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Bi-Attention Text-Keyword Matching for Law Recommendation
DING Na, LIU Peng, SHAO Huipeng, WANG Xuekui
Acta Scientiarum Naturalium Universitatis Pekinensis    2024, 60 (1): 79-88.   DOI: 10.13209/j.0479-8023.2023.077
Abstract78)   HTML    PDF(pc) (686KB)(43)       Save
This paper proposed a bi-directional attention based text-keyword matching model for law recommendation (BiAKLaw). In this model, BERT is utilized as a basic matching model, bi-directional attention mechanism is implemented to extract token-level alignment features and keyword-level differential features, and these features are fused with keyword attentive semantic representations for a better matching effect. The experimental results on the traffic accident and intentional injury datasets demonstrate that, compared with BERT, the proposed model increases F1 evaluation metric by 3.74% and 3.43% respectively.
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Mangrove Restoration Technology and Application in Difficult Site in Shenzhen Bay
SONG Xue, WANG Hui, SHI Jianya, WANG Xuguang, SHEN Xiaoxue, LI Ruili
Acta Scientiarum Naturalium Universitatis Pekinensis    2022, 58 (5): 929-936.   DOI: 10.13209/j.0479-8023.2022.077
Abstract455)   HTML    PDF(pc) (13167KB)(183)       Save
This research used three technical means of hollow bricks, customized bamboo basket I and customized bamboo basket II to carry out the mangrove restoration test under difficult site condition in Shenzhen Bay in 2016. The effect of plantation was evaluated in terms of colonization technology, economic cost, mangrove population characteristics and sediment environmental quality after 4 years. The results showed that 1) three technical methods in the mangrove plantation area could create an Aegiceras corniculatum restoration. The preservation rate of A. corniculatum gained over 87%. 2) The cost of the hollow brick technology was lower than those of the groups of customized bamboo basket I and customized bamboo basket II. 3) The total organic (TOC) and total phosphorus (TP) of the sediments in the mangrove planting area were significantly higher than those in the intertidal zone, which indicated that mangroves could promote the retention of organic matter and phosphorus and reduce the risk of their escape to the offshore marine environment. The conclusion is that the technical means of hollow bricks, customized bamboo basket I and customized bamboo basket II can successfully restore mangroves under the difficult site condition of Shenzhen Bay. Considering the restoration effect and economic cost, it is recommended to use hollow brick technology to restore mangrove under difficult site conditions.
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Circulation Classification and Source Analysis of Summer Ozone Pollution in Chengdu
SHI Wenbin, QU Kun, YAN Yu, QIU Peipei, WANG Xuesong, DONG Huabin
Acta Scientiarum Naturalium Universitatis Pekinensis    2022, 58 (3): 565-574.   DOI: 10.13209/j.0479-8023.2022.016
Abstract531)   HTML    PDF(pc) (2726KB)(222)       Save
In order to explore the impact of large-scale circulations on O3 pollution in Chengdu, based on the 700 hPa geopotential height field in the Sichuan Basin (SCB) and using the T-PCA method, the atmospheric circulations in the summer of 2015–2019 (June–August) were classified into five circulation patterns, and the characteristics of O3 pollution and O3 sources in Chengdu under different circulation patterns were identified. Among the five types of circulation patterns, the northeast-high pressure (NEH) pattern and the under-high pressure field (UNF) pattern generally led to higher air temperature, and lower humidity and cloud cover in the SCB. Air temperature change compared to the previous days showed an obvious increasing trend in the SCB under the UNF pattern, kept stable under the NEH pattern, and indicated cooling effects with varying intensities under the other three circulation patterns (the southeast-high pressure pattern, the northwest-low pressure pattern and the northwest-high pressure pattern). The meteorological conditions under NEH and UNF were more conducive to the photochemical production of O3 in the SCB. During the study period, O3 concentrations and the percentages of over-standard days of O3 in Chengdu under NEH and UNF were significantly higher than those under the other three circulation patterns, and thus NEH and UNF were the main circulation patterns that were related to O3 pollution in summer. Months with more severe O3 pollution in Chengdu tended to have higher proportion of days under the NEH and UNF patterns. The simulation studies of O3 sources in Chengdu in summer suggested that O3 was mainly derived from the SCB (55.0%), with local contribution of Chengdu (31.6%), and other important contributing cities including Deyang (5.4%), Chongqing (4.0%), Ziyang (3.9%) and Meishan (2.2%). However, O3 sources in Chengdu under different circulation patterns showed different characteristics. Under the NEH pattern, O3 transport within the Chengdu Plain had notable impact on O3 pollution in Chengdu, with a significant increasing contribution from Deyang (14.9%). By contrast, under the UNF pattern, O3 pollution in Chengdu became more localized, with nearly half (46.8%) of O3 contributed by local emissions. 
