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Evaluating the accuracy of two satellite-based Quantitative Precipitation Estimation products and their application for meteorological drought monitoring over the Lake Victoria Basin,East Africa

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Geo-Spatial Information Science 2022年第3期25卷 500-518页

作者： Priyanko Das zhenke zhang Hang Ren Center of African Studies Nanjing UniversityNanjingChina and School of Geographic and Oceanographic SciencesNanjing UniversityNanjingChina Center of African Studies Nanjing UniversityNanjingChina and School of Geographic and Oceanographic SciencesNanjing University Nanjing China Institute of Population Studies Nanjing University of Posts and TelecommunicationsNanjingJiangsu provinceChina

This study evaluates the high-resolution satellite estimated long-term precipitation data for monitor-ing the drought condition over the Lake Victoria Basin(LVB)from 1984 to *** Precipitation Indices(SPI)were used to capture the short,medium and long-term meteorological drought conditions at multiple time scales(i.e.3,6,and 12).For these,the following two primaries Quantitative Precipitation Estimation(QPEs)products were employed-1)Climate Hazards group Infra-Red Precipitation with Station(CHIRPS),and 2)the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Network-Climate Data Record(PERSIANN-CDR).This dataset was compared based on the observation data obtained from the Climate Research Unit(CRU)over the nine selected regions surrounding lake *** performance of these two QPEs products was evaluated using seven statistical *** findings of this study indicate that the CHIRPS and PERSIANN-CDR datasets could capture the behavior of drought magnitude based on the time scale of SPI-3,SPI-6,*** results indicate that 2012 and 2017 are significant severe drought years in the recent decade over ***,the CHIRPS datasets provide good agreement(Correlation Coefficient(CC)=0.65)with observation,whereas PERSIANN-CDR present satisfactory results(CC=0.54).In addition,Hurst(H)exponent was used to predict the future drought trend and found that the CHIRPS performed well to predict the degree of drought ***,this study considers the CHIRPS product for near-real-time drought monitoring and PERSIANN-CDR for historical drought ***,the outcome from the H values is greater than 0.5,which indicates the future drought trend would be decreased over *** results are useful for developing the strategies for drought hazards and water resource management in LVB.

关键词： CHIRPS CRU hurst exponent PERSIANN-CDR SPI

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A STUDY OF CRACK CLOSURE IN ELECTRIC-FIELD-INDUCED FATIGUE IN FERROELECTRIC CERAMICS

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Acta Mechanica Solida Sinica 2003年第1期16卷 41-46页

作者： zhang zhenke Fang Daining Tsing Hua Univ Dept Engn Mech Beijing 100084 Peoples R China

Considering the influence of the domain switching near the tip of a crack andapplying the idea of multiscale singularity fields in piezoelectric fracture, we have obtained anempirical criterion for the crack closure. Based on the domain switching in the electric yieldregion, referring to Yang's results on the small scale yield model for the electrical fatigue crack,a model of the crack closure during electric-field-induced fatigue is developed to analyze thecrack growth. In terms of the model we have obtained the formula of the rate of the crack growthunder cyclic electric loading. Finally we compare the theoretical predictions with the results givenby Cao and Evans experimentally. It should be pointed out that the model proposed is empirical andneeds to be verified by more experimental results.

关键词： electric fatigue crack closure domain switching

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Sedimentation and morphological changes at Yuantuojiao Point, estuary of the North Branch, Changjiang River

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Acta Oceanologica Sinica 2013年第2期32卷 24-34页

作者： XIE Li zhang zhenke zhang Yunfeng WANG Yaping HUANG Xianjin School of Geographic and Oceanographic Sciences Key Laboratory of Coast and Island Development of MOENanjing University School of Resources and Environment of Guangdong University of Business Studies

