190 research outputs found
Stability of rotating gaseous stars
We consider stability of rotating gaseous stars modeled by the Euler-Poisson
system with general equation of states. When the angular velocity of the star
is Rayleigh stable, we proved a sharp stability criterion for axi-symmetric
perturbations. We also obtained estimates for the number of unstable modes and
exponential trichotomy for the linearized Euler-Poisson system. By using this
stability criterion, we proved that for a family of slowly rotating stars
parameterized by the center density with fixed angular velocity profile, the
turning point principle is not true. That is, unlike the case of non-rotating
stars, the change of stability of the rotating stars does not occur at extrema
points of the total mass. By contrast, we proved that the turning point
principle is true for the family of slowly rotating stars with fixed angular
momentum distribution. When the angular velocity is Rayleigh unstable, we
proved linear instability of rotating stars. Moreover, we gave a complete
description of the spectra and sharp growth estimates for the linearized
Euler-Poisson equation.Comment: Minor corrections of typo
Nonlinear stability of non-rotating gaseous stars
For the non-rotating gaseous stars modeled by the compressible Euler-Poisson
system with general pressure law, Lin and Zeng [18] proved a turning point
principle, which gives the sharp linear stability/instability criteria for the
non-rotating gaseous stars. In this paper, we prove that the sharp linear
stability criterion for the non-rotating stars also implies nonlinear orbital
stability against general perturbations provided the global weak solutions
exist. If the perturbations are further restricted to be spherically symmetric,
then nonlinear stability holds true unconditionally in the sense that the
existence of global weak solutions near the non-rotating star can be proved.Comment: 30 page
The DKU-DukeECE Diarization System for the VoxCeleb Speaker Recognition Challenge 2022
This paper discribes the DKU-DukeECE submission to the 4th track of the
VoxCeleb Speaker Recognition Challenge 2022 (VoxSRC-22). Our system contains a
fused voice activity detection model, a clustering-based diarization model, and
a target-speaker voice activity detection-based overlap detection model.
Overall, the submitted system is similar to our previous year's system in
VoxSRC-21. The difference is that we use a much better speaker embedding and a
fused voice activity detection, which significantly improves the performance.
Finally, we fuse 4 different systems using DOVER-lap and achieve 4.75 of the
diarization error rate, which ranks the 1st place in track 4.Comment: arXiv admin note: substantial text overlap with arXiv:2109.0200
GraphPrompt: Biomedical Entity Normalization Using Graph-based Prompt Templates
Biomedical entity normalization unifies the language across biomedical
experiments and studies, and further enables us to obtain a holistic view of
life sciences. Current approaches mainly study the normalization of more
standardized entities such as diseases and drugs, while disregarding the more
ambiguous but crucial entities such as pathways, functions and cell types,
hindering their real-world applications. To achieve biomedical entity
normalization on these under-explored entities, we first introduce an
expert-curated dataset OBO-syn encompassing 70 different types of entities and
2 million curated entity-synonym pairs. To utilize the unique graph structure
in this dataset, we propose GraphPrompt, a prompt-based learning approach that
creates prompt templates according to the graphs. GraphPrompt obtained 41.0%
and 29.9% improvement on zero-shot and few-shot settings respectively,
indicating the effectiveness of these graph-based prompt templates. We envision
that our method GraphPrompt and OBO-syn dataset can be broadly applied to
graph-based NLP tasks, and serve as the basis for analyzing diverse and
accumulating biomedical data.Comment: 12 page
Numerical Study of Traffic Pollutant Dispersion within Different Street Canyon Configurations
The objective of this study is to numerically study flow and traffic exhaust dispersion in urban street canyons with different configurations to find out the urban-planning strategies to ease the air pollution. The Computational Fluid Dynamics (CFD) model used in this study-Open Source Field Operation and Manipulation (OpenFOAM) software package-was firstly validated against thewind-tunnel experiment data by using three different k-epsilon. turbulence models. And then the patterns of flow and dispersion within three different kinds of street canyon configuration under the perpendicular approaching flow were numerically studied. The result showed that the width and height of building can dramatically affect the pollution level inside the street canyon. As the width or height of building increases, the pollution at the pedestrian level increases. And the asymmetric configuration (step-up or step-down street canyon) could provide better ventilation. It is recommended to design a street canyon with nonuniform configurations. And the OpenFOAM software package can be used as a reliable tool to study flows and dispersions around buildings.Meteorology & Atmospheric SciencesSCI(E)[email protected]
Numerical Study of the Effects of Topography and Urbanization on the Local Atmospheric Circulations over the Beijing-Tianjin-Hebei, China
