313 research outputs found
Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals
We present results from the analysis of Fe I 630 nm measurements of the quiet
Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets
with noise levels of 1.2{\times}10-3 and 3{\times}10-4 are employed. We
determine the distribution of field strengths and inclinations by inverting the
two observations with a Milne-Eddington model atmosphere. The inversions show a
predominance of weak, highly inclined fields. By means of several tests we
conclude that these properties cannot be attributed to photon noise effects. To
obtain the most accurate results, we focus on the 27.4% of the pixels in the
second data set that have linear polarization amplitudes larger than 4.5 times
the noise level. The vector magnetic field derived for these pixels is very
precise because both circular and linear polarization signals are used
simultaneously. The inferred field strength, inclination, and filling factor
distributions agree with previous results, supporting the idea that
internetwork fields are weak and very inclined, at least in about one quarter
of the area occupied by the internetwork. These properties differ from those of
network fields. The average magnetic flux density and the mean field strength
derived from the 27.4% of the field of view with clear linear polarization
signals are 16.3 Mx cm-2 and 220 G, respectively. The ratio between the average
horizontal and vertical components of the field is approximately 3.1. The
internetwork fields do not follow an isotropic distribution of orientations.Comment: To appear in APJ, Vol 749, 201
Applicability of Milne-Eddington inversions to high spatial resolution observations of the quiet Sun
The physical conditions of the solar photosphere change on very small spatial
scales both horizontally and vertically. Such a complexity may pose a serious
obstacle to the accurate determination of solar magnetic fields. We examine the
applicability of Milne-Eddington (ME) inversions to high spatial resolution
observations of the quiet Sun. Our aim is to understand the connection between
the ME inferences and the actual stratifications of the atmospheric parameters.
We use magnetoconvection simulations of the solar surface to synthesize
asymmetric Stokes profiles such as those observed in the quiet Sun. We then
invert the profiles with the ME approximation. We perform an empirical analysis
of the heights of formation of ME measurements and analyze the uncertainties
brought about by the ME approximation. We also investigate the quality of the
fits and their relationship with the model stratifications. The atmospheric
parameters derived from ME inversions of high-spatial resolution profiles are
reasonably accurate and can be used for statistical analyses of solar magnetic
fields, even if the fit is not always good. We also show that the ME inferences
cannot be assigned to a specific atmospheric layer: different parameters sample
different ranges of optical depths, and even the same parameter may trace
different layers depending on the physical conditions of the atmosphere.
Despite this variability, ME inversions tend to probe deeper layers in granules
as compared with intergranular lanes.Comment: Accepted for publication in Astronomy and Astrophysic
Extracción de conocimiento para la predicción y análisis de los resultados de la prueba de calidad de la educación superior en Colombia
Se presentan y analizan los resultados de la prueba de la calidad de la educación superior en Colombia – Saber Pro. Se usó la metodología de extracción de conocimiento en bases de datos KDD sobre la cual se construyó una base de datos del desempeño académico del estudiante en áreas asociadas con los contenidos de la prueba Saber Pro, y se utilizó redes neuronales como técnica para la minería de datos. Las redes neuronales permitieron la predicción de los resultados de la prueba Saber Pro con alta exactitud tanto en rangos cualitativos como cuantitativos. Además, se comprobó una correlación entre el desempeño académico y los resultados de Saber Pro. Los hallazgos sugieren que la metodología usada es una excelente guía para el descubrimiento de patrones ocultos en los datos, y permite establecer estrategias de mejora de los resultados de las pruebas Saber Pro que involucren el desempeño académico del estudiante.In this paper, the prediction and results analysis of the quality test of higher education in Colombia - Saber Pro is performed. The knowledge extraction in databases methodology KDD was used, on which a database of the student's academic performance was built in areas associated with the contents of the Saber Pro test, and neural networks were used as a technique for data mining. The neural networks allowed the prediction of the results of the Saber Pro test with high exactness in both qualitative and quantitative ranges. A correlation between academic performance and Saber Pro results was also found. The findings suggest that the methodology used is an excellent guide for the discovery of hidden patterns in the data, and allows to establish strategies to improve the results of the Saber Pro tests that involve the student's academic performance
Model selection for spectro-polarimetric inversions
Inferring magnetic and thermodynamic information from spectropolarimetric
observations relies on the assumption of a parameterized model atmosphere whose
parameters are tuned by comparison with observations. Often, the choice of the
underlying atmospheric model is based on subjective reasons. In other cases,
complex models are chosen based on objective reasons (for instance, the
necessity to explain asymmetries in the Stokes profiles) but it is not clear
what degree of complexity is needed. The lack of an objective way of comparing
models has, sometimes, led to opposing views of the solar magnetism because the
inferred physical scenarios are essentially different. We present the first
quantitative model comparison based on the computation of the Bayesian evidence
ratios for spectropolarimetric observations. Our results show that there is not
a single model appropriate for all profiles simultaneously. Data with moderate
signal-to-noise ratios favor models without gradients along the line-of-sight.
