52,490 research outputs found
The Cardy-Verlinde Formula and Charged Topological AdS Black Holes
We consider the brane universe in the bulk background of the charged
topological AdS black holes. The evolution of the brane universe is described
by the Friedmann equations for a flat or an open FRW-universe containing
radiation and stiff matter. We find that the temperature and entropy of the
dual CFT are simply expressed in terms of the Hubble parameter and its time
derivative, and the Friedmann equations coincide with thermodynamic formulas of
the dual CFT at the moment when the brane crosses the black hole horizon. We
obtain the generalized Cardy-Verlinde formula for the CFT with an R-charge, for
any values of the curvature parameter k in the Friedmann equations.Comment: 10 pages, LaTeX, references adde
Black Holes in Gravity with Conformal Anomaly and Logarithmic Term in Black Hole Entropy
We present a class of exact analytic and static, spherically symmetric black
hole solutions in the semi-classical Einstein equations with Weyl anomaly. The
solutions have two branches, one is asymptotically flat and the other
asymptotically de Sitter. We study thermodynamic properties of the black hole
solutions and find that there exists a logarithmic correction to the well-known
Bekenstein-Hawking area entropy. The logarithmic term might come from non-local
terms in the effective action of gravity theories. The appearance of the
logarithmic term in the gravity side is quite important in the sense that with
this term one is able to compare black hole entropy up to the subleading order,
in the gravity side and in the microscopic statistical interpretation side.Comment: Revtex, 10 pages. v2: minor changes and to appear in JHE
Thermodynamic Geometry and Critical Behavior of Black Holes
Based on the observations that there exists an analogy between the
Reissner-Nordstr\"om-anti-de Sitter (RN-AdS) black holes and the van der
Waals-Maxwell liquid-gas system, in which a correspondence of variables is
, we study the Ruppeiner geometry, defined as
Hessian matrix of black hole entropy with respect to the internal energy (not
the mass) of black hole and electric potential (angular velocity), for the RN,
Kerr and RN-AdS black holes. It is found that the geometry is curved and the
scalar curvature goes to negative infinity at the Davies' phase transition
point for the RN and Kerr black holes.
Our result for the RN-AdS black holes is also in good agreement with the one
about phase transition and its critical behavior in the literature.Comment: Revtex, 18 pages including 4 figure
Holographic Thermodynamic on the Brane in Topological Reissner-Nordstr\"om de Sitter Space
We consider the brane universe in the bulk background of the topological
Reissner-Nordstr\"om de Sitter black holes. We show that the thermodynamic
quantities (including entropy) of the dual CFT take usual special forms
expressed in terms of Hubble parameter and its time derivative at the moment,
when the brane crosses the black hole horizon or the cosmological horizon. We
obtain the generalized Cardy-Verlinde formula for the CFT with an charge and
cosmological constant, for any values of the curvature parameter in the
Friedmann equations.Comment: 8 page
Multiple passages of light through an absorption inhomogeneity in optical imaging of turbid media
The multiple passages of light through an absorption inhomogeneity of finite
size deep within a turbid medium is analyzed for optical imaging using the
``self-energy'' diagram. The nonlinear correction becomes more important for an
inhomogeneity of a larger size and with greater contrast in absorption with
respect to the host background. The nonlinear correction factor agrees well
with that from Monte Carlo simulations for CW light. The correction is about
in near infrared for an absorption inhomogeneity with the typical
optical properties found in tissues and of size of five times the transport
mean free path.Comment: 3 figure
Cosmology with minimal length uncertainty relations
We study the effects of the existence of a minimal observable length in the
phase space of classical and quantum de Sitter (dS) and Anti de Sitter (AdS)
cosmology. Since this length has been suggested in quantum gravity and string
theory, its effects in the early universe might be expected. Adopting the
existence of such a minimum length results in the Generalized Uncertainty
Principle (GUP), which is a deformed Heisenberg algebra between minisuperspace
variables and their momenta operators. We extend these deformed commutating
relations to the corresponding deformed Poisson algebra in the classical limit.
Using the resulting Poisson and Heisenberg relations, we then construct the
classical and quantum cosmology of dS and Ads models in a canonical framework.
We show that in classical dS cosmology this effect yields an inflationary
universe in which the rate of expansion is larger than the usual dS universe.
Also, for the AdS model it is shown that GUP might change the oscillatory
nature of the corresponding cosmology. We also study the effects of GUP in
quantized models through approximate analytical solutions of the Wheeler-DeWitt
(WD) equation, in the limit of small scale factor for the universe, and compare
the results with the ordinary quantum cosmology in each case.Comment: 11 pages, 4 figures, to appear in IJMP
Influence of Homogeneous Interfaces on the Strength of 500 nm Diameter Cu Nanopillars
Interfaces play an important role in crystalline plasticity as they affect strength and often serve as obstacles to dislocation motion. Here we investigate effects of grain and nanotwin boundaries on uniaxial strength of 500 nm diameter Cu nanopillars fabricated by e-beam lithography and electroplating. Uniaxial compression experiments reveal that strength is lowered by introducing grain boundaries and significantly rises when twin boundaries are present. Weakening is likely due to the activation of grain-boundary-mediated processes, while impeding dislocation glide can be responsible for strengthening by twin boundaries
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