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Meteorological and Pollution Characteristics of PM2.5 under Atmosphric Circulation Types in Autumn and Winter in Shijiazhuang
XIAO Teng, LIN Tingkun, YAN Yu, WANG Xuesong
Acta Scientiarum Naturalium Universitatis Pekinensis    2021, 57 (3): 414-424.   DOI: 10.13209/j.0479-8023.2021.021
Abstract1036)   HTML    PDF(pc) (12978KB)(177)       Save
According to the ground and vertical meteorological characteristics of atmospheric circulation types during the autumns and winters (Nov.?Feb.) of 2013?2018 in Shijiazhuang, 11 types of atmospheric circulation were classified into five categories. The correlation between each category and PM2.5 pollution was discussed by combining the transport trajectories and the air quality data. Among those categories, Category I (type NW and type N, accounting for 16% of days) was the best condition for air pollution diffusion, characterized by the dominant west or northwest winds near surface with steady direction and high speed, as well as high planetary boundary layer (PBL) height. Category II (type NE, accounting for 9%) and Category III (type E and type SE, accounting for 12%) were the second-best conditions, characterized by high wind speed. Category II was dominated by north wind and medium PBL height, while Category III was dominated by northeast wind and low PBL height. Category IV (type A, 37%) was unfavorable for air pollution diffusion, which was characterized by low-speed, near-surface winds and low PBL height. Category V (type UM, type C, type S, type SW, type W, 26%) was the worst condition, characterized by near-surface winds with low speed and variable directions, as well as low PBL height and intensive temperature inversion in lower atmosphere. The potential areas of sources contributing to PM2.5 pollution in Shijiazhuang under different circulation types varied with different transport trajectories. Concerning the correlation between the PM2.5 pollution in Shijiazhuang during the autumns and winters and the diffusive conditions of different circulative types, the PM2.5 pollution tended to occur (the frequency of pollution was from 78% to 96%, and the frequency of heavy pollution and above was more than 55%) when the region was controlled by Category V; the condition of the PM2.5 pollution tended to change slowly under Category IV, but the PM2.5 concentration was more likely to increase under the continuous Category IV days; the frequency of PM2.5 pollution was lowest under Category I.
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Source Apportionment and Transport Characteristics of Ozone in Baoding during Summer Time
HUANG Zhengchao, HONG Linan, YIN Peiling, WANG Xuesong, ZHANG Yuanhang
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (3): 665-672.   DOI: 10.13209/j.0479-8023.2017.189
Abstract810)   HTML11)    PDF(pc) (6181KB)(246)       Save

Models-3/CMAQ and Brute Force method were applied to simulate the ozone pollution and to analyze how meteorological condition influenced the pollution characteristic and the source apportionment of ozone during July 2014 in Baoding. The distribution of ozone concentration in Baoding gradually increased from west to east. In July, the high ozone episode mainly occurred when southern air mass, southeastern air mass and eastern air mass arrived, and the percentages of polluted days were about 28%, 39% and 17%, respectively. During the maximum eight hours of ozone, background and cross regional transmission contributed about half of concentration of surface ozone. As for the regional contribution, Hebei contributed about 2/5 of the surface ozone. Henan contributed about 1/10 as well as Shandong and Jiangsu. The rapid increasing contribution from central Hebei and influences of vertical transportation from Henan and Shandong province leaded to rapid increasing of surface ozone concentration during the daytime in Baoding; most regional contribution changed gently except for central Hebei area, which resulted in high ozone concentration and long duration in the afternoon as well as the single peak diurnal variation.

