14,402 research outputs found
Measuring reproducibility of high-throughput experiments
Reproducibility is essential to reliable scientific discovery in
high-throughput experiments. In this work we propose a unified approach to
measure the reproducibility of findings identified from replicate experiments
and identify putative discoveries using reproducibility. Unlike the usual
scalar measures of reproducibility, our approach creates a curve, which
quantitatively assesses when the findings are no longer consistent across
replicates. Our curve is fitted by a copula mixture model, from which we derive
a quantitative reproducibility score, which we call the "irreproducible
discovery rate" (IDR) analogous to the FDR. This score can be computed at each
set of paired replicate ranks and permits the principled setting of thresholds
both for assessing reproducibility and combining replicates. Since our approach
permits an arbitrary scale for each replicate, it provides useful descriptive
measures in a wide variety of situations to be explored. We study the
performance of the algorithm using simulations and give a heuristic analysis of
its theoretical properties. We demonstrate the effectiveness of our method in a
ChIP-seq experiment.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS466 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
A logarithmic generalization of tensor product theory for modules for a vertex operator algebra
We describe a logarithmic tensor product theory for certain module categories
for a ``conformal vertex algebra.'' In this theory, which is a natural,
although intricate, generalization of earlier work of Huang and Lepowsky, we do
not require the module categories to be semisimple, and we accommodate modules
with generalized weight spaces. The corresponding intertwining operators
contain logarithms of the variables.Comment: 39 pages. Misprints corrected. Final versio
Spectral Energy Distributions of Gamma Ray Bursts Energized by External Shocks
Sari, Piran, and Narayan have derived analytic formulas to model the spectra
from gamma-ray burst blast waves that are energized by sweeping up material
from the surrounding medium. We extend these expressions to apply to general
radiative regimes and to include the effects of synchrotron self-absorption.
Electron energy losses due to the synchrotron self-Compton process are also
treated in a very approximate way. The calculated spectra are compared with
detailed numerical simulation results. We find that the spectral and temporal
breaks from the detailed numerical simulation are much smoother than the
analytic formulas imply, and that the discrepancies between the analytic and
numerical results are greatest near the breaks and endpoints of the synchrotron
spectra. The expressions are most accurate (within a factor of ~ 3) in the
optical/X-ray regime during the afterglow phase, and are more accurate when
epsilon_e, the fraction of swept-up particle energy that is transferred to the
electrons, is <~ 0.1. The analytic results provide at best order-of-magnitude
accuracy in the self-absorbed radio/infrared regime, and give poor fits to the
self-Compton spectra due to complications from Klein-Nishina effects and
photon-photon opacity.Comment: 16 pages, 7 figures, ApJ, in press, 537, July 1, 2000. Minor changes
in response to referee report, corrected figure
The measurement and analysis of age-related changes in Caenorhabditis elegans
Aging is characterized by progressive degenerative changes in tissue organization and function that increase the probability of mortality. Major goals of aging research include elucidating the series of events that cause degenerative changes and analyzing environmental and genetic factors that modulate these changes. The basis for mechanistic studies of aging are accurate and precise descriptions of age-related changes, since these descriptions define the aging phenotype. Here we review studies that describe age-related changes in C. elegans including measurements of integrated functions such as behavior, microscopic analyses of tissue organization, and biochemical studies of macromolecules. Genetic and environmental factors that influence these changes are described, and studies that analyze the relationships between different age-related changes are discussed. Together these studies provide fundamental insights into aging in C. elegans that may be relevant to aging in other animals
Differential gene expression associated with postnatal equine articular cartilage maturation
