57 research outputs found
Phase transitions for the Lifshitz black holes
We study possibility of phase transitions between Lifshitz black holes and
other configurations by using free energies explicitly. A phase transition
between Lifshitz soliton and Lifshitz black hole might not occur in three
dimensions. We find that a phase transition between Lifshitz and BTZ black
holes unlikely occurs because they have different asymptotes. Similarly, we
point out that any phase transition between Lifshitz and black branes unlikely
occurs in four dimensions since they have different asymptotes. This is
consistent with a necessary condition for taking a phase transition in the
gravitational system, which requires the same asymptote.Comment: 19 pages, 7 figures, a revised version to appear in EPJ
Absorption of fixed scalar in scattering off 4D N=4 black holes
We perform the perturbation analysis of the black holes in the 4D, N=4
supergravity. Analysis around the black holes reveals a complicated mixing
between the dilaton and other fields (metric and two U(1) Maxwell fields). It
turns out that considering both s-wave (l=0) and higher momentum modes (l \neq
0), the dilaton as a fixed scalar is the only propagating mode with and . We calculate the absorption cross-section for
scattering of low frequency waves of fixed scalar and U(1) Maxwell fields off
the extremal black hole.Comment: 11 pages in RevTeX, no figures, minor correction is included(third
version
Critical behavior for the dilaton black holes
We study the critical behavior in the black p-branes and four dimensional
charged dilaton black holes. We calculate the thermodynamic fluctuations in the
various (microcanonical, canonical, and grandcanonical) ensembles. It is found
that the extremal limit of some black configurations has a critical point and a
phase transition takes place from the extremal to nonextremal black
configurations. Some critical exponents are obtained, which satisfy the scaling
laws. This is related to the fact that the entropy of these black
configurations is a homogeneous function.Comment: 33 pages, RevTex, no figure
Stability analysis of f(R)-AdS black holes
We study the stability of f(R)-AdS (Schwarzschild-AdS) black hole obtained
from f(R) gravity. In order to resolve the difficulty of solving fourth order
linearized equations, we transform f(R) gravity into the scalar-tensor theory
by introducing two auxiliary scalars. In this case, the linearized curvature
scalar becomes a dynamical scalaron, showing that all linearized equations are
second order. Using the positivity of gravitational potentials and S-deformed
technique allows us to guarantee the stability of f(R)-AdS black hole if the
scalaron mass squared satisfies the Breitenlohner-Freedman bound. This is
confirmed by computing quasinormal frequencies of the scalaron for large
f(R)-AdS black hole.Comment: 17 pages, 1 figure, version to appear in EPJ
Shared Care, Elder and Family Member Skills Used to Manage Burden
Aim. The aim of this paper is to further develop the construct of Shared Care by comparing and contrasting it to related research, and to show how the construct can be used to guide research and practice.
Background. While researchers have identified negative outcomes for family caregivers caused by providing care, less is known about positive aspects of family care for both members of a family dyad. Understanding family care relationships is important to nurses because family participation in the care of chronically ill elders is necessary to achieve optimal outcomes from nursing interventions. A previous naturalistic inquiry identified a new construct, Shared Care, which was used to describe a family care interaction that contributed to positive care outcomes.
Methods. A literature review was carried out using the databases Medline, CINAHL, and Psych-info and the keywords home care, care receiver, disability, family, communication, decision-making and reciprocity. The results of the review were integrated to suggest how Shared Care could be used to study care difficulties and guide interventions.
Results. The literature confirmed the importance of dyad relationships in family care. Shared Care extended previous conceptualizations of family care by capturing three critical components: communication, decision-making, and reciprocity. Shared Care provides a structure to expand the conceptualization of family care to include both members of a care dyad and account for positive and negative aspects of care.
Conclusions. The extended view provided by the construct of Shared Care offers practitioners and scholars tools to use in the context of our ageing population to improve the effectiveness of family care relationships
Absorption and quasinormal modes of classical fields propagating on 3D and 4D de Sitter spacetime
We extensively study the exact solutions of the massless Dirac equation in 3D
de Sitter spacetime that we published recently. Using the Newman-Penrose
formalism, we find exact solutions of the equations of motion for the massless
classical fields of spin s=1/2,1,2 and to the massive Dirac equation in 4D de
Sitter metric. Employing these solutions, we analyze the absorption by the
cosmological horizon and de Sitter quasinormal modes. We also comment on the
results given by other authors.Comment: 31 page
Dynamical Behavior of dilaton in de Sitter space
We study the dynamical behavior of the dilaton in the background of
three-dimensional Kerr-de Sitter space which is inspired from the low-energy
string effective action. The perturbation analysis around the cosmological
horizon of Kerr-de Sitter space reveals a mixing between the dilaton and other
fields. Introducing a gauge (dilaton gauge), we can disentangle this mixing
completely and obtain one decoupled dilaton equation. However it turns out that
this belongs to the tachyon. The stability of de Sitter solution with J=0 is
discussed. Finally we compute the dilaton absorption cross section to extract
information on the cosmological horizon of de Sitter space.Comment: 11 pages, reference added and a version to appear in PL
Thermodynamics of Gauss-Bonnet black holes revisited
We investigate the Gauss-Bonnet black hole in five dimensional anti-de Sitter
spacetimes (GBAdS). We analyze all thermodynamic quantities of the GBAdS, which
is characterized by the Gauss-Bonnet coupling and mass , comparing with
those of the Born-Infeld-AdS (BIAdS), Reissner-Norstr\"om-AdS black holes
(RNAdS), Schwarzschild-AdS (SAdS), and BTZ black holes. For we cannot
obtain the black hole with positively definite thermodynamic quantities of
mass, temperature, and entropy because the entropy does not satisfy the
area-law. On the other hand, for , we find the BIAdS-like black hole,
showing that the coupling plays the role of pseudo-charge. Importantly, we
could not obtain the SAdS in the limits of , which means that the GBAdS
is basically different from the SAdS. In addition, we clarify the connections
between thermodynamic and dynamical stability. Finally, we also conjecture that
if a black hole is big and thus globally stable, its quasinormal modes may take
analytic expressions.Comment: 22 pages, 8 figures, version to appear in EPJ
Quasinormal modes from potentials surrounding the charged dilaton black hole
We clarify the purely imaginary quasinormal frequencies of a massless scalar
perturbation on the 3D charged-dilaton black holes. This case is quite
interesting because the potential-step appears outside the event horizon
similar to the case of the electromagnetic perturbations on the large
Schwarzschild-AdS black holes. It turns out that the potential-step type
provides the purely imaginary quasinormal frequencies, while the
potential-barrier type gives the complex quasinormal modes.Comment: 19 pages, 8 figure
Greybody Factors of Charged Dilaton Black Holes in 2 + 1 Dimensions
We have studied scalar perturbations of charged dilaton black holes in 2+1
dimensions. The black hole considered here is a solution to the low-energy
string theory in 2+1 dimensions. The exact decay rates and the grey body
factors for the massless minimally coupled scalar is computed for both the
charged and the uncharged dilaton black holes. The charged and the uncharged
black hole show similar behavior for grey body factors, reflection coefficients
and decay rates.Comment: The equation for the potential and figure:1 are changed. The changes
does not effect the result
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