Machine learning techniques to select Be star candidates. An application in the OGLE-IV Gaia south ecliptic pole field

Statistical pattern recognition methods have provided competitive solutions for variable star classification at a relatively low computational cost. In order to perform supervised classification, a set of features is proposed and used to train an automatic classification system. Quantities related to the magnitude density of the light curves and their Fourier coefficients have been chosen as features in previous studies. However, some of these features are not robust to the presence of outliers and the calculation of Fourier coefficients is computationally expensive for large data sets. We propose and evaluate the performance of a new robust set of features using supervised classifiers in order to look for new Be star candidates in the OGLE-IV Gaia south ecliptic pole field. We calculated the proposed set of features on six types of variable stars and on a set of Be star candidates reported in the literature. We evaluated the performance of these features using classification trees and random forests along with K-nearest neighbours, support vector machines, and gradient boosted trees methods. We tuned the classifiers with a 10-fold cross-validation and grid search. We validated the performance of the best classifier on a set of OGLE-IV light curves and applied this to find new Be star candidates. The random forest classifier outperformed the others. By using the random forest classifier and colour criteria we found 50 Be star candidates in the direction of the Gaia south ecliptic pole field, four of which have infrared colours consistent with Herbig Ae/Be stars. Supervised methods are very useful in order to obtain preliminary samples of variable stars extracted from large databases. As usual, the stars classified as Be stars candidates must be checked for the colours and spectroscopic characteristics expected for them

Holographic energy density, dark energy sound speed, and tensions in cosmological parameters: H0H_0 and S8S_8

Interesting discrepancies in cosmological parameters are challenging the success of the $\Lambda$CDM model. Direct measurements of the Hubble constant $H_0$ using Cepheid variables and supernovae turn out to be higher than inferred from the Cosmic Microwave Background (CMB). Weak galaxy lensing surveys consistently report values of the strength of matter clustering $\sigma_8$ lower than values derived from the CMB in the context of $\Lambda$CDM. In this paper we address these discrepancies in cosmological parameters by considering Dark Energy (DE) as a fluid with evolving equation of state $w_{\mathrm{de}}(z)$, constant sound speed squared $\hat{c}_{\mathrm{s}}^{2}$, and vanishing anisotropic stress $\sigma$. Our $w_{\mathrm{de}}(z)$ is derived from the Holographic Principle and can consecutively exhibit radiation-like, matter-like, and DE-like behaviour, thus affecting the sound horizon and the comoving angular diameter distance, hence $H_0$. Here we show DE sound speed plays a part in the matter clustering behaviour through its effect on the evolution of the gravitational potential. We compute cosmological constraints using several data set combinations including primary CMB, CMB lensing, redshift-space-distortions, local distance-ladder, supernovae, and baryon acoustic oscillations. In our analysis we marginalise over $\hat{c}_{\mathrm{s}}^{2}$ and find $\hat{c}_{\mathrm{s}}^{2}=1$ is excluded at $\gtrsim 3\sigma$. For our baseline result including the whole data set we found $H_0$ and $\sigma_8$ in good agreement (within $\approx 2\sigma$) with low redshift probes. Our constraint for the baryon energy density $\omega_{\rm{b}}$ is however in $\approx 3\sigma$ tension with BBN constraints. We conclude evolving DE also having non-standard clustering properties [e.g., $\hat{c}_{\mathrm{s}}^{2}(z,k)$] might be relevant for the solution of current discrepancies in cosmological parameters.Comment: 28 pages, 12 figures, 3 tables. References adde

A Catalogue of Be Stars in the Direction of the Galactic Bulge

Detailed studies of Be stars in environments with different metallicities like the Magellanic Clouds or the Galactic bulge are necessary to understand the formation and evolution mechanisms of the circumstellar disks. However, a detailed study of Be stars in the direction of the bulge of our own galaxy has not been performed until now. We report the first systematic search for Be star candidates in the direction of the Galactic Bulge. We present the catalogue, give a brief description of the stellar variability seen, and show some light curve examples. We searched for stars matching specific criteria of magnitude, color and variability in the I band. Our search was conducted on the 48 OGLE II fields of the Galactic Bulge.This search has resulted in 29053 Be star candidates, 198 of them showing periodic light variations. Nearly 1500 stars in this final sample are almost certainly Be stars, providing an ideal sample for spectroscopic multiobject follow-up studies.Comment: Accepted for publication in A &

