期刊文献+
共找到5,716篇文章
< 1 2 250 >
每页显示 20 50 100
Spatial and Temporal Distribution Characteristics of Snowstorm in Ulanqab City in Recent 30 Years
1
作者 Jie CHEN Jinhua LIU 《Meteorological and Environmental Research》 2024年第4期11-14,共4页
Based on the data of daily snowfall and weather phenomena of 11 national meteorological stations in Ulanqab City from 1991 to 2020,the spatial and temporal distribution characteristics of snowstorm were analyzed.The r... Based on the data of daily snowfall and weather phenomena of 11 national meteorological stations in Ulanqab City from 1991 to 2020,the spatial and temporal distribution characteristics of snowstorm were analyzed.The results show that the snowstorm in Ulanqab had obvious seasonal distribution characteristics,mainly happening in spring(March-May)and autumn(September-November).It also had obvious regional distribution in space,and the snowstorm center appeared in Chahar Right Wing Middle Banner and Jining District,namely the east side of the Yinshan Mountain.In the past 30 years,the amount of snowstorm in the whole year in Ulanqab showed a certain fluctuation trend,and the number of snowstorm days had shown an obvious upward trend since 2011. 展开更多
关键词 Ulanqab City SNOWSTORM spatial and temporal distribution characteristics
下载PDF
The Spatiotemporal Distribution Characteristics of Cloud Types and Phases in the Arctic Based on CloudSat and CALIPSO Cloud Classification Products
2
作者 Yue SUN Huiling YANG +5 位作者 Hui XIAO Liang FENG Wei CHENG Libo ZHOU Weixi SHU Jingzhe SUN 《Advances in Atmospheric Sciences》 SCIE CAS CSCD 2024年第2期310-324,共15页
The cloud type product 2B-CLDCLASS-LIDAR based on CloudSat and CALIPSO from June 2006 to May 2017 is used to examine the temporal and spatial distribution characteristics and interannual variability of eight cloud typ... The cloud type product 2B-CLDCLASS-LIDAR based on CloudSat and CALIPSO from June 2006 to May 2017 is used to examine the temporal and spatial distribution characteristics and interannual variability of eight cloud types(high cloud, altostratus, altocumulus, stratus, stratocumulus, cumulus, nimbostratus, and deep convection) and three phases(ice,mixed, and water) in the Arctic. Possible reasons for the observed interannual variability are also discussed. The main conclusions are as follows:(1) More water clouds occur on the Atlantic side, and more ice clouds occur over continents.(2)The average spatial and seasonal distributions of cloud types show three patterns: high clouds and most cumuliform clouds are concentrated in low-latitude locations and peak in summer;altostratus and nimbostratus are concentrated over and around continents and are less abundant in summer;stratocumulus and stratus are concentrated near the inner Arctic and peak during spring and autumn.(3) Regional averaged interannual frequencies of ice clouds and altostratus clouds significantly decrease, while those of water clouds, altocumulus, and cumulus clouds increase significantly.(4) Significant features of the linear trends of cloud frequencies are mainly located over ocean areas.(5) The monthly water cloud frequency anomalies are positively correlated with air temperature in most of the troposphere, while those for ice clouds are negatively correlated.(6) The decrease in altostratus clouds is associated with the weakening of the Arctic front due to Arctic warming, while increased water vapor transport into the Arctic and higher atmospheric instability lead to more cumulus and altocumulus clouds. 展开更多
关键词 CloudSat and CALIPSO cloud type cloud phase temporal and spatial distribution interannual variation
下载PDF
Temporal and spatial differences in human activities performed in Urban Green Spaces of Vilnius(Lithuania)
3
作者 Luís Valença Pinto Carla Sofia Santos Ferreira Paulo Pereira 《Geography and Sustainability》 CSCD 2024年第2期302-317,共16页
Urban green spaces(UGS)are relevant to city well-being,as recognized by the United Nations’Sustainable Development Goals(SDGs).However,few studies have studied the temporal use of UGS.This work assessed the seasonal,... Urban green spaces(UGS)are relevant to city well-being,as recognized by the United Nations’Sustainable Development Goals(SDGs).However,few studies have studied the temporal use of UGS.This work assessed the seasonal,weekly,and daily use of three urban green spaces(Vingis Park,Bernardino Garden,and Jomantas Park)in Vilnius(Lithuania).The study is based on an on-site observation-based survey,which recorded users’characteristics,activities,and weather conditions during summer and winter.The results showed that UGS’s seasonal,weekly,and daily use differed according to park and users’characteristics.Parks with a higher diversity of facilities had a high seasonal difference in the number of observed activities.User numbers were higher in the summer for activities with children,social activities,sports,and water activities than in the winter.Jomantas Park had the lowest variability in user characteristics.Weather variables were linked to changes in users’activities.Higher precipitation and lower temperature were associated with reducing the number of users and the diversity of registered activities.Most of the stationary activities were observed during summer.The diversity of the observed activities was associated with the available facilities rather than the park size.The distribution of stationary activities was spatially correlated with facility/equipment(benches,playgrounds,sports,and fitness equipment)and proximity to water features.The results of this study are relevant for UGS design,planning,and management. 展开更多
