeneous firms, love for variety and trade costs, and integrate it in the consumption CAPM model. This yields a structural gravity equation that includes an additional factor related to risk premia. Empirical evidence based on firm-level data confirms the importance of cross-sectional heterogeneity in risk and time-varying risk premia to shape bilateral trade flows. The structural gravity model augmented to account for fluctuations in risk premia offers a compelling explanation for trade collapses during abrupt economic downturns. [ABSTRACT FROM AUTHOR]

Identifying crucial nodes in complex networks is paid more attention in recent years. Some classical methods, such as degree centrality, betweenness centrality and closeness centrality, have their advantages and disadvantages. Recently, the gravity model is applied to describe the relationship of nodes in a complex network. However, the interaction force in gravity model follows the square law of distance, which is inconsistent with the actual situation. Most people are generally affected by those who are surrounding them, which means that local influence should be emphasized. To address this issue, we propose an indexing method called localized decreasing gravity centrality by maximizing the local influence of a node. In the proposed measure, the mass and radius of gravity model are redefined, which can represent the spreading ability of the node. In addition, a decreasing weight is added to strengthen the local influence of a node. To evaluate the performance of the proposed method, we utilize four different types of networks, including interaction networks, economic networks, collaboration networks and animal social networks. Also, two different infectious disease models, susceptible-infectious-recovered (SIR) and susceptible-exposed-low risk-high risk-recovered (SELHR), are utilized to examine the spreading ability of influential nodes. [ABSTRACT FROM AUTHOR]

The Modified Gravity Model (MOG) has been proposed as a solution to the dark matter problem, but it does not meet the gauge invariant condition. The aim of this work is to propose a gauge-invariant theory, which suggests that symmetry can break at a low temperature in the Universe, leading to the MOG theory. This theory has the potential to alter the dynamics of the early and late Universe and naturally produce cosmological inflation. [ABSTRACT FROM AUTHOR]

Post-seismic gravity change modelling is commonly based on earth model with Newtonian linear rheology. Here, we present a novel way of modelling post-seismic gravity change by using a non-linear power-law rheology earth model. The method is constructed based on the framework of spectral finite element method (SFEM). SFEM has been proven practical for the purpose of modelling gravity change occurring during megathrust earthquakes. Our method implements the strain rate expression of non-linear power-law rheology into the mathematical framework of SFEM. Using our method, simulations of geoid change caused by synthetic point source earthquakes were made. The results revealed the potential of using non-linear power-law rheology for the explanation of rapid gravity changes in the beginning of the post-seismic epoch. Further on, we computed the post-seismic gravity change of the 2011 M 9.0 Tohoku-Oki earthquake based on Maxwell non-linear power-law rheology in the upper mantle. It demonstrated the potential of power-law upper mantle flow as a possible candidate for the explanation of post-seismic gravity change after the earthquake occurs. However, a Maxwell non-linear power-law rheology alone is insufficient for the explanation of the post-seismic gravity change occurred. [ABSTRACT FROM AUTHOR]

We present mglens , a large series of modified gravity lensing simulations tailored for cosmic shear data analyses and forecasts in which cosmological and modified gravity parameters are varied simultaneously. Based on the forge and bridge N -body simulation suites presented in companion papers, we construct 100 × 5000 deg2 of mock Stage-IV lensing data from two 4D Latin hypercubes that sample cosmological and gravitational parameters in f (R) and nDGP gravity, respectively. These are then used to validate our inference analysis pipeline based on the lensing power spectrum, exploiting our implementation of these modified gravity models within the cosmosis cosmological inference package. Sampling this new likelihood, we find that cosmic shear can achieve 95 per cent CL constraints on the modified gravity parameters of log |$_{10}[f_{R_0}] \lt $| −4.77 and log10[ H 0 rc ] > 0.09, after marginalizing over intrinsic alignments of galaxies and including scales up to ℓ = 5000. We also investigate the impact of photometric uncertainty, scale cuts, and covariance matrices. We finally explore the consequences of analysing mglens data with the wrong gravity model, and report catastrophic biases for a number of possible scenarios. The Stage-IV mglens simulations, the forge and bridge emulators and the cosmosis interface modules will be made publicly available upon journal acceptance. [ABSTRACT FROM AUTHOR]

In the era of globalization, policy makers in both developing and developed countries have sought to expand their export destinations, with the expectation that export market diversification can boost export upgrading and economic development. Although extant literature has confirmed that exporters search for new markets in two distinct ways: direct search underpinned by the gravity effect and remote search driven by the extended gravity effect, it has not advanced very far due to the lack of adequate measures of those effects. This article presents a technique that uses available export data to develop measures of those two effects that capture a larger range of factors and thus allow us to more easily predict export market diversification. Our new indicator also simplifies the prediction by combining gravity and extended gravity effects. Empirical results show that the explanatory and predictive power of our new method is better than that of the traditional one based on gravity and extended gravity models. [ABSTRACT FROM AUTHOR]

