In order to simulate changes in the water quality of the Miyun Reservoir dueto continuous descent of surface water level, a 3-D ecological hydrodynamic model was developedthrough coupling the water quality analysis si...In order to simulate changes in the water quality of the Miyun Reservoir dueto continuous descent of surface water level, a 3-D ecological hydrodynamic model was developedthrough coupling the water quality analysis simulation program (WASP) with the environmental fluiddynamics code (EFDC). The model was then calibrated and verified. Four scenarios (S1, S21, S22 andS23) were simulated using the model. Results show that the water quality of the Miyun Reservoirunder conditions of low surface water level is apparently affected by different amounts of inflowand different total phosphorus (TP) loadings. The chlorophyll-a concentration might exceed 10 μg/Lin many areas of the Miyun Reservoir (This limitative value is seen as a critical value ofeutrophication) when large loadings of TP enter due to the amount of inflow increasing. Results ofscenario S23 indicate that control of TP loadings can decrease chlorophyll-a concentrationeffectively, and the water quality of the Miyun Reservoir will improve or retain its status quo.展开更多
本文利用形态学的方法确定聚类数目,并对单词-文档谱聚类方法进行改进.确定聚类数目主要分三个步骤:第一步将单词-文档谱聚类方法中产生的矩阵转换成可视化聚类趋势分析方法(visual assessment of tendency,VAT)灰度图,第二步利用灰度...本文利用形态学的方法确定聚类数目,并对单词-文档谱聚类方法进行改进.确定聚类数目主要分三个步骤:第一步将单词-文档谱聚类方法中产生的矩阵转换成可视化聚类趋势分析方法(visual assessment of tendency,VAT)灰度图,第二步利用灰度形态学、图像二值化、距离转换等图像处理技术过滤产生的VAT灰度图,第三步对过滤后的VAT灰度图建立信号图,并进行平滑处理,通过平滑后的信号图的波峰波谷数目确定文档集的聚类数目.实验表明,该方法能够提高单词-文档谱聚类方法的聚类效果.展开更多
The temperature change trends in January and July are analyzed and the results show that the trends descend in July but ascend in January except in South China and Southwest China. The relation between the temperature...The temperature change trends in January and July are analyzed and the results show that the trends descend in July but ascend in January except in South China and Southwest China. The relation between the temperature in January and July are discussed by using the wavelet. The results show that the trend phase in July and January are nearly in-phase in Southwest and South China, but are out-of-phase in other regions. Reconstruction of original temperature series in each of the regions indicates that their change trends are consistent with the original temperature series.展开更多
The main goal of this study was to assess the long-term impacts of global warming perturbation on water resources of the Kaidu River Basin in Northwest China. Temperature, precipitation and hydrology data during the p...The main goal of this study was to assess the long-term impacts of global warming perturbation on water resources of the Kaidu River Basin in Northwest China. Temperature, precipitation and hydrology data during the past 29 years from 1979 to 2007 were collected and analyzed using parametric and non-parametric methods, the connection between temperature and precipitation by the combination of grey correlation analysis method and the hypothesis testing for trend of climate change. The results show a high increase in temperature in the study area as well as an extreme and highly variable hydrological regime in this region, where flash floods can exceed the total runoff from a sequence of years. These variations may be due to the geographical location of the Kaidu River Basin in arid zone. It also reveals that precipitation has a much greater impact on stream flow than that of temperature. The development of new approaches was proposed as responses to climate change in this arid region.展开更多
With the series of annual and seasonal temperature during 1957 – 2001 in Dongguan, Guangdong, the statistical characteristic and power spectrum and secular trend and sudden change phenomena are computed in this paper...With the series of annual and seasonal temperature during 1957 – 2001 in Dongguan, Guangdong, the statistical characteristic and power spectrum and secular trend and sudden change phenomena are computed in this paper. From the results it is known that (1) the temperatures have obvious characteristics of monsoon climate but do not have normal distribution, showing biased distribution of high or low kurtosis; (2) over the recent half- century, the temperatures tend to rise, specially in the last 10 years, in which mean temperature have quickly ascended by about 1.5°C, and except for the spring, there were sudden change of seasonal temperature rising from the 1980’s to 1990’s, which really reflected the influence of developing and opening and urbanization on Dongguan temperature; (3) except for the spring, the temperature of other seasons show some oscillatory periods in Dongguan and some of them also include long-term variation trends.展开更多
