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...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.展开更多
Background: Knowledge of temporal evolution of preeclampsia (PE) in its various aspects is essential in strategies to reduce maternal and perinatal morbidity and mortality. Preeclampsia is a public health problem due ...Background: Knowledge of temporal evolution of preeclampsia (PE) in its various aspects is essential in strategies to reduce maternal and perinatal morbidity and mortality. Preeclampsia is a public health problem due to maternal mortality associated with it worldwide (5.6%). Improving quality of its management is a major challenge in low-income countries where, despite progress made in this field, PE remains a major factor in maternal morbidity and mortality. Objective: To evaluate temporal evolution of frequency, risk factors and complications of PE at the University clinics of Kinshasa (UCK). Methods: Descriptive and cross-sectional study concerning minimum simple size of 119 pregnant women who consulted for antenatal care at the University clinics of Kinshasa from January 2012 to December 2022. Results will be reported as percentage proportion, mean and standard deviation. Comparison of proportion and means between groups will be made using Student’s t-test and Pearson’s chi-square test, respectively. The test will be statistically significant for a p value ≤ less than 0.05. Data will be collected and analysed anonymously and confidentially. Conclusion: This study will allow us to evaluate the effectiveness of different prevention and treatment modalities used over time in management of preeclampsia in our setting.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
In this part, the temporal evolution and interaction across the equator of 30-50 day oscillation in the atmosphere are investigated further. The annual variation of 30-50 day oscillation is quite obvious in the mid-hi...In this part, the temporal evolution and interaction across the equator of 30-50 day oscillation in the atmosphere are investigated further. The annual variation of 30-50 day oscillation is quite obvious in the mid-high latitudes. In the tropical atmosphere, the obvious interannual variation is an important property for temporal evolution of 30-50 day oscillation. The low-frequency wavetrain across the equator over the central Pacific and central Atlantic area, the movement of the long-lived low-frequency system across the equator and the meridional wind component across the equator will obviously show the interaction of 30-50 day oscillation in the atmosphere across the equator.展开更多
Adsorption-desorption experiments on CO2-CH4 gas mixtures with varying compositions have been conducted to study the fractionation characteristics of CO2-CH4 on Haishiwan coal samples. These were carried out at consta...Adsorption-desorption experiments on CO2-CH4 gas mixtures with varying compositions have been conducted to study the fractionation characteristics of CO2-CH4 on Haishiwan coal samples. These were carried out at constant temperature but different equilibrium pressure conditions. Based on these experimental results, the temporal evolution of component fractionation in the field was investigated. The results show that the CO2 concentration in the adsorbed phase is always greater than that in the original gas mixture during the desorption process, while CH4 shows the opposite characteristics. This has confirmed that CO2 , with a greater adsorption ability has a predominant position in the competition with CH4 under different pressures. Where gas drainage is employed, the ratio of CO2 to CH4 varies with time and space in floor roadways used for gas drainage, and in the ventilation air in Nos.1 and 2 coal seams, which is consistent with laboratory results.展开更多
On the basis of considering electrochemical reactions and collision relations in detail, a direct numerical simulation model of a helicon plasma discharge with three-dimensional two-fluid equations was employed to stu...On the basis of considering electrochemical reactions and collision relations in detail, a direct numerical simulation model of a helicon plasma discharge with three-dimensional two-fluid equations was employed to study the characteristics of the temporal evolution of particle density and electron temperature. With the assumption of weak ionization, the Maxwell equations coupled with the plasma parameters were directly solved in the whole computational domain. All of the partial differential equations were solved by the finite element solver in COMSOL Multiphysics^（TM） with a fully coupled method. In this work, the numerical cases were calculated with an Ar working medium and a Shoji-type antenna. The numerical results indicate that there exist two distinct modes of temporal evolution of the electron and ground atom density, which can be explained by the ion pumping effect. The evolution of the electron temperature is controlled by two schemes： electromagnetic wave heating and particle collision cooling. The high RF power results in a high peak electron temperature while the high gas pressure leads to a low steady temperature. In addition, an OES experiment using nine Ar I lines was conducted using a modified CR model to verify the validity of the results by simulation, showing that the trends of temporal evolution of electron density and temperature are well consistent with the numerically simulated ones.展开更多
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...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.展开更多