This paper investigates three-way gravity models with multiplicative unobserved effects, which are popular in bilateral trade analysis and many other contexts. Such models are usually estimated by the fixed effects Poisson pseudo maximum likelihood method. As an alternative, we extend the estimation strategy proposed by Jochmans (2017) to our new settings by constructing moment conditions that are independent of the unobserved effects. Our method entails estimation of the conditional mean of a variety of functional forms. The generalized method of moments (GMM) estimator based on these moment conditions is N-consistent and asymptotically normally distributed. We also discuss the estimation of dynamic models by extending the linear feedback models to our three-way settings. Through various simulation designs, we show that our GMM estimator outperforms the competing Poisson pseudo maximum likelihood estimator. As an empirical application, we estimate the effects of the currency unions on exports. [ABSTRACT FROM AUTHOR]

With the emergence of the online gig economy, computer-based jobs can be completed by gig workers around the world. This raises the question whether the labour market for online gigs is truly boundless as distance no longer matters. Based on gravity models, we investigate the effect of geographical, institutional and cultural distance on almost 30 000 platform hirings between 26 European countries. While we find that online gig platforms are used to off-shore work from high- to low-wage countries, the online gig economy is not boundless as gig workers are still preferably hired from geographically close economies. A common language furthermore facilitates hirings between countries. Interestingly, though, differences in formal and informal institutions hardly affect hiring patterns across countries, suggesting that online platforms create their own institutional framework. We conclude that the online gig economy constitutes neither a boundless nor a frictionless labour market, implying that its promise of creating equal access to job opportunities is exaggerated. [ABSTRACT FROM AUTHOR]

We develop a multi-sector gravity model with heterogeneous workers to quantify the aggregate and group-level welfare effects of trade. The model generalizes the specific-factors intuition to a setting with labour reallocation, leads to a parsimonious formula for the group-level welfare effects from trade, and nests the aggregate results in Arkolakis, Costinot and Rodríguez-Clare (2012, "New Trade Models, Same Old Gains?", American Economic Review , 102 , 94–130). We estimate the model using the structural relationship between China-shock driven changes in manufacturing employment and average earnings across US groups defined as commuting zones. We find that the China shock increases average welfare but some groups experience losses as high as four times the average gain. However, adjusting for plausible measures of inequality aversion barely affects the welfare gains. We also develop and estimate an extension of the model that endogenizes labour force participation and unemployment, finding similar welfare effects from the China shock. [ABSTRACT FROM AUTHOR]

This paper studies the empirical relationship between common ownership and interlocking directorships. I estimate a gravity equation model for the probability that a pair of firms will have a common director, as a function of the geographic distance between the firms, their sizes, and a set of covariates, including measures of common ownership between the firms. The main finding is that, robustly across several measures of common ownership, firm pairs with higher levels of common ownership are associated with a higher likelihood of sharing directors. Also, their distance in the network of directors is smaller on average. Consistent with the "gravity" interpretation, larger firms are more likely to share directors, and firms that are geographically more distant are less likely to share directors. [ABSTRACT FROM AUTHOR]

We analyse how Brexit will affect European agrifood trade using a structural gravity model and by comparing the present deal to four alternative scenarios on the UK's trade policy. European Union (EU) countries will suffer marginal drops in imports, exports and real income, with stronger effects for Ireland. EU exports to the UK will drop by 10 per cent. European products will be redirected to both intra-EU and extra-EU markets and sold at slightly lower prices. Meat products will suffer the largest losses, Ireland being particularly vulnerable due to strong interconnections with British production chains and increased costs for accessing EU and extra-EU markets. [ABSTRACT FROM AUTHOR]

As 3-D geological models become more numerous and widely available, the opportunity arises to combine them into large regional compilations. One of the biggest challenges facing these compilations is the connection and alignment of individual models, especially in less explored areas or across political borders. In this regard, gravity modelling is suitable for revealing additional subsurface information that can support a harmonization of structural models. Here, we present an integrated geological and gravity modelling approach to support the harmonization process of two geological 3-D models of the North German Basin in the cross-border region between the federal states of Saxony-Anhalt and Brandenburg. Gravity gradient calculation, filtering and Euler deconvolution are utilized to reveal new insights into the local fault system and gravity anomaly sources. The independent models are merged and harmonized during 3-D forward and inverse gravity modelling. Herein, density gradients for individual layers are incorporated in the framework of model parametrization. The resulting geological 3-D model consists of harmonized interfaces and is consistent with the observed gravity field. To demonstrate the plausibility of the derived model, we discuss the new geophysical findings on the sedimentary and crustal structures of the cross-border region in the context of the regional geological setting. The cross-border region is dominated by an NW–SE oriented fault system that coincides with the Elbe Fault System. We interpret a low-density zone within the basement of the Mid-German Crystalline Rise as a northward continuation of the Pretzsch–Prettin Crystalline Complex into the basement of the North German Basin. Additionally, we observe two types of anticlines within the basin, which we link to provinces of contrasting basement rigidity. Our gravity modelling implies that the Zechstein salt has mostly migrated into the deeper parts of the basin west of the Seyda Fault. Finally, we identify a pronounced syncline that accommodates a narrow and up to 800 m deep Cenozoic basin. [ABSTRACT FROM AUTHOR]

