The value of the fine structure constant over cosmological times

The optical spectra of objects classified as QSOs in the SDSS DR6 are analyzed with the aim of determining the value of the fine structure constant in the past and then check for possible changes in the constant over cosmological timescales. The analysis is done by measuring the position of the fine structure lines of the [OIII] doublet (4959 and 5008) in QSO nebular emission. From the sample of QSOs at redshifts z < 0.8 a subsample was selected on the basis of the amplitude and width of the [OIII] lines. Two different method were used to determine the position of the lines of the [OIII] doublet, both giving similar results. Using a clean sample containing 1568 of such spectra, a value of Delta alpha /alpha=(+2.4 +-2.5) x 10^{-5} (in the range of redshifts 0-0.8) was determined. The use of a larger number of spectra allows a factor ~5 improvement on previous constraints based on the same method. On the whole, we find no evidence of changes in alpha on such cosmological timescales. The mean variation compatible with our results is 1/ Delta alpha/alpha=(+0.7 +- 0.7) x 10^{-14} yr^{-1}. The analysis was extended to the [NeIII] and [SII] doublets, although their usefulness is limited due to the fact that all these doublets in QSOs tend to be fainter than [OIII], and that some of them are affected by systematics.Comment: 22 pages, 10 figures. Accepted for publication in Astrophysical Journa

Two-dimensional Einstein manifolds in geometrothermodynamics

We present a class of thermodynamic systems with constant thermodynamic curvature which, within the context of geometric approaches of thermodynamics, can be interpreted as constant thermodynamic interaction among their components. In particular, for systems constrained by the vanishing of the Hessian curvature we write down the systems of partial differential equations. In such a case it is possible to find a subset of solutions lying on a circumference in an abstract space constructed from the first derivatives of the isothermal coordinates. We conjecture that solutions on the characteristic circumference are of physical relevance, separating them from those of pure mathematical interest. We present the case of a one-parameter family of fundamental relations that -- when lying in the circumference -- describe a polytropic fluid

ENSEÑANZA DE LA GEOMETRÍA EN SEGUNDO AÑO DE EDUCACIÓN SECUNDARIA BAJO EL ENFOQUE DE COMPETENCIAS

Keywords: learning; student; teacher; grade skills; methodologies; problem-solvingCIENCIA E INTERCULTURALIDAD, Volumen 6, No. 1 January-June 2010, 110-119El art&iacute;culo reporta una investigaci&oacute;n realizada en el Instituto Nacional Crist&oacute;bal Col&oacute;n durante el segundo semestre del a&ntilde;o 2009, ciudad de Bluefields, Nicaragua y propiamente se le dio seguimiento al proceso de ense&ntilde;anza de la geometr&iacute;a plana impartida en segundo a&ntilde;o bajo el enfoque por competencias, reci&eacute;n implementado. El estudio se centr&oacute; en: a) las metodolog&iacute;as de ense&ntilde;anza de los docentes de matem&aacute;ticas en el desarrollo de los contenidos de geometr&iacute;a plana de segundo a&ntilde;o, implementado el enfoque por competencias y b) la manera en que estas contribuyen al aprendizaje que adquieren los estudiantes de geometr&iacute;a. En este trabajo se hacen an&aacute;lisis sobre problemas en el proceso ense&ntilde;anza de la matem&aacute;tica, en especial de la geometr&iacute;a plana de segundo a&ntilde;o, de una muestra de 112 estudiantes se revela que los estudiantes tienen poco conocimiento de los contenidos de geometr&iacute;a de su nivel, mediante las entrevistas se descubri&oacute; que los docentes de matem&aacute;ticas no lograron impartir todos los contenidos de geometr&iacute;a planteados en el programa de estudio y deficiencias en el enfoque por competencia que se est&aacute; desarrollando en todas las escuelas del pa&iacute;s. El marco te&oacute;rico se encuentra referido a diversas teor&iacute;as de ense&ntilde;anzas priorizando las referidas a la matem&aacute;tica y la geometr&iacute;a; as&iacute; mismo en &eacute;l se encuentra definido el enfoque por competencia en el cual se basa la propuesta metodol&oacute;gica que se elabor&oacute;, para dar repuesta a los problemas detectados en transcurso de la investigaci&oacute;n. Palabras claves: Aprendizaje; estudiante; docente; competencias de grado; metodolog&iacute;as; resoluci&oacute;n de problemas. CIENCIA E INTERCULTURALIDAD, Volumen 6, a&ntilde;o 3 No. 1 Enero-Junio 2010, 110-11

Determinants of default in P2P lending

This paper studies P2P lending and the factors explaining loan default. This is an important issue because in P2P lending individual investors bear the credit risk, instead of financial institutions, which are experts in dealing with this risk. P2P lenders suffer a severe problem of information asymmetry, because they are at a disadvantage facing the borrower. For this reason, P2P lending sites provide potential lenders with information about borrowers and their loan purpose. They also assign a grade to each loan. The empirical study is based on loans'' data collected from Lending Club (N = 24, 449) from 2008 to 2014 that are first analyzed by using univariate means tests and survival analysis. Factors explaining default are loan purpose, annual income, current housing situation, credit history and indebtedness. Secondly, a logistic regression model is developed to predict defaults. The grade assigned by the P2P lending site is the most predictive factor of default, but the accuracy of the model is improved by adding other information, especially the borrower''s debt level

