Formation and evolution of rural settlement patterns in Lianzhou City,Guangdong Province were analyzed from the perspective of space and time,on the basis of its gazetteer and relevant historical data.The results show...Formation and evolution of rural settlement patterns in Lianzhou City,Guangdong Province were analyzed from the perspective of space and time,on the basis of its gazetteer and relevant historical data.The results show that Lianzhou was first founded in the sixth year of Yuanding Period of the Western Han Dynasty,and its development could be roughly classified into 6 stages according to the construction of south–north traffic lines and regional development progress,and it witnessed the fastest development in the Ming and Qing Dynasty.In terms of spatial distribution,rural settlements in the local area show spatial continuity,Lianzhou Town is the core of rural settlement growth in the city,and towns with the most concentrated rural settlements in all stages are located in central-west and northeast parts of the city,and those with lower density of rural settlements are mostly located in minority regions in the north and mountainous areas in the east.On the basis of the above facts,the paper studies the influence of natural geological conditions,immigrant,traffic,economic development and ethnic composition on the establishment and development of rural settlements in Lianzhou City.展开更多
[Objective] The paper aimed to reflect the spatial pattern and temporal and spatial evolution characteristics, the differences between inter-regional tourism economy was measured from the quality aspect, which provide...[Objective] The paper aimed to reflect the spatial pattern and temporal and spatial evolution characteristics, the differences between inter-regional tourism economy was measured from the quality aspect, which provided a reference for the local governments in the future tourism development. [Method] Using the location entropy methods, three time periods side of tourism-related date of 2000, 2005, 2007 were selected, from the angle of the spatial pattern and the evolution of the differences within the different scales, the spatial and temporal evolution characteristics of the economic development level of Jiangsu were analysed. [Result] The results showed that from the aspect of spatial evolution pattern, as time goes on, the economic development of Jiangsu tourism has experienced morphological evolution of concentration- dispersion decrease-stability; when it comes to the development of the tourism economy, in recent years, the overall gap between the tourism economy in Jiangsu did not widen, the gap mainly led by the region one after another. According to their volatility, it will be divided into four categories: A Stable type (Wuxi, Xuzhou, Lianyungang and Taizhou), B Increasing type (Huai’an), C Fluctuations type (Nanjing, Changzhou, Suzhou and Yangzhou) and D Depression type (Nantong, Yancheng, Zhenjiang and Suqian). [Conclusion] Location entropy was quoted into tourism economic analysis, the method was simple and easy to understand, the result was accurate and convincing, which provided a reference for travel economic development and investment decision-making of Jiangsu.展开更多
The issue of China＇s energy supply security is not only the key problem which af- fects China＇s rapid and sustainable development in the 21st century, but also the one which international attention focuses on. Based...The issue of China＇s energy supply security is not only the key problem which af- fects China＇s rapid and sustainable development in the 21st century, but also the one which international attention focuses on. Based on the notable characteristic of spatial imbalance between energy production and consumption in China, this paper takes the evolution of China＇s primary energy resources development（excluding hydropower） from 1949 to 2007 as the study object, with the aim to sum up the evolutive characteristics and laws of China＇s energy resources development in the past nearly 60 years. Then, based on comprehensive considerations of coal＇s, oil＇s and natural gas＇s basic reserves, qualities, geological conditions production status, and ecological service function of every province, this paper adopts development potential index （DP）to evaluate the development potential of every province＇s en- ergy resources, and divide them into different ranks. Conclusions are drawn as follows： （1） Generally speaking, China＇s gross energy production was increasing in waves from 1949 to 2007. From the viewpoint of spatial patterns, China＇s energy resources development has shown a characteristic of ＂concentrating to the north and central areas, and evolving from linear-shaped to ＂T-shaped＂ pattern gradually since 1949. （2） The structure evolution of China＇s energy resources development in general has shown a trend of ＂coal proportion is dominant but decreasing, while oil and gas proportions are increasing＂ since 1949. （3） At the provincial scale, China＇s energy resources development potential could be divided into large, sub-large, general and small ranks, four in all. In the future, the spatial pattern of China＇s energy production will evolve from ＂T-shaped＂ to ＂R-shaped pattern＂. These conclusions will help to clarify the temporal and spatial characteristics and laws of China＇s energy resources development, and will be beneficial for China to design scientific and rational energy development strategies and plans, coordinate spatial imbalance of energy production and consumption, ensure national energy supply, avoid energy resources waste and disorderly development, and promote regional sustainable development under the globalization back-ground with changeful international energy market.展开更多
According to the data of precise relevelling and deformation measurement across faults, the temporal and spatial evolution process of crustal deformation field in the source and peripheral regions of the Tangshan ea...According to the data of precise relevelling and deformation measurement across faults, the temporal and spatial evolution process of crustal deformation field in the source and peripheral regions of the Tangshan earthquake (1976, M S=7.8), from 22 years before the earthquake to 9 years after, is described with the method of crustal deforma tion pattern dynamics. The crustal unstable zones first occur in the exterior, and then surround the focal region by contracting from the exterior to the interior, when the focal region appears to be unstable but does not lose stability. After the transient stable state, the second unstable process from the exterior to interior appears, which results in the instability of focal region. 'Deformation gap', 'earthquake gap' and 'locked fault zone' occur before instability, and their spatial distributions overlap, but their occurrence times have little differences. The earthquake occurs after the impending pre slide of the faults in the focal region. The studied results of the evolution process of crustal deformation field are identical with each other and with that of numeric simulation of crustal stress field, which supports the evolution model of seismogenic system with a strong body as its core.展开更多
In this study, we developed an energy security evaluation model(ESEM) from three dimensions, energy supply-transport security, safety of energy utilization, and stability of political-socioeconomic environment, based ...In this study, we developed an energy security evaluation model(ESEM) from three dimensions, energy supply-transport security, safety of energy utilization, and stability of political-socioeconomic environment, based on the integrated application of subjective and objective weight allocation technique. Then the spatial-temporal evolution of global energy security pattern and its driving mechanism was analyzed with the method above, and the results are shown as follows:(1) since the 1990 s, the spatial patterns of global energy security have shown a deteriorating trend, with the growth of countries in at-risk type and relatively at-risk type.(2) The spatial distribution of countries with secure energy system shows a strong stability, and these countries are concentrated persistently in Western Europe and North America. The spatial evolution of countries with relatively secure energy system also presents a strong stability, which are mainly distributed in the periphery of the secure ones, namely Central and Southern Europe, South America and Eurasia, while countries with general energy system are mainly distributed in Asia, Africa and Southern Europe, and the spatial-temporal evolution of this type is the main cause for the deterioration of world energy security pattern. Countries with at-risk and relatively at-risk energy system are mainly concentrated in Africa, Asia, the Middle East and Eurasia, rendering spatial extension to the east and south.(3) In the past 20 years, the mechanism for world’s energy security pattern formation gradually transforms from the ‘unitary dimension dominated’ to the ‘binary dimension-dominated’, and the main factors influencing the global energy security pattern become more diverse.(4) In the pattern of world’s energy security, China’s performance on energy security has been the global average since the 1990 s, which shows a decreasing trend in safety of energy utilization dimension. Findings in this study can provide a reference for the government in terms of formulating strategic responses and policy options.展开更多
