26,075 research outputs found
Throughput Optimization in High Speed Downlink Packet Access (HSDPA)
In this paper, we investigate throughput optimization
in High Speed Downlink Packet Access (HSDPA). Specifically,
we propose offline and online algorithms for adjusting
the Channel Quality Indicator (CQI) used by the network to
schedule data transmission. In the offline algorithm, a given
target BLER is achieved by adjusting CQI based on ACK/NAK
history. By sweeping through different target BLERs, we can
find the throughput optimal BLER offline. This algorithm could
be used not only to optimize throughput but also to enable fair
resource allocation among mobile users in HSDPA. In the online
algorithm, the CQI offset is adapted using an estimated short
term throughput gradient without specifying a target BLER. An
adaptive stepsize mechanism is proposed to track temporal variation
of the environment. We investigate convergence behavior
of both algorithms. Simulation results show that the proposed
offline algorithm can achieve the given target BLER with good
accuracy. Both algorithms yield up to 30% HSDPA throughput
improvement over that with 10% target BLER
Dynamics of the two-dimensional S=1/2 dimer system (C5H6N2F)2CuCl4
Inelastic neutron scattering was used to study a quantum S=1/2
antiferromagnetic Heisenberg system-Bis(2-amino-5-fluoropyridinium)
Tetrachlorocuprate(II). The magnetic excitation spectrum was shown to be
dominated by long-lived excitations with an energy gap as 1.07(3) meV. The
measured dispersion relation is consistent with a simple two-dimensional square
lattice of weakly-coupled spin dimers. Comparing the data to a random phase
approximation treatment of this model gives the intra-dimer and inter-dimer
exchange constants J=1.45(2) meV and J'=0.31(3) meV, respectively.Comment: 4 pages, 4 figure
Spectroscopy of reflection-asymmetric nuclei with relativistic energy density functionals
Quadrupole and octupole deformation energy surfaces, low-energy excitation
spectra and transition rates in fourteen isotopic chains: Xe, Ba, Ce, Nd, Sm,
Gd, Rn, Ra, Th, U, Pu, Cm, Cf, and Fm, are systematically analyzed using a
theoretical framework based on a quadrupole-octupole collective Hamiltonian
(QOCH), with parameters determined by constrained reflection-asymmetric and
axially-symmetric relativistic mean-field calculations. The microscopic QOCH
model based on the PC-PK1 energy density functional and -interaction
pairing is shown to accurately describe the empirical trend of low-energy
quadrupole and octupole collective states, and predicted spectroscopic
properties are consistent with recent microscopic calculations based on both
relativistic and non-relativistic energy density functionals. Low-energy
negative-parity bands, average octupole deformations, and transition rates show
evidence for octupole collectivity in both mass regions, for which a
microscopic mechanism is discussed in terms of evolution of single-nucleon
orbitals with deformation.Comment: 36 pages, 21 figures, Accepted for Publication in Physical Review
Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear
We study the impact of catastrophic errors occurring in the photometric
redshifts of galaxies on cosmological parameter estimates with cosmic shear
tomography. We consider a fiducial survey with 9-filter set and perform photo-z
measurement simulations. It is found that a fraction of 1% galaxies at
z_{spec}~0.4 is misidentified to be at z_{phot}~3.5. We then employ both chi^2
fitting method and the extension of Fisher matrix formalism to evaluate the
bias on the equation of state parameters of dark energy, w_0 and w_a, induced
by those catastrophic outliers. By comparing the results from both methods, we
verify that the estimation of w_0 and w_a from the fiducial 5-bin tomographic
analyses can be significantly biased. To minimize the impact of this bias, two
strategies can be followed: (A) the cosmic shear analysis is restricted to
0.5<z<2.5 where catastrophic redshift errors are expected to be insignificant;
(B) a spectroscopic survey is conducted for galaxies with 3<z_{phot}<4. We find
that the number of spectroscopic redshifts needed scales as N_{spec} \propto
f_{cata}\times A where f_{cata}=1% is the fraction of catastrophic redshift
errors (assuming a 9-filter photometric survey) and A is the survey area. For
A=1000 {deg}^2, we find that N_{spec}>320 and 860 respectively in order to
reduce the joint bias in (w_0,w_a) to be smaller than 2\sigma and 1\sigma. This
spectroscopic survey (option B) will improve the Figure of Merit of option A by
