17,578 research outputs found
Hydrodynamic slip boundary condition at chemically patterned surfaces: A continuum deduction from molecular dynamics
We investigate the slip boundary condition for single-phase flow past a
chemically patterned surface. Molecular dynamics (MD) simulations show that
modulation of fluid-solid interaction along a chemically patterned surface
induces a lateral structure in the fluid molecular organization near the
surface. Consequently, various forces and stresses in the fluid vary along the
patterned surface. Given the presence of these lateral variations, a general
scheme is developed to extract hydrodynamic information from MD data. With the
help of this scheme, the validity of the Navier slip boundary condition is
verified for the chemically patterned surface, where a local slip length can be
defined. Based on the MD results, a continuum hydrodynamic model is formulated
using the Navier-Stokes equation and the Navier boundary condition, with a slip
length varying along the patterned surface. Steady-state velocity fields from
continuum calculations are in quantitative agreement with those from MD
simulations. It is shown that, when the pattern period is sufficiently small,
the solid surface appears to be homogeneous, with an effective slip length that
can be controlled by surface patterning. Such a tunable slip length may have
important applications in nanofluidics.Comment: 41 pages, 17 figure
Status of magnetic suspension technology
The reasons for the continuing interest in the Magnetic Suspension and Balance System (MSBS) are highlighted. Typical problems that can arise because of model-support interference in a transonic wind tunnel are shown to illustrate the need for MSBS. The two magnetic suspension systems in operation at Langley are the only ones active in the U.S. One of these systems is the 13 inch MSBS which was borrowed from the Air Force Arnold Engineering Development Center. The other system is the 6 inch MSBS which was developed by MIT Aerophysics Laboratory with NASA and DOD funding. Each of these systems is combined with a subsonic wind tunnel. Ongoing research in both of these systems is covered. Last year, Madison Magnetics, Inc., completed a contractual design and cost study utilizing some advance concepts for a large MSBS which would be compatible with an 8 foot transonic wind tunnel and the highlights of the study are presented. Sverdrup Technology, Inc., recently performed a study under contract for Langley on the potential usefulness to the aerospace industry of a proposed large MSBS combined with a suitable transonic wind tunnel. The results of that study are discussed. Langley has partially funded the MSBS work at the University of Southampton for about 6 years under a grant arrangement and the major results are summarized
A Dual Dutch Auction in Taipei: The Choice of Numeraire and Auction Form in Multi-Object Auctions with Bundling. .
In Taipei we observed a dual Dutch fish auction, like a conventional Dutch auction with bundling, but with reversed roles of price and quantity. We study dual and conventional auctions with symmetric, independent private values, when agents’ utilities are linear in money but strictly concave in fish. With known buyers’ values, conventional and dual auctions, English or Dutch, are equivalent. With values known to buyers but not the seller, the seller prefers conventional auctions. With private values, the seller can prefer a dual Dutch or a conventional English or Dutch auction, but prefers all three to a dual English auction.
Dynamics of opinion formation in a small-world network
The dynamical process of opinion formation within a model using a local
majority opinion updating rule is studied numerically in networks with the
small-world geometrical property. The network is one in which shortcuts are
added to randomly chosen pairs of nodes in an underlying regular lattice. The
presence of a small number of shortcuts is found to shorten the time to reach a
consensus significantly. The effects of having shortcuts in a lattice of fixed
spatial dimension are shown to be analogous to that of increasing the spatial
dimension in regular lattices. The shortening of the consensus time is shown to
be related to the shortening of the mean shortest path as shortcuts are added.
Results can also be translated into that of the dynamics of a spin system in a
small-world network.Comment: 10 pages, 5 figure
A Unified Gravity-Electroweak Model Based on a Generalized Yang-Mills Framework
Gravitational and electroweak interactions can be unified in analogy with the
unification in the Weinberg-Salam theory. The Yang-Mills framework is
generalized to include space-time translational group T(4), whose generators
T_{\mu}(=\p/\p x^{\mu}) do not have constant matrix representations. By
gauging in flat space-time, we have a new
tensor field which universally couples to all particles and
anti-particles with the same constant , which has the dimension of length.
In this unified model, the T(4) gauge symmetry dictates that all wave equations
of fermions, massive bosons and the photon in flat space-time reduce to a
Hamilton-Jacobi equation with the same `effective Riemann metric tensor' in the
geometric-optics limit. Consequently, the results are consistent with
experiments. We demonstrated that the T(4) gravitational gauge field can be
quantized in inertial frames.Comment: 12 pages. To be published in "Modern Physics Letters A
Multi-wavelength Stellar Polarimetry of the Filamentary Cloud IC5146: I. Dust Properties
We present optical and near-infrared stellar polarization observations toward
the dark filamentary clouds associated with IC5146. The data allow us to
investigate the dust properties (this paper) and the magnetic field structure
(Paper II). A total of 2022 background stars were detected in -, -,
-, and/or -bands to mag. The ratio of the polarization
percentage at different wavelengths provides an estimate of ,
the wavelength of peak polarization, which is an indicator of the small-size
cutoff of the grain size distribution. The grain size distribution seems to
significantly change at 3 mag, where both the average and dispersion
of decrease. In addition, we found
0.6-0.9 m for mag, which is larger than the 0.55 m
in the general ISM, suggesting that grain growth has already started in low
regions. Our data also reveal that polarization efficiency (PE ) decreases with as a power-law in -, -, and
-bands with indices of -0.710.10, -1.230.10 and -0.530.09.
However, -band data show a power index change; the PE varies with
steeply (index of -0.950.30) when mag but softly
(index of -0.250.06) for greater values. The soft decay of PE in
high regions is consistent with the Radiative Aligned Torque model,
suggesting that our data trace the magnetic field to mag.
Furthermore, the breakpoint found in -band is similar to the where we
found the dispersion significantly decreased. Therefore, the
flat PE- in high regions implies that the power index changes result
from additional grain growth.Comment: 31 pages, 17 figures, and 3 tables; accepted for publication in Ap
Flux-lattice melting in LaOFFeAs: first-principles prediction
We report the theoretical study of the flux-lattice melting in the novel
iron-based superconductor and
. Using the Hypernetted-Chain closure and an
efficient algorithm, we calculate the two-dimensional one-component plasma pair
distribution functions, static structure factors and direct correlation
functions at various temperatures. The Hansen-Verlet freezing criterion is
shown to be valid for vortex-liquid freezing in type-II superconductors.
Flux-lattice meting lines for and
are predicted through the combination of the density
functional theory and the mean-field substrate approach.Comment: 5 pages, 4 figures, to appear in Phys. Rev.
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