In hydrogeology it is of great interest to examine the temporal and spatial evolution of aquifers. There are different ways of modeling an aquifer: physical models, models based on analog and mathematical techniques. ...In hydrogeology it is of great interest to examine the temporal and spatial evolution of aquifers. There are different ways of modeling an aquifer: physical models, models based on analog and mathematical techniques. Usually, mathematical techniques involve complex operations difficult to understand for some people, such as differential or partial equations. In contrast, our method requires only a basic knowledge of geometry and trigonometry. Moreover, it is only necessary to know the static level of the aquifer at three different dates. Of course, the results may be limited compared to those that use advanced mathematical methods;however, our method provides a first approximation to determine the behavior of the aquifer through time. Overall, our results allowed us to follow the evolution of the aquifer in detail of various areas of increased extraction and in which removal has been increasing, but also of areas with a considerable recharge during the study period.展开更多
With basic information from 8353 archaeological sites, this study describes a holistic spatial-temporal distribution pattern of archaeological sites of the prehistoric culture sequence from 9.5 ka BP (ka BP = thousand...With basic information from 8353 archaeological sites, this study describes a holistic spatial-temporal distribution pattern of archaeological sites of the prehistoric culture sequence from 9.5 ka BP (ka BP = thousands of years before 0 BP, where "0 BP" is defined as the year AD 1950) to 2.3 ka BP in the region that extends from the Yanshan Mountains to the Liaohe River Plain(i.e., the Yan-Liao region) in northern China. Based on spatial statistics analysis – including the spatial density of the sites and Geographic Information System nearest-neighbour analysis, combined with a review of environmental and climatic data – this paper analyses cultural evolution, the spatial-temporal features of the archaeological sites and human activities against the backdrop of climatic and environmental changes in this region. The results reveal that prehistoric cultural evolution in the Yan-Liao region is extensively influenced by climatic and environmental changes. The Xinglongwa, Zhaobaogou and Fuhe cultures, which primarily developed during a habitable period from 8.5 ka BP to 6.0 ka BP with strong summer monsoons, have similar maximum density values, spatial patterns and subsistence strategies dominated by hunting-gathering. Significant changes occurred in the Hongshan and Lower Xiajiadian cultures, with a significant increase in numbers and densities of sites and a slump in average nearest-neighbour ratio when the environment began to deteriorate starting in 6.0 ka BP. Additionally, with the onset of a weak summer monsoon and the predominance of primitive agriculture, sites of these two cultures present a different type of concentric circle-shaped pattern in space. As the environment continuously deteriorated with increasing aridity and the spread of steppe, more sites were distributed towards the south, and primitive agriculture was replaced by livestock husbandry in the Upper Xiajiadian culture. The most densely populated areas of the studied cultures are centralized within a limited area. The Laohahe River and Jiaolaihe River basins formed the core area in which most archaeological sites were distributed during the strong summer monsoon period and the first few thousand years of the weak summer monsoon period.展开更多
The index of Risk Frequency (RF) and other relative indices are used to analyze the temporal and spatial patterns of environmental riskevents in the past 30 years in Shenyang city. The results show that thereexists si...The index of Risk Frequency (RF) and other relative indices are used to analyze the temporal and spatial patterns of environmental riskevents in the past 30 years in Shenyang city. The results show that thereexists significant difference of the RFs between periods of 1966-1977 and1978-1991 (t=7.353**, t0.01=2.807). During the past 30 years, there areno significant changes of the spatial patterns of the environmental risk,while the proportions of environmental risk among the districts are extremely different. In Shenyang city, there exists a series of high riskenterprises, and the chemical industry is the one with highest risk.展开更多
Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 198...Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 1984 to 2015 were selected to monitor the area of lakes in the Bashang Plateau and to analyze the spatiotemporal evolution and driving forces of lakes in the Bashang Plateau. The results showed that there were 47 lakes in the Bashang Plateau in 2015, with a total area of 37.63 km2, mainly distributed in the central and western regions of the region. From 1984 to 2015, the lakes in Bashang Plateau showed a shrinking trend. At the same time, there are obvious stage differences in lake changes. During 1984-1996, the number of lakes increased by 99 and the total area increased by 124.43 km2. From 1996 to 2015, the number of lakes decreased by 142, and the total area decreased by 183.96 km2. Before 1996, climate change was the dominant factor. However, the shrinkage of lakes after 1996 is the result of climate change and human activities. Among them, the large-scale planting of water consuming crops such as vegetables is the main human activity mode leading to lake shrinkage. This study will help to understand the expansion and contraction factors of the Bashang Plateau lakes in Hebei province and provide a reference for the future protection and management of the lakes.展开更多
Green innovation is an important driving force for high-quality development and an important guarantee for the revitalization of the old industrial base in Northeast China.However,research on green innovation is still...Green innovation is an important driving force for high-quality development and an important guarantee for the revitalization of the old industrial base in Northeast China.However,research on green innovation is still insufficient.Using the super-efficiency epsilon-based measure Malmquist model,kernel density estimation,and spatial econometric model,this study investigated the spatiotemporal evolution characteristics and influencing factors of green innovation efficiency(GIE)in Northeast China from 2005 to 2020.The results reveal that:1)The GIE in Northeast China has obvious phased characteristics,where 2005-2011 was a period of fluctuating decline while 2012-2020 was a period of fluctuating increase,reflecting the severe resource and environmental constraints faced by the green innovation process.2)The GIE in the Northeast China has a significant spatial dependence,which has not formed a relatively stable spatial club feature.The process for improving the GIE in the Northeast China in the future is still arduous and far off.3)The interweaving and mutual influence of nonequilibrium factors have led to the diversity and complexity of the spatiotemporal pattern evolution of GIE.Overall,the level of economic development and industrial structure has a positive effect,while foreign investment and industrial agglomeration have a negative effect.The direct effects of government regulation,resource endowment,science and technology,environmental regulation,and urbanization are not significant.The research conclusion of this article can provide important reference for the revitalization of Northeast China.展开更多