关键词 Urban parks Seasonal differences temporal use Time of day spatial distribution of UGS users
下载PDF
Temporal and Spatial Distribution of Lightning Activity in Ulanqab City
4
作者 Qiang MA 《Meteorological and Environmental Research》 CAS 2023年第1期60-62,共3页
From January 2020 to December 2021,Ulanqab Meteorological Bureau of Inner Mongolia used VLF/LF lightning locator to carry out three-dimensional lightning monitoring in Ulanqab City,and compared with ADTD lightning loc... From January 2020 to December 2021,Ulanqab Meteorological Bureau of Inner Mongolia used VLF/LF lightning locator to carry out three-dimensional lightning monitoring in Ulanqab City,and compared with ADTD lightning location data in the same period.The results show that both VLF/LF lightning locator and ADTD lightning locator had excellent monitoring ability for lightning during flood season in Ulanqab.VLF/LF lightning locator was slightly superior to ADTD lightning locator in observation accuracy,the observation ability of low-current cloud-to-ground lightning,intracloud lightning observation and so on.There were obvious temporal and spatial characteristics of cloud-to-ground lightning during flood season in Ulanqab,and there was a certain correlation between the areas where lightning appeared frequently and surface water.Intracloud lightning was mainly concentrated at a height of 1-7 km.Negative cloud-to-ground lightning accounted for about 75%of total cloud-to-ground lightning,and negative intracloud lightning accounted for 39%of total intracloud lightning. 展开更多
关键词 Lightning location Cloud-to-ground lightning Intracloud lightning temporal and spatial distribution
下载PDF
Spatiotemporal Distributions of Bacterioplankton Communities in the Qiantang River(Hangzhou Section),China
5
作者 XU Jiaojiao ZHAO Li +4 位作者 LUKWAMBE Betina NICHOLAUS Regan ZHU Jinyong YANG Wen ZHENG Zhongming 《Journal of Ocean University of China》 SCIE CAS CSCD 2024年第4期1102-1114,共13页
The spatial and temporal distribution of bacterioplankton communities plays a vital role in understanding the ecological dynamics and health of aquatic ecosystems.In this study,we conducted a comprehensive investigati... The spatial and temporal distribution of bacterioplankton communities plays a vital role in understanding the ecological dynamics and health of aquatic ecosystems.In this study,we conducted a comprehensive investigation of the bacterioplankton communities in the Qiantang River(Hangzhou section).Water samples were collected quarterly from seven sites over a one-year period.Physical and chemical parameters,including dissolved oxygen(DO),water temperature(WT),chemical oxygen demand(COD),nitrite(NO_(2)^(-)),active phosphate(PO_(4)^(3-))and other indices were determined.In this study,theαdiversity,βdiversity and abundance differences of bacterial communities were investigated using 16S rRNA high-throughput sequencing analysis.The spatial and temporal distribution characteristics and main driving factors of the bacterioplankton community structure and diversity were discussed.The results showed that a total of 57 phyla were detected in the bacterioplankton community,among which Proteobacteria and Actinomycetes were the two dominant groups with the highest relative abundance.The results of PCoA based on Bray-Curtis distance showed that the sampling season had a slightly greater effect on the changes in bacterioplankton community structure in the Qiantang River.Mantel and partial Mantel test showed that environmental variables(Mantel r=0.6739,P<0.0001;partial Mantel r=0.507,P=0.0001)were more important than geographical distance(Mantel r=0.5322,P<0.001;partial Mantel r=0.1563,P=0.001).The distance attenuation model showed that there was significant distance attenuation in all four seasons,and the maximum limit of bacterial community diffusion was found in spring.RDA analysis showed that nine environmental factors,including COD,WT and DO,significantly affected community distribution(P<0.05).This study provides valuable insights into the spatial and temporal distribution characteristics of bacterioplankton communities,shedding light on their ecological roles in the Qiantang River.The information obtained can guide future research on the interactions between bacterioplankton and their environment,enabling the development of effective conservation strategies and sustainable management practices for aquatic ecosystems. 展开更多
