8,804 research outputs found
The Anderson impurity model with a narrow-band host: from orbital physics to the Kondo effect
A particle-hole symmetric Anderson impurity model with a metallic host of
narrow bandwidth is studied within the framework of the local moment approach.
The resultant single-particle spectra are compared to unrestricted
Hartree-Fock, second order perturbation theory about the noninteracting limit,
and Lanczos spectra by Hofstetter and Kehrein. Rather accurate analytical
results explain the spectral evolution over almost the entire range of
interactions. These encompass, in particular, a rationale for the four-peak
structure observed in the low-energy sector of the Lanczos spectra in the
moderate-coupling regime. In weak coupling, the spectral evolution is governed
by orbital effects, while in the strong coupling Kondo limit, the model is
shown to connect smoothly to the generic Anderson impurity with a flat and
infinitely wide hybridization band.Comment: 17 pages, 7 figure
Jet-cloud interations and the brightening of the narrow line region in Seyfert galaxies
We study the kinematical and brightness evolution of emission line clouds in
the narrow line region (NLR) of Seyfert galaxies during the passage of a jet.
We derive a critical density above which a cloud remains radiative after
compression by the jet cocoon. The critical density depends mainly on the
cocoon pressure. Super-critical clouds increase in emission line brightness,
while sub-critical clouds generally are highly overheated reducing their
luminosity below that of the inter-cloud medium. Due to the pressure
stratification in the bow-shock of the jet, a cylindrical structure of nested
shells develops around the jet. The most compact and brightest compressed
clouds surround the cloud-free channel of the radio jet. To support our
analytical model we present a numerical simulation of a supersonic jet
propagating into a clumpy NLR. The position-velocity diagram of the simulated
H_alpha emission shows total line widths of the order of 500 km/s with
large-scale variations in the radial velocities of the clouds due to the
stratified pressure in the bow-shock region of the jet. Most of the luminosity
is concentrated in a few dense clouds surrounding the jet. These morphological
and kinematic signatures are all found in the well observed NLR of NGC1068 and
other Seyfert galaxies.Comment: 11 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Center Domains and their Phenomenological Consequences
We argue that the domain structure of deconfined QCD matter, which can be
inferred from the properties of the Polyakov loop, can simultaneously explain
the two most prominent experimentally verified features of the quark-gluon
plasma, namely its large opacity as well as its near ideal fluid properties
Photon State Tomography for Two-Mode Correlated Itinerant Microwave Fields
Continuous variable entanglement between two modes of a radiation field is
usually studied at optical frequencies. As an important step towards the
observation of entanglement between propagating microwave photons we
demonstrate the experimental state reconstruction of two field modes in the
microwave domain. In particular, we generate two-mode correlated states with a
Josephson parametric amplifier and detect all four quadrature components
simultaneously in a two-channel heterodyne setup using amplitude detectors.
Analyzing two-dimensional phase space histograms for all possible pairs of
quadratures allows us to determine the full covariance matrix and reconstruct
the four-dimensional Wigner function. We demonstrate strong correlations
between the quadrature amplitude noise in the two modes. Under ideal conditions
two-mode squeezing below the standard quantum limit should be observable in
future experiments.Comment: 4 pages, 4 figure
NGC 2362: a Template for Early Stellar Evolution
We present UBVRI photometry for the young open cluster NGC 2362. From
analysis of the appropriate color-color and color-magnitude diagrams we derive
the fundamental parameters of the NGC 2362 cluster to be: age = 5 (+1-2) Myr,
distance = 1480 pc, E(B-V)=0.10 mag. The cluster age was independently
determined for both high mass (2.1 - 36Msun) and low mass (0.7 - 1.2Msun) stars
with excellent agreement between the ages derived using post-main sequence and
pre-main sequence evolutionary tracks for the high and low mass stars
respectively. Analysis of this cluster's color-magnitude diagram reveals a well
defined pre-main sequence (covering DeltaV ~ 9 magnitudes in V and extending
from early A stars to near the hydrogen burning limit) which makes this cluster
an ideal laboratory for pre-main sequence evolution studies.Comment: 9 pages, 3 figures, to be published in ApJ
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