763,464 research outputs found
A GMRT 150 MHz search for variables and transients in Stripe 82
We have carried out a dedicated transient survey of 300 deg2 of the SDSS Stripe 82 region using the Giant Metrewave Radio Telescope (GMRT) at 150 MHz. Our multi-epoch observations, together with the TGSS survey, allow us to probe variability and transient activity on four different time-scales, beginning with 4 h and up to 4 yr. Data calibration, RFI flagging, source finding, and transient search were carried out in a semi-automated pipeline incorporating the SPAM recipe. This has enabled us to produce superior-quality images and carry out reliable transient search over the entire survey region in under 48 h post-observation. Among the few thousand unique point sources found in our 5σ single-epoch catalogues (flux density thresholds of about 24, 20, 16, and 18 mJy on the respective time-scales), we find <0.08 per cent, 0.01 per cent, <0.06 per cent, and 0.05 per cent to be variable (beyond a significance of 4σ and fractional variability of 30 per cent) on time-scales of 4 h, 1 d, 1 month, and 4 yr, respectively. This is substantially lower than that in the GHz sky, where ∼1 per cent of the persistent point sources are found to be variable. Although our survey was designed to probe a superior part of the transient phase space, our transient search did not yield any significant candidates. The transient (preferentially extragalactic) rate at 150 MHz is therefore <0.005 on time-scales of 1 month and 4 yr, and <0.002 on time-scales of 1 d and 4 h, beyond 7σ detection threshold. We put these results in perspective with the previous studies and give recommendations for future low-frequency transient surveys
Centrality dependence of elliptic flow and QGP viscosity
In the Israel-Stewart's theory of second order hydrodynamics, we have
analysed the recent PHENIX data on charged particles elliptic flow in Au+Au
collisions.
PHENIX data demand more viscous fluid in peripheral collisions than in
central collisions. Over a broad range of collision centrality (0-10%- 50-60%),
viscosity to entropy ratio () varies between 0-0.17.Comment: Final version to be publiashed in J. Phys. G. 8 pages, 6 figures and
3 table
Induced Magnetic Ordering by Proton Irradiation in Graphite
We provide evidence that proton irradiation of energy 2.25 MeV on
highly-oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism.
Measurements performed with a superconducting quantum interferometer device
(SQUID) and magnetic force microscopy (MFM) reveal that the magnetic ordering
is stable at room temperature.Comment: 3 Figure
Charmonium dissociation temperatures in lattice QCD with a finite volume technique
Dissociation temperatures of J/\psi, \psi', and \chi_c states play key roles
in the sequential J/\psi suppression scenario for high energy heavy ion
collisions. We report on a study of charmonium dissociation temperatures in
quenched lattice QCD. On anisotropic lattices, we first subtract the effects of
the constant mode in finite temperature meson correlators, which have lead to
unphysical results in previous studies. We then extract ground and first exited
state masses by diagonalizing correlation functions among different source and
sink operators. To distinguish bound states from scattering states, we first
compare the charmonium mass spectra under different spatial boundary
conditions, and examine the shape and the volume-dependence of their
Bethe-Salpeter wave functions. From these studies, we found so far no sign of
scattering states up to about 2.3T_c.Comment: 4pages, 2figures, proceedings of Quark Matter 2008 (QM2008), Jaipur,
India, Feb 4-10, 200
Control of nonenzymatic browning in intermediate-moisture foods
Series of compounds called humectants were found to decrease rate of browning when added to intermediate-moisture foods. Twenty percent level of humectant can increase shelf life of foods by factor of 5 or 6
Origin of Hysteresis in a Proximity Josephson Junction
We investigate hysteresis in the transport properties of Superconductor -
Normal metal - Superconductor (S-N-S) junctions at low temperatures by
measuring directly the electron temperature in the normal metal. Our results
demonstrate unambiguously that the hysteresis results from an increase of the
normal metal electron temperature once the junction switches to the resistive
state. In our geometry, the electron temperature increase is governed by the
thermal resistance of the superconducting electrodes of the junction
Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain
In order to study the interplay between Kondo and
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, we calculate the spin-spin
correlation functions between two Kondo impurities coupled to different sites
of a half-filled open Hubbard chain. Using the density-matrix renormalization
group (DMRG), we re-examine the exponents for the power-law decay of the
correlation function between the two impurity spins as a function of the
antiferromagnetic coupling J, the Hubbard interaction U, and the distance R
between the impurities. The exponents for finite systems obtained in this work
deviate from previously published DMRG calculations. We furthermore show that
the long-distance behavior of the exponents is the same for impurities coupled
to the bulk or to both ends of the chain. We note that a universal exponent for
the asymptotic behavior cannot be extracted from these finite-size systems with
open boundary conditions.Comment: 8 pages, 10 figures; v2: final version, references and Fig. 8 adde
Pairbreaking Without Magnetic Impurities in Disordered Superconductors
We study analytically the effects of inhomogeneous pairing interactions in
short coherence length superconductors, using a spatially varying
Bogoliubov-deGennes model. Within the Born approximation, it reproduces all of
the standard Abrikosov-Gor'kov pairbreaking and gaplessness effects, even in
the absence of actual magnetic impurities. For pairing disorder on a single
site, the T-matrix gives rise to bound states within the
BCS gap. Our results are compared with recent scanning tunneling microscopy
measurements on BiSrCaCuO with Zn or Ni impurities.Comment: 4 pages, 2 figures, submitted to PR
Effect of Spin-Orbit Interaction in Spin-Triplet Superconductor: Structure of -vector and Anomalous O-NQR Relaxation in SrRuO
Supposing the spin-triplet superconducting state of SrRuO, the
spin-orbit (SO) coupling associated with relative motion in Cooper pairs is
calculated by extending the method for the dipole-dipole coupling given by
Leggett in the superfluid He. It is shown that the SO coupling works only
in the equal-spin pairing (ESP) state to make the pair angular momentum
and the pair spin angular momentum parallel with each other. The SO coupling gives rise to the internal
Josephson effect in a chiral ESP state as in superfluid A-phase of He with
a help of an additional anisotropy arising from SO coupling of atomic origin
which works to direct the {\bf d}-vector into -plane. This resolves the
problem of the anomalous relaxation of O-NQR and the structure of {\bf
d}-vector in SrRuO.Comment: Accepted for publication in J. Phys. Soc. Jpn. vol.79 (2010), No.2
(February issue); 18 pages, 2 figure
Binomial level densities
It is shown that nuclear level densities in a finite space are described by a
continuous binomial function, determined by the first three moments of the
Hamiltonian, and the dimensionality of the underlying vector space.
Experimental values for Mn, Fe, and Ni are very well
reproduced by the binomial form, which turns out to be almost perfectly
approximated by Bethe's formula with backshift. A proof is given that binomial
densities reproduce the low moments of Hamiltonians of any rank: A strong form
of the famous central limit result of Mon and French. Conditions under which
the proof may be extended to the full spectrum are examined.Comment: 4 pages 2 figures Second version (previous not totally superseeded
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