Most Download articles

    Published in last 1 year | In last 2 years| In last 3 years| All| Most Downloaded in Recent Month | Most Downloaded in Recent Year|

    All
    Please wait a minute...
    For Selected: Toggle Thumbnails
    Research on Construction Land Evaluation Based on Land Ecological Sensitivity Analysis
    ZHANG Shiyi;FENG Changchun;LIU Xueping;WANG Fuliang;XIE Danxing
       2015, 51 (4): 631-638.   DOI: 10.13209/j.0479-8023.2015.071
    Abstract1527)      PDF(pc) (1029KB)(3104)       Save
    The methods of land ecological sensitivity analysis were discussed, based on the concept of “protection goes first” to the construction land pattern. With a combination of comprehensive index method, fuzzy evaluation method and RS/GIS approach, an integrated method of construction land suitability assessment was proposed. It offers three factors that mainly influence the construction land-use environment including land ecological sensitivity, natural condition and social economy environment, and it introduces the fuzzy membership functions to improve the model algorithm. The evaluation results would hierarchically display different land ecological sensitivity endowment and land-use environment, which leads to analyze the construction land spatial distribution in a land ecological security pattern. Taking Xiangjiang New District of Changsha City as a case, 14 indexes were chosen in accordance with the local conditions, to assess construction land suitability of this area. The results objectively show the region’s land ecological environment and land-use condition, and give an ecological security spatial arrangement of the construction land pattern, which can provide guidance to land-use planning of the “resource-economical and environment-friendly” society.
    Reference | Related Articles | Metrics | Comments0
    Logic Based Formal Verification Methods: Progress and Applications
    CHEN Gang, YU Linyu, QIU Zongyan, WANG Ying
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (2): 363-373.   DOI: 10.13209/j.0479-8023.2015.131
    Abstract1832)   HTML    PDF(pc) (538KB)(2412)       Save

    In recent years, formal methods have undergone a fast development. The authors give a brief review on the formal methods used in software and hardware verification. The main thread of the analysis consists of descriptions of logical systems and their related verification techniques and tools. The purpose is to help engineers to select formal tools and apply them to their work. This paper starts with a review of automated proving techniques based on propositional logic and temporal logic, including SAT, BDD, model checking, and SMT. For first order logic based theorem provers, the authors discuss ACL2, VDM method and B method. Among proof assistants which are based on higher order logics, the authors pick HOL, PVS and COQ. Advancements in commercial formal verification tools are discussed.

    Related Articles | Metrics | Comments0
    Review of PM2.5 Source Apportionment Methods in China
    ZHENG Mei,ZHANG Yanjun,YAN Caiqing,ZHU Xianlei,James J. Schauer,ZHANG Yuanhang
    Acta Scientiarum Naturalium Universitatis Pekinensis   
    Abstract1224)      PDF(pc) (545KB)(2241)       Save
    For the first time, PM2.5 source apportionment methods and techniques previously and currently applied in China are summarized, including sampling preparation, sampler selection, chemical speciation analysis, and source apportionment tools. The research direction for PM2.5 source apportionment work in China is also suggested. This review is expected to provide a fundamental understanding of PM2.5 source apportionment methods and to serve as an important reference for future source apportionment studies to be widely conducted in China and regulations or law for PM2.5 abatement in China.
    Related Articles | Metrics | Comments0
    Detection of Fast-Flux Domains Based on Passive DNS Analysis
    ZHOU Changling, CHEN Kai, GONG Xuxiao, CHEN Ping, MA Hao
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (3): 396-402.   DOI: 10.13209/j.0479-8023.2016.064
    Abstract1472)   HTML    PDF(pc) (625KB)(2130)       Save

    The authors use Passive DNS to log domain name query history of real campus network environment, and construct eighteen feature sets grouping by diversity, time, growth, and relevance, and then propose a model detect Fast-Flux Domains using random forest algorithm. The result shows that the proposed model can classify domains with accuracy over 90% by cross validation experiments. The model can detect Fast-Flux domains in the datasets used in this study more effectively compared with Fluxbuster.

    Related Articles | Metrics | Comments0
    Research on the Visualization Method of Social Crowd Emotion Based on Microblog Text Data Analysis
    LIU Cuijuan, LIU Zhen, CHAI Yanjie, FANG Hao, LIU Liangping
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (1): 178-186.   DOI: 10.13209/j.0479-8023.2016.021
    Abstract1215)   HTML    PDF(pc) (1441KB)(2126)       Save

    Existing sentiment analysis focus on the emotional tendency, which are lack of detailed description of all kinds of emotions, they can’t intuitively reflect the emotional change of social groups. An emotional analysis method based on the combination of dependency parsing and artificial tagging was proposed. Facial expression animation to present emotions analysis was realized. The microblog crowd’s emotion in different areas for different social events was visualized. The experimental results show that the model could closely and effectively simulate the crowd emotion, and it could provide a new way of the analysis of network public opinion based on large data.

