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Local Smooth Solutions to the 3-Dimensional Isentropic Relativistic Euler equations

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Chinese Annals of Mathematics,Series B 2014年第2期35卷 301-318页

作者： Yongcai GENG yachun li School of Science Shanghai Institute of Technology Department of Mathematics Shanghai Jiao Tong University

The authors consider the local smooth solutions to the isentropic relativistic Euler equations in(3+1)-dimensional space-time for both non-vacuum and vacuum *** local existence is proved by symmetrizing the system and applying the FriedrichsLax-Kato theory of symmetric hyperbolic *** the non-vacuum case,according to Godunov,firstly a strictly convex entropy function is solved out,then a suitable symmetrizer to symmetrize the system is *** the vacuum case,since the coefficient matrix blows-up near the vacuum,the authors use another symmetrization which is based on the generalized Riemann invariants and the normalized velocity.

关键词： Isentropic relativistic Euler equations local-in-time smooth solutions Strictly convex entropy Generalized Riemann invariants

GLOBAL STABIliTY OF SOLUTIONS WITH DISCONTINUOUS INITIAL DATA CONTAINING VACUUM STATES FOR THE RELATIVISTIC EULER EQUATIONS

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Chinese Annals of Mathematics,Series B 2005年第4期26卷 491-510页

作者： li yachun WANG liBO Department of Mathematics Shanghai Jiao Tong University Shanghai 200240 China.

The global stability of lipschitz continuous solutions with discontinuous initial data for the relativistic Euler equations is established in a broad class of entropy solutions in L∞ containing vacuum states. As a corollary, the uniqueness of lipschitz solutions with discontinuous initial data is obtained in the broad class of entropy solutions in L∞.

关键词： Relativistic Euler equations Entropy solutions Vacuum Uniqueness Global stability

Applications of the Kinetic Formulation for Scalar Conservation Laws with a Zero-Flux Type Boundary Condition

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Chinese Annals of Mathematics,Series B 2012年第3期33卷 351-366页

作者： Zhigang WANG yachun li Department of Mathematics Shanghai Jiao Tong UniversityShanghai 200240China Department of Mathematics Fuyang Teachers CollegeFuyang 236029AnhuiChina Department of Mathematics Shanghai Jiao Tong UniversityShanghai 200240China

The authors are concerned with a zero-flux type initial boundary value problem for scalar conservation ***,a kinetic formulation of entropy solutions is ***,by using the kinetic formulation and kinetic techniques,the uniqueness of entropy solutions is ***,the parabolic approximation is studied and an error estimate of order η 1/3 between the entropy solution and the viscous approximate solutions is established by using kinetic techniques,where η is the size of artificial viscosity.

关键词： Scalar conservation laws Entropy solutions Kinetic formulation Uniaueness Error estimate

Global Entropy Solutions of the Cauchy Problem for Nonhomogeneous Relativistic Euler System

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Chinese Annals of Mathematics,Series B 2006年第5期27卷 473-494页

作者： yachun li Anjiao WANG Department of Mathematics Shanghai Jiao Tong University Shanghai 200240 China

We analyze the 2 × 2 nonhomogeneous relativistic Euler equations for perfect fluids in special relativity. We impose appropriate conditions on the lower order source terms and establish the existence of global entrop... 详细信息

关键词： Relativistic Euler system Entropy solutions Riemann solutions Glimm scheme

First Look of Surface Vegetation from the Advanced Geostationary Radiation Imager(AGRI) onboard Fengyun-4B

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Journal of Meteorological Research 2023年第4期37卷 536-550页

作者： Shengqi li Xiuzhen HAN Yeping ZHANG yachun li Nanjing University of Information Science&Technology Nanjing 210044 National Satellite Meteorological Centre China Meteorological AdministrationBeijing 100081 Jiangsu Climate Centre Jiangsu Provincial Meteorological ServiceNanjing 210009

