20,266 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
Nearly Scale-Invariant Spectrum of Adiabatic Fluctuations May be from a Very Slowly Expanding Phase of the Universe
In this paper we construct an expanding phase with phantom matter, in which
the scale factor expands very slowly but the Hubble parameter increases
gradually, and assume that this expanding phase could be matched to our late
observational cosmology by the proper mechanism. We obtain the nearly
scale-invariant spectrum of adiabatic fluctuations in this scenario, different
from the simplest inflation and usual ekpyrotic/cyclic scenario, the tilt of
nearly scale-invariant spectrum in this scenario is blue. Although there exists
an uncertainty surrounding the way in which the perturbations propagate through
the transition in our scenario, which is dependent on the detail of possible
"bounce" physics, compared with inflation and ekpyrotic/cyclic scenario, our
work may provide another feasible cosmological scenario generating the nearly
scale-invariant perturbation spectrum.Comment: 4 pages, no figures, to appear in Phys. Rev. D. Many thanks for
referee's kind comments and criticism
Effect of Swirl on Rotordynamic Forces Caused by Front Shroud Pump Leakage
Unsteady forces generated by fluid flow through the impeller shroud leakage path of a centrifugal pump were investigated. The effect of leakage path inlet swirl (pump discharge swirl) on the rotordynamic forces was re-examined. It was observed that increasing the inlet swirl is destabilizing both for normal and tangential rotordynamic forces. Attempts to reduce the swirl within the leakage path using ribs and grooves as swirl brakes showed benefits only at low leakage flow rate
Analytic Photometric Redshift Estimator for Type Ia Supernovae From the Large Synoptic Survey Telescope
Accurate and precise photometric redshifts (photo-z's) of Type Ia supernovae
(SNe Ia) can enable the use of SNe Ia, measured only with photometry, to probe
cosmology. This dramatically increases the science return of supernova surveys
planned for the Large Synoptic Survey Telescope (LSST). In this paper we
describe a significantly improved version of the simple analytic photo-z
estimator proposed by Wang (2007) and further developed by Wang, Narayan, and
Wood-Vasey (2007). We apply it to 55,422 simulated SNe Ia generated using the
SNANA package with the LSST filters. We find that the estimated errors on the
photo-z's, \sigma_{z_{phot}}/(1+z_{phot}), can be used as filters to produce a
set of photo-z's that have high precision, accuracy, and purity. Using SN Ia
colors as well as SN Ia peak magnitude in the i band, we obtain a set of
photo-z's with 2 percent accuracy (with \sigma(z_{phot}-z_{spec})/(1+z_{spec})
= 0.02), a bias in z_{phot} (the mean of z_{phot}-z_{spec}) of -9 X 10^{-5},
and an outlier fraction (with |(z_{phot}-z_{spec})/(1+z_{spec})|>0.1) of 0.23
percent, with the requirement that \sigma_{z_{phot}}/(1+z_{phot})<0.01. Using
the SN Ia colors only, we obtain a set of photo-z's with similar quality by
requiring that \sigma_{z_{phot}}/(1+z_{phot})<0.007; this leads to a set of
photo-z's with 2 percent accuracy, a bias in z_{phot} of 5.9 X 10^{-4}, and an
outlier fraction of 0.32 percent.Comment: 10 pages, 8 figures, 2 tables. Revised version, accepted by MNRA
Luminosity Profiles of Merger Remnants
Using published luminosity and molecular gas profiles of the late-stage
mergers NGC 3921, NGC 7252 and Arp 220, we examine the expected luminosity
profiles of the evolved merger remnants, especially in light of the massive CO
complexes that are observed in their nuclei. For NGC 3921 and NGC 7252 we
predict that the resulting luminosity profiles will be characterized by an
r^{1/4} law. In view of previous optical work on these systems, it seems likely
that they will evolve into normal ellipticals as regards their optical
properties. Due to a much higher central molecular column density, Arp 220
might not evolve such a ``seamless'' light profile. We conclude that
ultraluminous infrared mergers such as Arp 220 either evolve into ellipticals
with anomalous luminosity profiles, or do not produce many low-mass stars out
of their molecular gas complexes.Comment: Final refereed version. Note new title. 4 pages, 2 encapsulated color
figures, uses emulateapj.sty. Accepted to ApJL. Also available at
http://www.cv.nrao.edu/~jhibbard/Remnants/remnants.htm
Techniques for n-Particle Irreducible Effective Theories
In this paper we show that the skeleton diagrams in the m-Loop nPI effective
action correspond to an infinite resummation of perturbative diagrams which is
void of double counting at the m-Loop level. We also show that the variational
equations of motion produced by the n-Loop nPI effective theory are equivalent
to the Schwinger-Dyson equations, up to the order at which they are consistent
with the underlying symmetries of the original theory. We use a diagrammatic
technique to obtain the 5-Loop 5PI effective action for a scalar theory with
cubic and quartic interactions, and verify that the result satisfies these two
statements.Comment: 43 pages, 48 figures, add a paragraph in conclusions, Figs. 25,45,46
changed, typos corrected, final version to appear in PR
Collision Integrals for the Transport Properties of Dissociating Air at High Temperatures
Collision integrals for the transport properties of dissociating air at high temperature
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