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The spatial relationship between salt marsh vegetation patterns,soil elevation and tidal channels using remote sensing at Chongming Dongtan Nature Reserve, China

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Acta Oceanologica Sinica 2016年第4期35卷 26-34页

作者： ZHENG Zongsheng zhou yunxuan TIAN Bo DING Xianwen State Key Laboratory of Estuarine and Coastal Research East China Normal University International Center for Marine Studies Shanghai Ocean University

The analysis of vegetation-environment relationships has always been a study hotspot in ecology. A number of biotic, hydrologic and edaphic factors have great influence on the distribution of macrophytes within salt *** the exotic species Spartina alterniflora（S. alterniflora） was introduced in 1995, a rapid expansion has occurred at Chongming Dongtan Nature Reserve（CDNR） in the Changjiang（Yangtze） River Estuary, *** important vegetation-environment factors including soil elevation, tidal channels density（TCD）,vegetation classification and fractional vegetation cover（FVC） were extracted by remote sensing method combined with field measurement. To ignore the details in interaction between biological and physical process,the relationship between them was discussed at a large scale of the whole saltmarsh. The results showed that Scirpus mariqueter（S. mariqueter） can endure the greatest elevation variance with 0.33 m throughout the marsh in CDNR. But it is dominant in the area less than 2.5 m with the occurrence frequency reaching 98%. S. alterniflora has usually been found on the most elevated soils higher than 3.5 m but has a narrow spatial distribution. The rapid decrease of S. mariqueter can be explained by stronger competitive capacity of S. alterniflora on the high tidal flat. FVC increases with elevation which shows significant correlation with elevation（r=0.30, p〈0.001）. But the frequency distribution of FVC indicates that vegetation is not well developed on both elevated banks near tidal channels from the whole scale mainly due to tidal channel lateral swing and human activities. The significant negative correlation（r=–0.20, p〈0.001） was found between FVC and TCD, which shows vegetation is restricted to grow in higher TCD area corresponding to lower elevation mainly occupied by S. mariqueter communities. The maximum occurrence frequency of this species reaches to 97% at the salt marsh with TCD more than 8 m/m2.

关键词： remote sensing vegetation patterns Chongming Dongtan Nature Reserve salt marshes environmental factors

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A new Doppler frequency anomaly algorithm for surface current measurement with SAR

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Journal of Oceanology and Limnology 2022年第2期40卷 470-484页

作者： Lihua WANG Yanghua GAO Peng LU Li FAN yunxuan zhou Department of Geography and Spatial Information Techniques Center for Land and Marine Spatial Utilization and Governance ResearchNingbo UniversityNingbo 315211China Institute of East China Sea Ningbo UniversityNingbo 315211China Chongqing Institute of Meteorological Sciences Chongqing 401147China College of Geo-Exploration Science and Technology Jilin UniversityChangchun 130026China State Key Laboratory of Estuarine and Coastal Research East China Normal UniversityShanghai 200062China

Values for Doppler center frequency are calculated from the echo signal at the satellite using the Doppler centroid method and so include the predicted Doppler frequency caused by the relative motion of the satellite and the Earth,which is the main component of Doppler center frequency and must be removed to obtain the Doppler frequency anomaly for ocean current *** this paper,a new Doppler frequency anomaly algorithm was proposed when measuring surface currents with synthetic aperture radar(SAR).The key of the proposed algorithm involved mean filtering method in the range direction and linear fitting in the azimuth direction to remove the radial and the azimuthal component of predicted Doppler frequency from the Doppler center frequency,*** basis is that the theoretical Doppler center frequency model of SAR exhibits an approximately linear characteristic in both the range direction and in the azimuth *** the help of the new algorithm for predicted Doppler frequency removal,the estimation error of Doppler frequency anomaly can be reduced by avoiding employing the theoretical antenna pattern and imperfect satellite attitude parameters in the conventional Doppler frequency *** measurement results demonstrated that,compared to the conventional Doppler frequency with/without error correction method,the proposed algorithm allows for a pronounced improvement in the current measuring accuracy in comparison with the global ocean multi-observation(MOB)*** addition,the eff ectiveness and robustness of the proposed Doppler algorithm has been demonstrated by its application in the high velocity current in the Kuroshio region.