关键词 Qiantang River bacterioplankton community spatial and temporal distribution 16S rRNA range attenuation
下载PDF
Spatial heterogeneity and driving mechanism of urban climbing and its impact on regional environment in varied landform types in the middle reaches of the Yellow River
6
作者 SUN Congjian CONG Jiamin CHEN Wei 《Journal of Mountain Science》 SCIE CSCD 2024年第10期3413-3433,共21页
Urbanization research is essential for the sustainable use of regional land resources and ecological environment protection.The expansion process and driving factors of urban construction land at different scales in t... Urbanization research is essential for the sustainable use of regional land resources and ecological environment protection.The expansion process and driving factors of urban construction land at different scales in the middle reaches of the Yellow River(MRYR)have not been comprehensively elucidated.In this study,we explored the distribution pattern of urban construction land on different slope gradients at different scales and analyzed its influencing factors.The main findings were as follows:(1)There has been significant expansion of urban construction land in the MRYR over the past 20 years.Spatial heterogeneity was observed in the regional urban construction land expansion process among different geomorphic regions.(2)The urban construction land in the MRYR was expanded vertically to areas with slopes of>5°,particularly in 2005–2010.Significant slope climbing of urban construction land was observed in the loess hilly-gully and rocky mountain areas.(3)In MRYR,68.45%of the counties were categorized as the slope-climbing types,including 37.38%high-slope-climbing types.(4)The regional population density and economic development level were closely associated with regional urban construction land area variability.(5)The climbing process of regional urban construction can effectively alleviate farmland encroachment and pressure on the regional ecological environment.The urban expansion of the metropolitan distribution areas in the Plain region(such as Xi'an,Taiyuan)had a relatively significant impact on the local carbon storage. 展开更多
关键词 Urban expansion temporal and spatial distribution Slope climbing Driving factors
下载PDF
Spatial Morphology Evolution Characteristics Analysis of the Resident Population Distribution in Henan, China
7
作者 Kaiguang Zhang Hongling Meng +1 位作者 Mingting Ba Danhuan Wen 《Journal of Geoscience and Environment Protection》 2024年第3期163-180,共18页
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
关键词 Resident Population spatial distribution spatial Morphology temporal and spatial Evolution Center Migration Standard Deviation Ellipse spatial Autocorrelation
下载PDF
Study on the Spatial and Temporal Distribution of Blue Algae in Lake Dianshan in Summer 被引量:2
8
作者 杨虹 由文辉 +3 位作者 汪益嫔 胡雪芹 徐春燕 童琰 《Meteorological and Environmental Research》 CAS 2010年第6期78-81,共4页
To understand the spatial and temporal variation characteristics of blue algae in summer in Lake Dianshan,the phytoplankton in Lake Dianshan from June to September in 2009 was surveyed. It found 11 genera and 28 speci... To understand the spatial and temporal variation characteristics of blue algae in summer in Lake Dianshan,the phytoplankton in Lake Dianshan from June to September in 2009 was surveyed. It found 11 genera and 28 species blue algae in total. Microcystis,Oscillatoria and Chroococcus were the main composition communities of blue algae in Lake Dianshan in summer. In the survey period,the average density of blue algae in Lake Dianshan was 16.48×106 cells/L which changed during 1.01×106-59.76×106 cells/L. The characteristics were:September > July > August > June. The mass propagation and aggregation of Microcystis in September caused that the water blooms phenomenon in the partial water areas was serious. In the space,the average density of blue algae in the west and southwest parts of Lake Dianshan was bigger than in the east and southeast. When the nutritive matter was sufficient,the temperature was the main factor which affected the generation and disappearance of blue algae water blooms. The wind direction was also an important factor which affected the distribution of blue algae. 展开更多
关键词 Blue algae spatial and temporal distribution Lake Dianshan SUMMER China
下载PDF
The Influence of Climate Change and Variability on Spatio-Temporal Rainfall and Temperature Distribution in Zanzibar
9
作者 Abdalla Hassan Abdalla Kombo Hamad Kai +4 位作者 Sara Abdalla Khamis Afredy Lawrence Kondowe Sarah E. Osima Philemon Henry King’uza Asya Omar Hamad 《Atmospheric and Climate Sciences》 CAS 2023年第2期282-313,共32页