This article presents the findings of a study of the spheres of urban influence with regard to all cities in China(not including Hong Kong,Macao and Taiwan Province of China)in the years 1990,2000 and 2009.An optimize...This article presents the findings of a study of the spheres of urban influence with regard to all cities in China(not including Hong Kong,Macao and Taiwan Province of China)in the years 1990,2000 and 2009.An optimized gravity model with comprehensive time distance was used to carry out a detailed analysis of the spatial patterns of Chinese spheres of urban influence and the spatial characteristics of urban agglomerations.Such urban agglomerations are characterized by high density population and a developed economy,which are also considered as the national competition unit.This paper initially identifies four spatial patterns of urban agglomerations based on the spatial layout of city groups during their evolution.Some basic characteristics of urban agglomerations are outlined,including the number of cities,the size of cities and the functions of urban centers.These characteristics are examined by using statistical methods and Geographic Information System(GIS).The main findings from this research are that the development stages and structures of urban agglomerations in China vary significantly.It is also clear that the stages and evolution of spatial patterns are strongly affected and dominated by both policy and location factors.展开更多
The study of sulfur hexafluoride(SF6) discharge is vital for its application in gas-insulated equipment. Direct current partial discharge(PD) may cause SF6 decomposition, and the decomposed products of SF6, such as F ...The study of sulfur hexafluoride(SF6) discharge is vital for its application in gas-insulated equipment. Direct current partial discharge(PD) may cause SF6 decomposition, and the decomposed products of SF6, such as F atoms, play a dominant role in the breakdown of insulation systems. In this study, the PD caused by metal protrusion defects is simulated by a needle-plate electrode using pulsed high voltage in SF6/Ar mixtures. The spatial and temporal characteristics of SF6/Ar plasma are analyzed by measuring the emission spectra of F and Ar atoms, which are important for understanding the characteristics of PD. The spatial resolved results show that both F and Ar atom spectral intensities increase first from the plate anode to the needle and then decrease under the conditions of a background pressure of400 Pa, peak voltage of-1000 V, frequency of 2 kHz, pulse width of 60 μs, and electrode gap of 5-9 mm. However, the distribution characteristics of F and Ar are significantly different. The temporal distribution results show that the spectral intensity of Ar decreasesfirst and then increases slowly, while the spectral intensity of F increases slowly for the duration of the pulsed discharge at the electrode gap of 5 mm and the pulse width of40-80 μs.展开更多
Spatio-temporal patterns of drought from 1961 to 2013 over the Beijing-Tianjin-Hebei(BTH) region of China were analyzed using the Palmer Drought Severity index(PDSI) based on 21 meteorological stations. Overall, chang...Spatio-temporal patterns of drought from 1961 to 2013 over the Beijing-Tianjin-Hebei(BTH) region of China were analyzed using the Palmer Drought Severity index(PDSI) based on 21 meteorological stations. Overall, changes in the mean-state of drought detected in recent decades were due to decreases in precipitation and potential evapotranspiration. The Empirical Orthogonal Functions(EOF) method was used to decompose drought into spatio-temporal patterns, and the first two EOF modes were analyzed. According to the first leading EOF mode(48.5%), the temporal variability(Principal Components, PC1) was highly positively correlated with annual series of PDSI(r=+0.99). The variance decomposition method was further applied to explain the inter-decadal temporal and spatial variations of drought relative to the total variation. We find that 90% of total variance was explained by time variance, and both total and time variance dramatically decreased from 1982 to 2013. The total variance was consistent with extreme climate events at the inter-decadal scale(r=0.71, p<0.01). Comparing the influence of climate change on the annual drought in two different long-term periods characterized by dramatic global warming(P1: 1961–1989 and P2: 1990–2013), we find that temperature sensitivity in the P2 was three times more than that in the P1.展开更多
Laser-Induced Breakdown Spectroscopy （LIBS） has been demonstrated to be an effective method for slag analysis. In order to better clarify the nature of the plasma generated from a slag sample, an Nd：YAG pulse laser...Laser-Induced Breakdown Spectroscopy （LIBS） has been demonstrated to be an effective method for slag analysis. In order to better clarify the nature of the plasma generated from a slag sample, an Nd：YAG pulse laser at 1064 nm wavelength was used to ablate the slag sample in air. The temporal and spatial evolutions of plasma parameters, including emission intensity, electronic density and plasma temperature, have been studied. It is shown that the electron density and plasma temperature drop off rapidly with the delay time as a result of plasma expansion and cooling. It has been found that the electron density of the whole plasma is close to that of the center regions in the plasma. The results of the spatial distributions on the two-dimensional plane have shown that there is a big region with lower electron density values caused by the recombination process in the center of the plasma. The maximum of the plasma temperature takes place at the regions close to the target, and the border of the plasma front-head has higher plasma temperatures than that of the center part.展开更多
The Da-Xiao Liangshan mountains are critical ecological function areas and essential ecological barriers in the upper reaches of the Yangtze River in China.This study selected a total of six periods of land use land c...The Da-Xiao Liangshan mountains are critical ecological function areas and essential ecological barriers in the upper reaches of the Yangtze River in China.This study selected a total of six periods of land use land cover(LULC)data from 1995 to 2020,to estimate the ecosystem service value(ESV)and analyzed its spatiotemporal evolution and topographic gradient divergence.The results showed that:(1)The ESV increased by 1.1 billion yuan,with an increase rate of 1.47%from 1995 to 2020.Two time periods,2005–2010 and 2015–2020,showed more significant increases than other periods.(2)The elevation and slope of mountainous areas determine the type of land use and further influence the spatial pattern of ESV.(3)Although woodland and grassland are the main land use types of the study area(more than 90%),the hydrological regulation function of the water area partially compensated for the impact of the encroachment of the built-up area on the ESV of grassland.(4)The spatial distribution of ESVs showed an inverted V-shaped characteristic as the topographic gradient increased,with the dominant position being the 5th topographic gradient zone.Finally,this study provided relevant recommendations for ecosystem protection and optimization.The findings of this study clarified the influence of topographical factors on the spatial differentiation of ESV and provided novel insights into ecosystem protection.展开更多
The rapid development of China’s economy and urbanization has given rise to noticeable environmental problems,among which the change of air quality has received extensive attention.The panel data of PM2.5(particles w...The rapid development of China’s economy and urbanization has given rise to noticeable environmental problems,among which the change of air quality has received extensive attention.The panel data of PM2.5(particles with an aerodynamic diameter of 2.5μm or less)in 343 prefecture-level cities in China from 1998 to 2016 were statistically analyzed to reveal the characteristics of the temporal evolution and spatial variation of China’s air quality in the past two decades.The results show that:1)the overall deterioration trend of air quality is obvious throughout the country.The variation trend of PM2.5 was divided into three phases:rapid-growth phase(1998–2007),lag phase(2006–2011)and mildly-incremental phase(2012–2016),with their average growth rates of 7.19%,-3.59%and 0.52%,respectively.2)The spatial difference of PM2.5 values in China increased significantly with time.Since 2003,the high-value area in the east has expanded rapidly,and polarization became much more pronounced.The change rate of PM2.5 is high in the east and west and low in the middle.The change rates of most areas in the west exceed more than 80%,and in the east lie somewhere between 40%and 60%.In the midlands,the change rate is not large and some regions even show a negative growth.3)The change rate of PM2.5 is also high in areas with higher values.However,in regions where the change rate of PM2.5 is high,the value of PM2.5 is not always high.The high change rate is mainly attributable to the low base value of PM2.5 and the cities concerned belong to sensitive areas.4)According to the PM2.5 warning index,the number of strong,medium,weak and non-warning areas in China is 45,85,159 and 54,respectively.展开更多
