Oak Ridge National Laboratory

About: Oak Ridge National Laboratory is a facility organization based out in Oak Ridge, Tennessee, United States. It is known for research contribution in the topics: Neutron & Ion. The organization has 31868 authors who have published 73724 publications receiving 2633689 citations. The organization is also known as: ORNL.

Filtered two‐fluid models for fluidized gas‐particle suspensions

Abstract: Starting from a kinetic theory based two-fluid model for gas-particle flows, we first construct filtered two-fluid model equations that average over small scale inhomogeneities that we do not wish to resolve in numerical simulations. We then outline a procedure to extract constitutive models for these filtered two-fluid models through highly resolved simulations of the kinetic theory based model equations in periodic domains. Two- and three-dimensional simulations show that the closure relations for the filtered two-fluid models manifest a definite and systematic dependence on the filter size. Linear stability analysis of the filtered two-fluid model equations reveals that filtering does indeed remove small scale structures that are afforded by the microscopic twofluid model. 2008 American Institute of Chemical Engineers AIChE J, 54: 1431–1448, 2008

Bulk superconductivity at 14 K in single crystals of Fe 1 + y Te x Se 1 − x

Abstract: Resistivity, magnetic susceptibility, and heat-capacity measurements are reported for single crystals of Fe{sub 1+y}Te{sub x}Se{sub 1-x} grown via a modified Bridgeman method with 0 < y < 0.15 and x = 1, 0.9, 0.75, 0. 67, 0.55, and 0.5. Although resistivity measurements show traces of superconductivity near 14 K for all x except x = 1, only crystals grown with compositions near x = 0.5 exhibit bulk superconductivity. The appearance of bulk superconductivity correlates with a reduction in the magnitude of the magnetic susceptibility at room temperature and smaller values of y, the concentration of Fe in the Fe(2) site.

Van der Waals density functional: an appropriate exchange functional

Abstract: In this Rapid Communication, an exchange functional which is compatible with the nonlocal Rutgers-Chalmers correlation functional [van der Waals density functional (vdW-DF)] is presented. This functional, when employed with vdW-DF, demonstrates remarkable improvements on intermolecular separation distances while further improving the accuracy of vdW-DF interaction energies. The key to the success of this three-parameter functional is its reduction in short-range exchange repulsion through matching to the gradient expansion approximation in the slowly varying/high-density limit while recovering the large reduced gradient, $s$, limit set in the revised Perdew-Burke-Ernzerhof (revPBE) exchange functional. This augmented exchange functional could be a solution to long-standing issues of vdW-DF lending to further applicability of density-functional theory to the study of relatively large, dispersion bound (van der Waals) complexes.