Climate change has resulted in serious social-economic ramifications and extremely catastrophic weather events in the world, Tanzania and Zanzibar in particular, with adaptation being the only option to reduce impacts... Climate change has resulted in serious social-economic ramifications and extremely catastrophic weather events in the world, Tanzania and Zanzibar in particular, with adaptation being the only option to reduce impacts. The study focuses on the influence of climate change and variability on spatio-temporal rainfall and temperature variability and distribution in Zanzibar. The station observation datasets of rainfall, T<sub>max</sub> and T<sub>min</sub> acquired from Tanzania Meteorological Authority (TMA) and the Coordinated Regional Climate Downscaling Experiment program (CORDEX) projected datasets from the Regional climate model HIRHAM5 under driving model ICHEC-EC-EARH, for the three periods of 1991-2020 used as baseline (HS), 2021-2050 as near future (NF) and 2051-2080 far future (FF), under two representative concentration pathways (RCP) of 4.5 and 8.5, were used. The long-term observed T<sub>max</sub> and T<sub>min</sub> were used to produce time series for observing the nature and trends, while the observed rainfall data was used for understanding wet and dry periods, trends and slope (at p ≤ 0.05) using the Standardized Precipitation Index (SPI) and the Mann Kendall test (MK). Moreover, the Quantum Geographic Information System (QGIS) under the Inverse Distance Weighting (IDW) interpolation techniques were used for mapping the three decades of 1991-2000 (hereafter D1), 2001-2010 (hereafter D2) and 2011-2020 (hereafter D3) to analyze periodical spatial rainfall distribution in Zanzibar. As for the projected datasets the Climate Data Operator Commands (CDO), python scripts and Grid analysis and Display System (GrADS) soft-wares were used to process and display the results of the projected datasets of rainfall, T<sub>max</sub> and T<sub>min</sub> for the HS, NF and FF, respectively. The results show that the observed T<sub>max</sub> increased by the rates of 0.035℃ yr<sup>-</sup><sup>1</sup> and 0.0169℃ yr<sup>-</sup><sup>1</sup>, while the T<sub>min</sub> was increased by a rate of 0.064℃ yr<sup>-</sup><sup>1</sup> and 0.104℃ yr<sup>-</sup><sup>1</sup> for Unguja and Pemba, respectively. The temporal distribution of wetness and dryness indices showed a climate shift from near normal to moderate wet during 2005 at Zanzibar Airport, while normal to moderately dry conditions, were observed in Pemba at Matangatuani. The decadal rainfall variability and distributions revealed higher rainfall intensity with an increasing trend and good spatial distribution in D3 from March to May (MAM) and October to December (OND). The projected results for T<sub>max</sub> during MAM and OND depicted higher values ranging from 1.7℃ - 1.8℃ to 1.9℃ - 2.0℃ and 1.5℃ to 2.0℃ in FF compared to NF under both RCPs. Also, higher T<sub>min</sub> values of 1.12℃ - 1.16℃ was projected in FF for MAM and OND under both RCPs. Besides, the rainfall projection generally revealed increased rainfall intensity in the range of 0 - 25 mm for Pemba and declined rainfall in the range of 25 - 50 mm in Unguja under both RCPs in perspectives of both NF and FF. Conclusively the study has shown that the undergoing climate change has posed a significant impact on both rainfall and temperature spatial and temporal distributions in Zanzibar (Unguja and Pemba), with Unguja being projected to have higher rainfall deficits while increasing rainfall strengths in Pemba. Thus, the study calls for more studies and formulation of effective adaptation, strategies and resilience mechanisms to combat the projected climate change impacts especially in the agricultural sector, water and food security. 展开更多
关键词 Climate Change Climate Variability spatial and temporal distribution Temperature RAINFALL CORDEX
下载PDF
Analysis on Features of Spatial and Temporal Distribution of Thunderstorm in Shanghai
10
作者 高晓东 杨仲江 刘晓东 《Meteorological and Environmental Research》 CAS 2010年第6期9-11,14,共4页
Based in 11 daily weather observation station data in Shanghai from 1971 to 2008,a careful research and analysis on the features of thunderstorms spatial and temporal distribution and thunderstorm movement in Shanghai... Based in 11 daily weather observation station data in Shanghai from 1971 to 2008,a careful research and analysis on the features of thunderstorms spatial and temporal distribution and thunderstorm movement in Shanghai was carried out by using the statistical software of SAS,the method of Mann-Kendall test and wavelets. The results showed that the average annual numbers of thunderstorms days were 26.1,and inter-annual thunderstorm variability was obvious,the annual number of thunderstorm days had a decreasing trend,its value of decreasing days was about-0.418 5 d/10 a. Mann-Kendall test showed that there was an abrupt change in 2000. The seasonal variation of thunderstorm in Shanghai was explicit. The period from March to September was the season when thunderstorm occurred most frequently,about 64.9% of the thunderstorms in a year took place in summer. The results from wavelets analysis showed that the variation cycle period of the annual number of thunderstorms days was about 3,5,12 and 20 years. 展开更多
