116,946 research outputs found
Dynamic response of some tentative compliant wall structures to convected turbulence fields
Some tentative compliant wall structures designed for possible skin friction drag reduction are investigated. Among the structural models considered is a ribbed membrane backed by polyurethane or PVS plastisol. This model is simplified as a beam placed on a viscoelastic foundation as well as on a set of evenly spaced supports. The total length of the beam may be either finite or infinite, and the supports may be either rigid or elastic. Another structural model considered is a membrane mounted over a series of pretensioned wires, also evenly spaced, and the entire membrane is backed by an air cavity. The forcing pressure field is idealized as a frozen random pattern convected downstream at a characteristic velocity. The results are given in terms of the frequency response functions of the system, the spectral density of the structural motion, and the spectral density of the boundary layer pressure including the effect of structural motion. These results are used in a parametric study of structural configurations capable of generating favorable wave lengths, wave amplitudes, and wave speeds in the structural motion for potential drag reduction
New high fill-factor triangular micro-lens array fabrication method using UV proximity printing
A simple and effective method to fabricate a high fill-factor triangular
microlens array using the proximity printing in lithography process is
reported. The technology utilizes the UV proximity printing by controlling a
printing gap between the mask and substrate. The designed approximate triangle
microlens array pattern can be fabricated the high fill-factor triangular
microlens array in photoresist. It is due to the UV light diffraction to
deflect away from the aperture edges and produce a certain exposure in
photoresist material outside the aperture edges. This method can precisely
control the geometric profile of high fill factor triangular microlens array.
The experimental results showed that the triangular micro-lens array in
photoresist could be formed automatically when the printing gap ranged from 240
micrometers to 840 micrometers. The gapless triangular microlens array will be
used to increases of luminance for backlight module of liquid crystal displays.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Probing annihilations and decays of low-mass galactic dark matter in IceCube DeepCore array: Track events
The deployment of DeepCore array significantly lowers IceCube's energy
threshold to about 10 GeV and enhances the sensitivity of detecting neutrinos
from annihilations and decays of light dark matter. To match this experimental
development, we calculate the track event rate in DeepCore array due to
neutrino flux produced by annihilations and decays of galactic dark matter. We
also calculate the background event rate due to atmospheric neutrino flux for
evaluating the sensitivity of DeepCore array to galactic dark matter
signatures. Unlike previous approaches, which set the energy threshold for
track events at around 50 GeV (this choice avoids the necessity of including
oscillation effect in the estimation of atmospheric background event rate), we
have set the energy threshold at 10 GeV to take the full advantage of DeepCore
array. We compare our calculated sensitivity with those obtained by setting the
threshold energy at 50 GeV. We conclude that our proposed threshold energy
significantly improves the sensitivity of DeepCore array to the dark matter
signature for GeV in the annihilation scenario and
GeV in the decay scenario.Comment: 19 pages, 5 figures; match the published versio
Modeling incompressible thermal flows using a central-moment-based lattice Boltzmann method
In this paper, a central-moment-based lattice Boltzmann (CLB) method for
incompressible thermal flows is proposed. In the method, the incompressible
Navier-Stokes equations and the convection-diffusion equation for the
temperature field are sloved separately by two different CLB equations. Through
the Chapman-Enskog analysis, the macroscopic governing equations for
incompressible thermal flows can be reproduced. For the flow field, the tedious
implementation for CLB method is simplified by using the shift matrix with a
simplified central-moment set, and the consistent forcing scheme is adopted to
incorporate forcing effects. Compared with several D2Q5
multiple-relaxation-time (MRT) lattice Boltzmann methods for the temperature
equation, the proposed method is shown to be better Galilean invariant through
measuring the thermal diffusivities on a moving reference frame. Thus a higher
Mach number can be used for convection flows, which decreases the computational
load significantly. Numerical simulations for several typical problems confirm
the accuracy, efficiency, and stability of the present method. The grid
convergence tests indicate that the proposed CLB method for incompressible
thermal flows is of second-order accuracy in space
Indirect exchange of magnetic impurities in zigzag graphene ribbon
We use quantum Monte Carlo method to study the indirect coupling between two
magnetic impurities on the zigzag edge of graphene ribbon, with respect to the
chemical potential . We find that the spin-spin correlation between two
adatoms located on the nearest sites in the zigzag edge are drastically
suppressed around the zero-energy. As we switch the system away from
half-filling, the antiferromagnetic correlation is first enhanced and then
decreased. If the two adatoms are adsorbed on the sites belonging to the same
sublattice, we find similar behavior of spin-spin correlation except for a
crossover from ferromagnetic to antiferromagentic correlation in the vicinity
of zero-energy. We also calculated the weight of different components of
d-electron wave function and local magnet moment for various values of
parameters, and all the results are consistent with those of spin-spin
correlation between two magnetic impurities.Comment: 3 pages, 4 figures, conference proceedin
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