Vacancy Ordering in Vanadium Carbides Based on V_6C_5

The ordered arrangement of carbon vacancies in vanadium carbides near V_6C_5 has been analysed by means of selected-area electron diffraction and high-voltage electron microscopy. A new type of ordered distribution of carbon vacancies is found at non-stoichiometric compositions between V_6C_5 and V_8C_7. This structure can be expressed as a long-period structure consisting of the enantiomorphic domains based on the structure V_6C_5 which was determined by Billingham, Bell and Lewis (1972). The periodic domain boundaries with spacing eleven times the nearest-neighbour interatomic distance are directly observed by electron microscopy

Constitution of the Indium-Rich Portion of the Indium-Magnesium System

The equilibrium phase diagram of the indium-magnesium system in the range up to 40 at.% Mg has been established by X-ray diffraction and thermal analysis. The solid-solubility of magnesium in indium does not exceed about 5 at.%. An intermediate solid solution, γ, with a face-centered cubic structure exists over a wide range of composition. An ordered phase, γ\u27, with superstructure of Cu_3Au-type, is formed near 28 at.% Mg at temperatures below 114℃. The axial ratio c/a of the primary solid solution of indium in magnesium changes as a function of electron/atom ratio as in the parallel case of the indium-cadmium system. Reasons are advanced to explain the conflict between the present results and those of earlier investigators

High-Energy Neutrino Astronomy

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature accelerates protons and photons to energies in excess of $10^{20}$ and $10^{13}$ eV, respectively. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos.Comment: 9 pages, Latex2e, uses ws-procs975x65standard.sty (included), 4 postscript figures. To appear in Proceedings of Thinking, Observing, and Mining the Universe, Sorrento, Italy, September 200

Discriminating the Progenitor Type of Supernova Remnants with Iron K-Shell Emission

Supernova remnants (SNRs) retain crucial information about both their parent explosion and circumstellar material left behind by their progenitor. However, the complexity of the interaction between supernova ejecta and ambient medium often blurs this information, and it is not uncommon for the basic progenitor type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here we present a powerful new observational diagnostic to discriminate between progenitor types and constrain the ambient medium density of SNRs solely using Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs and detect Fe K alpha emission from 23 young or middle-aged remnants, including five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in Type Ia remnants being significantly less ionized than in core-collapse SNRs. Within each progenitor group, the Fe K alpha luminosity and centroid are well correlated, with more luminous objects having more highly ionized Fe. Our results indicate that there is a strong connection between explosion type and ambient medium density, and suggest that Type Ia supernova progenitors do not substantially modify their surroundings at radii of up to several parsecs. We also detect a K-shell radiative recombination continuum of Fe in W49B and IC 443, implying a strong circumstellar interaction in the early evolutionary phases of these core-collapse remnants.Comment: Accepted by ApJL; 5 pages with just 1 table and 1 figur