14,153 research outputs found
Trailing Edge Noise Reduction by Passive and Active Flow Controls
This paper presents the results on the use of porous metal foams (passive control) and dielectric barrier surface plasma actuations (active control) for the reduction of vortex shedding tonal noises from the nonflat plate type trailing edge serration in a NACA0012 airfoil previously discussed in Chong et al. (AIAA J. Vol. 51, 2013, pp. 2665-2677). The use of porous metal foams to fill the interstices between adjacent members of the sawtooth can almost completely suppress the vortex shedding tonal noise, whilst the serration effect on the broadband noise reduction is retained. This concept will promote the nonflat plate type serrated trailing edge to become a genuine alternative to the conventional flat plate type serrated trailing edge, which is known to have drawbacks in the structural stability, aerodynamic performances and implementation issues. For the plasma actuators, configuration which produces electric wind in a tangential direction is found to be not very effective in suppressing the vortices emanated from the serration blunt root. On the other hand, for the plasma configuration which produces electric wind in a vertical direction, good level of vortex shedding tonal noise reduction has been demonstrated. However, the self noise produced by the plasma actuators negates the noise benefits on the tonal noise reduction. This characteristic illustrates the need to further develop the plasma actuators in a two pronged approach. First is to increase the electric wind speed, thereby allowing the plasma actuators to be used in a higher free jet velocity which naturally produces a larger level of jet noise. Second, the self noise radiated by the plasma actuators should be reduced
Sick and tired: how molecular regulators of human sleep schedules and duration impact immune function.
Why do we need to sleep? What regulates when we sleep? And what dictates the number of hours we require? These are often viewed as three separate biological questions. Here, we propose they share molecular etiologies, whereby regulators of sleep schedules and sleep duration also govern the physiological purposes of sleep. To support our hypothesis, we review Mendelian human genetic variants sufficient to advance sleep-wake onset (PER2) and shorten sleep length (DEC2), and evaluate their emerging roles in immune responses that may rely on a sound night of slumber
From zonal flow to convection rolls in Rayleigh-B\'enard convection with free-slip plates
Rayleigh-B\'enard (RB) convection with free-slip plates and horizontally
periodic boundary conditions is investigated using direct numerical
simulations. Two configurations are considered, one is two-dimension (2D) RB
convection and the other one three-dimension (3D) RB convection with a rotating
axis parallel to the plate. We explore the parameter range of Rayleigh numbers
Ra from 10^9Pr1100. We show
that zonal flow, which was observed, for example, by Goluskin \emph{et al}.
\emph{J. Fluid. Mech.} 759, 360-385 (2014) for \Gamma=2\GammaRaPr\Gamma\GammaRa=10^7Pr=0.71\Gamma=8\Gamma = 16\Gamma\Gamma=2\pi by von
Hardenberg \emph{et al}. \emph{Phys. Rev. Lett.} 15, 134501 (2015), completely
disappears for \Gamma=16\Gamma\Gamma =
8$, the convection roll state and the zonal flow state are both statistically
stable. What state is taken depends on the initial conditions, similarly as we
found for the 2D case.Comment: 26 pages, 12 figure
Superconductivity and Magnetism in REFeAsO1-xFx (RE=Rare Earth Elements)
Fluoride-doped iron-based oxypnictides containing rare-earth gadolinium
(GdFeAsO0.8F0.2) and co-doping with yttrium (Gd0.8Y0.2FeAsO0.8F0.2) have been
prepared via conventional solid state reaction at ambient pressure. The
non-yttrium substituted oxypnictide show superconducting transition as high as
43.9 K from temperature dependent resistance measurements with the Meissner
effect observed at a lower temperature of 40.8 K from temperature dependent
magnetization measurements. By replacing a small amount of gadolinium with
yttrium Tc was observed to be lowered by 10 K which might be caused by a change
in the electronic or magnetic structures since the crystal structure was not
altered.Comment: 4 pages, 4 figures, Journal of Physics: Conference Series
(Proceedings in the LT25 Low Temperature Physics Conference) Submitte
SUSY-QCD Corrections to Associated Production at the CERN Large Hadron Collider
We calculate the SUSY-QCD corrections to the inclusive total cross sections
of the associated production processes in the Minimal
Supersymmetric Standard Model(MSSM) at the CERN Large Hadron Collider(LHC). The
SUSY-QCD corrections can increase and decrease the total cross sections
depending on the choice of the SUSY parameters. When the SUSY-QCD
corrections increase the leading-order (LO) total cross sections significantly
for large tan (), which can exceed 10% and have the opposite
sign with respect to the QCD and the SUSY-EW corrections, and thus cancel with
them to some extent. Moreover, we also investigate the effects of the SUSY-QCD
on the differential distribution of cross sections in transverse momentum
and rapidity Y of W-boson, and the invariant mass .Comment: 24 pages, 10 figures; minor changes in references; two figures and
the corresponding disccusions added; a version to appear in PR
QCD Effects in High Energy Processes
In this talk, some important QCD effects in Higgs physics, supersymmetry and
top physics, as well as the factorization and resummation techniques in QCD are
reviewed.Comment: LaTeX, 13 pages, uses ws-ijmpa.cls. Based on an invited talk at the
International Conference on QCD and Hadronic Physics, Beijing, China, June
16--20, 2005. Minor change
Top quark rare three-body decays in the littlest Higgs model with T-parity
In the littlest Higgs model with T-parity (LHT), the mirror quarks have
flavor structures and will contribute to the top quark flavor changing neutral
current. In this work, we perform an extensive investigation of the top quark
rare three-body decays and at one-loop level. Our results show that the branching ratios
of and could reach in the
favorite parameter space of the littlest Higgs model with T-parity, which
implies that these decays may be detectable at the LHC or ILC, while for the
other decays, their rates are too small to be observable at the present or
future colliders.Comment: 12 pages, 10 figure
Threshold Resummation Effects in Direct Top Quark Production at Hadron Colliders
We investigate the threshold-enhanced QCD corrections to the cross sections
for direct top quark productions induced by model-independent flavor changing
neutral current couplings at hadron colliders. We use the soft-collinear
effective theory to describe the incoming massless partons and use the heavy
quark effective theory to treat the top quark. Then we construct the flavor
changing operator based on the above effective theories, and resum the large
logarithms near threshold arising from soft gluon emission. Our results show
that the resummed QCD corrections further enhance the next-to-leading order
cross sections significantly. Moreover, the resummation effects vastly reduce
the dependence of the cross sections on the renormalization and factorization
scales, especially in cases where the next-to-leading order results behave
worse than the leading order results. Our results are more sensitive to the new
physics effects. If signals of direct top quark production are found in future
experiments, it is more appropriate to use our results as the theoretical
inputs for extracting the anomalous couplings.Comment: 5 pages, 4 figures, use revtex4 and amsmath; version to appear in
Phys. Rev.
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