1,068 research outputs found
Magnetic Branes in Gauss-Bonnet Gravity
We present two new classes of magnetic brane solutions in
Einstein-Maxwell-Gauss-Bonnet gravity with a negative cosmological constant.
The first class of solutions yields an -dimensional spacetime with a
longitudinal magnetic field generated by a static magnetic brane. We also
generalize this solution to the case of spinning magnetic branes with one or
more rotation parameters. We find that these solutions have no curvature
singularity and no horizons, but have a conic geometry. In these spacetimes,
when all the rotation parameters are zero, the electric field vanishes, and
therefore the brane has no net electric charge. For the spinning brane, when
one or more rotation parameters are non zero, the brane has a net electric
charge which is proportional to the magnitude of the rotation parameter. The
second class of solutions yields a spacetime with an angular magnetic field.
These solutions have no curvature singularity, no horizon, and no conical
singularity. Again we find that the net electric charge of the branes in these
spacetimes is proportional to the magnitude of the velocity of the brane.
Finally, we use the counterterm method in the Gauss-Bonnet gravity and compute
the conserved quantities of these spacetimes.Comment: 17 pages, No figure, The version to be published in Phys. Rev.
Spacetimes with Longitudinal and Angular Magnetic Fields in Third Order Lovelock Gravity
We obtain two new classes of magnetic brane solutions in third order Lovelock
gravity. The first class of solutions yields an -dimensional spacetime
with a longitudinal magnetic field generated by a static source. We generalize
this class of solutions to the case of spinning magnetic branes with one or
more rotation parameters. These solutions have no curvature singularity and no
horizons, but have a conic geometry. For the spinning brane, when one or more
rotation parameters are nonzero, the brane has a net electric charge which is
proportional to the magnitude of the rotation parameters, while the static
brane has no net electric charge. The second class of solutions yields a
pacetime with an angular magnetic field. These solutions have no curvature
singularity, no horizon, and no conical singularity. Although the second class
of solutions may be made electrically charged by a boost transformation, the
transformed solutions do not present new spacetimes. Finally, we use the
counterterm method in third order Lovelock gravity and compute the conserved
quantities of these spacetimes.Comment: 15 pages, no figur
The Levantine Basin - crustal structure and origin
The origin of the Levantine Basin in the Southeastern Mediterranean Sea is related to the opening of the Neo-Tethys. The nature of its crust has been debated for decades. Therefore, we conducted a geophysical experiment in the Levantine Basin. We recorded two refraction seismic lines with 19 and 20 ocean bottom hydrophones, respectively, and developed velocity models. Additional seismic reflection data yield structural information about the upper layers in the first few kilometers. The crystalline basement in the Levantine Basin consists of two layers with a P-wave velocity of 6.06.4 km/s in the upper and 6.56.9 km/s in the lower crust. Towards the center of the basin, the Moho depth decreases from 27 to 22 km. Local variations of the velocity gradient can be attributed to previously postulated shear zones like the Pelusium Line, the DamiettaLatakia Line and the BaltimHecateus Line. Both layers of the crystalline crust are continuous and no indication for a transition from continental to oceanic crust is observed. These results are confirmed by gravity data. Comparison with other seismic refraction studies in prolongation of our profiles under Israel and Jordan and in the Mediterranean Sea near Greece and Sardinia reveal similarities between the crust in the Levantine Basin and thinned continental crust, which is found in that region. The presence of thinned continental crust under the Levantine Basin is therefore suggested. A β-factor of 2.33 is estimated. Based on these findings, we conclude that sea-floor spreading in the Eastern Mediterranean Sea only occurred north of the Eratosthenes Seamount, and the oceanic crust was later subducted at the Cyprus Arc
Hierarchical Re-estimation of Topic Models for Measuring Topical Diversity
A high degree of topical diversity is often considered to be an important
characteristic of interesting text documents. A recent proposal for measuring
topical diversity identifies three elements for assessing diversity: words,
topics, and documents as collections of words. Topic models play a central role
in this approach. Using standard topic models for measuring diversity of
documents is suboptimal due to generality and impurity. General topics only
include common information from a background corpus and are assigned to most of
the documents in the collection. Impure topics contain words that are not
related to the topic; impurity lowers the interpretability of topic models and
impure topics are likely to get assigned to documents erroneously. We propose a
hierarchical re-estimation approach for topic models to combat generality and
impurity; the proposed approach operates at three levels: words, topics, and
documents. Our re-estimation approach for measuring documents' topical
diversity outperforms the state of the art on PubMed dataset which is commonly
used for diversity experiments.Comment: Proceedings of the 39th European Conference on Information Retrieval
(ECIR2017
Asymptotically Flat Radiating Solutions in Third Order Lovelock Gravity
In this paper, we present an exact spherically symmetric solution of third
order Lovelock gravity in dimensions which describes the gravitational
collapse of a null dust fluid. This solution is asymptotically (anti-)de Sitter
or flat depending on the choice of the cosmological constant. Using the
asymptotically flat solution for with a power-law form of the mass
as a function of the null coordinate, we present a model for a gravitational
collapse in which a null dust fluid radially injects into an initially flat and
empty region. It is found that a naked singularity is inevitably formed whose
strength is different for the and cases. In the case,
the limiting focusing condition for the strength of curvature singularity is
satisfied. But for , the strength of curvature singularity depends on
the rate of increase of mass of the spacetime. These considerations show that
the third order Lovelock term weakens the strength of the curvature
singularity.Comment: 15 pages, no figure, references added, two appendix adde
Beneficial Effects of Role Reversal in Comparison to role-playing on negative cognitions about Other’s Judgments for Social Anxiety Disorder
