513 research outputs found
Extended Emission Line Gas in Radio Galaxies - PKS0349-27
PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a
spectacular, spiral-like structure in its extended emission line gas (EELG). We
have measured the velocity field in this gas and find that it splits into 2
cloud groups separated by radial velocities which at some points approach 400
km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta,
[SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence
for the type of HII region emission associated with starburst activity in
either velocity system. The measured emission line ratios are similar to those
found in the nuclei of narrow-line radio galaxies, but the extended
ionization/excitation cannot be produced by continuum emission from the active
nucleus alone. We present arguments which suggest that the velocity
disturbances seen in the EELG are most likely the result of a galaxy-galaxy
collision or merger but cannot completely rule out the possibility that the gas
has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.
Thermoelectric performance of granular semiconductors
We study thermoelectric properties of granular semiconductors with weak
tunneling conductance between the grains, g_t < 1. We calculate the thermopower
and figure of merit taking into account the shift of the chemical potential and
the asymmetry of the density of states in the vicinity of the Fermi surface due
to n- or p-type doping in the Efros-Shklovskii regime for temperatures less
than the charging energy. We show that for weakly coupled semiconducting grains
the figure of merit is optimized for grain sizes of order 5nm for typical
materials and its values can be larger than one. We also study the case of
compensated granular semiconductors and show that in this case the thermopower
can be still finite, although two to three orders of magnitude smaller than in
the uncompensated regime.Comment: 4 pages, 4 figure
Magnetic Properties of a Bose-Einstein Condensate
Three hyperfine states of Bose-condensed sodium atoms, recently optically
trapped, can be described as a spin-1 Bose gas. We study the behaviour of this
system in a magnetic field, and construct the phase diagram, where the
temperature of the Bose condensation increases with magnetic field.
In particular the system is ferromagnetic below and the magnetization
is proportional to the condensate fraction in a vanishing magnetic field.
Second derivatives of the magnetisation with regard to temperature or magnetic
field are discontinuous along the phase boundary.Comment: 5 pages, 5 figures included, to appear in Phys. Rev.
Mean Field Theory of Josephson Junction Arrays with Charge Frustration
Using the path integral approach, we provide an explicit derivation of the
equation for the phase boundary for quantum Josephson junction arrays with
offset charges and non-diagonal capacitance matrix. For the model with nearest
neighbor capacitance matrix and uniform offset charge , we determine,
in the low critical temperature expansion, the most relevant contributions to
the equation for the phase boundary. We explicitly construct the charge
distributions on the lattice corresponding to the lowest energies. We find a
reentrant behavior even with a short ranged interaction. A merit of the path
integral approach is that it allows to provide an elegant derivation of the
Ginzburg-Landau free energy for a general model with charge frustration and
non-diagonal capacitance matrix. The partition function factorizes as a product
of a topological term, depending only on a set of integers, and a
non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure
Domain Walls Motion and Resistivity in a Fully-Frustrated Josephson Array
It is identified numerically that the resistivity of a fully-frustrated
Josephson-junction array is due to motion of domain walls in vortex lattice
rather than to motion of single vortices
The Evolution of Early-Type Galaxies in Distant Clusters II: Internal Kinematics of 55 Galaxies in the z=0.33 Cluster CL1358+62
We define a large sample of galaxies for use in a study of the fundamental
plane in the intermediate redshift cluster CL1358+62 at . We have
analyzed high resolution spectra for 55 members of the cluster. The data were
acquired with the Low Resolution Imaging Spectrograph on the Keck I 10m
telescope. A new algorithm for measuring velocity dispersions is presented and
used to measure the internal kinematics of the galaxies. This algorithm has
been tested against the Fourier Fitting method so the data presented here can
be compared with those measured previously in nearby galaxies. We have measured
central velocity dispersions suitable for use in a fundamental plane analysis.
The data have high and the resulting random errors on the dispersions are
very low, typically . Uncertainties due to mismatch of the stellar
templates has been minimized through several tests and the total systematic
error is of order \about 5%. Good seeing enabled us to measure velocity
dispersion profiles and rotation curves for most of the sample and although a
large fraction of the galaxies display a high level of rotation, the gradients
of the total second moment of the kinematics are all very regular and similar
to those in nearby galaxies. We conclude that the data therefore can be
reliably corrected for aperture size in a manner consistent with nearby galaxy
samples.Comment: 30 pages, 13 figures; for publication in the ApJ (accepted on 23
August 1999
Edge effects in a frustrated Josephson junction array with modulated couplings
A square array of Josephson junctions with modulated strength in a magnetic
field with half a flux quantum per plaquette is studied by analytic arguments
and dynamical simulations. The modulation is such that alternate columns of
junctions are of different strength to the rest. Previous work has shown that
this system undergoes an XY followed by an Ising-like vortex lattice
disordering transition at a lower temperature. We argue that resistance
measurements are a possible probe of the vortex lattice disordering transition
as the linear resistance with
at intermediate temperatures due to dissipation at the array
edges for a particular geometry and vanishes for other geometries. Extensive
dynamical simulations are performed which support the qualitative physical
arguments.Comment: 8 pages with figs, RevTeX, to appear in Phys. Rev.
Minimum Thermal Conductivity of Superlattices
The phonon thermal conductivity of a multilayer is calculated for transport
perpendicular to the layers. There is a cross over between particle transport
for thick layers to wave transport for thin layers. The calculations shows that
the conductivity has a minimum value for a layer thickness somewhat smaller
then the mean free path of the phonons.Comment: new results added, to appear in PR
Chandra LETGS and XMM-Newton observations of NGC 4593
In this paper, we analyze spectra of the Seyfert 1 galaxy NGC 4593 obtained
with the Chandra Low Energy Transmission Grating Spectrometer (LETGS), the
Reflection Grating Spectrometer (RGS) and the European Photon Imaging Camera's
(EPIC) onboard of XMM-Newton. The two observations were separated by ~7 months.
In the LETGS spectrum we detect a highly ionized warm absorber corresponding to
an ionization state of 400x10^{-9} W m, visible as a depression at 10-18 \AA.
This depression is formed by multiple weak Fe and Ne lines. A much smaller
column density was found for the lowly ionized warm absorber, corresponding to
xi = 3x10^{-9} W m. However, an intermediate ionization warm absorber is not
detected. For the RGS data the ionization state is hard to constrain. The EPIC
results show a narrow Fe Kalpha line.Comment: 8 pages, 10 figures, accepted for publication in A&
Charging Effects and Quantum Crossover in Granular Superconductors
The effects of the charging energy in the superconducting transition of
granular materials or Josephson junction arrays is investigated using a
pseudospin one model. Within a mean-field renormalization-group approach, we
obtain the phase diagram as a function of temperature and charging energy. In
contrast to early treatments, we find no sign of a reentrant transition in
agreement with more recent studies. A crossover line is identified in the
non-superconducting side of the phase diagram and along which we expect to
observe anomalies in the transport and thermodynamic properties. We also study
a charge ordering phase, which can appear for large nearest neighbor Coulomb
interaction, and show that it leads to first-order transitions at low
temperatures. We argue that, in the presence of charge ordering, a non
monotonic behavior with decreasing temperature is possible with a maximum in
the resistance just before entering the superconducting phase.Comment: 15 pages plus 4 fig. appended, Revtex, INPE/LAS-00
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