The Energy of Scattering Solitons in the Ward Model

The energy density of a scattering soliton solution in Ward's integrable chiral model is shown to be instantaneously the same as the energy density of a static multi-lump solution of the \CP^3 sigma model. This explains the quantization of the total energy in the Ward model.Comment: 12 pages, 2 figure

Skyrmions, Rational Maps & Scaling Identities

Starting from approximate Skyrmion solutions obtained using the rational map ansatz, improved approximate Skyrmions are constructed using scaling arguments. Although the energy improvement is small, the change of shape clarifies whether the true Skyrmions are more oblate or prolate.Comment: 13 pages, 3 figure

Monetary Policy, Risk-Taking, and Pricing: Evidence from a Quasi-Natural Experiment

We analyse the impact of monetary policy on bank risk-taking and pricing. Bolivia provides us with an excellent experimental setting to identify this impact. Its small economy is not synchronized with the US economy but its banking system is almost fully dollarized. Consequently the US federal funds rate is the appropriate measure of monetary policy. We study the impact of the federal funds rate on the riskiness and pricing of new bank loans granted in Bolivia between 1999 and 2003, a period of significant variation in the federal funds rate. We find robust evidence that a decrease in the US federal funds rate prior to loan origination raises the monthly probability of default on individual bank loans. We also find that initiating loans with a subprime credit rating or loans to riskier borrowers with current or past non-performance become more likely when the federal funds rate is low. However, loan spreads do not increase, seemingly even decrease, in changes in the probability of default. Hence banks do not seem to price the additional risk taken. Furthermore, banks with more liquid assets and less funds from foreign financial institutions take more risk when the federal funds rate is low, and reduce loan spreads more despite the additional risk they seemingly take.monetary policy;federal funds rate;lending standards;credit risk;subprime borrowers;duration analysis

Stock prices and output growth: an examination of the credit channel

When stock market values fall, we know that investors expect lower economic growth in the future. But can stock market declines actually affect future growth? There is some evidence that they can-through the credit channel.Stock - Prices

Radon measurements along active faults in the Langadas Basin, northern Greece

A network of three radon stations has been established in the Langadas Basin, northern Greece for radon monitoring by various techniques in earthquake prediction studies. Specially made devices with plastic tubes including Alpha Tracketch Detectors (ATD) were installed for registering alpha particles from radon and radon decay products exhaled from the ground, every 2 weeks, by using LR-115, type II, non-strippable Kodak films, starting from December 1996. Simultaneous measurements started using Lucas cells alpha spectrometer for instantaneous radon measurements in soil gas, before and after setting ATDs at the radon stations. Continuous monitoring of radon gas exhaling from the ground started from the middle of August 1999 by using silicon diode detectors, which simultaneously register meteorological parameters, such as rainfall, temperature and barometric pressure. The obtained data were studied together with the data of seismic events, such as the magnitude, <i>M_L</i>, of earthquakes that occurred at the Langadas Basin during the period of measurements, as registered by the Laboratory of Geophysics, Aristotle University of Thessaloniki, in order to find out any association between them

Reduced dynamics of Ward solitons

The moduli space of static finite energy solutions to Ward's integrable chiral model is the space $M_N$ of based rational maps from \CP^1 to itself with degree $N$. The Lagrangian of Ward's model gives rise to a K\"ahler metric and a magnetic vector potential on this space. However, the magnetic field strength vanishes, and the approximate non--relativistic solutions to Ward's model correspond to a geodesic motion on $M_N$. These solutions can be compared with exact solutions which describe non--scattering or scattering solitons.Comment: Final version, to appear in Nonlinearit

Scattering of magnetic solitons in two dimensions

Solitons which have the form of a vortex-antivortex pair have recently been found in the Landau-Lifshitz equation which is the standard model for the ferromagnet. We simulate numerically head-on collisions of two vortex-antivortex pairs and observe a right angle scattering pattern. We offer a resolution of this highly nontrivial dynamical behavior by examining the Hamiltonian structure of the model, specifically the linear momentum of the two solitons. We further investigate the dynamics of vortices in a modified nonlinear sigma-model which arises in the description of antiferromagnets. We confirm numerically that a robust feature of the dynamics is the right angle scattering of two vortices which collide head-on. A generalization of our theory is given for this model which offers arguments towards an understanding of the observed dynamical behavior.Comment: 10 pages RevTeX, 9 figure

Topological discrete kinks

A spatially discrete version of the general kink-bearing nonlinear Klein-Gordon model in (1+1) dimensions is constructed which preserves the topological lower bound on kink energy. It is proved that, provided the lattice spacing h is sufficiently small, there exist static kink solutions attaining this lower bound centred anywhere relative to the spatial lattice. Hence there is no Peierls-Nabarro barrier impeding the propagation of kinks in this discrete system. An upper bound on h is derived and given a physical interpretation in terms of the radiation of the system. The construction, which works most naturally when the nonlinear Klein-Gordon model has a squared polynomial interaction potential, is applied to a recently proposed continuum model of polymer twistons. Numerical simulations are presented which demonstrate that kink pinning is eliminated, and radiative kink deceleration greatly reduced in comparison with the conventional discrete system. So even on a very coarse lattice, kinks behave much as they do in the continuum. It is argued, therefore, that the construction provides a natural means of numerically simulating kink dynamics in nonlinear Klein-Gordon models of this type. The construction is compared with the inverse method of Flach, Zolotaryuk and Kladko. Using the latter method, alternative spatial discretizations of the twiston and sine-Gordon models are obtained which are also free of the Peierls-Nabarro barrier.Comment: 14 pages LaTeX, 7 postscript figure

Deep stratosphere-to-troposphere transport (STT) over SE Europe: a complex case study captured by enhanced ⁷Be concentrations at the surface of a low topography region

International audienceIn this study we present a complex case study of a Stratosphere-to-Troposphere Transport (STT) event down to the surface of a low topography region in Northern Greece, during the second fortnight of March 2000. During this event our surface station at Livadi (23°15 E/40°32 N, 850 m a.s.l.), was influenced by very different synoptic systems developing over Eastern Europe, N. America and the N. Atlantic, the last one evolving to a cut-off low over France/Spain. This is the first study, to our knowledge, that presents a down to the surface STT event in the eastern Mediterranean. The intrusion is primarily captured with the use of the cosmogenic radionuclide 7Be, which increased to 9.07 mBq m-3 and 9.37 mBq m-3 on 30 and 31 March 2000, respectively. A 7Be concentration of around 8 mBq m-3 recorded during parallel measurements at Thessaloniki (20 m a.s.l.) gives strong evidence that air of stratospheric origins has even gone down to sea level. A rapid increase of 10?15 ppb is also observed in the surface ozone concentration on 31 March 2000. The relative increase of both tracers is consistent with a volume fraction of stratospheric air at the surface of about 5%, but the substantial increase in 7Be flags more clearly the event. Trajectory analyses, in conjunction with the evolution of the synoptic situation described by potential vorticity maps, are used for the exact identification of the different intrusions and the attribution of each intruding parcel of stratospheric air to a certain filament of high PV. Finally, the persistency of the stratospheric layers in the troposphere is another interesting point of this case study. The vast majority of the trajectories spent 7?10 days in the troposphere before reaching the surface at Livadi station