Toward a Clean Sample of Ultra-Luminous X-ray Sources

CONTEXT. Observational follow-up programmes for the characterization of ultra-luminous X-ray sources (ULXs) require the construction of clean samples of such sources in which the contamination by foreground/background sources is minimum. AIMS. In this article we calculate the degree of foreground/background contaminants among the ULX sample candidates in the Colbert & Ptak (2002) catalogue and compare these computations with available spectroscopical identifications. METHODS. We use statistics based on known densities of X-ray sources and AGN/QSOs selected in the optical. The analysis is done individually for each parent galaxy. The existing identifications of the optical counterparts are compiled from the literature. RESULTS. More than a half of the ULXs, within twice the distance of the major axis of the 25 mag/arcsec$^2$ isophote from RC3 nearby galaxies and with X-ray luminosities $L_X$[2-10 keV] $\ge 10^{39}$ erg/s, are expected to be high redshift background QSOs. A list of 25 objects (clean sample) confirmed to be real ULXs or to have a low probability of being contaminant foreground/background objects is provided.Comment: 9 pages, accepted in A&

Retos y oportunidades de la implantación de los bancos de agua en España

Con el fin de conseguir una buena gobernanza del agua, que trate de alcanzar un equilibrio entre los objetivos de eficiencia económica y sostenibilidad ambiental, durante las últimas décadas se ha potenciado el uso de instrumentos económicos para una mejor gestión de la demanda de los recursos hídricos, dada la dificultad de seguir aumentando la oferta de los mismos. En este contexto, este trabajo se centra en los bancos de agua como mecanismo de mercado que aporta la necesaria flexibilidad institucional en la asignación de los recursos hídricos entre los diferentes usuarios. La investigación realizada en este sentido ha permitido desarrollar una tipología de los bancos de agua que actualmente operan a nivel mundial en base a sus características operativas. Esta caracterización ha permitido igualmente realizar un análisis crítico de las experiencias de bancos de agua implementadas hasta la fecha, con el fin poder valorar el desempeño de este instrumento económico para la mejora de la gestión pública del agua. La investigación llevada a cabo revela que los bancos de agua son un instrumento útil para la gestión de los recursos hídricos, aportando sugerencias para la mejora de su implementación operativa en España mediante la correspondiente reforma de la Ley de Aguas.Ministerio de Economía y Competitividad (MINECO) AGL2013-48080-C2-1-RFondo Europeo de Desarrollo Regional (FEDER) AGL2013-48080-C2-1-

An extensive K-bentonite as an indicator of a super-eruption in northern Iberia 477 My ago

Zircon and monazite ID-TIMS U-Pb dating of four Lower Ordovician altered ash-fall tuff beds (K-Bentonites) in NW Iberia provided coetaneous ages of 477.5±1, 477±1.3 Ma, 477.2±1.1 Ma and 477.3±1 Ma, with a pooled concordia age of 477.2±0.74 Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using data from the Cantabrian Zone) returns a minimum volume for the preserved deposits of ca. 37.5 km3 (Volcanic Explosivity Index - VEI = 6, Colossal). When considering other putative equivalent beds in other parts of Iberia and neighbouring realms the volume of ejecta associated to this event would make it reach the Supervolcanic-Apocalyptic status (VEI=8, >1000 km3). Contrary to most cases of this kind of gargantuan eruption events, the studied magmatic event took place in relation to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically coincident large caldera event observed in the geological record of NW Iberia could be ground zero of this super-eruption

Обширные отложения K-бентонитов как индикатор супервзрыва в северной Иберии на уровне 477 миллионов лет назад

Zircon and monazite ID-TIMS U-Pb dating of four Lower Ordovician altered ash-fall tuff beds (K-Bentonites) in NW Iberia provided coetaneous ages of 477.5±1, 477±1.3 Ma, 477.2±1.1 Ma and 477.3±1 Ma, with a pooled concordia age of 477.2±0.74 Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using data from the Cantabrian Zone) returns a minimum volume for the preserved deposits of ca. 37.5 km3 (Volcanic Explosivity Index - VEI = 6, Colossal). When considering other putative equivalent beds in other parts of Iberia and neighboring realms the volume of ejecta associated to this event would make it reach the Supervolcanic-Apocalyptic status (VEI=8, >1000 km3). Contrary to most cases of this kind of gargantuan eruption events, the studied magmatic event took place in relation to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically coincident large caldera event observed in the geological record of NW Iberia could be ground zero of this super-eruption

Regular and complex singularities of the generalized thin film equation in two dimensions

A20We use a generalized version of the equation of motion for a thin film of liquid on a solid, horizontal substrate as a model system to study the formation of singularities in space dimensions greater than one. Varying both the exponent controlling long-ranged forces, as well as the exponent of the nonlinear mobility, we predict the structure of the singularity as the film thickness goes to zero. The spatial structure of rupture may be either ‘pointlike’ (approaching axisymmetry) or ‘quasi-one-dimensional’, in which case a one-dimensional singularity is unfolded into two or higher space dimensions. The scaling of the profile with time may be either strictly self-similar (the ‘regular’ case) or discretely self-similar and perhaps chaotic (the ‘irregular’ case). We calculate the phase boundaries between these regimes, and confirm our results by detailed comparisons with time-dependent simulations of the nonlinear thin film equation in two space dimensions.Junta de Andalucía P18-FR-3623Ministerio de Economía y Competitividad (MINECO). España 108278-RB-C3