The North Branch, separated by the Chongming Island, was once the main channel in the estuary of the Changjiang River. Reclamation and a decrease in runoffto the North Branch had led to the narrowing and shallowing of the channel. The Yuantuojiao Point is located at the intersecting point connecting the North Branch of the Changjiang River and the Jiangsu coastline. Erosion cliffs are developed between the typical silty-muddy tidal flat and the salt marsh occupied by Spartina alterniflorea, and this has changed rapidly over the past few years. The sediment grain size analysis results of the surficial and two core samples indi- cate that the Yuantuoiiao Point tidal fiat experienced continuous accretional processes. Based upon 137Cs analysis results of the YT and YY Cores sampled from the tidal flat at the Yuantuojiao Point, the average sed- imentation rate of the YT Core was 2.30 cm/a from 1963 to 2007, and 2.38 cm/a from 1954 to 2007 for the YY Core. The sedimentation rates of both core locations have declined since the 1960s corresponding to the seaward reclamation at the Yuantuojiao Point. The average sedimentation rates at the Yuantnojiao Point were similar to that of the silty-muddy tidal flat at the northern ]iangsu coast, but lower than that of the south of the Changjiang River Estuary. According to field morphological investigations from 2006 to 2008 on the salt marsh at the Yuantuojiao Point, cliffs retreated markedly by storm surges and disappeared gradu- ally because of the rapid sedimentation on the silty-muddy tidal flat. The maximum annual retreat reached 10 m. The recent sedimentation and morphological changes of the Yuantuojiao Point tidal flat not only displayed the retreat of the salt marsh and the disappearance of cliffs, but also was accompanied by rapid sedimentation of the silty-muddy tidal flat and the salt marsh, indicating the responses to the tidal currents, storm surges, Spartina alterniflorea trapping sediments and large-scale reclamation.

关键词： sedimentation rate morphological changes the tidal fiat salt marsh cliff seaward reclamation Yuantuojiao Point the North Branch of the Changjiang River

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Time lag effect of vegetation response to seasonal precipitation in the Mara River Basin

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Ecological Processes 2023年第1期12卷 665-679页

作者： Shouming Feng zhenke zhang Shuhe Zhao Xinya Guo Wanyi Zhu Priyanko Das School of Geography and Oceanography Sciences Nanjing UniversityNanjing 210023China Institute of African Studies Nanjing UniversityNanjing 210023China Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application Nanjing 210023China

Background Mara River Basin is an ecologically fragile area in East Africa,with a pattern of alternating wet and dry seasons shaped by periodic *** the regional biological traits and climatic change,the vegetation’s response to seasonal variation is complicated and frequently characterized by time *** study analyzed the variation of the Normalized Difference Vegetation Index(NDVI)and investigated its time lag to precipitation at the monthly *** characteristic peaks were proposed from the perspective of seasonal mechanisms and were quantified to assess the lag *** The results showed that the Anomaly Vegetation Index could identify low precipitation in 2006,2009,and *** NDVI showed an increasing trend in 75%of areas of the basin,while showed a decreased significance in 3.5%of areas,mainly in *** to the time lag,the 1-month lag effect dominated most months,and the spatiotemporal disparities were *** method considering the alternations of wet and dry seasons found that the time lag was approximately 30 *** on the time distribution of NDVI characteristic peaks,the average time lag was 35.5 days and increased with the range of *** The findings confirmed an increasing trend of NDVI in most regions from 2001 to 2020,while the trends were most obvious in the downstream related to human *** results could reflect the time lag of NDVI response to precipitation,and the 1-month lag effect dominated in most months with spatial *** NDVI characteristic peaks were found to be efficient indicators to assess the seasonal characteristics and had a great potential to quantify vegetation variation.

关键词： Mara River Basin NDVI Seasonal precipitation Characteristic peak Time lag

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Processes of small-scale tidal flat accretion and salt marsh changes on the plain coast of Jiangsu Province,China

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Acta Oceanologica Sinica 2017年第4期36卷 80-86页

作者： zhang Yunfeng zhang zhenke HE Huachun CHEN Yingying JIANG Songliu REN Hang Ministry of Education Key Laboratory for Coast and Island Development Nanjing University Nanjing 210023 China Key Laboratory of the Coastal Zone Exploitation and Protection Ministry of Land and Resource Nanjing 210024 China