Ski resorts are one of the bases for the development of ice-snow sports and tourism,and they are also a hot topic of social concern.Taking 117 ski resorts in Beijing,Tianjin and Hebei as the research object,geospatial...Ski resorts are one of the bases for the development of ice-snow sports and tourism,and they are also a hot topic of social concern.Taking 117 ski resorts in Beijing,Tianjin and Hebei as the research object,geospatial analysis methods such as kernel density and spatial autocorrelation were used to explore the spatial and temporal distribution patterns of the ski resorts.The geographic detector was used to deeply explore the underlying factors influencing the spatial and temporal distribution of ski resorts in terms of policy factors,natural factors and economic and social factors.This study found that the spatial and temporal distribution of ski resorts in the Beijing-Tianjin-Hebei Region showed a significant Olympic event-driven characteristic.From 2009 to 2021,the spatial pattern of Beijing-Tianjin-Hebei ski resorts has changed from“single-core development”,to a“single-core with multi-point”layout,and then to a“multi-core”layout.The spatial pattern has changed from agglomeration to diffusion.Cold and hot spots of the spatial and temporal characteristics in Beijing-Tianjin-Hebei ski resort have shifted from north to south,from the initial suburbs of Beijing to the southern cities of Baoding,Shijiazhuang,Xingtai and other cities in Hebei Province.The spatial and temporal distribution of Beijing-Tianjin-Hebei ski resorts has been influenced by many factors,from“GDP per capita”to“population density”to“policy quantity”,showing a shift from“Economic-driven”to“population-driven”to“policy-driven”processes.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 prevalence of mobile devices has spurred human mobility to be applied in mobile networking and communications by using network science, in which the temporal evolution of a network topology is of great importance ...The prevalence of mobile devices has spurred human mobility to be applied in mobile networking and communications by using network science, in which the temporal evolution of a network topology is of great importance for protocol design and performance analysis. This paper focuses on link generation in a temporal evolution network. Based on observations revealing the strong correlation between the connection patterns of different time periods, a link generation potential based on historical connections is proposed in this paper, aiming to provide a method for making topological predictions with less randomness. Using MIT Reality dataset, an evaluation of the accuracy of the proposed method was conducted. The experimental results demonstrate the proposal's adequacy in terms of its accuracy.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
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
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
Pioneering U-Pb isotopic studies by a small group of workers in the mid-late 1980s demonstrated the feasibility of using rare accessory mineral chronometers in mafic(gabbroic)intrusive rocks.These examples showed that...Pioneering U-Pb isotopic studies by a small group of workers in the mid-late 1980s demonstrated the feasibility of using rare accessory mineral chronometers in mafic(gabbroic)intrusive rocks.These examples showed that mafic layered intrusions and diabase/dolerite dyke swarms alike crystallized high-temperature展开更多
Suaeda salsa is an important local species in the intertidal beach of the Western Pacific coast. However,under the artificial cofferdam and Spartina alterniflora expansion,Suaeda marsh has degraded seriously. Therefor...Suaeda salsa is an important local species in the intertidal beach of the Western Pacific coast. However,under the artificial cofferdam and Spartina alterniflora expansion,Suaeda marsh has degraded seriously. Therefore,using Yancheng Nature Reserve as a case study area,taking ETM+images in 2000,2006 and 2011 as the basic data sources,we revealed the evolution characteristics of Salsa marsh which was impacted. The research results are as follows. From 2000 to 2011,Salsa marsh area in the artificial area tempestuously degraded,decreasing by 87. 158%,more than 22% than those in the natural area. The landscape was fragmentized. Landscape polymerization degree index dropped from 95. 780 to 65. 455,more than 16% than those in the natural area. The mean patch area fell down to 21. 429 ha from 389. 333 ha,more than 11% that in the natural area. Compared to the steady change in natural conditions,the area was reduced by 118. 167 ha/a from 2000 to 2006,while during 2006-2011,it was only 51. 500 ha/a in artificial area. As for spatial change of landscape,in artificial area,the Salsa marsh centroid moved forward to the southeast with 666. 350 m,but that in natural area moved forward to the north with 1 042. 710 m from 2000 to 2006. From 2006 to 2011,the centroid moved forward to east and north respectively. Artificial cofferdam transformed the area into freshwater ecosystem,and meanwhile the freshwater was beneficial to Reed marsh. During 2000 to 2006,in the artificial area,539 ha Salsa marsh controlled by cofferdam transferred into reed marsh and aquaculture ponds,of which the transformation rate was nearly 4% higher than that in natural area. From 2006 to 2011,178 ha Salsa marsh was transferred into reed marsh,the transformation rate was 20% higher than that in natural area. With rapid spreading and strong competition of Spartina species,the coastal wetland has formed the pattern of " Salsa – Spartina marshes". From 2000 to 2006,in artificial area,15. 24% of Salsa marsh was transferred into Spartina marsh,of which the transformation rate was13% higher than that in natural area. And from 2006 to 2011,30. 07% Salsa marsh was replaced by the Spartina marsh in artificial area,the rate was almost 10% higher than that in the natural area.展开更多
