1,465 research outputs found
Functional Mapping of Dynamic Traits with Robust t-Distribution
Functional mapping has been a powerful tool in mapping quantitative trait loci (QTL) underlying dynamic traits of agricultural or biomedical interest. In functional mapping, multivariate normality is often assumed for the underlying data distribution, partially due to the ease of parameter estimation. The normality assumption however could be easily violated in real applications due to various reasons such as heavy tails or extreme observations. Departure from normality has negative effect on testing power and inference for QTL identification. In this work, we relax the normality assumption and propose a robust multivariate -distribution mapping framework for QTL identification in functional mapping. Simulation studies show increased mapping power and precision with the distribution than that of a normal distribution. The utility of the method is demonstrated through a real data analysis
Spatial contrast sensitivity in adolescents with autism spectrum disorders
Adolescents with autism spectrum disorders (ASD) and typically developing (TD) controls underwent a rigorous psychophysical assessment that measured contrast sensitivity to seven spatial frequencies (0.5-20 cycles/degree). A contrast sensitivity function (CSF) was then fitted for each participant, from which four measures were obtained: visual acuity, peak spatial frequency, peak contrast sensitivity, and contrast sensitivity at a low spatial frequency. There were no group differences on any of the four CSF measures, indicating no differential spatial frequency processing in ASD. Although it has been suggested that detail-oriented visual perception in individuals with ASD may be a result of differential sensitivities to low versus high spatial frequencies, the current study finds no evidence to support this hypothesis
Decaying into the Hidden Sector
The existence of light hidden sectors is an exciting possibility that may be
tested in the near future. If DM is allowed to decay into such a hidden sector
through GUT suppressed operators, it can accommodate the recent cosmic ray
observations without over-producing antiprotons or interfering with the
attractive features of the thermal WIMP. Models of this kind are simple to
construct, generic and evade all astrophysical bounds. We provide tools for
constructing such models and present several distinct examples. The light
hidden spectrum and DM couplings can be probed in the near future, by measuring
astrophysical photon and neutrino fluxes. These indirect signatures are
complimentary to the direct production signals, such as lepton jets, predicted
by these models.Comment: 40 pages, 5 figure
An Electron Fixed Target Experiment to Search for a New Vector Boson A' Decaying to e+e-
We describe an experiment to search for a new vector boson A' with weak
coupling alpha' > 6 x 10^{-8} alpha to electrons (alpha=e^2/4pi) in the mass
range 65 MeV < m_A' < 550 MeV. New vector bosons with such small couplings
arise naturally from a small kinetic mixing of the "dark photon" A' with the
photon -- one of the very few ways in which new forces can couple to the
Standard Model -- and have received considerable attention as an explanation of
various dark matter related anomalies. A' bosons are produced by radiation off
an electron beam, and could appear as narrow resonances with small production
cross-section in the trident e+e- spectrum. We summarize the experimental
approach described in a proposal submitted to Jefferson Laboratory's PAC35,
PR-10-009. This experiment, the A' Experiment (APEX), uses the electron beam of
the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory
(CEBAF) at energies of ~1-4 GeV incident on 0.5-10% radiation length Tungsten
wire mesh targets, and measures the resulting e+e- pairs to search for the A'
using the High Resolution Spectrometer and the septum magnet in Hall A. With a
~1 month run, APEX will achieve very good sensitivity because the statistics of
e+e- pairs will be ~10,000 times larger in the explored mass range than any
previous search for the A' boson. These statistics and the excellent mass
resolution of the spectrometers allow sensitivity to alpha'/alpha one to three
orders of magnitude below current limits, in a region of parameter space of
great theoretical and phenomenological interest. Similar experiments could also
be performed at other facilities, such as the Mainz Microtron.Comment: 19 pages, 12 figures, 2 table
Low-Energy Probes of a Warped Extra Dimension
We investigate a natural realization of a light Abelian hidden sector in an
extended Randall-Sundrum (RS) model. In addition to the usual RS bulk we
consider a second warped space containing a bulk U(1)_x gauge theory with a
characteristic IR scale of order a GeV. This Abelian hidden sector can couple
