13,840 research outputs found
On a Speculated Relation Between Chv\'atal-Sankoff Constants of Several Sequences
It is well known that, when normalized by n, the expected length of a longest
common subsequence of d sequences of length n over an alphabet of size sigma
converges to a constant gamma_{sigma,d}. We disprove a speculation by Steele
regarding a possible relation between gamma_{2,d} and gamma_{2,2}. In order to
do that we also obtain new lower bounds for gamma_{sigma,d}, when both sigma
and d are small integers.Comment: 13 pages. To appear in Combinatorics, Probability and Computin
SPECIES I: Spectroscopic Parameters and atmosphEric ChemIstriEs of Stars
The detection and subsequent characterisation of exoplanets are intimately
linked to the characteristics of their host star. Therefore, it is necessary to
study the star in detail in order to understand the formation history and
characteristics of their companion(s). Our aims were to develop a community
tool that allows the automated calculation of stellar parameters for a large
number of stars, using high resolution echelle spectra and minimal photometric
magnitudes, and introduce the first results in this work. We measured the
equivalent widths of several iron lines and used them to solve the radiative
transfer equation assuming local thermodynamic equilibrium to obtain the
atmospheric parameters (, [Fe/H], logg and ). We used
these values to derive the abundance of 11 chemical elements in the stellar
photosphere (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Ni, Cu and Zn). Rotation and
macroturbulent velocity were obtained using temperature calibrators and
synthetic line profiles to match the observed spectra of five absorption lines.
Finally, by interpolating in a grid of MIST isochrones, we derived the mass,
radius and age using a Bayesian approach. SPECIES obtains bulk parameters that
are in good agreement with measured values from different existing catalogues,
including when different methods are used to derive them. We find excellent
agreement with previous works that used similar methodologies. We find
discrepancies in the chemical abundances for some elements with respect to
other works, which could be produced by differences in , or in
the line list or the atomic line data used to derive them. We also obtained
analytic relations to describe the correlations between different parameters,
and we implemented new methods to better handle these correlations, which
provides a better description of the uncertainties associated with the
measurements.Comment: 28 pages, 26 figures, resubmitted to A&
Metastable states influence on the magnetic behavior of the triangular lattice: Application to the spin-chain compound Ca3Co2O6
It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting
plateaus in the magnetization as a function of the magnetic field at low
temperatures. The origin of them is still controversial. In this paper we study
the thermal behavior of this compound with a single-flip Monte Carlo simulation
on a triangular lattice and demonstrate the decisive influence of metastable
states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We
consider the [Co2O6]n chains as giant magnetic moments described by large Ising
spins on planar clusters with open boundary conditions. With this simple
frozen-moment model we obtain stepped magnetization curves which agree quite
well with the experimental results for different sweeping rates. We describe
particularly the out-of-equilibrium states that split the low-temperature 1/3
plateau into three steps. They relax thermally to the 1/3 plateau, which has
long-range order at the equilibrium. Such states are further analyzed with
snapshots unveiling a domain-wall structure that is responsible for the
observed behavior of the 1/3 plateau. A comparison is also given of the exact
results in small triangular clusters with our Monte Carlo results, providing
further support for our thermal description of this compound.Comment: 8 pages, 11 figures, submitted to PR
The Ultraviolet Luminosity Density of the Universe from Photometric Redshifts of Galaxies in the Hubble Deep Field
Studies of the Hubble Deep Field (HDF) and other deep surveys have revealed
an apparent peak in the ultraviolet (UV) luminosity density, and therefore the
star-formation rate density, of the Universe at redshifts 1<z<2. We use
photometric redshifts of galaxies in the HDF to determine the comoving UV
luminosity density and find that, when errors (in particular, sampling error)
are properly accounted for, a flat distribution is statistically
indistinguishable from a distribution peaked at z~1.5. Furthermore, we examine
the effects of cosmological surface brightness (SB) dimming on these
measurements by applying a uniform SB cut to all galaxy fluxes after correcting
them to redshift z=5. We find that, comparing all galaxies at the same
intrinsic surface brightness sensitivity, the UV luminosity density contributed
by high intrinsic SB regions increases by almost two orders of magnitude from
z~0 to z~5. This suggests that there exists a population of objects with very
high star formation rates at high redshifts that apparently do not exist at low
redshifts. The peak of star formation, then, may occur somewhere beyond a
redshift z~>5.Comment: 4 pages total, including 3 embedded figures, to appear in the
proceedings of the Xth Rencontres de Blois, "The Birth of Galaxies." LaTeX
style file include
Efficient tomography with unknown detectors
We compare the two main techniques used for estimating the state of a
physical system from unknown measurements: standard detector tomography and
data-pattern tomography. Adopting linear inversion as a fair benchmark, we show
that the difference between these two protocols can be traced back to the
nonexistence of the reverse-order law for pseudoinverses. We capitalize on this
fact to identify regimes where the data-pattern approach outperforms the
standard one and vice versa. We corroborate these conclusions with numerical
simulations of relevant examples of quantum state tomography.Comment: 13 pages, 6 figures. Submitted for publication. Comments most
welcome
Intelligent Packaging Systems: Sensors and Nanosensors to Monitor Food Quality and Safety
Indexación: Web of Science y Scopus.The application of nanotechnology in different areas of food packaging is an emerging field that will grow rapidly in the coming years. Advances in food safety have yielded promising results leading to the development of intelligent packaging (IP). By these containers, it is possible to monitor and provide information of the condition of food, packaging, or the environment. This article describes the role of the different concepts of intelligent packaging. It is possible that this new technology could reach enhancing food safety, improving pathogen detection time, and controlling the quality of food and packaging throughout the supply chain.https://www.hindawi.com/journals/js/2016/4046061/cta
Variational approach for walking solitons in birefringent fibres
We use the variational method to obtain approximate analytical expressions
for the stationary pulselike solutions in birefringent fibers when differences
in both phase velocities and group velocities between the two components and
rapidly oscillating terms are taken into account. After checking the validity
of the approximation we study how the soliton pulse shape depends on its
velocity and nonlinear propagation constant. By numerically solving the
propagation equation we have found that most of these stationary solutions are
stable.Comment: LaTeX2e, uses graphicx package, 23 pages with 8 figure
- …