8,871 research outputs found
The HARPS search for southern extrasolar planets XXV. Results from the metal-poor sample
Searching for extrasolar planets around stars of different metallicity may
provide strong constraints to the models of planet formation and evolution. In
this paper we present the overall results of a HARPS (a high-precision
spectrograph mostly dedicated to deriving precise radial velocities) program to
search for planets orbiting a sample of 104 metal-poor stars (selected [Fe/H]
below -0.5). Radial velocity time series of each star are presented and
searched for signals using several statistical diagnostics. Stars with detected
signals are presented, including 3 attributed to the presence of previously
announced giant planets orbiting the stars HD171028, HD181720, and HD190984.
Several binary stars and at least one case of a coherent signal caused by
activity-related phenomena are presented. One very promising new, possible
giant planet orbiting the star HD107094 is discussed, and the results are
analyzed in light of the metallicity-giant planet correlation. We conclude that
the frequency of giant planets orbiting metal-poor stars may be higher than
previously thought, probably reflecting the higher precision of the HARPS
survey. In the metallicity domain of our sample, we also find evidence that the
frequency of planets is a steeply rising function of the stellar metal content,
as found for higher metallicity stars.Comment: Accepted for publication in A&
Quinoidization of regioregular oligo(THIENO[3,4-b]THIOPHENE)s
Caracterización de oligotiofenosUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tec
Cross-Domain Learning for Classifying Propaganda in Online Contents
As news and social media exhibit an increasing amount of manipulative polarized content, detecting such propaganda has received attention as a new task for content analysis. Prior work has focused on supervised learning with training data from the same domain. However, as propaganda can be subtle and keeps evolving, manual identification and proper labeling are very demanding. As a consequence, training data is a major bottleneck. In this paper, we tackle this bottleneck and present an approach to leverage cross-domain learning, based on labeled documents and sentences from news and tweets, as well as political speeches with a clear difference in their degrees of being propagandistic. We devise informative features and build various classifiers for propaganda labeling, using cross-domain learning. Our experiments demonstrate the usefulness of this approach, and identify difficulties and limitations in various configurations of sources and targets for the transfer step. We further analyze the influence of various features, and characterize salient indicators of propaganda
Phase Fluctuations and Vortex Lattice Melting in Triplet Quasi-One-Dimensional Superconductors at High Magnetic Fields
Assuming that the order parameter corresponds to an equal spin triplet
pairing symmetry state, we calculate the effect of phase fluctuations in
quasi-one-dimensional superconductors at high magnetic fields applied along the
y (b') axis. We show that phase fluctuations can destroy the theoretically
predicted triplet reentrant superconducting state, and that they are
responsible for melting the magnetic field induced Josephson vortex lattice
above a magnetic field dependent melting temperature Tm.Comment: 4 pages (double column), 1 eps figur
A brown dwarf companion to the intermediate-mass star HR6037
In the course of an imaging survey we have detected a visual companion to the
intermediate-mass star HR 6037. In this letter, we present two epoch
observations of the binary with NACO/VLT, and near-IR spectroscopy of the
secondary with ISAAC/VLT. The NACO observations allow us to confirm HR 6037B as
a co-moving companion. Its J and H band ISAAC spectra suggest the object has an
spectral type of M9+-1, with a surface gravity intermediate between that of 10
Myr dwarfs and field dwarfs with identical spectral type. The comparison of its
Ks-band photometry with evolutionary tracks allows us to derive a mass,
effective temperature, and surface gravity of 62+-20 MJup, Teff = 2330+-200 K,
and log g = 5.1+-0.2, respectively. The small mass ratio of the binary, -0.03,
and its long orbital period, -5000 yr, makes HR 6037 a rare and uncommon binary
system.Comment: (5 pages, 4 figures, accepted for publication in A&A Letters
Vortices in vibrated granular rods
We report the experimental observation of novel vortex patterns in vertically
vibrated granular rods. Above a critical packing fraction, moving ordered
domains of nearly vertical rods spontaneously form and coexist with horizontal
rods. The domains of vertical rods coarsen in time to form large vortices. We
investigate the conditions under which the vortices occur by varying the number
of rods, vibration amplitude and frequency. The size of the vortices increases
with the number of rods. We characterize the growth of the ordered domains by
measuring the area fraction of the ordered regions as a function of time. A
{\em void filling} model is presented to describe the nucleation and growth of
the vertical domains. We track the ends of the vertical rods and obtain the
velocity fields of the vortices. The rotation speed of the rods is observed to
depend on the vibration velocity of the container and on the packing. To
investigate the impact of the direction of driving on the observed phenomena,
we performed experiments with the container vibrated horizontally. Although
vertical domains form, vortices are not observed. We therefore argue that the
motion is generated due to the interaction of the inclination of the rods with
the bottom of a vertically vibrated container. We also perform simple
experiments with a single row of rods in an annulus. These experiments directly
demonstrate that the rod motion is generated when the rods are inclined from
the vertical, and is always in the direction of the inclination.Comment: 6 pages, 10 figure, 2 movies at http://physics.clarku.edu/vortex uses
revtex
Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program II. Activity and radial velocity
Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes
to find low-mass planets similar to Earth by using the radial velocity (RV)
method. However, stellar magnetic cycles could add noise or even mimic the RV
signal of a long-period companion. Following our previous work that studied the
correlation between activity cycles and long-term RV variations for K dwarfs we
now expand that research to the lower-end of the main sequence. Our objective
is to detect any correlations between long-term activity variations and the
observed RV of a sample of M dwarfs. We used a sample of 27 M-dwarfs with a
median observational timespan of 5.9 years. The cross-correlation function
(CCF) with its parameters RV, bisector inverse slope (BIS), full-width-at-half-
maximum (FWHM) and contrast have been computed from the HARPS spectrum. The
activity index have been derived using the Na I D doublet. These parameters
were compared with the activity level of the stars to search for correlations.
We detected RV variations up to ~5 m/s that we can attribute to activity cycle
effects. However, only 36% of the stars with long-term activity variability
appear to have their RV affected by magnetic cycles, on the typical timescale
of ~6 years. Therefore, we suggest a careful analysis of activity data when
searching for extrasolar planets using long-timespan RV data.Comment: 20 pages, 12 figures, 3 tables, accepted for publication in Astronomy
and Astophysic
Generalized parton distributions and double distributions for q q-bar pions
We consider two simple covariant models for pions (one with scalar and the
other with spin-1/2 constituents). Pion generalized parton distributions are
derived by integration over the light-cone energy. The model distributions are
consistent with all known properties of generalized parton distributions,
including positivity. We also construct the corresponding double distributions
by appealing to Lorentz invariance. These ostensibly constructed double
distributions lead to different generalized parton distributions that need not
respect the positivity constraints. This inconsistency arises from the
ambiguity inherent in defining double distributions in a one-component
formalism (even in the absence of the Polyakov-Weiss term). We demonstrate that
the correct model double distributions can be calculated from non-diagonal
matrix elements of twist-two operators.Comment: 10 pages, 7 figures, RevTex4, reference added, typos correcte
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