Black holes in extended gravity theories in Palatini formalism

We consider several physical scenarios where black holes within classical gravity theories including $R^2$ and Ricci-squared corrections and formulated \`a la Palatini can be analytically studied.Comment: 4 pages, contribution to the "Spanish Relativity Meeting in Portugal 2012 (Progress in Mathematical Relativity, Gravitation and Cosmology)", Springer Proceedings in Mathematics (to appear

Halflife of 56Ni in cosmic rays

A measurement of the 56Ni cosmic ray abundance has been discussed as a possible tool to determine the acceleration time scale of relativistic particles in cosmic rays. This conjecture will depend on the halflife of totally ionized 56Ni which can only decay by higher-order forbidden transitions. We have calculated this halflife within large-scale shell model calculations and find t_{1/2} \approx 4 \times 10^4 years, only slightly larger than the currently available experimental lower limit, but too short for 56Ni to serve as a cosmic ray chronometer.Comment: 3 pages, 1 figur

The evolution of the bi-modal colour distribution of galaxies in SDSS groups

We analyse $u-r$ colour distributions for several samples of galaxies in groups drawn from the Fourth Data Release of the Sloan Digital Sky Survey. For all luminosity ranges and environments considered the colour distributions are well described by the sum of two Gaussian functions. We find that the fraction of galaxies in the red sequence is an increasing function of group virial mass. We also study the evolution of the galaxy colour distributions at low redshift, $z\le0.18$ in the field and in groups for galaxies brighter than $M_r-5\log(h)=-20$, finding significant evidence of recent evolution in the population of galaxies in groups. The fraction of red galaxies monotonically increases with decreasing redshift, this effect implies a much stronger evolution of galaxies in groups than in the field.Comment: 7 pages, 6 figures, submited to MNRAS after minor revisio

Perpendicular transport properties of YBa_2Cu_3O_{7-\delta}/PrBa_2Cu_3O_{7-\delta} superlattices

The coupling between the superconducting planes of YBa2Cu3O{7-\delta}/ PrBa2Cu3O{7-\delta} superlattices has been measured by c-axis transport. We show that only by changing the thickness of the superconducting YBa2Cu3O{7-\delta} layers, it is possible to switch between quasi-particle and Josephson tunneling. From our data we deduce a low temperature c-axis coherence length of 0.27 nm.Comment: Presented at LT22, contains 2 pages and 2 figures. to appear in Physica