Study of candidate Be stars in the Magellanic Clouds using near-infrared photometry and optical spectroscopy

Mennickent et al. and Sabogal et al. identified a large number of classical Be (CBe) candidates (∼3500) in the Large and Small Magellanic Clouds (LMC and SMC) based on their photometric variability using the OGLE II data base. They classified these stars into four different groups based on the appearance of their variability. In order to refine and understand the nature of this large number of stars, we studied the infrared properties of the sample and the spectroscopic properties of a subsample. We cross‐correlated the optical sample with the IRSF‐MCPS catalogue to obtain the J, H, Ks magnitudes of all the four types of stars (∼2500) in the LMC and SMC. Spectra of 120 stars belonging to the types 1, 2 and 3 were analysed to study their spectral properties. Among the four types, the type 4 stars are the dominant group, with ∼60 and ∼65 per cent of the total sample in the LMC and SMC, respectively. The near‐infrared (NIR) colour–colour diagrams suggest that the type 4 stars in the LMC have a subclass, which is not found in our Galaxy or in the SMC. This subclass is ∼18 per cent of the type 4 sample. The main type 4 sample which is ∼49 per cent of the total sample has NIR properties similar to the Galactic CBe stars and the SMC type 4 stars. Though the new subclass of type 4 stars have high E(B−V) ∼ 0.75, they are not located close to regions with high reddening. The type 3 stars (∼6 per cent and 7.3 per cent in the LMC and SMC) are found to have large Hα equivalent width (EW) in the SMC and some are found to have large NIR excess. This small fraction of stars are unlikely to be CBe stars. Three stars among the type 3 stars in the LMC are found to be double periodic variables. The type 2 stars are found in larger fraction in the SMC (∼14.5 per cent), when compared to the LMC (∼6 per cent). The spectroscopic and the NIR properties suggest that these could be CBe stars. The type 1 stars are relatively more in the LMC (∼24 per cent) when compared to the SMC (∼13 per cent). The SMC type 1 stars have relatively large Hα EW and this class has properties similar to CBe stars. The spectroscopic sample of type 1 stars which show Hα in emission and are confirmed as CBe stars are more abundant in the SMC by a factor of 2.6. If the effect of metallicity is to cause more CBe stars in the SMC, when compared to the LMC, then type 1, type 2 and type 4 stars follow this rule, with an enhancement of 2.6, 2.4 and 1.3, respectively

A Circular Economy of Electrochemical Energy Storage Systems: Critical Review of SOH/RUL Estimation Methods for Second-Life Batteries

Humanity is facing a gloomy scenario due to global warming, which is increasing at unprecedented rates. Energy generation with renewable sources and electric mobility (EM) are considered two of the main strategies to cut down emissions of greenhouse gasses. These paradigm shifts will only be possible with efficient energy storage systems such as Li-ion batteries (LIBs). However, among other factors, some raw materials used on LIB production, such as cobalt and lithium, have geopolitical and environmental issues. Thus, in a context of a circular economy, the reuse of LIBs from EM for other applications (i.e., second-life batteries, SLBs) could be a way to overcome this problem, considering that they reach their end of life (EoL) when they get to a state of health (SOH) of 70–80% and still have energy storage capabilities that could last several years. The aim of this chapter is to make a review of the estimation methods employed in the diagnosis of LIB, such as SOH and remaining useful life (RUL). The correct characterization of these variables is crucial for the reassembly of SLBs and to extend the LIBs operational lifetime

