1,604 research outputs found
Estimations of the weather effects on brain functions using functional MRI: A cautionary note
Scalar charmonium and glueball mixing in
We study the possibility of the scalar charmonium and glueball mixing in annihilation at GeV. The effects can be used to explain
the unexpected large cross section ( fb) and the anomalous angular
distribution () of the exclusive process observed by Belle experiments at KEKB. We calculate
the helicity amplitudes for the process in
NRQCD, where is the mixed state. We present a detailed analysis on
the total cross section and various angular asymmetries which could be useful
to reveal the existence of the scalar glueball state.Comment: 10 pages, 4 figures,references updated,typos corrected. Published
Version: Phys. Lett. B 594, 118-126 (2004
Spectra of Empirical Auto-Covariance Matrices
We compute spectra of sample auto-covariance matrices of second order
stationary stochastic processes. We look at a limit in which both the matrix
dimension and the sample size used to define empirical averages
diverge, with their ratio kept fixed. We find a remarkable scaling
relation which expresses the spectral density of sample
auto-covariance matrices for processes with dynamical correlations as a
continuous superposition of appropriately rescaled copies of the spectral
density for a sequence of uncorrelated random
variables. The rescaling factors are given by the Fourier transform
of the auto-covariance function of the stochastic process. We also obtain a
closed-form approximation for the scaling function
. This depends on the shape parameter , but
is otherwise universal: it is independent of the details of the underlying
random variables, provided only they have finite variance. Our results are
corroborated by numerical simulations using auto-regressive processes.Comment: 4 pages, 2 figure
One-Loop QCD Mass Effects in the Production of Polarized Bottom and Top Quarks
The analytic expressions for the production cross sections of polarized
bottom and top quarks in annihilation are explicitly derived at the
one-loop order of strong interactions. Chirality-violating mass effects will
reduce the longitudinal spin polarization for the light quark pairs by an
amount of , when one properly considers the massless limit for the final
quarks. Numerical estimates of longitudinal spin polarization effects in the
processes and are presented.Comment: 17 p. (5 figs available upon request), LaTeX, MZ-TH/93-30, RAL/93-81,
FTUV/93-4
Replica theory for learning curves for Gaussian processes on random graphs
Statistical physics approaches can be used to derive accurate predictions for
the performance of inference methods learning from potentially noisy data, as
quantified by the learning curve defined as the average error versus number of
training examples. We analyse a challenging problem in the area of
non-parametric inference where an effectively infinite number of parameters has
to be learned, specifically Gaussian process regression. When the inputs are
vertices on a random graph and the outputs noisy function values, we show that
replica techniques can be used to obtain exact performance predictions in the
limit of large graphs. The covariance of the Gaussian process prior is defined
by a random walk kernel, the discrete analogue of squared exponential kernels
on continuous spaces. Conventionally this kernel is normalised only globally,
so that the prior variance can differ between vertices; as a more principled
alternative we consider local normalisation, where the prior variance is
uniform
Measuring the Higgs boson's parity using tau --> rho nu
We present a very promising method for a measurement of the Higgs boson
parity using the H/A -> tau^+ tau^- --> rho^+ nu rho^- nu --> pi^+ pi^0 nu pi^-
pi^0 nu decay chain. The method is both model independent and independent of
the Higgs production mechanism. Angular distributions of the tau decay products
which are sensitive to the Higgs boson parity are defined and are found to be
measurable using typical properties of a future detector for an e^+ e^- linear
collider. The prospects for the measurement of the parity of a Higgs boson with
a mass of 120 GeV are quantified for the case of e^+ e^- collisons of 500 GeV
center of mass energy with an integrated luminosity of 500 fb^-1. The Standard
Model Higgsstrahlung production process is used as an example.Comment: 10 pages, 4 figures, LaTeX, version of Phys. Lett.
