81 research outputs found
A new form of the rotating C-metric
In a previous paper, we showed that the traditional form of the charged
C-metric can be transformed, by a change of coordinates, into one with an
explicitly factorizable structure function. This new form of the C-metric has
the advantage that its properties become much simpler to analyze. In this
paper, we propose an analogous new form for the rotating charged C-metric, with
structure function G(\xi)=(1-\xi^2)(1+r_{+}A\xi)(1+r_{-}A\xi), where r_\pm are
the usual locations of the horizons in the Kerr-Newman black hole. Unlike the
non-rotating case, this new form is not related to the traditional one by a
coordinate transformation. We show that the physical distinction between these
two forms of the rotating C-metric lies in the nature of the conical
singularities causing the black holes to accelerate apart: the new form is free
of torsion singularities and therefore does not contain any closed timelike
curves. We claim that this new form should be considered the natural
generalization of the C-metric with rotation.Comment: 13 pages, LaTe
Pair of accelerated black holes in an anti-de Sitter background: the AdS C-metric
The anti-de Sitter C-metric (AdS C-metric) is characterized by a quite
interesting new feature when compared with the C-metric in flat or de Sitter
backgrounds. Indeed, contrarily to what happens in these two last exact
solutions, the AdS C-metric only describes a pair of accelerated black holes if
the acceleration parameter satisfies A>1/L, where L is the cosmological length.
The two black holes cannot interact gravitationally and their acceleration is
totally provided by the pressure exerted by a strut that pushes the black holes
apart. Our analysis is based on the study of the causal structure, on the
description of the solution in the AdS 4-hyperboloid in a 5D Minkowski
embedding spacetime, and on the physics of the strut. We also analyze the cases
A=1/L and A<1/L that represent a single accelerated black hole in the AdS
background.Comment: 20 pages, 15 figures (RevTeX4). Published version: typo in fig. 5
corrected, references adde
Melvin universe as a limit of the C-metric
It is demonstrated that the Melvin universe representing the spacetime with a
strong 'homogeneous' electric field can by obtained from the spacetime of two
accelerated charged black holes by a suitable limiting procedure. The behavior
of various invariantly defined geometrical quantities in this limit is also
studied.Comment: 5 pages, no figures [v2: two references added
Boost-rotation symmetric type D radiative metrics in Bondi coordinates
The asymptotic properties of the solutions to the Einstein-Maxwell equations
with boost-rotation symmetry and Petrov type D are studied. We find series
solutions to the pertinent set of equations which are suitable for a late time
descriptions in coordinates which are well adapted for the description of the
radiative properties of spacetimes (Bondi coordinates). By calculating the
total charge, Bondi and NUT mass and the Newman-Penrose constants of the
spacetimes we provide a physical interpretation of the free parameters of the
solutions. Additional relevant aspects on the asymptotics and radiative
properties of the spacetimes considered, such as the possible polarization
states of the gravitational and electromagnetic field, are discussed through
the way
Radiation from accelerated black holes in an anti-de Sitter universe
We study gravitational and electromagnetic radiation generated by uniformly
accelerated charged black holes in anti-de Sitter spacetime. This is described
by the C-metric exact solution of the Einstein-Maxwell equations with a
negative cosmological constant Lambda. We explicitly find and interpret the
pattern of radiation that characterizes the dependence of the fields on a null
direction from which the (timelike) conformal infinity is approached. This
directional pattern exhibits specific properties which are more complicated if
compared with recent analogous results obtained for asymptotic behavior of
fields near a de Sitter-like infinity. In particular, for large acceleration
the anti-de Sitter-like infinity is divided by Killing horizons into several
distinct domains with a different structure of principal null directions, in
which the patterns of radiation differ.Comment: 19 pages, 11 colour figures, submitted to Phys. Rev. D [Low quality
figures are included in this version because of arXive size restrictions. The
version with the standard quality figures is available at
http://utf.mff.cuni.cz/~podolsky/jppubl.htm.
Growth performance and gut health parameters of finishing broilers supplemented with plant extracts and exposed to daily increased temperature
The effects of three plant extracts, i.e. lemon peel extract (LPE), orange peel extract (OPE) and Curcuma xanthorrhiza
essential oil (CXEO), on the performance and gut health parameters of broilers exposed to high temperature
was investigated. A total of 336 unsexed Ross 308 broilers were distributed to seven dietary treatments, a control
diet and six diets containing 200 or 400 mg kg�1 feed of one of the three products between d 25-38 (12 chicks
per pen, four replicates). To induce chronic heat stress, the temperature was increased to 34°C with 50% relative humidity
for 5 h daily starting from d 28 until d 38. At d 38, four animals per pen were sampled for morphological characteristics
(duodenum, jejunum and ileum) and microbial counts (ileo-cecal contents). Plant extracts did not affect
the bird performance. The bursa weight of the control birds was lower (p < 0.05) comparing to those fed 400 mg kg�1
OPE and 200 and 400 mg kg�1 CXEO diets. Feeding 400 mg kg�1 of LPE decreased the duodenal villus:crypt ratio
compared to control and 200 mg kg�1 OPE fed birds. Plant extracts did not have effect on ileal histo-morphology. Feeding
with 400 mg kg�1 of LPE and CXEO caused a decrease in coliform counts in ileum and feeding of 400 mg kg�1
CXEO diet decreased coliform counts in caecum compared to control birds (p < 0.05). These results elucidate that
CXEO, OPE and LPE might modify some microbial and intestinal traits, but without beneficial effect on performance
of broilers under heat stress
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