2,607 research outputs found
Far-ultraviolet imaging of the Hubble Deep Field-North: Star formation in normal galaxies at z < 1
We present far-ultraviolet (FUV) imaging of the Hubble Deep Field-North (HDF-N) taken with the Solar Blind Channel of the Advanced Camera for Surveys (ACS SBC) and the FUV MAMA detector of the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The full WFPC2 deep field has been observed at 1600 Å. We detect 134 galaxies and one star down to a limit of FUV_(AB) ~ 29. All sources have counterparts in the WFPC2 image. Redshifts (spectroscopic or photometric) for the detected sources are in the range 0 < z < 1. We find that the FUV galaxy number counts are higher than those reported by GALEX, which we attribute at least in part to cosmic variance in the small HDF-N field of view. Six of the 13 Chandra sources at z < 0.85 in the HDF-N are detected in the FUV, and those are consistent with starbursts rather than active galactic nuclei. Cross-correlating with Spitzer sources in the field, we find that the FUV detections show general agreement with the expected L_(IR)/L_(UV) versus β relationship. We infer star formation rates (SFRs), corrected for extinction using the UV slope, and find a median value of 0.3 M_☉ yr^(-1) for FUV-detected galaxies, with 75% of detected sources having SFR < 1 M_☉ yr^(-1). Examining the morphological distribution of sources, we find that about half of all FUV-detected sources are identified as spiral galaxies. Half of morphologically selected spheroid galaxies at z < 0.85 are detected in the FUV, suggesting that such sources have had significant ongoing star formation in the epoch since z ~ 1
Reflection of light from a disordered medium backed by a phase-conjugating mirror
This is a theoretical study of the interplay of optical phase-conjugation and
multiple scattering. We calculate the intensity of light reflected by a
phase-conjugating mirror when it is placed behind a disordered medium. We
compare the results of a fully phase-coherent theory with those from the theory
of radiative transfer. Both methods are equivalent if the dwell time
\tau_{dwell} of a photon in the disordered medium is much larger than the
inverse of the frequency shift 2\Delta\omega acquired at the phase-conjugating
mirror. When \tau_{dwell} \Delta\omega < 1, in contrast, phase coherence
drastically affects the reflected intensity. In particular, a minimum in the
dependence of the reflectance on the disorder strength disappears when
\Delta\omega is reduced below 1/\tau_{dwell}. The analogies and differences
with Andreev reflection of electrons at the interface between a normal metal
and a superconductor are discussed.Comment: 27 pages RevTeX with 11 figures included with psfi
Random graph states, maximal flow and Fuss-Catalan distributions
For any graph consisting of vertices and edges we construct an
ensemble of random pure quantum states which describe a system composed of
subsystems. Each edge of the graph represents a bi-partite, maximally entangled
state. Each vertex represents a random unitary matrix generated according to
the Haar measure, which describes the coupling between subsystems. Dividing all
subsystems into two parts, one may study entanglement with respect to this
partition. A general technique to derive an expression for the average
entanglement entropy of random pure states associated to a given graph is
presented. Our technique relies on Weingarten calculus and flow problems. We
analyze statistical properties of spectra of such random density matrices and
show for which cases they are described by the free Poissonian
(Marchenko-Pastur) distribution. We derive a discrete family of generalized,
Fuss-Catalan distributions and explicitly construct graphs which lead to
ensembles of random states characterized by these novel distributions of
eigenvalues.Comment: 37 pages, 24 figure
Reflection Symmetric Ballistic Microstructures: Quantum Transport Properties
We show that reflection symmetry has a strong influence on quantum transport
properties. Using a random S-matrix theory approach, we derive the
weak-localization correction, the magnitude of the conductance fluctuations,
and the distribution of the conductance for three classes of reflection
symmetry relevant for experimental ballistic microstructures. The S-matrix
ensembles used fall within the general classification scheme introduced by
