Journals
  Publication Years
  Keywords
Search within results Open Search
Please wait a minute...
For Selected: Toggle Thumbnails
Reducing Multi-model Biases for Robust Visual Question Answering
ZHANG Fengshuo, LI Yu, LI Xiangqian, XU Jin’an, CHEN Yufeng
Acta Scientiarum Naturalium Universitatis Pekinensis    2024, 60 (1): 23-33.   DOI: 10.13209/j.0479-8023.2023.072
Abstract80)   HTML    PDF(pc) (5709KB)(50)       Save
In order to enhance the robustness of the visual question answering model, a bias reduction method is proposed. Based on this, the influence of language and visual information on bias effect is explored. Furthermore, two bias learning branches are constructed to capture the language bias, and the bias caused by both language and images. Then, more robust prediction results are obtained by using the bias reduction method. Finally, based on the difference in prediction probabilities between standard visual question answering and bias branches, samples are dynamically weighted, allowing the model to adjust learning levels for samples with different levels of bias. Experiments on VQA-CP v2.0 and other data sets demonstrate the effectiveness of the proposed method and alleviate the influence of bias on the model.
Related Articles | Metrics | Comments0
Efficient Combined Simulation Research of Finite Element Analysis for Bolt Assembly Process
LI Xiang, SHEN Chao, LIU Zhao, LIU Caishan, LIU Yan, LIU Chao
Acta Scientiarum Naturalium Universitatis Pekinensis    2023, 59 (6): 923-933.   DOI: 10.13209/j.0479-8023.2023.087
Abstract168)   HTML    PDF(pc) (16629KB)(77)       Save
Current finite element (FE) simulating methods for pre-tightening process of thread fasteners have some shortcomings. In order to ensure the accuracy and efficiency simultaneously, the interference fit method and the direct torsion method are combined via ANSYS APDL to form a new pre-tightening means. Firstly, FE models of the thread pair structure before and after simulating the necking plastic forming process are obtained. Further assembly process simulation of the necking anti-loosening nuts is realized. Via different pre-tightening methods for simulating the assembly process, the thread pair load distribution, the contact stress state and the torsion-tension relationship can be obtained. Via comparing the numerical results of the zero closure amount nuts with some theoretical solutions, the reliabilities of the FE models and the simulation process are verified. Furthermore, the calculation time and numerical results of different pre-tightening methods are compared to prove the combined pre-tightening method is reliable and effective. 
Related Articles | Metrics | Comments0
Impact of Urbanization and Industrial Collaborative Agglomeration on Land Use Efficiency of Resource-Based Cities in the Yellow River Basin, China
LI Xiaojing, HAO Jianhua, CAI Yinfei, SUN Yanan
Acta Scientiarum Naturalium Universitatis Pekinensis    2023, 59 (4): 681-694.   DOI: 10.13209/j.0479-8023.2023.009
Abstract181)   HTML    PDF(pc) (1337KB)(108)       Save
Based on the panel data of 41 prefecture-level resource-based cities in the Yellow River Basin from 2000 to 2019 and the relationship between urbanization and industrial collaborative agglomeration on land use efficiency, this paper uses spatial autocorrelation analysis and spatial Durbin model to analyze the spatial spillover effect of urbanization and industrial collaborative agglomeration on land use efficiency. The threshold regression model is used to discuss the threshold characteristics of industrial collaborative agglomeration in resource-based cities, and the crowding effect matrix table is innovatively constructed. The results show that the land use efficiency among resource-based cities in the Yellow River Basin is geographically correlated with the same high agglomeration or the same low agglomeration in space, and the spatial spillover inhibitory effect of urbanization accounts for 70% of the total inhibitory effect, showing an inhibitory effect. The spatial spillover growth effect of industrial collaborative agglomeration accounts for 70% of the total growth effect, and the spatial spillover inhibitory effect accounts for 20% of the total inhibitory effect, which shows the role of rapid promotion and gradual inhibition. After 2014, the agglomeration effect of some resource-based cities in the Yellow River Basin has accelerated to the threshold, among which Luoyang, Shizuishan, Shuozhou, Wuhai and Jinchang perform well and have the best agglomeration. Baotou and Ordos form a collaborative relationship between cities. The industrial agglomeration of most resource-based cities is still insufficient or crowded, and the future development should combine the characteristics of the city itself to play a synergistic role between adjacent cities.
