110 research outputs found
Thermodynamics of doubly charged CGHS model and D1-D5-KK black holes of IIB supergravity
We study the doubly charged Callan-Giddings-Harvey-Strominger (CGHS) model,
which has black hole solutions that were found to be U-dual to the D1-D5-KK
black holes of the IIB supergravity. We derive the action of the model via a
spontaneous compactification on S^3 of the IIB supergravity on S^1*T^4 and
obtain the general static solutions including black holes corresponding to
certain non-asymptotically flat black holes in the IIB supergravity.
Thermodynamics of them is established by computing the entropy, temperature,
chemical potentials, and mass in the two-dimensional setup, and the first law
of thermodynamics is explicitly verified. The entropy is in precise agreement
with that of the D1-D5-KK black holes, and the mass turns out to be consistent
with the infinite Lorentz boost along the M theory circle that is a part of the
aforementioned U-dual chain.Comment: 21 pages, Revte
Twisted sectors in three-dimensional gravity
Twisted sectors --solutions to the equations of motion with non-trivial
monodromies-- of three dimensional Euclidean gravity are studied. We argue that
upon quantization this new sector of the theory provides the necessary (and no
more) degrees of freedom to account for the Bekenstein-Hawking entropy.Comment: An unnecessary restriction removed. To appear in PRD. Revtex, no
figures, 20 p
Surface Terms as Counterterms in the AdS/CFT Correspondence
We examine the recently proposed technique of adding boundary counterterms to
the gravitational action for spacetimes which are locally asymptotic to anti-de
Sitter. In particular, we explicitly identify higher order counterterms, which
allow us to consider spacetimes of dimensions d<=7. As the counterterms
eliminate the need of ``background subtraction'' in calculating the action, we
apply this technique to study examples where the appropriate background was
ambiguous or unknown: topological black holes, Taub-NUT-AdS and Taub-Bolt-AdS.
We also identify certain cases where the covariant counterterms fail to render
the action finite, and we comment on the dual field theory interpretation of
this result. In some examples, the case of vanishing cosmological constant may
be recovered in a limit, which allows us to check results and resolve
ambiguities in certain asymptotically flat spacetime computations in the
literature.Comment: Revtex, 18 pages. References updated and few typo's fixed. Final
versio
Three-Dimensional Gravity with Conformal Scalar and Asymptotic Virasoro Algebra
Strominger has derived the Bekenstein-Hawking entropy of the BTZ black hole
using asymptotic Virasoro algebra. We apply Strominger's method to a black hole
solution found by Martinez and Zanelli (MZ). This is a solution of
three-dimensional gravity with a conformal scalar field. The solution is not
, but it is asymptotically ; therefore, it has the asymptotic
Virasoro algebra. We compute the central charge for the theory and compares
Cardy's formula with the Bekenstein-Hawking entropy. It turns out that the
functional form does agree, but the overall numerical coefficient does not.
This is because this approach gives the "maximum possible entropy" for the
numerical coefficient.Comment: 26 pages, LaTeX; v2: minor correction
Charged BTZ-like Black Holes in Higher Dimensions
Motivated by many worthwhile paper about (2 + 1)-dimensional BTZ black holes,
we generalize them to to (n + 1)-dimensional solutions, so called BTZ-like
solutions. We show that the electric field of BTZ-like solutions is the same as
(2 + 1)-dimensional BTZ black holes, and also their lapse functions are
approximately the same, too. By these similarities, it is also interesting to
investigate the geometric and thermodynamics properties of the BTZ-like
solutions. We find that, depending on the metric parameters, the BTZ-like
solutions may be interpreted as black hole solutions with inner (Cauchy) and
outer (event) horizons, an extreme black hole or naked singularity. Then, we
calculate thermodynamics quantities and conserved quantities, and show that
they satisfy the first law of thermodynamics. Finally, we perform a stability
analysis in the canonical ensemble and show that the BTZ-like solutions are
stable in the whole phase space.Comment: 5 pages, two column format, one figur
Thermodynamics of higher dimensional topological charged AdS black branes in dilaton gravity
In this paper, we study topological AdS black branes of -dimensional
Einstein-Maxwell-dilaton theory and investigate their properties. We use the
area law, surface gravity and Gauss law interpretations to find entropy,
temperature and electrical charge, respectively. We also employ the modified
Brown and York subtraction method to calculate the quasilocal mass of the
solutions. We obtain a Smarr-type formula for the mass as a function of the
entropy and the charge, compute the temperature and the electric potential
through the Smarr-type formula and show that these thermodynamic quantities
coincide with their values which are calculated through using the geometry.
Finally, we perform a stability analysis in the canonical ensemble and
investigate the effects of the dilaton field and the size of black brane on the
thermal stability of the solutions. We find that large black branes are stable
but for small black brane, depending on the value of dilaton field and type of
horizon, we encounter with some unstable phases.Comment: 21 pages, 21 figures, references updated, minor editing, accepted in
EPJC (DOI: 10.1140/epjc/s10052-010-1483-3
Sulfonated Styrene-(ethylene-co-butylene)-styrene/Montmorillonite Clay Nanocomposites: Synthesis, Morphology, and Properties
Sulfonated styrene-(ethylene-butylene)-styrene triblock copolymer (SSEBS) was synthesized by reaction of acetyl sulfate with SEBS. SSESB-clay nanocomposites were then prepared from hydrophilic Na-montmorillonite (MT) and organically (quaternary amine) modified hydrophobic nanoclay (OMT) at very low loading. SEBS did not show improvement in properties with MT-based nanocomposites. On sulfonation (3 and 6 weight%) of SEBS, hydrophilic MT clay-based nanocomposites exhibited better mechanical, dynamic mechanical, and thermal properties, and also controlled water–methanol mixture uptake and permeation and AC resistance. Microstructure determined by X-ray diffraction, atomic force microscopy, and transmission electron microscopy due to better dispersion of MT nanoclay particles and interaction of MT with SSEBS matrix was responsible for this effect. The resulting nanocomposites have potential as proton transfer membranes for Fuel Cell applications
Effects of annealing treatment prior to cold rolling on delayed fracture properties in ferrite-austenite duplex lightweight steels
Tensile properties of recently developed automotive high-strength steels containing about 10 wt pct of Mn and Al are superior to other conventional steels, but the active commercialization has been postponed because they are often subjected to cracking during formation or to the delayed fracture after formation. Here, the delayed fracture behavior of a ferrite-austenite duplex lightweight steel whose microstructure was modified by a batch annealing treatment at 1023 K (750 A degrees C) prior to cold rolling was examined by HCl immersion tests of cup specimens, and was compared with that of an unmodified steel. After the batch annealing, band structures were almost decomposed as strong textures of {100}aOE (c) 011 > alpha-fibers and {111}aOE (c) 112 > gamma-fibers were considerably dissolved, while ferrite grains were refined. The steel cup specimen having this modified microstructure was not cracked when immersed in an HCl solution for 18 days, whereas the specimen having unmodified microstructure underwent the delayed fracture within 1 day. This time delayed fracture was more critically affected by difference in deformation characteristics such as martensitic transformation and deformation inhomogeneity induced from concentration of residual stress or plastic strain, rather than the difference in initial microstructures. The present work gives a promise for automotive applications requiring excellent mechanical and delayed fracture properties as well as reduced specific weight.ope
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