Background Although thyroid hormone (TH) has important effects on lipid metabolism, the relationship between TH and statin responsiveness has never been investigated. We hypothesize that TH plays an important role i...Background Although thyroid hormone (TH) has important effects on lipid metabolism, the relationship between TH and statin responsiveness has never been investigated. We hypothesize that TH plays an important role in statin responsiveness in patients with acute myocardial infarction (AMI). Methods Consecutive 1091 hospitalized AMI patients in Fuwai hospital (Beijing, China) were enrolled into this current study. The study population was divided into three groups based on the intensity of statin treatment: low-intensity (n = 221), moderate-intensity (n = 712) and high-intensity (n = 158). Lipid levels were measured after statin therapy lasting for 10-14 days. The association between TH, lipid profile levels and achievement of low-density lipoprotein cholesterol (LDL-C) lowering goals was explored in patients with AMI on statin therapy. Results By general linear analysis, a significant linear trend between free triiodothyronine (FT3) and LDL-C level (linear coefficient r = -0.082, P = 0.001) and FT3 and total cholesterol (TC) level (r = -0.105, P = 0.031) was observed in the moderate-intensity statin group. A more apparent linear trend was detected in the high-intensity statin group (for LDL-C: r = -0.113, P = 0.005; for TC: r = -0.172, P = 0.029, respectively). However, no significant correlation was observed in the low-intensity statin group. Compared with the low-FT3 group (defined as FT3 〈 1.79 pg/mL), the OR (95% CI) for attaining a LDL-C 〈 3.0mmol/L was found to be 2.217 (1.001–4.839) in the higher FT3 group (〉 2.95 pg/mL). The OR (95% CI) for attaining the more intensive goal (LDL-C 〈 1.8mmol/L) was 2.836 (1.014–5.182). Conclusions Our study reveals that variation in FT3 levels is related to the cholesterol-lowering responsiveness of statins in AMI patients. These findings suggest that low FT3 may be a factor responsible for lack of LDL-C goal attainment and patients’ poor responsiveness to statin treatment.展开更多
Trend analysis and change point detection in a time series are frequent analysis tools.Change point detection is the identification of abrupt variation in the process behaviour due to natural or artificial changes,whe...Trend analysis and change point detection in a time series are frequent analysis tools.Change point detection is the identification of abrupt variation in the process behaviour due to natural or artificial changes,whereas trend can be defined as estimation of gradual departure from past norms.We analyze the time series data in the presence of trend,using Cox-Stuart methods together with the change point algorithms.We applied the methods to the nearsurface wind speed time series for Australia as an example.The trends in near-surface wind speeds for Australia have been investigated based upon our newly developed wind speed datasets,which were constructed by blending observational data collected at various heights using local surface roughness information.The trend in wind speed at 10 m is generally increasing while at 2 m it tends to be decreasing.Significance testing,change point analysis and manual inspection of records indicate several factors may be contributing to the discrepancy,such as systematic biases accompanying instrument changes,random data errors(e.g.accumulation day error)and data sampling issues.Homogenization technique and multiple-period trend analysis based upon change point detections have thus been employed to clarify the source of the inconsistencies in wind speed trends.展开更多
Australian dollar (AUD) maintains a fluctuant increase for long period, but in recent two years, this currency represents an anomalistic change. In order to forecast the trend of AUD, this essay examines the exchang...Australian dollar (AUD) maintains a fluctuant increase for long period, but in recent two years, this currency represents an anomalistic change. In order to forecast the trend of AUD, this essay examines the exchange rate of AUD in then years from March of 2000 to March of 2010, and argues the factors which create these trend changes. By means of secondary research and graphs analysis, the relevant evidence and argument was selected into four terms below: relative raw materials prices changes, relative domestic price level and Import-Expert changes, relative interest rate changes, and other factors. The examples based on the theoretics, graphs, statistics and experts' opinions.展开更多