Dyson, but because the conductance couples blocks of the S-matrix of different
parity, the resulting conductance properties are highly non-trivial.Comment: 4 pages, includes 3 postscript figs, uses revte
DIFFUSION IN ONE DIMENSIONAL RANDOM MEDIUM AND HYPERBOLIC BROWNIAN MOTION
Classical diffusion in a random medium involves an exponential functional of
Brownian motion. This functional also appears in the study of Brownian
diffusion on a Riemann surface of constant negative curvature. We analyse in
detail this relationship and study various distributions using stochastic
calculus and functional integration.Comment: 18 page
Conductance Fluctuations in a Disordered Double-Barrier Junction
We consider the effect of disorder on coherent tunneling through two barriers
in series, in the regime of overlapping transmission resonances. We present
analytical calculations (using random-matrix theory) and numerical simulations
(on a lattice) to show that strong mode-mixing in the inter-barrier region
induces mesoscopic fluctuations in the conductance of universal magnitude
for a symmetric junction. For an asymmetric junction, the
root-mean-square fluctuations depend on the ratio of the two tunnel
resistances according to ,
where in the presence (absence) of time-reversal symmetry.Comment: 12 pages, REVTeX-3.0, 2 figures, submitted to Physical Review
Effective Non-Hermitian Hamiltonians for Studying Resonance Statistics in Open Disordered Systems
We briefly discuss construction of energy-dependent effective non-hermitian
hamiltonians for studying resonances in open disordered systemsComment: Latex, 20 pages, 1 fig. Expanded version of a talk at the Workshop on
Pseudo-Hermitian Hamiltonians in Quantum Physics IX, June 21-24 2010,
Zhejiang University, Hangzhou, China. Accepted for publication in the
Internationa Journal of Theoretical Physics (Springer Verlag
Signatures of the correlation hole in total and partial cross sections
In a complex scattering system with few open channels, say a quantum dot with
leads, the correlation properties of the poles of the scattering matrix are
most directly related to the internal dynamics of the system. We may ask how to
extract these properties from an analysis of cross sections. In general this is
very difficult, if we leave the domain of isolated resonances. We propose to
consider the cross correlation function of two different elastic or total cross
sections. For these we can show numerically and to some extent also
analytically a significant dependence on the correlations between the
scattering poles. The difference between uncorrelated and strongly correlated
poles is clearly visible, even for strongly overlapping resonances.Comment: 25 pages, 13 Postscript figures, typos corrected and references adde
Fokker-Planck description of the transfer matrix limiting distribution in the scattering approach to quantum transport
The scattering approach to quantum transport through a disordered
quasi-one-dimensional conductor in the insulating regime is discussed in terms
of its transfer matrix \bbox{T}. A model of one-dimensional wires which
are coupled by random hopping matrix elements is compared with the transfer
matrix model of Mello and Tomsovic. We derive and discuss the complete
Fokker-Planck equation which describes the evolution of the probability
distribution of \bbox{TT}^{\dagger} with system length in the insulating
regime. It is demonstrated that the eigenvalues of \ln\bbox{TT}^{\dagger}
have a multivariate Gaussian limiting probability distribution. The parameters
of the distribution are expressed in terms of averages over the stationary
distribution of the eigenvectors of \bbox{TT}^{\dagger}. We compare the
general form of the limiting distribution with results of random matrix theory
and the Dorokhov-Mello-Pereyra-Kumar equation.Comment: 25 pages, revtex, no figure
Vacuum Polarization of Massless Spinor Field in Global Monopole Spacetime
We calculate the renormalized vacuum average of the energy-momentum tensor of
massless left-handed spinor field in the pointlike global monopole spacetime
using point-separation approach. The general structure of the vacuum average of
the energy-momentum tensor is obtained and expressed in terms of
component, explicit form of which is analyzed in great details
for arbitrary solid angle deficit.Comment: 12 pages, REVTEX, print error was correcte
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