13,834 research outputs found
Correlating the interstellar magnetic field with protostellar jets and its sources
This article combines new CCD polarimetric data with previous information
about protostellar objects in a search for correlations involving the
interstellar magnetic field. Specifically, we carried out an optical
polarimetric study of a sample of 28 fields of 10 X 10 arcmin^2 located in the
neighborhood of protostellar jets and randomly spread over the Galaxy. The
polarimetry of a large number of field stars is used to estimate both the
average and dispersion of the interstellar magnetic field (ISMF) direction in
each region. The results of the applied statistical tests are as follows.
Concerning the alignment between the jet direction and the interstellar
magnetic field, the whole sample does not show alignment. There is, however, a
statistically significant alignment for objects of Classes 0 and I. Regarding
the interstellar magnetic field dispersion, our sample presents values slightly
larger for regions containing T Tauri objects than for those harboring younger
protostars. Moreover the ISMF dispersion in regions containing high-mass
objects tends to be larger than in those including only low-mass protostars. In
our sample, the mean interstellar polarization as a function of the average
interstellar extinction in a region reaches a maximum value around 3% for A(V)
= 5, after which it decreases. Our data also show a clear correlation of the
mean value of the interstellar polarization with the dispersion of the
interstellar magnetic field: the larger the dispersion, the smaller the
polarization. Based on a comparison of our and previous results, we suggest
that the dispersion in regions forming stars is larger than in quiescent
regions.Comment: ApJ accepte
On simulation of local fluxes in molecular junctions
We present a pedagogical review of current density simulation in molecular
junction models indicating its advantages and deficiencies in analysis of local
junction transport characteristics. In particular, we argue that current
density is a universal tool which provides more information than traditionally
simulated bond currents, especially when discussing inelastic processes.
However, current density simulations are sensitive to choice of basis and
electronic structure method. We note that discussing local current conservation
in junctions one has to account for source term caused by open character of the
system and intra-molecular interactions. Our considerations are illustrated
with numerical simulations of a benzenedithiol molecular junction.Comment: 10 pages, 6 figure
Charge order induced by electron-lattice interaction in NaV2O5
We present Density Matrix Renormalization Group calculations of the
ground-state properties of quarter-filled ladders including static
electron-lattice coupling. Isolated ladders and two coupled ladders are
considered, with model parameters obtained from band-structure calculations for
-NaVO. The relevant Holstein coupling to the lattice
causes static out-of-plane lattice distortions, which appear concurrently with
a charge-ordered state and which exhibit the same zigzag pattern observed in
experiments. The inclusion of electron-lattice coupling drastically reduces the
critical nearest-neighbor Coulomb repulsion needed to obtain the
charge-ordered state. No spin gap is present in the ordered phase. The charge
ordering is driven by the Coulomb repulsion and the electron-lattice
interaction. With electron-lattice interaction, coupling two ladders has
virtually no effect on or on the characteristics of the charge-ordered
phase. At V=0.46\eV, a value consistent with previous estimates, the lattice
distortion, charge gap, charge order parameter, and the effective spin coupling
are in good agreement with experimental data for NaVO_5$.Comment: 7 pages, 9 figure
Teleportation in a noisy environment: a quantum trajectories approach
We study the fidelity of quantum teleportation for the situation in which
quantum logic gates are used to provide the long distance entanglement required
in the protocol, and where the effect of a noisy environment is modeled by
means of a generalized amplitude damping channel. Our results demonstrate the
effectiveness of the quantum trajectories approach, which allows the simulation
of open systems with a large number of qubits (up to 24). This shows that the
method is suitable for modeling quantum information protocols in realistic
environments.Comment: 9 pages, 2 figure
Probing the Density in the Galactic Center Region: Wind-Blown Bubbles and High-Energy Proton Constraints
Recent observations of the Galactic center in high-energy gamma-rays (above
0.1TeV) have opened up new ways to study this region, from understanding the
emission source of these high-energy photons to constraining the environment in
which they are formed. We present a revised theoretical density model of the
inner 5pc surrounding Sgr A* based on the fact that the underlying structure of
this region is dominated by the winds from the Wolf-Rayet stars orbiting Sgr
A*. An ideal probe and application of this density structure is this high
energy gamma-ray emission. We assume a proton-scattering model for the
production of these gamma-rays and then determine first whether such a model is