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Investigations on Irradiation Effects of Ni60Nb40 Amorphous Alloy and Hastelloy-N Alloy by 3 MeV Au Ion
LIU Shiyi;XU Guangyue;ZHANG Yanwen;WANG Xu;TANG Meixiong;ZHAO Ziqiang;WEI Bingchen
Acta Scientiarum Naturalium Universitatis Pekinensis    2015, 51 (5): 783-790.   DOI: 10.13209/j.0479-8023.2015.056
Abstract1306)      PDF(pc) (6305KB)(603)       Save
3 MeV Au ions were used to irradiate Hastelloy-N and Ni60Nb40 amorphous alloy, and total doses were 2.3×1015 cm–2 and 5×1016 cm–2. X-ray Diffraction results presented that Ni60Nb40 amorphous alloy showed good stability in crystal state, but Hastelloy-N had apparent strain increment after irradiation. Nano-Indenter test found that softening of Ni60Nb40 amorphous alloy and hardening of Hastelloy-N were mainly caused by atom displacement damage. Through measuring step heigh created by half-shielding irradiation with an Atomic Force Micoscope, the authors found that the irradiation swelling of both materials were approximate. Scan Electron Micoscope observation showed that the critical dose of Ni60Nb40 amorphous alloy surface viscous flow induced by 3 MeV Au ions was larger than 2.3×1015 cm–2. The surface viscous flow critical dose was not uniform, which may be caused by surface stress induced by mechanical polishing. Ni60Nb40 amorphous alloy should be potential to be protective coating against corrosion and irradiation damage, for its self-healing of surface defects through viscous flow mechanism.
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Ozone Source Apportionment of Typical Photochemical Pollution Episodes in the Pearl River Delta in Autumn
CHEN Hao;WANG Xuesong;SHEN Jin;LU Keding;ZHANG Yuanhang
   2015, 51 (4): 620-630.   DOI: 10.13209/j.0479-8023.2015.089
Abstract1295)      PDF(pc) (4166KB)(747)       Save
The Comprehensive Air Quality Model with extensions (CAMx), a 3-D regional chemical transport model, was used to simulate ozone concentrations in the Pearl River Delta (PRD) in November, 2009. Ozone Source Apportionment Technology (OSAT) was applied to investigate sources of two typical ozone episodes and a clean day as comparison. The results showed that emissions from urban Guangzhou and Dongguan mainly contributed to local areas and the southwestern part of PRD (15–30 μL/m3), while emissions from Shenzhen Baoan district (15–25 μL/m3) mainly affected the Pearl River Estuary. Mobile sources and solvent usage sources were two major contributors to ozone formation and had an influence in most areas of the central and western PRD. Mobile sources could contribute as much as 50 μL/m3 hourly ozone concentration to the boarding area of Foshan and Guangzhou. Trans-boundary import of ozone made episodes more likely to occur in PRD under unfavorable weather conditions, however, the ozone precursors emitted within the PRD region were the main cause of high ozone concentrations during ozone episodes. As a result, the strategies on controlling emissions within the PRD region are the key to the reduction of ozone pollutions in PRD.
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Impact of Typical Meteorological Conditions on the O3 and PM10 Pollution Episodes in the Pearl River Delta in Autumn
ZHANG Haoyue,WANG Xuesong,LU Keding,ZHANG Yuanhang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract752)      PDF(pc) (5988KB)(1545)       Save
The Community Multi-Scale Air Quality (CMAQ) modeling system was applied to simulate the meteorology field, O3 and PM10 in the Pearl River Delta (PRD) region in the autumn of 2008, in order to elucidate the impact of the typical meteorological conditions on the O3 and PM10 pollution episodes. It was found that PRD pollution characteristics presents periodic variation affected by cold air processes in the autumn of 2008. In general, good air quality was presented when cold air passing through while serious pollution was took place before and after the cold air invasion. 1) Before the cold air invasion, when the weather system “cold front front part” was presented, the height of the mixing layer was often low due to a presence of temperature inversion. Therefore, the PM10 emitted or formed at night was continuously accumulated in the morning hours causing the air pollution in northern and central PRD; the afterwards transport of the O3 during daytime and PM10 during nighttime with northern wind would cause the air pollution in southern PRD. 2) Before the cold air invasion, when the weather system “high-pressured base” was presented, an inversion layer was built up to prevent vertical mixing; both O3 and PM10 was then mainly horizontally transported with northeasterly wind; consequently forming air pollution in southwestern PRD. 3) After the cold air invasion, under the control of a ridge high pressure type of weather condition, temperature inversion was built up near the surface and a stagnant condition was presented; thus, O3 and PM10 was trapped in the source regions such as western, northwestern and central PRD, resulted in serious local pollutions.