The Normalized Difference Vegetation Index(NDVI), as a key indicator of vegetation growth, effectively provides information regarding vegetation growth status. Based on the Global Inventory Monitoring and Modeling S...The Normalized Difference Vegetation Index(NDVI), as a key indicator of vegetation growth, effectively provides information regarding vegetation growth status. Based on the Global Inventory Monitoring and Modeling System(GIMMS) NDVI time series data for Kazakhstan from 1982 to 2015, we analyzed the spatial pattern and changes in the vegetation growth trend. Results indicated that the three main types of vegetation in Kazakhstan are cropland, grassland and shrubland, and these are distributed from north to south. While the regional distribution pattern is obvious, the vegetation index decreased from north to south. The average NDVI values of the three main vegetation types are in the order of cropland grassland shrubland. During the period from 1982 to 2015, the NDVI initially increased(1982–1992), then decreased(1993–2007), and then increased again(2008–2015). The areas where NDVI decreased significantly accounted for 24.0% of the total land area. These areas with vegetation degradation are mainly distributed in the northwest junction between cropland and grassland, and in the cropland along the southern border. The proportions of total grassland, cropland and shrubland areas that were degraded are 23.5%, 48.4% and 13.7%, respectively. Areas with improved vegetation, accounting for 11.8% of the total land area, were mainly distributed in the mid-east cropland area, and the junction between cropland and grassland in the mid-east region.展开更多
Extreme climate events play an important role in studies of long-term climate change. As the Earth’s Third Pole, the Tibetan Plateau(TP) is sensitive to climate change and variation. In this study on the TP, the spat...Extreme climate events play an important role in studies of long-term climate change. As the Earth’s Third Pole, the Tibetan Plateau(TP) is sensitive to climate change and variation. In this study on the TP, the spatiotemporal changes in climate extreme indices(CEIs) are analyzed based on daily maximum and minimum surface air temperatures and precipitation at 98 meteorological stations, most with elevations of at least 4000 m above sea level, during 1960–2012. Fifteen temperature extreme indices(TEIs) and eight precipitation extreme indices(PEIs) were calculated. Then, their long-term change patterns, from spatial and temporal perspectives, were determined at regional, eco-regional and station levels. The entire TP region exhibits a significant warming trend, as reflected by the TEIs. The regional cold days and nights show decreasing trends at rates of-8.9 d(10 yr)-1(days per decade) and-17.3 d(10 yr)-1, respectively. The corresponding warm days and nights have increased by 7.6 d(10 yr)-1 and 12.5 d(10 yr)-1, respectively. At the station level, the majority of stations indicate statistically significant trends for all TEIs, but they show spatial heterogeneity. The eco-regional TEIs show patterns that are consistent with the entire TP. The growing season has become longer at a rate of 5.3 d(10 yr)^-1. The abrupt change points for CEIs were examined, and they were mainly distributed during the 1980 s and 1990 s. The PEIs on the TP exhibit clear fluctuations and increasing trends with small magnitudes. The annual total precipitation has increased by 2.8 mm(10 yr)^-1(not statistically significant). Most of the CEIs will maintain a persistent trend, as indicated by their Hurst exponents. The developing trends of the CEIs do not show a corresponding change with increasing altitude. In general, the warming trends demonstrate an asymmetric pattern reflected by the rapid increase in the warming trends of the cold TEIs, which are of greater magnitudes than those of the warm TEIs. This finding indicates a positive shift in the distribution of the daily minimum temperatures throughout the TP. Most of the PEIs show weak increasing trends, which are not statistically significant. This work aims to delineate a comprehensive picture of the extreme climate conditions over the TP that can enhance our understanding of its changing climate.展开更多
As an important foundation for promoting social progress and economic development, natural resources play an important role in the sustainable development of cities. However, the increasing demand of human beings for ...As an important foundation for promoting social progress and economic development, natural resources play an important role in the sustainable development of cities. However, the increasing demand of human beings for natural resources has led to various ecological environmental problems, such as excessive population density, serious environmental pollution, the continuous decline of total natural resources and per capita resources, all of which have hindered sustainable development. Therefore, the study of natural resources and sustainable development has become the focus of many current scholars. In this paper, CiteSpace is used as an analysis tool to analyze the literature on natural resources and sustainable development over the past 20 years. First of all, this paper deeply analyzes the research status of this field in terms of academic research trends, authors and research institutions, co-occurrence of keywords, etc., and on this basis, it then deeply analyzes its evolutionary path and research hot spots in the past 20 years through keyword emergence. Finally, according to the visualization of the analysis results, the future development trends of this research field are speculated:(1) Grasp the current research focus;(2) Improve the research accuracy;(3) Enrich the theoretical system of research;and(4) Establish an interdisciplinary research system.展开更多
