28,869 research outputs found
The First Calculation for the Mass of the Ground Glueball State on Lattice
Under the quenched approximation, we perform a lattice calculation for the
mass of the ground glueball state in channel on a
lattice. Our calculation shows that the mass of this state is
, which rules out the or mainly
glueball interpretation for .Comment: 10 pages and 1 figur
A Tractable Model of the LTE Access Reservation Procedure for Machine-Type Communications
A canonical scenario in Machine-Type Communications (MTC) is the one
featuring a large number of devices, each of them with sporadic traffic. Hence,
the number of served devices in a single LTE cell is not determined by the
available aggregate rate, but rather by the limitations of the LTE access
reservation protocol. Specifically, the limited number of contention preambles
and the limited amount of uplink grants per random access response are crucial
to consider when dimensioning LTE networks for MTC. We propose a low-complexity
model of LTE's access reservation protocol that encompasses these two
limitations and allows us to evaluate the outage probability at click-speed.
The model is based chiefly on closed-form expressions, except for the part with
the feedback impact of retransmissions, which is determined by solving a fixed
point equation. Our model overcomes the incompleteness of the existing models
that are focusing solely on the preamble collisions. A comparison with the
simulated LTE access reservation procedure that follows the 3GPP
specifications, confirms that our model provides an accurate estimation of the
system outage event and the number of supported MTC devices.Comment: Submitted, Revised, to be presented in IEEE Globecom 2015; v3: fixed
error in eq. (4
A Limit Relation between Black Hole Mass and H Width: Testing Super-Eddington Accretion in Active Galactic Nuclei
(abbreviated) We show that there is a limit relation between the black hole
mass and the width at the half maximum of H for active galactic nuclei
(AGNs) with super-Eddington accretion rates. When a black hole has a
super-Eddington accretion rate, the empirical relation of reverberation mapping
has two possible ways. First, it reduces to a relation between the black hole
mass and the size of the broad line region due to the photon trapping effects
inside the accretion disk. For the Kaspi et al.'s empirical reverberation
relation, we get the limit relation as , called as the
Eddington limit. Second, the Eddington limit luminosity will be relaxed if the
trapped photons can escape from the magnetized super-Eddington accretion disk
via the photon bubble instability, and the size of the broad line region will
be enlarged according to the empirical reverberation relation, leading to a
relatively narrow width of H. We call this the Begelman limit.
Super-Eddington accretions in a sample composed of 164 AGNs have been
searched by this limit relation. We find there are a handful of objects locate
between the Eddington and Begelman limit lines, they may be candidates of
super-Eddington accretors in a hybrid structure of photon trapping and photon
bubble instability. The maximum width of H is in the reange of km s for the maximum mass black holes with
super-Eddington accretion rates among AGNs. We suggest that this limit relation
is more reliable and convenient to test whether a source is super-Eddington and
useful to probe the structure of the super-Eddington accretion process.Comment: 5 pages (emulateapj5.sty), 1 figure. Astronomical Journal, 125 (June
Issue 2003) in pres
The composition and size distribution of the dust in the coma of comet Hale-Bopp
We discuss the composition and size distribution of the dust in the coma of
comet Hale-Bopp. We do this by fitting simultaneously the infrared emission
spectrum measured by the infrared space observatory (ISO) and the measured
degree of linear polarization of scattered light at various phase angles and 12
different wavelengths. The effects of particle shape on the modeled optical
properties of the dust grains are taken into account. We constrain our fit by
forcing the abundances of the major rock forming chemical elements to be solar.
The infrared spectrum at long wavelengths reveals that large grains are needed
in order to fit the spectral slope. The size and shape distribution we employ
allows us to estimate the sizes of the crystalline silicates. The ratios of the
strength of various forsterite features show that the crystalline silicate
grains in Hale-Bopp must be submicron sized. We exclude the presence of large
crystalline silicate grains in the coma. Because of this lack of large
crystalline grains combined with the fact that we do need large amorphous
grains to fit the emission spectrum at long wavelengths, we need only
approximately 4% of crystalline silicates by mass. After correcting for
possible hidden crystalline material included in large amorphous grains, our
best estimate of the total mass fraction of crystalline material is
approximately 7.5%, significantly lower than deduced in previous studies in
which the typical derived crystallinity is 20-30%. The implications of this on
the possible origin and evolution of the comet are discussed. The crystallinity
we observe in Hale-Bopp is consistent with the production of crystalline
silicates in the inner solar system by thermal annealing and subsequent radial
mixing to the comet forming region.Comment: Accepted for publication in Icaru
NP-hardness of decoding quantum error-correction codes
Though the theory of quantum error correction is intimately related to the
classical coding theory, in particular, one can construct quantum error
correction codes (QECCs) from classical codes with the dual containing
property, this does not necessarily imply that the computational complexity of
decoding QECCs is the same as their classical counterparts. Instead, decoding
QECCs can be very much different from decoding classical codes due to the
degeneracy property. Intuitively, one expect degeneracy would simplify the
decoding since two different errors might not and need not be distinguished in
order to correct them. However, we show that general quantum decoding problem
is NP-hard regardless of the quantum codes being degenerate or non-degenerate.
This finding implies that no considerably fast decoding algorithm exists for
the general quantum decoding problems, and suggests the existence of a quantum
cryptosystem based on the hardness of decoding QECCs.Comment: 5 pages, no figure. Final version for publicatio
Two-Component Structure of the Hbeta Broad-Line Region in Quasars. I. Evidence from Spectral Principal Component Analysis
We report on a spectral principal component analysis (SPCA) of a sample of
816 quasars, selected to have small Fe II velocity shifts with spectral
coverage in the rest wavelength range 3500--5500 \AA. The sample is explicitly
designed to mitigate spurious effects on SPCA induced by Fe II velocity shifts.
We improve the algorithm of SPCA in the literature and introduce a new
quantity, \emph{the fractional-contribution spectrum}, that effectively
identifies the emission features encoded in each eigenspectrum. The first
eigenspectrum clearly records the power-law continuum and very broad Balmer
emission lines. Narrow emission lines dominate the second eigenspectrum. The
third eigenspectrum represents the Fe II emission and a component of the Balmer
lines with kinematically similar intermediate velocity widths. Correlations
between the weights of the eigenspectra and parametric measurements of line
strength and continuum slope confirm the above interpretation for the
eigenspectra. Monte Carlo simulations demonstrate the validity of our method to
recognize cross talk in SPCA and firmly rule out a single-component model for
broad Hbeta. We also present the results of SPCA for four other samples that
contain quasars in bins of larger Fe II velocity shift; similar eigenspectra
are obtained. We propose that the Hbeta-emitting region has two kinematically
distinct components: one with very large velocities whose strength correlates
with the continuum shape, and another with more modest, intermediate velocities
that is closely coupled to the gas that gives rise to Fe II emission.Comment: 22 pages, 17 figures, accepted for publication in The Astrophysical
Journa
Further Development of the Improved QMD Model and its Applications to Fusion Reaction near Barrier
The Improved Quantum Molecular Dynamics model is further developed by
introducing new parameters in interaction potential energy functional based on
Skyrme interaction of SkM and SLy series. The properties of ground states
of selected nuclei can be reproduced very well. The Coulomb barriers for a
series of reaction systems are studied and compared with the results of the
proximity potential. The fusion excitation functions for a series of fusion
reactions are calculated and the results are in good agreement with
experimental data.Comment: 17 pages, 10 figures, PRC accepte
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