    Related Articles | Metrics | Comments0
    The Fundamental Equations in Analytical Mechanics for Nonholonomic Systems
    LIU Caishan
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (4): 756-766.   DOI: 10.13209/j.0479-8023.2016.082
    Abstract1363)   HTML    PDF(pc) (454KB)(1989)       Save

    Analytical mechanics is established based on d’Almbert-Lagrange Principle, Gauss principle, Jourdian principle and Hamilton principle, to deal with the dynamics of mechanical systems subject to holonomic or nonholonomic constraints. The governing equation of the systems are derived either by introducing Lagrange’s multipliers to adjoin with the limitation equations for the virtual displacements, or by directly eliminating the constraint equations to achieve minimal formulations. The author presents a survey for the history of analytical mechanics, and explains some basic concepts, such as virtual displacement, ideal constraint, and the correlations between the Lagrange multipliers and the real constraint forces.

    Related Articles | Metrics | Comments0
    Collinear Equation Linearized Matrix Model
    XU Zhenliang, LI Yanhuan, YAN Li, YAN Lei
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (3): 403-408.   DOI: 10.13209/j.0479-8023.2016.056
    Abstract1606)   HTML    PDF(pc) (258KB)(1879)       Save

    Using the matrix expression form of computer vision projection equation, the collinear equation is constructed into matrix equation. With the projection matrix element as a composite function, this paper realizes the unification derivation of each variable of the collinear equation based on the matrix analysis method. Compared with the traditional analytical method of linearization, the form of matrix analysis process is quite succinct and easy to understand, which can be used to the numerical solution of linear library application. For the various construction form of the rotation matrix, this method has better adaptability. The constructed matrix of collinear equation has important enlightenment significance for using computer vision method.

    Related Articles | Metrics | Comments0
    Urban Expansion Extraction Using Landsat Series Data and DMSP/OLS Nighttime Light Data: A Case Study of Tianjin Area
    CHAI Baohui, LI Peijun, ZHANG Ruijie, ZHAO Peng
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (3): 475-485.   DOI: 10.13209/j.0479-8023.2015.138
    Abstract1541)   HTML    PDF(pc) (3037KB)(1878)       Save

    By taking Tianjin urban area as an example, a method is proposed to extract urban expansion by combining multi-temporal Landsat TM/ETM+ images and DMSP/OLS nighttime light data, and validated and analyzed. First, the candidate built-up area extent were obtained from DMSP/OLS data. Multitemporal Landsat TM/ETM+ images and derived multivariate textures of the obtained urban extent were classified to extract built-up areas for different dates. Urban expansions for different time intervals were obtained by post-classification comparison method. In addition, the thresholding method was applied to multitemporal DMSP/OLS nighttime light data to extract urban extents for different years and urban expansions of different time intervals were produced. The urban expansion results from DMSP/OLS data and urban statistical data were used to verify the Landsat TM/ETM+ results. The results demonstrate that the combination of Landsat data and DMSP/OLS data effectively reduce the spectral confusion between bare land and urban area and thus produce higher accuracy than useing spectral data from Landsat TM/TM+ images alone in extraction of urban built-up area expansion. Combination of Landsat TM/ETM+ data and DMSP/OLS nighttime light data provides an effective method for urban expansion extraction in mega-city areas.

    Related Articles | Metrics | Comments0
    Entity Recognition Research in Online Medical Texts
    SU Ya, LIU Jie, HUANG Yalou
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (1): 1-9.   DOI: 10.13209/j.0479-8023.2016.020
    Abstract1503)   HTML    PDF(pc) (1120KB)(1851)       Save

    The authors design recognition features with the consideration of medical field characteristic for the online medical text, and the experiment of the entity recognition is carried out on the self-built data set. Concerned about five common diseases: gastritis, lung cancer, asthma, hypertension and diabetes. In the experiment, an advanced machine learning model Conditional Random Field is used for training and testing. The target entities include five kinds: disease, symptoms, drugs, treatment methods and check. The effectiveness of the proposed features is verified by using the experimental method, and the accuracy of the total 81.26% is obtained and the recall rate is 60.18%. Subsequently, the further analysis is given for the recognition features.

