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