In this paper, we use a censored regression model to investigate data on the international trade of small arms and ammunition provided by the Norwegian Initiative on Small Arms Transfers. Taking a network‐based view on the transfers, we do not only rely on exogenous covariates but also estimate endogenous network effects. We apply a spatial autocorrelation gravity model with multiple weight matrices. The likelihood is maximized employing the Monte Carlo expectation maximization algorithm. Our approach reveals strong and stable endogenous network effects. Furthermore, we find evidence for a substantial path dependence as well as a close connection between exports of civilian and military small arms. The model is then used in a 'forensic' manner to analyse latent network structures and thereby to identify countries with higher or lower tendency to export or import than reflected in the data. The approach is also validated using a simulation study. [ABSTRACT FROM AUTHOR]

In this paper, we document border effects in the award of public contracts in the European single market. We use a dataset of 1.8 million contract awards, which we match to geolocations to estimate a gravity model of procurement flows between European NUTS3 region pairs. We find very sizable cross-national border effects for all types of goods and services, even after controlling for physical distance, currency, cultural differences and other variables. For example, 'local' bidders for IT services contracts are almost 250 times more likely to be awarded a contract than 'foreign' bidders. More surprisingly, we find substantial cross-regional border effects within countries. While we document that firms' bidding decisions are subject to border effects, we cannot exclude a home bias of contracting authorities in the award of public contracts. [ABSTRACT FROM AUTHOR]

The geographic pattern of cropland is an important risk factor for invasion and saturation by crop-specific pathogens and arthropods. Understanding cropland networks supports smart pest sampling and mitigation strategies. We evaluate global networks of cropland connectivity for key vegetatively propagated crops (banana and plantain, cassava, potato, sweet potato, and yam) important for food security in the tropics. For each crop, potential movement between geographic location pairs was evaluated using a gravity model, with associated uncertainty quantification. The highly linked hub and bridge locations in cropland connectivity risk maps are likely priorities for surveillance and management, and for tracing intraregion movement of pathogens and pests. Important locations are identified beyond those locations that simply have high crop density. Cropland connectivity risk maps provide a new risk component for integration with other factors—such as climatic suitability, genetic resistance, and global trade routes—to inform pest risk assessment and mitigation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multilevel gravity model of migration to study the under-researched topic of urban to urban migration in China. Many previous studies have looked at rural to urban migration in the context of urbanisation and economic development, and at return migration. Very few have looked at what is becoming more important in increasingly urbanised countries, which is the movement from one urban location to another. In the study, we develop a new method that allows for the interconnections between migration flows: between those that share an origin, those that share a destination, and where there is a reciprocal flow between places. A conventional gravity model of migration ignores those connections, risking erroneous estimation of the regression parameters and of their statistical significance. It also ignores that those connections are of substantive interest—they reveal the interconnections between places regarding the numbers of migrants that they send and receive. We motivate and illustrate the advantages of our approach using 2010 interprovincial migration census data for China. The results obtained from the model confirm the effect of distance, of population size and of regional income levels. They show that there is greater variation in the numbers of migrants received by provinces than there is in the numbers sent, and that reciprocal migration between pairs of provinces is an important feature of what is happening in China, especially between the neighbouring provinces of Sichuan and Tibet. [ABSTRACT FROM AUTHOR]

This article studies the determinants of international students' mobility at the university level, focusing specifically on the role of tuition fees. We derive a gravity model from a Random Utility Maximization model of location choice for international students in the presence of capacity constraints of the hosting institutions. The last layer of the model is estimated using new data on student migration flows at the university level for Italy. We control for the potential endogeneity of tuition fees through a classical IV approach based on the status of the university. We obtain evidence for a robust and negative effect of fees on international student mobility, with an elasticity around −0.8. The estimations also confirm the positive impact of the quality of the education and support an important role of additional destination-specific variables such as host capacity, the expected return of education, the cost of living and the existence of education programs taught in English. [ABSTRACT FROM AUTHOR]

In global agricultural value-chains, private food standards are proliferating. Yet, their trade effects remain poorly understood. This paper assesses the effect of GlobalGAP certification on exports of apples, bananas and grapes. We estimate a structural gravity model using a global dataset of certified producers and the share of certified land area in total harvest area. While our results confirm GlobalGAP standards as catalysts to trade, we find that the trade-enhancing effect varies across products and destination markets. Furthermore, the trade effect is driven more by growth in the area of certified farms than by new certified producers. [ABSTRACT FROM AUTHOR]

The abundant trade literature offers little insight on how diesel prices affect intranational trade. We fill this gap by calibrating a structural gravity model to recent U.S. interstate trade data. We discover that, for any distance, the elasticity of trade to diesel prices is much greater for low-valued commodities than for high-valued commodities. The general equilibrium result shows that a nationwide diesel price increase leads to heterogeneous decreases in trade across distances from the exporting state because of adjustments in multilateral costs and trade portfolio. Moreover, it increases the share of high-valued commodities in interstate trade. [ABSTRACT FROM AUTHOR]