Desertification research plays a key role in the survival and development of all mankind.The Normalized Comprehensive Hotspots Index(NCH)is a comprehensive index that reveals the spatial distribution of research hotsp...Desertification research plays a key role in the survival and development of all mankind.The Normalized Comprehensive Hotspots Index(NCH)is a comprehensive index that reveals the spatial distribution of research hotspots in a given research field based on the number of relevant scientific papers.This study uses Web Crawler technology to retrieve the full text of all Chinese journal articles spanning the 1980s-2018 in the Chinese Academic Journal full-text database(CAJ)from CNKI.Based on the 253,055 articles on desertification that were retrieved,we have constructed a research hotspot extraction model for desertification in China by means of the NCH Index.This model can reveal the spatial distribution and dynamic changes of research hotspots for desertification in China.This analysis shows the following:1)The spatial distribution of research hotspots on desertification in China can be effectively described by the NCH Index,although its application in other fields still needs to be verified and optimized.2)According to the NCH Index,the research hotspots for desertification are mainly distributed in the Agro-Pastoral Ecotone and grassland in Inner Mongolia,the desertification areas of Qaidam Basin in the Western Alpine Zone and the Oasis-Desert Ecotone in Xinjiang(including the extension of the central Tarim Basin to the foothills of the Kunlun Mountains,the sporadic areas around the Tianshan Mountains and the former hilly belt of the southern foothills of the Altai Mountains).Among these three,the Agro-Pastoral Ecotone in the middle and eastern part of Inner Mongolia includes the most prominent hotspots in the study of desertification.3)Since the 1980s,the research hotspots for desertification in China have shown a general downward trend,with a significant decline in 219 counties(10.37%of the study area).This trend is dominated by the projects carried out since 2002.The governance of desertification in the eastern part of the Inner Mongolia-Greater Khingan Range still needs to be strengthened.The distribution of desertification climate types reflects the distribution of desertification in a given region to some extent.The Normalized Comprehensive Hotspots Index provides a new approach for researchers in different fields to analyze research progress.展开更多
文摘In order to simulate changes in the water quality of the Miyun Reservoir dueto continuous descent of surface water level, a 3-D ecological hydrodynamic model was developedthrough coupling the water quality analysis simulation program (WASP) with the environmental fluiddynamics code (EFDC). The model was then calibrated and verified. Four scenarios (S1, S21, S22 andS23) were simulated using the model. Results show that the water quality of the Miyun Reservoirunder conditions of low surface water level is apparently affected by different amounts of inflowand different total phosphorus (TP) loadings. The chlorophyll-a concentration might exceed 10 μg/Lin many areas of the Miyun Reservoir (This limitative value is seen as a critical value ofeutrophication) when large loadings of TP enter due to the amount of inflow increasing. Results ofscenario S23 indicate that control of TP loadings can decrease chlorophyll-a concentrationeffectively, and the water quality of the Miyun Reservoir will improve or retain its status quo.
文摘本文利用形态学的方法确定聚类数目,并对单词-文档谱聚类方法进行改进.确定聚类数目主要分三个步骤:第一步将单词-文档谱聚类方法中产生的矩阵转换成可视化聚类趋势分析方法(visual assessment of tendency,VAT)灰度图,第二步利用灰度形态学、图像二值化、距离转换等图像处理技术过滤产生的VAT灰度图,第三步对过滤后的VAT灰度图建立信号图,并进行平滑处理,通过平滑后的信号图的波峰波谷数目确定文档集的聚类数目.实验表明,该方法能够提高单词-文档谱聚类方法的聚类效果.
文摘The temperature change trends in January and July are analyzed and the results show that the trends descend in July but ascend in January except in South China and Southwest China. The relation between the temperature in January and July are discussed by using the wavelet. The results show that the trend phase in July and January are nearly in-phase in Southwest and South China, but are out-of-phase in other regions. Reconstruction of original temperature series in each of the regions indicates that their change trends are consistent with the original temperature series.