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 ...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.展开更多
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 lase...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.展开更多
[ Objective] The research aimed to study the spatio-temporal change characteristics of summer mean temperature in northeast China during 1974 -2004 based on geostatistics. [ Method ] By combining climate tendency rate...[ Objective] The research aimed to study the spatio-temporal change characteristics of summer mean temperature in northeast China during 1974 -2004 based on geostatistics. [ Method ] By combining climate tendency rate with geostatistics, the spatio-temporal change characteris- tics of summer mean temperature in northeast China during 1974 -2004 were discussed. [ Result] Summer mean temperature distribution in north- east China for many years showed a trend of decreasing from south and west to north and east. Summer mean temperature in northeast China overall showed rise trend, and the biggest temperature rise magnitude was in Liaoning Province. Summer average temperature in 1994 was significantly higher than that in other years, and climate was abnormal. The rise speed of summer mean temperature in northeast China showed a trend of decreasing from southeast Jilin Province to other areas. [ Conclusion ] The research contributed to recognize spatio-temporal structure and change characteristics of the temperature in northeast China.展开更多
In quantum optics, unitary transformations of arbitrary states are evaluated by using the Taylor series expansion. However, this traditional approach can become cumbersome for the transformations involving non-commuti...In quantum optics, unitary transformations of arbitrary states are evaluated by using the Taylor series expansion. However, this traditional approach can become cumbersome for the transformations involving non-commuting operators. Addressing this issue, a nonstandard unitary transformation technique is highlighted here with new perspective. In a spirit of “quantum” series expansions, the transition probabilities between initial and final states, such as displaced, squeezed and other nonlinearly transformed coherent states are obtained both numerically and analytically. This paper concludes that, although this technique is novel, its implementations for more extended systems are needed.展开更多
To understand the research trends and areas of focus on the grassland degradation(GD),a bibliometric study based on the Science Citation Index-Expanded(SCI-E)was performed.This study presented a comprehensive overview...To understand the research trends and areas of focus on the grassland degradation(GD),a bibliometric study based on the Science Citation Index-Expanded(SCI-E)was performed.This study presented a comprehensive overview of the field based on the annual papers,research areas,temporal trends in keywords,marked journals,institutions,and authors.In the SCI-E database,GD publications first appeared in1970.Thus,we chose the study period between 1970 and 2020.The results showed that the annual number of publications increased in exponential model,with an especially rapid increase after 2009.Dong S.K.,Wang S.P.,and Liu S.L.were the most competitive authors based on their large numbers of papers and citations.A keyword analysis indicated that“grazing,alpine grassland,soil carbon and nitrogen,plant diversity,vegetation restoration”was the most popular study area.The institution with the greatest research publications and most citations was the Chinese Academy of Sciences.Journal of Arid Environments was one of the most popular journals for researchers to publish their research and had greater influence in the field with larger citations than other journals.Environmental science and ecology,soil science,plant science,biodiversity protection,geoscience,and water resources were the most popular Web of Science research areas.The keywords knowledge map mainly divides into four clusters,which are“vegetation”,“soil carbon”,“climate change”,and“grazing”.The ten clusters of the author’s co-occurrence analysis showed that the research areas of GD mainly concentrate on alpine grassland of Qinghai Tibetan Plateau and temperate steppe of Inner Mongolia.Especially under global climate change and the increasing human activities,they were continually increasing close attention to the present.The research methods are mainly in the combination of micro and macro view,such as high-throughput sequencing of the microbial community,remote sensing,quantitative analysis of models,etc.The current international research frontiers are alpine meadow degradation and the assessment of ecosystem service in degraded grassland.To distinguish human activities and climate change to the GD rate is also a new research hotspot in recent years.As the first bibliometrics paper in GD,this paper presents an attempt to better understanding of the progress on GD research.展开更多
基金Sponsored by National Natural Science Foundation of China(42161008)Ningxia Natural Science Foundation(2021AAC03070)。
文摘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.
