60,624 research outputs found
Black holes in extended gravity theories in Palatini formalism
We consider several physical scenarios where black holes within classical
gravity theories including 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 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,
in the field and in groups for galaxies brighter than
, 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
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