5,162 research outputs found
Zero biasing and growth processes
The tools of zero biasing are adapted to yield a general result suitable for
analyzing the behavior of certain growth processes. The main theorem is applied
to prove central limit theorems, with explicit error terms in the L^1 metric,
for certain statistics of the Jack measure on partitions and for the number of
balls drawn in a Polya-Eggenberger urn process.Comment: 21 pages. Error in one term of the bound of the main theorem has been
corrected, resulting in some changes to the bound for urn proces
On the fairness of the main galaxy sample of SDSS
Flux-limited and volume-limited galaxy samples are constructed from SDSS data
releases DR4, DR6 and DR7 for statistical analysis. The two-point correlation
functions , monopole of three-point correlation functions ,
projected two-point correlation function and pairwise velocity dispersion
are measured to test if galaxy samples are fair for these
statistics. We find that with increment of sky coverage of SDSS, of
flux-limited sample is extremely robust and insensitive to local structures at
low redshift. But for volume-limited samples fainter than at large scales
s>\sim 10\hmpc, deviation of and of DR7 to those of DR4
and DR6 increases with larger absolute magnitude. In the weakly nonlinear
regime, there is no agreement between of different data releases in
all luminosity bins. Furthermore, of volume-limited samples of DR7 in
luminosity bins fainter than are significantly larger,
and of the two faintest volume-limited samples of DR7 display
very different scale dependence than results of DR4 and DR6. Our findings call
for cautions in understanding clustering analysis results of SDSS faint galaxy
samples, and higher order statistics of SDSS volume-limited samples in the
weakly nonlinear regime. The first zero-crossing points of of
volume-limited samples are also investigated and discussed.Comment: 16 pages, 12 figures, accepte
Finite-temperature critical point of a glass transition
We generalize the simplest kinetically constrained model of a glass-forming
liquid by softening kinetic constraints, allowing them to be violated with a
small finite rate. We demonstrate that this model supports a first-order
dynamical (space-time) phase transition, similar to those observed with hard
constraints. In addition, we find that the first-order phase boundary in this
softened model ends in a finite-temperature dynamical critical point, which we
expect to be present in natural systems. We discuss links between this critical
point and quantum phase transitions, showing that dynamical phase transitions
in dimensions map to quantum transitions in the same dimension, and hence
to classical thermodynamic phase transitions in dimensions. We make these
links explicit through exact mappings between master operators, transfer
matrices, and Hamiltonians for quantum spin chains.Comment: 10 pages, 5 figure
Identification of gene pathways implicated in Alzheimer's disease using longitudinal imaging phenotypes with sparse regression
We present a new method for the detection of gene pathways associated with a
multivariate quantitative trait, and use it to identify causal pathways
associated with an imaging endophenotype characteristic of longitudinal
structural change in the brains of patients with Alzheimer's disease (AD). Our
method, known as pathways sparse reduced-rank regression (PsRRR), uses group
lasso penalised regression to jointly model the effects of genome-wide single
nucleotide polymorphisms (SNPs), grouped into functional pathways using prior
knowledge of gene-gene interactions. Pathways are ranked in order of importance
using a resampling strategy that exploits finite sample variability. Our
application study uses whole genome scans and MR images from 464 subjects in
the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. 66,182 SNPs
are mapped to 185 gene pathways from the KEGG pathways database. Voxel-wise
imaging signatures characteristic of AD are obtained by analysing 3D patterns
of structural change at 6, 12 and 24 months relative to baseline. High-ranking,
AD endophenotype-associated pathways in our study include those describing
chemokine, Jak-stat and insulin signalling pathways, and tight junction
interactions. All of these have been previously implicated in AD biology. In a
secondary analysis, we investigate SNPs and genes that may be driving pathway
selection, and identify a number of previously validated AD genes including
CR1, APOE and TOMM40
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