Journals
  Publication Years
  Keywords
Search within results Open Search
Please wait a minute...
For Selected: Toggle Thumbnails
A Case Study on Organization Features of Successive Mesoscale Convective Systems in the Environment of Northeast China Cold Vortex
ZHU Yuning, MENG Zhiyong, LEI Lei, YI Xiaoyuan, LIU Hongjun, LI Sa
Acta Scientiarum Naturalium Universitatis Pekinensis    2022, 58 (3): 421-433.   DOI: 10.13209/j.0479-8023.2022.033
Abstract512)   HTML    PDF(pc) (8390KB)(165)       Save
The evolution of the organizations and the synoptic features of four successive mesoscale convective systems (MCSs) in the Beijing-Tianjin area under the background of the Northeast China cold vortex (NCCV) during 21 hours from 0400 UTC to 2400 UTC on July 22, 2009 was examined by using radar, surface observations, sounding data and ERA5 reanalysis data. The results showed that the convections in the four processes had different organizational patterns owing to the complex interaction among the shallow trough in the northwesterly flow in the middle troposphere to the southwest of the NCCV, the associated lower troposphere trough and cyclonic vortex, the southwesterly warm and moist flow, and cold pools under the background of long-lasting northwesterly flow to the southwest of the NCCV. The first process was triggered in north Hebei Province by the frontogenesis caused by a shallow trough on the west to the NCCV. A southwest-northeast oriented weak convective line was formed with the cell in north Beijing and developed the fastest and strongest. It evolved into a supercell and a bow echo later on. It produced cold pool which lifted the warm and humid air from the southwest producing series cells to a northwest-southeast oriented backbuilding pattern across the Beijing-Tianjin area. The second process was triggered by the cold pool of the first process on the south of Beijing and formed a supercell. The westward outflow of new convection of the first process made the supercell evolve into a southwest-northeast oriented backbuilding convective line. In the third process, a vortex in the lower troposphere formed corresponding to the strengthening of the trough to the south of the NCCV. The northerly wind on the west of the vortex in the lower troposphere converged with the southerly wind on the northwest side of the high-pressure ridge in the lower troposphere, producing multiple northwest-southeast oriented linear backbuilding convective lines. The echo training of these backbuilding convective lines caused heavy rainfall in Tianjin.. The fourth process started with two linear convections triggered respectively by the frontogenesis generated by another shallow mid-troposphere trough on the westsouth to the NCCV and the shear line generated by the NCCV in north Tianjin. The two linear convections merged into one due to the shear line in the lower troposphere with the southern part evolving into a bow echo. Some of the bow echoes had bow and arrow structure in the evolution of the four processes.
Related Articles | Metrics | Comments0
Responses of Vegetation Growth to Climate Change in Permafrost Distribution Region in Northeast China
LI Yunyun, LIU Hongyan
Acta Scientiarum Naturalium Universitatis Pekinensis    2021, 57 (4): 783-789.   DOI: 10.13209/j.0479-8023.2021.056
Abstract988)   HTML    PDF(pc) (7008KB)(212)       Save
The interannual change rate of the normalized vegetation index (NDVI) and its correlation with climate factors were compared under different permafrost degradation and vegetation types. The results indicated that NDVI of the coniferous forest accelerated, which was positively correlated with the temperature and negatively with the precipitation in the growing season. As the permafrost active layer deepens, the rate of increase in NDVI of coniferous forests gradually decreases from north to south. The grassland NDVI accelerated in non-permafrost regions, which was positively correlated with growing season precipitation. There is a clear difference between the response of mixed forests to climate in permafrost and non-permafrost regions. In permafrost regions, mixed forest NDVI is positively correlated with growing season temperature and negatively correlated with growing season precipitation. As the permafrost active layer deepens, the correlation coefficient between the NDVI of mixed forest and growing season temperature shifts from positive to negative, and the correlation coefficient with growing season precipitation shifts from negative to positive. This may be related to the different water supply caused by different active layer thickness. The results imply that under the coupling effects of climate and permafrost, climate warming will lead to gradual northward shifting of coniferous forests and mixed forests, and occupation by grasslands in non-permafrost regions.
Related Articles | Metrics | Comments0
Response of Different Altitude Vegetation to Climate Change in Taibai Mountain Alpine Zone during the Past about 2000 Years
YANG Xiuyun, GAO Yishen, CHENG Ying, WANG Hongya, LIU Hongyan
