2,507 research outputs found
General Rotating Charged Kaluza-Klein AdS Black Holes in Higher Dimensions
I construct exact solutions for general nonextremal rotating, charged
Kaluza-Klein black holes with a cosmological constant and with arbitrary
angular momenta in all higher dimensions. I then investigate their
thermodynamics and find their generalizations with the NUT charges. The metrics
are given in both Boyer-Lindquist coordinates and a form very similar to the
famous Kerr-Schild ansatz, which highlights its potential application to
include multiple electric charges into solutions yet to be found in gauged
supergravity. It is also observed that the metric ansatz in dimensions
is similar to those previously suggested by Yilmaz and later by Bekenstein.Comment: 5 pages, revtex4.cl
Revisit of cosmic age problem
We investigate the cosmic age problem associated with 9 extremely old
globular clusters in M31 galaxy and 1 very old high- quasar APM 08279 + 5255
at . These 9 globular clusters have not been used to study the cosmic
age problem in the previous literature. By evaluating the age of the universe
in the CDM model with the observational constraints from the SNIa, the
BAO, the CMB, and the independent measurements, we find that the
existence of 5 globular clusters and 1 high- quasar are in tension (over
2 confidence level) with the current cosmological observations. So if
the age estimates of these objects are correct, the cosmic age puzzle still
remains in the standard cosmology. Moreover, we extend our investigations to
the cases of the interacting dark energy models. It is found that although the
introduction of the interaction between dark sectors can give a larger cosmic
age, the interacting dark energy models still have difficulty to pass the
cosmic age test.Comment: 11 pages, 5 figures, 1 table, accepted for publication in PR
Thermal Bremsstrahlung Radiation in a Two-Temperature Plasma
In the normal one-temperature plasma the motion of ions is usually neglected
when calculating the Bremsstrahlung radiation of the plasma. Here we calculate
the Bremsstrahlung radiation of a two-temperature plasma by taking into account
of the motion of ions. Our results show that the total radiation power is
always lower if the motion of ions is considered. We also apply the
two-temperature Bremsstrahlung radiation mechanism for an analytical
Advection-Dominated Accretion Flow (ADAF) model; we find the two-temperature
correction to the total Bremsstrahlung radiation for ADAF is negligible.Comment: 5 pages, 4 figures, accepted for publication in CHJAA. Some
discussions and references adde
Competitive Analysis and Market Power of China’s Soybean Import Market
This research conducts a competitive structure analysis of the Chinese soybean import market which leads to the hypothesis that China’s soybean importers may have stronger market power in China’s soybean import market. Then, this research develops and simultaneously estimates a two-country partial equilibrium trade model to test U.S.-China market power of soybean trade. The empirical result supports our hypothesis that Chinese soybean importers have stronger market power relative to U.S. soybean exporters. This Chinese market power can be countered by U.S. and South American companies through developing new and expanding existing markets for soybeans throughout the world and investing in Chinese soybean storage and crushing capacity.Chinese soybean import market, competitive structure analysis, market power, two-country partial equilibrium trade model, International Relations/Trade, Marketing, Research Methods/ Statistical Methods, Q10, Q12, Q17,
Exploring the Latest Union2 SNIa Dataset by Using Model-Independent Parametrization Methods
We explore the cosmological consequences of the recently released Union2
sample of 557 Type Ia supernovae (SNIa). Combining this latest SNIa dataset
with the Cosmic microwave background (CMB) anisotropy data from the Wilkinson
Microwave Anisotropy Probe 7 year (WMAP7) observations and the baryon acoustic
oscillation (BAO) results from the Sloan Digital Sky Survey (SDSS) Data Release
7 (DR7), we measure the dark energy density function as a free function of redshift. Two
model-independent parametrization methods (the binned parametrization and the
polynomial interpolation parametrization) are used in this paper. By using the
statistic and the Bayesian information criterion, we find that the
current observational data are still too limited to distinguish which
parametrization method is better, and a simple model has advantage in fitting
observational data than a complicated model. Moreover, it is found that all
these parametrizations demonstrate that the Union2 dataset is still consistent
with a cosmological constant at 1 confidence level. Therefore, the
Union2 dataset is different from the Constitution SNIa dataset, which more
favors a dynamical dark energy.Comment: 11 pages, 8 figures, 2 tables, accepted for publication in PR
High-Field Shubnikov-de Haas Oscillations in the Topological Insulator BiTeSe
We report measurements of the surface Shubnikov de Haas oscillations (SdH) on
crystals of the topological insulator BiTeSe. In crystals with large
bulk resistivity (4 cm at 4 K), we observe 15 surface SdH
oscillations (to the = 1 Landau Level) in magnetic fields up to 45
Tesla. Extrapolating to the limit , we confirm the -shift
expected from a Dirac spectrum. The results are consistent with a very small
surface Lande -factor.Comment: Text expanded, slight changes in text, final version; Total 6 pages,
6 figure
Landau-Zener-St\"uckelberg Spectroscopy of a Superconducting Flux Qubit
We proposed a new method to measure the energy spectrum of a superconducting
flux qubit. Different from the conventional frequency spectroscopy, a short
triangle pulse is used to drive the qubit through the anticrossing and
generates Landau-Zener-St\"uckelberg interference patterns, from which the
information of the energy spectrum can be extracted. Without installing
microwave lines one can simplify the experimental setup and reduce the unwanted
effects of noise. Moreover, the method can be applied to other quantum systems,
opening the possibility of calibrating and manipulating qubits with linear
pulses.Comment: 7 pages, 5 figure
XMM-Newton Spectra of Intermediate-Mass Black Hole Candidates: Application of a Monte-Carlo Simulated Model
We present a systematic spectral analysis of six ultraluminous X-ray sources
(NGC1313 X-1/X-2, IC342 X-1, HoIX X-1, NGC5408 X-1 and NGC3628 X-1) observed
with XMM-Newton Observatory. These extra-nuclear X-ray sources in nearby
late-type galaxies have been considered as intermediate-mass black hole
candidates. We have performed Monte-Carlo simulations of Comptonized
multi-color black-body accretion disks. This unified and self-consistent
spectral model assumes a spherically symmetric, thermal corona around each disk
and accounts for the radiation transfer in the Comptonization. We find that the
model provides satisfactory fits to the XMM-Newton spectra of thesources. The
characteristic temperatures of the accretion disks (T_in), for example, are in
the range of ~ 0.05-0.3 keV, consistent with the intermediate-mass black hole
interpretation. We find that the black hole mass is typically about a few times
10^3 M_\odot and has an accretion rate ~ 10^{-6} - 10^{-5} M_\odot yr^{-1}. For
the spectra considered here, we find that the commonly used multi-color
black-body accretion disk model with an additive power law component, though
not physical, provides a good mathematical approximation to the Monte-Carlo
simulated model. However, the latter model provides additional constraints on
the properties of the accretion systems, such as the disk inclination angles
and corona optical depths.Comment: 23 pages, 4 figures, 5 tables. ApJ accepted, July 2004 issu
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