714 research outputs found
Alternativas de modernización demandadas por los regantes de los regadíos tradicionales de la Vega Baja del Segura
Probing 3D and NLTE models using APOGEE observations of globular cluster stars
Hydrodynamical (or 3D) and non-local thermodynamic equilibrium (NLTE) effects
are known to affect abundance analyses. However, there are very few
observational abundance testsof 3D and NLTE models. We developed a new way of
testing the abundance predictions of 3D and NLTE models, taking advantage of
large spectroscopic survey data. We use a line-by-line analysis of the Apache
Point Observatory Galactic Evolution Experiment (APOGEE) spectra (H band) with
the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS).
We compute line-by-line abundances of Mg, Si, Ca, and Fe for a large number of
globular cluster K giants in the APOGEE survey. We compare this line-by-line
analysis against NLTE and 3D predictions. While the 1D-NLTE models provide
corrections in the right direction, there are quantitative discrepancies
between different models. We observe a better agreement with the data for the
models including reliable collisional cross-sections. The agreement between
data and models is not always satisfactory when the 3D spectra are computed in
LTE. However, we note that for a fair comparison, 3D corrections should be
computed with self-consistently derived stellar parameters, and not on 1D
models with identical stellar parameters. Finally, we focus on 3D and NLTE
effects on Fe lines in the H band, where we observe a systematic difference in
abundance relative to the value from the optical. Our results suggest that the
metallicities obtained from the H band are more accurate in metal-poor giants.
More atomic data and extended self-consistent 3D-NLTE computations need to be
made. The method we have developed for testing 3D and NLTE models could be
extended to other lines and elements, and is particularly suited for large
spectroscopic surveys.Comment: 13 pages, 9 figures, accepted in A&
Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H-TaS 2 and 2H-TaSe 2
We present measurements of the superconducting and charge density wave
critical temperatures (Tc and TCDW) as a function of pressure in the transition
metal dichalchogenides 2H-TaSe2 and 2H-TaS2. Resistance and susceptibility
measurements show that Tc increases from temperatures below 1 K up to 8.5 K at
9.5 GPa in 2H-TaS2 and 8.2 K at 23 GPa in 2H-TaSe2. We observe a kink in the
pressure dependence of TCDW at about 4 GPa that we attribute to the lock-in
transition from incommensurate CDW to commensurate CDW. Above this pressure,
the commensurate TCDW slowly decreases coexisting with superconductivity within
our full pressure range.Comment: Published in Phys. Rev B 93, 184512 (2016
Silver-Derived Antimicrobial Coatings for the Prevention of Microbial Biofilms in Metal Pipes
The authors of this study would like to acknowledge the financial and technical support of the CETAQUA Foundation; without the said support, this work would not have been possible.The datasets generated during the current
study are available from the corresponding author on reasonable requeBiodeterioration is one of the most important processes in metal pipeline corrosion, and it can be due to physical, chemical, and biological factors. Coatings rich in silver have been used to inhibit this undesirable phenomenon. In this study, the antimicrobial properties of several silver-containing products used as a coating in pipelines were determined on a pilot scale in order to evaluate the ability of silver to inhibit biofilm formation. The results showed that the coating with silver zeolite at a concentration of 2000 mg L-1 inhibited the formation of a microbial biofilm and prevented the biodeterioration process. Therefore, from our study, it can be concluded that silver zeolite shows greater protection capacity than other silver preparations and presents advantages in relation to other silver coatings that are currently availableCETAQUA Foundatio
Opacity for realistic 3D MHD simulations of cool stellar atmospheres
Context. Realistic 3D time-dependent simulations of stellar near-surface
convection employ the opacity binning method for efficient and accurate
computation of the radiative energy exchange. The method provides several
orders of magnitude of speed-up, but its implementation includes a number of
free parameters. Aims. Our aim is to evaluate the accuracy of the opacity
binning method as a function of the choice of these free parameters. Methods.
The monochromatic opacities computed with the SYNSPEC code are used to
construct opacity distribution function (ODF) that is then verified through
detailed comparison with the results of the ATLAS code. The opacity binning
method is implemented with the SYNSPEC opacities for four representative cool
main-sequence stellar spectral types (F3V, G2V, K0V, and M2V). Results. The
ODFs from SYNSPEC and ATLAS show consistent results for the opacity and
bolometric radiative energy exchange rate Q in case of the F, G, and K -- type
stars. Significant differences, coming mainly from the molecular line lists,
are found for the M -- type star. It is possible to optimise a small number of
bins to reduce the deviation of the results coming from the opacity grouping
with respect to the ODF for the F, G, and K -- type stars. In the case of the M
-- type star, the inclusion of splitting in wavelength is needed in the
grouping to get similar results, with a subsequent increase in computing time.
