The low-mass diskless population of Corona Australis

We combine published optical and near-infrared photometry to identify new low-mass candidate members in an area of about 0.64 deg^2 in Corona Australis with the S-parameter method. Five new candidate members of the region are selected. They have estimated ages between 3 and 15 Myr and masses between 0.05 and 0.15 M_⊙. With Spitzer photometry we confirm that these objects are not surrounded by optically thick disks. However, one of them is found to display excess at 24 μm, thus suggesting it harbors a disk with an inner hole. With an estimated mass of 0.07 M_⊙ according to the SED fitting, this is one of the lowest-mass objects reported to possess a transitional disk. Including these new members, the fraction of disks is about 50% among the total Corona Australis population selected by the same criteria, lower than the 70% fraction reported earlier for this region. Even so, we find a ratio of transitional to primordial disks (45%) very similar to the value derived by previous authors. This ratio is higher than for solar-type stars (5–10%), suggesting that disk evolution is faster in the latter, and/or that the “transitional disk” stage is not such a short-lived step for very low-mass objects. However, this impression needs to be confirmed with better statistics

Detection of a Variable Infrared Excess Around SDSS 121209.31+013627.7

We present near-infrared $JHK_s$ photometry and light curves of the candidate magnetic white dwarf+brown dwarf binary SDSS J121209.31+013627.7 and report on the detection of near-infrared excess and variability in the $K_s-$band. The observed near-infrared excess can be explained by the presence of an L7 brown dwarf and an extra emission source. The $J$ and $H$ light curves appear flat, which rules out eclipses deeper than 0.2 mag and the presence of an accretion hot spot on the white dwarf. From the variable $K_s$ lightcurve, we get a refined period for the system of 88$\pm$1 minutes. We show that the observed variability in $K_s-$band can be explained by cyclotron emission, which can be modeled by a small spot on the surface of the white dwarf. SDSS 1212 exhibits similarities to the ultra-short period polar EF Eridani, however the lack of evidence for Roche-lobe overflow accretion suggests it may be a pre-polar.Comment: 13 pages, 2 figures, accepted to ApJ

Long-time behavior of an angiogenesis model with flux at the tumor boundary

This paper deals with a nonlinear system of partial differential equations modeling a simplified tumor-induced angiogenesis taking into account only the interplay between tumor angiogenic factors and endothelial cells. Considered model assumes a nonlinear flux at the tumor boundary and a nonlinear chemotactic response. It is proved that the choice of some key parameters influences the long-time behaviour of the system. More precisely, we show the convergence of solutions to different semi-trivial stationary states for different range of parameters.Comment: 17 page

Absolute properties of the low-mass eclipsing binary CM Draconis

Spectroscopic and eclipsing binary systems offer the best means for determining accurate physical properties of stars, including their masses and radii. The data available for low-mass stars have yielded firm evidence that stellar structure models predict smaller radii and higher effective temperatures than observed, but the number of systems with detailed analyses is still small. In this paper we present a complete reanalysis of one of such eclipsing systems, CM Dra, composed of two dM4.5 stars. New and existing light curves as well as a radial velocity curve are modeled to measure the physical properties of both components. The masses and radii determined for the components of CM Dra are M1=0.2310+/-0.0009 Msun, M2=0.2141+/-0.0010 Msun, R1=0.2534+/-0.0019 Rsun, and R2=0.2396+/-0.0015 Rsun. With relative uncertainties well below the 1% level, these values constitute the most accurate properties to date for fully convective stars. This makes CM Dra a valuable benchmark for testing theoretical models. In comparing our measurements with theory, we confirm the discrepancies reported previously for other low-mass eclipsing binaries. These discrepancies seem likely to be due to the effects of magnetic activity. We find that the orbit of this system is slightly eccentric, and we have made use of eclipse timings spanning three decades to infer the apsidal motion and other related properties.Comment: 19 pages, 9 figures. Accepted for publication in Ap

GJ 3236: a new bright, very low-mass eclipsing binary system discovered by the MEarth observatory