Negative air ions are natural components of the air we breathe Forests are the main continuous natural source of negative air ions （NAI）. The spatio-temporal patterns of negative air ions were explored in Shanghai, ...Negative air ions are natural components of the air we breathe Forests are the main continuous natural source of negative air ions （NAI）. The spatio-temporal patterns of negative air ions were explored in Shanghai, based on monthly monitoring in 15 parks from March 2009 to February 2010. In each park, sampling sites were selected in forests and open spaces. The annual variation in negative air ion concentrations （NAIC） showed peak values from June to October and minimum values from December to January. NAIC were highest in summer and autumn, intermediate in spring, and lowest in winter. During spring and summer, NAIC in open spaces were significantly higher in rural areas than those in suburban areas. However, there were no significant differences in NAIC at forest sites among seasons. For open spaces, total suspended particles （TSP） were the dominant determining factor of NAIC in sum- mer, and air temperature and air humidity were the dominant determining factors of NAIC in spring, which were tightly correlated with Shanghai＇s ongoing urbanization and its impacts on the environment. R is suggested that urbanization could induce variation in NAIC along the urban-rural gradient, but that may not change the temporal variation pattern. Fur- thermore, the effects of urbanization on NAIC were limited in non-vegetated or less-vegetated sites, such as open spaces, but not in well-vegetated areas, such as urban forests. Therefore, we suggest that urban greening, especially urban forest, has significant resistance to theeffect of urbanization on NAIC.展开更多
Fuel retention measurement on plasma-facing components is an active field of study in magnetic confinement nuclear fusion devices.The laser-induced breakdown spectroscopy(LIBS)diagnostic method has been well demonstra...Fuel retention measurement on plasma-facing components is an active field of study in magnetic confinement nuclear fusion devices.The laser-induced breakdown spectroscopy(LIBS)diagnostic method has been well demonstrated to detect the elemental distribution in PFCs.In this work,an upgraded co-axis LIBS system based on a linear fiber bundle collection system has been developed to measure the hydrogen(H) retention on a tantalum(Ta) sample under a vacuum condition.The spatial resolution measurement of the different positions of the LIBS plasma can be achieved simultaneously with varying delay times.The temporal and spatial evolution results of LIBS plasma emission show that the H plasma observably expands from the delay times of 0-200 ns.The diameter of Ta plasma is about 6 mm which is much less than the size of H plasma after 200 ns.The difference in the temporal and spatial evolution behaviors between H plasma and Ta plasma is due to the great difference in the atomic mass of H and Ta.The depth profile result shows that H retention mainly exists on the surface of the sample.The temporal and spatial evolution behaviors of the electron excited temperature are consistent with that of the Ta emission.The result will further improve the understanding of the evolution of the dynamics of LIBS plasma and optimize the current collection system of in situ LIBS in fusion devices.展开更多
Urban air pollution is a prominent problem related to the urban development in China, especially in the densely populated urban agglomerations. Therefore, scientific examination of regional variation of air quality an...Urban air pollution is a prominent problem related to the urban development in China, especially in the densely populated urban agglomerations. Therefore, scientific examination of regional variation of air quality and its dominant factors is of great importance to regional environmental management. In contrast to traditional air pollution researches which only concentrate on a single year or a single pollutant, this paper analyses spatiotemporal patterns and determinants of air quality in disparate regions based on the air quality index(AQI) of the Yangtze River Delta region(YRD) of China from 2014 to 2016. Results show that the annual average value of the AQI in the YRD region decreases from 2014 to 2016 and exhibit a basic characteristic of ‘higher in winter, lower in summer and slightly high in spring and autumn'. The attainment rate of the AQI shows an apparently spatial stratified heterogeneity, Hefei metropolitan area and Nanjing metropolitan area keeping the worst air quality. The frequency of air pollution occurring in large regions was gradually decreasing during the study period. Drawing from entropy method analysis, industrialization and urbanization represented by per capita GDP and total energy consumption were the most important factors. Furthermore, population agglomeration is a factor that cannot be ignored especially in some mega-cities. Limited to data collection, more research is needed to gain insight into the spatiotemporal pattern and influence mechanism in the future.展开更多
Understanding crop patterns and their changes on regional scale is a critical re- quirement for projecting agro-ecosystem dynamics. However, tools and methods for mapping the distribution of crop area and yield are st...Understanding crop patterns and their changes on regional scale is a critical re- quirement for projecting agro-ecosystem dynamics. However, tools and methods for mapping the distribution of crop area and yield are still lacking. Based on the cross-entropy theory, a spatial production allocation model （SPAM） has been developed for presenting spa- tio-temporal dynamics of maize cropping system in Northeast China during 1980-2010. The simulated results indicated that （1） maize sown area expanded northwards to 48~N before 2000, after that the increased sown area mainly occurred in the central and southern parts of Northeast China. Meanwhile, maize also expanded eastwards to 127°E and lower elevation （less than 100 m） as well as higher elevation （mainly distributed between 200 m and 350 m）; （2） maize yield has been greatly promoted for most planted area of Northeast China, espe- cially in the planted zone between 42°N and 48°N, while the yield increase was relatively homogeneous without obvious longitudinal variations for whole region; （3） maize planting density increased gradually to a moderately high level over the investigated period, which reflected the trend of aggregation of maize cultivation driven by market demand.展开更多
基金Sponsored by Fundamental Research Funds for the Central Universities(GK201303006)National Natural Science Foundation of China(41171139)Key Projects of Humanities and Social Sciences Research Base of Guangdong Colleges and Universities(09JDXM84001)
文摘Formation and evolution of rural settlement patterns in Lianzhou City,Guangdong Province were analyzed from the perspective of space and time,on the basis of its gazetteer and relevant historical data.The results show that Lianzhou was first founded in the sixth year of Yuanding Period of the Western Han Dynasty,and its development could be roughly classified into 6 stages according to the construction of south–north traffic lines and regional development progress,and it witnessed the fastest development in the Ming and Qing Dynasty.In terms of spatial distribution,rural settlements in the local area show spatial continuity,Lianzhou Town is the core of rural settlement growth in the city,and towns with the most concentrated rural settlements in all stages are located in central-west and northeast parts of the city,and those with lower density of rural settlements are mostly located in minority regions in the north and mountainous areas in the east.On the basis of the above facts,the paper studies the influence of natural geological conditions,immigrant,traffic,economic development and ethnic composition on the establishment and development of rural settlements in Lianzhou City.