In the limit of a large number of bins, the deviation for all the binning
configurations tested saturates and the results do not converge to the ODF
solution. Due to this saturation, the Q rate cannot be improved by increasing
the number of bins to more than about 20 bins. The more effective strategy is
to select the optimal location of fewer bins.Comment: 26 pages, 29 figures. Accepted for publication in section 15
(Numerical methods and codes) of Astronomy and Astrophysic
The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
We investigate the mass function in the substellar domain down to a few
Jupiter masses in the young sigma Orionis open cluster (3+/-2 Ma, d =
360^+70_-60 pc). We have performed a deep IJ-band search, covering an area of
790 arcmin^2 close to the cluster centre. This survey was complemented with an
infrared follow-up in the HKs- and Spitzer 3.6-8.0 mum-bands. Using
colour-magnitude diagrams, we have selected 49 candidate cluster members in the
magnitude interval 16.1 mag < I < 23.0 mag. Accounting for flux excesses at 8.0
mum and previously known spectral features of youth, 30 objects are bona fide
cluster members. Four are first identified from our optical-near infrared data.
Eleven have most probable masses below the deuterium burning limit and are
classified as planetary-mass object candidates. The slope of the substellar
mass spectrum (Delta N / Delta M = a M^-alpha) in the mass interval 0.11 Msol M
< 0.006 Msol is alpha = +0.6+/-0.2. Any opacity mass-limit, if these objects
form via fragmentation, may lie below 0.006 Msol. The frequency of sigma
Orionis brown dwarfs with circumsubstellar discs is 47+/-15 %. The continuity
in the mass function and in the frequency of discs suggests that very low-mass
stars and substellar objects, even below the deuterium-burning mass limit, may
share the same formation mechanism.Comment: Accepted for publication in A&A (12/04/2007). It has not been edited
for language ye
Small farmers' perception of factors influencing regional chemical control of Diaphorina citri
Regional Control Areas (RCAs) have been implemented in Mexico as a strategy to delay the spread of Candidatus Liberibacter asiaticus, the causal bacterium of the disease known as Huanglongbing (HLB). The implementation of an effective management of the vector insect, Diaphorina citri in the RCAs requires the knowledge, acceptance and coordinated engagement of small agricultural producers. This research assessed the perception and knowledge of 62 citrus growers regarding the operational, sociocultural and environmental factors influencing chemical control of D. citri in four RCAs within Veracruz State. According to their responses, the following factors have been identified as the operational factors with the highest influence on the effectiveness of insecticides against D. citri within RCAs: the lack of knowledge about the use of surfactants, application speed, poor calibration of sprayers and incorrect water quality. The most significant sociocultural factors are the general unawareness of the pest and the safe and proper application of pesticides. The most relevant environmental factors during application: temperature, relative humidity, and wind speed. Sociocultural index correlated with the perception of effectiveness. Therefore, it becomes necessary to consider differences among citrus growers in each region and setting out the most appropriatestrategies for vector and disease management.
Highlights
Some operational practices that citrus growers are not aware of may influence their perception of chemical control.
The sociocultural context of growers determines their decision-taking on insecticide applications.
During the application of insecticides in regional control areas (RCAs), growers do not take into account weather conditions.
The effective management of D. citri requires a coordinated engagement of small growers' in RCAs.Regional Control Areas (RCAs) have been implemented in Mexico as a strategy to delay the spread of Candidatus Liberibacter asiaticus, the causal bacterium of the disease known as Huanglongbing (HLB). The implementation of an effective management of the vector insect, Diaphorina citri in the RCAs requires the knowledge, acceptance and coordinated engagement of small agricultural producers. This research assessed the perception and knowledge of 62 citrus growers regarding the operational, sociocultural and environmental factors influencing chemical control of D. citri in four RCAs within Veracruz State. According to their responses, the following factors have been identified as the operational factors with the highest influence on the effectiveness of insecticides against D. citri within RCAs: the lack of knowledge about the use of surfactants, application speed, poor calibration of sprayers and incorrect water quality. The most significant sociocultural factors are the general unawareness of the pest and the safe and proper application of pesticides. The most relevant environmental factors during application: temperature, relative humidity, and wind speed. Sociocultural index correlated with the perception of effectiveness. Therefore, it becomes necessary to consider differences among citrus growers in each region and setting out the most appropriatestrategies for vector and disease management.