Acta Scientiarum Naturalium Universitatis Pekinensis    2020, 56 (5): 844-854.   DOI: 10.13209/j.0479-8023.2020.053
Abstract947)   HTML    PDF(pc) (1003KB)(123)       Save
Based on organic geochemical indicators of a lake-sediment profile from Western Foye Chi (3410 m), the study reconstructs the climate change of the Taibai Mountain alpine zone during the past about 2000 years. In order to explore the similarities and differences of vegetation response to the climate change at different altitudes in the alpine zone, pollen analysis of the profile was carried out, and cluster analysis was performed on the results in combination with the published pollen data of Paomaliang (3556 m), Sanqingchi (3080 m) and Fangxiangsi (3000 m) in Taibai Mountain. These analyses suggest that the responses of the vegetation to relatively cold and dry climate have good consistency at different altitudes, which is even more noticeablein the transition zone of timberline. Besides, along with the modern warming period, the responses of vegetation to climate change are mainly determined by the altitude. This study can provide some references for understanding the coupling relationship between climate and vegetation of alpine environmental systems during the Late Holocene.
Related Articles | Metrics | Comments0
Indicative Significance of Tree Tracheid Size on Forest Growth and Environmental Adaptability in the Forest-Grass Ecotone of Southern Siberia
XUE Jiaxin, LIU Hongyan, XU Chongyang, Oleg A. Anenkhonov, Denis V. Sandanov, Andrey Yu. Korolyuk, JIANG Zihan, LIU Xu, Larisa D. Balsanova, Bulat B. Naidanov
Acta Scientiarum Naturalium Universitatis Pekinensis    2020, 56 (3): 531-538.   DOI: 10.13209/j.0479-8023.2020.027
Abstract793)   HTML    PDF(pc) (13226KB)(116)       Save
In order to study the relationship of three growth features of cell, tree and forest that indicate adaptation of trees to water deficit, we measured the tree-ring widths of 725 tree-cores sampled from sites dominated by Larix sibirica and Pinus sylvestris and then 195 of them were randomly selected to measure the tracheid size. The results show that the tracheid size is significantly correlated to the radial growth and the inter-annual variation in ring width, at both levels of the tree individual and forest community, regardless of local environment and tree species. This result suggests that small mean tracheid cells indicate low growth rate and more growth variation. The study implies that the mean tracheid size could serve as a robust indicator of tree or forest adaptation to habitat humidity for conifers in the semi-arid region and reveals the trade-off between growth adaptation and growth safety of trees by regulating tracheid size. As an important xylem trait of conifer forests, the size of tracheid is valuable for the further physiological study of drought adaptation of trees in the semi-arid region.
Related Articles | Metrics | Comments0
Seasonal Patterns and Their Determinants of Non-structural Carbohydrates in Different Tree Species at Xeric Timberline
SHANGGUAN Huailiang, LIU Hongyan, HU Guozheng, GUO Weichao
Acta Scientiarum Naturalium Universitatis Pekinensis    2019, 55 (3): 553-560.   DOI: 10.13209/j.0479-8023.2019.016
Abstract988)   HTML    PDF(pc) (2134KB)(94)       Save
To examine the seasonal patterns of non-structural carbohydrates (NSC) in different tree species and the roles of biotic (tree species) and abiotic (climate) factors on these patterns at xeric timberline, the authors monitored seasonal patterns of non-structural carbohydrates in four different tree species (Pinus sylvestris var. mongolica, Betula platyphylla, Populus simonii and Larix principis-rupprechtii) in southeastern Inner Mongolian Plateau of China. The results show that tree species with different foliar habit types have broadly similar seasonal non-structural carbohydrates (NSC) patterns (NSC concentration increased at the beginning of the growing season, and reduced in summer because of high growth rate, then increased slowly in the end), which suggests a climatic determination. Significant differences (p<0.05) in NSC concentrations are observed between four tree species. NSC concentration in birch is significant higher than that in pine, reproducing the pattern that deciduous species have higher NSC pool than ever green ones, which suggests a biotic determination. Due to the relatively drier climates, NSC concentration in larch and poplar turn to be lower than that in pine, implying a combined effect of both biotic and abiotic factors. The sugar and TNC (total non-structural carbohydrates) concentrations in leaf are significantly higher than those in stem, but the starch concentration in leaf is lower, which is consistent with the different roles of leaf and stem. 
Related Articles | Metrics | Comments0
Research on Sentiment Analysis Based on Representation Learning
LI Xiaojun, SHI Hanxiao, CHEN Nannan, LIU Hong, ZOU Yi
Acta Scientiarum Naturalium Universitatis Pekinensis    2019, 55 (1): 105-112.   DOI: 10.13209/j.0479-8023.2018.066
Abstract972)   HTML    PDF(pc) (931KB)(174)       Save