Related Articles | Metrics | Comments0
Review of Regionalization and Remote Sensing Based Method for Hydrological Model Parameters Calibration in Ungauged Basins
JIANG Lulu, WU Huan, Lorenzo Alfieri, LI Xiaomeng, John S. Kimball, CHEN Xiuwan
Acta Scientiarum Naturalium Universitatis Pekinensis    2020, 56 (6): 1152-1164.   DOI: 10.13209/j.0479-8023.2020.076
Abstract904)   HTML    PDF(pc) (4416KB)(274)       Save
Challenges in calibration of hydrological model parameters in ungauged basins were discussed, and the latest advances in regionalization method and remote sensing based method were summarized. First, the common problems in the hydrological model calibration (derivation of hydrographic parameters, construction of objective function and selection of optimization method) and their influences on the results of parameter optimization) were analyzed and leading-edge solutions were then provided. Next, fundamental principles and study progress of regionalization method were introduced, and the importance of stream gauge network density of donor catchments for the streamflow prediction was emphasized. The advance of remote sensing based hydrological model calibration method was discussed in terms of model spatial domain, model structure, satellite data source, and
calibration target. Finally, the advantages and disadvantages and the future development prospect between regionalization method and remote sensing based method were compared and analyzed, and potential practical strategies for continuous streamflow prediction in ungauged basins in China are suggested.
Related Articles | Metrics | Comments0
Basic Supply Service Model of Beijing-Tianjin-Hebei Region Based on LUCC-ESs Matrix
LI Xiaojing, GAO Yang, LI Shuangcheng
Acta Scientiarum Naturalium Universitatis Pekinensis    2020, 56 (5): 950-958.   DOI: 10.13209/j.0479-8023.2020.064
Abstract783)   HTML    PDF(pc) (2252KB)(126)       Save
As the traditional ecosystem service evaluation methods have the disadvantageous as high subjectivity and low comparability, a LUCC-ESs matrix evaluation method is improved. Based on the land use/cover types, the proposed method calculates the ecosystem service units, then builds the LUCC-ESs matrix to evaluate the ecosystem services. This method can avoid different outcomes obtained by different calculation methods, and make these test results comparable and practical. The application of the basic supply service in the Beijing-Tianjin-Hebei region indicates that the spatial pattern of the basic supply services is regional and highly connected with resource reserves and land productivities. The spatial pattern of the demand service appears the same movement and aggregation characteristics as that of the population, which decreases from the city center to suburban. The basic services both inside and outside Beijing-Tianjin-Hebei region converge to the urban center. 
Related Articles | Metrics | Comments0
Analysis of Bi-directional Reranking Model for Uyghur-Chinese Neural Machine Translation
ZHANG Xinlu, LI Xiao, YANG Yating, WANG Lei, DONG Rui
Acta Scientiarum Naturalium Universitatis Pekinensis    2020, 56 (1): 31-38.   DOI: 10.13209/j.0479-8023.2019.093
Abstract1291)   HTML    PDF(pc) (899KB)(188)       Save
The fitting training of neural machine translation is easy to fall into a local optimal solution on a lowresource corpus such as Uyghur to Chinese, resulting in the translation result of a single model may not be a global optimal solution. In order to solve this problem, the probability distribution predicted by multiple models is effectively integrated through the ensemble strategy, and multiple translation models are taken as a whole. At the same time, the translation models with opposite decoding directions are integrated by the reordering method based on cross entropy, and the candidate translation with the highest comprehensive score is selected as the output. The experiment on CWMT2015 Uighur-Chinese parallel corpus shows that proposed method has 4.82 BLEU values improvement compared with a single transformer model.