For many years, the status of surface vegetation has been monitored by using polar-orbiting satellite imagers such as Moderate Resolution Imaging Spectroradiometer(MODIS). However, limited availability of clear-sky samples makes the derived vegetation index dependent on multiple days of observations. High-frequency observations from the geostationary Fengyun(FY) satellites can significantly reduce the influence of clouds on the synthesis of terrestrial normalized difference vegetation index(NDVI). In this study, we derived the land surface vegetation index based on observational data from the Advanced Geostationary Radiation Imager(AGRI) onboard the FY-4B geostationary satellite. First, the AGRI reflectance of visible band and near-infrared band is corrected to the land surface reflectance by the 6S radiative transfer model. The bidirectional reflectance distribution function(BRDF) model is then used to normalize the AGRI surface reflectance at different observation angles and solar geometries, and an angle-independent reflectance is derived. The AGRI surface reflectance is further corrected to the MODIS levels according to the AGRI spectral response function(SRF). Finally, the daily AGRI data are used to synthesize the surface vegetation index. It is shown that the spatial distribution of NDVI images retrieved by single-day AGRI is consistent with that of 16-day MODIS data. At the same time, the dynamic range of the revised NDVI is closer to that of MODIS.

关键词： atmospheric correction normalized difference vegetation index(NDVI) spectral response function(SRF) bidirectional reflectance distribution function(BRDF)

Estimation of Chlorophyll-a Concentration in Lake Taihu from Gaofen-1 Wide-Field-of-View Data through a Machine Learning Trained Algorithm

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Journal of Meteorological Research 2022年第1期36卷 208-226页

作者： Xin HANG yachun li Xinyi li Meng XU liangxiao SUN Jiangsu Climate Center Jiangsu Meteorological BureauNanjing 210008 Nanjing Joint Institute for Atmospheric Sciences Nanjing 210009

Wide-field-of-view(WFV) imager that observes the earth environment with four solar reflective bands in a spatial resolution of 16 m is equipped on board Gaofen-1(GF-1) satellite. Chlorophyll-a(Chl-a) concentration in Lake Taihu, China from 2018 to 2019 is collected and collocated with GF-1 satellite data. This study develops a general and reliable estimation of Chl-a concentration from GF-1 WFV data under turbid inland water conditions. The collocated data are classified according to season and used in random forest(RF) regression to train models for retrieving the lake Chl-a concentration. A composite index is developed to select the most important variables in the models. The models trained for each season show a better performance than the model trained by using the whole year data in terms of the coefficient of determination(R^(2)) between retrievals and observations. Specifically, the R2 values in spring, summer, autumn, and winter are 0.88, 0.88, 0.94, and 0.74, respectively;whereas that using the whole year data is only 0.71. The Chl-a concentration in Lake Taihu exhibits an obvious seasonal change with the highest in summer, followed by autumn and spring, and the lowest in winter. The Chl-a concentration also displays an obvious spatial variation with season. A high concentration occurs mainly in the northwest of the lake. The temporal and spatial changes of Chl-a concentration are almost consistent with the changes in the areas and times of cyanobacteria blooms based on Moderate Resolution Imaging Spectroradiometer(MODIS) data. The proposed algorithm can be operated without a priori knowledge on atmospheric conditions and water quality. Our study also demonstrates that GF-1 data are increasingly valuable for monitoring the Chl-a concentration of inland water bodies in China at a high spatial resolution.

关键词： chlorophyll-a concentration Gaofen-1(GF-1) wide-field-of-view random forest algorithm Lake Taihu

Approximations to Isentropic Planar Magneto-Hydrodynamics Equations by Relaxed Euler-Type Systems

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Chinese Annals of Mathematics,Series B 2024年第3期45卷 413-440页

作者： yachun li Zhaoyang SHANG Chenmu WANG liang ZHAO School of Mathematical Sciences CMA-ShanghaiMOE-LSC and SHL-MACShanghai Jiao Tong UniversityShanghai 200240China School of Finance Shanghai Lixin University of Accounting and FinanceShanghai 201209China School of Mathematical Sciences Shanghai Jiao Tong UniversityShanghai 200240China School of Mathematical Sciences Harbin Engineering UniversityHarbin 150001China Mathematical Modelling&Data Analytics Center Oxford Suzhou Centre for Advanced ResearchSuzhou 215123JiangsuChina