Highlights
Some operational practices that citrus growers are not aware of may influence their perception of chemical control.
The sociocultural context of growers determines their decision-taking on insecticide applications.
During the application of insecticides in regional control areas (RCAs), growers do not take into account weather conditions.
The effective management of D. citri requires a coordinated engagement of small growers' in RCAs
Constraining the X-ray reflection in low accretion rate AGN using XMM-Newton, NuSTAR and Swift
An interesting feature in active galactic nuclei (AGN) accreting at low rate
is the weakness of the reflection features in their X-ray spectra, which can
result from the gradual disappearance of the torus with decreasing accretion
rates. It has been suggested that low luminosity AGN (LLAGN) would have a
different reflector configuration compared with high luminosity AGN, either
covering a smaller fraction of the sky or simply having less material.
Additionally, we note that the determination of the spectral index ()
and the cut-off energy of the primary power-law emission is affected by the
inclusion of reflection models, showing the importance of using them to study
the accretion mechanism, especially in the case of the LLAGN that have
previously shown a high dispersion on the relation between and the
accretion rate. Our purpose is to constrain the geometry and column density of
the reflector in a sample of LLAGN covering a broad X-ray range of energy
combining data from XMM-Newton + NuSTAR + Swift of a hard X-ray-flux limited
sample of 17 LLAGN from BASS/DR2 with accretion rates =L/L<10. We fit all spectra using the reflection model
for torus (borus02) and accretion disk (Xillver) reflectors. We found a
tentative correlation between the torus column density and the accretion rate,
LLAGN shows a lower column density compared with the high-luminosity objects.
We also confirm the relation between and , with a
smaller scatter than previously reported, thanks to the inclusion of
high-energy data and the reflection models. Our results are consistent with a
break at , suggestive of a different accretion
mechanism compared with higher accretion AGN.Comment: Accepted for publication in Astronomy & Astrophysic
Lithium and Hα in stars and brown dwarfs of σ Orionis
We present intermediate- and low-resolution optical spectra around Hα and Li I λ6708 Å for a sample of 25 low mass stars and 2 brown dwarfs with confirmed membership in the pre-main sequence stellar σ Orionis cluster. Our observations are intended to investigate the age of the cluster. The spectral types derived for our target sample are found to be in the range K6–M8.5, which corresponds to a mass interval of roughly 1.2–0.02 M⊙ on the basis of state-of-the-art evolutionary models. Radial velocities (except for one object) are found to be consistent with membership in the Orion complex. All cluster members show considerable Hα emission and the Li I resonance doublet in absorption, which is typical of very young ages. We find that our pseudo-equivalent widths of Hα and Li I (measured relative to the observed local pseudo-continuum formed by molecular absorptions) appear rather dispersed (and intense in the case of Hα) for objects cooler than M3.5 spectral class, occurring at the approximate mass where low mass stars are expected to become fully convective. The least massive brown dwarf in our sample, S Ori 45 (M8.5, ~0.02 M⊙), displays variable Hα emission and a radial velocity that differs from the cluster mean velocity. Tentative detection of forbidden lines in emission indicates that this brown dwarf may be accreting mass from a surrounding disk. We also present recent computations of Li I λ6708 Å curves of growth for low gravities and for the temperature interval (about 4000–2600 K) of our sample. The comparison of our observations to these computations allows us to infer that no lithium depletion has yet taken place in σ Orionis, and that the observed pseudo-equivalent widths are consistent with a cluster initial lithium abundance close to the cosmic value. Hence, the upper limit to the σ Orionis cluster age can be set at 8 Myr, with a most likely value around 2–4 Myr
Análisis del comportamiento del magnetómetro kerr longitudinal para diferentes ángulos de incidencia
En este trabajo se realiza un análisis experimental de la relación entre el ángulo de incidencia y la intensidad de la señal Kerr, que influye en la forma del ciclo de histéresis, planteándose una relación directa entre ambos para la configuración longitudinal en el magnetómetro Kerr. Los resultados obtenidos evidencian un mejor comportamiento de dicha curva para el rango comprendido entre 10° y 60 ° del ángulo de incidencia
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