Spatial and Temporal Evolution Characteristics of Extreme Precipitation and Isohyets in Ningxia

The multi-scale spatial and temporal evolution characteristics of extreme precipitation and isohyets in Ningxia were studied using daily,monthly,and annual precipitation data from 20 meteorological stations in Ningxia over the last 60 years.The results revealed that the intensity of rainstorms in Ningxia had decreased slightly over the previous 60 years,with the intensity of rainstorms in southern and central Ningxia being higher than in northern areas.Ningxia's annual and seasonal precipitation varied regionally,declining from the southeast to the northwest.Annual,spring and autumn precipitation exhibited a significantly declining trend from 1960 to the early 21^(st)century;summer precipitation displayed a slightly decreasing trend;and winter precipitation showed a significantly increasing trend.Nevertheless,there was a noticeable increase in annual and seasonal precipitation after 2005.From the 1960s to the 2000s,the 200 mm isohyet moved slowly southward,while the 400 mm isohyet jumped southward twice in the 1970s and 2000s before jumping considerably northward in the 2010s to reach their northernmost region.

Spatial Morphology Evolution Characteristics Analysis of the Resident Population Distribution in Henan, China

The population spatial distribution pattern and its evolving pattern play an important role in regional allocation of social resources and production factors, formulation of regional development plans, construction of a better life society, and promotion of regional economic development. Based on the resident population statistics data of Henan province from 2006 to 2021, with county as the basic study unit, the paper studies the spatial morphology characteristics and its evolution patterns of resident population distribution, by using spatial analysis methods such as population distribution center, standard deviation ellipse, and spatial auto correlation analysis. The results show that: the resident population spatial distribution shows unbalanced state, the population agglomeration areas mainly distribute in the northeast part and north part, where the resident population growth rate is significantly higher than other regions, over time, this trend is gradually becoming significant. The resident population distribution has a trend of centripetal concentration, with the degree and trend of centripetal gradually strengthening. The resident population distribution has obvious directional characteristics, but the significance is not high, the weighted resident population average center is approximately located at (4.13740˚N, 113.8935˚E), and the azimuth of the distribution axis is approximately 11.19˚. The population distribution has obvious agglomeration characteristics, with the built-up areas of Zhengzhou and Luoyang as their centers, where have a significant siphon effect on the surrounding population. The southern and southwestern regions in the province form a relatively stable belt area of Low-Low agglomeration areas.

Spatial-temporal evolution of vegetation evapotranspiration in Hebei Province,China

Evapotranspiration(ET)is the sum of soil or water body evaporation and plant transpiration from the earth surface and ocean to the atmosphere,and thus plays a significant role in regulating carbon and water resource cycles.The time-series data set from the remote sensing MOIDS product(MOD16)was used to study the spatial-temporal evolution of vegetation evapotranspiration in salinized areas during 2000–2014 by analyzing the variability,spatial patterns and Mann-Kendall(MK)nonparametric trends for the time series.The results indicate that inter-annual and intra-annual variations of ET across various vegetated areas show seasonal changes,with the abnormal months identified.The cultivated land displays a greater degree of spatial heterogeneity and the spatial pattern of ET in the area covered by broadleaved deciduous forests corresponds to a higher ET rate and increased water consumption.A widespread decline of ET is observed only in cultivated areas.However,agricultural cultivation doesn’t worsen water shortage and soil salinization problems in the region,and water shortage problems are worsening for other vegetated areas.This research provides a basis of reference for the reasonable allocation of water resources and restructuring of vegetation patterns in salinized areas.

Temporal and Spatial Evolution of Laser-Induced Plasma from a Slag Sample

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.

Temporal and spatial evolution measurement of laser-induced breakdown spectroscopy on hydrogen retention in tantalum

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.

Spatial-temporal Evolution Pattern of Agricultural Productivity in Northwestern Sichuan Plateau

Currently,the agricultural growth in developed countries mainly relies on the improvement of productivity,which is also the target for China.Accordingly,the purpose of this study was to describe the spatial-temporal evolution pattern of agricultural productivity,to reveal changes in total factor productivity in 2000-2010,and analyze the impact of these changes in northwestern Sichuan plateau,China.Using data envelopment analysis(DEA) and the Malmquist Index,an in-depth study was conducted on agricultural productivity and changes in total factor productivity of 31 counties in northwestern Sichuan plateau.Results indicated that:(1) geographically,counties with optimal efficiency were mainly located in the north of northwestern Sichuan plateau and those with the lowest efficiency,in the south;(2) relative to pure technical efficiency,scale efficiency was the dominant factor in determining agricultural productivity;(3) the redundancy rate of input factors in 2010 was slightly lower than that in 2000,thereby indicating an improved utilization of input factors to a certain extent and a great potential for further improving such utilization;(4) during the 2000-2010 period,the agricultural total factor productivity had an average annual growth rate of 8.3%,but the growth rates in various regions differed widely;(5) technical progress was the dominant factor promoting the improvement of total factor productivity in agriculture.The disparities in spatial distribution may be due to the differences of natural conditions,former level agricultural productivity between counties.The findings are valuable for the government to make sustainable development policies for agriculture and improving agricultural development in northwestern Sichuan plateau.