Related Articles | Metrics | Comments0
Research on Transformer Oil Aging by Nuclear Magnetic Resonance Spectroscopy of Relaxation Time
LI Xiaonan, LIU Guoqiang, ZHANG Laifu, WANG Zhipeng, DING Guangxin, ZHAO Shilong, XIA Hui
Acta Scientiarum Naturalium Universitatis Pekinensis    2019, 55 (5): 865-870.   DOI: 10.13209/j.0479-8023.2019.068
Abstract736)   HTML    PDF(pc) (2398KB)(108)       Save
According to the limitations of conventional thermal aging detection of transformer oil insulation (not accurate or complicated process), a low field nuclear magnetic resonance relaxation time spectrum detection method is proposed. Based on the principle that hydrocarbon compounds in oil are cracked in high-pressure discharge environment and the molecular structure of hydrogen-containing molecules is changed, a transverse NMR relaxation spectrum detection system for thermal aging of transformer oil is designed. An algorithm for obtaining relaxation time spectrum based on inversion is described by using the peak point of time domain signal of oil samples collected by spin echo sequence. With the oil samples from the 110 kV power station in Changzhi City, the aging factor was detected by the nuclear magnetic resonance relaxation spectroscopy. The oil samples were used for 1, 10 and 20 year, individually. The results show that, in a 17.173 MHz condition, the relaxation time is 203.83, 145.82 and 141.95 ms, respectively. The detection time is controlled within 1 minute. The decreasing trend of relaxation time indicates that the high temperature causes the breaking of molecular chemical bonds and the precipitation of small hydrocarbon gases.
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
Abstract974)   HTML    PDF(pc) (931KB)(176)       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
Accumulation Process and Control Factors of Jurassic-Cretaceous Distant-Source and Secondary-Filled Reservoirs in the Hinterland of Junggar Basin
MA Weijiao, WEI Yanzhao, LI Xia, TAO Shizhen, LI Yongguang, ZHAO Zhengya
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (6): 1195-1204.   DOI: 10.13209/j.0479-8023.2018.073
Abstract924)   HTML    PDF(pc) (3206KB)(192)       Save

Homogenization temperature of fluid inclusions, stratigraphic burial-thermal history, paeleostructure of accumulation period, known reservoirs and geochemical index are analyzed. Hydrocarbon accumulation periods, hydrocarbon transport system, trap-forming conditions of the Jurassic-Cretaceous in the hinterland of Junggar Basin are discussed. Thus, the dynamic accumulation process of the distant sourced, secondary-accumulated reservoirs is revealed. Results show that there are two periods of oil and gas charging in the Jurassic and cretaceous reservoirs in the hinterland of Junggar Basin, which are primary reservoirs formed in the early Cretaceous and secondary-filled reservoirs formed in the late paleogene till now. Both the primary reservoirs and sencondary accumulated reservoirs are widely spread in the hinterland area. Faults-sand bodies-unconformities act as three dimensional transporting systems for hydrocarbon migration and accumulation. The formation of primary reservoirs is controlled by paleostructure of accumulation period. During the later dissolution of paleostructure, primary reservoirs are destroyed and oil and gas migrate towards the north. Reservoirs types are decided by trap conditions on the migration pathways. At present, low-amplitude anticline, fault block and litho-stratigraphic reservoirs are the most discovered.

