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,

Hyperon bulk viscosity in the presence of antikaon condensate

We investigate the hyperon bulk viscosity due to the non-leptonic process $n + p \rightleftharpoons p + \Lambda$ in $K^-$ condensed matter and its effect on the r-mode instability in neutron stars. We find that the hyperon bulk viscosity coefficient in the presence of antikaon condensate is suppressed compared with the case without the condensate. The suppressed hyperon bulk viscosity in the superconducting phase is still an efficient mechanism to damp the r-mode instability in neutron stars.Comment: AASTeX; 21 pages including 5 figures; change in the title and replaced by the revised versio