Position dependent photodetector from large area reduced graphene oxide thin films

We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemically synthesis and interconnecting sheets

A Common Explanation for the Atmospheric, Solar-Neutrino and Double Beta Decay Anomalies

We make a number of small changes, including correcting an error in our heavy-neutrino decay rate. None of our analysis is changed, either in substance or detail.Comment: 25 pages, 6 Figures, McGill-93/1

The Earth Effect in the MSW Analysis of the Solar Neutrino Experiments

We consider the Earth effect in the MSW analysis of the Homestake, Kamiokande, GALLEX, and SAGE solar neutrino experiments. Using the time-averaged data and assuming two-flavor oscillations, the large-angle region of the combined fit extends to much smaller angles (to $\sin^22\theta \simeq 0.1$) than when the Earth effect is ignored. However, the additional constraint from the Kamiokande II day-night data excludes most of the parameter space sensitive to the Earth effect independent of astrophysical uncertainties, and leaves only a small large-angle region close to maximal mixing at 90\% C.L. The nonadiabatic solution remains unaffected by the Earth effect and is still preferred. Both theoretical and experimental uncertainties are included in the analysis.Comment: (11 pages, Revtex 3.0 (can be changed to Latex), 3 postscript figures included, UPR-0570T

Standard Model Contributions to the Neutrino Index of Refraction in the Early Universe

With the standard electroweak interactions, the lowest-order coherent forward scattering amplitudes of neutrinos in a CP symmetric medium (such as the early universe) are zero, and the index of refraction of a propagating neutrino can only arise from the expansion of gauge boson propagators, from radiative corrections, and from new physics interactions. Motivated by nucleosynthesis constraints on a possible sterile neutrino (suggested by the solar neutrino deficit and a possible $17\ keV$ neutrino), we calculate the standard model contributions to the neutrino index of refraction in the early universe, focusing on the period when the temperature was of the order of a few $MeV$. We find sizable radiative corrections to the tree level result obtained by the expansion of the gauge boson propagator. For $\nu_e+e(\bar{e})\to \nu_e+e(\bar{e})$ the leading log correction is about $+10\%$, while for $\nu_e+\nu_e(\bar{\nu}_e)\to \nu_e+\nu_e(\bar{\nu}_e)$ the correction is about $+20\%$. Depending on the family mixing (if any), effects from different family scattering can be dominated by radiative corrections. The result for $\nu+\gamma\to\nu+\gamma$ is zero at one-loop level, even if neutrinos are massive. The cancellation of infrared divergence in a coherent process is also discussed.Comment: 46pp, 13 figures (not included), UPR-0495

Oscillation effects on supernova neutrino rates and spectra and detection of the shock breakout in a liquid Argon TPC

A liquid Argon TPC (ICARUS-like) has the ability to detect clean neutrino bursts from type-II supernova collapses. In this paper, we consider for the first time the four possible detectable channels, namely, the elastic scattering on electrons from all neutrino species, $\nu_e$ charged current absorption on $Ar$ with production of excited $K$, $\bar\nu_e$ charged current absorption on $Ar$ with production of excited $Cl$ and neutral current interactions on $Ar$ from all neutrino flavors. We compute the total rates and energy spectra of supernova neutrino events including the effects of the three--flavor neutrino oscillation with matter effects in the propagation in the supernova. Results show a dramatic dependence on the oscillation parameters and in the energy spectrum, especially for charged-current events. The shock breakout phase has also been investigated using recent simulations of the core collapse supernova. We stress the importance of the neutral current signal to decouple supernova from neutrino oscillation physics.Comment: 40 pages, 19 figures, version v2 accepted for publication in JCAP. accepted in JCA

Common Origin for the Solar and Atmospheric Neutrino Deficits

Some typos corrected, slightly different abstract, same plots, results and conclusions.Comment: 14 Latex pages, 3 figures attached as postscript files, IFP-472-UNC, PRL-TH-93/1

Oscillations of Pseudo-Dirac Neutrinos and the Solar Neutrino Problem

The oscillations of pseudo-Dirac neutrinos in matter are discussed and applied to the solar neutrino problem. Several scenarios such as both $\nu_e$ and $\nu_{\mu}$ being pseudo-Dirac and only $\nu_e$ or $\nu_{\mu}$ being pseudo-Dirac are examined. It is shown that the allowed region in the mass-mixing angle parameter space obtained by comparing the solar neutrino data with the calculations based on the standard solar model and the MSW effect is not unique. The results depend on the nature of neutrinos; for example, if both $\nu_e$ and $\nu_{\mu}$ are pseudo-Dirac, the allowed region determined by the current solar neutrino data does not overlap with that obtained in the usual case of pure Dirac or Majorana neutrinos.Comment: 12 pages, 2 figures (not included

Periodic Oscillations of Josephson-Vortex Flow Resistance in Oxygen-Deficient Y1Ba2Cu3Ox

We measured the Josephson vortex flow resistance as a function of magnetic field applied parallel to the ab-planes using annealed Y1Ba2Cu3Ox intrinsic Josephson junctions having high anisotropy (around 40) by oxygen content reduction. Periodic oscillations were observed in magnetic fields above 45-58 kOe, corresponding to dense-dilute boundary for Josephson vortex lattice. The observed period of oscillations, agrees well with the increase of one fluxon per two junctions ($H_{p}$\textit{=$\Phi$}$_{0}$\textit{/2Ls}), may correspond to formation of a triangular lattice of Josephson vortices as has been reported by Ooi et al. for highly anisotropic (larger than 200) Bi-2212 intrinsic Josephson junctions.Comment: 5 pages, 4 figure