6,548 research outputs found
Solar analogs with and without planets: T trends and galactic evolution
We explore a sample of 148 solar-like stars to search for a possible
correlation between the slopes of the abundance trends versus condensation
temperature (known as the Tc slope) both with stellar parameters and Galactic
orbital parameters in order to understand the nature of the peculiar chemical
signatures of these stars and the possible connection with planet formation. We
find that the Tc slope correlates at a significant level with the stellar age
and the stellar surface gravity. We also find tentative evidence that the Tc
slope correlates with the mean galactocentric distance of the stars (Rmean),
suggesting that stars that originated in the inner Galaxy have fewer refractory
elements relative to the volatile ones. We found that the chemical
peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is
probably a reflection of their older age and their inner Galaxy origin. We
conclude that the stellar age and probably Galactic birth place are key to
establish the abundances of some specific elements.Comment: Proceedings of the GREAT-ITN conference: The Milky Way Unravelled by
Gaia. Will be published in the "EAS Publications Series
Exploring the alpha-enhancement of metal-poor planet-hosting stars. The Kepler and HARPS samples
Recent studies showed that at low metallicities Doppler-detected
planet-hosting stars have preferably high alpha-content and belong to the thick
disk. We used the reconnaissance spectra of 87 Kepler planet candidates and
data available from the HARPS planet search survey to explore this phenomena.
Using the traditional spectroscopic abundance analysis methods we derived Ti,
Ca, and Cr abundances for the Kepler stars. In the metallicity region -0.65 <
[Fe/H] < -0.3 dex the fraction of Ti-enhanced thick-disk HARPS planet harboring
stars is 12.3 +/- 4.1 % and for their thin-disk counterparts this fraction is
2.2 +/- 1.3 %. The binomial statistics gives a probability of 0.008 that this
could have occurred by chance. Combining the two samples (HARPS + Kepler)
reinforces the significance of this result (P ~ 99.97 %). Since most of these
stars are harboring small-mass/size planets we can assume that, although
terrestrial planets can be found at low-iron regime, they are mostly enhanced
by alpha-elements. This implies that early formation of rocky planets could get
started in the Galactic thick disk, where the chemical conditions for their
formation were more favorable.Comment: 5 pages, 3 figure
Desarrollo experimental de controladores Fuzzy para procesos térmicos y neumáticos
In this project, a Fuzzy control system is proposed in an industrial process training module with two independent systems between them, one thermal and the other pneumatic. The control algorithm is developed in Python language v3.6 executed by a Raspberry Pi B+, both controllers depend on the error and change in error that are updated in times of 2 s and 1 s, for temperature and pressure respectively, communication with the plants uses A/D and D/A converters, the thermal Fuzzy was analyzed with three temperature references [50,100 and 150]°C, with a rise time of 191 s, 360 s and 505 s; steady state error of 5.5%, 0.7% y 0.7%, in the pneumatic system the speed of change between references is evaluated from 10 psi to 15 psi varying the activation of the compressor at the beginning of the experiments, the settling times obtained are 111 s and 106 s, with the compressor off the result is 116 s and 88 s, besides a maximum excess of 13% with inherent oscillations to the type system that are in an acceptable range. En este proyecto, se propone un sistema de control Fuzzy en un módulo de entrenamiento de procesos industriales con dos sistemas independientes entre sí, uno térmico y otro neumático, el algoritmo de control se desarrolla en lenguaje Python v3.6 ejecutado por una Raspberry Pi B+, ambos controladores dependen del error y cambio en el error que se actualizan en tiempos de 2 s y 1 s, para temperatura y presión respectivamente, la comunicación con las plantas emplea conversores A/D y D/A, el Fuzzy térmico se analizo con tres referencias de temperatura [50,100 y 150]°C, con un tiempo de subida de 191 s, 360 s y 505 s; error de estado estacionario de 5.5 %, 0.7% y 0.7 %, en el sistema neumático se evalúo la velocidad de cambio entre referencias de 10 psi a 15 psi variando la activación del compresor al inicio de los experimentos, los tiempos de asentamiento que se obtienen son 111 s y 106 s, con el compresor apagado el resultado es de 116 s y 88 s, además de un sobrepaso máximo de 13% con oscilaciones inherentes al tipo sistema que se encuentran en un rango aceptable. 