The authors propose C&W-SP model — a text sentiment analysis model based on the representation learning. Firstly, an improved training model based on C&W model is proposed which can integrate emotional information and part of speech information in the training process of word embedding. The evaluation of data sets of NLP&CC’2013 is used to compare experimental results with different models. The experimental results show that the C&W-SP model which combines emotion information and part of speech information has the best performance and confirm the effectiveness of the proposed method.

Related Articles | Metrics | Comments0
Origin of Mg-Rich-Fluids and Dolomitization of Lower Ordovician Penglaiba Formation at Tongguzibulong Outcrop in the Northwestern Margin of Tarim Basin
HE Yong, LIU Bo, LIU Hongguang, SHI Kaibo, WANG Yuanchong, JIANG Weimin
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (4): 781-791.   DOI: 10.13209/j.0479-8023.2018.006
Abstract871)   HTML    PDF(pc) (34391KB)(138)       Save

Based on comprehensive analysis of field work, petrological and geochemical characteristics, the authors study the sources of dolomitizing fluids and the models of dolomitization of the Lower Ordovician Penglaiba Formation in Tongguzibulong Outcrop, the northwestern margin of Tarim Basin, China. Four types of
dolomite are recognized: euhedral-subhedral powder crystallized dolomite, euhedral-subhedral fine crystallized dolomite, subhedral-xenotopic medium crystallized dolomite and subhedral-xenotopic coarse crystallized dolomite. Powder-fine crystallized dolomite is distributed in the lower part of Penglaiba Formation, and has cloudy center surrounded by clear rim. With residual sand texture, inter-crystal pores and inter-partical pores, medium-coarse crystallized dolomite is distributed in the upper part of Penglaiba Formation. The REE patterns of dolomite and contemporaneous limestone rich in LREE and deplete in HREE, present a trait of unobvious Ce anomaly and Eu negative anomaly, the values of C-O isotope locate in the scope of contemporaneous marine dolomite, and Eu negative anomaly. All these denote that the dolomitizing fluid is normal or slightly concentrated seawater. Besides, Powder-fine crystallized dolomite present a low value of Fe, Mn and a high value of Sr, Ba, formed by reflux seepage dolomitization in penesaline seawater. Cloudy center surrounded by clear rim texture and multi-rimmed texture are the results of over-dolomitization. Medium-coarse crystallized dolomite with residual grain texture, interbedded with sand limestone, are controlled by high frequency sea level change. With a higher value of Fe, Mn and a lower value of Sr, Ba when compared with powder-fine crystallized dolomite, medium-coarse dolomite formed by the early reflux seepage dolomitization and intensified by the subsequent burial recrystallization.