文摘[Objective] The paper aimed to reflect the spatial pattern and temporal and spatial evolution characteristics, the differences between inter-regional tourism economy was measured from the quality aspect, which provided a reference for the local governments in the future tourism development. [Method] Using the location entropy methods, three time periods side of tourism-related date of 2000, 2005, 2007 were selected, from the angle of the spatial pattern and the evolution of the differences within the different scales, the spatial and temporal evolution characteristics of the economic development level of Jiangsu were analysed. [Result] The results showed that from the aspect of spatial evolution pattern, as time goes on, the economic development of Jiangsu tourism has experienced morphological evolution of concentration- dispersion decrease-stability; when it comes to the development of the tourism economy, in recent years, the overall gap between the tourism economy in Jiangsu did not widen, the gap mainly led by the region one after another. According to their volatility, it will be divided into four categories: A Stable type (Wuxi, Xuzhou, Lianyungang and Taizhou), B Increasing type (Huai’an), C Fluctuations type (Nanjing, Changzhou, Suzhou and Yangzhou) and D Depression type (Nantong, Yancheng, Zhenjiang and Suqian). [Conclusion] Location entropy was quoted into tourism economic analysis, the method was simple and easy to understand, the result was accurate and convincing, which provided a reference for travel economic development and investment decision-making of Jiangsu.
基金Key Project of National Science and Technology Supporting Program, No.2006038053001 Key Project of National Natural Science Foundation of China, No.40535026 Environment Protection and Public Welfare Project of Ministry of Science and Technology, No.08L80370AJ
文摘The issue of China＇s energy supply security is not only the key problem which af- fects China＇s rapid and sustainable development in the 21st century, but also the one which international attention focuses on. Based on the notable characteristic of spatial imbalance between energy production and consumption in China, this paper takes the evolution of China＇s primary energy resources development（excluding hydropower） from 1949 to 2007 as the study object, with the aim to sum up the evolutive characteristics and laws of China＇s energy resources development in the past nearly 60 years. Then, based on comprehensive considerations of coal＇s, oil＇s and natural gas＇s basic reserves, qualities, geological conditions production status, and ecological service function of every province, this paper adopts development potential index （DP）to evaluate the development potential of every province＇s en- ergy resources, and divide them into different ranks. Conclusions are drawn as follows： （1） Generally speaking, China＇s gross energy production was increasing in waves from 1949 to 2007. From the viewpoint of spatial patterns, China＇s energy resources development has shown a characteristic of ＂concentrating to the north and central areas, and evolving from linear-shaped to ＂T-shaped＂ pattern gradually since 1949. （2） The structure evolution of China＇s energy resources development in general has shown a trend of ＂coal proportion is dominant but decreasing, while oil and gas proportions are increasing＂ since 1949. （3） At the provincial scale, China＇s energy resources development potential could be divided into large, sub-large, general and small ranks, four in all. In the future, the spatial pattern of China＇s energy production will evolve from ＂T-shaped＂ to ＂R-shaped pattern＂. These conclusions will help to clarify the temporal and spatial characteristics and laws of China＇s energy resources development, and will be beneficial for China to design scientific and rational energy development strategies and plans, coordinate spatial imbalance of energy production and consumption, ensure national energy supply, avoid energy resources waste and disorderly development, and promote regional sustainable development under the globalization back-ground with changeful international energy market.
文摘According to the data of precise relevelling and deformation measurement across faults, the temporal and spatial evolution process of crustal deformation field in the source and peripheral regions of the Tangshan earthquake (1976, M S=7.8), from 22 years before the earthquake to 9 years after, is described with the method of crustal deforma tion pattern dynamics. The crustal unstable zones first occur in the exterior, and then surround the focal region by contracting from the exterior to the interior, when the focal region appears to be unstable but does not lose stability. After the transient stable state, the second unstable process from the exterior to interior appears, which results in the instability of focal region. 'Deformation gap', 'earthquake gap' and 'locked fault zone' occur before instability, and their spatial distributions overlap, but their occurrence times have little differences. The earthquake occurs after the impending pre slide of the faults in the focal region. The studied results of the evolution process of crustal deformation field are identical with each other and with that of numeric simulation of crustal stress field, which supports the evolution model of seismogenic system with a strong body as its core.
基金National Natural Science Foundation of China,No.41671126,No.41171147Special Funds for Scientific Research Institutes from Science&Technology Department of Fujian Province,No.2016R1032-5
文摘In this study, we developed an energy security evaluation model(ESEM) from three dimensions, energy supply-transport security, safety of energy utilization, and stability of political-socioeconomic environment, based on the integrated application of subjective and objective weight allocation technique. Then the spatial-temporal evolution of global energy security pattern and its driving mechanism was analyzed with the method above, and the results are shown as follows:(1) since the 1990 s, the spatial patterns of global energy security have shown a deteriorating trend, with the growth of countries in at-risk type and relatively at-risk type.(2) The spatial distribution of countries with secure energy system shows a strong stability, and these countries are concentrated persistently in Western Europe and North America. The spatial evolution of countries with relatively secure energy system also presents a strong stability, which are mainly distributed in the periphery of the secure ones, namely Central and Southern Europe, South America and Eurasia, while countries with general energy system are mainly distributed in Asia, Africa and Southern Europe, and the spatial-temporal evolution of this type is the main cause for the deterioration of world energy security pattern. Countries with at-risk and relatively at-risk energy system are mainly concentrated in Africa, Asia, the Middle East and Eurasia, rendering spatial extension to the east and south.(3) In the past 20 years, the mechanism for world’s energy security pattern formation gradually transforms from the ‘unitary dimension dominated’ to the ‘binary dimension-dominated’, and the main factors influencing the global energy security pattern become more diverse.(4) In the pattern of world’s energy security, China’s performance on energy security has been the global average since the 1990 s, which shows a decreasing trend in safety of energy utilization dimension. Findings in this study can provide a reference for the government in terms of formulating strategic responses and policy options.