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Characteristics of the Spatial Distributions of Ozone-Precursor Sensitivity Regimes in Summer over Beijing
NIE Teng,LI Xuan,WANG Xuesong,SHAO Min,ZHANG Yuanhang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract877)      PDF(pc) (610KB)(839)       Save
Models-3/CMAQ was applied to simulate the ozone-precursor sensitivity during June, July, and August, 2010 in Beijing. Frequencies of ozone-precursor sensitivity regimes were used to represent the characteristics of the spatial distributions of the regimes. Results showed that ozone formation was VOCs-sensitive in urban Beijing, and turned to be mixed sensitive and NOx-sensitive in suburban areas and more remote areas of Beijing. In urban Beijing, the number of days that a reduction of anthropogenic VOCs could reduce ozone efficiently accounted for about 50% of the whole summer; while in Changping, Yanqing and Huairou, the number of days that a reduction of anthropogenic NOx could reduce ozone efficiently accounted for 40%~50%. The situation that ozone gave little response to the reduction of both two precursors occurred in every district/county. The number of days in this situation accounted for more than 70% in eastern and southern districts/counties. The distributions of the sensitivity regimes of maximum 8-hour ozone concentration were similar to that of 1-hour ozone concentration.
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Non-rigid 3D Shape Retrieval Based on Automatic Anti-articulating
WANG Xulei,ZHA Hongbin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract828)      PDF(pc) (1394KB)(458)       Save
The authors propose a new non-rigid 3D shape retrieval method based on automatic anti-articulating. First, feature points are extracted on the 3D shape, and then are used in shape partition and skeleton extraction. Then, the mesh editing technique is employed to automatically regularize the articulation, in order to generate a rigid 3D shape without deformation, which is used as the isometry-invariant canonical form. Finally, shape descriptors are constructed on the canonical form, and Earth Mover’s distance is employed to measure the intrinsic similarities between non-rigid objects. The method introduces less geometric distortion and requires much less computational cost. Experimental results demonstrate a significant performance improvement in retrieving non-rigid 3D shapes.
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Interaction of Ambient PM10 among the Cities over the Pearl River Delta
HU Xiaoyu,LI Yunpeng,LI Jinfeng,WANG Xuesong,ZHANG Yuanhang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract505)            Save
The Models-3/CMAQ modeling system was applied to investigate PM10 pollution over the Pearl River Delta (PRD) region during October 2006. Sensitivity analysis was conducted to examine the relationship between the reduction of different source emissions and the consequent change of PM10 concentrations, and to quantify the interaction of air pollution among adjacent cities. The results show that PM10 pollution is a regional-scale issue in PRD. Guangzhou, Foshan, Jiangmen, and Dongguan contribute to the PM10 in PRD remarkably. The relative sensitivity coefficient was proposed to determine the impact of regional pollution sources. The PM10 concentrations in Zhuhai, Jiangmen, Zhongshan, and Foshan cities are significantly influenced by regional source emissions. The intercity transport has been the important factor of PM10 pollution in PRD. To improve the air quality in PRD area, effective control of emission sources should be highly reinforced, together with consentaneous programming, intensive collaboration, joint prevention and control.
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A Novel Method for Characterizing Acid-Base Properties of Atmospheric Particulate Matter
SUN Qian,HUO Mingqun,XIE Peng,LI Jinlong,BAI Yuhua,LIU Zhaorong,WANG Xuesong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract710)            Save
Six representative acid-base components are proposed to quantitatively characterize acid-base properties of particulate matter. Micro-titration and determination of water-soluble ion concentrations are applied to water-soluble particulate matter extract, then the acid-base balance principle and the principle of charge conservation are adopted to calculate the concentrations of representative components. Polynomial regression is conducted to analyze the relationship between the amounts of hydrogen ions neutralized by particulate matter of unit mass and the initial pH values of absorption solutions, and a series of empirical equations are obtained, which are applicable to estimate the change in pH derived by the particles absorbed by the precipitation with lower ion concentrations.