Related Articles | Metrics | Comments0
Diagenesis Types and Evolution of the Lower-Middle Ordovician Carbonates in Yubei Area, Tarim Basin
LIU Hongguang, LIU Bo, ZHANG Xuefeng, CAO Jianhua, HUANG Chenjun, LIU Geyun, WU Shuanglin
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (2): 373-384.   DOI: 10.13209/j.0479-8023.2017.135
Abstract1177)   HTML1)    PDF(pc) (62505KB)(284)       Save

The Lower-Middle Ordovician carbonate rocks are studied by core observation, thin section observation, geochemical analysis to restore the diagenetic evolution history of the Yubei area, Tarim Basin. Dissolution, dolomitization, silicification and cataclasis are studied and the diagenetic evolution history is divided into four stages. The grained texture dominated limestone in the relative geomorphic high location exposes to the ground and undergoes penecontemporaneous dissolution due to the fluctuation of the sea level. Caves and pores with structural selectivity parallel to the sedimentary bed are generated by the penecontemporaneous dissolution. The dolomitization developed mainly in early diagenetic stage enhances the resistance of carbonates to compaction and pressure solution, which benefits the preservation of early pores and caves. The fractures formed during the Middle-Late Caledonian and Early Hercynian in this stage are mostly closed and filled due to complicated compaction and cementation. Hydrothermal activity in middle diagenetic stage damages the reservoir slightly by the presence of pyrite and dolomite with wavy extinction and saddle structure in the reservoir space. The late diagenetic stage is characterized by the silica and calcareous fluid activity, which fill the early space partially. The development degree of fractures formed during Late Hercynian and Himalayan epoch is weaker than early diagenetic stage. However, the fractures formed during late diagenetic stage keep open due to weak diagenetic transformation and become efficient migration channel and reservoir spaces in Yubei area.

Related Articles | Metrics | Comments0
Climatic and Environmental Changes in More Than the Past 1800 Years as Recorded by Isotopic Carbon and Nitrogen in Organic Matter of Sediments from Western Foye Chi (Buddha Pond) on Taibai Mountain
GAO Yishen, WANG Hongya, CHENG Ying, LIU Hongyan, ZHU Chenyi
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (1): 94-104.   DOI: 10.13209/j.0479-8023.2017.075
Abstract869)   HTML11)    PDF(pc) (7631KB)(259)       Save

A 50-cm core (hereafter referred to as “XFYC12-2”) was retrieved from western Foye Chi (Buddha Pond), a glacier-scour lake on southern slope of Taibai Mountain that is the main massif and peak of Qinling Mountain Range. Accelerator mass spectrometry (AMS) 14C dating and analyses of isotopic carbon and nitrogen of organic matter were performed on samples from XFYC12-2. Climatic and environmental changes occurring around this alpine during over the past ~1800 years were therefore reconstructed. Climatic and environmental conditions were still fairly cool and arid during 1811−1380 (or 1440) aBP. In 1380 (or 1440)−840 aBP, the climate and environment were warm and humid. This episode is probably corresponding to Medieval Warm Period (MWP). Climatic and environmental conditions deteriorated subsequently and were thus cold and dry over the period of 840?460 (or 520) aBP. This phase may correspond to Little Ice Age (LIA). Climatic and environmental conditions have turned to be warm and wet again during 460 (or 520)−100 aBP. The aforementioned process of climatic and environmental changes appears quite similar to what was reconstructed around another two lakes at the high altitudes of Taibai Mountain, what was generalized for eastern China and what was identified at another four study areas in eastern China.

Related Articles | Metrics | Comments0
Design of a Humidified Nephelometer System with High Time Resolution
LIU Hongjian, ZHAO Chunsheng
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (6): 999-1004.   DOI: 10.13209/j.0479-8023.2016.053
Abstract870)   HTML    PDF(pc) (1533KB)(651)       Save

In order to study the diurnal variations of aerosol hygroscopic properties in North China, a new humidified nephelometer system is designed with the advantage of high time resolution and high humidification efficiency. In this system, two water baths are used for the first time to control humidification process in turn, reducing the circulation cycle from two to three hours to about one hour. Besides the nephelometer lamp power is reduced from 75 W to 25 W, and a piece of heat mirror is set ahead of the lamp. After those modifications, the temperature rising inside the chamber decreases from 4.3 ºC to 2.3 ºC and humidification efficiency rises. The original RH sensor inside the chamber is inaccurate, so two Vaisala sensors are set at the inlet and outlet of the nephelometer to correct the RH inside the chamber. In the future, this humidified nephelometer system will be used in in situ measurement in North China to get the diurnal variation properties of aerosol light scattering enhancement factor.