consistent with the observations and second whether we can use these
observations to further constrain the density distribution in the Galactic
center.Comment: 36 pages including 17 figures, submitted to ApJ, comments welcom
Duodenal intraepithelial lymphocytes of children with cow milk allergy preferentially bind the glycan-binding protein galectin-3
A breakdown in intestinal homeostasis results in inflammatory bowel diseases including coeliac disease and allergy. Galectins, evolutionarily conserved beta-galactoside-binding proteins, can modulate immune-epithelial cell interactions by influencing immune cell fate and cytokine secretion. In this study we investigated the glycosylation signature, as well as the regulated expression of galectin-1 and -3 in human duodenal samples of allergic and non-allergic children. Whereas galectin-1 was predominantly localized in the epithelial compartment (epithelial cells and intraepithelial lymphocytes) and the underlying lamina propria (T cells, macrophages and plasma cells), galectin-3 was mainly expressed by crypt epithelial cells and macrophages in the lamina propria. Remarkably, expression of these galectins was not significantly altered in allergic versus non-allergic patients. Investigation of the glycophenotype of the duodenal inflammatory microenvironment revealed substantial alpha2-6-linked sialic acid bound to galactose in lamina propria plasma cells, macrophages and intraepithelial lymphocytes and significant levels of asialo core 1 O-glycans in CD68+ macrophages and enterocytes. Galectin-1 preferentially bound to neutrophils, plasma cells and enterocytes, while galectin-3 binding sites were mainly distributed on macrophages and intraepithelial lymphocytes. Notably, galectin-3, but not galectin-1 binding, was substantially increased in intraepithelial gut lymphocytes of allergic patients compared to non-allergic subjects, suggesting a potential role of galectin-3-glycan interactions in shaping epithelial-immune cell connections during allergic inflammatory processes.Fil: Mercer, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Guzman, Luciana. Provincia de Buenos Aires. Ministerio de Salud. Hospital de Niños "Sor María Ludovica" de la Plata; ArgentinaFil: Cueto Rua, Eduardo. Provincia de Buenos Aires. Ministerio de Salud. Hospital de Niños "Sor María Ludovica" de la Plata; ArgentinaFil: Drut, Ricardo. Provincia de Buenos Aires. Ministerio de Salud. Hospital de Niños "Sor María Ludovica" de la Plata; ArgentinaFil: Ahmed, H.. University of Maryland; Estados UnidosFil: Vasta, G. R.. University of Maryland; Estados UnidosFil: Toscano, Marta Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Rabinovich, Gabriel Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Docena, Guillermo H.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; Argentin
High Resolution X-Ray Spectra of Capella: Initial Results from the Chandra High Energy Transmission Grating Spectrometer
High resolution spectra of the active binary Capella (G8 III + G1 III)
covering the energy range 0.4-8.0 keV (1.5-30 Angstroms) show a large number of
emission lines, demonstrating the performance of the HETGS. A preliminary
application of plasma diagnostics provides information on coronal temperatures
and densities. Lines arising from different elements in a range of ionization
states indicate that Capella has plasma with a broad range of temperatures,
from log T = 6.3 to 7.2, generally consistent with recent results from
observations with the Extreme Ultraviolet Explorer (EUVE) and the Advanced
Satellite for Cosmology and Astrophysics (ASCA). The electron density is
determined from He-like O VII lines, giving the value N_e=10^10 cm^-3 at
T_e=2*10^6 K; He-like lines formed at higher temperatures give only upper
limits to the electron density. The density and emission measure from O VII
lines together indicate that the coronal loops are significantly smaller than
the stellar radius.Comment: 9 pages, 3 figures (1 color) accepted for ApJ
X-Ray Photoabsorption in KLL Resonances of O VI And Abundance Analysis
It is shown that photoabsorption via autoionizing resonances may be
appreciable and used for abundance analysis. Analogous to spectral lines, the
`resonance oscillator strength' f_r may be defined and evaluated in terms of
the differential oscillator strength df/d(epsilon) that relates bound and
continuum absorption. X-ray photoabsorption in KLL (1s2s2p) resonances of O VI
is investigated using highly resolved relativistic photoionization cross
sections with fine structure. It is found that f_r is comparable to that for UV
dipole transition in O VI (2s - 2p) and the X-ray (1s^2 ^1S_0 - 1s2p ^1P^o_1)
transition in O VII. The dominant O VI(KLL) components lie at 22.05 and 21.87
Angstroms. These predicted absorption features should be detectable by the
Chandra X-Ray Observatory (CXO) and the X-Ray Multi-Mirror Mission (XMM). The
combined UV/X-ray spectra of O VI/O VII should yield valuable information on
the ionization structure and abundances in sources such as the `warm absorber'
region of active galactic nuclei and the hot intergalactic medium. Some general
implications of resonant photoabsorption are addressed.Comment: Astrophys. J. Letters (in press), 9 pages, 3 figure
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