关键词 THUNDERSTORM spatial-temporal distribution Wavelet analysis SAS China
下载PDF
Study on the Temporal and Spatial Distribution Characteristic of Acid Rain in Guangxi Based on EOF Analysis 被引量:1
11
作者 孙崇智 梁骏 +1 位作者 王超球 郑凤琴 《Meteorological and Environmental Research》 CAS 2010年第11期56-58,63,共4页
Based on acid rain data from ten monitoring sites in Guangxi from 2003 to 2009,the temporal and spatial distribution characteristic of acid rain in Guangxi were analyzed by means of empirical orthogonal function resol... Based on acid rain data from ten monitoring sites in Guangxi from 2003 to 2009,the temporal and spatial distribution characteristic of acid rain in Guangxi were analyzed by means of empirical orthogonal function resolution(EOF).The results showed that there was fluctuating change of acid rain frequency in Guangxi,and acid rain pollution became severer in 2004-2008;acid rain frequency changed conformably in the whole region and it was obviously higher in eastern and northwestern Guangxi,while acid rain pollution became severe in western Guangxi;acid rain frequency varied out of phase between northeastern and southwestern Guangxi in an individual year. 展开更多
关键词 Acid rain temporal and spatial distribution characteristic Eof analysis China
下载PDF
Analysis on the Spatial and Temporal Distribution of Extremely Maximum Temperature in Liaoning Province Based on REOF 被引量:2
12
作者 王震 王颖 《Meteorological and Environmental Research》 CAS 2010年第11期1-3,8,共4页
By selecting the daily maximum temperatures during 1961-2005 in 35 representative stations in Liaoning Province, the temporal and spatial distribution characteristics of extremely maximum temperature event were studie... By selecting the daily maximum temperatures during 1961-2005 in 35 representative stations in Liaoning Province, the temporal and spatial distribution characteristics of extremely maximum temperature event were studied. By using REOF, the mean-square deviation and so on, the variation and distribution situation of extremely maximum temperature in the different regions of Liaoning were reflected. The results showed that the extremely maximum temperature in Liaoning Province could be divided into 3 regions where were respectively the northeast area, the west and the northwest area, the south and the southeast area. The distribution characteristic of extremely maximum temperature threshold value in Liaoning Province was basically consistent with the distribution characteristic of average temperature. The zone where the extremely maximum temperature threshold was relatively high was in the northwest area of Liaoning, and the low threshold zone was in the southeast area and most areas in the east. The variation of extremely maximum temperature in winter was the greatest and in summer was the smallest. The variation of extremely maximum temperature days was the greatest in summer and wasn’t great in spring, autumn, winter. 展开更多
关键词 Extremely maximum temperature spatial and temporal distribution REof analysis China
下载PDF
Temporal and spatial distribution characteristics of water resources in Guangdong Province based on a cloud model 被引量:9
13
作者 Qi Zhou Wei Wang +2 位作者 Yong Pang Zhi-yong Zhou Hui-ping Luo 《Water Science and Engineering》 EI CAS CSCD 2015年第4期263-272,共10页
With a focus on the difficulty of quantitatively describing the degree of nonuniformity of temporal and spatial distributions of water resources, quantitative research was carried out on the temporal and spatial distr... With a focus on the difficulty of quantitatively describing the degree of nonuniformity of temporal and spatial distributions of water resources, quantitative research was carried out on the temporal and spatial distribution characteristics of water resources in Guangdong Province from 1956 to 2000 based on a cloud model. The spatial variation of the temporal distribution characteristics and the temporal variation of the spatial distribution characteristics were both analyzed. In addition, the relationships between the numerical characteristics of the cloud model of temporal and spatial distributions of water resources and precipitation were also studied. The results show that, using a cloud model, it is possible to intuitively describe the temporal and spatial distribution characteristics of water resources in cloud images. Water resources in Guangdong Province and their temporal and spatial distribution characteristics are differentiated by their geographic locations. Downstream and coastal areas have a larger amount of water resources with greater uniformity and stronger stability in terms of temporal distribution. Regions with more precipitation possess larger amounts of water resources, and years with more precipitation show greater nonuniformity in the spatial distribution of water resources. The correlation between the nonuniformity of the temporal distribution and local precipitation is small, and no correlation is found between the stability of the nonuniformity of the temporal and spatial distributions of water resources and precipitation. The amount of water resources in Guangdong Province shows an increasing trend from 1956 to 2000, the nonuniformity of the spatial distribution of water resources declines, and the stability of the nonuniformity of the spatial distribution of water resources is enhanced. 展开更多