Related Articles | Metrics | Comments0
Petrogenesis of the Early Cretaceous Qingcaoshan Strongly Peraluminous S-Type Granitic Pluton, Southern Qiangtang, Northern Tibet: Constraints from Whole-Rock Geochemistry and Zircon U-Pb Geochronology
LIU Hong, ZHANG Hui, LI Guangming, HUANG Hanxiao, XIAO Wanfeng, YOU Qin, MA Dongfang, ZHANG Hai, ZHANG Hong
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (5): 848-860.   DOI: 10.13209/j.0479-8023.2016.045
Abstract1455)   HTML    PDF(pc) (2447KB)(584)       Save

The Qingcaoshan granitic pluton, located in the Zhapu-Duobuza magmatic arc in southern Qiangtang, consists of granite porphyry and quartz monzonitic porphyry. However, the age and genesis are not studied due to absence of geochemical and geochronological data. The weighted average 206Pb/238U age of 122±1 Ma (MSWD=3.9) for quartz monzonitic porphyry and 114.6±1.2 Ma (MSWD=1.1) for granite porphyry is present by LA-ICPMS and SHRIMP zircon U-Pb dating. The intrusion have minor muscovite and cordierite, no hornblende. The granitic pluton is characterized by enriched Al (A12O3: 14.81%-15.86%), depleted Ca (CaO: 1.10%-2.44%), and high content of alkali (K2O+Na2O: 6.86%-8.80%). Father more, it is also characterized by ASI of 1.1 (A/CNK: 1.06-1.20), corundum (1.20%-2.86%) and absence of diopside showed through CIPW calculation, which are indicative of peraluminous sub-alkaline S-type graniten. The intrusive rock is relatively enriched in large ion lithophile elements (Rb, Th, U, K, La, Ce) and depleted in high field strength elements (Ta, Nb, P, Ti, Y), and exhibits LREE-enriched ((La/Yb)N: 3.24-16.20) with right-inclined REE distribution patterns. A synthesis of all these characteristics indicates that the Qingcaoshan granitic pluton was probably derived from partial melting of greywacke components in the upper crust as a result of norward subduction of the Bangong Co-Nujiang oceanic crust towards the Qiangtang block.

Related Articles | Metrics | Comments0
The Characteristics and Implication of Origin of the Giant Patch Dolomite of the Lower-Middle Ordovician in Wuligezitag Area NE Tarim Basin, China
WU Shuanglin, SHI Kaibo, LIU Hongguang, LIU Jianqiang, WANG Yuxi, LIU Bo
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (3): 444-456.   DOI: 10.13209/j.0479-8023.2015.118
Abstract1029)   HTML    PDF(pc) (1812KB)(823)       Save

Based on comprehensive analysis of field work, petrological and geochemical characteristics, this paper studies the characteristics and origin of giant patch dolomite of the Lower-Middle Ordovician HangGuletag Formation in Wuligezitag area, NE Tarim Basin, China. It can be seen in the field that the grayish yellow giant patch dolomite partially develops in the black thin-bedded micritic limestone, with an irregular boundary not controlled by sedimentation. The giant patches are several meters in size (the largest >10 m) which is larger than and quite different from the several-centimeter (decimeter) burrow-related dolomite or leopard fur dolomite. Microscopically, it consists of micro-finely and planare(s) dolomite crystals with a size near 100 μm. Besides, it is also characterized by its unique geochemical features: 1) δ13CPDB (−1.34‰-−0.62‰) accords with the range of Early Ordovician seawater while δ18OPDB (−8.01‰ -−4.79‰) is higher; 2) 87Sr/86Sr  (0.711000-0.711535, AVG=0.710863) is much higher than that of limestone and contemporaneous seawater; 3) average high Fe and Mn content (2001.32 and 601.73 μg/g, respectively) and low Sr and Ba (33.14 and 8.27 μg/g, respectively) content versus that of limestone; 4) dolomite has slightly negative Eu anomaly and similar REE composition and distribution patterns compared with limestone; 5) low order degree value (AVG=0.6). This study reveals that the dolomitization was related to fault and occurred in low-temperature and shallow-burial environment in Early-Middle Ordovician. Dolomitizing fluid was generated from the concentrated formation fluid in lower-middle member of HangGuletag Formation and underlying Tursaktag Group. Most Mg2+ came from the stabilization of quasi-stable carbonate minerals, and the transformation of clay minerals of (calcareous) mud in the limestone strata not only provided a little Mg2+ but caused the rise of 87Sr/86Sr. Dolomitizing fluid was likely to be richened in Xingdi-related normal fault and fractures which also acted as the main fluid pathways, and it finally caused the partial dolomitization of nearby limestone strata.