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Assessment of Turbulence State and Analysis of Flux Footprint over Complex Terrain
WANG Xue,CAI Xuhu,KANG Ling,ZHANG Hongsheng,CHEN Jiayi
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract619)            Save
The authors used the observed turbulence data in wintertime and summertime of 2006 in Xiaomo Mountain, Hunan Province to study the state of local turbulence. The difference between the observed σu, w/u* and the results calculated from similarity function was large, and there was not clear relationship between σu, w/u* with wind directions. It is suggested that the local turbulence was generally not developed completely and was easily disturbed. By using a footprint model, it is found that the flux measurements in Xiaomo Mountain were representative of two types of topography: plain region and hilly region. In winter, the northern plain regions played a major role in the overall footprint sources, and the contribution of hilly area only accounted for 21% . While in summer, the influence of southern hilly area was large, with the contribution of 54% .
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Construction Fugitive PM10Emission and Its Influences on Air Quality in Guiyang
ZHANG Wenting,WANG Xuesong,LIU Zhaorong,ZHANG Yuanhan,SHAO Min,CHENG Qun,WU Degang,IAN Wei
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract683)            Save
To study influences of construction fugitive in Guiyang, construction fugitive PM10emission in 2002 was estimated based on an extensive survey of construction activities in Guiyang. The contribution of construction fugitive dust to ambient PM10was simulated using the CALPUFF model, and the seasonal variation as well as influencing factors were addressed. The results show that fugitive PM10emission from construction activities was up to 416 tons, accounting for 4% of all PM10 source emissions in the urban area of Guiyang. Construction fugitive dust showed great impact on the ambient PM10level in Guiyang, and contributed 12% to the annual mean concentration of PM10over the urban area. Significant seasonal variation of the contribution of construction fugitive dust was found due to the change of construction activities and meteorological conditions ( wind and precipitation).
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An Observation Study of Turbulent Flux Measured on Tower in Hilly Area, Central China
WANG Xue,CAI Xuhui,KANG Ling,ZHANG Hongsheng,SONG Yu,CHEN Jiayi
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract582)            Save
An observation tower was erected on Xiaomo Mountain, Hunan Province. Besides the collection of turbulence information, routine meteorological data were collected during 2006. Diurnal variances of wind and temperature profiles in winter and summer were analyzed as well as seasonal variances of wind speed and wind direction. Furthermore, sensible heat fluxes calculated using classical flux-profile relationship (Hc) are compared with the directly measured values (Hm) . It is found that the complexterrain around the tower has a distinct impact onthe values of roughness length z0 and calculated sensible heat flux (Hc); therefore it is necessaryto divide the data into 2-3 groups according to the wind directions. The following analysis show that z0 in the south part of the tower is much higher because of the hilly terrain, and the mountain slope affects the sensible heat flux remarkably. When upslope wind blows, the value of Hc is higher than Hm, and vice versa. Since the trend of the mountain is southwest-northeast, the value of Hc is similar to Hm whenthe windis fromsouthwest. Finally, Hc is corrected and the agreement between Hc and Hm is largely improved.
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3D Partial Shape Retrieval Based on Local Bag-of-Words Models
LIU Yi,WANG Xulei,ZHA Hongbin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract565)            Save
The authors propose a new 3D shape representation, “local bag-of-words models”and use overlapped “local bag-of-words models”which improves the robustness of the algorithm by avoiding shape segmentation. The detailed steps are also proposed to apply the “Earth Mover’s distance”and “pyramid match kernels”algorithms to quantify partial shape similarity. It proves that the proposed distance measure mitigates the distance under-estimation problemof global bag-of-words model. Finally, the experiments firmly demonstratethe effectiveness of the proposed approach to 3Dpartial shape retrieval.
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Gas-Assisted Etching of Micro-Hole Lattice Array on Lithium Niobate with Focused Ion Beam
XU Xuefeng,YAN Sha,WANG Keming,WANG Xuelin,XUE Jianming,WANG Yugang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract801)            Save
Two-dimensional micro-hole lattice arrays with specified structure parameters were fabricated on LiNbO3 (LN) substrateby means of focused ion beam (FIB) etching, and the influence of etching parameters, such as spot current, etching time full rate, were investaged. In order to etch good quality holes, the authors used gas-assisted etching (GAE) with focused ion beam. The results show that GAE can reduce the effect of redeposition and obtain better hole profile compared with FIB etching. According to simulative calculation, the photonic bandgap of lattice array, etched by GAE with XeF2, is more close to the ideal photonic bandgap.