We analyze a large data set of commercial records produced by Assyrian merchants in the nineteenth century BCE. Using the information from these records, we estimate a structural gravity model of long-distance trade in the Bronze Age. We use our structural gravity model to locate lost ancient cities. In many cases, our estimates confirm the conjectures of historians who follow different methodologies. In some instances, our estimates confirm one conjecture against others. We also structurally estimate ancient city sizes and offer evidence in support of the hypothesis that large cities tend to emerge at the intersections of natural transport routes, as dictated by topography. Finally, we document persistent patterns in the distribution of city sizes across four millennia, find a distance elasticity of trade in the Bronze Age close to modern estimates, and show suggestive evidence that the distribution of ancient city sizes, inferred from trade data, is well approximated by Zipf's law. [ABSTRACT FROM AUTHOR]

The ice cap covering Antarctica has long limited our understanding of the continental-scale crustal model due to its inaccessibility and the resulting logistical difficulties when executing geophysical field work, such as seismograph deployment. Resolving a high spatial resolution crustal model for Antarctica where seismographs are sparsely distributed stimulates scientific interest in this relatively less studied continent. In this study, we utilize satellite gravity observations from the global gravity model EIGEN-6C4 to create an alternative crustal thickness model of Antarctica. The gravity data were corrected for sediments, topography and ice cover. Furthermore, we considered the gravity effect due to vertical deformation of the lithosphere caused by ice load besides the earth's curvature in the modelling. We inverted the corrected gravity data using the regularized Bott's inversion method in spherical approximation and constrained the results by seismic observations. This crustal thickness model shows a thicker average crust in East Antarctica and a thinner one in West Antarctica. The thickest crust is in the Gamburtsev Subglacial Mountains with a Moho depth of over 40 km. The thicker crust is particularly evident along the Transantarctic Mountains and the Dronning Maud lands. Comparisons with existing models show a good correlation in gravity-constrained areas. Differences appear in the sedimentary basins and crust with thickness closer to seismic point observations. Overall, our crustal model is relatively improved than the existing gravity derived models. [ABSTRACT FROM AUTHOR]

A study is presented using a mesh-free approach and a radial basis function generated finite difference (RBF-FD) method for numerically modelling 3-D gravity data. The gravity responses, that is, vertical gravity and gravity gradients, are obtained by solving the partial differential equation (PDE), that is, the Poisson's equation for gravitational potential. The mesh-free approach discretizes PDEs using exclusively a cloud of unconnected nodes, instead of traditional tessellated meshes as used by mesh-based numerical methods such as finite difference, finite element and finite volume. Thus, the potentially computationally expensive and unstable creation and manipulation of 3-D meshes can be entirely avoided. A new type of finite-smoothness radial basis functions (RBFs), namely, the quintic-order polyharmonic spline (PHS) RBF, is proposed here in the RBF-FD frame for solving the gravity problem. Previous geophysical data modelling studies using RBF-FD have employed the infinitely smooth RBFs, such as the popular Gaussian (GA) RBFs. Here, both GA and PHS RBFs were tested with different numbers of nodes per mesh-free subdomain and with various shape parameter values (only GA RBFs have a shape parameter). The test results show that the PHS RBF-FD method is more computationally efficient than the GA RBF-FD counterpart. To achieve more efficiency, unstructured node distributions are proposed in discretizing the density models. For both quasi-uniform and unstructured node distributions, numerical results from the proposed PHS RBF-FD demonstrate that the computed vertical gravity and gravitational potential values agree well with analytical solutions with a reasonable number of degrees of freedom. A comparison study of modelling a complex density model with the PHS RBF-FD scheme and nodal finite-element method shows that the RBF-FD scheme generates sparse, asymmetric, linear systems of equations, supports unstructured nodal discretization and local refinement, and can have nonlinear h -convergence under refinement. Finally, the proposed RBF-FD method was applied to obtain the vertical gravity and gravity gradients over a real-world density model, where the benefits of mesh-free discretization are clearly illustrated. [ABSTRACT FROM AUTHOR]

A new strategy for the reconstruction of |$f(R)$| gravity models has been attempted using the Raychaudhuri equation. Two examples, one for an eternally accelerating universe and the other for one that mimics a lambda cold dark matter expansion history, have been worked out. For both the cases, the relevant |$f=f(R)$| can be found out analytically. In the first case, |$f(R)$| is found to be a combination of power-law terms and the expression for the second case involves hypergeometric functions. The evolution history of an universe, given as specific values of the kinematical quantities like the jerk or the deceleration parameter, serves as the input. It is found that the corresponding |$f(R)$| gravity models, in both the examples, are not viable options. [ABSTRACT FROM AUTHOR]

Summary: The growth of the global airline network has increased the importance of modelling origin–destination air passenger flows for better operational planning and scheduling. Origin–destination air passenger flows are correlated both spatially and temporally because of spatial and temporal relationships of human behaviours and environments. However, most existing studies for modelling air passenger flows have assumed that these relationships are independent; few studies have considered either spatial or temporal dependences. To consider both, we develop a spatiotemporal auto‐regressive model for monthly origin–destination air passenger flows. Benefitting from the special structure of a spatiotemporal dependence matrix, the model proposed can be extended to incorporate multi‐dimensional auto‐regressive coefficients for more flexible modelling. Its application to a real open access aviation data set demonstrates the effectiveness of the proposed model in forecasting monthly air passenger flows. [ABSTRACT FROM AUTHOR]