Analysis of Bidirectional Associative Memory using SCSNA and Statistical Neurodynamics
Bidirectional associative memory (BAM) is a kind of an artificial neural
network used to memorize and retrieve heterogeneous pattern pairs. Many efforts
have been made to improve BAM from the the viewpoint of computer application,
and few theoretical studies have been done. We investigated the theoretical
characteristics of BAM using a framework of statistical-mechanical analysis. To
investigate the equilibrium state of BAM, we applied self-consistent signal to
noise analysis (SCSNA) and obtained a macroscopic parameter equations and
relative capacity. Moreover, to investigate not only the equilibrium state but
also the retrieval process of reaching the equilibrium state, we applied
statistical neurodynamics to the update rule of BAM and obtained evolution
equations for the macroscopic parameters. These evolution equations are
consistent with the results of SCSNA in the equilibrium state.Comment: 13 pages, 4 figure
Transmitter-side antennas correlation in SVD-assisted MIMO systems
MIMO techniques allow increasing wireless channel performance by decreasing the BER and increasing the channel throughput and in consequence are included in current mobile communication standards. MIMO techniques are based on benefiting the existence of multipath in wireless communications and the application of appropriate signal processing techniques. The singular value decomposition (SVD) is a popular signal processing technique which, based on the perfect channel state information (PCSI) knowledge at both the transmitter and receiver sides, removes inter-antenna interferences and improves channel performance. Nevertheless, the proximity of the multiple antennas at each front-end produces the so called antennas correlation effect due to the similarity of the various physical paths. In consequence, antennas correlation drops the MIMO channel performance. This investigation focuses on the analysis of a MIMO channel under transmitter-side antennas correlation conditions. First, antennas correlation is analyzed and characterized by the correlation coefficients. The analysis describes the relation between antennas correlation and the appearance of predominant layers which significantly affect the channel performance. Then, based on the SVD, pre- and post-processing is applied to remove inter-antenna interferences. Finally, bit- and power allocation strategies are applied to reach the best performance. The resulting BER reveals that antennas correlation effect diminishes the channel performance and that not necessarily all MIMO layers must be activated to obtain the best performance
Hall conductance of Bloch electrons in a magnetic field
We study the energy spectrum and the quantized Hall conductance of electrons
in a two-dimensional periodic potential with perpendicular magnetic field
WITHOUT neglecting the coupling of the Landau bands. Remarkably, even for weak
Landau band coupling significant changes in the Hall conductance compared to
the one-band approximation of Hofstadter's butterfly are found. The principal
deviations are the rearrangement of subbands and unexpected subband
contributions to the Hall conductance.Comment: to appear in PRB; Revtex, 9 pages, 5 postscript figures; figures with
better resolution may be obtained from http://www.chaos.gwdg.d
UCLALES–SALSA v1.0: a large-eddy model with interactive sectional microphysics for aerosol, clouds and precipitation
Challenges in understanding the aerosol–cloud interactions and their impacts
on global climate highlight the need for improved knowledge of the underlying
physical processes and feedbacks as well as their interactions with cloud and
boundary layer dynamics. To pursue this goal, increasingly sophisticated
cloud-scale models are needed to complement the limited supply of
observations of the interactions between aerosols and clouds. For this
purpose, a new large-eddy simulation (LES) model, coupled with an interactive
sectional description for aerosols and clouds, is introduced. The new model
builds and extends upon the well-characterized UCLA Large-Eddy Simulation
Code (UCLALES) and the Sectional Aerosol module for Large-Scale Applications
(SALSA), hereafter denoted as UCLALES-SALSA. Novel strategies for the
aerosol, cloud and precipitation bin discretisation are presented. These
enable tracking the effects of cloud processing and wet scavenging on the
aerosol size distribution as accurately as possible, while keeping the
computational cost of the model as low as possible. The model is tested with
two different simulation set-ups: a marine stratocumulus case in the
DYCOMS-II campaign and another case focusing on the formation and evolution
of a nocturnal radiation fog. It is shown that, in both cases, the
size-resolved interactions between aerosols and clouds have a critical
influence on the dynamics of the boundary layer. The results demonstrate the
importance of accurately representing the wet scavenging of aerosol in the
model. Specifically, in a case with marine stratocumulus, precipitation and
the subsequent removal of cloud activating particles lead to thinning of the
cloud deck and the formation of a decoupled boundary layer structure. In
radiation fog, the growth and sedimentation of droplets strongly affect their
radiative properties, which in turn drive new droplet formation. The
size-resolved diagnostics provided by the model enable investigations of
these issues with high detail. It is also shown that the results remain
consistent with UCLALES (without SALSA) in cases where the dominating
physical processes remain well represented by both models
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