Bose-Einstein Correlations from Random Walk Models

We argue that strong final state rescattering among the secondary particles created in relativistic heavy ion collisions is essential to understand the measured Bose-Einstein correlations. The recently suggested ``random walk models'' which contain only initial state scattering are unable to reproduce the measured magnitude and K_\perp-dependence of R_\perp in Pb+Pb collisions and the increase of R_l with increasing size of the collision system.Comment: 5 pages, REVTEX, 1 figure included with epsf.sty, revised version to be published in Phys.Lett.

Standardization for Defence Procurement - European Handbook : CEN Workshop 10

The European Commission (EC), DG Enterprise, endeavours the competitiveness of the European Defence Industry. The plethora of (national) standards, more than 10.000, are recognised by the EC as a major constraint and cost driver. Electromagnetic Compatibility (EMC) or Electromagnetic Environmental Effects (EEE) are considered by the EC as a major topic, with 7 other topics such as environmental engineering, energetic materials, batteries, electrical interfaces. An EMC expert group with representatives from industry, including Aerotech Telub, Intellect, EADS, Ericsson Microwave, Fincantieri, MBDA, Thales, and national MoDs rationalized in 2004 a list of 329 EEE standards, implicitly abandoning national, including American, standards, and develop guidelines for the procurement process. A limited number of widely accepted and cost effective standards, suitable for use by MoD’s (acquisition) and industry (product development), has been defined after making comparisons. Comparisons were carried out on some standards against STANAG 4370 AECTP 500. The Expert Group agreed; That no one standard is better or worse than another in achieving an end goal. Differences are not sufficient to prevent the use of AECTP 500. There are sufficient similarities to AECTP 500 to adopt this as the fundamental replacement standard. There was sufficient agreement on NATO-, IEC- and EN-produced standards to make worthwhile agreement to use a number of standards as replacement for some (or some parts) of existing National Standards. This document gives recommendations on the use of the standards, the scope and \ud limitations. It also emphasizes the constraints with respect to the standardisation process of National MoD’s, NATO, Industry and EN/IEC

Density-based mixing parameter for hybrid functionals

A very popular ab-initio scheme to calculate electronic properties in solids is the use of hybrid functionals in density functional theory (DFT) that mixes a portion of Fock exchange with DFT functionals. In spite of their success, a major problem still remains, related to the use of one single mixing parameter for all materials. Guided by physical arguments that connect the mixing parameter to the dielectric properties of the solid, and ultimately to its band gap, we propose a method to calculate this parameter from the electronic density alone. This method is able to cut significantly the error of traditional hybrid functionals for large and small gap materials, while retaining a good description of structural properties. Moreover, its implementation is simple and leads to a negligible increase of the computational time.Comment: submitte

Topological Insulators in Ternary Compounds with a Honeycomb Lattice

One of the most exciting subjects in solid state physics is a single layer of graphite which exhibits a variety of unconventional novel properties. The key feature of its electronic structure are linear dispersive bands which cross in a single point at the Fermi energy. This so-called Dirac cone is closely related to the surface states of the recently discovered topological insulators. The ternary compounds, such as LiAuSe and KHgSb with a honeycomb structure of their Au-Se and Hg-Sb layers feature band inversion very similar to HgTe which is a strong precondition for existence of the topological surface states. In contrast to graphene with two Dirac cones at K and K' points, these materials exhibit the surface states formed by only a single Dirac cone at the \Gamma -point together with the small direct band gap opened by a strong spin-orbit coupling (SOC) in the bulk. These materials are centro-symmetric, therefore, it is possible to determine the parity of their wave functions, and hence, their topological character. Surprisingly, the compound KHgSb with the strong SOC is topologically trivial, whereas LiAuSe is found to be a topological non-trivial insulator.Comment: 4 pages + 1 page supplementa