文摘In hydrogeology it is of great interest to examine the temporal and spatial evolution of aquifers. There are different ways of modeling an aquifer: physical models, models based on analog and mathematical techniques. Usually, mathematical techniques involve complex operations difficult to understand for some people, such as differential or partial equations. In contrast, our method requires only a basic knowledge of geometry and trigonometry. Moreover, it is only necessary to know the static level of the aquifer at three different dates. Of course, the results may be limited compared to those that use advanced mathematical methods;however, our method provides a first approximation to determine the behavior of the aquifer through time. Overall, our results allowed us to follow the evolution of the aquifer in detail of various areas of increased extraction and in which removal has been increasing, but also of areas with a considerable recharge during the study period.
基金National Natural Science Foundation of China,No.41371148Major Program of National Social Science Fund of China,No.13&ZD082
文摘With basic information from 8353 archaeological sites, this study describes a holistic spatial-temporal distribution pattern of archaeological sites of the prehistoric culture sequence from 9.5 ka BP (ka BP = thousands of years before 0 BP, where "0 BP" is defined as the year AD 1950) to 2.3 ka BP in the region that extends from the Yanshan Mountains to the Liaohe River Plain(i.e., the Yan-Liao region) in northern China. Based on spatial statistics analysis – including the spatial density of the sites and Geographic Information System nearest-neighbour analysis, combined with a review of environmental and climatic data – this paper analyses cultural evolution, the spatial-temporal features of the archaeological sites and human activities against the backdrop of climatic and environmental changes in this region. The results reveal that prehistoric cultural evolution in the Yan-Liao region is extensively influenced by climatic and environmental changes. The Xinglongwa, Zhaobaogou and Fuhe cultures, which primarily developed during a habitable period from 8.5 ka BP to 6.0 ka BP with strong summer monsoons, have similar maximum density values, spatial patterns and subsistence strategies dominated by hunting-gathering. Significant changes occurred in the Hongshan and Lower Xiajiadian cultures, with a significant increase in numbers and densities of sites and a slump in average nearest-neighbour ratio when the environment began to deteriorate starting in 6.0 ka BP. Additionally, with the onset of a weak summer monsoon and the predominance of primitive agriculture, sites of these two cultures present a different type of concentric circle-shaped pattern in space. As the environment continuously deteriorated with increasing aridity and the spread of steppe, more sites were distributed towards the south, and primitive agriculture was replaced by livestock husbandry in the Upper Xiajiadian culture. The most densely populated areas of the studied cultures are centralized within a limited area. The Laohahe River and Jiaolaihe River basins formed the core area in which most archaeological sites were distributed during the strong summer monsoon period and the first few thousand years of the weak summer monsoon period.
文摘The index of Risk Frequency (RF) and other relative indices are used to analyze the temporal and spatial patterns of environmental riskevents in the past 30 years in Shenyang city. The results show that thereexists significant difference of the RFs between periods of 1966-1977 and1978-1991 (t=7.353**, t0.01=2.807). During the past 30 years, there areno significant changes of the spatial patterns of the environmental risk,while the proportions of environmental risk among the districts are extremely different. In Shenyang city, there exists a series of high riskenterprises, and the chemical industry is the one with highest risk.
文摘Lakes are important ecological water sources in the Bashang Plateau. Its expansion or shrinkage directly affects the ecological security of the plateau and its surrounding areas. In this study, Landsat images from 1984 to 2015 were selected to monitor the area of lakes in the Bashang Plateau and to analyze the spatiotemporal evolution and driving forces of lakes in the Bashang Plateau. The results showed that there were 47 lakes in the Bashang Plateau in 2015, with a total area of 37.63 km2, mainly distributed in the central and western regions of the region. From 1984 to 2015, the lakes in Bashang Plateau showed a shrinking trend. At the same time, there are obvious stage differences in lake changes. During 1984-1996, the number of lakes increased by 99 and the total area increased by 124.43 km2. From 1996 to 2015, the number of lakes decreased by 142, and the total area decreased by 183.96 km2. Before 1996, climate change was the dominant factor. However, the shrinkage of lakes after 1996 is the result of climate change and human activities. Among them, the large-scale planting of water consuming crops such as vegetables is the main human activity mode leading to lake shrinkage. This study will help to understand the expansion and contraction factors of the Bashang Plateau lakes in Hebei province and provide a reference for the future protection and management of the lakes.
基金Under the auspices of the National Natural Science Foundation of China(No.42571228,42401212)National Natural Science Foundation of Shandong(No.ZR2024MD022)。
文摘Green innovation is an important driving force for high-quality development and an important guarantee for the revitalization of the old industrial base in Northeast China.However,research on green innovation is still insufficient.Using the super-efficiency epsilon-based measure Malmquist model,kernel density estimation,and spatial econometric model,this study investigated the spatiotemporal evolution characteristics and influencing factors of green innovation efficiency(GIE)in Northeast China from 2005 to 2020.The results reveal that:1)The GIE in Northeast China has obvious phased characteristics,where 2005-2011 was a period of fluctuating decline while 2012-2020 was a period of fluctuating increase,reflecting the severe resource and environmental constraints faced by the green innovation process.2)The GIE in the Northeast China has a significant spatial dependence,which has not formed a relatively stable spatial club feature.The process for improving the GIE in the Northeast China in the future is still arduous and far off.3)The interweaving and mutual influence of nonequilibrium factors have led to the diversity and complexity of the spatiotemporal pattern evolution of GIE.Overall,the level of economic development and industrial structure has a positive effect,while foreign investment and industrial agglomeration have a negative effect.The direct effects of government regulation,resource endowment,science and technology,environmental regulation,and urbanization are not significant.The research conclusion of this article can provide important reference for the revitalization of Northeast China.
