6 research outputs found
Ultra-High-Energy Cosmic Ray Acceleration by Magnetic Reconnection in Newborn Accretion Induced Collapse Pulsars
We here investigate the possibility that the ultra-high energy cosmic ray
(UHECR) events observed above the GZK limit are mostly protons accelerated in
reconnection sites just above the magnetosphere of newborn millisecond pulsars
which are originated by accretion induced collapse (AIC). We show that
AIC-pulsars with surface magnetic fields G and spin periods , are able to
accelerate particles to energies eV. Because the expected rate
of AIC sources in our Galaxy is very small (\sim 10^{-5} yr^{-1}), the
corresponding contribution to the flux of UHECRs is neglegible, and the total
flux is given by the integrated contribution from AIC sources produced by the
distribution of galaxies located within the distance which is unaffected by the
GZK cutoff ( Mpc). We find that the reconnection efficiency factor
needs to be in order to reproduce the observed flux of
UHECRs.Comment: Latex file, 16 pages, 2 figures, replaced with revised version
accepted for publication in the ApJ letter
Electronic structure and band gap of oxygen bearing c-Zr3N4 and of c-Hf3N4by soft X-ray spectroscopy
Electronic band structures of two novel semiconducting nitrides of the group-IV elements of Th3P4-type crystal structure, c-M3N4, where M[DOUBLE BOND]Zr or Hf, is investigated using an element specific soft X-ray spectroscopy for the first time. From the pairs of N 1s X-ray absorption and N 2p [RIGHTWARDS ARROW] 1s resonant X-ray emission spectra partial densities of states (PDOS) of nitrogen, predicted to be strongly hybridized with those of the metals, are obtained for both compounds. From these data the electronic band gaps of oxygen bearing c-Zr3N4 and of c-Hf3N4, predicted before to be direct or nearly direct, are derived to be Eg = 1.6 eV and Eg = 1.8 eV, respectively. While the experimentally determined Eg for c-Hf3N4 agrees with the theoretical one obtained using the local density approximation (LDA) method, the Eg measured for oxygen bearing c-Zr3N4 is significantly higher than those calculated using both the LDA and the generalized gradient approximation method. The examined compounds, having high hardness, elastic moduli and oxidation resistance, appear to be multifunctional materials suitable also for applications as (opto)electronic materials. Band gap evolution in c-M3N4 nitrides as a function of the cation type, Zr or Hf