to the standard model via gauge kinetic mixing on a common UV brane. We show
that if such a coupling induces significant mixing between the lightest U(1)_x
gauge mode and the standard model photon and Z, it can also induce significant
mixing with the heavier U(1)_x Kaluza-Klein (KK) modes. As a result it might be
possible to probe several KK modes in upcoming fixed-target experiments and
meson factories, thereby offering a new way to investigate the structure of an
extra spacetime dimension.Comment: 26 pages, 1 figure, added references, corrected minor typos, same as
journal versio
Randomization in Laboratory Procedure Is Key to Obtaining Reproducible Microarray Results
The quality of gene expression microarray data has improved dramatically since the first arrays were introduced in the late 1990s. However, the reproducibility of data generated at multiple laboratory sites remains a matter of concern, especially for scientists who are attempting to combine and analyze data from public repositories. We have carried out a study in which a common set of RNA samples was assayed five times in four different laboratories using Affymetrix GeneChip arrays. We observed dramatic differences in the results across laboratories and identified batch effects in array processing as one of the primary causes for these differences. When batch processing of samples is confounded with experimental factors of interest it is not possible to separate their effects, and lists of differentially expressed genes may include many artifacts. This study demonstrates the substantial impact of sample processing on microarray analysis results and underscores the need for randomization in the laboratory as a means to avoid confounding of biological factors with procedural effects
Randomization in Laboratory Procedure Is Key to Obtaining Reproducible Microarray Results
The quality of gene expression microarray data has improved dramatically since the first arrays were introduced in the late 1990s. However, the reproducibility of data generated at multiple laboratory sites remains a matter of concern, especially for scientists who are attempting to combine and analyze data from public repositories. We have carried out a study in which a common set of RNA samples was assayed five times in four different laboratories using Affymetrix GeneChip arrays. We observed dramatic differences in the results across laboratories and identified batch effects in array processing as one of the primary causes for these differences. When batch processing of samples is confounded with experimental factors of interest it is not possible to separate their effects, and lists of differentially expressed genes may include many artifacts. This study demonstrates the substantial impact of sample processing on microarray analysis results and underscores the need for randomization in the laboratory as a means to avoid confounding of biological factors with procedural effects
Synthesis and Growth Mechanism of Ni Nanotubes and Nanowires
Highly ordered Ni nanotube and nanowire arrays were fabricated via electrodeposition. The Ni microstructures and the process of the formation were investigated using conventional and high-resolution transmission electron microscope. Herein, we demonstrated the systematic fabrication of Ni nanotube and nanowire arrays and proposed an original growth mechanism. With the different deposition time, nanotubes or nanowires can be obtained. Tubular nanostructures can be obtained at short time, while nanowires take longer time to form. This formation mechanism is applicable to design and synthesize other metal nanostructures and even compound nanostuctures via template-based electrodeposition
Femtosecond Carrier Dynamics in In2O3Nanocrystals
We have studied carrier dynamics in In2O3nanocrystals grown on a quartz substrate using chemical vapor deposition. Transient differential absorption measurements have been employed to investigate the relaxation dynamics of photo-generated carriers in In2O3nanocrystals. Intensity measurements reveal that Auger recombination plays a crucial role in the carrier dynamics for the carrier densities investigated in this study. A simple differential equation model has been utilized to simulate the photo-generated carrier dynamics in the nanocrystals and to fit the fluence-dependent differential absorption measurements. The average value of the Auger coefficient obtained from fitting to the measurements was γ = 5.9 ± 0.4 × 10−31 cm6 s−1. Similarly the average relaxation rate of the carriers was determined to be approximately τ = 110 ± 10 ps. Time-resolved measurements also revealed ~25 ps delay for the carriers to reach deep traps states which have a subsequent relaxation time of approximately 300 ps
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