A semi-staggered dilation-free finite volume method for the numerical solution of viscoelastic fluid flows on all-hexahedral elements

The dilation-free semi-staggered finite volume method presented in Sabin [M. Sahin, A preconditioned semi-staggered dilation-free finite volume method for the incompressible Navier-Stokes equations on all-hexahedral elements, Int. J. Numer. Methods Fluids 49 (2005) 959-974] has been extended for the numerical solution of viscoelastic fluid flows on all-quadrilateral (2D) / hexahedral (3D) meshes. The velocity components are defined at element node points, while the pressure term and the extra stress tensor are defined at element centroids. The continuity equation is satisfied exactly within each element. An upwind least square method is employed for the calculation of the extra stresses at control volume faces in order to maintain stability for hyperbolic constitutive equations. The time stepping algorithm used decouples the calculation of the extra stresses from the evaluation of the velocity and pressure fields by solving a generalised Stokes problem. The resulting linear systems are solved using the GMRES method provided by the PETSc library with an ILU(k) preconditioner obtained from the HYPRE library. We apply the method to both two- and three-dimensional flow of an Oldroyd-B fluid past a confined circular cylinder in a channel with blockage ratio 0.5. Crown Copyright (C) 2007 Published by Elsevier B.V. All rights reserved

Adsorption of Alkali, Alkaline Earth and Transition Metal Atoms on Silicene

The adsorption characteristics of alkali, alkaline earth and transition metal adatoms on silicene, a graphene-like monolayer structure of silicon, are analyzed by means of first-principles calculations. In contrast to graphene, interaction between the metal atoms and the silicene surface is quite strong due to its highly reactive buckled hexagonal structure. In addition to structural properties, we also calculate the electronic band dispersion, net magnetic moment, charge transfer, workfunction and dipole moment of the metal adsorbed silicene sheets. Alkali metals, Li, Na and K, adsorb to hollow site without any lattice distortion. As a consequence of the significant charge transfer from alkalis to silicene metalization of silicene takes place. Trends directly related to atomic size, adsorption height, workfunction and dipole moment of the silicene/alkali adatom system are also revealed. We found that the adsorption of alkaline earth metals on silicene are entirely different from their adsorption on graphene. The adsorption of Be, Mg and Ca turns silicene into a narrow gap semiconductor. Adsorption characteristics of eight transition metals Ti, V, Cr, Mn, Fe, Co, Mo and W are also investigated. As a result of their partially occupied d orbital, transition metals show diverse structural, electronic and magnetic properties. Upon the adsorption of transition metals, depending on the adatom type and atomic radius, the system can exhibit metal, half-metal and semiconducting behavior. For all metal adsorbates the direction of the charge transfer is from adsorbate to silicene, because of its high surface reactivity. Our results indicate that the reactive crystal structure of silicene provides a rich playground for functionalization at nanoscale.Comment: 8 Figures, 1 Table. under publication Physical Review B (2013

Resonant Production of Color Octet Electron at the LHec

In composite models with colored preons leptogluons (l_(8)) has a same status with leptoquarks, excited leptons and quarks etc. We analyze resonant production of color octet electron (e_(8)) at QCD Explorer stage of the Large Hadron electron Collider (LHeC). It is shown that the e_(8) discovery at the LHeC will simultaneously determine the compositeness scale.Comment: 13 pages, 12 figures, 5 table