Related Articles | Metrics | Comments0
Differences in Exhaled VOCs from Patients with Upper Respiratory Tract Infection and Healthy Ones
WANG Jue, ZHENG Yunhao, LIU Zhaorong, YAO Maosheng, LI Xiaoguang, ZHUANG Jia, PENG Wangyuan
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (4): 807-814.   DOI: 10.13209/j.0479-8023.2017.191
Abstract1063)   HTML    PDF(pc) (757KB)(166)       Save

Analysis of exhaled VOCs from health and patients may help building association between VOCs and different diseases condition, which could offer a possibility of noninvasive monitoring of disease. VOCs were collected in 30 healthy subjects and 60 patients with upper respiratory tract infection. Analysis of 97 VOCs was
performed by gas chromatography and mass spectrometry (GC-MS). The concentration of alkanes, alkenes, halogenated hydrocarbon, oxygenated hydrocarbons and aromatic hydrocarbons in health and patients breath was analyzed. Analysis of variance (ANOVA), principal component analysis (PCA) were used to analyze the VOC differences from patients and healthy ones. The results show that the concentration of isoprene differ among patients, healthy ones and indoor air (P<0.05). Patients show higher concentration of n-pentane compared to healthy ones (P<0.05). Patients with bacterial upper respiratory tract infection show higher concentration of propanal compared to healthy ones. The results of PCA show that there were significant VOC differences between patients with upper respiratory tract infection and healthy ones (P=0.019), but no differences between bacterial and non-bacterial upper respiratory tract infection.

Related Articles | Metrics | Comments0
Research of Carrying Capacity on Resource and Environment in Core Cities of Central Henan Urban Agglomeration
YU Yang, HAN Peng, YANG Nan, LI Xiaolei, GUO Yunhao
Acta Scientiarum Naturalium Universitatis Pekinensis    2018, 54 (2): 407-414.   DOI: 10.13209/j.0479-8023.2017.160
Abstract893)   HTML1)    PDF(pc) (569KB)(315)       Save

By analyzing the characteristic of urban agglomeration areas, proposing that considering the mobility of resource is essential in researching carrying capacity, the research used core cities of Central Henan urban agglomeration as cases to study, referencing press-state-response model to build the target system of carrying capacity, considering resource supply and consumption & environmental pollution and treatment, using AHP method to evaluate. Reliant exponential is used to evaluate the dependence severity. The result shows that according to the comparison of two results considering resource fluidity or not in Zhengzhou in 2004?2014, only considering resource fluidity can reflect the real condition of an area. Core cities of Central Henan urban agglomeration are short of water and energy resources but are enough to use with the supply of external resources. The orders of the carrying capacity index on resource and environment are Luohe, Xuchang, Xinxiang, Zhengzhou, Jiyuan, Jiaozuo, Luoyang, Pingdingshan and Kaifeng. According to the reliant exponential of external resources, grain resources in these nine cities are self-sufficiency. External energy resources are needed in Kaifeng, Xinxiang, etc. External water resources are needed in Zhengzhou, Kaifeng, etc. More external water resources are needed than external water resources.

Related Articles | Metrics | Comments0
Geometry and Tectonic Evolution of the Laojunmiao Break-Thrust Belt in the Northern Margin of Qilian Mountain
XIAO Yuxiang, DU Wenbo, ZHANG Bo, ZHANG Jinjiang, HOU Xiulin, WANG Wei, HE Xin, LI Xiaojun, YIN Congyuan
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (5): 891-901.   DOI: 10.13209/j.0479-8023.2016.054
Abstract1585)   HTML    PDF(pc) (6159KB)(1469)       Save

On the base of the 3D seismic profile interpretations, combined with the previous findings, geometry and tectonic evolution across and along the Laojunmiao break-thrust belt in the northern margin of the Northern Qilian belt are deciphered. The Laojunmiao belt is a bi-layer thrust system, consisting of a trishear faultpropagation fold system in the upper part, wedge-shaped thrust in the lower part. The Laojunmiao thrust system is linked with the NE-SW striking-slip 134 fault in the western segment, which forms a unified system of fracture on the Laojunmiao belt. Thrusting sheet above the hanging wall of the 134-Laojunmiao fault system is folded under nearly E-S compressive stress field, which results in the N-S striking folding to superpose on the Cenozoic bedding.