Abundance trend with condensation temperature for stars with different Galactic birth places
During the past decade, several studies reported a correlation between
chemical abundances of stars and condensation temperature (also known as Tc
trend). However, the real astrophysical nature of this correlation is still
debated. The main goal of this work is to explore the possible dependence of
the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality
spectra of about 40 stars observed with the HARPS and UVES spectrographs to
derive precise stellar parameters, chemical abundances, and stellar ages. A
differential line-by-line analysis was applied to achieve the highest possible
precision in the chemical abundances. We confirm previous results that [X/Fe]
abundance ratios depend on stellar age and that for a given age, some elements
also show a dependence on Rmean. When using the whole sample of stars, we
observe a weak hint that the Tc trend depends on Rmean. The observed dependence
is very complex and disappears when only stars with similar ages are
considered. To conclude on the possible dependence of the Tc trend on the
formation place of stars, a larger sample of stars with very similar
atmospheric parameters and stellar ages observed at different Galactocentric
distances is neededComment: Accepted by A&
Performance evaluation of a hybrid vehicle and sensor network to prevent traffic accidents
In recent years, wireless networks have become a widespread communication technology as well as a research challenge. Many contributions have been made on ad hoc networks, such as wireless sensor networks (WSNs) and vehicular ad hoc networks (VANETs). Recently, the number of cars on our streets, roads, and highways has been increasing, giving rise to a great interest in vehicular communication technologies. This paper presents an hybrid sensor and vehicular network (HSVN) platform, as well as the description and evaluation of a communication protocol between VANETs and WSNs using a network simulator for its evaluation
Exploring the capability of yeasts isolated from colombian fermented cocoa beans to form and degrade biogenic amines in a lab-scale model system for cocoa fermentation
Yeast starters for cocoa fermentation are usually tested according to their enzymatic activities in terms of mucilage degradation and flavor improvement, disregarding their influence on the production or elimination of toxic compounds as biogenic amines (BAs), important for human health. In this work, we tested 145 strains belonging to 12 different yeast species and isolated from the Colombian fermented cocoa beans (CB) for their capability of producing BAs in vitro. Sixtyfive strains were able to decarboxylate at least one of the amino acids tested. Pichia kudriavzevii ECA33 (Pk) and Saccharomyces cerevisiae 4 (Sc) were selected to evaluate their potential to modulate BAs, organic acids, and volatile organic compounds (VOCs) accumulation during a simulated cocoa fermentation. The growth of Sc or Pk in the presence of CB caused a significant reduction (p < 0.05) of 2-phenylethylamine (84% and 37%) and cadaverine (58% and 51%), and a significant increase of tryptamine and putrescine with a strong influence of temperature in BA formation and degradation. In addition, our findings pointed out that Pk induced a major production of fatty acidand amino acid-derived VOCs, while Sc induced more VOCs derived from fatty acids metabolism. Our results suggest the importance of considering BA production in the choice of yeast starters for cocoa fermentation
Resonance expansions in quantum mechanics
The goal of this contribution is to discuss various resonance expansions that
have been proposed in the literature.Comment: 10 pages and 1 figure; presented at the Istanbul workshop on
pseudo-Hermitian Hamiltonian
Mechanochromic Luminescent Tetrathiazolylthiophenes: Evaluating the Role of Intermolecular Interactions through Pressure and Temperature-Dependent Raman Spectroscopy
The Raman spectrum
of the mechanochromic luminescent tetrathiazolylthiophene
has been investigated as a function of pressure and temperature. This
study verifies the sensitivity of the Raman spectroscopy as a technique
to characterize and understand the structural effects causing any
mechanochromic changes. Continuous and evident Raman shifts and changes
in intensities of the strongest lines in the spectra occur while increasing
pressure or lowering temperature. These spectral changes are related
to the modulation of intermolecular
C–H···N hydrogen bonding previously identified
for this system. The Raman bands involved are assigned to collective
normal modes associated to the CC bond stretching of the rings and
reveal that the modulation of local hydrogen bonding interaction has
indeed an effect that has an impact on the whole conjugated structure
of the molecule. Pressure-dependent Raman spectra have been also computed
by means of periodic density functional theory calculations of the
crystal, giving an accurate prediction of the experimental trends
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