4,321 research outputs found
Dust and ionized gas in active radio elliptical galaxies
The authors present broad and narrow bandwidth imaging of three southern elliptical galaxies which have flat-spectrum active radio cores (NGC 1052, IC 1459 and NGC 6958). All three contain dust and extended low excitation optical line emission, particularly extensive in the case of NGC 1052 which has a large H alpha + (NII) luminosity. Both NGC 1052 and IC 1459 have a spiral morphology in emission-line images. All three display independent strong evidence that a merger or infall event has recently occurred, i.e., extensive and infalling HI gas in NGC 1052, a counter-rotating core in IC 1459 and Malin-Carter shells in NGC 6958. This infall event is the most likely origin for the emission-line gas and dust, and the authors are currently investigating possible excitation mechanisms (Sparks et al. 1990)
Morphology of the Nuclear Disk in M87
A deep, fuly sampled diffraction limited (FWHM ~ 70 mas) narrow-band image of
the central region in M87 was obtained with the Wide Filed and Planetary Camera
2 of the Hubble Space Telescope using the dithering technique. The
H-alpha+[NII] continuum subtracted image reveals a wealth of details in the
gaseous disk structure described earlier by Ford et al. (1994). The disk
morphology is dominated by a well defined three-arm spiral pattern. In
addition, the major spiral arms contain a large number of small "arclets"
covering a range of sizes (0.1-0.3 arcsec = 10-30 pc). The overall surface
brightness profile inside a radius ~1.5" (100 pc) is well represented by a
power-law I(mu) ~ mu^(-1.75), but when the central ~40 pc are excluded it can
be equally well fit by an exponential disk. The major axis position angle
remains constant at about PA_disk ~ 6 deg for the innermost ~1", implying the
disk is oriented nearly perpendicular to the synchrotron jet (PA_jet ~ 291
deg). At larger radial distances the isophotes twist, reflecting the gas
distribution in the filaments connecting to the disk outskirts. The ellipticity
within the same radial range is e = 0.2-0.4, which implies an inclination angle
of i~35 deg. The sense of rotation combined with the dust obscuration pattern
indicate that the spiral arms are trailing.Comment: 5 pages, 3 postscript figures, to appear in the Proceedings of the
M87 Workshop, Ringberg castle, Germany, 15-19 Sep 1997, also available from
http://jhufos.pha.jhu.edu/~zlatan/papers.htm
Temporal behavior of the inverse spin Hall voltage in a magnetic insulator-nonmagnetic metal structure
It is demonstrated that upon pulsed microwave excitation, the temporal
behavior of a spin-wave induced inverse spin Hall voltage in a magnetic
insulator-nonmagnetic metal structure is distinctly different from the temporal
evolution of the directly excited spin-wave mode from which it originates. The
difference in temporal behavior is attributed to the excitation of long-lived
secondary spin-wave modes localized at the insulator-metal interface
Real structured singular value synthesis using the scaled Popov criterion
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77238/1/AIAA-21537-608.pd
Plane-wave based electronic structure calculations for correlated materials using dynamical mean-field theory and projected local orbitals
The description of realistic strongly correlated systems has recently
advanced through the combination of density functional theory in the local
density approximation (LDA) and dynamical mean field theory (DMFT). This
LDA+DMFT method is able to treat both strongly correlated insulators and
metals. Several interfaces between LDA and DMFT have been used, such as (N-th
order) Linear Muffin Tin Orbitals or Maximally localized Wannier Functions.
Such schemes are however either complex in use or additional simplifications
are often performed (i.e., the atomic sphere approximation). We present an
alternative implementation of LDA+DMFT, which keeps the precision of the
Wannier implementation, but which is lighter. It relies on the projection of
localized orbitals onto a restricted set of Kohn-Sham states to define the
correlated subspace. The method is implemented within the Projector Augmented
Wave (PAW) and within the Mixed Basis Pseudopotential (MBPP) frameworks. This
opens the way to electronic structure calculations within LDA+DMFT for more
complex structures with the precision of an all-electron method. We present an
application to two correlated systems, namely SrVO3 and beta-NiS (a
charge-transfer material), including ligand states in the basis-set. The
results are compared to calculations done with Maximally Localized Wannier
functions, and the physical features appearing in the orbitally resolved
spectral functions are discussed.Comment: 15 pages, 17 figure
Two Clusters with Radio-quiet Cooling Cores
Radio lobes inflated by active galactic nuclei at the centers of clusters are
a promising candidate for halting condensation in clusters with short central
cooling times because they are common in such clusters. In order to test the
AGN-heating hypothesis, we obtained Chandra observations of two clusters with
short central cooling times yet no evidence for AGN activity: Abell 1650 and
Abell 2244. The cores of these clusters indeed appear systematically different
from cores with more prominent radio emission. They do not have significant
central temperature gradients, and their central entropy levels are markedly
higher than in clusters with stronger radio emission, corresponding to central
cooling times ~ 1 Gigayear. Also, there is no evidence for fossil X-ray
cavities produced by an earlier episode of AGN heating. We suggest that either
(1) the central gas has not yet cooled to the point at which feedback is
necessary to prevent it from condensing, possibly because it is conductively
stabilized, or (2) the gas experienced a major heating event Gyr in
the past and has not required feedback since then. The fact that these clusters
with no evident feedback have higher central entropy and therefore longer
central cooling times than clusters with obvious AGN feedback strongly suggests
that AGNs supply the feedback necessary to suppress condensation in clusters
with short central cooling times.Comment: ApJ Letter, in pres
Vitamin D Deficiency in Cystic Fibrosis
Cystic Fibrosis is the most common inherited genetic respiratory disorder in the Western World. Hypovitaminosis D is almost universal in CF patients, likely due to a combination of inadequate absorption, impaired metabolism, and lack of sun exposure. Inadequate levels are associated with the high prevalence of bone disease or osteoporosis in CF patients, which is associated with increased morbidity including fractures, kyphosis, and worsening pulmonary status. Treatment goals include regular monitoring 25 hydroxyvitamin D (25OHD) levels with aggressive treatment for those with levels <75 nmol/L (<30 ng/mL). More research is needed to determine optimal supplementation goals and strategies
Static displacements and chemical correlations in alloys
Recent experiments in metallic solid solutions have revealed interesting
correlations between static pair-displacements and the ordering behavior of
these alloys. This paper discusses a simple theoretical model which
successfully explains these observations and which provides a natural framework
for analyzing experimental measurements of pair-displacements and chemical
correlations in solid solutions. The utility and scope of this model is
demonstrated by analyzing results of experiments on and alloys
and results of simulations of and alloys.Comment: 12 page
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