Spatial-temporal evolution of gas migration pathways in coal during shear loading

Custom designed and built meso shear test equipment was used to examine the shear crack propagation in gassy coal under different gas pressures.The spatial-temporal evolution of gas migration pathways in the coal during shear loading was also researched.The results show that gas pressure can hasten crack growth at the shear fracture surface,can reduce the shear strength of gassy coal,and can accelerate the shear failure process.Shear failure in gassy coal exhibits five stages:the pre-crack stage;the stable crack growth stage;the unsteady crack growth stage;the fracture stage;and,finally,the friction crack stage.The shear breaking creates two kinds of crack,shear cracks and tensile cracks.Cracks first appear in the shear plane at both ends and then extend toward the center until a shear fracture surface forms.The direction of shear crack propagation diverges from the predetermined shear plane by an angle of about 5°-10°.

Spatial-temporal Patterns and Evolution History of Rural Settlements from the Perspective of Inheritance——A Case Study of Lianzhou City,Guangdong Province

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.

The Analysis of Spatial-Temporal Evolution of City Accessibility Based on Highway Network in Henan Province in China

Accessibility is an important tool to evaluate the maturity of a regional traffic network structure which describes the traffic convenience in the traffic network. The paper defines a new accessibility index by using the resident population weighted average value of the sum of inverse of the traveling time distance and time threshold coming from ordinary traffic network, and then uses this accessibility index to analyze the spatial-temporal characteristics of Henan highway network, as well as its evolution patterns from 2005 to 2020. The results show that with the expansion and improvement of Henan highway network, city accessibility level has been significantly improved, spatial convergence is obvious, the cities in the north central are always High-High aggregation area, the cities in the south are always Low-Low aggregation area, gradually forming the characteristics of Northwest high and Southeast low, relative balance between East and West. There is some non-conforming phenomenon in highway mileage growth and improvement of the city accessibility levels, but this situation is being weakened, the highway network layout is gradually rationalized, the spatial distribution of city accessibility and that of population are beginning to converge.

Study of spatial and temporal evolution of Ar and F atoms in SF6/Ar microsecond pulsed discharge by optical emission spectroscopy

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.

Spatial and Temporal Evolution Characteristics of PM2.5 in China from 1998 to 2016

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.

Research on temporal and spatial distribution,evolutionary character and mechanism of crustal deformation field before and after the Tangshan earthquake

Ｒｅｓｅａｒｃｈｏｎｔｅｍｐｏｒａｌａｎｄｓｐａｔｉａｌｄｉｓｔｒｉｂｕ┐ｔｉｏｎ，ｅｖｏｌｕｔｉｏｎａｒｙｃｈａｒａｃｔｅｒａｎｄｍｅｃｈａｎｉｓｍｏｆｃｒｕｓｔａｌｄｅｆｏｒｍａｔｉｏｎｆｉｅｌｄｂｅｆｏｒｅａｎｄａｆｔｅｒｔｈｅＴａｎｇｓｈａｎ...

Spatial and Temporal Evolution of the Static Water Level of the Cuauhtemoc Aquifer during the Years 1973, 1991 and 2000: A Geographical Approach

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.

Temporal and Spatial Evolution of Lakes in the Bashang Plateau for Nearly Recent 30 Years

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.

Spatial-temporal Analysis of Daily Air Quality Index in the Yangtze River Delta Region of China During 2014 and 2016

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.

Temporal and spatial study of differently charged ions emitted by ns-laser-produced tungsten plasmas using time-of-flight mass spectroscopy

Tungsten(W)is an important material in tokamak walls and divertors.The W ion charge state distribution and the dynamic behavior of ions play important roles in the investigation of plasma–wall interactions using laser-ablation-based diagnostics such as laser-induced breakdown spectroscopy and laser-induced ablation spectroscopy.In this work,we investigate the temporal and spatial evolutions of differently charged ions in a nanosecond-laser-produced W plasma in vacuum using time-of-flight mass spectroscopy.Ions with different charge states from 1 to 7(W+to W7+)are all observed.The temporal evolutions of the differently charged ions show that ions with higher charge states have higher velocities,indicating that space separation occurs between the differently charged ion groups.Spatially-resolved mass spectroscopy measurements further demonstrate the separation phenomenon.The temporal profile can be accurately fitted by a shifted Maxwell–Boltzmann distribution,and the velocities of the differently charged ions are also obtained from the fittings.It is found that the ion velocities increase continuously from the measured position of 0.75 cm to 2.25 cm away from the target surface,which indicates that the acceleration process lasts through the period of plasma expansion.The acceleration and space separation of the differently charged ions confirm that there is a dynamic plasma sheath in the laser-produced plasma,which provides essential information for the theoretical laser-ablation model with plasma formation and expansion.