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Chemical Characters and Sources Identification of PM_10 in Guangzhou Area
CUI Mingming,WANG Xuesong,SU Hang,ZHANG Yuanhang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract606)            Save
PM10 samples were collected from seven sites in Gua ngzhou area and associated chemical species including seventeen elements(Na, Mg,Al, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, As, Se, Cd, Ba, and Pb), five water solub le ions(SO2-, NO-, F-,Cl- and NH4+) ,and organic an d elemental carbons were a nalyzed. This paper discusses chemical characters, the changes of PM10 and maincomponents under different meteorological conditions, and also sources identification of PM10 by principal factor analysis. The results indicated that the averagePM10 concentration was 125.8μg/m3 and organic matter, sulfate and crustal dustwere maj or components with proportions of 24%-32% ,17%-21% and 10%-12%, respective ly in the seven sites. Principal factor analysis indicated that soil dust, oil burning, industry source(including metallurgy, chemistry and electric industry), coalburning, secondary source (by photochemical reaction) and biomass burning were t he main sources of PM10, accounting for 20.7%, 17.8%, 16.3%, 14.3%, 10.4%, and 6.3%, respectively of the total variance in the data set.
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Current Status of Nitrogen Oxides Related Pollution in China and Integrated Control Strategy
ZHOU Wei,WANG Xuesong ,ZHANG Yuanhang,SU Hang,LU Keding
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract534)            Save
Current status of nitrogen oxides-related pollution in China was analyzed, including NOx pollution and the related pollution of ozone, acid rain,particulate matter. Then the NOx and related air quality standards were reviewed. Finally, strategy for integrated and multi-target control of NOx pollution were put forward: executing ozone air quality standard, establishing the regional photochemical smog monitoring network; pursuing air quality modeling and control for Beijing, Pearl River Delta etc megacities; strengthening the control of NOx emission from power station and vehicles and setting NOx-related scientific research program.
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Study on WARMF Model for SS Simulation in Hangbu-Fengle River Watershed
LUO Dinggui,ZHANG Wei ZHENG Yi SUN Lining WANG Xuejun
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract525)            Save
Watershed Analysis Risk Management Framework (WARMF) model was applied for hydrologic and sediment simulation and temporal and spatial variation features of suspended sediment in the Hangbu-Fengle River Watershed of Chao Lake. The catchments classification and soil profile were determined based on analysis of the relation between topography and soil type within the study area, the soil profile structure and groundwater table etc. Observed hydrologic data and suspended sediment data in 2000-2003 were used for model calibration and validation. Study on calibration and validation of hydrologic and sediment parameters indicates that WARMF model is applicable for hydrologic and sediment simulation in Hangbu-Fengle River watershed. Non-point sources spatial variation analysis at three levels of watershed-subwatershed-catchment indicates that the agricultural land and forest land are the major sources of SS. Hangbu River branch is the key area for non-point sources sediment control. The SS contribution from the Class A, Class B and Class C sub-catchments is 86.53%, so they can be considered as the key SS control zones. Study on temporal changes of non-point sources SS loads into the lake indicates that SS loads are concentrated mainly from May to August, which is the key period for non-point SS pollution control.
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Intensity Variation of Influence Factors on Floating Dust in the Tarim Basin
MA Yu,WANG Xu,KANG Fengqin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract717)            Save
Based on daily observation data from 27 meteorological stations in the peripheral regions of Tarim Basin from 1961 to 2003, the authors sort out 40 meteorological factors and show the existence of consistency among the analogical meteorological factors with correlation analysis. 15 among the 40 factors, such as daily mean and 6, hour variation of sea level pressure, air temperature and wind speed, daily mean of relative humidity, daily precipitation and daily maximum depth of frozen soil, are considered having influences on floating dust weathers, while others are neglected due to their self, consistencies. The degree of correlations between these 15 factors and floating dust weathers has significant changes from one month to another. Analyses of multivariate linear regression show significant seasonal changes. At 08:00, 14:00 temperature variation and daily, mean relative humidity are the dominant factors of influencing on floating dust weathers in all seasons. At 14:00, 20:00 in spring and summer, pressure variation is the secondary factor. At 08:00, 14:00 in autumn variation of wind speed is important. Daily, mean wind speed is important in all seasons, with more prominent influences in spring and winter.
