13,574 research outputs found
Haro15: Is it actually a low metallicity galaxy?
We present a detailed study of the physical properties of the nebular
material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long
slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study
the physical conditions (electron density and temperature), ionic and total
chemical abundances of several atoms, reddening and ionization structure. The
latter was derived by comparing the oxygen and sulphur ionic ratios to their
corresponding observed emission line ratios (the eta and eta' plots) in
different regions of the galaxy. Applying direct and empirical methods for
abundance determination, we perform a comparative analysis between these
regions.Comment: (Poster paper) 2 pages, 2 figure
The IACOB project: A grid-based automatic tool for the quantitative spectroscopic analysis of O-stars
We present the IACOB grid-based automatic tool for the quantitative
spectroscopic analysis of O-stars. The tool consists of an extensive grid of
FASTWIND models, and a variety of programs implemented in IDL to handle the
observations, perform the automatic analysis, and visualize the results. The
tool provides a fast and objective way to determine the stellar parameters and
the associated uncertainties of large samples of O-type stars within a
reasonable computational time.Comment: 8 pages, 2 figures, 1 table. Proceedings of the "GREAT-ESF Stellar
Atmospheres in the Gaia Era Workshop
Extracting topological features from dynamical measures in networks of Kuramoto oscillators
The Kuramoto model for an ensemble of coupled oscillators provides a
paradigmatic example of non-equilibrium transitions between an incoherent and a
synchronized state. Here we analyze populations of almost identical oscillators
in arbitrary interaction networks. Our aim is to extract topological features
of the connectivity pattern from purely dynamical measures, based on the fact
that in a heterogeneous network the global dynamics is not only affected by the
distribution of the natural frequencies, but also by the location of the
different values. In order to perform a quantitative study we focused on a very
simple frequency distribution considering that all the frequencies are equal
but one, that of the pacemaker node. We then analyze the dynamical behavior of
the system at the transition point and slightly above it, as well as very far
from the critical point, when it is in a highly incoherent state. The gathered
topological information ranges from local features, such as the single node
connectivity, to the hierarchical structure of functional clusters, and even to
the entire adjacency matrix.Comment: 11 pages, 10 figure
2D granular flows with the rheology and side walls friction: a well balanced multilayer discretization
We present here numerical modelling of granular flows with the
rheology in confined channels. The contribution is twofold: (i) a model to
approximate the Navier-Stokes equations with the rheology through an
asymptotic analysis. Under the hypothesis of a one-dimensional flow, this model
takes into account side walls friction; (ii) a multilayer discretization
following Fern\'andez-Nieto et al. (J. Fluid Mech., vol. 798, 2016, pp.
643-681). In this new numerical scheme, we propose an appropriate treatment of
the rheological terms through a hydrostatic reconstruction which allows this
scheme to be well-balanced and therefore to deal with dry areas. Based on
academic tests, we first evaluate the influence of the width of the channel on
the normal profiles of the downslope velocity thanks to the multilayer approach
that is intrinsically able to describe changes from Bagnold to S-shaped (and
vice versa) velocity profiles. We also check the well balance property of the
proposed numerical scheme. We show that approximating side walls friction using
single-layer models may lead to strong errors. Secondly, we compare the
numerical results with experimental data on granular collapses. We show that
the proposed scheme allows us to qualitatively reproduce the deposit in the
case of a rigid bed (i. e. dry area) and that the error made by replacing the
dry area by a small layer of material may be large if this layer is not thin
enough. The proposed model is also able to reproduce the time evolution of the
free surface and of the flow/no-flow interface. In addition, it reproduces the
effect of erosion for granular flows over initially static material lying on
the bed. This is possible when using a variable friction coefficient
but not with a constant friction coefficient
Fast generation of spin-squeezed states in bosonic Josephson junctions
We describe methods for fast production of highly coherent-spin-squeezed
many-body states in bosonic Josephson junctions (BJJs). We start from the known
mapping of the two-site Bose-Hubbard (BH) Hamiltonian to that of a single
effective particle evolving according to a Schr\"odinger-like equation in Fock
space. Since, for repulsive interactions, the effective potential in Fock space
is nearly parabolic, we extend recently derived protocols for shortcuts to
adiabatic evolution in harmonic potentials to the many-body BH Hamiltonian. The
best scaling of the squeezing parameter for large number of atoms N is \xi^2_S
~ 1/N.Comment: Improved and enlarged version, accepted at Phys. Rev.
Analysis and test of the central-blue-spot infall hallmark
The infall of material onto a protostar, in the case of optically thick line
emission, produces an asymmetry in the blue- and red-wing line emission. For an
angularly resolved emission, this translates in a blue central spot in the
first-order moment (intensity weighted velocity) map. An analytical expression
for the first-order moment intensity as a function of the projected distance
was derived, for the cases of infinite and finite infall radius. The effect of
a finite angular resolution, which requires the numerical convolution with the
beam, was also studied. This method was applied to existing data of several
star-forming regions, namely G31.41+0.31 HMC, B335, and LDN 1287, obtaining
good fits to the first-order moment intensity maps, and deriving values of the
central masses onto which the infall is taking place (G31.41+0.31 HMC: 70-120
; B335: 0.1 ; Guitar Core of LDN 1287: 4.8 ). The
central-blue-spot infall hallmark appears to be a robust and reliable indicator
of infall.Comment: Accepted for publication in A&
Testing models with non-minimal Higgs sector through the decay t->q+WZ
We study the contribution of charged Higgs boson to the rare decay of the top
quark t->q+WZ (q=d,s,b) in models with Higgs sector that includes doublets and
triplets. Higgs doublets are needed to couple charged Higgs with quarks,
whereas the Higgs triplets are required to generate the non-standard vertex HWZ
at tree-level. It is found that within a model that respect the custodial SU(2)
symmetry and avoids flavour changing neutral currents by imposing discrete
symmetries, the decay mode t->b+WZ, can reach a branching ratio of order
0.0178, whereas the decay modes t->(d,s)+WZ, can reach a similar branching
ratio in models where flavour changing neutral currents are suppressed by
flavour symmetries.Comment: Typeset using REVTEX and EPSF, 5 pag, 2 figure
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