Observational Search for PeV-EeV Tau Neutrino from GRB081203A

We report the first observational search for tau neutrinos from gamma ray bursts (GRBs) using one of the Ashra light collectors. The earth-skimming tau-neutrino technique of imaging Cherenkov tau showers was applied as a detection method. We set stringent upper limits on the tau-neutrino fluence in PeV-EeV region for 3780 s (between 2.83 and 1.78 hours before) and another 3780 s (between 21.2 and 22.2 hours after) surrounding GRB081203A triggered by the Swift satellite. This first search for PeV-EeV tau neutrino complements other experiments in energy range and methodology, and suggests the prologue of "multi-particle astronomy" with a precise determination of time and location.Comment: 13 pages, 4 figure

Molecular-Dynamics Simulation of Lattice Thermal Conductivity in Pb_<1-x>Sn_xTe and Pb_<1-x>Ge_xTe at High Temperature

The molecular-dynamics studies on lattice thermal conductivity (κ_L) of Pb_Sn_xTe and Pb_Ge_xTe are carried out by employing ion model potential for mutual ion-ion interactions at the average temperatures 300 and 500 K under non-equilibrium condition. Special emphasis of investigation is on the alloying effects on κ_L by changing the alloying content x of Sn and Ge in PbTe. It has been shown that a remarkable reduction of κ_L at finite x is demonstrated in Pb_Sn_xTe and Pb_Ge_xTe without a relying on a phonon scattering description. We have compared our results with ones evaluated by the Abeles' formula of lattice thermal conductivity due to phonon scattering from alloy fluctuations

Deep-level traps in lightly Si-doped n-GaN on free-standing m-oriented GaN substrates

In this study, we investigated the deep-level traps in Si-doped GaN epitaxial layers by metal-organic chemical vapor deposition on c-oriented and m-oriented free-standing GaN substrates. The c-oriented and m-oriented epitaxial layers, grown at a temperature of 1000 °C and V/III ratio of 1000, contained carbon atomic concentrations of 1.7×1016 and 4.0×1015 cm–3, respectively. A hole trap was observed at about 0.89 eV above the valence band maximum by minority carrier transient spectroscopy. The trap concentrations in the c-oriented and m-oriented GaN epitaxial layers were consistent with the carbon atomic concentrations from secondary ion mass spectroscopy and the yellow luminescence intensity at 2.21 eV from photoluminescence. The trap concentrations in the m-oriented GaN epitaxial layers were lower than those in the c-oriented GaN. Two electron traps, 0.24 and 0.61 eV below the conduction band (EC) minimum, were observed in the c-oriented GaN epitaxial layer. In contrast, the m-oriented GaN epitaxial layer was free from the electron trap at EC – 0.24 eV, and the trap concentration at EC – 0.61 eV in the m-oriented GaN epitaxial layer was lower than that in the c-oriented GaN epitaxial layer. The m-oriented GaN epitaxial layer exhibited fewer hole and electron traps compared to the c-oriented GaN epitaxial layers