基金Under the auspices of National Natural Science Foundation of China(No.40901088,41271174)
文摘This article presents the findings of a study of the spheres of urban influence with regard to all cities in China(not including Hong Kong,Macao and Taiwan Province of China)in the years 1990,2000 and 2009.An optimized gravity model with comprehensive time distance was used to carry out a detailed analysis of the spatial patterns of Chinese spheres of urban influence and the spatial characteristics of urban agglomerations.Such urban agglomerations are characterized by high density population and a developed economy,which are also considered as the national competition unit.This paper initially identifies four spatial patterns of urban agglomerations based on the spatial layout of city groups during their evolution.Some basic characteristics of urban agglomerations are outlined,including the number of cities,the size of cities and the functions of urban centers.These characteristics are examined by using statistical methods and Geographic Information System(GIS).The main findings from this research are that the development stages and structures of urban agglomerations in China vary significantly.It is also clear that the stages and evolution of spatial patterns are strongly affected and dominated by both policy and location factors.
基金supported by National Natural Science Foundation of China (Nos. 11605023, 11805028, and 11705020)the National Key R&D Program of China (No. 2017YFE0301300)+1 种基金the China Postdoctoral Science Foundation (Nos. 2017T100172 and 2016M591423)the Fundamental Research Funds for the Central Universities (Nos. DUT17RC(4)53 and DUT18LK38)
文摘The study of sulfur hexafluoride(SF6) discharge is vital for its application in gas-insulated equipment. Direct current partial discharge(PD) may cause SF6 decomposition, and the decomposed products of SF6, such as F atoms, play a dominant role in the breakdown of insulation systems. In this study, the PD caused by metal protrusion defects is simulated by a needle-plate electrode using pulsed high voltage in SF6/Ar mixtures. The spatial and temporal characteristics of SF6/Ar plasma are analyzed by measuring the emission spectra of F and Ar atoms, which are important for understanding the characteristics of PD. The spatial resolved results show that both F and Ar atom spectral intensities increase first from the plate anode to the needle and then decrease under the conditions of a background pressure of400 Pa, peak voltage of-1000 V, frequency of 2 kHz, pulse width of 60 μs, and electrode gap of 5-9 mm. However, the distribution characteristics of F and Ar are significantly different. The temporal distribution results show that the spectral intensity of Ar decreasesfirst and then increases slowly, while the spectral intensity of F increases slowly for the duration of the pulsed discharge at the electrode gap of 5 mm and the pulse width of40-80 μs.
基金National Key Research and Development Program of China,No.2016YFC0401401,No.2016YFA0602402Key Program of the Chinese Academy of Sciences,No.ZDRW-ZS-2017-3-1+1 种基金The Chinese Academy of Sciences(CAS)Pioneer Hundred Talents ProgramNational Natural Science Foundation of China,No.41601035
文摘Spatio-temporal patterns of drought from 1961 to 2013 over the Beijing-Tianjin-Hebei(BTH) region of China were analyzed using the Palmer Drought Severity index(PDSI) based on 21 meteorological stations. Overall, changes in the mean-state of drought detected in recent decades were due to decreases in precipitation and potential evapotranspiration. The Empirical Orthogonal Functions(EOF) method was used to decompose drought into spatio-temporal patterns, and the first two EOF modes were analyzed. According to the first leading EOF mode(48.5%), the temporal variability(Principal Components, PC1) was highly positively correlated with annual series of PDSI(r=+0.99). The variance decomposition method was further applied to explain the inter-decadal temporal and spatial variations of drought relative to the total variation. We find that 90% of total variance was explained by time variance, and both total and time variance dramatically decreased from 1982 to 2013. The total variance was consistent with extreme climate events at the inter-decadal scale(r=0.71, p<0.01). Comparing the influence of climate change on the annual drought in two different long-term periods characterized by dramatic global warming(P1: 1961–1989 and P2: 1990–2013), we find that temperature sensitivity in the P2 was three times more than that in the P1.
基金supported by National Natural Science Foundation of China(No.11075184)the Knowledge Innovation Program of the Chinese Academy of Sciences(No.Y03RC21124)
文摘Laser-Induced Breakdown Spectroscopy （LIBS） has been demonstrated to be an effective method for slag analysis. In order to better clarify the nature of the plasma generated from a slag sample, an Nd：YAG pulse laser at 1064 nm wavelength was used to ablate the slag sample in air. The temporal and spatial evolutions of plasma parameters, including emission intensity, electronic density and plasma temperature, have been studied. It is shown that the electron density and plasma temperature drop off rapidly with the delay time as a result of plasma expansion and cooling. It has been found that the electron density of the whole plasma is close to that of the center regions in the plasma. The results of the spatial distributions on the two-dimensional plane have shown that there is a big region with lower electron density values caused by the recombination process in the center of the plasma. The maximum of the plasma temperature takes place at the regions close to the target, and the border of the plasma front-head has higher plasma temperatures than that of the center part.
基金supported by the National Natural Science Foundation of China(Grant No.52078423)the Sichuan Province Science and Technology Support Program(Grant No.2020YFS0309 and 2020YFS0054)+1 种基金the China Engineering Science and Technology Strategic Consulting Project(Grant No.2022JDR0356)the Key Research Institution of Philosophy and Social Sciences in Sichuan Province:Research Center of National Parks(Grant No.GJGY2023-YB001)。
文摘The Da-Xiao Liangshan mountains are critical ecological function areas and essential ecological barriers in the upper reaches of the Yangtze River in China.This study selected a total of six periods of land use land cover(LULC)data from 1995 to 2020,to estimate the ecosystem service value(ESV)and analyzed its spatiotemporal evolution and topographic gradient divergence.The results showed that:(1)The ESV increased by 1.1 billion yuan,with an increase rate of 1.47%from 1995 to 2020.Two time periods,2005–2010 and 2015–2020,showed more significant increases than other periods.(2)The elevation and slope of mountainous areas determine the type of land use and further influence the spatial pattern of ESV.(3)Although woodland and grassland are the main land use types of the study area(more than 90%),the hydrological regulation function of the water area partially compensated for the impact of the encroachment of the built-up area on the ESV of grassland.(4)The spatial distribution of ESVs showed an inverted V-shaped characteristic as the topographic gradient increased,with the dominant position being the 5th topographic gradient zone.Finally,this study provided relevant recommendations for ecosystem protection and optimization.The findings of this study clarified the influence of topographical factors on the spatial differentiation of ESV and provided novel insights into ecosystem protection.