关键词 Water resources temporal and spatial distribution characteristics Cloud model Guangdong Province
下载PDF
Spatial and temporal distribution of forest fire frequency and forest area burnt in Jilin Province, Northeast China 被引量:5
14
作者 Qiang Liu Yanlong Shan +2 位作者 Lifu Shu Pingyan Sun Shuai Du 《Journal of Forestry Research》 SCIE CAS CSCD 2018年第5期1233-1239,共7页
Forest fires caused by natural forces or human activities are one of the major natural risks in Northeast China.The incidence and spatial distribution of these fires vary over time and across the forested areas in Jil... Forest fires caused by natural forces or human activities are one of the major natural risks in Northeast China.The incidence and spatial distribution of these fires vary over time and across the forested areas in Jilin Province,Northeast China.In this study,the incidence and distribution of 6519 forest fires from 1969 to 2013 in the province were investigated.The results indicated that the spatiotemporal distribution of the burnt forest area and the fire frequency varied significantly by month,year,and region.Fire occurrence displayed notable temporal patterns in the years after forest fire prevention measures were strictly implemented by the provincial government.Generally,forest fires in Jilin occurred in months when stubble and straw were burned and human activities were intense during traditional Chinese festivals.Baishan city,Jilin city,and Yanbian were defined as fire-prone regions for their high fire frequency.Yanbian had the highest frequency,and the fires tended to be large with the highest burned area per fire.Yanbian should thus be listed as the key target area by the fire management agency in Jilin Province for better fire prevention. 展开更多
关键词 Fire intensity Forest fire temporal distribution spatial distribution
下载PDF
Three-dimensional spatial and temporal distributions of dust in roadway tunneling 被引量:6
15
作者 Haifei Yao Haiyan Wang +1 位作者 Yanchuan Li Lei Jin 《International Journal of Coal Science & Technology》 EI 2020年第1期88-96,共9页
To study the three-dimensional spatial and temporal distributions of dust in tunneling roadways,and to solve the problems of inadequate time and limited number of monitoring points,this paper designs a device for the ... To study the three-dimensional spatial and temporal distributions of dust in tunneling roadways,and to solve the problems of inadequate time and limited number of monitoring points,this paper designs a device for the real-time monitoring and storage of data on the concentrations of dust at multiple measuring points in the same section of a tunnel.The proposed device can measure the total concentration of dust and that of respirable dust in real time at different instances and locations,and using different working procedures.These measurements are used to study the temporal and spatial migration of dust.The results show that there was a sharp fluctuation zone 0–25 m from the heading face,about 25–40 m was high speed subsidence,beyond 40 m was gentle subsidence,The change of respiratory dust is much smoother.At different distances from the heading face,the total dust concentration exhibited a process of“violent oscillation–rapid descent–stable descent,”while the respirable dust exhibited a process of“fluctuating ascent–gradual subsidence.”Changes in the concentrations of total dust and respirable dust dust were consistent at different positions in the same section of the tunnel.The concentration of dust near the wall was low,and those along the sidewalk and air duct of the roadway were slightly higher than in the middle.The concentration of dust farther down the air duct decreased more slowly than that in the remaining lines of measurement.Small amounts of dust featuring large particles settled quickly.High concentrations of dust were observed to be intermittent,and the background value of dust concentration within 100 m of heading face was between 0.5 and 3 mg/m3. 展开更多
关键词 Excavation roadway DUST Real-time monitoring spatial and temporal distribution
下载PDF
Temporal and spatial distribution of phytoplankton functional groups and role of environment factors in a deep subtropical reservoir 被引量:5
16
作者 LI Lei LI Qiuhua +3 位作者 CHEN Jing'an WANG Jingfu JIAO Shulin CHEN Fengfeng 《Journal of Oceanology and Limnology》 SCIE CAS CSCD 2018年第3期761-771,共11页