    Related Articles | Metrics | Comments0
    Terrace Sequences and Their Formation Ages in Pantang-Heiyukou Area, Northern Shanxi-Shaanxi Gorge, China
    LIU Yunming, LI Youli, ZHOU Baohua
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (2): 257-264.   DOI: 10.13209/j.0479-8023.2015.139
    Abstract1423)   HTML    PDF(pc) (797KB)(1657)       Save

    Based on field work, four Quaternary terraces are found according to overlapped loess sequences at Pantang-Heiyukou area and its surroundings in northern Chinese Shanxi-Shaanxi Gorge. These four terraces, which are 12, 50, 80 and 130 m above present the Yellow River level respectively, are all rock-seated terraces. The thicknesses of overlapped loess from the lowest terrace to the highest Quaternary terrace are about 20, 33, 37 and 43 m respectively. ESR dating samples were collected from river sediments on T2, T3 and T4. ESR dating result reveals that the formation ages of these three terraces are 0.609, 0.876 and 0.97±0.107 Ma in turn from T2 to T4. In order to corroborate the dating results, powder samples and oriented samples were collected from sections on T3 and T4. Paleomagnetic result shows that section bottom on T3 does not reach the boundary of B/M (Brunhes/Matuyama), which means a formation age younger than 0.78 Ma. This age is younger than that gotten from ESR dating. The bottom age of T4 section reaches an age of 1.07 Ma, which is a bit older than ESR dating result but within its range. The formation ages of the terraces are in accord with other terraces in upper and lower reach of the Yellow River such as Lanzhou and Sanmenxia which suggests river terraces controlled by tectonic movement exist universally in the domain of the Yellow River. A Late Tertiary section was resampled and measured as an improvement to former works. The result is used to discuss the incision rate of different terraces in this region.

    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
    Abstract1645)   HTML    PDF(pc) (401KB)(1653)       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
    Constructing Chinese Remote Associates Test (RAT) with Application of Item Response Theory
    XIAO Wei, YAO Xiang, QIU Yongtao
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (2): 354-362.   DOI: 10.13209/j.0479-8023.2015.123
    Abstract1645)   HTML    PDF(pc) (426KB)(1631)       Save

    The aim of the current study is to construct the Remote Associates Test (RAT) in Chinese version, which is based on the theory of associative creativity. Item response theory (IRT) with Binary Logistic Models was used for item selection. Participants were 2659 middle-school students from Guangdong, Gansu, and Hubei Province. Based on the principle of Criterion-Referenced Test, the item difficulty was limited between ?3.00 and 3.00, the item discrimination was limited between 0.30 and 2.50, and the item information was above 0.20. In addition, the RAT scores were positively correlated with scores on the Torrance Test of Creativity, Runco Test, and Raven’s Standard Progressive Matrices. Results of RAT were also positively correlated with teachers’ evaluations of creativity and could significantly predict middle-school academic performance. Potential applications of RAT are also discussed.

    Related Articles | Metrics | Comments0
    Economic and Environmental Effects of Improved Auto Fuel Economy Standard in China: A CGE Analysis
    LIU Qing, LIU Yu, XU Jintao
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (3): 515-527.   DOI: 10.13209/j.0479-8023.2016.032
    Abstract1223)   HTML    PDF(pc) (821KB)(1569)       Save

    The authors use CHINAGEM, a computable general equilibrium model to investigate the economic effect and pollution reduction impacts of improved auto fuel economy standard in China. The policy change is modelled as shocks to production tax rate of two industries — petrol refine and motor vehicle parts. The results show that the shocks lead to higher labor cost, slightly decreased GDP and improved terms of trade. The majority of industries, such as motor vehicle manufacturing, will undergo downsizing because of new standards and substitution of imported motor vehicles for domestic ones. However, with improved emission standard and slowdown of vehicle production growth, air pollution problem will be alleviated. Based on the model prediction, the annual emission reductions of carbon monoxide, hydrocarbons, nitrogen oxides and total particulate matter amount to 39.52, 37.51, 11.63 and 1.66 million tons respectively, which are 32, 36, 63, and 87 percentage reduction from the respective business-as-usual levels.

