1,727 research outputs found
Universal charge transport of the Mn oxides in the high temperature limit
We have found that various Mn oxides have the universal resistivity and
thermopower in the high temperature limit. The resistivities and thermopowers
of all the samples go toward constant values of 71 mcm and
3 V/K, which are independent of carrier density and crystal
structures. We propose that the electric conduction occurs in a highly
localized way in the high temperature limit, where the exchange of entropy and
charge occurs in the neighboring Mn and Mn ions.Comment: 4 pages, 4 eps figures, to be published in J. Appl. Phy
A major star formation region in the receding tip of the stellar Galactic bar
We present an analysis of the optical spectroscopy of 58 stars in the
Galactic plane at \arcdeg, where a prominent excess in the flux
distribution and star counts have been observed in several spectral regions, in
particular in the Two Micron Galactic Survey (TMGS) catalog. The sources were
selected from the TMGS, to have a magnitude brighter than +5 mag and be
within 2 degrees of the Galactic plane. More than 60% of the spectra correspond
to stars of luminosity class I, and a significant proportion of the remainder
are very late giants which would also be fast evolving. This very high
concentration of young sources points to the existence of a major star
formation region in the Galactic plane, located just inside the assumed origin
of the Scutum spiral arm. Such regions can form due to the concentrations of
shocked gas where a galactic bar meets a spiral arm, as is observed at the ends
of the bars of face-on external galaxies. Thus, the presence of a massive star
formation region is very strong supporting evidence for the presence of a bar
in our Galaxy.Comment: 13 pages (latex) + 4 figures (eps), accepted in ApJ Let
Bulk antiferromagnetism in single crystals
Susceptibility, specific heat, and muon spin rotation measurements on
high-quality single crystals of have revealed bulk
antiferromagnetism with N\'{e}el temperature K and an
ordered moment perpendicular to the layers. The magnetic order
encompasses nearly 100% of the crystal volume. The susceptibility exhibits a
broad peak around 30 K, characteristic of two-dimensional antiferromagnetic
fluctuations. The in-plane resistivity is metallic at high temperatures and
exhibits a minimum at .Comment: published versio
A search for counterparts to massive X-ray binaries using photometric catalogues
(abridged) INTEGRAL has discovered large numbers of new hard X-ray sources,
many of which are believed to be high mass X-ray binaries. However, for a
significant fraction, their counterparts remain unidentified. We explore the
use of photometric catalogues to find optical counterparts to high mass X-ray
binaries. Candidates were selected from 2MASS photometry by means of a
reddening free Q parameter. Sufficiently bright candidates were
spectroscopically observed. Many of the candidates selected turned out to be
moderately reddened late A or early F stars, but our method is able to identify
the counterpart to IGR J16207-5129, confirmed by a Chandra localisation. We
classify this object as a B0 supergiant. In the field of AX J1820.5-1434, we
find a mid or early B-type star, but we cannot confirm it as the counterpart.
For AX J1700.2-4220, we do not find any suitable candidate within the ASCA
error circle. We classify HD 153295, a marginal candidate to be the
counterpart, as B0.5IVe, and find a distance compatible with membership in Sco
OB1. We derive a spectral type B0IIIe for HD100199, previously identified as
the counterpart to IGR J11305-6256. In the case of IGR J17091-3624, the object
associated with a variable radio source in the field is a late F star. The
procedure used is able to correctly identify OB stars and, in about one third
of the cases, may lead to the localisation of the correct counterpart. However,
the majority of INTEGRAL error circles do not contain any suitable optically
visible counterpart. Deep infrared searches are going to be necessary in order
to locate the counterparts to these sources.Comment: 10 pages, 6 figures; Accepted for publication in Astronomy &
Astrophysics (Sept 25th
Transient evolution of C-type shocks in dusty regions of varying density
Outflows of young stars drive shocks into dusty, molecular regions. Most
models of such shocks assume that they are steady and propagating perpendicular
to the magnetic field. Real shocks often violate both of these assumptions and
the media through which they propagate are inhomogeneous. We use the code
employed previously to produce the first time-dependent simulations of
fast-mode, oblique C-type shocks interacting with density perturbations. We
include a self-consistent calculation of the thermal and ionisation balances
and a fluid treatment of grains. We identify features that develop when a
multifluid shock encounters a density inhomogeneity to investigate whether any
part of the precursor region ever behaves in a quasi-steady fashion. If it does
the shock may be modelled approximately without solving the time-dependent
hydromagnetic equations. Simulations were made for initially steady oblique
C-type shocks encountering density inhomogeneities. For a semi-finite
inhomogeneity with a density larger than the surrounding medium, a transmitted
shock evolves from being J-type to a steady C-type shock on a timescale
comparable to the ion-flow time through it. A sufficiently upstream part of the
precursor of an evolving J-type shock is quasi-steady. The ion-flow timescale
is also relevant for the evolution of a shock moving into a region of
decreasing density. The models for shocks propagating into regions in which the
density increases and then decreases to its initial value cannot be entirely
described in terms of the results obtained for monotonically increasing and
decreasing densities. For the latter model, the long-term evolution to a C-type