文摘Background: Knowledge of temporal evolution of preeclampsia (PE) in its various aspects is essential in strategies to reduce maternal and perinatal morbidity and mortality. Preeclampsia is a public health problem due to maternal mortality associated with it worldwide (5.6%). Improving quality of its management is a major challenge in low-income countries where, despite progress made in this field, PE remains a major factor in maternal morbidity and mortality. Objective: To evaluate temporal evolution of frequency, risk factors and complications of PE at the University clinics of Kinshasa (UCK). Methods: Descriptive and cross-sectional study concerning minimum simple size of 119 pregnant women who consulted for antenatal care at the University clinics of Kinshasa from January 2012 to December 2022. Results will be reported as percentage proportion, mean and standard deviation. Comparison of proportion and means between groups will be made using Student’s t-test and Pearson’s chi-square test, respectively. The test will be statistically significant for a p value ≤ less than 0.05. Data will be collected and analysed anonymously and confidentially. Conclusion: This study will allow us to evaluate the effectiveness of different prevention and treatment modalities used over time in management of preeclampsia in our setting.
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This study was supported in part by National Natural Science Foundation of China
文摘In this part, the temporal evolution and interaction across the equator of 30-50 day oscillation in the atmosphere are investigated further. The annual variation of 30-50 day oscillation is quite obvious in the mid-high latitudes. In the tropical atmosphere, the obvious interannual variation is an important property for temporal evolution of 30-50 day oscillation. The low-frequency wavetrain across the equator over the central Pacific and central Atlantic area, the movement of the long-lived low-frequency system across the equator and the meridional wind component across the equator will obviously show the interaction of 30-50 day oscillation in the atmosphere across the equator.
基金financially supported by the Natural Science Foundation for the Youth of China (No. 41202118)the Fundamental Research Funds for the Central Universities (No.2012QNB03)
文摘Adsorption-desorption experiments on CO2-CH4 gas mixtures with varying compositions have been conducted to study the fractionation characteristics of CO2-CH4 on Haishiwan coal samples. These were carried out at constant temperature but different equilibrium pressure conditions. Based on these experimental results, the temporal evolution of component fractionation in the field was investigated. The results show that the CO2 concentration in the adsorbed phase is always greater than that in the original gas mixture during the desorption process, while CH4 shows the opposite characteristics. This has confirmed that CO2 , with a greater adsorption ability has a predominant position in the competition with CH4 under different pressures. Where gas drainage is employed, the ratio of CO2 to CH4 varies with time and space in floor roadways used for gas drainage, and in the ventilation air in Nos.1 and 2 coal seams, which is consistent with laboratory results.
基金funding from National Natural Science Foundation of China under grant agreement No. 11305265 (research on the acceleration mechanism of an electric double layer in a helicon plasma with a divergent magnetic field)
文摘On the basis of considering electrochemical reactions and collision relations in detail, a direct numerical simulation model of a helicon plasma discharge with three-dimensional two-fluid equations was employed to study the characteristics of the temporal evolution of particle density and electron temperature. With the assumption of weak ionization, the Maxwell equations coupled with the plasma parameters were directly solved in the whole computational domain. All of the partial differential equations were solved by the finite element solver in COMSOL Multiphysics^（TM） with a fully coupled method. In this work, the numerical cases were calculated with an Ar working medium and a Shoji-type antenna. The numerical results indicate that there exist two distinct modes of temporal evolution of the electron and ground atom density, which can be explained by the ion pumping effect. The evolution of the electron temperature is controlled by two schemes： electromagnetic wave heating and particle collision cooling. The high RF power results in a high peak electron temperature while the high gas pressure leads to a low steady temperature. In addition, an OES experiment using nine Ar I lines was conducted using a modified CR model to verify the validity of the results by simulation, showing that the trends of temporal evolution of electron density and temperature are well consistent with the numerically simulated ones.
文摘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.
基金The National Natural Science Foundation of China(42071199).
