23,559 research outputs found
Of mice and men: Sparse statistical modeling in cardiovascular genomics
In high-throughput genomics, large-scale designed experiments are becoming
common, and analysis approaches based on highly multivariate regression and
anova concepts are key tools. Shrinkage models of one form or another can
provide comprehensive approaches to the problems of simultaneous inference that
involve implicit multiple comparisons over the many, many parameters
representing effects of design factors and covariates. We use such approaches
here in a study of cardiovascular genomics. The primary experimental context
concerns a carefully designed, and rich, gene expression study focused on
gene-environment interactions, with the goals of identifying genes implicated
in connection with disease states and known risk factors, and in generating
expression signatures as proxies for such risk factors. A coupled exploratory
analysis investigates cross-species extrapolation of gene expression
signatures--how these mouse-model signatures translate to humans. The latter
involves exploration of sparse latent factor analysis of human observational
data and of how it relates to projected risk signatures derived in the animal
models. The study also highlights a range of applied statistical and genomic
data analysis issues, including model specification, computational questions
and model-based correction of experimental artifacts in DNA microarray data.Comment: Published at http://dx.doi.org/10.1214/07-AOAS110 in the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A New Statistic for Analyzing Baryon Acoustic Oscillations
We introduce a new statistic omega_l for measuring and analyzing large-scale
structure and particularly the baryon acoustic oscillations. omega_l is a
band-filtered, configuration space statistic that is easily implemented and has
advantages over the traditional power spectrum and correlation function
estimators. Unlike these estimators, omega_l can localize most of the acoustic
information into a single dip at the acoustic scale while also avoiding
sensitivity to the poorly constrained large scale power (i.e., the integral
constraint) through the use of a localized and compensated filter. It is also
sensitive to anisotropic clustering through pair counting and does not require
any binning. We measure the shift in the acoustic peak due to nonlinear effects
using the monopole omega_0 derived from subsampled dark matter catalogues as
well as from mock galaxy catalogues created via halo occupation distribution
(HOD) modeling. All of these are drawn from 44 realizations of 1024^3 particle
dark matter simulations in a 1h^{-1}Gpc box at z=1. We compare these shifts
with those obtained from the power spectrum and conclude that the results
agree. This indicates that any distance measurements obtained from omega_0 and
P(k) will be consistent with each other. We also show that it is possible to
extract the same amount of acoustic information using either omega_0 or P(k)
from equal volume surveys.Comment: 12 pages, 7 figures. ApJ accepted. Edit: Now updated with final
accepted versio
The Dropping of In-Medium Hadron Mass in Holographic QCD
We study the baryon density dependence of the vector meson spectrum using the
D4/D6 system together with the compact D4 baryon vertex. We find that the
vector meson mass decreases almost linearly in density at low density for small
quark mass, but saturates to a finite non-zero value for large density. We also
compute the density dependence of the mass and the
velocity. We find that in medium, our model is consistent with the GMOR
relation up to a few times the normal nuclear density. We compare our hQCD
predictions with predictions made based on hidden local gauge theory that is
constructed to model QCD.Comment: 20 pages, 7 figure
Electronic properties of correlated metals in the vicinity of a charge order transition: optical spectroscopy of -(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl)
The infrared spectra of the quasi-two-dimensional organic conductors
-(BEDT-TTF)Hg(SCN) ( = NH, Rb, Tl) were measured in
the range from 50 to 7000 \cm down to low temperatures in order to explore the
influence of electronic correlations in quarter-filled metals. The
interpretation of electronic spectra was confirmed by measurements of pressure
dependant reflectance of -(BEDT-TTF)KHg(SCN) at T=300 K. The
signatures of charge order fluctuations become more pronounced when going from
the NH salt to Rb and further to Tl compounds. On reducing the temperature,
the metallic character of the optical response in the NH and Rb salts
increases, and the effective mass diminishes. For the Tl compound, clear
signatures of charge order are found albeit the metallic properties still
dominate. From the temperature dependence of the electronic scattering rate the
crossover temperature is estimated below which the coherent charge-carriers
response sets in. The observations are in excellent agreement with recent
theoretical predictions for a quarter-filled metallic system close to charge
order
Assembly and force measurement with SPM-like probes in holographic optical tweezers
We report a high fidelity tomographic reconstruction of the quantum state of photon pairs generated by parametric down-conversion with orbital angular momentum (OAM) entanglement. Our tomography method allows us to estimate an upper and lower bound for the entanglement between the down-converted photons. We investigate the two-dimensional state subspace defined by the OAM states ±ℓ and superpositions thereof, with ℓ=1, 2, ..., 30. We find that the reconstructed density matrix, even for OAMs up to around ℓ=20, is close to that of a maximally entangled Bell state with a fidelity in the range between F=0.979 and F=0.814. This demonstrates that, although the single count-rate diminishes with increasing ℓ, entanglement persists in a large dimensional state space
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