Related Articles | Metrics | Comments0
Climatic and Environmental Changes Occurring during the Last 5520 Years on Alpine Belt of Taibai Mountain: the Records of a Few Proxies of Sediments from Foye Chi and Their Interpretations
ZHANG Caina, WANG Hongya, LIU Hongyan, CHENG Ying, SONG Yaqiong, LUO Yao, DENG Lei
Acta Scientiarum Naturalium Universitatis Pekinensis    2015, 51 (6): 1091-1101.   DOI: 10.13209/j.0479-8023.2015.078
Abstract863)      PDF(pc) (1013KB)(476)       Save

Foye Chi is a small lake developing in a cirque in the alpine belt of southern slope of Taibai Mountain which is the peak of the Qinling Mountain Range. A 70 cm deep pit was excavated on the desiccated floor of this lake and sediments were sampled from the pit’s wall. AMS 14C dating was performed for three samples from this sediment profile. For all the 56 samples, analysis of total organic carbon content (TOC) and carbon-nitrogen ratio (C/N) and measurements of low-frequency magnetic susceptibility (χlf) and anhysteretic remanent magnetization (ARM) were undertaken. So were analyses of particle-size and pollen. ARM/χlf was further calculated as well. A chronological framework was developed based on the dating results. Variations in TOC, C/N, χlf, ARM, ARM/χlf, mean particle-size and percentage of Quercus pollen of this sequence were interpreted and climatic and environmental changes occurring around Foye Chi since 5520 aBP were so preliminarily inferred. The climate and environment were generally cold and arid during 5520-3800 aBP and the coldest and driest during 5100-4300 aBP. During 3800-2300 aBP, the climate and environment have turned to be warm and humid. The climate and environment were even wetter during 2300-1300 aBP and warmer during 1300-700 aBP which might be the warmest phase of the last ~5500 years. During 700-500 aBP, the climate and environment tended to be cool and arid again. These climate-environment changes happening during the middle and late Holocene in alpine belt of Taibai Mountain are generally similar to the changes at some sites in the region influenced by the East Asian monsoon in China since these sites are all under the influence of East Asian monsoon.

