29,041 research outputs found
Cosmological Three-Point Function: Testing The Halo Model Against Simulations
We perform detailed comparison of the semi-analytic halo model predictions
with measurements in numerical simulations of the two and three point
correlation functions (3PCF), as well as power spectrum and bispectrum. We
discuss the accuracy and self-consistency of the halo model description of
gravitational clustering in the non-linear regime and constrain halo model
parameters. We exploit the recently proposed multipole expansion of three point
statistics that expresses rotation invariance in the most natural way. This not
only offers technical advantages by reducing the integrals required for the
halo model predictions, but amounts to a convenient way of compressing the
information contained in the 3PCF. We find that, with an appropriate choice of
the halo boundary and mass function cut-off, halo model predictions are in good
agreement with the bispectrum measured in numerical simulations. However, the
halo model predicts less than the observed configuration dependence of the 3PCF
on ~ Mpc scales. This effect is mainly due to quadrupole moment deficit,
possibly related to the assumption of spherical halo geometry. Our analysis
shows that using its harmonic decomposition, the full configuration dependence
of the 3PCF in the non-linear regime can be compressed into just a few numbers,
the lowest multipoles. Moreover, these multipoles are closely related to the
highest signal to noise eigenmodes of the 3PCF. Therefore this estimator may
simplify future analyses aimed at constraining cosmological and halo model
parameters from observational data.Comment: Minor corrections. Accepted for publication by Ap
The ergodicity bias in the observed galaxy distribution
The spatial distribution of galaxies we observed is subject to the given
condition that we, human beings are sitting right in a galaxy -- the Milky Way.
Thus the ergodicity assumption is questionable in interpretation of the
observed galaxy distribution. The resultant difference between observed
statistics (volume average) and the true cosmic value (ensemble average) is
termed as the ergodicity bias. We perform explicit numerical investigation of
the effect for a set of galaxy survey depths and near-end distance cuts. It is
found that the ergodicity bias in observed two- and three-point correlation
functions in most cases is insignificant for modern analysis of samples from
galaxy surveys and thus close a loophole in precision cosmology. However, it
may become non-negligible in certain circumstances, such as those applications
involving three-point correlation function at large scales of local galaxy
samples. Thus one is reminded to take extra care in galaxy sample construction
and interpretation of the statistics of the sample, especially when the
characteristic redshift is low.Comment: Revised version published as JCAP08(2010)01
Strategies for Proteome-Wide Quantification of Glycosylation Macro- and Micro-Heterogeneity
Protein glycosylation governs key physiological and pathological processes in human cells. Aberrant glycosylation is thus closely associated with disease progression. Mass spectrometry (MS)-based glycoproteomics has emerged as an indispensable tool for investigating glycosylation changes in biological samples with high sensitivity. Following rapid improvements in methodologies for reliable intact glycopeptide identification, site-specific quantification of glycopeptide macro- and micro-heterogeneity at the proteome scale has become an urgent need for exploring glycosylation regulations. Here, we summarize recent advances in N- and O-linked glycoproteomic quantification strategies and discuss their limitations. We further describe a strategy to propagate MS data for multilayered glycopeptide quantification, enabling a more comprehensive examination of global and site-specific glycosylation changes. Altogether, we show how quantitative glycoproteomics methods explore glycosylation regulation in human diseases and promote the discovery of biomarkers and therapeutic targets
Amelioration of normothermic canine liver ischemia with prostacyclin.
A model of hepatic ischemia was developed in dogs using a pump-driven splanchnic-to-jugular vein bypass during crossclamping of the portal triad. An LD50 was established with three hours of ischemia. PGI2 given for one hour before the ischemic insult ameliorated the ischemic injury and increased survival
Conformative Filtering for Implicit Feedback Data
Implicit feedback is the simplest form of user feedback that can be used for
item recommendation. It is easy to collect and is domain independent. However,
there is a lack of negative examples. Previous work tackles this problem by
assuming that users are not interested or not as much interested in the
unconsumed items. Those assumptions are often severely violated since
non-consumption can be due to factors like unawareness or lack of resources.
Therefore, non-consumption by a user does not always mean disinterest or
irrelevance. In this paper, we propose a novel method called Conformative
Filtering (CoF) to address the issue. The motivating observation is that if
there is a large group of users who share the same taste and none of them have
consumed an item before, then it is likely that the item is not of interest to
the group. We perform multidimensional clustering on implicit feedback data
using hierarchical latent tree analysis (HLTA) to identify user `tastes' groups
and make recommendations for a user based on her memberships in the groups and
on the past behavior of the groups. Experiments on two real-world datasets from
different domains show that CoF has superior performance compared to several
common baselines
Quasispecies distribution of Eigen model
We study sharp peak landscapes (SPL) of Eigen model from a new perspective
about how the quasispecies distribute in the sequence space. To analyze the
distribution more carefully, we bring forth two tools. One tool is the variance
of Hamming distance of the sequences at a given generation. It not only offers
us a different avenue for accurately locating the error threshold and
illustrates how the configuration of the distribution varies with copying
fidelity in the sequence space, but also divides the copying fidelity into
three distinct regimes. The other tool is the similarity network of a certain
Hamming distance , by which we can get a visual and in-depth result
about how the sequences distribute. We find that there are several local optima
around the center (global optimum) in the distribution of the sequences
reproduced near the threshold. Furthermore, it is interesting that the
distribution of clustering coefficient follows lognormal distribution
and the curve of clustering coefficient of the network versus
appears as linear behavior near the threshold.Comment: 13 pages, 6 figure
Identifying Collective Modes via Impurities in the Cuprate Superconductors
We show that the pinning of collective charge and spin modes by impurities in
the cuprate superconductors leads to qualitatively different fingerprints in
the local density of states (LDOS). In particular, in a pinned (static) spin
droplet, the creation of a resonant impurity state is suppressed, the
spin-resolved LDOS exhibits a characteristic spatial pattern, and the LDOS
undergoes significant changes with increasing magnetic field. Since all of
these fingerprints are absent in a charge droplet, impurities are a new probe
for identifying the nature and relative strength of collective modes.Comment: 4 pages, 4 figure
Novel Cascaded Ultra Bright Pulsed Source of Polarization Entangled Photons
A new ultra bright pulsed source of polarization entangled photons has been
realized using type-II phase matching in spontaneous parametric down conversion
process in two cascaded crystals. The optical axes of the crystals are aligned
in such a way that the extraordinarily (ordinarily) polarized cone from one
crystal overlaps with the ordinarily (extraordinarily) polarized cone from the
second crystal. This spatial overlapping removes the association between the
polarization and the output angle of the photons that exist in a single type-II
down conversion process. Hence, entanglement of photons originating from any
point on the output cones is possible if a suitable optical delay line is used.
This delay line is particularly simple and easy to implement.Comment: 8 pages 8 figure
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