文摘Ski resorts are one of the bases for the development of ice-snow sports and tourism,and they are also a hot topic of social concern.Taking 117 ski resorts in Beijing,Tianjin and Hebei as the research object,geospatial analysis methods such as kernel density and spatial autocorrelation were used to explore the spatial and temporal distribution patterns of the ski resorts.The geographic detector was used to deeply explore the underlying factors influencing the spatial and temporal distribution of ski resorts in terms of policy factors,natural factors and economic and social factors.This study found that the spatial and temporal distribution of ski resorts in the Beijing-Tianjin-Hebei Region showed a significant Olympic event-driven characteristic.From 2009 to 2021,the spatial pattern of Beijing-Tianjin-Hebei ski resorts has changed from“single-core development”,to a“single-core with multi-point”layout,and then to a“multi-core”layout.The spatial pattern has changed from agglomeration to diffusion.Cold and hot spots of the spatial and temporal characteristics in Beijing-Tianjin-Hebei ski resort have shifted from north to south,from the initial suburbs of Beijing to the southern cities of Baoding,Shijiazhuang,Xingtai and other cities in Hebei Province.The spatial and temporal distribution of Beijing-Tianjin-Hebei ski resorts has been influenced by many factors,from“GDP per capita”to“population density”to“policy quantity”,showing a shift from“Economic-driven”to“population-driven”to“policy-driven”processes.
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supported by the National Natural Science Foundation of China(Grant No.61300183)the National Science Fund for Distinguished Young Scholars in China(Grant No.61425012)
文摘The prevalence of mobile devices has spurred human mobility to be applied in mobile networking and communications by using network science, in which the temporal evolution of a network topology is of great importance for protocol design and performance analysis. This paper focuses on link generation in a temporal evolution network. Based on observations revealing the strong correlation between the connection patterns of different time periods, a link generation potential based on historical connections is proposed in this paper, aiming to provide a method for making topological predictions with less randomness. Using MIT Reality dataset, an evaluation of the accuracy of the proposed method was conducted. The experimental results demonstrate the proposal's adequacy in terms of its accuracy.
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 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.
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.
文摘Pioneering U-Pb isotopic studies by a small group of workers in the mid-late 1980s demonstrated the feasibility of using rare accessory mineral chronometers in mafic(gabbroic)intrusive rocks.These examples showed that mafic layered intrusions and diabase/dolerite dyke swarms alike crystallized high-temperature
基金Supported by National Natural Science Foundation of China(41771199)Basic Research Project of Jiangsu Province,China(BK20171277)
文摘Suaeda salsa is an important local species in the intertidal beach of the Western Pacific coast. However,under the artificial cofferdam and Spartina alterniflora expansion,Suaeda marsh has degraded seriously. Therefore,using Yancheng Nature Reserve as a case study area,taking ETM+images in 2000,2006 and 2011 as the basic data sources,we revealed the evolution characteristics of Salsa marsh which was impacted. The research results are as follows. From 2000 to 2011,Salsa marsh area in the artificial area tempestuously degraded,decreasing by 87. 158%,more than 22% than those in the natural area. The landscape was fragmentized. Landscape polymerization degree index dropped from 95. 780 to 65. 455,more than 16% than those in the natural area. The mean patch area fell down to 21. 429 ha from 389. 333 ha,more than 11% that in the natural area. Compared to the steady change in natural conditions,the area was reduced by 118. 167 ha/a from 2000 to 2006,while during 2006-2011,it was only 51. 500 ha/a in artificial area. As for spatial change of landscape,in artificial area,the Salsa marsh centroid moved forward to the southeast with 666. 350 m,but that in natural area moved forward to the north with 1 042. 710 m from 2000 to 2006. From 2006 to 2011,the centroid moved forward to east and north respectively. Artificial cofferdam transformed the area into freshwater ecosystem,and meanwhile the freshwater was beneficial to Reed marsh. During 2000 to 2006,in the artificial area,539 ha Salsa marsh controlled by cofferdam transferred into reed marsh and aquaculture ponds,of which the transformation rate was nearly 4% higher than that in natural area. From 2006 to 2011,178 ha Salsa marsh was transferred into reed marsh,the transformation rate was 20% higher than that in natural area. With rapid spreading and strong competition of Spartina species,the coastal wetland has formed the pattern of " Salsa – Spartina marshes". From 2000 to 2006,in artificial area,15. 24% of Salsa marsh was transferred into Spartina marsh,of which the transformation rate was13% higher than that in natural area. And from 2006 to 2011,30. 07% Salsa marsh was replaced by the Spartina marsh in artificial area,the rate was almost 10% higher than that in the natural area.
