Aspect-ratio dependence of the spin stiffness of a two-dimensional XY model

We calculate the superfluid stiffness of 2D lattice hard-core bosons at half-filling (equivalent to the S=1/2 XY-model) using the squared winding number quantum Monte Carlo estimator. For L_x x L_y lattices with aspect ratio L_x/L_y=R, and L_x,L_y -> infinity, we confirm the recent prediction [N. Prokof'ev and B.V. Svistunov, Phys. Rev. B 61, 11282 (1999)] that the finite-temperature stiffness parameters \rho^W_x and \rho^W_y determined from the winding number differ from each other and from the true superfluid density \rho_s. Formally, \rho^W_y -> \rho_s in the limit in which L_x -> infinity first and then L_y -> infinity. In practice we find that \rho^W_y converges exponentially to \rho_s for R>1. We also confirm that for 3D systems, \rho^W_x = \rho^W_y = \rho^W_z = \rho_s for any R. In addition, we determine the Kosterlitz-Thouless transition temperature to be T_KT/J=0.34303(8) for the 2D model.Comment: 7 pages, 8 figures, 1 table. Minor changes to published versio

Materials Characterization Center program plan

The Materials Characterization Center (MCC) has been established at Pacific Northwest Laboratory as part of the Materials Characterization Organization for providing an authoritative, referenceable basis for establishing nuclear waste material properties and test methods. The MCC will provide a data base that will include information on the components of the waste emplacement package - the spent fuel or processed waste form and the engineered barriers - and their interaction with each other and as affected by the environment. The MCC will plan materials testing, develop and document procedures, collect and analyze existing materials data, and conduct tests as necessary

Mental health problems in young male offenders with and without sex offences: a comparison based on the MAYSI-2

New methods for child psychiatric diagnosis and treatment outcome evaluatio