Zero-field Time Correlation Functions of Four Classical Heisenberg Spins on a Ring

A model relevant for the study of certain molecular magnets is the ring of N=4 classical spins with equal near-neighbor isotropic Heisenberg exchange interactions. Assuming classical Heisenberg spin dynamics, we solve explicitly for the time evolution of each of the spins. Exact triple integral representations are derived for the auto, near-neighbor, and next-nearest-neighbor time correlation functions for any temperature. At infinite temperature, the correlation functions are reduced to quadrature. We then evaluate the Fourier transforms of these functions in closed form, which are double integrals. At low temperatures, the Fourier transform functions explicitly demonstrate the presence of magnons. Our exact results for the infinite temperature correlation functions in the long-time asymptotic limit differ qualitatively from those obtained assuming diffusive spin dynamics. Whether such explicitly non-hydrodynamic behavior would be maintained for large-N rings is discussed.Comment: 18 pages, 21 figure

The Virtue Epistemologists. Interview with Ernest Sosa

Entrevista con Ernesto Sosa realizada por Richard Marshall, publicada en la revista 3:A

Rethinking 'multi-user': an in-the-wild study of how groups approach a walk-up-and-use tabletop interface

Multi-touch tabletops have been much heralded as an innovative technology that can facilitate new ways of group working. However, there is little evidence of these materialising outside of research lab settings. We present the findings of a 5-week in-the-wild study examining how a shared planning application – designed to run on a walk-up- and-use tabletop – was used when placed in a tourist information centre. We describe how groups approached, congregated and interacted with it and the social interactions that took place – noting how they were quite different from research findings describing the ways groups work around a tabletop in lab settings. We discuss the implications of such situated group work for designing collaborative tabletop applications for use in public settings

When the fingers do the talking: A study of group participation for different kinds of shareable surfaces

and other research outputs When the fingers do the talking: A study of group par-ticipation for different kinds of shareable surface