关键词： synthetic aperture radar(SAR) Doppler frequency Doppler frequency anomaly current retrieval ocean surface currents

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Mapping sea surface velocities in the Changjiang coastal zone with advanced synthetic aperture radar

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Acta Oceanologica Sinica 2014年第11期33卷 141-149页

作者： WANG Lihua zhou yunxuan GE Jianzhong JOHANNESSEN Johnny A. SHEN Fang State Key Laboratory of Estuarine and Coastal Research East China Normal University Nansen Environmental and Remote Sensing Center Geophysical Institute University of Bergen

Range Doppler velocities derived from the Envisat advanced synthetic aperture radar（ASAR） wide swath images are analyzed and assessed against the numerically simulated surface current fields derived from the finite volume coastal ocean model（FVCOM） for the Changjiang Estuary. Comparisons with the FVCOM simulations show that the European Space Agency（ESA） Envisat ASAR based Doppler shift anomaly retrievals have the capability to capture quantitative information of the surface currents in the Changjiang Estuary. The uncertainty analysis of the ASAR range Doppler velocity estimates are discussed with regard to the azimuthal and range bias corrections, radar incidence angles, inaccuracy in the wind field corrections and the presence of rain *** corrected range Doppler velocities for the Changjiang Estuary area are highly valuable as they exhibit quantitative expressions related to the multiscale upper layer dynamics and surface current variability around the East China Sea, including the Changjiang Estuary.

关键词： advanced synthetic aperture radar Changjiang coast Doppler centroid anomaly range Doppler velocity finite volume coastal ocean model

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Probing the Structural Stability, Mechanical, Electronic, and Thermodynamic Properties of Mg-Y-Zn Ternary Compounds via First-Principles Calculations

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Acta Metallurgica Sinica(English Letters) 2024年第10期37卷 1703-1720页

作者： Wenjun Tian yunxuan zhou Tao Deng Tao Chen Jun Tan Xianhua Chen Fusheng Pan National Engineering Research Center for Magnesium Alloys College of Materials Science and EngineeringChongqing UniversityChongqing400044China Lanxi Magnesium Materials Research Institute Lanxi321100China National Key Laboratory of Advanced Casting Technologies Chongqing UniversityChongqing400044China

Magnesium alloys have large reserves and good strength,attracting a lot of ***,the thermodynamic,elastic constants,and electronic properties of the Mg-Y-Zn ternary compounds were calculated;among them,MgYZn_(2) belongs to the cubic structure,MgYZn,Mg_(3)Y_(2)Zn_(4),and Mg_(14)YZn-1 belong to the hexagonal structure,Mg_(6)YZn-1,Mg_(6)YZn-2,MgY_(2)Zn,and Mg_(14)YZn-2 possess the orthorhombic structure,and Mg_(3)Y_(2)Zn_(3) is trigonal *** calculated cohesive energies of the results show that all compounds are thermodynamically ***,the MgYZn_(2) compound exhibits the highest modulus of 76.84 MPa,and the Mg_(3)Y_(2)Zn_(3) has the biggest hardness of 6.6 *** addition,the Mg_(6)YZn-2 has the strongest elastic anisotropic with A^(U) of 6.14 and A_(G) of 0.38,*** to the population analysis,the Mg-Y covalent bond is due to the biggest bond *** shortest weighted average bond length indicates that MgYZn_(2) has better elastic ***,the calculated limiting thermal conductivity results show that Mg_(14)YZn-2 has better thermal conductivity with maximum values of 0.94 W·m^(−1)·K^(−1) and 0.74 W·m^(−1)·K^(−1) for Clarke’s and Cahill’s models.

