2,696 research outputs found
Thermodynamics of Schwarzschild-de Sitter black hole: thermal stability of Nariai black hole
We study thermodynamics of the Schwarzschild-de Sitter black hole in five
dimensions by introducing two temperatures based on the standard and
Bousso-Hawking normalizations. We use the first-law of thermodynamics to derive
thermodynamic quantities. The two temperatures indicate that the Nariai black
hole is thermodynamically unstable. However, it seems that black hole
thermodynamics favors the standard normalization, and does not favor the
Bousso-Hawking normalization.Comment: 13 pages, 4 figures, version to appear in PR
Spectral Theory of Discrete Processes
We offer a spectral analysis for a class of transfer operators. These
transfer operators arise for a wide range of stochastic processes, ranging from
random walks on infinite graphs to the processes that govern signals and
recursive wavelet algorithms; even spectral theory for fractal measures. In
each case, there is an associated class of harmonic functions which we study.
And in addition, we study three questions in depth:
In specific applications, and for a specific stochastic process, how do we
realize the transfer operator as an operator in a suitable Hilbert space?
And how to spectral analyze once the right Hilbert space has
been selected? Finally we characterize the stochastic processes that are
governed by a single transfer operator.
In our applications, the particular stochastic process will live on an
infinite path-space which is realized in turn on a state space . In the case
of random walk on graphs , will be the set of vertices of . The
Hilbert space on which the transfer operator acts will then
be an space on , or a Hilbert space defined from an energy-quadratic
form.
This circle of problems is both interesting and non-trivial as it turns out
that may often be an unbounded linear operator in ; but even
if it is bounded, it is a non-normal operator, so its spectral theory is not
amenable to an analysis with the use of von Neumann's spectral theorem. While
we offer a number of applications, we believe that our spectral analysis will
have intrinsic interest for the theory of operators in Hilbert space.Comment: 34 pages with figures removed, for the full version with all the
figures please go to http://www.siue.edu/~msong/Research/spectrum.pd
Mobility and Saturation Velocity in Graphene on SiO2
We examine mobility and saturation velocity in graphene on SiO2 above room
temperature (300-500 K) and at high fields (~1 V/um). Data are analyzed with
practical models including gated carriers, thermal generation, "puddle" charge,
and Joule heating. Both mobility and saturation velocity decrease with rising
temperature above 300 K, and with rising carrier density above 2x10^12 cm^-2.
Saturation velocity is >3x10^7 cm/s at low carrier density, and remains greater
than in Si up to 1.2x10^13 cm^-2. Transport appears primarily limited by the
SiO2 substrate, but results suggest intrinsic graphene saturation velocity
could be more than twice that observed here
Reddening Behaviors of Galaxies in the SDSS Photometric System
We analyze the behaviors of reddening vectors in the SDSS photometric system
for galaxies of different morphologies, ages, and redshifts. As seen in other
photometric systems, the dependence of reddening on the spectral energy
distribution (SED) and the nonlinearity of reddening are likewise
non-negligible for the SDSS system if extinction is significant (~> 1 mag).
These behaviors are most significant for the g filter, which has the largest
bandwidth-to-central wavelength ratio among SDSS filters. The SDSS colors
involving adjacent filters show greater SED-dependence and nonlinearity. A
procedure for calculating the correct amount of extinction from an observed
color excess is provided. The relative extinctions between (i.e., the
extinction law for) SDSS filters given by Schlegel et al., which were
calculated with an older version of filter response functions, would
underestimate the amount of extinction in most cases by ~5 to 10 % (maximum ~20
%). We recommend A/A_{5500} values of 1.574, 1.191, 0.876, 0.671 & 0.486 for
the u, g, r, i, & z filters, respectively, as a representative extinction law
for the SDSS galaxies with a small extinction (i.e., for cases where the
nonlinearity and SED-dependence of the reddening is not important). The
dependence of reddening on redshift at low extinction is the largest for colors
involving the g filter as well, which is due to the Balmer break.Comment: Published in PASP, 119, 1449 (Dec. 2007
Slowly rotating black holes in the Horava-Lifshitz gravity
We investigate slowly rotating black holes in the Ho\v{r}ava-Lifshitz (HL)
gravity. For and , we find a slowly rotating black
hole of the Kehagias-Sfetsos solution in asymptotically flat spacetimes. We
discuss their thermodynamic properties by computing mass, temperature, angular
momentum, and angular velocity on the horizon.Comment: 12 pages, no figures, version to appear in EPJ
Holographic interacting dark energy in the braneworld cosmology
We investigate a model of brane cosmology to find a unified description of
the radiation-matter-dark energy universe. It is of the interacting holographic
dark energy with a bulk-holographic matter . This is a five-dimensional
cold dark matter, which plays a role of radiation on the brane. Using the
effective equations of state instead of the
native equations of state , we show that this model
cannot accommodate any transition from the dark energy with to the phantom regime . Furthermore, the case of interaction between cold dark matter and
five dimensional cold dark matter is considered for completeness. Here we find
that the redshift of matter-radiation equality is the same order
as . Finally, we obtain
a general decay rate which is suitable for describing all interactions
including the interaction between holographic dark energy and cold dark matter.Comment: 17 pages, 4 figure
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