207 research outputs found
Linking the actors and policies throughout the disaster management cycle by "Agreement on Objectives" â a new output-oriented management approach
Current management of disaster risks is often fragmented due to a lack of coordination between involved actors, i.e. civil protection and spatial planning â a phenomenon which is known as the "problem of interplay". This paper presents an output-oriented risk management approach ("parametric governance"). Here, the modality of the achievement of objectives remains in the hands of the given addressees. This implies a shift from a top-down to a more collaborative, process-oriented form of decision-making. The approach has been successfully applied in two hazard cases and three administrative contexts: (a) the City of Dortmund (Germany) facing flash floods, (b) East Attica region (Greece) facing forest fires, and (c) Lazio Region (Italy) also facing forest fires. As proved by the applications of the concept, a dialogue among experts, stakeholders, and decision-makers is indispensable in order to guarantee inclusion of all diverse and competing values, opinions, and claims. Moreover, a structured communication path is needed to meet the requirements of a risk governance process. Finally, a win-win-situation among the involved actors has to be created to reach an agreement on common goals and actions to achieve them in due time
Conformally dressed black hole in 2+1 dimensions
A three dimensional black hole solution of Einstein equations with negative
cosmological constant coupled to a conformal scalar field is given. The
solution is static, circularly symmetric, asymptotically anti-de Sitter and
nonperturbative in the conformal field. The curvature tensor is singular at the
origin while the scalar field is regular everywhere. The condition that the
Euclidean geometry be regular at the horizon fixes the temperature to be
. Using the Hamiltonian formulation including
boundary terms of the Euclidean action, the entropy is found to be
of the standard value (), and in agreement with
the first law of thermodynamics.Comment: LaTeX ,RevTeX, 13pages, no figure
Chaos in black holes surrounded by gravitational waves
The occurrence of chaos for test particles moving around Schwarzschild black
holes perturbed by a special class of gravitational waves is studied in the
context of the Melnikov method. The explicit integration of the equations of
motion for the homoclinic orbit is used to reduce the application of this
method to the study of simple graphics.Comment: 15 pages, LaTex
No Scalar Hair Theorem for a Charged Spherical Black Hole
This paper consolidates noscalar hair theorem for a charged spherically
symmetric black hole in four dimension in general relativity as well as in all
scalar tensor theories, both minimally and nonminimally coupled, when the
effective Newtonian constant of gravity is positive. However, there is an
exception when the matter field itself is coupled to the scalar field, such as
in dilaton gravity.Comment: 13 pages, Latex format, some minor corrections are made, accepted for
publication in Physical Review
Behavior of Quasilocal Mass Under Conformal Transformations
We show that in a generic scalar-tensor theory of gravity, the ``referenced''
quasilocal mass of a spatially bounded region in a classical solution is
invariant under conformal transformations of the spacetime metric. We first
extend the Brown-York quasilocal formalism to such theories to obtain the
``unreferenced'' quasilocal mass and prove it to be conformally invariant. The
appropriate reference term in this case is defined by generalizing the
Hawking-Horowitz prescription, which was originally proposed for general
relativity. For such a choice of reference term, the referenced quasilocal mass
for a general spacetime solution is obtained. This expression is shown to be a
conformal invariant provided the conformal factor is a monotonic function of
the scalar field. We apply this expression to the case of static spherically
symmetric solutions with arbitrary asymptotics to obtain the referenced
quasilocal mass of such solutions. Finally, we demonstrate the conformal
invariance of our quasilocal mass formula by applying it to specific cases of
four-dimensional charged black hole spacetimes, of both the asymptotically flat
and non-flat kinds, in conformally related theories.Comment: LaTeX, 31 pages, one ps figur
Black holes in the Brans-Dicke-Maxwell theory
The black hole solutions in the higher dimensional Brans-Dicke-Maxwell theory
are investigated. We find that the presence of the nontrivial scalar field
depends on the spacetime dimensions (D). When D=4, the solution corresponds to
the Reissner-Nordstr\"{o}m black hole with a constant scalar field. In higher
dimensions (D>4), one finds the charged black hole solutions with the
nontrivial scalar field. The thermal properties of the charged black holes are
discussed and the reason why the nontrivial scalar field exists are explained.
Also the solutions for higher dimensional Brans-Dicke theory are given for
comparison.Comment: Revtex, 5 pages, no figures, contents were rewritten and new
references were adde
Collisions of Einstein-Conformal Scalar Waves
A large class of solutions of the Einstein-conformal scalar equations in
D=2+1 and D=3+1 is identified. They describe the collisions of asymptotic
conformal scalar waves and are generated from Einstein-minimally coupled scalar
spacetimes via a (generalized) Bekenstein transformation. Particular emphasis
is given to the study of the global properties and the singularity structure of
the obtained solutions. It is shown, that in the case of the absence of pure
gravitational radiation in the initial data, the formation of the final
singularity is not only generic, but is even inevitable.Comment: 17 pages, LaTe
On Black Hole Scalar Hair in Asymptotically Anti de Sitter Spacetimes
The unexpected discovery of hairy black hole solutions in theories with
scalar fields simply by considering asymptotically Anti de-Sitter, rather than
asymptotically flat, boundary conditions is analyzed in a way that exhibits in
a clear manner the differences between the two situations.
It is shown that the trivial Schwarzschild Anti de Sitter becomes unstable in
some of these situations, and the possible relevance of this fact for the
ADS/CFT conjecture is pointed out.Comment: 12 pages. Published versio
Kerr-Schild Symmetries
We study continuous groups of generalized Kerr-Schild transformations and the
vector fields that generate them in any n-dimensional manifold with a
Lorentzian metric. We prove that all these vector fields can be intrinsically
characterized and that they constitute a Lie algebra if the null deformation
direction is fixed. The properties of these Lie algebras are briefly analyzed
and we show that they are generically finite-dimensional but that they may have
infinite dimension in some relevant situations. The most general vector fields
of the above type are explicitly constructed for the following cases: any
two-dimensional metric, the general spherically symmetric metric and
deformation direction, and the flat metric with parallel or cylindrical
deformation directions.Comment: 15 pages, no figures, LaTe
Lifshitz black holes in Brans-Dicke theory
We present an exact asymptotically Lifshitz black hole solution in
Brans-Dicke theory of gravity in arbitrary dimensions in presence of
a power-law potential. In this solution, the dynamical exponent is
determined in terms of the Brans-Dicke parameter and . Asymptotic
Lifshitz condition at infinity requires , which corresponds to
. On the other hand, the no-ghost condition
for the scalar field in the Einstein frame requires . We
compute the Hawking temperature of the black hole solution and discuss the
problems encountered and the proposals in defining its thermodynamic
properties. A generalized solution charged under the Maxwell field is also
presented.Comment: 32 pages, no figure. v2: revised version. Section 3.1 and Appendix B
improved. The argument in Appendix A clarified. v3: References added. v4:
analysis on the black hole thermodynamical properties corrected. Final
version to appear in JHE
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