基金supported by the State Key Development Program for Basic Research of China (973 program (Grant No. 2010CB951002)the Natural Sciences Foundation of China (Grant No. 40871027)+1 种基金the Project from Xinjiang Key Laboratory of Water Cycle and Utilization in Arid Zone (Grant No. XJYS0907-2011-03)the Knowledge Innovation project of Chinese Academy of Science (KZCX2-YW-334) for financial supports
文摘The main goal of this study was to assess the long-term impacts of global warming perturbation on water resources of the Kaidu River Basin in Northwest China. Temperature, precipitation and hydrology data during the past 29 years from 1979 to 2007 were collected and analyzed using parametric and non-parametric methods, the connection between temperature and precipitation by the combination of grey correlation analysis method and the hypothesis testing for trend of climate change. The results show a high increase in temperature in the study area as well as an extreme and highly variable hydrological regime in this region, where flash floods can exceed the total runoff from a sequence of years. These variations may be due to the geographical location of the Kaidu River Basin in arid zone. It also reveals that precipitation has a much greater impact on stream flow than that of temperature. The development of new approaches was proposed as responses to climate change in this arid region.
文摘With the series of annual and seasonal temperature during 1957 – 2001 in Dongguan, Guangdong, the statistical characteristic and power spectrum and secular trend and sudden change phenomena are computed in this paper. From the results it is known that (1) the temperatures have obvious characteristics of monsoon climate but do not have normal distribution, showing biased distribution of high or low kurtosis; (2) over the recent half- century, the temperatures tend to rise, specially in the last 10 years, in which mean temperature have quickly ascended by about 1.5°C, and except for the spring, there were sudden change of seasonal temperature rising from the 1980’s to 1990’s, which really reflected the influence of developing and opening and urbanization on Dongguan temperature; (3) except for the spring, the temperature of other seasons show some oscillatory periods in Dongguan and some of them also include long-term variation trends.
基金We acknowledge the help from Wei LI, Yang WANG and Yan-Yan ZHAO (Medical Research & Biometrics Center, Fuwai Hospital, National Center for Cardiovascular Disease, China) with the statistical analyses. This work was supported by the National Natural Science Foundation of China (No. 81470485), Capital Clinical Featured Application Research Project (No. z151100004015175), and CAMS Innovation Fund for Medical Sciences (CIFMS 2016-I2M- 1-009). The authors have no potential conflict of interest to declare.
文摘Background Although thyroid hormone (TH) has important effects on lipid metabolism, the relationship between TH and statin responsiveness has never been investigated. We hypothesize that TH plays an important role in statin responsiveness in patients with acute myocardial infarction (AMI). Methods Consecutive 1091 hospitalized AMI patients in Fuwai hospital (Beijing, China) were enrolled into this current study. The study population was divided into three groups based on the intensity of statin treatment: low-intensity (n = 221), moderate-intensity (n = 712) and high-intensity (n = 158). Lipid levels were measured after statin therapy lasting for 10-14 days. The association between TH, lipid profile levels and achievement of low-density lipoprotein cholesterol (LDL-C) lowering goals was explored in patients with AMI on statin therapy. Results By general linear analysis, a significant linear trend between free triiodothyronine (FT3) and LDL-C level (linear coefficient r = -0.082, P = 0.001) and FT3 and total cholesterol (TC) level (r = -0.105, P = 0.031) was observed in the moderate-intensity statin group. A more apparent linear trend was detected in the high-intensity statin group (for LDL-C: r = -0.113, P = 0.005; for TC: r = -0.172, P = 0.029, respectively). However, no significant correlation was observed in the low-intensity statin group. Compared with the low-FT3 group (defined as FT3 〈 1.79 pg/mL), the OR (95% CI) for attaining a LDL-C 〈 3.0mmol/L was found to be 2.217 (1.001–4.839) in the higher FT3 group (〉 2.95 pg/mL). The OR (95% CI) for attaining the more intensive goal (LDL-C 〈 1.8mmol/L) was 2.836 (1.014–5.182). Conclusions Our study reveals that variation in FT3 levels is related to the cholesterol-lowering responsiveness of statins in AMI patients. These findings suggest that low FT3 may be a factor responsible for lack of LDL-C goal attainment and patients’ poor responsiveness to statin treatment.
