256 research outputs found
Differentially expressed gene detection with covariate selection under small sample size genomic setting
In the genomic setting, most data have relative small sample size (n) considering large number of covariates (p). For this type of data structure, it is not appropriate to fit simple linear regression models since the variance would be large and it could encounter over-fitting. Methods for restraining the number of variables contained in the model are necessary.
In this study, constrained best subset (CBS) and LASSO methods were performed to select covariates and detect differentially expressed (DE) genes. For comparison purpose, we set two different simulation settings for each method. Under univariate settings, all methods had type I error well controlled and CBS methods were more powerful than LASSO. However, LASSO had better prediction results compared to CBS methods even though it had more false positive covariates selected. Under genome-wide simulation settings, FDR only well controlled for larger sample size (n=50, 100). Other results have a similar trend as in the univariate setting.
Beyond simulations, eight transcriptomic studies from post-mortem brain tissues of major depressive disorder (MDD) patients were used as a real data application to further compare the CBS2 method and LASSO. As the result of meta-analysis combining all eight studies, CBS2 method generated more DE genes compared to LASSO. It also detected more significant pathways compared to LASSO. Our evaluations suggest that no method performs universally the best in the small-n-large-p scenario and selection of the best method depends on sample size, dimensionality and the desired biological purpose. From the public health significance perspective, using CBS2 method under small sample size genomic setting could help us detect more DE genes as well as more meaningful pathways
Mobile Formation Coordination and Tracking Control for Multiple Non-holonomic Vehicles
This paper addresses forward motion control for trajectory tracking and
mobile formation coordination for a group of non-holonomic vehicles on SE(2).
Firstly, by constructing an intermediate attitude variable which involves
vehicles' position information and desired attitude, the translational and
rotational control inputs are designed in two stages to solve the trajectory
tracking problem. Secondly, the coordination relationships of relative
positions and headings are explored thoroughly for a group of non-holonomic
vehicles to maintain a mobile formation with rigid body motion constraints. We
prove that, except for the cases of parallel formation and translational
straight line formation, a mobile formation with strict rigid-body motion can
be achieved if and only if the ratios of linear speed to angular speed for each
individual vehicle are constants. Motion properties for mobile formation with
weak rigid-body motion are also demonstrated. Thereafter, based on the proposed
trajectory tracking approach, a distributed mobile formation control law is
designed under a directed tree graph. The performance of the proposed
controllers is validated by both numerical simulations and experiments
Stroke and Liver Cirrhosis: A Brief Review of Current Evidence
Stroke and liver cirrhosis are common in our everyday clinical practice, both of which can lead to serious complications. Their association is unclear. In this chapter, we briefly summarized the epidemiology of liver cirrhosis in stroke, reviewed the current evidence regarding the association between liver cirrhosis and stroke, and discussed the potential mechanisms for explaining such an association, such as coagulopathy, hypoperfusion, cardiac diseases, diabetes, and dyslipidemia
Deep Imaging of the HCG 95 Field.I.Ultra-diffuse Galaxies
We present a detection of 89 candidates of ultra-diffuse galaxies (UDGs) in a
4.9 degree field centered on the Hickson Compact Group 95 (HCG 95) using
deep - and -band images taken with the Chinese Near Object Survey
Telescope. This field contains one rich galaxy cluster (Abell 2588 at
=0.199) and two poor clusters (Pegasus I at =0.013 and Pegasus II at
=0.040). The 89 candidates are likely associated with the two poor clusters,
giving about 50 60 true UDGs with a half-light radius kpc
and a central surface brightness mag arcsec. Deep
'-band images are available for 84 of the 89 galaxies from the Dark Energy
Camera Legacy Survey (DECaLS), confirming that these galaxies have an extremely
low central surface brightness. Moreover, our UDG candidates are spread over a
wide range in color, and 26% are as blue as normal star-forming
galaxies, which is suggestive of young UDGs that are still in formation.
Interestingly, we find that one UDG linked with HCG 95 is a gas-rich galaxy
with H I mass detected by the Very Large Array,
and has a stellar mass of . This
indicates that UDGs at least partially overlap with the population of nearly
dark galaxies found in deep H I surveys. Our results show that the high
abundance of blue UDGs in the HCG 95 field is favored by the environment of
poor galaxy clusters residing in H I-rich large-scale structures.Comment: Published in Ap
SDSS-IV MaNGA: The Roles of AGNs and Dynamical Processes in Star Formation Quenching in Nearby Disk Galaxies
We study how star formation (SF) is quenched in low-redshift disk galaxies
with integral-field spectroscopy. We select 131 face-on spiral galaxies with
stellar mass greater than , and with spatially
resolved spectrum from MaNGA DR13. We subdivide the sample into four groups
based on the offset of their global specific star formation rate (SFR) from the
star-forming main sequence and stack the radial profiles of stellar mass and
SFR. By comparing the stacked profiles of quiescent and star-forming disk
galaxies, we find that the decrease of the global SFR is caused by the
suppression of SF at all radii, but with a more significant drop from the
center to the outer regions following an inside-out pattern. As the global
specific SFR decreases, the central stellar mass, the fraction of disk galaxies
hosting stellar bars, and active galactic nuclei (AGNs; including both LINERs
and Seyferts) all increase, indicating dynamical processes and AGN feedback are
possible contributors to the inside-out quenching of SF in the local universe.
However, if we include only Seyferts, or AGNs with ,
the increasing trend of AGN fraction with decreasing global sSFR disappears.
Therefore, if AGN feedback is contributing to quenching, we suspect that it
operates in the low-luminosity AGN mode, as indicated by the increasing large
bulge mass of the more passive disk galaxies.Comment: 12 pages, 7 figures, published in ApJ, typos corrected, references
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Fault Separation Based on An Excitation Operator with Application to a Quadrotor UAV
This paper presents an excitation operator based fault separation
architecture for a quadrotor unmanned aerial vehicle (UAV) subject to loss of
effectiveness (LoE) faults, actuator aging, and load uncertainty. The actuator
fault dynamics is deeply excavated, containing the deep coupling information
among the actuator faults, the system states, and control inputs. By explicitly
considering the physical constraints and tracking performance, an excitation
operator and corresponding integrated state observer are designed to estimate
separately actuator fault and load uncertainty. Moreover, a fault separation
maneuver and a safety controller are proposed to ensure the tracking
performance when the excitation operator is injected. Both comparative
simulation and flight experiments have demonstrated the effectiveness of the
proposed scheme while maintaining high levels of tracking performance
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