Large-scaled reclamation modifies the coastal environment dramatically while accelerating the disappearance of salt marshes,which causes the degradation of the coastal ecosystem and the biodiversity *** this study,we explored the changes of tidal flat and salt marsh coverage in a small-scale tidal flat with an area of ~160 000 m^2 in the plain coast of Jiangsu Province,*** activities（e.g.,the construction of dikes） are a crucial contributor that benefits for the tidal flat accretions and the following changes of salt marsh *** in the front of the man-made ＂concave coastline＂,the study area is suitable for sediment accretion after the dike construction in the end of *** the basis of the annual tidal surface elevation survey from 2007 to 2012,the sedimentation rates in the human influenced tidal flat varied from a few centimeters per year to 23 cm/*** study area experienced a rapid accretion in the tidal flat and the expansion of the salt marsh,with the formation of a longshore bar,and a subsequent decline of the salt *** waves during the flooding tide brought much sediment from the adjacent tidal flat to the study area,which caused burial and degeneration of the salt *** vertical grain size changes within a 66 cm long core in the study area also demonstrated the above changes in the tidal *** study indicates that the responses of small-scale tidal flat changes to reclamation are significant,and the rational reclamation would benefit for the new salt marsh formation in front of the *** research about the evolution of small scale tidal flat as well as the spatial planning of the polder dike should be strengthened for the purpose to maintain a healthier coastal environment.

关键词： tidal flat salt marsh small-scale tidal flat response to reclamation plain coast of Jiangsu Province

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Environmental evolution and southwest monsoon changes in mid-Holocene recorded by lake sediments in Erhai Lake

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Chinese Science Bulletin 1999年第1期44卷 94-96页

作者： zhenke zhang Sumin Wang Ruijin Wu Chinese Acad Sci Nanjing Inst Geop & Limnol Lake Sediment & Environm Lab Nanjing 210008 Peoples R China Yantai Normal Univ Dept Geog Yantai 264025 Peoples R China

IN recent years, much progress has been made in the research of the temporal and spatial changes of East Asian monsoon. To research the environmental evolution and monsoon variations in Holocene in the region of Southwest China, a 310-cm continuous lake sediments core in Erhai Lake, Yunnan Province was sampled with Livingston sampler on July 6, 1996. The lake sediments were separated at 2-cm intervals and the core samples were analyzed with chronology, stable isotope ratios of organic carbon and diatoms determination. Three 14C ages are （4 473±40）a B.P. （98—102 cm）, （5 825±85） a B. P. （144—148 cm） and （7 754±45） a B.P. （198—202 cm）. By 137Cs dating, the sedimentation rate is about 0.3 mm/a and this result is close to the 14C dating results. The average sedimentation rates

关键词： lake sediments southwest monsoon changes mid-Holocene environmental evolution Erhai Lake.

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Spatial Pattern and Benefit Allocation in Regional Collaborative Innovation of the Yangtze River Delta, China

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Chinese Geographical Science 2021年第5期31卷 900-914页

作者： WANG Yue WANG Chengyun MAO Xiyan Liu Binglin zhang zhenke JIANG Shengnan School of Geography and Ocean Science Nanjing UniversityNanjing 210023China Collaborative Imnovation Center of SouthChina Sea Studies Nanjing UniversityNanjing 210093China School of Environmental and Geographical Sciences Shanghai Normal UniversiryShanghai 200234China

As an important step enhancing regional innovation, researches on collaborative innovation have attracted much more attention recently. One significant reason is that cities can get excessive benefits while they take collaborative innovation activities. Based on the theories of innovation geography, this paper takes the collaborative innovation of the Yangtze River Delta(YRD) Urban Agglomeration as a case study and measures the collaborative innovation capacity from innovation actors and innovation cities by adopting the catastrophe progression model. Then on this basis, the study depicts the spatial pattern and the benefit allocation of collaborative innovation by using the coupling collaborative degree model and benefit allocation model of collaborative innovation. The results show that:1) The collaborative innovation capacity of cities in the Yangtze River Delta has strengthened largely, while the capacity still is not high enough. Cities with high collaborative innovation capacity are concentrated in Shanghai, the southern part of Jiangsu, and Hangzhou Bay, yet the cooperation of the universities-industries-research institutes need to improve. 2) The spatial pattern of collaborative innovation of the Yangtze River Delta presents several innovation circles, which are in Suzhou-Wuxi-Changzhou Metropolitan Circle, Nanjing Metropolitan Circle, Hangzhou Metropolitan Circle, Ningbo Metropolitan Circle, and Hefei Metropolitan Circle. Shanghai plays the role of the central city of collaborative innovation, while Suzhou, Nanjing, Hangzhou, Ningbo, and Hefei act as sub-central cities. 3) The benefit each city allocated from collaborative innovation activities has increased. However, the allocations of the benefit show that cities with higher innovation capacity have significant advantages in most cases, which lead to serious disparities in space.