Measurements of redshift space distortions (RSD) provide a means to test models of gravity on large scales. We use mock galaxy catalogues constructed from large N -body simulations of standard and modified gravity models to measure galaxy clustering in redshift space. We focus our attention on two of the most representative and popular families of modified gravity models: the Hu & Sawicki f (R) gravity and the normal branch of the Dvali−Gabadadze−Porrati (DGP) model. The galaxy catalogues are built using a halo occupation distribution (HOD) prescription with the HOD parameters in the modified gravity models tuned to match with the number density and the real-space clustering of boss-cmass galaxies. We employ two approaches to model RSD: the first is based on linear perturbation theory and the second models non-linear effects on small scales by assuming standard gravity and including biasing and RSD effects. We measure the monopole to real-space correlation function ratio, the quadrupole to monopole ratio, clustering wedges, and multipoles of the correlation function and use these statistics to find the constraints on the distortion parameter, β. We find that the linear model fails to reproduce the N -body simulation results and the true value of β on scales |$s \lt 40\, h^{-1}\, {\rm Mpc}$|⁠, while the non-linear modelling of RSD recovers the value of β on the scales of interest for all models. RSD on large scales (⁠|$s\gtrsim 20\!-\!40\, h^{-1}\, {\rm Mpc}$|⁠) have been found to show significant deviations from the prediction of standard gravity in the DGP models. However, the potential to use RSD to constrain f (R) models is less promising, due to the different screening mechanism in this model. [ABSTRACT FROM AUTHOR]

The 13°N segment of the Mid-Atlantic Ridge is an example of a morphologically well-studied slow spreading ridge segment populated with oceanic core complexes (OCCs). In this paper we present the results of an ∼200-km-long 2-D seismic and gravity transect through this segment, the bounding fracture zones to the south and the ridge discontinuity to the north. We use this transect to consider the two end-member models of OCC evolution in which one, referred to as the Segment-scale model, implies they are interconnected with their detachments being part of a single segment-long feature, and the other, the Localized model, that each OCC is structurally isolated. We show, using the 7.5 km s−1 velocity contour as the base of crust marker, that the crust is consistently relatively thin ridge-parallel, at ∼5 km thick on average, and that, beneath the OCCs, the Moho marks the top of a velocity gradient transition into the mantle, rather than a distinct velocity discontinuity. Although each OCC is not traversed in an identical structural location, they show a different crustal velocity–density structure with depth, with along axis variations in this structure mirrored by the bathymetric deeps between them. Older OCCs have a contrasting velocity–depth signature to the currently active 13°20′N OCC. The 13°20′N OCC is distinct in that it does not show higher relative velocity at shallower crustal depth like its neighbours, while the 13°30′N OCC has an apparently thinner crust. Our combined P -wave seismic traveltime tomography and gravity forward modelling suggests that the OCCs of the 13°N segment are not interconnected at depth. To the north of the 13°30′N OCC, our modelling also suggests that the crust is being magmatically refreshed, or that the ridge axis is currently undergoing magmatic accretion with an associated ridge tip propagation occurring across the ridge discontinuity that marks its northern edge. The profile also crosses the Marathon and Mercurius fracture zones that mark the southern limit of the 13°N segment and the southern ridge-transform intersection outside corner. Along profile, Marathon fracture zone offsets younger (∼1 Myr versus ∼8 Myr) oceanic crust than Mercurius fracture zone (∼8 Myr versus ∼11 Myr). When considered in combination, both seismic and gravity modelling suggest crustal thinning in the direct vicinity of the bathymetric valley of Marathon fracture zone, coupled with a region of low density that, most likely, reflects serpentinization of the uppermost mantle. In addition, the crust captured between fracture zones appears relatively rotated about an E–W axis and uplifted to the north, with the upwards motion accommodated on the northern lateral edge of the bathymetric depression rather than in its centre. Both the outside corner and the crust bounded by fracture zones have velocity–depth characteristics similar to that of the 13°N segment OCCs rather than normally accreted oceanic crust, particularly in the upper-to-middle crust. Overall, our results support the Localized model of OCC evolution and suggest that fracture zones do not become locked immediately on transform-to-fracture transition as current models dictate. [ABSTRACT FROM AUTHOR]

An earthquake (2016M5.8_GY) occurred on 2016 September 12 due to the SW−NE movement of the Yangsan fault in the Gyeongsang Basin in the southeastern part of the Korean Peninsula and caused more than 600 aftershocks within a 1-yr period. To find out the causes and process of the 2016M5.8_GY and its aftershocks, we conducted 3-D underground structural modelling of the Gyeongju area using a combined interpretation of geological, petrophysical and potential field data and hence calculated the density- and magnetic-field distribution along the Yangsan fault. The results of the 3-D modelling indicate that the 2016M5.8_GY occurred in the ductile region of the fault, which is tectonically very unstable, and is therefore highly likely to be significantly affected by any future seismological stress. The crustal structure most affected by the 2016M5.8_GY is the Cretaceous Granite, which has a vertical relief of approximately 12 km with a relatively lower density material than the surrounding country rock and rests on highly ductile material. Therefore, the lower part of the granite is enough unstable that it was probably crushed by the main shock. That is also the reason, why so many aftershocks occurred beneath the granites. [ABSTRACT FROM AUTHOR]

