Migraciones: ¿qué describen el Censo de 2001 y la Estadística de Variaciones Residenciales?

Comunicación presentada en el IX Encuentro de Economía Aplicada, Jaén, 8-10 junio 2006.

La migración de retirados europeos al mercado de viviendas español: una evidencia sobre sus efectos

La migración internacional de retirados no es un fenómeno nuevo entre los países de la Unión Europea. Hay un buen número de sociólogos que han descrito el proceso y sus implicaciones en las formas de vida, especialmente en los casos de migración de los hogares de jóvenes retirados desde los países del norte de Europa hacia los soleados del sur. Muchos de estos movimientos afectan al mercado de viviendas desde el mismo momento de la llegada al país de destino y, en muchos casos, los flujos de población generados por esta migración contribuyen al cambio en las tendencias de edificación en los casos en que los destinos tienen bajos niveles de renta. Estos flujos tienen también implicaciones futuras como la necesidad de aumentar los servicios de atención a la tercera edad o en salud lo que, hoy por hoy, implican un elevado gasto público para el sistema español. Este artículo se interesa por las implicaciones en el corto plazo, así como en indagar en el fenómeno en sí. A través de la explotación de parte de los resultados de un proyecto de investigación denominado REVIcVAL (Retirados y vivienda en la Comunidad Valenciana), el artículo muestra algunas características de este flujo migratorio así como la racionalidad a la hora de tomar la decisión de comprar una vivienda. El ejercicio empírico utiliza información primaria recogida a través de un cuestionario recopilando información de retirados ingleses y alemanes en la costa de Alicante durante los años 2005 y 2006, con una base municipal, y estima la racionalidad en la toma de decisión de compra de viviendas.

3XMM J185246.6+003317: another low magnetic field magnetar

We study the outburst of the newly discovered X-ray transient 3XMMJ185246.6+003317, re-analyzing all available XMM-Newton observations of the source to perform a phase-coherent timing analysis, and derive updated values of the period and period derivative. We find the source rotating at P = 11.55871346(6) s (90% confidence level; at epoch MJD 54728.7) but no evidence for a period derivative in the seven months of outburst decay spanned by the observations. This translates to a 3σ upper limit for the period derivative of ˙ P <1.4×10−13 s s−1, which, assuming the classical magneto-dipolar braking model, gives a limit on the dipolar magnetic field of Bdip < 4.1×1013 G. The X-ray outburst and spectral characteristics of 3XMM J185246.6+003317 confirm its identification as a magnetar, but the magnetic field upper limit we derive defines it as the third “low-B” magnetar discovered in the past 3 yr, after SGR 0418+5729 and Swift J1822.3−1606. We have also obtained an upper limit to the quiescent luminosity (<4×1033 erg s−1), in line with the expectations for an old magnetar. The discovery of this new low field magnetar reaffirms the prediction of about one outburst per year from the hidden population of aged magnetars.

Spectral features in isolated neutron stars induced by inhomogeneous surface temperatures

The thermal X-ray spectra of several isolated neutron stars display deviations from a pure blackbody. The accurate physical interpretation of these spectral features bears profound implications for our understanding of the atmospheric composition, magnetic field strength and topology, and equation of state of dense matter. With specific details varying from source to source, common explanations for the features have ranged from atomic transitions in the magnetized atmospheres or condensed surface, to cyclotron lines generated in a hot ionized layer near the surface. Here, we quantitatively evaluate the X-ray spectral distortions induced by inhomogeneous temperature distributions of the neutron star surface. To this aim, we explore several surface temperature distributions, we simulate their corresponding general relativistic X-ray spectra (assuming an isotropic, blackbody emission), and fit the latter with a single blackbody model. We find that, in some cases, the presence of a spurious ‘spectral line’ is required at a high significance level in order to obtain statistically acceptable fits, with central energy and equivalent width similar to the values typically observed. We also perform a fit to a specific object, RX J0806.4−4123, finding several surface temperature distributions able to model the observed spectrum. The explored effect is unlikely to work in all sources with detected lines, but in some cases it can indeed be responsible for the appearance of such lines. Our results enforce the idea that surface temperature anisotropy can be an important factor that should be considered and explored also in combination with more sophisticated emission models like atmospheres.

Experiences Using an Open Source Sofware Library to Teach Computer Vision Subjects

Machine vision is an important subject in computer science and engineering degrees. For laboratory experimentation, it is desirable to have a complete and easy-to-use tool. In this work we present a Java library, oriented to teaching computer vision. We have designed and built the library from the scratch with enfasis on readability and understanding rather than on efficiency. However, the library can also be used for research purposes. JavaVis is an open source Java library, oriented to the teaching of Computer Vision. It consists of a framework with several features that meet its demands. It has been designed to be easy to use: the user does not have to deal with internal structures or graphical interface, and should the student need to add a new algorithm it can be done simply enough. Once we sketch the library, we focus on the experience the student gets using this library in several computer vision courses. Our main goal is to find out whether the students understand what they are doing, that is, find out how much the library helps the student in grasping the basic concepts of computer vision. In the last four years we have conducted surveys to assess how much the students have improved their skills by using this library.