Background and objectives: Negative beliefs about other’s judgments play an important role in the development and maintenance of social anxiety disorder. The present experiment examined the effects of role-playing followed by role reversal compared to role-playing twice on altering these negative cognitions. Methods: Thirty-six adult social anxiety patients were randomized into two conditions: a role-playing condition in which 18 participants role-played an anxiety-provoking social situation twice, or a role reversal condition in which 18 participants role-played an anxiety-provoking social situation followed by enacting the same situation using role reversal. Before the start of the experiment, patients were asked to report their negative cognitions about the other’s judgments. Next, they were asked to rate the believability of these negative cognitions, as well as the probability and cost estimates of negative judgments by the other person, at three time-points: before the first block of role-playing, after the first block of role-playing, and after the second block of the experiment. Results: Results demonstrated that role-playing followed by role reversal had a stronger effect on the most negative cognitions than role-playing twice. Limitations: The most important limitation of the present study is that there was no control group to assess the effects of role-playing alone. Moreover, the second block of the experiment was repetitive in role-playing, however, it was a new task in role reversal. Conclusions: The results support the hypothesis that role reversal is an effective technique that can be used to correct negative cognitions about other’s judgments in SAD
Thermodynamics of a Kerr Newman de Sitter Black Hole
We compute the conserved quantities of the four-dimensional Kerr-Newman-dS
(KNdS) black hole through the use of the counterterm renormalization method,
and obtain a generalized Smarr formula for the mass as a function of the
entropy, the angular momentum and the electric charge. The first law of
thermodynamics associated to the cosmological horizon of KNdS is also
investigated. Using the minimal number of intrinsic boundary counterterms, we
consider the quasilocal thermodynamics of asymptotic de Sitter
Reissner-Nordstrom black hole, and find that the temperature is equal to the
product of the surface gravity (divided by ) and the Tolman redshift
factor. We also perform a quasilocal stability analysis by computing the
determinant of Hessian matrix of the energy with respect to its thermodynamic
variables in both the canonical and the grand-canonical ensembles and obtain a
complete set of phase diagrams. We then turn to the quasilocal thermodynamics
of four-dimensional Kerr-Newman-de Sitter black hole for virtually all possible
values of the mass, the rotation and the charge parameters that leave the
quasilocal boundary inside the cosmological event horizon, and perform a
quasilocal stability analysis of KNdS black hole.Comment: REVTEX4, 12 pages, 12 figures, references added and some points in
Sec II have been clarified, version to appear in Can. J. Phy
Magnetic Branes in -dimensional Einstein-Maxwell-dilaton gravity
We construct two new classes of spacetimes generated by spinning and
traveling magnetic sources in -dimensional Einstein-Maxwell-dilaton
gravity with Liouville-type potential. These solutions are neither
asymptotically flat nor (A)dS. The first class of solutions which yields a
-dimensional spacetime with a longitudinal magnetic field and
rotation parameters have no curvature singularity and no horizons, but have a
conic geometry. We show that when one or more of the rotation parameters are
nonzero, the spinning branes has a net electric charge that is proportional to
the magnitude of the rotation parameters. The second class of solutions yields
a static spacetime with an angular magnetic field, and have no curvature
singularity, no horizons, and no conical singularity. Although one may add
linear momentum to the second class of solutions by a boost transformation, one
does not obtain a new solution. We find that the net electric charge of these
traveling branes with one or more nonzero boost parameters is proportional to
the magnitude of the velocity of the branes. We also use the counterterm method
and calculate the conserved quantities of the solutions.Comment: 15 pages, the last version to appear in PR
Counterterm Method in Lovelock Theory and Horizonless Solutions in Dimensionally Continued Gravity
In this paper we, first, generalize the quasilocal definition of the stress
energy tensor of Einstein gravity to the case of Lovelock gravity, by
introducing the tensorial form of surface terms that make the action
well-defined. We also introduce the boundary counterterm that removes the
divergences of the action and the conserved quantities of the solutions of
Lovelock gravity with flat boundary at constant and . Second, we obtain
the metric of spacetimes generated by brane sources in dimensionally continued
gravity through the use of Hamiltonian formalism, and show that these solutions
have no curvature singularity and no horizons, but have conic singularity. We
show that these asymptotically AdS spacetimes which contain two fundamental
constants are complete. Finally we compute the conserved quantities of these
solutions through the use of the counterterm method introduced in the first
part of the paper.Comment: 15 pages, references added, typos correcte
Magnetic Branes Supported by Nonlinear Electromagnetic Field
Considering the nonlinear electromagnetic field coupled to Einstein gravity
in the presence of cosmological constant, we obtain a new class of
-dimensional magnetic brane solutions. This class of solutions yields a
spacetime with a longitudinal nonlinear magnetic field generated by a static
source. These solutions have no curvature singularity and no horizons but have
a conic geometry with a deficit angle . We investigate the effects
of nonlinearity on the metric function and deficit angle and also find that for
the special range of the nonlinear parameter, the solutions are not asymptotic
AdS. We generalize this class of solutions to the case of spinning magnetic
solutions, and find that when one or more rotation parameters are nonzero, the
brane has a net electric charge which is proportional to the magnitude of the
rotation parameters. Then, we use the counterterm method and compute the
conserved quantities of these spacetimes. Finally, we obtain a constrain on the
nonlinear parameter, such that the nonlinear electromagnetic field is
conformally invariant.Comment: 15 pages, one eps figur
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