滨海城市灾害韧性的时空演化特征研究--以深圳为例

近年来,我国自然灾害频发,特别是广东沿海一带的滨海城市频繁遭遇自然灾害的袭击,给滨海地区人民带来巨大的生命威胁和财产损失。该文以深圳市为研究对象,依托深圳市1980年—2019年的面板数据,从经济韧性指数、社会韧性指数、生态韧性指数和工程韧性指数四个维度,构建深圳市灾害韧性评价指标体系,运用极值熵值法等评价方法,研究深圳市近四十年灾害韧性的时空演变特征,包括不同维度、不同指标的韧性高低情况、韧性趋势变化。研究结果表明:①深圳市整体灾害韧性呈现出上升趋势。②深圳市灾害韧性的空间分布不均衡,中等韧性区的数量最多,低韧性和较低韧性区的数量基本维持不变,较高韧性和高韧性区的数量较少。③深圳市各区的LISA集聚情况较明显。

基于FLUS-Markov模型的玉溪市生态系统服务价值时空演变与预测

基于玉溪市2010年、2020年2期生态景观类型数据和粮食产量经济价值修正生态系统服务价值系数,分析玉溪市生态景观类型及生态系统服务价值分布特征,采用FLUS-Markov模型预测玉溪市2030年生态系统服务价值及其分布。结果表明,该模型预测结果的Kappa系数提高至0.8969,整体精度为0.9393,精度较高;2010—2020年玉溪市林地、草地的面积呈减少趋势,以林地、草地、水域为主的生态系统仍然面临威胁;2030年玉溪市生态系统服务价值为535.0471亿元,变化率为-0.1297%,玉溪市应加强对林地、草地的保护,加强退耕还林、退耕还草政策的实施,合理控制草地、林地向耕地的转化;2030年玉溪市生态系统服务价值依然表现为西部>中部>东部;2030年玉溪市各县市区生态系统服务价值贡献率由高到低依次为新平县、元江县、峨山县、易门县、华宁县、红塔区、江川区、澄江市、通海县。

主体功能区视角下的滇中城市群人口-经济-资源环境时空耦合分析

[目的]探析人口、经济和资源环境三者之间协调及发展水平状况,阐明各县耦合协调关系及影响因素,为主体功能区规划实施提供有力支撑。[方法]基于2010年、2015年、2020年滇中城市群的自然、经济及人文数据,从主体功能区视角建立人口-经济-资源环境耦合协调发展评价指标体系。运用序关系分析法(G1)与熵权法(EW)确定综合权重,通过耦合协调度模型度量各县耦合协调关系,定量分析了2010年、2015年、2020年滇中城市群人口-经济-资源环境耦合协调演变状况,探析其发展规律。[结果](1)3个时段内,研究区人口在县域尺度呈空间正相关关系,且空间聚集性逐渐增强,呈现西部低人口密度聚集和中部高人口密度聚集态势且常年稳定;(2)2010—2020年,人口、经济和资源环境三者之间的耦合协调度综合发展水平有微弱提升,严重失调的协调类型逐渐消除,濒临失调占比46.94%成为最主要的协调类型;(3)人口、经济和资源环境两两耦合协调分布不均,其中2020年人口-经济综合耦合协调指数最低为0.4543,协调度水平时空分布与三系统协调评价结果吻合度是两两耦合协调评价中最高的,对人口-经济-资源环境耦合协调评价结果影响最大;(4)在主体功能区划实施前后,国家重点开发区两两耦合协调水平变化显著,人口-经济-资源环境整体耦合协调水平较低且有倒退趋势,省级重点开发区长期稳定可控;(5)研究区的人口、经济和资源环境三者之间存在较强的相互作用关系,但协调性在一定程度上处于制约状况。[结论]高耦合协调性主要依赖于人口对市县区经济的带动作用。重点开发区的有效实施必须抓好人口与经济协同发展,人口和经济协调是未来优化主体功能区的重点方向。

Spatio-temporal Variation of PM_(2.5) in China from 1998 to 2016

With the rapid development of China's economy,people's demand for a healthy living environment is increasing,and air quality has gradually been widely concerned by all sectors of society.Using the big data of air quality monitoring from 1998 to 2016,based on the exploratory spatio-temporal analysis method,this paper explored the spatio-temporal evolution of PM_(2.5) at the national scale,and drew the following conclusions:①PM_(2.5) heavy pollution is mainly in central and eastern China,north and south China,and the pollution degree is relatively light in northwest and northeast China.Meanwhile,PM_(2.5) concentration in heavily polluted areas increased significantly over time,while PM_(2.5) concentration in low-polluted areas showed a long-term stable trend.②The number and area of cities with moderate and high PM_(2.5) pollution levels showed an inverted U-shaped curve from 1998 to 2016,and 2007 was the inflection point.③The spatial autocorrelation coefficient of PM_(2.5) is high over the years,and the spatial neighbor effect of PM_(2.5) is significant.The high-pollution clusters are mainly concentrated in the Beijing-Tianjin-Hebei region,the Yangtze River Delta and the Pearl River Delta,and the pollution concentration in these three regions has increased rapidly in recent years.It is necessary to focus on joint prevention and control.