<p>Abstract</p> <p>Background</p> <p>Articular cartilage undergoes an important maturation process from neonate to adult that is reflected by alterations in matrix protein organization and increased heterogeneity of chondrocyte morphology. In the horse, these changes are influenced by exercise during the first five months of postnatal life. Transcriptional profiling was used to evaluate changes in articular chondrocyte gene expression during postnatal growth and development.</p> <p>Methods</p> <p>Total RNA was isolated from the articular cartilage of neonatal (0–10 days) and adult (4–5 years) horses, subjected to one round of linear RNA amplification, and then applied to a 9,367-element equine-specific cDNA microarray. Comparisons were made with a dye-swap experimental design. Microarray results for selected genes (COL2A1, COMP, P4HA1, TGFB1, TGFBR3, TNC) were validated by quantitative polymerase chain reaction (qPCR).</p> <p>Results</p> <p>Fifty-six probe sets, which represent 45 gene products, were up-regulated (p < 0.01) in chondrocytes of neonatal articular cartilage relative to chondrocytes of adult articular cartilage. Conversely, 586 probe sets, which represent 499 gene products, were up-regulated (p < 0.01) in chondrocytes of adult articular cartilage relative to chondrocytes of neonatal articular cartilage. Collagens, matrix-modifying enzymes, and provisional matrix non-collagenous proteins were expressed at higher levels in the articular cartilage of newborn foals. Those genes with increased mRNA abundance in adult chondrocytes included leucine-rich small proteoglycans, matrix assembly, and cartilage maintenance proteins.</p> <p>Conclusion</p> <p>Differential expression of genes encoding matrix proteins and matrix-modifying enzymes between neonates and adults reflect a cellular maturation process in articular chondrocytes. Up-regulated transcripts in neonatal cartilage are consistent with growth and expansion of the articular surface. Expression patterns in mature articular cartilage indicate a transition from growth to homeostasis, and tissue function related to withstanding shear and weight-bearing stresses.</p
Poisson valuations
We study Poisson valuations and provide their applications in solving
problems related to rigidity, automorphisms, Dixmier property, isomorphisms,
and embeddings of Poisson algebras and fields.Comment: 47 page
Weighted Poisson polynomial rings
We discuss Poisson structures on a weighted polynomial algebra defined by a homogeneous element , called a potential. We
start with classifying potentials of degree degdegdeg
with any positive weight (deg, deg, deg) and list all with
isolated singularity. Based on the classification, we study the rigidity of
in terms of graded twistings and classify Poisson fraction fields of
for irreducible potentials. Using Poisson valuations, we
characterize the Poisson automorphism group of when has an
isolated singularity extending a nice result of
Makar-Limanov-Turusbekova-Umirbaev. Finally, Poisson cohomology groups are
computed for new classes of Poisson polynomial algebras.Comment: 37 page
Robust Quantitative Susceptibility Mapping via Approximate Message Passing
Purpose: It is challenging to recover magnetic susceptibility in the presence
of phase errors, which may be caused by noise or strong local-susceptibility
shifts in cases of brain hemorrhage and calcification. We propose a Bayesian
formulation for quantitative susceptibility mapping (QSM) where a customized
Gaussian-mixture distribution is used to model the long-tailed noise
distribution.
Theory: Complex exponential functions of the phase are used as nonlinear
measurements. Wavelet coefficients of the susceptibility map are modeled by the
Laplace distribution. Measurement noise is modeled by a two-component
Gaussian-mixture distribution, where the second component is reserved to model
the noise outliers. The susceptibility map and distribution parameters are
jointly recovered using approximate message passing (AMP).
Methods: The proposed AMP with built-in parameter estimation (AMP-PE) is
compared with the state-of-the-art nonlinear L1-QSM and MEDI approaches that
adopt the L1-norm and L2-norm data-fidelity terms respectively. They are tested
on the simulated and in vivo datasets.
Results: On the simulated Sim2Snr1 dataset, AMP-PE achieved the lowest NRMSE
and SSIM, MEDI achieved the lowest HFEN. On the in vivo datasets, AMP-PE is
more robust and better at preserving structural details and removing streaking
artifacts in the hemorrhage cases than L1-QSM and MEDI.
Conclusion: By leveraging a customized Gaussian-mixture noise prior, AMP-PE
achieves better performance in challenging cases of brain hemorrhage and
calcification. It is equipped with built-in parameter estimation, which avoids
subjective bias from the usual visual-tuning step of in vivo reconstruction.Comment: Keywords: Approximate message passing, Compressive sensing, Parameter
estimation, QS
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