In this paper, we quantify the "Cost of Non-Europe", that is, the trade-related welfare gains each country member has reaped from the European Union (EU). Thirty years after the terminology of Non-Europe was used to give estimates of the gains from further integration, we use modern versions of the gravity model to estimate the trade creation implied by the EU, and apply those to counterfactual exercises where for instance the EU returns to a "normal," shallow-type regional agreement, or reverts to WTO rules. Those scenarios are envisioned with or without the exit of the United Kingdom from the EU (Brexit) happening, which points to interesting cross-country differences and potential cascade effects in doing and undoing of trade agreements. [ABSTRACT FROM AUTHOR]

This article considers the effect of China's Belt and Road Initiative on supply-chain trade for 64 economies in the period 2002–2011. We employ a structural gravity equation to estimate the impact of trade-cost reducing measures—notably infrastructural improvements and the creation of free trade agreements—on supply-chain trade and welfare in general equilibrium. We find that infrastructural investments will yield asymmetric benefits to China, Russia and Southeast Asian countries stemming from greater European market access. Our results also suggest that China's alternatives to foster (inter)regional economic growth through the Regional Comprehensive Economic Partnership and the Trans-Pacific Partnership offer much less attractive economic prospects. [ABSTRACT FROM AUTHOR]

We study the gains from trade liberalization in models with monopolistic competition, firm-level heterogeneity, and variable markups. For a large class of demand functions used in the international macro and trade literature, we derive a parsimonious generalization of the welfare formula in Arkolakis et al. (2012). We then use both estimates from micro-level trade data and evidence regarding firm-level pass-through to quantify the implications of this new formula. Within the class of models that we consider, our main finding is that gains from trade liberalization predicted by models with variable markups are equal to, at best, and slightly lower than, at worst, those predicted by models with constant markups. In this sense, pro-competitive effects of trade are elusive. [ABSTRACT FROM AUTHOR]

We analyse the two-point and marked correlation functions (mCFs) of haloes and galaxies in three variants of the chameleon f (R) gravity model using N -body simulations, and compare to a fiducial Λ cold dark matter model based on general relativity (GR). Using a halo occupation distribution (HOD) prescription, we populate dark matter haloes with galaxies, where the HOD parameters have been tuned such that the galaxy number densities and the real-space galaxy two-point correlation functions in the modified gravity models match those in GR to within 1–3 per cent. We test the idea that since the behaviour of gravity is dependent on environment, mCFs may display a measurable difference between the models. For this we test marks based on the density field and the Newtonian gravitational potential. We find that the galaxy mCF shows significant differences measured in different models on scales smaller than r ≲ 20  h −1 Mpc. Guided by simulations to identify a suitable mark, this approach could be used as a new probe of the accelerated expansion of the Universe. [ABSTRACT FROM AUTHOR]

Migration facilitates the flow of information between countries, thereby reducing informational frictions that potentially hamper cross-country financial flows. Using a gravity model, migration is found to be highly correlated with financial flows from the migrant's host country to her home country. The correlation is strongest where information problems are more acute (e.g., between culturally more distant countries), for asset types that are more informational sensitive, and for the type of migrants that are most able to enhance the flow of information on their home countries, namely, skilled migrants. These differential effects are interpreted as evidence for the role of migration in reducing information frictions between countries. [ABSTRACT FROM AUTHOR]

This article explores the effect of neighborhood land use on land use change in Mato Grosso, Brazil, one of the world's most dynamic agricultural frontiers. Using an innovative combination of spatial statistics and remotely sensed data, this research shows that the likelihood of an area being converted to agriculture is closely tied to how land is used in a location's surroundings. The results also suggest that this spatial spillover effect cannot be tied exclusively to the distribution of natural suitability characteristics. Rather, the likelihood of an area being converted to agriculture appears to reflect the dynamic socio-economic conditions of a location's surroundings. The findings imply that (i) agricultural agencies or experts seeking to support developing agricultural regions should recognize the importance of returns to scale and local clustering and that (ii) land use modeling can be improved by accounting for suitability and land uses in nearby locations. [ABSTRACT FROM AUTHOR]

This article analyses the determinants of growing demand for agricultural land in developing countries. We propose some determinants that are specific to foreign acquisitions of agricultural land as a subset of agricultural foreign direct investment (FDI) and empirically examine the corresponding locational choice. Using a gravity model and a data set on land acquisitions worldwide, we find that the determinants partly overlap with those for other forms of FDI but are specific in certain regards. Rich investors target (poorer) economies with abundant land and water resources, and the effects of the quality of institutions are ambiguous. [ABSTRACT FROM AUTHOR]