    Related Articles | Metrics | Comments0
    Analysis of Carbon Emissions and the Influence Factors in the Process of Urbanization among Chinese Provinces
    ZHAO Donglin, LI Tianhong
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (5): 947-958.   DOI: 10.13209/j.0479-8023.2016.060
    Abstract1371)   HTML    PDF(pc) (2569KB)(1536)       Save

    The article analyzes carbon emissions from industrial and living departments from 1995 to 2012, and urbanization rate is measured by three indicators, namely ratio of build-up area, ratio of non-agriculture population, and ratio of urban population. The results show that 1) the total amount of carbon emissions as well as the per capita carbon emissions is rising in 1995–2012, accordingly carbon emissions per unit of output present a decreasing trend. 2) In process of urbanization, Beijing, Shanghai and Tianjin have relatively lower carbon emissions and higher urbanization rates in urbanization stages. 3) The carbon emission of unit urbanization rate measured by three indicators show that most provinces present reduction trend till 2000 and then increase. Inner magnolia ranks the top in the carbon emission per urbanization rate 1. Hebei, Henan and Shandong rank the top in carbon emission per urbanization rate 2 and 3. 4) In the view of provinces, energy structure has limited impacts on carbon emissions, energy intensity has negative effect, and industrial structure has both positive and negative effect while economic level and population size have positive effect for all provinces. The results can provide scientific reference for the regional carbon emission reduction strategy.

    Related Articles | Metrics | Comments0
    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   
    Abstract741)      PDF(pc) (5988KB)(1536)       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.
    Related Articles | Metrics | Comments0
    A Camshift Motion Tracking Algorithm Based on Kalman Filter
    ZHAI Weixin;CHENG Chengqi
    Acta Scientiarum Naturalium Universitatis Pekinensis    2015, 51 (5): 799-804.  
    Abstract719)      PDF(pc) (3288KB)(1510)       Save
    Related Articles | Metrics | Comments0
    Impact of the Uncertainty of the Remotely Sensed AOD and Ångström Exponent on the Calculation of Ultraviolet Index
    RAO Junfeng, ZHANG Xianfeng, PAN Yifan
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (2): 210-218.   DOI: 10.13209/j.0479-8023.2015.114
    Abstract1375)   HTML    PDF(pc) (1538KB)(1455)       Save

    The research is to assess the uncertainty of aerosol optical depth (AOD) and Ångström exponent products retrieved from the Multi-angle Imaging SpectroRadiometer (MISR) data by means of comparing them with ground measured data in Hong Kong in the period of 2005 to 2013. Further analysis of how these uncertainties are spread into the calculation of UV Index (UVI) is conducted based on a radiative transfer model. The results indicate that the maximum values of UVI uncertainty caused by MISR/AOD uncertainty are 0.55 and 0.36 in summer and winter, respectively. The maximum of UVI uncertainty caused by Ångström exponent uncertainty are 0.13 and 0.11 in summer and winter, respectively. Compared with the UVI exposure grades put forward by the World Health Organization, the uncertainty of both AOD and Ångström exponent can cause at most one grade deviation in the worst situation. In this sense, MISR/AOD and Ångström exponent products are reliable as input in the calculation of UVI.

    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
    Abstract1569)   HTML    PDF(pc) (6159KB)(1444)       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
    Study on Globe Spatial Grid Reference System Construction
    CHENG Chengqi, WU Feilong, WANG Rong, QIN Yonggang, TONG Xiaochong, CHEN Bo
    Acta Scientiarum Naturalium Universitatis Pekinensis    2016, 52 (6): 1041-1049.   DOI: 10.13209/j.0479-8023.2016.051
    Abstract2392)   HTML    PDF(pc) (1724KB)(1427)       Save

    To supplement the deficiency of the latitude and longitude existed as location code, such as complex description, non-regional characteristics and complex computation, a globe spatial grid reference system is constructed based on GeoSOT from Peking University. The grid system, built from a perfect quadtree with one degree, one minute and one second grid, could be fit for air-earth joint action. It designs a simple and practical location coding method, which also supports distance simple calculation. It could realize multi-source spatial data integrated retrieval, and develop methods of efficient code operation, framework of spatial computing, and 3D-earth grid system. Globe Spatial Grid Reference System will definitely play an important role in the future of big spatial data applications.

    Related Articles | Metrics | Comments0
    Identification of Topic Sentence about Key Event in Chinese News
    WANG Wei,ZHAO Dongyan,ZHAO Wei
    Acta Scientiarum Naturalium Universitatis Pekinensis   
    Abstract991)      PDF(pc) (571KB)(1427)       Save
    The authors propose an approach to extract topic sentences that describe key event from a news article. Considering the special structure of news articles, the relations between news articles and key events reported in them is studied, as well as the characteristics of a news headline in three aspects: information, form and language. A novel method based on the information aspect of a headline is used to extract a topic sentence which contains the key event information from a news story. The method first classifies a news headline as informative or non-informative, and then considers text and semantic features of a sentence, such as word frequency, sentence length, location in the text and word co-concurrency with the headline, to evaluate the importance for each sentence and select the most important one as the topic sentence. Experiment results show that this method can identify a topic sentence accurately and the proposed approach makes a good preparation for event information extraction.
    Related Articles | Metrics | Comments0