a factor \times 1.5 thus making such a survey strongly desirable.Comment: 25 pages, 9 figures. Revised version, as accepted for publication in
Ap
Selection and Mid-infrared Spectroscopy of Ultraluminous Star-Forming Galaxies at z~2
Starting from a sample of 24 \micron\ sources in the Extended Groth Strip, we
use 3.6 to 8 \micron\ color criteria to select ultraluminous infrared galaxies
(ULIRGs) at . Spectroscopy from 20-38 \micron\ of 14 objects verifies
their nature and gives their redshifts. Multi-wavelength data for these objects
imply stellar masses \Msun\ and star formation rates 410
\Msun yr. Four objects of this sample observed at 1.6 \micron\
(rest-frame visible) with {\it HST}/WFC3 show diverse morphologies, suggesting
that multiple formation processes create ULIRGs. Four of the 14 objects show
signs of active galactic nuclei, but the luminosity appears to be dominated by
star formation in all cases.Comment: 33 pages, 13 figures, accepted by Ap
An Implication on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the New BABAR Data
The new BABAR data on the pion-photon transition form factor arouses people's
new interests on the determination of pion distribution amplitude. To explain
the data, we take both the leading valence quark state's and the non-valence
quark states' contributions into consideration, where the valence quark part up
to next-to-leading order is presented and the non-valence quark part is
estimated by a phenomenological model based on its limiting behavior at both
and . Our results show that to be consistent with the
new BABAR data at large region, a broader other than the asymptotic-like
pion distribution amplitude should be adopted. The broadness of the pion
distribution amplitude is controlled by a parameter . It has been found that
the new BABAR data at low and high energy regions can be explained
simultaneously by setting to be around 0.60, in which the pion distribution
amplitude is closed to the Chernyak-Zhitnitsky form.Comment: 19 pages, 6 figures, 2 tables. Slightly changed, references updated.
To be published in Phys.Rev.
Characterizing entanglement by momentum-jump in the frustrated Heisenberg ring at quantum phase transition
We study the pairwise concurrences, a measure of entanglement, of the ground
states for the frustrated Heisenberg ring to explore the relation between
entanglement and quantum phase transition associated with the momentum jump.
The groundstate concurrences between any two sites are obtained analytically
and numerically. It shows that the summation of all possible pairwise
concurrences is an appropriate candidate to depict the phase transition. We
also investigate the role that the momentum takes in the jump of concurrence at
the critical points. We find that an abrupt momentum change rusults in the
maximal concurrence difference of two degenerate ground states.Comment: 7 pages, 5 figure
Small ball probability, Inverse theorems, and applications
Let be a real random variable with mean zero and variance one and
be a multi-set in . The random sum
where are iid copies of
is of fundamental importance in probability and its applications.
We discuss the small ball problem, the aim of which is to estimate the
maximum probability that belongs to a ball with given small radius,
following the discovery made by Littlewood-Offord and Erdos almost 70 years
ago. We will mainly focus on recent developments that characterize the
structure of those sets where the small ball probability is relatively
large. Applications of these results include full solutions or significant
progresses of many open problems in different areas.Comment: 47 page
Self-organized Boolean game on networks
A model of Boolean game with only one free parameter that denotes the
strength of herd behavior is proposed where each agent acts according to the
information obtained from his neighbors in network and those in the minority
are rewarded. The simulation results indicate that the dynamic of system is
sensitive to network topology, where the network of larger degree variance,
i.e. the system of greater information heterogeneity, leads to less system
profit. The system can self-organize to a stable state and perform better than
random choice game, although only the local information is available to the
agents. In addition, in heterogeneity networks, the agents with more
information gain more than those with less information for a wide extent of
herd strength .Comment: 5 pages, 5 eps figure
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