We report the detection of eclipses in GJ 3236, a bright (I = 11.6) very low mass binary system with an orbital period of 0.77 days. Analysis of light- and radial velocity curves of the system yielded component masses of 0.38 +/- 0.02 and 0.28 +/- 0.02 Msol. The central values for the stellar radii are larger than the theoretical models predict for these masses, in agreement with the results for existing eclipsing binaries, although the present 5% observational uncertainties limit the significance of the larger radii to approximately 1 sigma. Degeneracies in the light curve models resulting from the unknown configuration of surface spots on the components of GJ 3236 currently dominate the uncertainties in the radii, and could be reduced by obtaining precise, multi-band photometry covering the full orbital period. The system appears to be tidally synchronized and shows signs of high activity levels as expected for such a short orbital period, evidenced by strong Halpha emission lines in the spectra of both components. These observations probe an important region of mass-radius parameter space around the predicted transition to fully-convective stellar interiors, where there are a limited number of precise measurements available in the literature.Comment: 14 pages, 5 figures, 10 tables, emulateapj format. Accepted for publication in Ap

Numerical study of efficiencies for box type solar cooker with internal reflectors

En este trabajo se muestran los resultados del estudio de las eficiencias termodinámicas de 1.a y 2.a ley aplicadas a 4 arreglos diferentes de estufas solares de tipo caja con reflectores internos. La estufa solar tiene 2 vidrios en su cubierta para disminuir la pérdida de calor por radiación y convección, y crear así el efecto invernadero. El interior de la estufa tiene espejos colocados a diferentes ángulos para dirigir la radiación solar hacia un recipiente con agua que se encuentra también dentro de la estufa. Los resultados obtenidos están basados en las temperaturas de calentamiento del agua, las cuales fueron obtenidas por medio de una simulación numérica que permite comparar los 4 arreglos de estufas solares bajo condiciones idénticas. El tratamiento de los resultados revela que la cantidad de energía que impacta en las estufas solares no es aprovechada de manera adecuada para los fines de calentamiento de agua. La mayor parte de la energía aprovechable se almacena en los vidrios de la tapa, lo que evidencia la necesidad de trabajar en el desarrollo de mejores materiales para mejorar tal situación.In this work, results of efficiencies for first and second law of thermodynamics applied to four box-type solar cookers with internal reflectors are shown. The solar cooker has two glasses on its cover to diminish the losses of heat for radiation and convection, besides creating the effect hothouse inside the cooker. The interior of the cooker has flat mirrors placed at different angles to reflect the solar radiation toward a recipient with water inside the cooker. The obtained results are based on heating water temperatures which were obtained by means of numeric simulation, allowing comparison under identical conditions of four solar cookers. The treatment of the results revealed that the quantity of energy that impacts on the solar cookers is not used in right way for the heating water ends. Most of the profitable energy is stored in the glasses of the cover, what evidences the necessity to work in the development of better materials to diminish such situation.Peer Reviewe

Applications of Direct Injection Soft Chemical Ionisation-Mass Spectrometry for the Detection of Pre-blast Smokeless Powder Organic Additives

Analysis of smokeless powders is of interest from forensics and security perspectives. This article reports the detection of smokeless powder organic additives (in their pre-detonation condition), namely the stabiliser diphenylamine and its derivatives 2-nitrodiphenylamine and 4-nitrodiphenylamine, and the additives (used both as stabilisers and plasticisers) methyl centralite and ethyl centralite, by means of swab sampling followed by thermal desorption and direct injection soft chemical ionisation-mass spectrometry. Investigations on the product ions resulting from the reactions of the reagent ions H3O+ and O2+ with additives as a function of reduced electric field are reported. The method was comprehensively evaluated in terms of linearity, sensitivity and precision. For H3O+, the limits of detection (LoD) are in the range of 41-88 pg of additive, for which the accuracy varied between 1.5 and 3.2%, precision varied between 3.7 and 7.3% and linearity showed R20.9991. For O2+, LoD are in the range of 72 to 1.4 ng, with an accuracy of between 2.8 and 4.9% and a precision between 4.5 and 8.6% and R20.9914. The validated methodology was applied to the analysis of commercial pre-blast gun powders from different manufacturers.(VLID)4826148Accepted versio

