42,883 research outputs found
A stability condition for turbulence model: From EMMS model to EMMS-based turbulence model
The closure problem of turbulence is still a challenging issue in turbulence
modeling. In this work, a stability condition is used to close turbulence.
Specifically, we regard single-phase flow as a mixture of turbulent and
non-turbulent fluids, separating the structure of turbulence. Subsequently,
according to the picture of the turbulent eddy cascade, the energy contained in
turbulent flow is decomposed into different parts and then quantified. A
turbulence stability condition, similar to the principle of the
energy-minimization multi-scale (EMMS) model for gas-solid systems, is
formulated to close the dynamic constraint equations of turbulence, allowing
the heterogeneous structural parameters of turbulence to be optimized. We call
this model the `EMMS-based turbulence model', and use it to construct the
corresponding turbulent viscosity coefficient. To validate the EMMS-based
turbulence model, it is used to simulate two classical benchmark problems,
lid-driven cavity flow and turbulent flow with forced convection in an empty
room. The numerical results show that the EMMS-based turbulence model improves
the accuracy of turbulence modeling due to it considers the principle of
compromise in competition between viscosity and inertia.Comment: 26 pages, 13 figures, 2 table
Holographic entanglement of purification for thermofield double states and thermal quench
We explore the properties of holographic entanglement of purification (EoP)
for two disjoint strips in the Schwarzschild-AdS black brane and the Vaidya-AdS
black brane spacetimes. For two given strips on the same boundary of
Schwarzschild-AdS spacetime, there is an upper bound of the separation beyond
which the holographic EoP will always vanish no matter how wide the strips are.
In the case that two strips are in the two boundaries of the spacetime
respectively, we find that the holographic EoP exists only when the strips are
wide enough. If the width is finite, the EoP can be nonzero in a finite time
region. For thermal quench case, we find that the equilibrium time of
holographic EoP is only sensitive to the width of strips, while that of the
holographic mutual information is sensitive not only to the width of strips but
also to their separation.Comment: 23 pages, 12 figures, major correction of section
Statistics of Flares Sweeping across Sunspots
Flare ribbons are always dynamic, and sometimes sweep across sunspots.
Examining 588 (513 M-class and 75 X-class) flare events observed by Transition
Region and Coronal Explorer (TRACE) satellite and Hinode Solar Optical
Telescope (SOT) from 1998 May to 2009 May, we choose the event displaying that
one of the flare ribbons completely sweeps across the umbra of a main sunspot
of the corresponding active region, and finally obtain 20 (7 X-class and 13
M-class) events as our sample. In each event, we define the main sunspot
completely swept across by the flare ribbon as A-sunspot, and its nearby
opposite polarity sunspots, B-sunspot. Observations show that the A-sunspot is
a following polarity sunspot in 18 events, and displays flux emergence in 13
cases. All the B-sunspots are relatively simple, exhibiting either one main
sunspot or one main sunspot and several small neighboring sunspots (pores). In
two days prior to the flare occurrence, the A-sunspot rotates in all the cases,
while the B-sunspot, in 19 events. The total rotating angle of the A-sunspot
and B-sunspot is 193 degrees on average, and the rotating directions, are the
same in 12 events. In all cases, the A-sunspot and B-sunspot manifest shear
motions with an average shearing angle of 28.5 degrees, and in 14 cases, the
shearing direction is opposite to the rotating direction of the A-sunspot. We
suggest that the emergence, the rotation and the shear motions of the A-sunspot
and B-sunspot result in the phenomenon that flare ribbons sweep across sunspots
completely.Comment: 12 pages, 3 figures, 2 tables, accepted by ApJ Letter
Probing signatures of bounce inflation with current observations
The aim of this paper is to probe the features of the bouncing cosmology with
the current observational data. Basing on bounce inflation model, with high
derivative term, we propose a general parametrization of primordial power
spectrum which includes the typical bouncing parameters, such as bouncing
time-scale, and energy scale. By applying Markov Chain Monto Carlo analysis
with current data combination of Planck 2015, BAO and JLA, we report the
posterior probability distributions of the parameters. We find that, bouncing
models can well explain CMB observations, especially the deficit and
oscillation on large scale in TT power spectrum.Comment: 17 pages, 8 figure
An Open Source Testing Tool for Evaluating Handwriting Input Methods
This paper presents an open source tool for testing the recognition accuracy
of Chinese handwriting input methods. The tool consists of two modules, namely
the PC and Android mobile client. The PC client reads handwritten samples in
the computer, and transfers them individually to the Android client in
accordance with the socket communication protocol. After the Android client
receives the data, it simulates the handwriting on screen of client device, and
triggers the corresponding handwriting recognition method. The recognition
accuracy is recorded by the Android client. We present the design principles
and describe the implementation of the test platform. We construct several test
datasets for evaluating different handwriting recognition systems, and conduct
an objective and comprehensive test using six Chinese handwriting input methods
with five datasets. The test results for the recognition accuracy are then
compared and analyzed.Comment: 5 pages, 3 figures, 11 tables. Accepted to appear at ICDAR 201
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