Related Articles | Metrics | Comments0
New Word Detection Based on an Improved PMI Algorithm for Enhancing Segmentation System
DU Liping, LI Xiaoge, YU Gen, LIU Chunli, LIU Rui
Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (1): 35-40.   DOI: 10.13209/j.0479-8023.2016.024
Abstract1659)   HTML    PDF(pc) (401KB)(1662)       Save

This paper presents an unsupervised method to identify internet new words from the large scale web corpus, which combines with an improved Point-wise Mutual Information (PMI), PMIk algorithm, and some basic rules. This method can recognize internet new words with length from 2 to n (n is any number as needed). Experimented based on 257 MB Baidu Tieba corpus, the precision of proposed system achieves 97.39% when the parameter value of PMIk algorithm is equal to 10, and the precision increases 28.79%, compared to PMI method. The results show that proposed system is significant and efficient for detecting new word from the large scale web corpus. Compiling the results of new word discovery into user dictionary and then loading the user dictionary into ICTCLAS (Institute of Computing Technology, Chinese Lexical Analysis System), experimented with 10 KB Baidu Tieba corpus, the precision, the recall and F-measure were promoted 7.93%, 3.73% and 5.91% respectively, compared with ICTCLAS. The result show that new word discovery could improve the performance of segmentation for web corpus significantly.

Related Articles | Metrics | Comments0
Calculation of Full Carbon Emission and Evaluation of Carbon Emission Performance
ZHANG Xuehua;LI Xiang;YE Wenhu;ZHANG Baoan
   2015, 51 (4): 639-646.   DOI: 10.13209/j.0479-8023.2015.073
Abstract1535)      PDF(pc) (495KB)(526)       Save
A full carbon emission calculation method is proposed, whose accounts include energy consumption carbon emission, potential carbon consumption of biomass resource consumption, and potential carbon consumption of waste emission. The solar emergy is used as a tool of the same normalized dimension for calculating the amount of full carbon emission. Based on the full carbon emission calculation, population carrying capacity of one unit carbon emission, economic output of one unit carbon emission, and per capita disposable income of one unit carbon emission are considered into one package to construct an index to evaluate the carbon efficiency and development coordination level of a region, and the index is named carbon emission performance integrated index. Taking Beijing and Chongqing as examples, an assessment is made from 2001 to 2011 with the result that the proportion of energy consumption carbon emission in the full carbon emission of the two cities is raised continuously, which indicates that even in the view of full carbon emission, energy consumption is still the main factor affecting carbon emission; however, the effects from modes of both life and production on carbon emission also cannot be neglected. Compared with the traditional carbon efficiency evaluation with only energy carbon emission and carbon production rate considered, the carbon integrated performance evaluation based on “full carbon emission calculation” can fairly and objectively reflect carbon performance of a region, thus it provides a scientific method to identify the responsibility of regional carbon emission reduction.
Reference | Related Articles | Metrics | Comments0
An Online Content Analysis on Honeymoon Destination Choice by Chinese Market
WANG Fei;SONG Meng;XIN Xin;LI Xiaodan;WU Bihu
Acta Scientiarum Naturalium Universitatis Pekinensis    DOI: 10.13209/j.0479-8023.2014.157
Methodology and Case Study of Sea Level Prediction Based on Secular Tide Gauge Data
DUAN Xiaofeng,XU Xuegong,CHEN Manchun,LI Xiang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract729)      PDF(pc) (548KB)(321)       Save
Based on the periodic, trending, and stochasticcharacteristics of secular tide gauge data, a predictive methodology using stochastic-dynamic model was present to the sea level change research. The periodic term was resolved by wavelet and spectrum analysis. Stepwise regression was applied to the trending term analysis. The residual sequence was fitted by autoregression moving average model. Least-squares iteration method was applied for parameter estimation ofthe superposition model, which was composed of significant period model, trending term model and the residual sequenceautoregression moving average model. The stochasticdynamic model is applied to 57 years’monthly mean sea level data from Tanggu tide gauge for case study. The results show that the predictive methodology based on stochastic-dynamic model is feasible and efficient in sea level change prediction. Considering the high accuracy of modeling and predicting, this methodology can be used as a reference for future studies in sea level change.