Related Articles | Metrics | Comments0
Relationship between Shrubs Distribution and Slope: A Case Study in Mountains of the Beijing-Tianjin-Hebei Region
WANG Tao;HAO Qian;LIU Hongyan
   2015, 51 (4): 685-693.   DOI: 10.13209/j.0479-8023.2015.091
Abstract983)      PDF(pc) (1019KB)(399)       Save
Shrublands in the Beijing-Tianjin-Hebei region were selected to unveil relationships between the area percentage of shrubland and the slope angle. Gridded data of vegetation and slope angle were correlated for the whole region as well as different climatic regimes with piecewise regression analysis. The results show that there is a tipping point on the fitted curve between percentage of shrubs and slope angle, instead of a monotonous linear fit. On gentle slopes, percentage of shrubs increases with the increase of slope angle, which might be caused by the decrease of human cultivation. On steep slopes, there are divergent patterns, percentage of shrublands except that dominated by Vitex negundo var. heterophylla and Zizyphus jujuba var. spinosa decreases with the increase of slope angle, which might be caused by resource limitation. Percentage of this shrubland type does not show trend of decline with slope angle increase, which might be caused by its distribution on low elevations and its adaptation to varied habitats. In addition, the tipping point mostly fixes around 15 degree of slope angle when the region is taken as a whole; it changes under different climatic regimes.
Reference | Related Articles | Metrics | Comments0
Theory and Application of Numerical Simulation of Asymmetric Hydraulic Fractures in Ultra-Low Permeability Reservoirs
WU Wenjuan,SHI Yongmin,WANG Xiaojun,LIU Hongtao,QIN Xiaoshuang,WANG Lei,CHAI Zhi,LI Xiaomin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract663)      PDF(pc) (1679KB)(324)       Save
Based on Chang-6 formation of Yanchang group in Erdos basin, built the geology, 3D rock mechanics and 3D stress field models with core and logging data, and obtained the properties of any point between wellbores. With the fracturing principle, the actual geometry of the fractures can be calculated, and the asymmetry fractures model can be built, including the length, height, width and the direction of the fractures. With the analysis of production history, the residual oil distribution can be obtained, and the multiple fracturing procedure can be designed. With the guidance of the asymmetric fracture models, the daily increase of production is more than 4 ton.
Related Articles | Metrics | Comments0
Factors Affecting Soil Organic Carbon Density (SOCD) and Total Nitrogen Density (TND) in Inner Mongolian Steppe
CHEN Xi,LIU Hongyan
Acta Scientiarum Naturalium Universitatis Pekinensis   
Performance Analysis of Opportunistic Relaying with Regenerative Relays in Wireless Networks Based on the Randomly Distributed Nodes
LIU Hong,CHENG Yuxin,REN Shubo,XIANG Haige
Acta Scientiarum Naturalium Universitatis Pekinensis   
Verifiable Multi-secret Sharing Scheme Based on Homogeneous Linear Recursion
CHEN Yangkui,YU Jia,CHENG Xiangguo,HAO Rong,LIU Hongyan,LI Xin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract619)            Save
A new multi-secret sharing scheme based on homogeneous linear recursion is proposed, and then it is converted into a verifiable scheme. In the distribution phase, very few of public values are needed to publish. In the recovery phase, each participant only needs to submit a pseudo shadow instead of his secret shadow, and his secret shadow cannot be disclosed. When secrets are changed, secret shadows don?t need to be redistributed, which makes secret shadow able to be used multiple times. The proposed scheme has many advantages, for example, the secret shares can be used multiple times and the scheme publishes very few parameters as well as the reconstructed polynomial has a low degree. This makes the proposed scheme more efficient. Therefore, it better satisfies demands of various applications.
Related Articles | Metrics | Comments0
Soil Wind Erosion under Different Land Use Types in Bashang of Hebei Province
SUN Yanrong,LIU Hongyan,FAN Tao,MA Liguo,ZHANG Mingjie
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract540)            Save
By the trace of 137Cs and soil granularity analysis, the relationship between land-use and soil wind erosion was investigated in Bashang of Hebei Province. The results indicate that the land use types with erosion intensity, from the higher to the lower, are sandy hilly grassland > cultivated land > grassland converted from cultivated land > artificial forest > gravel hill grassland. Hence, to recover the vegetation, the gravel hilly grassland in this region should be reserved and the original vegetation in it should be protected.
Related Articles | Metrics | Comments0
Vegetation Development and Aeolian Activities in Bashang Area of Hebei Province and Otindag Sandy Land of Inner Mongolia
HE Gang,LIU Hongyan
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract315)            Save
