Magnetic transition and polaron crossover in a two-site single polaron model including double exchange interaction

A two-site double exchange model with a single polaron is studied using a perturbation expansion based on the modified Lang-Firsov transformation. The antiferromagnetic to ferromagnetic transition and the crossover from small to large polaron are investigated for different values of the antiferromagnetic interaction ($J$) between the core spins and the hopping ($t$) of the itinerant electron. Effect of the external magnetic field on the small to large polaron crossover and on the polaronic kinetic energy are studied. When the magnetic transition and the small to large polaron crossover coincide for some suitable range of $J/t$, the magnetic field has very pronounced effect on the transport.Comment: REVTEX and ps files, accepted in the European Physical Jour.

A ROAD AHEAD FROM CANCUN? WEIGHING UP SOME GIVE-AND-TAKE SCENARIOS IN A DDA SPIRIT

Given that around 20 percent of the members of the World Trade Organisation (WTO) are identified as least developed countries (LDC's), global trade negotiations, resumed after the Cancun fiasco of September 2003, must address some major development issues in the spirit of the Doha Development Agenda (DDA), if they are to make any headway. This will, predictably, involve some sensible give-and-take not only between the developed countries and the LDC's, but also amongst the LDC's themselves, and between them and other developing countries. Issues of restrictions affecting agricultural trade - a major factor in the failure at Cancun - need re-addressing; but non-agricultural trade issues must also feature in the negotiations as that could make some acceptable policy compromises possible. This paper investigates, in a computable-general-equilibrium (CGE) framework, the welfare impacts on selected developed and developing country groupings of several scenarios of trade liberalisation that are likely to enhance agricultural and non-agricultural trade flows within the LDC's, and between them and other developing countries. The scenarios will involve experimentation with selected commodities that are of special export interest to LDC's to identify some modalities of trade liberalisation and policy reciprocity, that are more likely to be acceptable to all parties.International Relations/Trade,

Probing dense matter in neutron stars with axial w-modes

We study the problem of extracting information about composition and equation of state of dense matter in neutron star interior using axial w-modes. We determine complex frequencies of axial w-modes for a set of equations of state involving hyperons as well as Bose-Einstein condensates of antikaons adopting the continued fraction method. Hyperons and antikaon condensates result in softer equations of state leading to higher frequencies of first axial w-modes than that of nuclear matter case, whereas the opposite happens in case of damping times. The presence of condensates may lead to the appearance of a new stable branch of superdense stars beyond the neutron star branch called the third family. The existence of same mass compact stars in both branches are known as neutron star twins. Further investigation of twins reveal that first axial w-mode frequencies of superdense stars in the third family are higher than those of the corresponding twins in the neutron star branch.Comment: LaTeX; 23 pages including two tables and 11 figure