If the observations shows clear circular and linear polarization signals above
the noise level, models with gradients along the line are preferred. As a
general rule, observations with large signal-to-noise ratios favor more complex
models. We demonstrate that the evidence ratios correlate well with simple
proxies. Therefore, we propose to calculate these proxies when carrying out
standard least-squares inversions to allow for model comparison in the future.Comment: 16 pages, 2 figures, 8 tables, accepted for publication in Ap
Solar Intranetwork Magnetic Elements: bipolar flux appearance
The current study aims to quantify characteristic features of bipolar flux
appearance of solar intranetwork (IN) magnetic elements. To attack such a
problem, we use the Narrow-band Filter Imager (NFI) magnetograms from the Solar
Optical Telescope (SOT) on board \emph{Hinode}; these data are from quiet and
an enhanced network areas. Cluster emergence of mixed polarities and IN
ephemeral regions (ERs) are the most conspicuous forms of bipolar flux
appearance within the network. Each of the clusters is characterized by a few
well-developed ERs that are partially or fully co-aligned in magnetic axis
orientation. On average, the sampled IN ERs have total maximum unsigned flux of
several 10^{17} Mx, separation of 3-4 arcsec, and a lifetime of 10-15 minutes.
The smallest IN ERs have a maximum unsigned flux of several 10^{16} Mx,
separations less than 1 arcsec, and lifetimes as short as 5 minutes. Most IN
ERs exhibit a rotation of their magnetic axis of more than 10 degrees during
flux emergence. Peculiar flux appearance, e.g., bipole shrinkage followed by
growth or the reverse, is not unusual. A few examples show repeated
shrinkage-growth or growth-shrinkage, like magnetic floats in the dynamic
photosphere. The observed bipolar behavior seems to carry rich information on
magneto-convection in the sub-photospheric layer.Comment: 26 pages, 14 figure
The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and Te-based literature data
The use of IFS is since recently allowing to measure the emission line fluxes
of an increasingly large number of star-forming galaxies both locally and at
high redshift. The main goal of this study is to review the most widely used
empirical oxygen calibrations, O3N2 and N2, by using new direct abundance
measurements. We pay special attention to the expected uncertainty of these
calibrations as a function of the index value or abundance derived and the
presence of possible systematic offsets. This is possible thanks to the
analysis of the most ambitious compilation of Te-based HII regions to date.
This new dataset compiles the Te-based abundances of 603 HII regions extracted
from the literature but also includes new measurements from the CALIFA survey.
Besides providing new and improved empirical calibrations for the gas
abundance, we also present here a comparison between our revisited calibrations
with a total of 3423 additional CALIFA HII complexes with abundances derived
using the ONS calibration by Pilyugin et al. (2010). The combined analysis of
Te-based and ONS abundances allows us to derive their most accurate calibration
to date for both the O3N2 and N2 single-ratio indicators, in terms of all
statistical significance, quality and coverage of the space of parameters. In
particular, we infer that these indicators show shallower abundance
dependencies and statistically-significant offsets compared to those of Pettini
and Pagel (2004), Nagao et al. (2006) and P\'erez-Montero and Contini (2009).