POTENTIAL DIVIDENDS AND ACTUAL CASH FLOWS. A REGIONAL LATIN AMERICAN ANALYSIS

Dividendos potenciales y flujos de caja: un análisis regional para América Latina Se examina el valor que el mercado asigna a los componentes del flujo de caja del accionista, incluidos los dividendos potenciales. Se estudia empresas transadas de cinco países de América Latina. El modelo incluye cuatro variables: valor de mercado del patrimonio, los dividendos pagados, cambio en la inversión de patrimonio y cambio en activos líquidos (dividendos potenciales) y se regresaron con el valor de mercado del patrimonio como variable dependiente. Las pruebas estadísticas dan resultados sólidos. Conclusiones: El mercado asigna menos de 1 dólar a un dólar futuro para cualquiera de las variables. Los dividendos potenciales destruyen valor.Un dólar invertido en activos líquidos tiene un valor presente neto negativo.Confirmamos los costos de agencia de no distribuir los flujos de caja.Examinámos o valor que o mercado determina para componentes do fluxo de caixa, e para valoração do património, incluindo potenciais dividendos. Estudámos firmas não financeiras de capital aberto de cinco países Latino Americanos. O modelo inclui as quatro variáveis seguintes: valoração de patrimônio no mercado, dividendos pagos, mudança no investimento de patrimônio, e mudança em ativos disponíveis (potenciais dividendos). Foi realizada uma análise de regressão a essas variáveis usando valor de património real como uma variável dependente. Os testes efetuados produziram resultados fortes. As conclusões principais são as seguintes: o mercado determina menos de um dólar para um futuro dólar por qualquer das variáveis em revista. Potenciais dividendos destruem o valor. Um dólar investido em ativos disponíveis tem um Valor Líquido Presente negativo e não é investimento zero VPL. Nós confirmámos os custos da agência por manter fluxos de caixa retidos.We examine the value market assigns to components of the cash flow to equity including potential dividends. We study non financial publicly traded firms from five Latin American countries. The model includes four variables: market value of equity, dividends paid, change in equity investment and change in liquid assets (potential dividends) and are regressed with actual equity value as dependent variable. Tests applied give robust results. The main conclusions: Market assigns less than one dollar to a future dollar for any of the variables studied. Potential dividends destroy value. A dollar invested in liquid assets has a negative Net Present Value and it is not zero NPV investments. We confirm the agency costs of keeping undistributed cash flows

Diretrizes técnicas para a exploração de impacto reduzido em operações florestais de Terra Firme na Amazônia Brasileira.

Apresentação geral das diretrizes técnicas. Diretrizes para as atividades pré-exploratórias. diretrizes para as atividades de exploração florestal. Diretrizes para as atividades pós-exploratórias.bitstream/item/63188/1/Oriental-Doc64.pd

La grafomotricidad en el proceso de aprendizaje de los ni?os de 5 a?os de la instituci?n t?cnica Sumapaz Sede Santa Clara

64 p. Recurso Electr?nico?Este proyecto atenido como objetivo principal, Establecer como el proceso de aprendizaje en los ni?os de 5 a?os, a trav?s diversas estrategias, desarrollando actividades que aporten a mejorar las destrezas de las manos, los dedos y su posici?n corporal para que tengan una buena motricidad al escribir y desarrollar las habilidades b?sicas para la iniciaci?n a la escritura, basada en el desarrollo de procesos motores b?sicos como: tipos y conservaciones de trazos, precisi?n en el uso de instrumentos y el desarrollo de habilidades grafomotoras. El t?rmino grafomotricidad en el nivel inicial es esencialmente un acto mot?rico que tiene por finalidad educar y corregir la ejecuci?n de los movimientos b?sicos que intervienen en la escritura. Estrada, R. (2006) aporta diciendo que la grafomotricidad es una fase previa a la escritura ya que supone el entrenamiento para la realizaci?n de movimientos b?sicos que forman parte de la correcta direccionalidad y trazado de las letras. Se puede afirmar que la grafomotricidad es una posibilidad que se plantea en este proyecto como una alternativa metodol?gica para facilitar el proceso de la escritura en los ni?os de la instituci?n educativa t?cnica sumapaz sede santa clara. Palabras claves: grafomotricidad, iniciaci?n en la escrituraThis project is considered as main objective, to establish learning strategies in the children of 5 years of the technical educational institution sumapaz seed Santa Clara headquarters, through diverse activities, developing exercises that contribute to improve the skills of the hands, the fingers and their body position To have a good motor skills in writing and develop the basic skills for initiation to writing, based on the development of basic motor processes such as types and conservations of strokes, precision in the use of instruments and the development of graphing skills. The term grafomotricidad in the initial level is essentially a motor act that has as purpose to educate and to correct the execution of the basic movements that take part in the writing. Estrada, R. (2006) contends that grafomotricidad is a pre-writing phase since it involves training for the realization of basic movements that are part of the correct directionality and layout of the letters. It is possible to affirm that the grafomotricidad is a possibility that arises in this project as a methodological alternative to facilitate the process of writing in the children of the technical educational institution sumapaz seed Santa Clara Keywords: grafomotricidad, initiation in the writin