文摘Trend analysis and change point detection in a time series are frequent analysis tools.Change point detection is the identification of abrupt variation in the process behaviour due to natural or artificial changes,whereas trend can be defined as estimation of gradual departure from past norms.We analyze the time series data in the presence of trend,using Cox-Stuart methods together with the change point algorithms.We applied the methods to the nearsurface wind speed time series for Australia as an example.The trends in near-surface wind speeds for Australia have been investigated based upon our newly developed wind speed datasets,which were constructed by blending observational data collected at various heights using local surface roughness information.The trend in wind speed at 10 m is generally increasing while at 2 m it tends to be decreasing.Significance testing,change point analysis and manual inspection of records indicate several factors may be contributing to the discrepancy,such as systematic biases accompanying instrument changes,random data errors(e.g.accumulation day error)and data sampling issues.Homogenization technique and multiple-period trend analysis based upon change point detections have thus been employed to clarify the source of the inconsistencies in wind speed trends.
文摘Australian dollar (AUD) maintains a fluctuant increase for long period, but in recent two years, this currency represents an anomalistic change. In order to forecast the trend of AUD, this essay examines the exchange rate of AUD in then years from March of 2000 to March of 2010, and argues the factors which create these trend changes. By means of secondary research and graphs analysis, the relevant evidence and argument was selected into four terms below: relative raw materials prices changes, relative domestic price level and Import-Expert changes, relative interest rate changes, and other factors. The examples based on the theoretics, graphs, statistics and experts' opinions.
基金National Key Research and Development Program of China(2016YFC0503700)
文摘The Normalized Difference Vegetation Index(NDVI), as a key indicator of vegetation growth, effectively provides information regarding vegetation growth status. Based on the Global Inventory Monitoring and Modeling System(GIMMS) NDVI time series data for Kazakhstan from 1982 to 2015, we analyzed the spatial pattern and changes in the vegetation growth trend. Results indicated that the three main types of vegetation in Kazakhstan are cropland, grassland and shrubland, and these are distributed from north to south. While the regional distribution pattern is obvious, the vegetation index decreased from north to south. The average NDVI values of the three main vegetation types are in the order of cropland grassland shrubland. During the period from 1982 to 2015, the NDVI initially increased(1982–1992), then decreased(1993–2007), and then increased again(2008–2015). The areas where NDVI decreased significantly accounted for 24.0% of the total land area. These areas with vegetation degradation are mainly distributed in the northwest junction between cropland and grassland, and in the cropland along the southern border. The proportions of total grassland, cropland and shrubland areas that were degraded are 23.5%, 48.4% and 13.7%, respectively. Areas with improved vegetation, accounting for 11.8% of the total land area, were mainly distributed in the mid-east cropland area, and the junction between cropland and grassland in the mid-east region.
基金National Natural Science Foundation of China(41601478,41571391)National Key Research and Development Program of China(2018YFB0505301,2016YFC0500103)
文摘Extreme climate events play an important role in studies of long-term climate change. As the Earth’s Third Pole, the Tibetan Plateau(TP) is sensitive to climate change and variation. In this study on the TP, the spatiotemporal changes in climate extreme indices(CEIs) are analyzed based on daily maximum and minimum surface air temperatures and precipitation at 98 meteorological stations, most with elevations of at least 4000 m above sea level, during 1960–2012. Fifteen temperature extreme indices(TEIs) and eight precipitation extreme indices(PEIs) were calculated. Then, their long-term change patterns, from spatial and temporal perspectives, were determined at regional, eco-regional and station levels. The entire TP region exhibits a significant warming trend, as reflected by the TEIs. The regional cold days and nights show decreasing trends at rates of-8.9 d(10 yr)-1(days per decade) and-17.3 d(10 yr)-1, respectively. The corresponding warm days and nights have increased by 7.6 d(10 yr)-1 and 12.5 d(10 yr)-1, respectively. At the station level, the majority of stations indicate statistically significant trends for all TEIs, but they show spatial heterogeneity. The eco-regional TEIs show patterns that are consistent with the entire TP. The growing season has become longer at a rate of 5.3 d(10 yr)^-1. The abrupt change points for CEIs were examined, and they were mainly distributed during the 1980 s and 1990 s. The PEIs on the TP exhibit clear fluctuations and increasing trends with small magnitudes. The annual total precipitation has increased by 2.8 mm(10 yr)^-1(not statistically significant). Most of the CEIs will maintain a persistent trend, as indicated by their Hurst exponents. The developing trends of the CEIs do not show a corresponding change with increasing altitude. In general, the warming trends demonstrate an asymmetric pattern reflected by the rapid increase in the warming trends of the cold TEIs, which are of greater magnitudes than those of the warm TEIs. This finding indicates a positive shift in the distribution of the daily minimum temperatures throughout the TP. Most of the PEIs show weak increasing trends, which are not statistically significant. This work aims to delineate a comprehensive picture of the extreme climate conditions over the TP that can enhance our understanding of its changing climate.
