Step energies and equilibrium shape of strained monolayer islands

Using a simple atomistic model of anharmonic nearest-neighbors interaction, we have calculated the step energies of strained hexagonal monolayer islands. These have been found to decrease with the absolute value of the misfit due to the strain relaxation at steps. The effect is significantly more pronounced in the case of positive misfit owing to the stronger repulsive interatomic forces. Furthermore, (111)-faceted steps are favored at positive misfit (compressed islands) and, to a lesser extent, (100)-faceted steps at negative misfits (tensile islands). The result is rationalized in terms of the different bonding geometries at step edges and a comparison with experiments is included. Thus, the equilibrium shape transforms from regular hexagons at zero misfit to threefold symmetric hexagons with increasing misfit.Comment: 6 pages, 5 figures, 1 table. Improved, finally accepted version including a new figure, a new table and several minor modifications resulting from discussions with referee

Study of the spring and autumn daemon-flux maxima at the Baksan Neutrino Observatory

Detection of daemons in low-background conditions in September 2005 and March 2006 has provided evidence for the expected to occur at that times maxima in the flux of daemons with V ~ 10-15 km s-1, which hit the Earth from near-Earth, almost circular heliocentric orbits. The ability of some FEU-167-1 PM tubes with a thicker inner Al coating to detect directly daemon passage through them has also been demonstrated, an effect increasing ~100-fold the detector efficiency. As a result, the daemon flux recorded at the maxima was increased from ~10-9 to ~10-7 cm-2 s-1. The intensity and direction of the flux during maxima depend on the time of day and latitude of observations (therefore, synchronous measurements in the Northern and Southern Earth's hemispheres are desirable). All the experimental results obtained either support the conclusions following from the daemon paradigm or find a simple interpretation within it.Comment: 15 pages, including 8 figures and 3 table