3,301 research outputs found
Energy and Momentum Distributions of a (2+1)-dimensional black hole background
Using Einstein, Landau-Lifshitz, Papapetrou and Weinberg energy-momentum
complexes we explicitly evaluate the energy and momentum distributions
associated with a non-static and circularly symmetric three-dimensional
spacetime. The gravitational background under study is an exact solution of the
Einstein's equations in the presence of a cosmological constant and a null
fluid. It can be regarded as the three-dimensional analogue of the Vaidya
metric and represents a non-static spinless (2+1)-dimensional black hole with
an outflux of null radiation. All four above-mentioned prescriptions give
exactly the same energy and momentum distributions for the specific black hole
background. Therefore, the results obtained here provide evidence in support of
the claim that for a given gravitational background, different energy-momentum
complexes can give identical results in three dimensions. Furthermore, in the
limit of zero cosmological constant the results presented here reproduce the
results obtained by Virbhadra who utilized the Landau-Lifshitz energy-momentum
complex for the same (2+1)-dimensional black hole background in the absence of
a cosmological constant.Comment: 19 pages, LaTeX, v3: references added, to appear in Int.J.Mod.Phys.
L'Aeroport de Barcelona com a infraestructura de connexió internacional
Els aeroports són un factor essencial per al creixement econòmic de les regions on s'ubiquen.Germà Bel shows the importance of Barcelonas Prat airport. It is a strategic trade point, important
not only for the growth of the country in general but also for the areas where it is established
Economia i polÃtica de la privatització local
L'autor del treball guardonat amb el 6è Premi Societat Catalana d'Economia en fa un resum,
EconomÃa y polÃtica de la privatización local.
Es tracta d'un llibre d'edició recent (Marcial Pons, Ediciones JurÃdicas y Sociales, ISBN:
84-9768-325-0), fruit d'una investigació de l'autor, finançada per la Fundación Rafael del Pino i
que ha comptat amb l'estÃmul i el suport d'Amadeu Petitbò, el seu director.The book presented at this conference seeks to find the answer tomany questions related to local
privatization such as: success,why decisions aremade andwhat their effects are on the economy. It is an innovative and very useful book for academics, policymakers and public service managers
- …