Vortexje - An Open-Source Panel Method for Co-Simulation

This paper discusses the use of the 3-dimensional panel method for dynamical system simulation. Specifically, the advantages and disadvantages of model exchange versus co-simulation of the aerodynamics and the dynamical system model are discussed. Based on a trade-off analysis, a set of recommendations for a panel method implementation and for a co-simulation environment is proposed. These recommendations are implemented in a C++ library, offered on-line under an open source license. This code is validated against XFLR5, and its suitability for co-simulation is demonstrated with an example of a tethered wing, i.e, a kite. The panel method implementation and the co-simulation environment are shown to be able to solve this stiff problem in a stable fashion.Comment: 13 pages, 8 figure

Uncertainty Aversion and Backward Induction

In the context of the centipede game this paper discusses a solution concept for extensive games that is based on subgame perfection and uncertainty aversion. Players who deviate from the equilibrium path are considered non- rational. Rational players who face non-rational opponents face genuine uncertainty and may have non-additive beliefs about their future play. Rational players are boundedly uncertainty averse and maximise Choquet expected utility. It is shown that if the centipede game is sufficiently long, then the equilibrium strategy is to play `Across' early in the game and to play `Down' late in the game.

Assessing Vulnerability Before, During and After a Natural Disaster in Fragile Regions: Case Study of the 2004 Indian Ocean Tsunami in Sri Lanka and Indonesia

Current approaches of measuring vulnerability to natural hazards generally use a rather static perspective that focuses on a single point in time?often before a hazardous event occurs. In contrast, the paper argues that vulnerability assessment should also take into account the changing dynamics during and after a disaster. This paper provides a comparative analysis of the situation in Sri Lanka and Indonesia within the context of the 2004 Indian Ocean tsunami. The author presents concepts for measuring revealed vulnerabilities and methods of assessing the recovery process, and highlights the differing ways in which the tsunami affected the ongoing civil conflicts in both regions.vulnerability, dynamics, transition, natural hazards, fragile regions, Sri Lanka, Indonesia, coastal regions, tsunami

Uncertainty aversion and equilibrium in extensive games.

This paper formulates a rationality concept for extensive games in which deviations from rational play are interpreted as evidence of irrationality. Instead of confirming some prior belief about the nature of nonrational play, we assume that such a deviation leads to genuine uncertainty. Assuming complete ignorance about the nature of non-rational play and extreme uncertainty aversion of the rational players, we formulate an equilibrium concept on the basis of Choquet expected utility theory. Equilibrium reasoning is thus only applied on the equilibrium path, maximin reasoning applies off the equilibrium path. The equilibrium path itself is endogenously determined. In general this leads to strategy profiles differ qualitatively from sequential equilibria, but still satisfy equilibrium and perfection requirements. In the centipede game and the finitely repeated prisoners’ dilemma this approach can also resolve the backward induction paradox.

The influence of strong magnetic fields and instantons on the phase structure of the two-flavor NJL model

Both in heavy-ion collisions as in magnetars very strong magnetic fields are produced, which has its influence on the phases of matter involved. In this paper we investigate the effect of strong magnetic fields (B = 5 m_pi^2 /e = 1.7 x 10^19 G) on the chiral symmetry restoring phase transition using the Nambu-Jona-Lasinio model. It is observed that the pattern of phase transitions depends on the relative magnitude of the magnetic field and the instanton interaction strength. We study two specific regimes in the phase diagram, high chemical potential and zero temperature and vice versa, which are of relevance for neutron stars and heavy-ion collisions respectively. In order to shed light on the behavior of the phase transitions we study the dependence of the minima of the effective potential on the occupation of Landau levels. We observe a near-degeneracy of multiple minima with differing occupation numbers, of which some become the global minimum upon changing the magnetic field or the chemical potential. These minima differ considerably in the amount of chiral symmetry breaking and in some cases also of isospin breaking.Comment: 11 pages, 8 figures, references added and some minor change