2,430 research outputs found
The evolution of energy in flow driven by rising bubbles
We investigate by direct numerical simulations the flow that rising bubbles
cause in an originally quiescent fluid. We employ the Eulerian-Lagrangian
method with two-way coupling and periodic boundary conditions. In order to be
able to treat up to 288000 bubbles, the following approximations and
simplifications had to be introduced: (i) The bubbles were treated as
point-particles, thus (ii) disregarding the near-field interactions among them,
and (iii) effective force models for the lift and the drag forces were used. In
particular, the lift coefficient was assumed to be 1/2, independent of the
bubble Reynolds number and the local flow field. The results suggest that large
scale motions are generated, owing to an inverse energy cascade from the small
to the large scales. However, as the Taylor-Reynolds number is only in the
range of 1, the corresponding scaling of the energy spectrum with an exponent
of -5/3 cannot develop over a pronounced range. In the long term, the property
of local energy transfer, characteristic of real turbulence, is lost and the
input of energy equals the viscous dissipation at all scales. Due to the lack
of strong vortices the bubbles spread rather uniformly in the flow. The
mechanism for uniform spreading is as follows: Rising bubbles induce a velocity
field behind them that acts on the following bubbles. Owing to the shear, those
bubbles experience a lift force which make them spread to the left or right,
thus preventing the formation of vertical bubble clusters and therefore of
efficient forcing. Indeed, when the lift is artifically put to zero in the
simulations, the flow is forced much more efficiently and a more pronounced
energy accumulates at large scales is achieved.Comment: 9 pages, 7 figure
Evolution of the Small Magellanic Cloud
Based on the results of N-body simulations on the last 2.5 Gyr evolution of
the Large and Small Magellanic Clouds (LMC and SMC, respectively) interacting
with the Galaxy, we firstly show when and where the leading arms (LAs) of the
Magellanic stream (MS) can pass through the Galactic plane after the MS
formation. We secondly show collisions between the outer Galactic HI disk and
the LAs of the MS can create giant HI holes and chimney-like structures in the
disk about 0.2 Gyr ago. We thirdly show that a large amount of metal-poor gas
is stripped from the SMC and transfered to the LMC during the tidal interaction
between the Clouds and the Galaxy about 0.2 and 1.3 Gyr ago. We thus propose
that this metal-poor gas can closely be associated with the origin of LMC's
young and intermediate-age stars and star clusters with distinctively
low-metallicities with [Fe/H] < -0.6.Comment: 4 pages, 3 figures, to appear in the proceedings of ``Galaxies in the
Local Volume'', Sydney, 8 to 13 July, 200
Exciton diffusion in air-suspended single-walled carbon nanotubes
Direct measurements of the diffusion length of excitons in air-suspended
single-walled carbon nanotubes are reported. Photoluminescence microscopy is
used to identify individual nanotubes and to determine their lengths and chiral
indices. Exciton diffusion length is obtained by comparing the dependence of
photoluminescence intensity on the nanotube length to numerical solutions of
diffusion equations. We find that the diffusion length in these clean, as-grown
nanotubes is significantly longer than those reported for micelle-encapsulated
nanotubes.Comment: 4 pages, 4 figure
Gate-induced blueshift and quenching of photoluminescence in suspended single-walled carbon nanotubes
Gate-voltage effects on photoluminescence spectra of suspended single-walled
carbon nanotubes are investigated. Photoluminescence microscopy and excitation
spectroscopy are used to identify individual nanotubes and to determine their
chiralities. Under an application of gate voltage, we observe slight blueshifts
in the emission energy and strong quenching of photoluminescence. The
blueshifts are similar for different chiralities investigated, suggesting
extrinsic mechanisms. In addition, we find that the photoluminescence intensity
quenches exponentially with gate voltage.Comment: 4 pages, 4 figure
Evolution from Non-Fermi to Fermi Liquid Transport Properties by Isovalent Doping in BaFe2(As1-xPx)2 Superconductors
The normal-state charge transport is studied systematically in high-quality
single crystals of BaFe(AsP) (). By
substituting isovalent P for As, the spin-density-wave (SDW) state is
suppressed and the dome-shaped superconducting phase ( K)
appears. Near the SDW end point (), we observe striking linear
temperature () dependence of resistivity in a wide -range, and remarkable
low- enhancement of Hall coefficient magnitude from the carrier number
estimates. We also find that the magnetoresistance apparently violates the
Kohler's rule and is well scaled by the Hall angle as
. These non-Fermi liquid
transport anomalies cannot be attributed to the simple multiband effects. These
results capture universal features of correlated electron systems in the
presence of strong antiferromagnetic fluctuations.Comment: 4 pages, 4 figure
Effects of human hair and nail proteins and their films on rat mast cells
The original publication is available at www.springerlink.comArticleJOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE. 19(6): 2335-2342 (2008)journal articl
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