The effects of the topography and urbanization on the local atmospheric circulations over the Beijing-Tianjin-Hebei (BTH) region were studied by the weather research and forecasting (WRF) model, as well as the interactions among these local atmospheric circulations. It was found that, in the summer day time, the multiscale thermally induced local atmospheric circulations may exist and interact in the same time over the BTH region; the topography played a role in the strengthening of the sea breeze circulations; after sunset, the inland progress of sea breeze was slowed down by the opposite mountain breeze; when the land breeze circulation dominated the Bohai bay, the mountain breeze circulation can couple with the land breeze circulation to form a large circulation ranging from the coastline to the mountains. And the presence of cities cannot change the general state of the sea-land breeze (SLB) circulation and mountain-valley breeze (MVB) circulation but acted to modify these local circulations slightly. Meanwhile, the development of the urban heat island (UHI) circulation was also strongly influenced by the nearby SLB circulation and MVB circulation
Warming effect of dust aerosols modulated by overlapping clouds below
Due to the substantial warming effect of dust aerosols overlying clouds and its poor representation in climate models, it is imperative to accurately quantify the direct radiative forcing (DRF) of above-cloud dust aerosols. When absorbing aerosol layers are located above clouds, the warming effect of aerosols strongly depends on the cloud macro- and micro-physical properties underneath, such as cloud optical depth and cloud fraction at visible wavelength. A larger aerosol-cloud overlap is believed to cause a larger warming effect of absorbing aerosols, but the influence of overlapping cloud fraction and cloud optical depth remains to be explored. In this study, the impact of overlapping cloud properties on the shortwave all-sky DRF due to springtime above-cloud dust aerosols is quantified over northern Pacific Ocean based on 10-year satellite measurements. On average, the DRF is roughly 0.62 Wm^(−2). Furthermore, the warming effect of dust aerosols linearly increases with both overlapping cloud fraction and cloud optical depth. An increase of 1% in overlapping cloud fraction will amplify this warming effect by 1.11 Wm^(−2)τ^(−1). For the springtime northern Pacific Ocean, top-of-atmosphere cooling by dust aerosols turns into warming when overlapping cloud fraction is beyond 0.20. The variation of critical cloud optical depth beyond which dust aerosols switch from exerting a net cooling to a net warming effect depends on the concurrent overlapping cloud fraction. When the overlapping cloud coverage range increases from 0.2 to –0.4 to 0.6–0.8, the corresponding critical cloud optical depth reduces from 6.92 to 1.16. Our results demonstrate the importance of overlapping cloud properties for determining the springtime warming effect of dust aerosols
Simulating Flow and Dispersion by Using WRF-CFD Coupled Model in a Built-Up Area of Shenyang, China
Results are presented from a series of numerical studies designed to investigate the atmospheric boundary layer structure, ambient wind, and pollutant source location and their impacts on the wind field and pollutant distribution within the built-up areas of Shenyang, China. Two models, namely, Open Source Field Operation and Manipulation (OpenFOAM) software package and Weather Research and Forecasting (WRF) model, are used in the present study. Then the high resolution computational fluid dynamics (CFD) numerical experiments were performed under the typical simulated atmospheric boundary conditions. It was found that the atmospheric boundary structure played a crucial role in the pollution within the building cluster, which determined the potential turbulent diffusion ability of the atmospheric surface layer; the change of the ambient wind direction can significantly affect the dispersion pattern of pollutants, which was a more sensitive factor than the ambient wind speed; under a given atmospheric state, the location of the pollution sources would dramatically determine the pollution patterns within built-up areas. The WRF-CFD numerical evaluation is a reliable method to understand the complicated flow and dispersion within built-up areas
Turning a native or corroded Mg alloy surface into an anti-corrosion coating in excited CO2
Despite their energy-efficient merits as promising light-weight structural materials, magnesium (Mg) based alloys suffer from inadequate corrosion resistance. One primary reason is that the native surface film on Mg formed in air mainly consists of Mg(OH)2 and MgO, which is porous and unprotective, especially in humid environments. Here, we demonstrate an environmentally benign method to grow a protective film on the surface of Mg/Mg alloy samples at room temperature, via a direct reaction of already-existing surface film with excited CO2. Moreover, for samples that have been corroded obviously on surface, the corrosion products can be converted directly to create a new protective surface. Mechanical tests show that compared with untreated samples, the protective layer can elevate the yield stress, suppress plastic instability and prolong compressive strains without peeling off from the metal surface. This environmentally friendly surface treatment method is promising to protect Mg alloys, including those already-corroded on the surface.China. Ministry of Science and Technology. National Key Research and Development Program (No. 2017YFB0702001)National Natural Science Foundation of China (51621063)National Natural Science Foundation of China (51601141)National Natural Science Foundation of China ( 51401239)Shaanxi Sheng (China). Science and Technology Department (2016KTZDGY-04-03)Shaanxi Sheng (China). Science and Technology Department (2016KTZDGY-04-04)China Postdoctoral Science Foundation (2016M600788)China University of Petroleum. Science Foundation (No. 2462018BJC005)China University of Petroleum. Science Foundation (C201603)National Science Foundation (U.S.) (ECCS-1610806
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