关键词： Magnesium alloys First-principles calculations Elastic properties Electronic properties Thermodynamic properties

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Vegetation dynamics in response to human and climatic factors in the Tanzanian Coast

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Frontiers of Earth Science 2021年第3期15卷 595-605页

作者： Herrieth MACHIWA Bo TIAN Dhritiraj SENGUPTA Qian CHEN Michael MEADOWS yunxuan zhou State Key Laboratory of Estuarine and Coastal Research East China Normal UniversityShanghai 200241China University of Dar es Salaam College of Information and Communication TechnologiesDepartment of Computer Science and EngineeringDar es Salaam 33335Tanzania Key Laboratory of Geographic Information Science(Ministry of Education) School of Geographical SciencesEast China Normal UniversityShanghai 200241China Department of Environmental&Geographical Sciences University of Cape TownRondebosch 7701South Africa College of Geography and Environmental Sciences Zhejiang Normal UniversityJinhua 321004China

This study of vegetation dynamics in the coastal region of Tanzania provides a fundamental basis to better understand the nature of the factors that underlie observed *** Tanzanian coast,rich in biodiversity,is economically and environmentally important although the understanding of the nature and causes of vegetation change is very *** paper presents an investigation of the relationship between vegetation dynamics in response to climate variations and human activities using Moderate Resolution Imaging Spectro-radiometer(MODIS),Normalized Difference Vegetation Index(NDVI),meteorological,and Globeland30 Landsat data ***-temporal trends and the relationship of NDVI to selected meteorological variables were statistically analyzed for the period 2000-2018 using the Mann-Kendall test and Pearson correlation *** results reveal a significant positive trend in temperature(/?>0,Z=2.87)and a non-significant trend in precipitation(|Z|<1.96).A positive relationship between NDVI and precipitation is *** Tanzania has therefore experienced increased temperatures and variable moisture conditions which threaten natural vegetation and ecosystems at *** land cover maps obtained from GlobeLand30 were analyzed to identify the nature and scale of human impact on the *** analysis of land use and land cover in the region reveals an increase in cultivated land,shrubland,grassland,built-up land and bare land,while forests,wetland and water all decreased between 2000 and *** decrease in forest vegetation is attributable to the fact that most livelihoods in the region are dependent on agriculture and harvesting of forest products(firewood,timber,charcoal).The findings of this study highlight the need for appropriate land-use planning and sustainable utilization of forest resources.

关键词： remote sensing NDVI climate variations spatio-temporal changes LULCC coastal Tanzania

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Radial velocity of ocean surface current estimated from SAR Doppler frequency measurements—a case study of Kuroshio in the East China Sea

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Acta Oceanologica Sinica 2021年第12期40卷 135-147页

作者： Lihua Wang Benwei Shi yunxuan zhou Hui Sheng Yanghua Gao Li Fan Ziheng Yang Department of Geography and Spatial Information Techniques/Center for Land and Marine Spatial Utilization and Governance Research Ningbo UniversityNingbo 315211China State Key Laboratory of Estuarine and Coastal Research East China Normal UniversityShanghai 200062China Chongqing Institute of Meteorological Sciences Chongqing 401147China College of Resources and Environment Chengdu University of Information TechnologyChengdu 610225China

Ocean currents are a key element in ocean processes and in meteorology,affecting material transport and modulating climate change *** Doppler frequency shift information of the synthetic aperture radar(SAR)echo signal can reflect the dynamic characteristics of the sea surface,and has become an essential sea surface dynamic remote sensing *** have verified that the instantaneous Doppler frequency shift can realize the SAR detection of the sea surface ***,the validation of SAR-derived ocean current data and a thorough analysis of the errors associated with them remain *** this study,we derive high spatial resolution flow measurements for the Kuroshio in the East China Sea from SAR data using a theoretical model of shifts in Doppler frequency driven by ocean surface *** ocean multi observation(MOB)products and global surface Lagrangian drifter(GLD)data are used to validate the Kuroshio flow retrieved from the SAR *** show that the central flow velocity for the Kuroshio derived from the SAR is 0.4–1.5 m/*** error distribution between SAR ocean currents and MOB products is an approximate standard normal distribution,with the 90%confidence interval concentrated between–0.1 m/s and 0.1 m/*** analysis of SAR ocean current and GLD products,the correlation coefficient is 0.803,which shows to be significant at a confidence level of 99%.The cross-validation of different ocean current dataset illustrate that the SAR radial current captures the positions and dynamics of the Kuroshio central flow and the Kuroshio Counter Current,and has the capability to monitor current velocity over a wide range of values.