关键词： Yangtze River Delta(YRD) collaborative innovation spatial pattern benefits allocation

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Climatic variations recorded by the sediments from Erhai Lake,Yunnan Province,southwest China during the past 8000 a

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Chinese Science Bulletin 2001年第S1期46卷 80-82页

作者： zhang zhenke YANG Xiangdong SHEN Ji LI Shengfeng ZHU Yuxin WU Ruijin Department of Geo&Ocean Sciences Nanjing UniversityNanjing 210093China Nanjing Institute of Geography and Limnology Chinese Academy of SciencesNanjing 210008China

Erhai Lake is a large lake with important climatic significance in Yunnan Province, southwest China. The multi-proxy sedimentary records from Erhai Lake indicate the 9 stages of climatic changes with the alternation of warm-dry and cool-wet during the past 8000 a. The variations of Asian monsoon systems were the main cause for the climatic changes in southwest China. The warm-dry period was coincident with the intensification of India monsoon and Northwest Pacific Sub-tropical High Pressure, and the cool-wet corresponding to weak of India monsoon and its main rain belt moving back to southwest China.

关键词： climatic variation monsoon lake sediment Erhai Lake.

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越南海洋鱼类捕捞量演变特征及对中国的启示

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东南亚研究 2016年第6期 20-30页

作者：任航杨钿张振克南京大学地理与海洋科学学院南京210023 南京大学中国南海研究协同创新中心南京210023

文章通过对越南1995—2014年海洋渔业数据进行整理,运用GIS空间分析方法,对其沿海地区海洋鱼类捕捞量的演变过程进行研究。结果表明,1995—2014年间,越南海洋捕捞业呈现出迅猛发展的势头,其中北部湾沿岸省份整体增速较快;产量分布的空... 详细信息

文章通过对越南1995—2014年海洋渔业数据进行整理,运用GIS空间分析方法,对其沿海地区海洋鱼类捕捞量的演变过程进行研究。结果表明,1995—2014年间,越南海洋捕捞业呈现出迅猛发展的势头,其中北部湾沿岸省份整体增速较快;产量分布的空间差异明显,呈现出平均产量"南高北低",平均增速"北快南慢"的发展特点;发展重心有所波动,但整体呈现出向北发展的趋势。可以判断,未来在南海地区,尤其是西沙、南沙海域的渔业资源,受到来自越南方面非法捕捞的威胁会逐渐增加,中越在上述地区爆发渔业冲突的可能性在增长。文章最后结合中国海洋渔业发展现状,从渔业合作、渔业执法和深海渔业发展等方面提出了中国的应对之策。

关键词：越南南海海洋鱼类捕捞演变特征对策建议

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Environmental changes during modern period from the record of Gaoyou Lake sediments, Jiangsu

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Journal of Geographical Sciences 2007年第1期17卷 62-72页

作者： LI Shuheng FU Guanghe GUO Wei HE Huachun zhang zhenke The Key Laboratory of Coast ＆ Island Development of Ministry of Education Nanjing University Nanjing 210093 China

Based on analysis of parameters of cores taken from Gaoyou Lake, including magnetic susceptibility, grain-size characteristics and sedimentary rate, environmental changes during the modern period were examined with the assistance of historical records and Gaoyou Lake water level materials. It is concluded that during the modern period a higher value of magnetic susceptibility and a lower sediment grain size coincided with a wet climate, while a lower value of magnetic susceptibility and a higher grain size were related with a dry climate. The results indicate that the climate in the 123 years period from 1880 to 2003AD can be divided into four stages： two low water level stages （1880-1915AD, 1948-1981AD） and two high water level stages （1915-1948AD, 1981-2003AD）. It appears that the regional climate generally underwent a dry-wet-dry-wet pattern in 30-year cycles. At present, it is at the end of a wet period, so the regional climate is expected to become dry in the near future. This conclusion corresponds with the climate records in the historical literature of the Gaoyou area, and it also matches with the climatic changes in North Jiangsu area.

关键词： Gaoyou Lake environmental changes lake sediments

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