Individuals that consume different baskets of goods are differentially affected by relative price changes caused by international trade. We develop a methodology to measure the unequal gains from trade across consumers within countries. The approach requires data on aggregate expenditures and parameters estimated from a nonhomothetic gravity equation. We find that trade typically favors the poor, who concentrate spending in more traded sectors. JEL Codes: D63, F10, F60. [ABSTRACT FROM AUTHOR]

We present efficient Fourier-domain algorithms for modelling gravity effects due to topographic masses. The well-known Parker's formula originally based on the standard fast Fourier transform (FFT) algorithm is modified by applying the Gauss-FFT method instead. Numerical precision of the forward and inverse Fourier transforms embedded in Parker's formula and its extended forms are significantly improved by the Gauss-FFT method. The topographic model is composed of two major aspects, the geometry and the density. Versatile geometric representations, including the mass line model, the mass prism model, the polyhedron model and smoother topographic models interpolated from discrete data sets using high-order splines or pre-defined by analytical functions, in combination with density distributions that vary both laterally and vertically in rather arbitrary ways following exponential or general polynomial functions, now can be treated in a consistent framework by applying the Gauss-FFT method. The method presented has been numerically checked by space-domain analytical and hybrid analytical/numerical solutions already established in the literature. Synthetic and real model tests show that both the Gauss-FFT method and the standard FFT method run much faster than space-domain solutions, with the Gauss-FFT method being superior in numerical accuracy. When truncation errors are negligible, the Gauss-FFT method can provide forward results almost identical to space-domain analytical or semi-numerical solutions in much less time. [ABSTRACT FROM AUTHOR]

This article empirically investigates the impact of trade barriers on the world wine trade focusing on trade costs impeding exports, including transport, tariffs, technical barriers and sanitary and phytosanitary (SPS) standards. Agravity model is estimated using data from the main importing and exporting countries for the years 1997-2010. The Poison pseudo-maximum likelihood estimator accounts for heteroskedasticity and the presence of zero trade flows. Our results identify which regulations can adversely affect trade providing useful information to policy-makers involved in negotiations on trade frictions. While SPS measures do not seem to obstruct exports, technical barriers have a varying impact on trade. A decreasing trend for tariffs has largely been compensated by more stringent technical barriers. The overall result is that frictions in the world wine trade have not changed during the past 15 years. [ABSTRACT FROM AUTHOR]

Statistical analyses of health programme participation seek to address a number of objectives that are compatible with the evaluation of demand for current resources. In this spirit, a spatial hierarchical model is developed for disentangling patterns in participation at the small area level, as a function of population-based demand and additional variation. For the former, a constrained gravity model is proposed to quantify factors associated with spatial choice and to account for competition effects, for programmes delivered by multiple clinics. The implications of gravity model misspecification within a mixed effects framework are also explored. The model proposed is applied to participation data from a no-fee mammography programme in Brisbane, Australia. Attention is paid to the interpretation of various model outputs and their relevance for public health policy. [ABSTRACT FROM AUTHOR]

This paper presents efficient numerical schemes for 3-D gravity field inversion. We propose a 2-D multilayer model to approximate a 3-D density distribution, and prove that the solution of the multilayer model will converge to the discretized 3-D solution. Differed from the conventional fast Fourier transform (FFT) based methods in which FFT is applied to the kernel, the proposed approach directly generates the Block-Toeplitz Toeplitz-Block (BTTB) structure by discretizing the multilayer model and the BTTB matrix is embedded into a Block-Circulant Circulant-Block (BCCB) matrix such that FFT can be utilized. In this approach, both regularization and optimal pre-conditioning operator can be constructed in the form of BTTB matrix. Consequently, very efficient solvers can be developed, and tremendous reduction in storage requirement and computing time can be achieved. To validate the new approach, numerical simulations using synthetic and real field data are reported, and numerical analysis is carried out for the inversion problems. Based on this study, we conclude that the proposed methods are capable of performing large-scale 3-D density inversions with amodest computing resource. [ABSTRACT FROM AUTHOR]

Gravity variations associated with Earth's oblateness (J2) have been observed by satellite laser ranging (SLR) since 1976. The J2 time-series has been used to measure and help understand many geophysical processes within the Earth system ranging from the mantle to the atmosphere. While post glacial rebound and the Earth climate system are believed to be the primary driving forces of long-termand seasonal J2 variations, the physical cause of decadal and longer timescale J2 variations has remained uncertain, although recent evidence indicates that polar ice mass changes are important. In this study, we estimate a variety of climate contributions to J2 over the period 1979-2010, and find that ice mass variations in Greenland and Antarctica are the dominant cause of observed decadal and longer J2 variations. Residual variations at periods near 10-11 years may reflect limitations of numerical climate models in estimating mass change variability at long periods, but are also suggestive of potential contribution related to variable solar activity. [ABSTRACT FROM AUTHOR]