Related Articles | Metrics | Comments0
Research on Speech Synthesis for Large-Scale Corpora
YU Yansuo,ZHU Fengyun,LI Xiangang,LIU Yi,WU Xihong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract862)      PDF(pc) (419KB)(892)       Save
Aiming at roughly labeled corpora with several hundred hours of speech, a novel approach of constructing text-to-speech system is proposed. This approach realizes automatically cleaning and labeling of large-scale corpora by means of speech recognition, text alignment and syntactic parsing. Furthermore, in order to solve the problems of memory space expansion and time consumption for acoustic model training of large-scale corpora, a fast training method, which can ensure the accuracy of acoustic model, is realized through the optimization of conventional process of model training. Subjective evaluations show that the exploitation of large-scale corpora with rough transcription can achieve significant improvement at 0.5 MOS score in contrast with small-scale corpora with exact transcription.
Related Articles | Metrics | Comments0
A Single Device Clock Loaded Contention Constrained RAM Latch Design
JIA Song,LIU Li,LI Tao,LI Xiayu,WANG Yuan,ZHANG Ganggang
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract794)      PDF(pc) (417KB)(274)       Save
A new structure of RAM type latch is proposed in which parallel charging branches are used to solve the contradiction of the switching current and the charging speed. Compared with the conventional structure, new latch can maintain a relatively high rate of charging and reduce the short-circuit power. Furthermore only one MOS transistor is needed as clock load, saving the power consumption of clocking. HSPICE simulation results show that the proposed RAM n-Latch and p-Latch exhibits 12.8% and 25.5% speed improvement, 19.8% and 26.9% PDP (power-delay product) reduction compared to reported structure.
Related Articles | Metrics | Comments0
Volcanic Debris Flow: A New Type of Lower Cretaceous Reservoir in Hailar-Tamtsag Basin
LI Xiaomin,SHI Yongmin,JIANG Hongfu,WANG Lei,QIN Xiaoshuang,WU Wenjuan,CHAI Zhi
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract599)      PDF(pc) (7884KB)(366)       Save
The lower cretaceous oil-bearing reservoir of Hailar-Tamtsag basin is composed of several NNE trending volcanic rift basin group during the early cretaceous. In the early phase, large-scale volcanic debris flow sediment filled in the lacustrine basin center where the source was prolific, which then caused the formation of endogenous volcanic debris flow oil and gas reservoirs that became a new and major reservoir type in the basin. The petrology experiments suggest that the combination of lithology in this reservoir is different from the usual pyroclastic rock such as “tuffaceous sandstone” and “tuff glutenite”. Its mixed facies are caused by rapid accumulation of volcanic debris flow with specific sedimentary origin and paleogeographic environment, which is also a new type of reservoir sedimentary origin on which there is less domestic and international research. The characteristics of this reservoir includes mélange accumulation of tuff and normal glutenite, complex types of pore space, strong water-sensitivity, low permeability, fast change of facies, strong heterogeneity. Since the reservoir is a special type of reservoir with unstable physics and chemistry, it has strong sensibilities and weak cementation, which likely causes strong water-sensitivity, speed-sensitivity, casing damages and deformations, sand productions, and the development is difficult. The investigation of the genetic mechanism of volcanic debris flow reservoir will provide the theoretical basis for optimizing the development method, making rational policy and exploiting economically and effectively.
Related Articles | Metrics | Comments0
A Dynamic Density-Based Clustering Algorithm Appropriate to Large-Scale Text Processing
LI Xia,JIANG Shengyi,ZHANG Qiansheng,ZHU Jing
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract688)      PDF(pc) (524KB)(272)       Save
Because of the high time complexity and complicated parameter setting in traditional density-based clustering algorithm, a new density definition is proposed, which just needs one parameter and can find clusters with different densities. The authors also expand the algorithm to a two-stage dynamic density-based clustering algorithm, which can process large-scale text corpus data. Experiments on synthetic dataset, large-scale dataset from UCI, English text corpus and Chinese text corpus show that TSDDBCA algorithm has the characteristic of easy parameter setting and high clustering efficiency, and can be applied to clustering process to large-scale text data.