基金The National Natural Science Foundation of China (41601581)The Science Technology Plan Project for Construction Industry of Anhui Province (2011YF-32)。
文摘As an important foundation for promoting social progress and economic development, natural resources play an important role in the sustainable development of cities. However, the increasing demand of human beings for natural resources has led to various ecological environmental problems, such as excessive population density, serious environmental pollution, the continuous decline of total natural resources and per capita resources, all of which have hindered sustainable development. Therefore, the study of natural resources and sustainable development has become the focus of many current scholars. In this paper, CiteSpace is used as an analysis tool to analyze the literature on natural resources and sustainable development over the past 20 years. First of all, this paper deeply analyzes the research status of this field in terms of academic research trends, authors and research institutions, co-occurrence of keywords, etc., and on this basis, it then deeply analyzes its evolutionary path and research hot spots in the past 20 years through keyword emergence. Finally, according to the visualization of the analysis results, the future development trends of this research field are speculated:(1) Grasp the current research focus;(2) Improve the research accuracy;(3) Enrich the theoretical system of research;and(4) Establish an interdisciplinary research system.
基金The National Key Research and Development Program of China(2016YFC0503701,2016YFB0501502)The Strategic Priority Research Program of Chinese Academy of Sciences(XDA19040301,XDA20010202,XDA23100201)The Key Project of the High Resolution Earth Observation System in China(00-Y30B14-9001-14/16)
文摘Desertification research plays a key role in the survival and development of all mankind.The Normalized Comprehensive Hotspots Index(NCH)is a comprehensive index that reveals the spatial distribution of research hotspots in a given research field based on the number of relevant scientific papers.This study uses Web Crawler technology to retrieve the full text of all Chinese journal articles spanning the 1980s-2018 in the Chinese Academic Journal full-text database(CAJ)from CNKI.Based on the 253,055 articles on desertification that were retrieved,we have constructed a research hotspot extraction model for desertification in China by means of the NCH Index.This model can reveal the spatial distribution and dynamic changes of research hotspots for desertification in China.This analysis shows the following:1)The spatial distribution of research hotspots on desertification in China can be effectively described by the NCH Index,although its application in other fields still needs to be verified and optimized.2)According to the NCH Index,the research hotspots for desertification are mainly distributed in the Agro-Pastoral Ecotone and grassland in Inner Mongolia,the desertification areas of Qaidam Basin in the Western Alpine Zone and the Oasis-Desert Ecotone in Xinjiang(including the extension of the central Tarim Basin to the foothills of the Kunlun Mountains,the sporadic areas around the Tianshan Mountains and the former hilly belt of the southern foothills of the Altai Mountains).Among these three,the Agro-Pastoral Ecotone in the middle and eastern part of Inner Mongolia includes the most prominent hotspots in the study of desertification.3)Since the 1980s,the research hotspots for desertification in China have shown a general downward trend,with a significant decline in 219 counties(10.37%of the study area).This trend is dominated by the projects carried out since 2002.The governance of desertification in the eastern part of the Inner Mongolia-Greater Khingan Range still needs to be strengthened.The distribution of desertification climate types reflects the distribution of desertification in a given region to some extent.The Normalized Comprehensive Hotspots Index provides a new approach for researchers in different fields to analyze research progress.