The 2003 CAP reform introduced decoupled income transfers as a prominent policy instrument. However, member states were given discretion over the degree and timing of the reform implementation. As a result, different implementation schemes coexist, keeping certain parts of the income support coupled. This coexistence leads to distortions of production incentives, factor misallocations and artificial trade flows. Here, we examine these effects in the beef sector where full decoupling was not obligatory. We derive a sector-specific trade model to examine the effects of different implementation schemes on intra-European calf trade. Empirical results confirm that trade flow distortions occurred. [ABSTRACT FROM AUTHOR]

This paper describes an alternative acceleration approach for determining GRACE monthly gravity field models. The main differences compared to the traditional acceleration approach can be summarized as: (1) The position errors of GRACE orbits in the functional model are taken into account; (2) The range ambiguity is eliminated via the difference of the range measurements and (3) The mean acceleration equation is formed based on Cowell integration. Using this developed approach, a new time-series of GRACE monthly solution spanning the period January 2003 to December 2010, called Tongji_Acc RL01, has been derived. The annual signals from the Tongji_Acc RL01 time-series agree well with those from the GLDAS model. The performance of Tongji_Acc RL01 shows that this new model is comparable with the RL05 models released by CSR and JPL as well as with the RL05a model released by GFZ. [ABSTRACT FROM AUTHOR]

Though the concept of innovation systems has become influential in both academia and policy-making, an analytical approach to understanding innovation systems is still lacking. In particular, there is no analytical framework to measure 'Mode 1' and 'Mode 2' knowledge production. We propose a framework based on the proximity concept. Mode 1 and Mode 2 knowledge production are characterized by collaborations with cognitive, organizational, social, institutional and geographical proximity, and distance, respectively. Using a gravity model approach we apply our framework to the case of type 2 diabetes research and provide a characterization of the global innovation system and a comparative analysis of the North American and European innovation systems. Our main results hold that although collaborative research on type 2 diabetes generally follows a logic of proximity and hence is not characterized as Mode 2, important differences and similarities exist between the North American and European innovation systems. [ABSTRACT FROM AUTHOR]

Recent years have seen a surge in economic integration agreements (EIAs) and the development of non-tariff measures (NTMs). As a consequence, a growing number of EIAs include provisions on NTMs. However, little attention has been given in the literature to the effects of NTM liberalization in the context of EIAs. In this paper, we focus on provisions for technical regulations and analyze whether the North-South harmonization of technical barriers affects international trade. Using a gravity equation, we test whether, as a result of the deep integration associated with standards provisions included in the EIA, the Southern partners' trade expands with the North, but at the expense of their trade with non-bloc Southern partners. Empirical results provide strong support for this conjecture. Moreover, harmonization on the basis of regional standards negatively impacts the exports of developing countries to the North. [ABSTRACT FROM AUTHOR]

This paper studies the impacts and determinants of trade policy: preferential trade agreements and multilateral opening. I estimate sector-level trade elasticities to calibrate a multi-sector Armington model of trade. I then use it to compute the price and real wage impacts of trade policy over 2001-2007, as well as the impacts of hypothetical, nonsigned trade agreements. I find that real wage gains positively predict the probability to sign a preferential agreement. Gains from multilateral opening reduce this probability. Finally, expected production price increases, reflecting market access gains, are a stronger determinant of the signing of PTAs than gains in the form of lower consumption prices. [ABSTRACT FROM AUTHOR]

While most research on foreign direct investment (FDI) focuses on the ‘real’ economy, at least 30% of global FDI stock is intermediated through tax havens. Using 2010 IMF data on FDI stocks, this article sheds new light on geographical, historical and political determinants of offshore FDI. Despite its intangibility, offshore FDI is as sensitive to physical distance as real FDI. Offshore FDI links are particularly strong between colonial powers and their current and former colonies. The OECD, while officially leading an agenda against tax evasion, internalizes significant offshore FDI within its membership. Indeed, offshore FDI is pervasive, affecting wealthy economies as much as developing countries. [ABSTRACT FROM PUBLISHER]

Genetic distance, geographic proximity, and economic variables are strongly correlated. Disentangling the effects of these factors is crucial for interpreting these correlations. We show that geographic factors that shaped genetic patterns in the past are also relevant for current transportation costs and could explain the correlation between trading flows and genetic distance. After controlling for geography, the impact of genetic distance on trade disappears. We make our point by constructing a database on geographical barriers, by introducing a novel dataset on transportation costs, and by proposing a new classification of goods according to the ease with which they can be transported. [ABSTRACT FROM PUBLISHER]

In the analysis of bilateral trade flows, reported trade of zero or missing observations is quite common and this is a problem when estimating log-linear gravity equations. This has caused many researchers to either ignore the zero trade flows or replace the zero with a small positive number. Both of these actions bias the resulting parameter estimates of the gravity equation. In this study, we correct for this misspecification by using the Heckman selection model to estimate bilateral trade flows for 46 agrifood products, for the period 1990–2000, for 52 countries. In our sample, selection bias rarely affects the signs of variables but often has a substantial effect on the magnitude, statistical significance and economic interpretation of the marginal effects. Hence, treating zero trade flows properly is important from both a statistical and an economics perspective. [ABSTRACT FROM AUTHOR]