基金Supported by the National Natural Science Foundation of China(51808413)General Project of Hubei Social Science Fund(Later Funded Project)(2020158)Innovation and Entrepreneurship Training Program for College Students in Hubei Province(S202010490027)。
文摘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.
基金supported by the National Key R&D Program of China(No.2017YFE0301304)National Natural Science Foundation of China(No.12005034)the China Postdoctoral Science Foundation(No.2019M661087)supported by the US Department of Energy,Office of Defense Nuclear Nonproliferation Research and Development,under contract number DE-AC02-05CH11231 at the Lawrence Berkeley National Laboratory。
文摘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.
基金Supported by Undergraduate Innovation Experiment Plan Key Project,China University of Geosciences (Beijing) ( 2011CXZ022 )Undergraduate Science Research Plan Project in Beijing,China
文摘[ Objective] The research aimed to study the spatio-temporal change characteristics of summer mean temperature in northeast China during 1974 -2004 based on geostatistics. [ Method ] By combining climate tendency rate with geostatistics, the spatio-temporal change characteris- tics of summer mean temperature in northeast China during 1974 -2004 were discussed. [ Result] Summer mean temperature distribution in north- east China for many years showed a trend of decreasing from south and west to north and east. Summer mean temperature in northeast China overall showed rise trend, and the biggest temperature rise magnitude was in Liaoning Province. Summer average temperature in 1994 was significantly higher than that in other years, and climate was abnormal. The rise speed of summer mean temperature in northeast China showed a trend of decreasing from southeast Jilin Province to other areas. [ Conclusion ] The research contributed to recognize spatio-temporal structure and change characteristics of the temperature in northeast China.
文摘In quantum optics, unitary transformations of arbitrary states are evaluated by using the Taylor series expansion. However, this traditional approach can become cumbersome for the transformations involving non-commuting operators. Addressing this issue, a nonstandard unitary transformation technique is highlighted here with new perspective. In a spirit of “quantum” series expansions, the transition probabilities between initial and final states, such as displaced, squeezed and other nonlinearly transformed coherent states are obtained both numerically and analytically. This paper concludes that, although this technique is novel, its implementations for more extended systems are needed.
基金This research is supported by the International Partnership Program of Chinese Academy of Sciences(Grant No.121311KYSB20170004-04)land the CAS Strategic Priority Research Programme,Grant(No.XDA20050103).
文摘To understand the research trends and areas of focus on the grassland degradation(GD),a bibliometric study based on the Science Citation Index-Expanded(SCI-E)was performed.This study presented a comprehensive overview of the field based on the annual papers,research areas,temporal trends in keywords,marked journals,institutions,and authors.In the SCI-E database,GD publications first appeared in1970.Thus,we chose the study period between 1970 and 2020.The results showed that the annual number of publications increased in exponential model,with an especially rapid increase after 2009.Dong S.K.,Wang S.P.,and Liu S.L.were the most competitive authors based on their large numbers of papers and citations.A keyword analysis indicated that“grazing,alpine grassland,soil carbon and nitrogen,plant diversity,vegetation restoration”was the most popular study area.The institution with the greatest research publications and most citations was the Chinese Academy of Sciences.Journal of Arid Environments was one of the most popular journals for researchers to publish their research and had greater influence in the field with larger citations than other journals.Environmental science and ecology,soil science,plant science,biodiversity protection,geoscience,and water resources were the most popular Web of Science research areas.The keywords knowledge map mainly divides into four clusters,which are“vegetation”,“soil carbon”,“climate change”,and“grazing”.The ten clusters of the author’s co-occurrence analysis showed that the research areas of GD mainly concentrate on alpine grassland of Qinghai Tibetan Plateau and temperate steppe of Inner Mongolia.Especially under global climate change and the increasing human activities,they were continually increasing close attention to the present.The research methods are mainly in the combination of micro and macro view,such as high-throughput sequencing of the microbial community,remote sensing,quantitative analysis of models,etc.The current international research frontiers are alpine meadow degradation and the assessment of ecosystem service in degraded grassland.To distinguish human activities and climate change to the GD rate is also a new research hotspot in recent years.As the first bibliometrics paper in GD,this paper presents an attempt to better understanding of the progress on GD research.