关键词： Doppler frequency radial velocity ocean current SAR Kuroshio

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A First-principles Study on the Adhesion Strength,Interfacial Stability,and Electronic Properties of Mg/Mg_(2)Y Interface

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Acta Metallurgica Sinica(English Letters) 2024年第3期37卷 537-550页

作者： yunxuan zhou Wenjun Tian Quan Dong Hailian Wang Jun Tan Xianhua Chen Kaihong Zheng Fusheng Pan College of Materials Science and Engineering National Engineering Research Center for Magnesium AlloysChongqing UniversityChongqing 400044China State Key Laboratory of Mechanical Transmission Chongqing UniversityChongqing 400044China Institute of New Materials Guangdong Academy of SciencesGuangzhou 510650China

The interfacial microstructures and configurations directly affect the comprehensive properties of the composites,but their interfacial adhesion mechanism is complicated to expound by experimental *** this work,based on the stacking sequence of the Mg/Mg_(2)Y interface models,nine different Mg/Mg_(2)Y interface configurations with top site,bridge site,and hollow site(HCP)under Mg1,Mg_(2),and Y terminations were successfully constructed and systematically explored by first-principles *** results showed that the Mg_(2)Y(0001)surface with Y termination is the most stable when the yttrium chemical potential()is less than-1.09 eV;otherwise,Mg_(2)Y(0001)surface with Mg1 termination is the most *** seven-layer Mg(0001)and eleven-layer Mg_(2)Y(0001)slabs are employed to reflect the bulk-like interior ***,the Mg(0001)/Mg_(2)Y(0001)with the Y-HCP stacking has the largest interface thermodynamic stability with the value of 2.383 J/m^(2) in all interface configurations owing to its largest work of *** addition,the interfacial energy of Y-HCP stacking is significantly smaller than those of Mg1-HCP when is approximately less than-0.55 eV,showing that it is more *** thermodynamic stability of Mg/Mg_(2)Y with Y-HCP is due to Mg-Y chemical bonds formed between Mg and Y ***,the Mg/Mg_(2)Y interfaces are strong interfaces based on the Griffith fracture theory.

关键词： Mg/Mg_(2)Y interface Interface stability Work of adhesion Electronic structure First-principles calculations

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Recent advancements in thermal conductivity of magnesium alloys

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Journal of Magnesium and Alloys 2024年第5期12卷 1687-1708页

作者： Hao Lv Jun Tan Qian Yuan Fanglei Wang yunxuan zhou Quan Dong Aitao Tang Jürgen Eckert Bin Jiang Fusheng Pan National Engineering Research Center for Magnesium Alloys College of Materials Science and EngineeringChongqing UniversityChongqing 400044China National Key Laboratory of Advanced Casting Technologies Chongqing UniversityChongqing 400044China Department of Materials Science Chair of Materials PhysicsMontanuniversität LeobenJahnstraße 12Leoben A-8700Austria Erich Schmid Institute of Materials Science Austrian Academy of SciencesJahnstraße 12Leoben A-8700Austria