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   
Abstract664)      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
Analysis of Predominant Factors of Volcanic Reservoirs in Carboniferous of Junggar Basin
QIN Xiaoshuang,SHI Yongmin,WU Wenjuan,KOU Yu,WANG Lei,LI Xiaomin,CHAI Zhi
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract702)      PDF(pc) (6688KB)(355)       Save
According to the core observation and statistics of physical properties, it is found that weathering, tectonism, lithology and litho-facies are the predominant factors of volcanic reservoirs in Carboniferous of Junggar Basin. The reservoir space includes primary fractures, primary porosity, secondary porosity and secondary fractures. The permeability is mostly controlled by fractures. Weathering crust is the main reservoir of volcanic rock in Carboniferous. High quality reservoirs are mainly located 250 m from the top of weathering crust. Among all the high quality reservoirs, the paleohigh around the depression is the better position. As the distance from the top of weathering crust increases, the filling degree of fractures as well as porosity becomes higher and this degrades the reservoir quality.
Related Articles | Metrics | Comments0
Life Cycle Greenhouse Gas Emission Assessment of Fuel Ethanol Based on EIO-LCA
LI Xiaohuan,JI Junping,MA Xiaoming,WANG Jingtian
  
Pressure Sensitivity and Its Genetic Mechanism of Igneous Rock Formations in Changshen Gas Field
WANG Lei,SHI Yongmin,SONG Qiuguo,CHAI Zhi,QIN Xiaoshuang,LI Xiaomin,WU Wenjuan
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract551)      PDF(pc) (1330KB)(397)       Save
The core samples of igneous rock formations with low permeability and low porosity in Jilin Changshen well block are tested for their pressure sensitivity. The result shows that permeability recovery rate of these samples is not more than 11%, which indicates high pressure sensitivity of the formations. By observing core samples and comparing the result of pressure sensitivity tests with those from igneous rock core samples of other regions, it shows that the pressure sensitivity of igneous rock formations is relevant to lithology, structure, construction, development and type of porosity and fracture. Different from the unitary diagenesis of sandstone, the complex diagenesis of igneous rock leads to different pressure sensitivity in different areas. Therefore the pressure sensitivity of different igneous rock formations should be treated differently. Meanwhile, pressure sensitivity of a certain well may not be the same in different igneous layers.
Related Articles | Metrics | Comments0
Multi-Scale Fluctuation of European Temperature Revealed by EEMD Analysis
WANG Bing,LI Xiaodong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract806)            Save
Ensemble empirical mode decomposition (EEMD), a newly developed nonlinear data analysis method, is employed to derive climate change signals, such as annual cycle, low-frequency components and trends, etc. The data sets for the analysis are the well-homegenized, longer than 150 years, daily temperature series of five stations in Europe. The decomposed results indicate that there are three main time scales, e.g. interannual, interdecadal and century scales, for the low-frequency variations of all five stations. The intensities of the annual cycle were weak during the two warm periods: 1910?1940 and the last 30 years since 1970. And the weak trend was more obvious in the last 30 years. In addition, summers become more longer and winters shorter since the late of 1970s compared with that of warm period in 1910?1940.
Related Articles | Metrics | Comments0
SIMS Zircon U-Pb Age of a Rhyolite Layer from the Halahatang Area, Northern Tarim, NW China: Constraint on the Eruption Age of Major Pulse of Tarim Flood Basalt
SHANGGUAN Shimai,TIAN Wei,LI Xianhua,GUAN Ping,PAN Mao,CHEN Mimi,PAN Wenqing
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract842)            Save
Seismological interpretation revealed that basalts are overlain by rhyolite in the Halahatang area, Northern Tarim, Northwest China. The overlying rhyolite is dated by SIMS zircon U-Pb method, yielding a precise concordia age of 287.3 ±2.0 Ma, which limits the latest eruption age of the underlying basalt and reveals that the eruption age of the main pulse of the Tarim flood basalt is before 287 Ma, not ~275 Ma.