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Climatological Characteristics of Dust Weathers in the Tarim Basin
MA Yu,XIAO Kaiti,WANG Xu
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract870)            Save
The authors study the temporal and spatial distributions of dust weathers and the trends in occurring days of dust weathers using data from 28 observational stations in the Tarim Basin during the period of 1961-2003. Five meteorological factors, which affect dust weathers, are analyzed, including air temperature, daily range of ground temperature, air pressure, average wind speed and precipitation on dust weathers with the method of linear multi-regression. Based on the analyses, the indices of dust weathers are constructed. The results show that the regions where dust weathers occur most frequently are in the Taklimakan Desert and its southern marginal zone. The temporal and spatial distributions of dust weathers are different in these regions. Dust weathers occur most frequently in spring. The days of dust weathers are closely related to daily variations of the meteorological factors. Dust-weather days have a tendency toward decrease. Interannual variations of dust-weather days have a period of about 6-9 years. According to their importance in affecting the occurrence of dust weathers, the factors are in an order of average wind speed, precipitation and daily range of ground temperature over March-September. In spring, the dominant factor is precipitation. The dominant factor is average wind speed over June-September. Indices of dust weathers are constructed to demonstrate the temporal series of dust weathers and to predict the occurrence of dust weathers.
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A Case Study of a Black Storm at the Northern Foothills of Tianshan Mountains
MA Yu,WANG Xu,XIAO Kaiti,LIU Xiaomei,TAN Jiang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract839)            Save
Using conventional observational data, autographic records and satellite images, the authors studied a black storm caused by a dry squall line associated with a southern cold front at the northern foothills of Tianshan Mountains in Xinjiang on April 18, 1998. The results show that winds, pressure, temperatures and humidity all have abrupt changes when the black storm passes through meteorological stations, changes associated with the black storm are much stronger than that with dust storms. The dust wall is almost isothermal, with horizontal thickness of about 4-9km. Strong surface winds were mainly caused by rapid intensification of the cold front and the cold advection. Meanwhile, the development of a upper level jet and strong downward transport of momentum by the sinking branch of the upper level jet's secondary circulation are also important for the formation of strong surface winds. The mixed layer is the crucial stratification factor affecting the formation of black storm because it can minimize the energy required to develop the deep dry convection and so is favorable for the formation of black storm in drought region. In this case primary reason that the black storm occurres at the northern foothills of Tianshan Mountain is the formation of deep mixed layer, which is induced by the surface heating for a long time. So the deep dry convection can be developed when the cold front passes and the black storm occurres there.
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The Issues of Application for the Fission Track Dating and Its Geological Significance
ZHANG Zhicheng,WANG Xuesong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract881)            Save
Unlike most methods of radiometric dating, fission track dating measures the effect, rather than the products, of radioactive decay events. External detector dating method can calculate individual grain ages. There are three assembled ages for single sample, which are pooled age, mean age and central age. It is very important that the fission track ages have no unambiguous geological significance. Tracks are randomly oriented in three dimensional space. However, the measurements of track density used in age eterminations are based on a two dimensional sample of tracks intersecting an internal surface. With the increasing of the temperature, the fission tracks are progressively shortened from their ends, resulting in a reduction in the observed area density of the tracks and therefore a reduction in the measured fission track age. Because the fission track age is associated with the length of tracks, the length and distribution of tracks are the most important parameters in the fission track analysis. By modelling of thermal histories from apatite fission track data, the thermal histories of samples can be reconstructed.
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The Application of ANN Realized by MATLAB to Underground Water Quality Assessment
LUO Dinggui,WANG Xuejun,GUO Qing
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract769)            Save
The realizing function of RBF network is provided in the toolbox of MATLAB 6.5 and the method of calculating this function possesses properties such as adaptation for determining the construction network and independence of initial weight value on person. A favorable outcome appeared after we apply this function to evaluating the quality of the underground water environment in FuZhou City, attempting to use the RAND function in MATLAB to construct enough training samples, checking samples and outputs of their targets through interpolation between grades of the water quality evaluation standard, use the PREMNMX function to pretreat the original data, determine the limits of water quality grades. The methods in this paper is meaningful in improving the precision and objectivity of underground water environment quality evaluation.