shock cannot be approximated by quasi-steady models.Comment: 11 pages, 9 figure
Optical properties of polycrystalline Cd(1-x)Mn(x)Te
Bulk polycrystalline cadmium manganese telluride, Cd(l-x)Mn(x)Te, was manufactured in several compositions by a synthesis process. The structure of the obtained compounds was the characteristic zinc-blende polycrystalline pattern being the grain size lOOj=20 nm. These materials are manufactured to replace single-crystal compounds in some magneto-optical devices. The cut-off wavelength and the Verdet constant are the same as the single-crystals with identical composition. A polarized laser beam, after having passed through a sample of 0.76 mm thickness, was depolarized less than 2.5%, and 90% of its energy was spread into a 2Âș cone. Scattering of light is produced because of the polycrystalline structure of these ompounds. Some scattering diagrams, due to the diffraction and Mie scattering in the polycrystalline grains are shown
Upregulated complement receptors correlate with Fc gamma receptor 3A-positive natural killer and natural killer-T cells in neuromyelitis optica spectrum disorder
BACKGROUND AND OBJECTIVES: Inhibition of terminal complement in neuromyelitis optica spectrum disorder (NMOSD) using eculizumab helps prevent relapses, but the exact mechanism of action of the drug remains unclear. Similarly, genetic variants in the Fc Gamma receptor 3A (FCGR3A), also known as CD16, are correlated with outcomes in NMOSD, but the immune cells expressing those CD16 are unknown. We compared CD16 expression on immune cells modulated by complement activity in natural killer (NK) cells and natural killer-T (NKT) cells in NMOSD to disease and normal-healthy controls. METHODS: Peripheral blood cell (PBMC) samples from 45 patients with NMOSD with aquaporin 4 (AQP4)-IgG, 18 disease controls, and 19 normal controls were analyzed for CD16 expression and complement receptors in vitro. RESULTS: At baseline, the number of NKT cells was increased in NMOSD (pâ<â0.001), but the proportion that was CD16 positive was lower compared to normal and disease controls (pâ=â0.0012). NK cell count was normal, but the ratio that was CD16 positive was also significantly lower (pâ<â0.001). In both NK cells and NKT cells from NMOSD, C5 complement receptor expression was much higher than normal and disease controls (pâ<â0.001 for both). We also evaluated activation markers CD69 and CD83, which were also significantly higher in NK and NKT cells from NMOSD patients. FCGR3A p158 V/V genotype group in NMOSD patients showed decreased NK cell proportion with activation, and fewer CD16-expressing NKT cells than the F/F genotype group. DISCUSSION: Our results support an immunopathogenesis model in which complement pathway activation in NK/NKT cells upregulates CD16 expression that binds to antibody/antigen complexes. In the context of NMOSD, these complement-sensitive cells may be responsible for the escalating autoimmune activity
Quantized reduction as a tensor product
Symplectic reduction is reinterpreted as the composition of arrows in the
category of integrable Poisson manifolds, whose arrows are isomorphism classes
of dual pairs, with symplectic groupoids as units. Morita equivalence of
Poisson manifolds amounts to isomorphism of objects in this category.
This description paves the way for the quantization of the classical
reduction procedure, which is based on the formal analogy between dual pairs of
Poisson manifolds and Hilbert bimodules over C*-algebras, as well as with
correspondences between von Neumann algebras. Further analogies are drawn with
categories of groupoids (of algebraic, measured, Lie, and symplectic type). In
all cases, the arrows are isomorphism classes of appropriate bimodules, and
their composition may be seen as a tensor product. Hence in suitable categories
reduction is simply composition of arrows, and Morita equivalence is
isomorphism of objects.Comment: 44 pages, categorical interpretation adde
Synthetic Spectra and Color-Temperature Relations of M Giants
As part of a project to model the integrated spectra and colors of elliptical
galaxies through evolutionary synthesis, we have refined our synthetic spectrum
calculations of M giants. After critically assessing three effective
temperature scales for M giants, we adopted the relation of Dyck et al. (1996)
for our models. Using empirical spectra of field M giants as a guide, we then
calculated MARCS stellar atmosphere models and SSG synthetic spectra of these
cool stars, adjusting the band absorption oscillator strengths of the TiO bands
to better reproduce the observational data. The resulting synthetic spectra are
found to be in very good agreement with the K-band spectra of stars of the
appropriate spectral type taken from Kleinmann & Hall (1986) as well. Spectral
types estimated from the strengths of the TiO bands and the depth of the
bandhead of CO near 2.3 microns quantitatively confirm that the synthetic
spectra are good representations of those of field M giants. The broad-band
colors of the models match the field relations of K and early-M giants very
well; for late-M giants, differences between the field-star and synthetic
colors are probably caused by the omission of spectral lines of VO and water in
the spectrum synthesis calculations. Here, we present four grids of K-band
bolometric corrections and colors -- Johnson U-V and B-V; Cousins V-R and V-I;
Johnson-Glass V-K, J-K and H-K; and CIT/CTIO V-K, J-K, H-K and CO -- for models
having 3000 K < Teff < 4000 K and -0.5 < log g < 1.5. These grids, which have
[Fe/H] = +0.25, 0.0, -0.5 and -1.0, extend and supplement the color-temperature
relations of hotter stars presented in a companion paper (astro-ph/9911367).Comment: To appear in the March 2000 issue of the Astronomical Journal. 60
pages including 15 embedded postscript figures (one page each) and 6 embedded
postscript tables (10 pages total
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