Phytoplankton and environment factors were investigated in 2015 and phytoplankton functional groups were used to understand their temporal and spatial distribution and their driving factors in Wanfeng Reservoir. Seven... Phytoplankton and environment factors were investigated in 2015 and phytoplankton functional groups were used to understand their temporal and spatial distribution and their driving factors in Wanfeng Reservoir. Seventeen functional groups(B, D, E, F, G, J, Lo, MP, P, S1, T, W1, W2, X1, X2, Xph, Y) were identified based on 34 species. The dominant groups were: J/B/P/D in dry season, X1/J/Xph/G/T in normal season and J in flood season. Phytoplankton abundance ranged from 5.33×10~4 cells/L to 3.65×10~7 cells/L, with the highest value occurring in flood season and lowest in dry season. The vertical profi le of dominant groups showed little differentiation except for P, which dominated surface layers over 20 m as a result of mixing water masses and higher transparency during dry season. However, the surface waters presented higher values of phytoplankton abundance than other layers, possibly because of greater irradiance. The significant explaining variables and their ability to describe the spatial distribution of the phytoplankton community in RDA diff ered seasonally as follows: dry season, NH4-N, NO_3-N, NO_2-N, TN:TP ratio and transparency(SD); normal season, temperature(WT), water depth, TN, NH4-N and NO_3-N; flood season, WT, water depth, NO_3-N and NO_2-N. Furthermore, nitrogen, water temperature, SD and water depth were significant variables explaining the variance of phytoplankton communities when datasets included all samples. The results indicated that water physical conditions and hydrology were important in phytoplankton community dynamics, and nitrogen was more important than phosphorus in modifying phytoplankton communities. Seasonal differences in the relationship between the environment and phytoplankton community should be considered in water quality management. 展开更多
关键词 phytoplankton functional groups temporal and spatial distribution growth strategy driving factors Wanfeng Reservoir
下载PDF
Analysis of temporal and spatial distribution characteristics of ammonium chloride smoke particles in confined spaces 被引量:3
17
作者 Chen-youshi Xu Bing-ting Zha +2 位作者 Jia-qian Bao He Zhang Hong-xia Li 《Defence Technology(防务技术)》 SCIE EI CAS CSCD 2022年第7期1269-1280,共12页
In response to the demand for short-range detection of anti-smoke environment interference by laser fuzes,this study proposes a smoke environment simulation of non-uniform continuous point source diffusion and investi... In response to the demand for short-range detection of anti-smoke environment interference by laser fuzes,this study proposes a smoke environment simulation of non-uniform continuous point source diffusion and investigates an experimental laboratory smoke environment using an ammonium chloride smoke agent.The particle size distribution,composition,and mass flow distribution of the smoke were studied.Based on a discrete phase model and a kεturbulence model,a numerical simulation was developed to model the smoke generation and diffusion processes of the smoke agent in a confined space.The temporal and spatial distribution characteristics of the smoke mass concentration,velocity,and temperature in the space after smoke generation were analyzed,and the motion law governing the smoke diffusion throughout the entire space was summarized.Combined with the experimental verification of the smoke environment laboratory,the results showed that the smoke plume changed from fan-shaped to umbrella-shaped during smoke generation,and then continued to spread around.Meanwhile,the mass concentration of smoke in the space decreased from the middle outward;the changes in temperature and velocity were small and stable.In the diffusion stage(after 900 s),the mass concentration of smoke above 0.8 m was relatively uniform across an area of smoke that was 12 m thick.The concentration decreased over time,following a consistent decreasing trend,and the attenuation was negligible in a very short time.Therefore,this system was suitable for conducting experimental research on laser fuzes in a smoke environment.Owing to the stability of the equipment and facilities,the setup could reproduce the same experimental smoke environment by artificially controlling the smoke emission of the smoke agent.Overall,this work provides a theoretical reference for subsequent research efforts regarding the construction of uniform smoke environments and evaluating laser transmission characteristics in smoky environments. 展开更多
关键词 Laser fuze Smoke environment temporal distribution spatial distribution Confined space Smoke agent
下载PDF
A Precision-Positioning Method for a High-Acceleration Low-Load Mechanism Based on Optimal Spatial and Temporal Distribution of Inertial Energy 被引量:5
18
作者 Xin Chen Youdun Bai +2 位作者 Zhijun Yang Jian Gao Gongfa Chen 《Engineering》 SCIE EI 2015年第3期391-398,共8页