Bashang area of Hebei Province and Otindag Sandy Land of Inner Mongolia are key regions in desertification studies. Studies on vegetation development and desertification in this area are critically reviewed and commented. Vegetation degradation is the general trend during the past 6000 years in millennium scale. Although human cultivation has a relatively short history, vegetation degraded remarkably during the past 50 years. Vegetation degradation and desertification are strongly correlated with the frequently occurred sandstorms in Beijing area; however, the detailed mechanism is still unclear. Three key problems for future studies are suggested. They are: (1) Integrated study on a ecological transect from Beijing to Otindag Sandy Land; (2) Modeling vegetation development and aeolian activities; (3) Tempo-spatial patterns of desertification.
Related Articles | Metrics | Comments0
Vegetation Development and Aeolian Activities in Bashang Area of Hebei Province and Otindag Sandy Land of Inner Mongolia
HE Gang,LIU Hongyan
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract631)            Save
Bashang area of Hebei Province and Otindag Sandy Land of Inner Mongolia are key regions in desertification studies. Studies on vegetation development and desertification in this area are critically reviewed and commented. Vegetation degradation is the general trend during the past 6000 years in millennium scale. Although human cultivation has a relatively short history, vegetation degraded remarkably during the past 50 years. Vegetation degradation and desertification are strongly correlated with the frequently occurred sandstorms in Beijing area; however, the detailed mechanism is still unclear. Three key problems for future studies are suggested. They are: (1) Integrated study on a ecological transect from Beijing to Otindag Sandy Land; (2) Modeling vegetation development and aeolian activities; (3) Tempo-spatial patterns of desertification.
Related Articles | Metrics | Comments0
Motion Detection for Human Bodies Basing Adaptive Background Subtraction by Using an Omnidirectional Camera
PI Wenkai,LIU Hong,ZHA Hongbin
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract592)            Save
A new real-time omnidirectional vision system is proposed for tracking multiple targets in indoor environments. In this system, an omnidirectional camera is used to obtain the 360°view images of the global scene. First, it builds the background model by observing the scene without people in it. When the detecting process starts, omnidirectional images are changed into the cylindrical panoramic images, and an adaptive background subtraction method is utilized to segment the moving regions and locate the positions of human bodies. Thus, multiple human bodies can be tracked. Experimental results show that the proposed system performs well in indoor, complex environments.
Related Articles | Metrics | Comments0
A New Automatic Seal Image Retrieval Method Based on Curves Matching
SONG Yong,LIU Hong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract706)            Save
Chinese characters have many smooth vertical and horizontal strokes. According to that, two kinds of retrieval features in Chinese characters images are proposed and named as outer edge contour feature and orientation projection density feature. Further, by formularizing the two features with functional curves, matching of Chinese characters is transformed into matching of functional curves. Experiments show that these two kinds of features are stable and the curves matching based seal image retrieval method is effective.
Related Articles | Metrics | Comments0
The Effect of Supercool on Liquid Phase Epitaxy Growth of III-IV Quinary AlGaInPAs
XU Ziliang,XU Wanjin,LI Li,YANG Chengqing,LIU Hongdu
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract734)            Save
The contour of the energy bandgap of III-V quinary, AlGaInPAs, lattice matched to GaAs has been calculated, and the segregation coefficient of Al in the solution used for growing AlGaInPAs/GaAs has been analysised. The effect of supercool on the solid composition of AlGaInPAs on GaAs, resulted from Al's segregating from the solution, has been demonstrated experimentally, no effect on other characteres was found.
Related Articles | Metrics | Comments0
Surface Pollen and Its Climatical Significance of Vertical Zone in Beitai, Xiaowutai Mountain
YU Pengtao,LIU Hongyan
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract792)            Save
After a broad survey of the vertical zone in Beitai, Xiaowutaishan mountain, a surface pollen spectrum is established. The climatical significance of some important species, such as Picea meyeri, Larix principis-ruprechtii and Betula is also analysed. This research demonstrated: Surface pollen content of Betula and Pinus is much more than their coverage in community, so they have extra-representation; Surface Pollen content of Picea is corresponded with its coverage in community; Because Larix has low pollen productivity and bad preservation ability of pollen, it has low representation for its coverage in community. As for their climatical significance, Picea meyeri indicates cool-wet habitat; Larix principis-ruprechtii indicates cool-dry climate; Betula has a broad ecological amplification, Betula albo-sinensis has a natural inclination for cool climate, Betula platyphylla has a natural inclination for dry climate.
Related Articles | Metrics | Comments0