Related Articles | Metrics | Comments0
Application of Network Generalized Extreme Value Model to Estimate Residential Location and Commute Mode Choice
LI Xia,SHAO Chunfu,QU Tianshu,YANG Liya,WANG Jiangfeng
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract717)            Save
Relationship between jobs-housing spatial distribution and travel to work were studied from a microscopic perspective. Based on random utility maximization theory, factors depicting the individual and socio-economic characteristics and attribute of travel and land use are defined as exogenous variables, meanwhile, the model choice sets are the combination of residential location choice and commute mode choice subsets. Discrete choice model specified as Network Generalised Extreme Value(NetworkGEV) is employed to investigate the joint decisions of where to live and how to get to workplace which attempts to describe the change of aggravated traffic congestion and discover the potential change caused by residential relocation and travel mode shift under different employment location patterns. This model is estimated in Biogeme, and the direct and cross elasticities are calculated to analyze the change of alternatives probability brought by factors variation. The results reveal that the model yields plausible estimation of exogenous variables in the joint residential location and travel mode choice context. Compared with suburban commuters, commuters in CBD are more sensitive to the increase of travel time and intend to change travel mode and residential location thus trading off the disutility of traffic congestion.
Related Articles | Metrics | Comments0
Research on the Property of Aluminum-Metallic Glass-Aluminum Sandwich Panel against Shaped Charge Jet Penetration
LIU Weidong,FENG Rongxin,LIU Kaixin,YAN Honghao,LI Xiaojie
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract875)            Save
An aluminum-metallic glass-aluminum sandwich panel was fabricated by explosive welding technique and its property against shaped charge jet penetration was studied experimentally and numerically. Considering the small dimension of the sandwich panel, an experimental scheme was presented for penetration experiment on small specimen (character dimension less than 50 mm); a numerical calculation scheme for simulating the experimental process was developed based on ANSYS/ LS-DYNA. The experimental results indicate that the shaped charge could produce jet with small diameter and good stabilization; wide region petalling is found on the upper surface of the aluminum-metallic glass-aluminum sandwich panel; metallic glass near the jet receives crushing damage, which obstructs the jet penetration; the numerical calculation scheme could simulate the process of penetration effectively; the depth of the penetration, the diameter of the penetration channel and the failure mode obtained by numerical simulation accord with the corresponding experimental results.
Related Articles | Metrics | Comments0
Correction of Atmospheric Effects on Repeat-Pass Interferometric SAR Using MERIS and ASAR Synchronous Data
LI Xiaofan,LI Ying,ZENG Qi ming,ZHAO Yonghong
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract628)            Save
The purpose is to discuss how to correct the atmospheric effects on repeat-pass InSAR. A specific way integrated with MERIS and ASAR was put forward with its elaborate characters andtheory. Taking a differential inter ferogram with test site located in Yangtze River side as a sample, this specific correcting model was applied and tested. Results show that the RMS of deformation in the range direction is obviously decreased and the precision of measurement is enhanced greatly.
Related Articles | Metrics | Comments0
RiTLB: iTLB Design Based on Memory Region Reusing
XIE Jinsong,TONG Dong,LI Xianfeng,PANGJiufeng,WANG Keyi,CHENG Xu
Acta Scientiarum Naturalium Universitatis Pekinensis   
Abstract781)            Save
In order to design iTLB by memory region reusing, its comparison bits of lookup are reduced through the memory region encoding technology firstly, which encodes the higher-order bits of VPN with a very shorter memory region ID before the VPNis sent to iTLB. Secondly, the memory region IDis reused before the next memory region is switched into. Compared to the baseline iTLB, experimental results show the average dynamic power, delay and area of the new design decrease by 62.84%, 9.96% and 44.78% respectively, with only 0.23% average IPC reduction.
Related Articles | Metrics | Comments0