Approximating the maximum ergodic average via periodic orbits

Let sigma: Sigma(A) -> Sigma(A) be a subshift of finite type, let M-sigma be the set of all sigma-invariant Borel probability measures on Sigma(A), and let f : Sigma(A) -> R be a Holder continuous observable. There exists at least one or-invariant measure A which maximizes integral f d mu. The following question was asked by B. R. Hunt, E. Ott and G. Yuan: how quickly can the maximum of the integrals integral f d mu be approximated by averages along periodic orbits of period less than p? We give an example of a Holder observable f for which this rate of approximation is slower than stretched-exponential in p

Bulge RR Lyrae stars in the VVV tile b201\textit{b201}

The VISTA Variables in the V\'ia L\'actea (VVV) Survey is one of the six ESO public surveys currently ongoing at the VISTA telescope on Cerro Paranal, Chile. VVV uses near-IR ($ZYJHK_{\rm s}$) filters that at present provide photometry to a depth of $K_{\rm s} \sim 17.0$ mag in up to 36 epochs spanning over four years, and aim at discovering more than 10$^6$ variable sources as well as trace the structure of the Galactic bulge and part of the southern disk. A variability search was performed to find RR Lyrae variable stars. The low stellar density of the VVV tile $\textit{b201}$, which is centered at ($\ell, b$) $\sim$ ($-9^\circ, -9^\circ$), makes it suitable to search for variable stars. Previous studies have identified some RR Lyrae stars using optical bands that served to test our search procedure. The main goal is to measure the reddening, interstellar extinction, and distances of the RR Lyrae stars and to study their distribution on the Milky Way bulge. A total of 1.5 sq deg were analyzed, and we found 39 RR Lyrae stars, 27 of which belong to the ab-type and 12 to the c-type. Our analysis recovers all the previously identified RR Lyrae variables in the field and discovers 29 new RR Lyrae stars. The reddening and extinction toward all the RRab stars in this tile were derived, and distance estimations were obtained through the period--luminosity relation. Despite the limited amount of RR Lyrae stars studied, our results are consistent with a spheroidal or central distribution around $\sim 8.1$ and $\sim 8.5$ kpc. for either the Cardelli or Nishiyama extinction law.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and Astrophysic

Low EUV Luminosities Impinging on Protoplanetary Disks

The amount of high-energy stellar radiation reaching the surface of protoplanetary disks is essential to determine their chemistry and physical evolution. Here, we use millimetric and centimetric radio data to constrain the EUV luminosity impinging on 14 disks around young (~2-10Myr) sun-like stars. For each object we identify the long-wavelength emission in excess to the dust thermal emission, attribute that to free-free disk emission, and thereby compute an upper limit to the EUV reaching the disk. We find upper limits lower than 10$^{42}$ photons/s for all sources without jets and lower than $5 \times 10^{40}$ photons/s for the three older sources in our sample. These latter values are low for EUV-driven photoevaporation alone to clear out protoplanetary material in the timescale inferred by observations. In addition, our EUV upper limits are too low to reproduce the [NeII] 12.81 micron luminosities from three disks with slow [NeII]-detected winds. This indicates that the [NeII] line in these sources primarily traces a mostly neutral wind where Ne is ionized by 1 keV X-ray photons, implying higher photoevaporative mass loss rates than those predicted by EUV-driven models alone. In summary, our results suggest that high-energy stellar photons other than EUV may dominate the dispersal of protoplanetary disks around sun-like stars.Comment: Accepted for publication to The Astrophysical Journa

El Estado marroquí ante sus emigrantes y la ciudadanía marroquí en la diáspora

El Estado marroquí se esfuerza desde hace años para mantener el vínculo y la identificación de sus emigrantes con el país de origen y por aumentar su influencia internacional a través de ellos. Un elemento esencial para entender las sociedades árabes del siglo XXI, y especialmente las magrebíes, es la existencia de importantes comunidades de emigrantes instalados en otros países de la región y fuera de ella, sobre todo en Europa. Estas migraciones constituyen la base de vínculos económicos y políticos entre los Estados implicados. El esfuerzo del Estado marroquí para garantizar la vinculación de sus emigrantes con el país plantea en los últimos años nuevos escenarios de participación y pretende modernizar los términos de debate. Frente a ello reaccionan las asociaciones ya existentes, generando a su vez nuevas iniciativas y discursos. Estas migraciones suponen a medio plazo la generación de dinámicas de construcción ciudadana transnacional que plantean numerosos retos no sólo para los individuos que las protagonizan y sus familias sino también para los Estados y sus sociedades civiles

El cuerpo, hipermodernidad y medicina

El cuerpo es uno de los grandes ausentes de la filosofía médica en México; el cuerpo se instala en un todo y su interpretación es pobre. en Medicina, el análisis del cuerpo transita entre la salud y la enfermedad, aquí se realiza una reflexión en torno al cuerpo, la hipermodernidad y la medicina