High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit (IC) packaging equipment. In this paper, we derive the transient nonlinear dynamicres... High-speed and precision positioning are fundamental requirements for high-acceleration low-load mechanisms in integrated circuit (IC) packaging equipment. In this paper, we derive the transient nonlinear dynamicresponse equations of high-acceleration mechanisms, which reveal that stiffness, frequency, damping, and driving frequency are the primary factors. Therefore, we propose a new structural optimization and velocity-planning method for the precision positioning of a high-acceleration mechanism based on optimal spatial and temporal distribution of inertial energy. For structural optimization, we first reviewed the commonly flexible multibody dynamic optimization using equivalent static loads method (ESLM), and then we selected the modified ESLM for optimal spatial distribution of inertial energy; hence, not only the stiffness but also the inertia and frequency of the real modal shapes are considered. For velocity planning, we developed a new velocity-planning method based on nonlinear dynamic-response optimization with varying motion conditions. Our method was verified on a high-acceleration die bonder. The amplitude of residual vibration could be decreased by more than 20% via structural optimization and the positioning time could be reduced by more than 40% via asymmetric variable velocity planning. This method provides an effective theoretical support for the precision positioning of high-acceleration low-load mechanisms. 展开更多
关键词 high-acceleration low-load mechanism precision positioning spatial and temporal distribution inertial energy equivalent static loads method (ESLM) velocity planning
下载PDF
Study on spatial and temporal distribution of planktonic amphipoda in the East China Sea 被引量:4
19
作者 JIANGMei WANGYunlong YUANQi CHENYaqu 《Acta Oceanologica Sinica》 SCIE CAS CSCD 2004年第2期329-336,共8页
Quantitative distribution of planktonic amphipoda in the East China Sea is analyzed and the relation with environmental factors and mackerel and scad fishing grounds is studied. The result shows that the characteristi... Quantitative distribution of planktonic amphipoda in the East China Sea is analyzed and the relation with environmental factors and mackerel and scad fishing grounds is studied. The result shows that the characteristic of biomass is great seasonal and interannual variety during the passing three decades. The distribution of planktonic amphipoda basically reflects the movement, decay and intensification of the different water systems in the survey area. 展开更多
关键词 East China Sea amphipoda biomass spatial and temporal distribution environmental factors mackerel and scad fishing grounds
下载PDF
Types, Metallogenic Environments and Characteristics of Temporal and Spatial Distribution of Copper Deposits in China 被引量:6
20
作者 Wang Zhitian and Qin Kezhang Beijing Institute of Geology for Mineral Resources, CNNC, Beijing Zhang Zhongmin 《Acta Geologica Sinica(English Edition)》 SCIE CAS CSCD 1989年第1期79-92,共14页
Based upon a comprehensive study of 123 copper deposits in China. this paper reaches the following conclusions: 1. The crust in China was solidified pretty late; with the accretion of the plate, the copper mineralizat... Based upon a comprehensive study of 123 copper deposits in China. this paper reaches the following conclusions: 1. The crust in China was solidified pretty late; with the accretion of the plate, the copper mineralization moved towards its margin in space and became successively younger in age. 2. The major copper ore types ever found in the world have mostly been discovered in China, in which the porphyry type seems to be the most important and the massive sulfide type in the transitional bed between marine clastic and carbonate rocks is clearly defined. 3. Carbonate strata are widespread in China and their deposition lasted for a long geological period, so the proportion of copper deposits occurring in them is large as compared with other parts of the world. 4. Seven metallogenic epochs can be recognized, in which the Mesozoic one plays the leading role and the middle(late) Palaeozoic and Cenozoic ones are next in importance. Mineralization was comparatively simple in the early geological period. and became diversified later on. In the early epochs copper deposits related to basaltic magmatism and metamorphosed marine sediments predominated, whereas in the later epochs those related to granitic magmatism and continental sedimentation were dominant. 5. There exist in China thirteen metallogenic provinces, of which the Lower Yangtze downwarping belt, Sanjiang fold system, Jiangnan axis and Xikang-Yunnan axis are of greater significance. 6. The crustal mobility in China was rather pronounced, the polycyclic evolution of the crust has resulted in such obvious phenomena as the inheritance of mineralization, the coexistence of various types and the superposition of different genetic types. 展开更多
关键词 Metallogenic Environments and Characteristics of temporal and spatial distribution of Copper Deposits in China TYPES
下载PDF
上一页 1 2 250 下一页 到第
使用帮助 返回顶部