The O3N2 and N2 indicators can be empirically applied to derive oxygen
abundances calibrations from either direct abundance determinations with random
errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a
large amount of data) reaching an average precision of 0.08 and 0.09 dex
(random) and 0.02 and 0.08 dex (systematic; compared to the direct
estimations),respectively.Comment: 12 pages, 5 figures, accepted for publication in A&
The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and T e-based literature data
Astronomy and Astrophysics 559 (2013): A114 reproduced with permission from Astronomy and AstrophysicsThe use of integral field spectroscopy is since recently allowing to measure the emission line fluxes of an increasingly large number of star-forming galaxies, both locally and at high redshift. Many studies have used these fluxes to derive the gas-phase metallicity of the galaxies by applying the so-called strong-line methods. However, the metallicity indicators that these datasets use were empirically calibrated using few direct abundance data points (Te-based measurements). Furthermore, a precise determination of the prediction intervals of these indicators is commonly lacking in these calibrations. Such limitations might lead to systematic errors in determining the gas-phase metallicity, especially at high redshift, which might have a strong impact on our understanding of the chemical evolution of the Universe. The main goal of this study is to review the most widely used empirical oxygen calibrations, O3N2 and N2, by using newdirect abundance measurements. We pay special attention to (1) the expected uncertainty of these calibrations as a function of the index value or abundance derived and (2) the presence of possible systematic offsets. This is possible thanks to the analysis of the most ambitious compilation of Te-based H ii regions to date. This new dataset compiles the Te-based abundances of 603 H ii regions extracted from the literature but also includes new measurements from the CALIFA survey. Besides providing new and improved empirical calibrations for the gas abundance, we also present a comparison between our revisited calibrations with a total of 3423 additional CALIFA H ii complexes with abundances derived using the ONS calibration from the literature. The combined analysis of T e-based and ONS abundances allows us to derive their most accurate calibration to date for both the O3N2 and N2 single-ratio indicators, in terms of all statistical significance, quality, and coverage of the parameters space. In particular, we infer that these indicators show shallower abundance dependencies and statistically significant offsets compared to others'. The O3N2 and N2 indicators can be empirically applied to derive oxygen abundances calibrations from either direct abundance determinations with random errors of 0.18 and 0.16, respectively, or from indirect ones (but based on a large amount of data), reaching an average precision of 0.08 and 0.09 dex (random) and 0.02 and 0.08 dex (systematic; compared to the direct estimations), respectivelyR.A. Marino is funded by the Spanish program of International Campus of Excellence Moncloa (CEI).
D. Mast thank the Plan Nacional de Investigación y Desarrollo funding programs, AYA2012-31935 of the Spanish Ministerio de Economía y Competitividad, for the support given to this project. S.F.S thanks the the Ramón y Cajal project RyC-2011-07590 of the spanish Ministerio de Economía y Competitividad, for the support giving to this project. F.F.R.O. acknowledges the Mexican National Council for Science and Technology
(CONACYT) for financial support under the program Estancias Postdoctorales y Sabáticas al Extranjero para la Consolidación de Grupos de Investigación, 2010-2012. We acknowledge financial support for the ESTALLIDOS collaboration by the Spanish Ministerio de Ciencia e Innovación under grant AYA2010- 21887-C04-03. BG-L also acknowledges support from the Spanish Ministerio de Economía y Competitividad (MINECO) under grant AYA2012- 39408-C02-02. J.F.-B. acknowledges financial support from the Ramón y Cajal Program and grant AYA2010-21322-C03-02 from the Spanish Ministry of Economy and Competitiveness (MINECO), as well as to the DAGAL network
from the People’s Program (Marie Curie Actions) of the European Union’s Seventh Framework Program FP7/2007-2013/ under REA grant agreement number PITN-GA-2011-289313. CK has been funded by project AYA2010-21887 from the Spanish PNAYA. P.P. acknowledges support by the Fundação para a Ciência e a Tecnologia (FCT) under project FCOMP-01-0124-FEDER-029170 (Reference FCT PTDC/FIS-AST/3214/2012), funded by FCT-MEC (PIDDAC) and FEDER (COMPETE). R.M.G.D. and R.G.B. also acknowledge support from the Spanish Ministerio de Economía y Competitividad (MINECO) under grant AyA2010-15081. V.S., L.G., and A.M.M. acknowledge financial support from the Fundação para a Ciência e a Tecnologia (FCT) under program Ciência 2008 and the research grant PTDC/CTE-AST/112582/200
Application of molecular topology to the prediction of the repellent activity of a group of carboxyamides against Aedes aegypti