The impact of culture on the management of subsidiary organizations: the case of Viettel in Peru

As south-south investments increase so do the issues experienced by investing companies. One of these is the impact of culture. This article analyzes the effects of the subsidiary country culture on an investing firm’s organizational culture and the managerial practices used to address them. Data is gathered from cultural databases, a company-wide survey and semi structured interviews. Descriptive statistics are used to reveal country and organizational culture differences, with content analysis to expose management responses. There is a clear difference between the firm’s Vietnamese and Peruvian workers, with the company’s practices more amenable to the Vietnamese employees. Recognition of this has resulted in a number of initiatives to reduce its impact. The study’s results offer suggestions that may be valued by other foreign companies interested in operating in Peru and may be especially relevant to Southeast Asia and Asian companies interested in investing in or looking to start operations in Latin America.A medida que aumentan las inversiones sur-sur, también incrementan los problemas experimentados por las empresas inversoras. Uno de ellos es el impacto de la cultura. Este artículo analiza los efectos de la cultura del país filial en la cultura organizativa de una empresa inversora y las prácticas de gestión utilizadas para abordarlos. Los datos se recopilan de bases de datos culturales (Hofstede), una encuesta para analizar cultura organizacional (Modelo de Denison) y entrevistas semi-estructuradas. Existen diferencias culturales entre los trabajadores vietnamitas y peruanos. Las prácticas de la empresa favorecen más a los empleados vietnamitas debido a su cultura organizacional. Los reconocimientos de estas diferencias han generado iniciativas para reducir el impacto de la cultura nacional peruana sobre la cultura organizacional de la empresa. Las empresas extranjeras que operan en Perú, especialmente las del sudeste asiático y de Asia interesadas en invertir en América Latina pueden usar esto como un ejemplo para abordar las diferencias culturales nacionales y su impacto sobre las culturas organizacionales

Stellar Diameters and Temperatures II. Main Sequence K & M Stars

We present interferometric diameter measurements of 21 K- and M- dwarfs made with the CHARA Array. This sample is enhanced by literature radii measurements to form a data set of 33 K-M dwarfs with diameters measured to better than 5%. For all 33 stars, we compute absolute luminosities, linear radii, and effective temperatures (Teff). We develop empirical relations for \simK0 to M4 main- sequence stars between the stellar Teff, radius, and luminosity to broad-band color indices and metallicity. These relations are valid for metallicities between [Fe/H] = -0.5 and +0.1 dex, and are accurate to ~2%, ~5%, and ~4% for Teff, radius, and luminosity, respectively. Our results show that it is necessary to use metallicity dependent transformations to convert colors into stellar Teffs, radii, and luminosities. We find no sensitivity to metallicity on relations between global stellar properties, e.g., Teff-radius and Teff-luminosity. Robust examinations of single star Teffs and radii compared to evolutionary model predictions on the luminosity-Teff and luminosity-radius planes reveals that models overestimate the Teffs of stars with Teff < 5000 K by ~3%, and underestimate the radii of stars with radii < 0.7 R\odot by ~5%. These conclusions additionally suggest that the models overestimate the effects that the stellar metallicity may have on the astrophysical properties of an object. By comparing the interferometrically measured radii for single stars to those of eclipsing binaries, we find that single and binary star radii are consistent. However, the literature Teffs for binary stars are systematically lower compared to Teffs of single stars by ~ 200 to 300 K. Lastly, we present a empirically determined HR diagram for a total of 74 nearby, main-sequence, A- to M-type stars, and define regions of habitability for the potential existence of sub-stellar mass companions in each system. [abridged]Comment: 73 pages, 12 Tables, 18 Figures. Accepted for publication in The Astrophysical Journa