基金Under the auspices of the National Social Science Foundation of China(No.18ZDA052)the National Natural Science Foundation of China(No.41301154)。
文摘The rapid development of China’s economy and urbanization has given rise to noticeable environmental problems,among which the change of air quality has received extensive attention.The panel data of PM2.5(particles with an aerodynamic diameter of 2.5μm or less)in 343 prefecture-level cities in China from 1998 to 2016 were statistically analyzed to reveal the characteristics of the temporal evolution and spatial variation of China’s air quality in the past two decades.The results show that:1)the overall deterioration trend of air quality is obvious throughout the country.The variation trend of PM2.5 was divided into three phases:rapid-growth phase(1998–2007),lag phase(2006–2011)and mildly-incremental phase(2012–2016),with their average growth rates of 7.19%,-3.59%and 0.52%,respectively.2)The spatial difference of PM2.5 values in China increased significantly with time.Since 2003,the high-value area in the east has expanded rapidly,and polarization became much more pronounced.The change rate of PM2.5 is high in the east and west and low in the middle.The change rates of most areas in the west exceed more than 80%,and in the east lie somewhere between 40%and 60%.In the midlands,the change rate is not large and some regions even show a negative growth.3)The change rate of PM2.5 is also high in areas with higher values.However,in regions where the change rate of PM2.5 is high,the value of PM2.5 is not always high.The high change rate is mainly attributable to the low base value of PM2.5 and the cities concerned belong to sensitive areas.4)According to the PM2.5 warning index,the number of strong,medium,weak and non-warning areas in China is 45,85,159 and 54,respectively.
基金supported by the National Natural Science Foundation of China(No.40971041)
文摘Negative air ions are natural components of the air we breathe Forests are the main continuous natural source of negative air ions （NAI）. The spatio-temporal patterns of negative air ions were explored in Shanghai, based on monthly monitoring in 15 parks from March 2009 to February 2010. In each park, sampling sites were selected in forests and open spaces. The annual variation in negative air ion concentrations （NAIC） showed peak values from June to October and minimum values from December to January. NAIC were highest in summer and autumn, intermediate in spring, and lowest in winter. During spring and summer, NAIC in open spaces were significantly higher in rural areas than those in suburban areas. However, there were no significant differences in NAIC at forest sites among seasons. For open spaces, total suspended particles （TSP） were the dominant determining factor of NAIC in sum- mer, and air temperature and air humidity were the dominant determining factors of NAIC in spring, which were tightly correlated with Shanghai＇s ongoing urbanization and its impacts on the environment. R is suggested that urbanization could induce variation in NAIC along the urban-rural gradient, but that may not change the temporal variation pattern. Fur- thermore, the effects of urbanization on NAIC were limited in non-vegetated or less-vegetated sites, such as open spaces, but not in well-vegetated areas, such as urban forests. Therefore, we suggest that urban greening, especially urban forest, has significant resistance to theeffect of urbanization on NAIC.
基金supported by National Key R&D Program of China(No.2017TFE0301300)the National Natural Science Foundation of China(Nos.11605023,11805028,11861131010)the China Postdoctoral Science Foundation(Nos.2017T100172,2016M591423)。
文摘Fuel retention measurement on plasma-facing components is an active field of study in magnetic confinement nuclear fusion devices.The laser-induced breakdown spectroscopy(LIBS)diagnostic method has been well demonstrated to detect the elemental distribution in PFCs.In this work,an upgraded co-axis LIBS system based on a linear fiber bundle collection system has been developed to measure the hydrogen(H) retention on a tantalum(Ta) sample under a vacuum condition.The spatial resolution measurement of the different positions of the LIBS plasma can be achieved simultaneously with varying delay times.The temporal and spatial evolution results of LIBS plasma emission show that the H plasma observably expands from the delay times of 0-200 ns.The diameter of Ta plasma is about 6 mm which is much less than the size of H plasma after 200 ns.The difference in the temporal and spatial evolution behaviors between H plasma and Ta plasma is due to the great difference in the atomic mass of H and Ta.The depth profile result shows that H retention mainly exists on the surface of the sample.The temporal and spatial evolution behaviors of the electron excited temperature are consistent with that of the Ta emission.The result will further improve the understanding of the evolution of the dynamics of LIBS plasma and optimize the current collection system of in situ LIBS in fusion devices.
基金Under the auspices of Key Projects of the National Social Science Fund(No.16AJL015)Youth Project of Natural Science Foundation of Jiangsu Province(No.BK20170440)+1 种基金Open Foundation of Key Laboratory of Watershed Geographical Science(No.WSGS2017004)Project of Nantong Key Laboratory(No.CP12016005)
文摘Urban air pollution is a prominent problem related to the urban development in China, especially in the densely populated urban agglomerations. Therefore, scientific examination of regional variation of air quality and its dominant factors is of great importance to regional environmental management. In contrast to traditional air pollution researches which only concentrate on a single year or a single pollutant, this paper analyses spatiotemporal patterns and determinants of air quality in disparate regions based on the air quality index(AQI) of the Yangtze River Delta region(YRD) of China from 2014 to 2016. Results show that the annual average value of the AQI in the YRD region decreases from 2014 to 2016 and exhibit a basic characteristic of ‘higher in winter, lower in summer and slightly high in spring and autumn'. The attainment rate of the AQI shows an apparently spatial stratified heterogeneity, Hefei metropolitan area and Nanjing metropolitan area keeping the worst air quality. The frequency of air pollution occurring in large regions was gradually decreasing during the study period. Drawing from entropy method analysis, industrialization and urbanization represented by per capita GDP and total energy consumption were the most important factors. Furthermore, population agglomeration is a factor that cannot be ignored especially in some mega-cities. Limited to data collection, more research is needed to gain insight into the spatiotemporal pattern and influence mechanism in the future.
基金Foundation： National Natural Science Foundation of China, No.41171328, No.41201184, No.41101537 National Basic Program of China, No.2010CB951502
文摘Understanding crop patterns and their changes on regional scale is a critical re- quirement for projecting agro-ecosystem dynamics. However, tools and methods for mapping the distribution of crop area and yield are still lacking. Based on the cross-entropy theory, a spatial production allocation model （SPAM） has been developed for presenting spa- tio-temporal dynamics of maize cropping system in Northeast China during 1980-2010. The simulated results indicated that （1） maize sown area expanded northwards to 48~N before 2000, after that the increased sown area mainly occurred in the central and southern parts of Northeast China. Meanwhile, maize also expanded eastwards to 127°E and lower elevation （less than 100 m） as well as higher elevation （mainly distributed between 200 m and 350 m）; （2） maize yield has been greatly promoted for most planted area of Northeast China, espe- cially in the planted zone between 42°N and 48°N, while the yield increase was relatively homogeneous without obvious longitudinal variations for whole region; （3） maize planting density increased gradually to a moderately high level over the investigated period, which reflected the trend of aggregation of maize cultivation driven by market demand.