El mosquito Aedes aegypti presenta características biológicas que lo convierten en un vector importante en el ciclo de transmisión de diferentes patógenos, en especial arbovirus. Durante la última década, la carga de dengue y otras enfermedades tales como la fiebre del zika o fiebre chikungunya se han incrementado. La expansión de dengue ocasionada por este vector, principalmente en América, representa actualmente uno de los problemas más grandes de salud pública, siendo endémico en más de 30 países. Frente a la falta de tratamientos específicos para tratar las infecciones transmitidas por este mosquito, los esfuerzos por hacerle frente se han focalizado en el control vectorial, aplicando diversas estrategias de combate, entre las que se incluye la aplicación de insecticidas y larvicidas para conseguir su eliminación, así como el uso de repelentes como estrategia de protección individual. La búsqueda de nuevos repelentes puede realizarse mediante diferentes herramientas, donde se incluye la topología molecular. En este contexto, computacionalmente a través de un modelo topológico-matemático, evaluamos la potencial actividad repelente de una serie de carboxiamidas preseleccionadas mediante el uso de análisis discriminante lineal y de regresión multilineal. Tras este cribado virtual basado en el modelo seleccionado, proponemos nuevas estructuras químicas con una actividad potencialmente activa como repelentes contra Aedes aegypti.Due to its biological characteristics, the mosquito Aedes aegypti is an important vector in the transmission cycle of various pathogens, especially of arboviruses. The burden of dengue and
other diseases such as the Zika virus infection or the chikungunya fever has increased over the
last decade. The spread of dengue caused by this vector, mainly in America, represents one of
the greatest public health problems, being endemic in more than 30 countries. Faced with the
lack of specific treatments to treat the infections caused by this mosquito, efforts have focused on
controlling the vector, applying various combat strategies, including the application of Due to its biological characteristics, the mosquito Aedes aegypti is an important vector in the
transmission cycle of various pathogens, especially of arboviruses. The burden of dengue and
other diseases such as the Zika virus infection or the chikungunya fever has increased over the
last decade. The spread of dengue caused by this vector, mainly in America, represents one of
the greatest public health problems, being endemic in more than 30 countries. Faced with the
lack of specific treatments to treat the infections caused by this mosquito, efforts have focused on
controlling the vector, applying various combat strategies, including the application of insecticides
and larvicides to directly eliminate the mosquito population, as well as the use of repellants,
as an individual protection strategy. The search for new repellants can be done using different
tools, including molecular topology. In this context, using a topological-mathematical model, we
evaluated the potential repellent activity of a series of preselected carboxyamides by using linear
discriminant and multilinear regression analysis. After carrying out a virtual screening based on
the selected model, new chemical structures with potential activity as repellants against Aedes
aegypti are proposed.Ciencias Experimentale
Reflexiones universitarias. San Pedro Valencia: renovación urbana, saneamiento ambiental y emprendimientos turísticos. Otoño 2015
Los trabajos que aquí se presentan se elaboraron por las y los estudiantes como parte de las actividades del Proyecto de Aplicación Profesional (PAP) “San Pedro Valencia: renovación urbana, saneamiento ambiental y emprendimientos turísticos”, durante el periodo de Otoño de 2015. A lo largo del periodo los autores compartieron sus reflexiones en torno a su percepción sobre el contexto en el que actúa el PAP; sobre las alternativas posibles a la problemática detectada y lo que significa pensar una alternativa; sobre los sujetos con los que se ha interactuado a lo largo de la experiencia de trabajo y sobre el papel del profesionista y del ciudadano en un mundo como el que nos tocó vivir. La obra está compuesta por reflexiones personales de las y los estudiantes que, explorando estas temáticas, comparten sus aprendizajes y observaciones de forma vívida.ITESO, A.C
Evidence for the photospheric excitation of incompressible chromospheric waves
Observing the excitation mechanisms of incompressible transverse waves is vital for determining how energy propagates through the lower solar atmosphere. We aim to show the connection between convectively driven photospheric flows and incompressible chromospheric waves. The observations presented here show the propagation of incompressible motion through the quiet lower solar atmosphere, from the photosphere to the chromosphere. We determine photospheric flow vectors to search for signatures of vortex motion and compare results to photospheric flows present in convective simulations. Further, we search for the chromospheric response to vortex motions. Evidence is presented that suggests incompressible waves can be excited by the vortex motions of a strong magnetic flux concentration in the photosphere. A chromospheric counterpart to the photospheric vortex motion is also observed, presenting itself as a quasi-periodic torsional motion. Fine-scale, fibril structures that emanate from the chromospheric counterpart support transverse waves that are driven by the observed torsional motion. A new technique for obtaining details of transverse waves from time-distance diagrams is presented and the properties of transverse waves (e.g., amplitudes and periods) excited by the chromospheric torsional motion are measured
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