High U(1) charges in type IIB models and their F-theory lift

We construct models with U(1) gauge group and matter with charges up to 6, in the context of type IIB compactifications. We show explicitly that models with charges up to 4 can be derived from corresponding models in F-theory by applying the Sen weak coupling limit. We derive which type IIB models should be the limit of charge 5 and 6 F-theory models. Explicit six dimensional type IIB models with maximal charge 5 and 6 are constructed on an algebraic K3 surface that is the double cover of \u2102\u2119 2 . By using type IIB results we are also able to rediscover the F-theory charge 4 model in a straightforward way

A closer look at the X-ray transient XTE J1908+094: identification of two new near-infrared candidate counterparts

We had reported in Chaty, Mignani, Israel (2002) on the near-infrared (NIR) identification of a possible counterpart to the black hole candidate XTE J1908+094 obtained with the ESO/NTT. Here, we present new, follow-up, CFHT adaptive optics observations of the XTE J1908+094 field, which resolved the previously proposed counterpart in two objects separated by about 0.8". Assuming that both objects are potential candidate counterparts, we derive that the binary system is a low-mass system with a companion star which could be either an intermediate/late type (A-K) main sequence star at a distance of 3-10 kpc, or a late-type ($>$K) main sequence star at a distance of 1-3 kpc. However, we show that the brighter of the two objects (J ~ 20.1, H ~ 18.7, K' ~ 17.8) is more likely to be the real counterpart of the X-ray source. Its position is more compatible with our astrometric solution, and colours and magnitudes of the other object are not consistent with the lower limit of 3 kpc derived independently from the peak bolometric flux of XTE J1908+094. Further multi-wavelength observations of both candidate counterparts are crucial in order to solve the pending identification.Comment: accepted for publication in MNRAS, 5 pages, 3 figure

Un programa de estiramiento en Educación Física realizado una vez a la semana también mejora la extensibilidad isquiosural en escolares: Un diseño controlado aleatorio por grupos

Introduction: physical education teachers are required to carry out intervention programs for students to achieve health-enhancing flexibility levels. Unfortunately, to our knowledge, there are no studies examining the effect of a stretching program carried out only once a week on schoolchildren. Objectives: the purpose of the present study was to compare the effects of a short-term stretching intervention program performed once and twice a week on hamstring extensibility among schoolchildren in the physical education setting. Methods: a sample of 180 high school students aged 12-14 years old was randomly assigned (by natural groups) to a control group, experimental group 1 and experimental group 2. During physical education classes, experimental group students performed a stretching program for eight weeks. The experimental group 1 and 2 performed the stretching program once and twice a week, respectively. Results: the analysis of variance results showed that the students of both experimental groups improved statistically significantly their hamstring extensibility when compared with the control group students (p 0.05). Conclusions: a short-term stretching program performed only once a week improves hamstring extensibility in schoolchildren. When the stretching program is performed twice a week, the improvement in students ́ hamstring extensibility is not statistically higher.Introducción: los profesores de educación física deben llevar a cabo programas de intervención para que los estudiantes alcancen niveles de flexibilidad saludables. Lamentablemente, no se conocen estudios que examinen el efecto de un programa de estiramiento llevado a cabo solo una vez por semana en escolares. Objetivos: el objetivo del presente estudio fue comparar los efectos de un programa de intervención de estiramiento a corto plazo realizado una y dos veces por semana sobre la extensibilidad isquiosural en escolares en el contexto de la educación física. Métodos: una muestra de 180 estudiantes de educación secundaria de 12-14 años fue asignado aleatoriamente (por grupos naturales) a los grupos control, experimental 1 y experimental 2. Durante las clases de educación física, los estudiantes experimentales realizaron un programa de estiramiento durante ocho semanas. El grupo experimental 1 y 2 realizaron el programa de estiramiento una y dos veces por semana, respectivamente. Resultados: los resultados del análisis de varianza mostraron que los estudiantes de ambos grupos experimentales obtuvieron una mejora estadísticamente significativa de la extensibilidad isquiosural, comparado con los estudiantes del grupo de control (p 0,05). Conclusiones: un programa de estiramiento a corto plazo realizado una vez por semana mejora la extensibilidad isquiosural en escolares. Cuando el programa de estiramiento se lleva a cabo dos veces por semana, la mejora en la extensibilidad isquiosural de los estudiantes no es estadísticamente mayor.Daniel Mayorga-Vega is supported by a research grant from the Spanish Ministry of Education, Culture and Sport (AP2010-5905)

Sub-arcsecond radio and optical observations of the likely counterpart to the gamma-ray source 2FGL J2056.7+4939

We have searched and reviewed all multi- wavelength data available for the region towards the gamma-ray source 2FGL J2056.7+4939 in order to con- strain its possible counterpart at lower energies. As a result, only a point-like optical/infrared source with flat-spectrum radio emission is found to be consistent with all X-ray and gamma-ray error circles. Its struc- ture is marginally resolved at radio wavelengths at the sub-arcsecond level. An extragalactic scenario appears to be the most likely interpretation for this object.Comment: 5 pages, 3 figures, 1 tabl