6,344 research outputs found
CHORIZOS: a CHi-square cOde for parameteRized modelIng and characteriZation of phOtometry and Spectrophotometry
We have developed a CHi-square cOde for parameteRized modelIng and
characteriZation of phOtometry and Spectrophotometry (CHORIZOS). CHORIZOS can
use up to two intrinsic free parameters (e.g. temperature and gravity for
stars; type and redshift for galaxies; or age and metallicity for stellar
clusters) and two extrinsic ones (amount and type of extinction). The code uses
chi-square minimization to find all models compatible with the observed data in
the model N-dimensional (N=1,2,3,4) parameter space. CHORIZOS can use either
correlated or uncorrelated colors as input and is especially designed to
identify possible parameter degeneracies and multiple solutions. The code is
written in IDL and is available to the astronomical community. Here we present
the techniques used, test the code, apply it to a few well-known astronomical
problems, and suggest possible applications. As a first scientific result from
CHORIZOS, we confirm from photometry the need for a revised
temperature-spectral type scale for OB stars previously derived from
spectroscopy.Comment: 32 pages, 13 figures. To appear in the September 2004 issue of PAS
Robust predictions for an oscillatory bispectrum in Planck 2015 data from transient reductions in the speed of sound of the inflaton
We update the search for features in the Cosmic Microwave Background (CMB)
power spectrum due to transient reductions in the speed of sound, using Planck
2015 CMB temperature and polarisation data. We enlarge the parameter space to
much higher oscillatory frequencies of the feature, and define a robust prior
independent of the ansatz for the reduction, guaranteed to reproduce the
assumptions of the theoretical model and exhaustive in the regime in which the
feature is easily distinguishable from the baseline cosmology. We find a fit to
the -- minus/plus structure in Planck TT power spectrum, as
well as features spanning along the higher 's (--).
For the last ones, we compute the correlated features that we expect to find in
the CMB bispectrum, and asses their signal-to-noise and correlation to the
ISW-lensing secondary bispectrum. We compare our findings to the shape-agnostic
oscillatory template tested in Planck 2015, and we comment on some tantalising
coincidences with some of the traits described in Planck's 2015 bispectrum
data.Comment: 19 pages - matches published versio
Hierarchy of inequalities for quantitative duality
We derive different relations quantifying duality in a generic two-way
interferometer. These relations set different upper bounds to the visibility V
of the fringes measured at the output port of the interferometer. A hierarchy
of inequalities is presented which exhibits the influence of the availability
to the experimenter of different sources of which-way information contributing
to the total distinguishability D of the ways. For mixed states and unbalanced
interferometers an inequality is derived, V^2+ Xi^2 \leq 1, which can be more
stringent than the one associated with the distinguishability (V^2+ D^2 \leq
1).Comment: 7 pages, 4 figure
Novel characterization method of impedance cardiography signals using time-frequency distributions
The purpose of this document is to describe a methodology to select the most adequate time-frequency distribution (TFD) kernel for the characterization of impedance cardiography signals (ICG). The predominant ICG beat was extracted from a patient and was synthetized using time-frequency variant Fourier approximations. These synthetized signals were used to optimize several TFD kernels according to a performance maximization. The optimized kernels were tested for noise resistance on a clinical database. The resulting optimized TFD kernels are presented with their performance calculated using newly proposed methods. The procedure explained in this work showcases a new method to select an appropriate kernel for ICG signals and compares the performance of different time-frequency kernels found in the literature for the case of ICG signals. We conclude that, for ICG signals, the performance (P) of the spectrogram with either Hanning or Hamming windows (P¿=¿0.780) and the extended modified beta distribution (P¿=¿0.765) provided similar results, higher than the rest of analyzed kernels.Peer ReviewedPostprint (published version
Synchronization of networks with variable local properties
We study the synchronization transition of Kuramoto oscillators in scale-free
networks that are characterized by tunable local properties. Specifically, we
perform a detailed finite size scaling analysis and inspect how the critical
properties of the dynamics change when the clustering coefficient and the
average shortest path length are varied. The results show that the onset of
synchronization does depend on these properties, though the dependence is
smooth. On the contrary, the appearance of complete synchronization is
radically affected by the structure of the networks. Our study highlights the
need of exploring the whole phase diagram and not only the stability of the
fully synchronized state, where most studies have been done up to now.Comment: 5 pages and 3 figures. APS style. Paper to be published in IJBC
(special issue on Complex Networks' Structure and Dynamics
Improved routing strategies for Internet traffic delivery
We analyze different strategies aimed at optimizing routing policies in the
Internet. We first show that for a simple deterministic algorithm the local
properties of the network deeply influence the time needed for packet delivery
between two arbitrarily chosen nodes. We next rely on a real Internet map at
the autonomous system level and introduce a score function that allows us to
examine different routing protocols and their efficiency in traffic handling
and packet delivery. Our results suggest that actual mechanisms are not the
most efficient and that they can be integrated in a more general, though not
too complex, scheme.Comment: Final versio
Controlling the nature of a charged impurity in a bath of Feshbach dimers
We theoretically study the dynamics of a trapped ion that is immersed in an
ultracold gas of weakly bound atomic dimers created by a Feshbach resonance.
Using quasi-classical simulations, we find a crossover from dimer dissociation
to molecular ion formation depending on the binding energy of the dimers. The
location of the crossover strongly depends on the collision energy and the
time-dependent fields of the Paul trap. Deeply bound dimers lead to fast
molecular ion formation, with rates approaching the Langevin collision rate
cms. The kinetic energies
of the created molecular ions have a median below mK, such that they will
stay confined in the ion trap. We conclude that interacting ions and Feshbach
molecules may provide a novel approach towards the creation of ultracold
molecular ions with applications in precision spectroscopy and quantum
chemistry.Comment: 9 pages and 12 figures including appendice
Paths to Synchronization on Complex Networks
The understanding of emergent collective phenomena in natural and social
systems has driven the interest of scientists from different disciplines during
decades. Among these phenomena, the synchronization of a set of interacting
individuals or units has been intensively studied because of its ubiquity in
the natural world. In this paper, we show how for fixed coupling strengths
local patterns of synchronization emerge differently in homogeneous and
heterogeneous complex networks, driving the process towards a certain global
synchronization degree following different paths. The dependence of the
dynamics on the coupling strength and on the topology is unveiled. This study
provides a new perspective and tools to understand this emerging phenomena.Comment: Final version published in Physical Review Letter
Spin torque contribution to the a.c. spin Hall conductivity
Using the recently proposed definition of a conserved spin-current operator
[J. Shi et al., Phys. Rev. Lett. 96, 076604 (2006)] we explore the frequency
dependent spin Hall conductivity for a two-dimensional electron gas with Rashba
and Dresselhaus spin-orbit interaction in response to an oscillating electric
field. We show that the optical spectrum of the spin Hall conductivity exhibit
remarkable changes when the new definition of spin current is applied. Such
behavior is mainly due to a significant contribution of the spin torque term
which is absent in the conventional form of the spin current. In addition, it
is observed that the magnitude and direction of the dynamic spin Hall current
strongly depends on the electric field frequency as with the interplay of the
spin-orbit coupling strengths.Comment: 8 pages, 4 figures, pape
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