In this paper, the authors consider an approximation to the isentropic planar Magneto-hydrodynamics(MHD for short) equations by a kind of relaxed Euler-type system. The approximation is based on the generalization of the Maxwell law for nonNewtonian fluids together with the Maxwell correction for the Ampe`re law, hence the approximate system becomes a first-order quasilinear symmetrizable hyperbolic systems with partial dissipation. They establish the global-in-time smooth solutions to the approximate Euler-type equations in a small neighbourhood of constant equilibrium states and obtain the global-in-time convergence towards the isentropic planar MHD equations. In addition, they also establish the global-in-time error estimates of the limit based on stream function techniques and energy estimates for error variables.

关键词： Planar MHD equations Relaxation limits Global convergence Stream function

Advances in Ecological Applications of Fengyun Satellite Data

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Journal of Meteorological Research 2021年第5期35卷 743-758页

作者： Xiuzhen HAN Hao GAO Jun YANG yachun li Weicheng GENG National Satellite Meteorological Center China Meteorological AdministrationBeijing 100081 Jiangsu Climate Center Jiangsu Provincial Meteorological BureauNanjing 210008

In recent years,the remote sensing based on meteorological satellite observations has become an important tool for assessing global ecological *** the early 2000,Fengyun(FY)satellite data have been widely used to derive the key parameters of ecological environment in *** integrated earth-observation system has been developed in China through using FY satellite data,including retrievals the key ecological parameters as well as to constructions of long-term data records of vegetation index,land surface temperature,net primary production,vegetation health index,and so *** progress has thus been made in the application and service for prevention of air pollution,management and control of ecological redline,ecological monitoring for the Belt and Road Initiative,and assessment of ecological environment for human *** order to monitor the ecological parameters in real time and with a full dynamic coverage,it is necessary to improve the technology in application of ecological remote sensing from meteorological satellites,and further enhance the ecological meteorological service.

关键词： Fengyun satellite ecological environment remote sensing assessing and monitoring operational service

Assessing the Ecological Quality of Nanjing during Its Urbanization Process by Using Satellite,Meteorological,and Socioeconomic Data

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Journal of Meteorological Research 2020年第2期34卷 280-293页

作者： Xin HANG yachun li Xiaochun LUO Min XU Xiuzhen HAN Jiangsu Climate Center Jiangsu Meteorological BureauNanjing 210008 Jiangsu Meteorological Service Center Jiangsu Meteorological BureauNanjing 210008 National Satellite Meteorological Center China Meteorological AdministrationBeijing 100081

Assessing the ecological status of different districts within a city undergoing urbanization is challenging given their complex surface types and fast pace of *** this study,we utilized satellite data obtained from Landsat5/TM(Thematic Mapper)and Landsat 8/Oli(Operational Land Imager)images in conjunction with meteorological and socioeconomic data to construct a remote sensing ecological index(RSEI)for monitoring the ecological quality of Nanjing,Jiangsu Province.A higher RSEI value corresponded to better ecological *** ratings were associated with RSEI values of city districts:very poor,poor,average,good,and *** Nanjing,the percentage of areas evidencing good RSEI ratings decreased from 55.9%in 2000 to 48.0%in 2018,whereas there was a slight increase in areas with very poor RSEI ratings during this *** the 11 city districts,16.8%,21.8%,and 61.4%respectively evidenced the increasing,decreasing,and stable ecological quality relative to their quality in *** the11 administrative districts in Nanjing,the main urban districts evidenced increased RSEI values in 2018 compared with those in 2000,with the improved areas exceeding the ones that had deteriorated in these ***,the ecological quality of new urban and ed because of the urban expansion,with areas that had deteriorated exceeding the improved *** the three protected ecological zones,the quality of Zijin Mountain National Forest Park was considerably better than that of Laoshan and ***,the urbanization rate and RSEI evidenced a high negative correlation coefficient value(-0.76).The urbanization process of Nanjing induced a declining trend for the ecological quality,indicating the need of strong protection measures for the maintenance or improvement of its ecological environment.

关键词： ecological quality remote sensing ecological index(RSEI) urbanization