Detection of chromatic microlensing in Q 2237+0305 A

We present narrowband images of the gravitational lens system Q~2237+0305 made with the Nordic Optical Telescope in eight different filters covering the wavelength interval 3510-8130 \AA. Using point-spread function photometry fitting we have derived the difference in magnitude versus wavelength between the four images of Q~2237+0305. At $\lambda=4110$ \AA, the wavelength range covered by the Str\"omgren-v filter coincides with the position and width of the CIV emission line. This allows us to determine the existence of microlensing in the continuum and not in the emission lines for two images of the quasar. Moreover, the brightness of image A shows a significant variation with wavelength which can only be explained as consequence of chromatic microlensing. To perform a complete analysis of this chromatic event our observations were used together with Optical Gravitational Lensing Experiment light curves. Both data sets cannot be reproduced by the simple phenomenology described under the caustic crossing approximation; using more realistic representations of microlensing at high optical depth, we found solutions consistent with simple thin disk models ($r_{s}\varpropto \lambda^{4/3}$); however, other accretion disk size-wavelength relationships also lead to good solutions. New chromatic events from the ongoing narrow band photometric monitoring of Q~2237+0305 are needed to accurately constrain the physical properties of the accretion disk for this system.Comment: 9 pages, 9 figures, 2 tables. Matches ApJ published version. Some references adde

Sedimentología de los yesos del sector central de la Depresión del Duero

En el sector central de la Depresión del Duero afloran sedimentosneógenos, terrígenos, carbonatados y yesíferos. En los depósitos yesiferos se han diferenciado facies de yeso primario, secundario y retrabajado que junto a las facies carbonatadas se ordenan en secuencias y megasecuencias positivas y negativas. Las megasecuencias se interpretan como retracciones o expansiones del sistema lacustre. Se relacionan las secuencias con los modelos paleogeográficos establecidos y se analizan los factores que controlaron la evolución de los depósitos yesíferos en el tiempo

Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?

From optical R band data of the double quasar QSO 0957+561A,B, we made two new difference light curves (about 330 days of overlap between the time-shifted light curve for the A image and the magnitude-shifted light curve for the B image). We observed noisy behaviours around the zero line and no short-timescale events (with a duration of months), where the term event refers to a prominent feature that may be due to microlensing or another source of variability. Only one event lasting two weeks and rising - 33 mmag was found. Measured constraints on the possible microlensing variability can be used to obtain information on the granularity of the dark matter in the main lensing galaxy and the size of the source. In addition, one can also test the ability of the observational noise to cause the rms averages and the local features of the difference signals. We focused on this last issue. The combined photometries were related to a process consisting of an intrinsic signal plus a Gaussian observational noise. The intrinsic signal has been assumed to be either a smooth function (polynomial) or a smooth function plus a stationary noise process or a correlated stationary process. Using these three pictures without microlensing, we derived some models totally consistent with the observations. We finally discussed the sensitivity of our telescope (at Teide Observatory) to several classes of microlensing variability.Comment: MNRAS, in press (LaTeX, 14 pages, 22 eps figures

International Manufacturing Networks Supply Strategy Design Aided by Simulation Tools: An Empirical Study in the Wind Sector

[ENG] In the last decades, many manufacturing companies are suffering a trend toward multisite location and greater fragmentation of theirs productive and logistic processes. This fact out lights that the open of boundaries in Eastern Europe and the irruptions of countries in the global trade economy, have forced to develop value added activities such as engineering, purchasing, manufacturing and assembly in different places, even in different countries

Effects of grade retention policies: a literature review of empirical studies applying causal inference

The identification of the causal effects of grade retention policies is of enormous relevance for researchers and policymakers alike. Taking advantage of the availability of more detailed longitudinal datasets, researchers have been able to apply different identification strategies that address the classical problems of selection bias and unobserved heterogeneity that have plagued previous studies on the effect of retention. We present a systematic literature review of empirical studies aiming to unveil the causal effects of retention. This study underlines the need to consider and evaluate different kinds of grade retention polices as their effects vary depending on several dimensions (such as timing of the policy, comparison groups, length of the effects or institutional settings). According to the results of our review, we conclude that grade retention is unlikely to be an efficient policy as the costs associated to the policy can easily outweigh the potential (weak) benefits of retention. It is therefore necessary to consider alternative policies to retention, or policies that can be used in combination with it, in order to enhance the performance of low achievers, in particular those students at risk characterized by a low ability profile

Primera versión española del NEPSY para la evaluación neuropsicológica del desarrollo en una muestra de niños españoles

All the subtests of the first Spanish language version of the NEPSY were administered to a sample of 415 children aged 3 to 12 years old: 193 boys and 222 girls. For statistical analysis, the sample was divided into two groups: one comprising 98 children aged 3-4, and the other 317 children aged 5-12. First, the adjustment of the distribution of the different items of this Spanish version of the NEPSY subtests to the normal curve was checked. The usefulness of these subtests to assess the level of children’s development according to their chronological age was then tested using regression analysis. Finally, we checked that the raw scores on the subtest items of this Spanish version ofthe NEPSY differed significantly between 3 and 4 year olds and between 5 and 6 year olds: in each age pair, the mean scores of the older group increased inaccuracy and decreased in runtime and errors.Se administran todos los subtests de la primera versión en castellano del NEPSY a una muestra de 415 niños de 3 a 12 años de edad: 193 varones y 222 niñas. Para las tareas estadísticas, se separan en dos grupos: uno de 98 niños de 3-4 años y otro de 317 de 4-12 años. En primer lugar, se comprueba el ajuste de las distribuciones de las distintas variables de los subtest de esta versión española del NEPSY a la curva normal. Posteriormente se comprueba la utilidad de estos para verificar el nivel de desarrollo de los niños por su edad cronológica, mediante un análisis de regresión. Finalmente, se verifica que las diferencias en las puntuaciones directas de las distintas variables de los subtestsde esta versión española del NEPSY, entre los niños de 3 y 4 años y entre losde 5 y 6 años, son estadísticamente significativas, de forma que ambos grupos de niños mayores aumentan las medias en exactitud y disminuyen las del tiempo de ejecución y los errores en las diferentes tareas