Non-spiky density of states of an icosahedral quasicrystal

The density of states of the ideal three-dimensional Penrose tiling, a quasicrystalline model, is calculated with a resolution of 10 meV. It is not spiky. This falsifies theoretical predictions so far, that spikes of width 10-20 meV are generic for the density of states of quasicrystals, and it confirms recent experimental findings. The qualitative difference between our results and previous calculations is partly explained by the small number of k points that has usually been included in the evaluation of the density of states of periodic approximants of quasicrystals. It is also shown that both the density of states of a small approximant of the three-dimensional Penrose tiling and the density of states of the ideal two-dimensional Penrose tiling do have spiky features, which also partly explains earlier predictions.Comment: 8 pages, 4 figures. Changes in this version: longer introduction, details of figures shown in inset

Supplementary Material for States Without Archaeological Correlates? A Report from Hawai‘i James M. Bayman, Thomas S. Dye, and Timothy M. Rieth

This file contains links to the OxCal input files used to create Figures 1–3 in the paper, "States Without Archaeological Correlates? A Report from Hawai‘i" (table 1). It also includes source code for the R statistical software routines used to produce the graphic files for the figures.This file contains links to the OxCal input files used to create Figures 1–3 in the paper, "States Without Archaeological Correlates? A Report from Hawai‘i" (table 1). It also includes source code for the R statistical software routines used to produce the graphic files for the figures

High pulse number thermal shock testing of tungsten alloys produced by powder injection molding

The investigation of plasma facing materials (PFM) subjected to a large number (≥10,000) of thermal shocks is of interest to determine long term morphological changes which might influence component lifetime in and plasma performance of a fusion reactor. The electron beam facility JUDITH 2 was used to simulate these conditions experimentally. In this study eight different tungsten grades produced by powder injection molding (PIM) were investigated: Two pure tungsten grades, one with 2 wt% Y₂O₃, three with 1, 2 and 3 wt% TiC, and two with 0.5 and 1 wt% TaC. Samples of 10 × 10 × 4 mm³ were brazed to a copper cooling structure and subjected to 10⁵ thermal shocks of 0.5 ms duration and an intensity of L$_{abs}$=0.55 GW/m² (F$_{HF}$=12 MWs½/m2) at a base temperature of T$_{base}$ = 700 °C. The PIM grades showed damages in general comparable with a sintered and forged pure tungsten reference grade (>99.97 wt% W) that complies with the ITER specifications. One exception was the 2 wt% TiC doped material which failed early during the experiment by delamination of a large part of the surface. The Y₂O₃ doped material showed a comparatively good performance with respect to crack width (<15 μm) and roughening (R$_{a}$ = 0.75 μm), but showed melt droplets of ∼3–4 μm diameter, while the 1 wt% TiC doped material showed wide cracks (up to 50 μm) and strong roughening (R$_{a}$ = 2.5 μm). The paper discusses the post-mortem analysis of all grades, comparing them with respect to roughness (from laser profilometry), crack network characteristics and local melt droplet formation or other special morphological features (from SEM images) as well as crack depth (from metallographic cross sections)

Stability of an Exciton bound to an Ionized Donor in Quantum Dots

Total energy, binding energy, recombination rate (of the electron hole pair) for an exciton (X) bound in a parabolic two dimensional quantum dot by a donor impurity located on the z axis at a distance d from the dot plane, are calculated by using the Hartree formalism with a recently developed numerical method (PMM) for the solution of the Schroedinger equation. As our analysis indicates there is a critical dot radius such that for radius less than the critical radius the complex is unstable and with an increase of the impurity distance this critical radius increases. Furthermore, there is a critical value of the mass ratio such that for mass ratio less than the critical value the complex is stable. The appearance of this stability condition depends both on the impurity distance and the dot radius, in a way that with an increase of the impurity distance we have an increase in the maximum dot radius where this stability condition appears. For dot radii greater than this maximum dot radius (for fixed impurity distance) the complex is always stable.Comment: 17 pages, 7 figures Applying a new numerical method which is based on the adiabatic stability of quantum mechanics, we study the stability of an exciton (X) bound in a parabolic two dimensional quantum dot by a donor impurity located on the z axis at a distance d from the dot plan