Notions of optimal transport theory and how to implement them on a computer

This article gives an introduction to optimal transport, a mathematical theory that makes it possible to measure distances between functions (or distances between more general objects), to interpolate between objects or to enforce mass/volume conservation in certain computational physics simulations. Optimal transport is a rich scientific domain, with active research communities, both on its theoretical aspects and on more applicative considerations, such as geometry processing and machine learning. This article aims at explaining the main principles behind the theory of optimal transport, introduce the different involved notions, and more importantly, how they relate, to let the reader grasp an intuition of the elegant theory that structures them. Then we will consider a specific setting, called semi-discrete, where a continuous function is transported to a discrete sum of Dirac masses. Studying this specific setting naturally leads to an efficient computational algorithm, that uses classical notions of computational geometry, such as a generalization of Voronoi diagrams called Laguerre diagrams.Comment: 32 pages, 17 figure

Chiral tensor fields and spontaneous breaking of Lorentz symmetry

Antisymmetric tensor fields interacting with quarks and leptons have been proposed as a possible solution to the gauge hierarchy problem. We compute the one-loop beta function for a quartic self-interaction of the chiral antisymmetric tensor fields. Fluctuations of the top quark drive the corresponding running coupling to a negative value as the renormalization scale is lowered. This may indicate a non-vanishing expectation value of the tensor field, and thus a spontaneous breaking of Lorentz invariance. Settling this issue will need the inclusion of tensor loops.Comment: 15 pages, 4 figure

On the Channel and Type of Aid: The Case of International Disaster Assistance

The aim of this paper is to determine the drivers of a donor’s decision on the composition of aid. We apply a dataset on international post-disaster assistance between 2000 and 2007 that includes information on the channel (bilateral vs. multilateral) and type (cash vs. in-kind) of each aid flow. Our results suggest that the choice of the channel and type of disaster assistance is mainly determined by strategic interests and transaction costs. Moreover, we find differences in the allocation behavior of OECD and non-OECD countries.Foreign aid, natural disasters, bilateral vs. multilateral, type of aid

Aid, natural disasters and the samaritan's dilemma

This paper discusses the impact of foreign aid on the recipient country's preparedness against natural disasters. The theoretical model shows that foreign aid can have two opposing effects on a country's level of mitigating activities. In order to test the theoretical propositions, the authors analyze the effect of foreign aid dependence on ex-ante risk-management activity proxied by the death toll from major storms, floods and earthquakes occurring worldwide between 1980 and 2002. They find evidence that the crowding-out effect of foreign aid outweighs the preventive effect in the case of storms, while there is mixed evidence in the case of floods and earthquakes.Natural Disasters,Hazard Risk Management,Disaster Management,Population Policies,Post Conflict Reconstruction

On the channel and type of international disaster aid

Research suggests that a donor country’s decision to provide post-disaster assistance is not only driven by the severity of a disaster and the resulting humanitarian needs in the recipient country, but also by strategic considerations. The authors argue that the identification of the determinants of the size of disaster assistance is a first step in the analysis of the donor’s behavior. Since all aid is not motivated by the same reasons, the evaluation of the donor country’s behavior requires a second step accounting for the type and the channel of aid provided. Using data on international disaster assistance between 2000 and 2007, the analysis examines both the donor countries'decision on the channel (bilateral versus multilateral) and the type of disaster relief (cash versus in-kind). The empirical results suggest that international disaster relief is not as much driven by the needs of the recipient country, but also by strategic interests (for example, oil or trade relationships) of the donor country. Bilateral and cash transfers are used as a vehicle to signal strategic interests, while multilateral and in-kind transfers are chosen to control for misuse in badly governed recipient countries.Hazard Risk Management,Natural Disasters,Gender and Health,Development Economics&Aid Effectiveness,Governance Indicators