As highly integrated circuits continue to advance,accompanied by a growing demand for energy efficiency and weight reduction,materials are confronted with mounting challenges pertaining to thermal conductivity and lightweight *** virtue of numerous intrinsic mechanisms,as a result,the thermal conductivity and mechanical properties of the Mg alloys are often inversely related,which becomes a bottleneck limiting the application of Mg *** on several effective modification methods to improve the thermal conductivity of Mg alloys,this paper describes the law of how they affect the mechanical properties,and clearly indicates that peak aging treatment is one of the best ways to simultaneously enhance an alloy's thermal conductivity and mechanical *** the most frequently used Mg alloy,cast alloys exhibit substantial potential for achieving high thermal ***,recent reports indicate that hot deformation can significantly improve the mechanical properties while maintaining,and potentially slightly enhancing,the alloy's thermal *** presents a meaningful way to develop Mg alloys for applications in the field of small-volume heat dissipation components that require high *** comprehensive review begins by outlining standard testing and prediction methods,followed by the theoretical models used to predict thermal conductivity,and then explores the primary influencing factors affecting thermal *** review summarizes the current development status of Mg alloys,focusing on the quest for alloys that offer both high thermal conductivity and high *** concludes by providing insights into forthcoming prospects and challenges within this field.

关键词： Mg alloy Thermal conductivity Mechanical properties Solute atom Second phase

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A Review of Mineral Resources and GIS Applications in Mineral Resource Assessment in Northeast China

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Global Geology 2000年第2期5卷 169-180页

作者： zhou yunxuan Wang Lei Liu Wansong Xu Huiping Sun Fengyue Changchun Institute of Geography Chinese Academy of Sciences Changchun 130021 P. R. China College of GeoExploration and Information Technology Jilin University Changchun 130026 P. R. China College of GeoExploration and Information Technology Jilin University Changchun 130026 P. R. China College of Earth Sciences Jilin University Changchun 130061 P. R. China

Northeast China is one of the regions in China that possesses a great abundance of mineral resources. Coal. petroleum, natural gas, gold, iron, magnesite, graphite, talc, molding sand, glass sand and some others account for large portion in reserves and yields of that in the whole country. The region faced also shortages of copper, molybdenum, oil shale, zirconium, tantalum, rare earth, and beryllium, although they have large reserves, but limited by economical and technical factors. Geological mapping and mineral exploration activities have been intensive. Only the north part of Daxinanling Mountains in the region leaves unexplored. GIS applications in mineral resource assessment in the region start not long. Databases for GIS applications are on the way of construction. Well - trained technical staff and expertise do not meet the demand. This article reviews the situation of mineral resources and GIS applications for mineral resource assessment in the region. Suggestions on multi - lateral cooperation and GIS training are also made.

关键词： Northeast China Mineral resources Assessment Geographic information Systems (GIS)

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大通站水沙关系演变驱动因素分析

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吉林大学学报（地球科学版） 2018年第1期48卷 226-233页

作者：王利花周云轩成都信息工程大学资源环境学院成都610225 华东师范大学河口海岸学国家重点实验室上海200062

大通水文站是长江进入河口的第一个关键界面,其水沙关系的变化不但直接影响河流本身的发展演变,也影响着河口三角洲的发育过程。深入研究大通站水沙关系的驱动因素,有助于更好地认识长江流域的输沙规律,可为流域地貌演变和对人类活动响... 详细信息

大通水文站是长江进入河口的第一个关键界面,其水沙关系的变化不但直接影响河流本身的发展演变,也影响着河口三角洲的发育过程。深入研究大通站水沙关系的驱动因素,有助于更好地认识长江流域的输沙规律,可为流域地貌演变和对人类活动响应的深入研究提供科学依据。本文基于数理统计方法,重点从降水变化、径流变化、水利水土工程等方面定性定量地研究了气候变化和人类活动对大通站水沙演变过程的影响,结果表明:1954—2000年间降水量和输沙量变化特征较为一致,说明气候变化在一定程度上影响着大通站泥沙输移的变化过程,其更多地体现在对泥沙输移长期性变化的影响方面;2001—2010年输沙量急剧下降,大型水利工程的实施等人类活动对泥沙输移的影响是近10年来大通站入海泥沙急剧变化的直接诱因和主要原因,其主要体现在短时间尺度上。

关键词：大通站水沙降水水利工程气候变化人类活动

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