22,692 research outputs found
Probing embedded star clusters in the HII complex NGC 6357 with VVV
NGC 6357 is an active star-forming region located in the Sagittarius arm
displaying several star clusters, which makes it a very interesting target to
investigate star formation and early cluster evolution. We explore NGC 6357
with the "VISTA Variables in the V\'ia a L\'actea" (VVV) photometry of seven
embedded clusters (ECs), and one open cluster (OC) projected in the outskirts
of the complex.Photometric and structural properties (age, reddening, distance,
core and total radii) of the star clusters are derived. VVV saturated stars are
replaced by their 2MASS counterparts. Field-decontaminated VVV photometry is
used to analyse Colour-Magnitude Diagrams (CMDs), stellar radial density
profiles (RDPs) and determine astrophysical parameters. We report the discovery
of four ECs and one intermediate-age cluster in the complex area. We derive a
revised distance estimate for NGC 6357 of 1.780.1 kpc based on the cluster
CMD morphologies. Among the ECs, one contains the binary star the WR 93, while
the remaining ones are dominated by pre-main sequence (PMS) stars,
young-stellar objects (YSO) and/or and have a developed main sequence. These
features reflect a significant age spread among the clusters. Evidence is found
that the relatively populous cluster Pismis 24 hosts two subclusters.Comment: This article will be published in the A&A. 11 pages, 15 figures and 3
table
Inertial-Hall effect: the influence of rotation on the Hall conductivity
Inertial effects play an important role in classical mechanics but have been
largely overlooked in quantum mechanics. Nevertheless, the analogy between
inertial forces on mass particles and electromagnetic forces on charged
particles is not new. In this paper, we consider a rotating non-interacting
planar two-dimensional electron gas with a perpendicular uniform magnetic field
and investigate the effects of the rotation in the Hall conductiv
New coupled quintessence cosmology
A component of dark energy has been recently proposed to explain the current
acceleration of the Universe. Unless some unknown symmetry in Nature prevents
or suppresses it, such a field may interact with the pressureless component of
dark matter, giving rise to the so-called models of coupled quintessence. In
this paper we propose a new cosmological scenario where radiation and baryons
are conserved, while the dark energy component is decaying into cold dark
matter (CDM). The dilution of CDM particles, attenuated with respect to the
usual scaling due to the interacting process, is characterized by a
positive parameter , whereas the dark energy satisfies the equation
of state (). We carry out a joint statistical
analysis involving recent observations from type Ia supernovae, baryon acoustic
oscillation peak, and Cosmic Microwave Background shift parameter to check the
observational viability of the coupled quintessence scenario here proposed.Comment: 7 pages, 7 figures. Minor corrections to match published versio
Levantameto de vírus em cucurbitáceas no Brasil, no período 2008-2010.
Visando conhecer a frequência de ocorrência dos vírus mais importantes (Papaya ringspot virus - type watermelor PRSV-W; Zucchini yellow mosaic virus - ZYMV; Watermelon mosaic virus - WMV; Cucumber mosaic virus - CMV; Zucchini lethal cholorosis virus - ZLCV) que infecta essas culturas no Brasil, realizou-se no período de 2008 a 2010, um levantamento em 25 áreas produtoas de 21 municípios, abrangendo sete estados, além do Distrito Federal.bitstream/item/57213/1/BPD-76.pd
Is the transition redshift a new cosmological number?
Observations from Supernovae Type Ia (SNe Ia) provided strong evidence for an
expanding accelerating Universe at intermediate redshifts. This means that the
Universe underwent a transition from deceleration to acceleration phases at a
transition redshift of the order unity whose value in principle depends
on the cosmology as well as on the assumed gravitational theory. Since
cosmological accelerating models endowed with a transition redshift are
extremely degenerated, in principle, it is interesting to know whether the
value of itself can be observationally used as a new cosmic
discriminator. After a brief discussion of the potential dynamic role played by
the transition redshift, it is argued that future observations combining SNe
Ia, the line-of-sight (or "radial") baryon acoustic oscillations, the
differential age of galaxies, as well as the redshift drift of the spectral
lines may tightly constrain , thereby helping to narrow the parameter
space for the most realistic models describing the accelerating Universe.Comment: 12 pages, 5 figures. Some discussions about how to estimate the
transition redshift have been added. New data by Planck and H(z) data have
been mentioned. New references have been adde
Physical properties of single-crystalline fibers of the colossal-magnetoresistance manganite La0.7Ca0.3MnO3
We have grown high-quality single crystals of the colossal-magnetoresistance
(CMR) material La0.7Ca0.3MnO3 by using the laser heated pedestal growth (LHPG)
method. Samples were grown as fibers of different diameters, and with lengths
of the order of centimeters. Their composition and structure were verified
through X-ray diffraction, scanning electron microcopy with EDX (Energy
Dispersive X-ray Analysis) and by Rietveld analysis. The quality of the
crystalline fibers was confirmed by Laue and EBSD (Electron Backscatter
Diffraction) patterns. Rocking curves performed along the fiber axis revealed a
half-height width of 0.073 degrees. The CMR behavior was confirmed by
electrical resistivity and magnetization measurements as a function of
temperature.Comment: 11 pages (including 3 figures); to appear in Appl. Phys. Let
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