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Investigation of the Mechanisms of Isoprene and Monoterpene Emissions from Hevea brasiliensis in Xishuangbanna
WANG Zhihui,BAI Yuhua,WANG Xuesong,LIU Zhaorong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract820)            Save
Based on the authors investigation of the isoprene and monoterpene emissions from Hevea brasiliensis (H.B.K) Muell.-Arg in Xishuangbanna, it was found that the isoprene emission was low (emission factor varies between 0 and 1μgC·g-1h-1) and the monoterpene emissions were high (emission factor varies between 10 and 100μgC·g-1h-1). It was presumed that the scarcity of the isoprene synthase in the chloroplast of hevea brasiliensis leaves dominated the special emission character.
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A Numerical Simulation Study of PM10 Pollution in Beijing during Summer Time
WANG Xuesong,LI Jinlong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract612)            Save
A 3-D Eulerian regional air quality model, CAMx, is used to simulate the temporal variation and spatial distribution of PM10 in Beijing during summertime. The results show the prominent temporal and spatial variation characters of PM10. PM10 diurnal variation shows peaks around midnight and in the morning, an increasing trend around noon in urban areas because of the secondary aerosol production from photochemical reactions, a lowest concentration in early evening. The spatial distribution of PM10 has close relation to the source emission and is affected by the secondary aerosol production from photochemical reactions around noon. The secondary aerosol is an important portion of PM10. The secondary aerosol plays a main role on the concentration variation of sulfate and nitrate, while the concentration level and variation of organic carbon aerosol and PM10 is determined mainly by the primary aerosol.
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A Case Study of Ozone Source Apportionment in Beijing
WANG Xuesong,LI Jinlong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract641)            Save
The Comprehensive Air Quality Model with extensions (CAMx), a 3-D Eulerian regional air quality model, was used to simulate the tropospheric photochemical pollution in Beijing and Tianjin areas. Ozone Source Apportionment Technology (OSAT) was applied to track the contributions of multiple source areas and source categories to ozone formation in Beijing. The results showed that the source emissions in the urban and suburban areas of Beijing contributed much to ozone formation in local and downwind areas; among all the source categories, mobile source contributed most to ozone formation, followed by the pollutants from oil products and organic solvents and those emitted by industrial source, while biogenic source and other anthropogenic area source contributed less in Beijing. The results also showed that the ozone episode in Beijing area was regional in extent, meteorological fields and pollutant emissions were important impact factors to ozone formation and distribution.
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Effects of Strong Winds on Sandstorms in Xinjiang
CHEN Hongwu,WANG Xu,MA Yu
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract880)            Save
With observational data spanning 1961-1999 from 90 meteorological stations in Xinjiang, the spatial and temporal characteristics of sandstorms and strong winds, and the contribution of strong winds to the occurrence of sandstorms are analyzed. Moreover, the dominant wind direction and minimum wind speeds during sandstorm periods are discussed. The research shows that although possessing similar climatic trends, sandstorms and strong winds in Xinjiang have opposite geographical distributions, i.e. places with more sandstorms show fewer strong winds. The contribution of strong winds to sandstorms in northern Xinjiang is larger than that in southern Xinjiang. The dominant wind directions clearly indicate the paths of the weather systems that introduced the sandstorms. The minimum wind speeds in the sandstorms were over 10m/s in northern and eastern Xinjiang and in the Turpan and Yanqi Basins of southern Xinjiang. In Tarim Basin of southern Xinjiang, however, the minimum wind speed was about 6~8m/s, and even 6m/s at its southern edge.
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Analysis on the Climate Characteristics of Sandstorms in North Xinjiang
WANG Xu,MA Yu,WANG Hongwei,TAO Zuyu
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract690)            Save
The temporal-spatial distribution characteristics of sandstorm that occurred in North Xinjiang has been revealed by counting and analyzing 39-year sandstorm date collection(1961-1999) gathered from 40 weather stations in North Xinjiang. The results show that in North Xinjiang,the sandstorms occur most frequently in Gurbantuguter desert, more frequently in the southern periphery of the desert than in the others.The annual variation shows that the sandstorm usually occurs during the months from April to August. The daily variation shows that the occurrence of sandstorm is more frequent during 15-23 o'clock in local time. The duration of most sandstorms in North Xinjiang is within one hour or so. The longest persistence time is 16 hours.
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