检索结果-南通市图书馆

Debris Flow Hazard Assessment Based on Support Vector Machine

在线全文

学校读者我要写书评

暂无评论

Wuhan University Journal of Natural sciences 2006年第4期11卷 897-900页

作者： YUAN Lifeng 1, 2., ZHANG Youshui 3 1. Institute of Mountain Hazards and Environment, chinese academy of {2., Chengdu 610041, Sichuan, China 2. graduate University of chinese academy of {2., beijing 100049, China 3. Institute of Geographical {2. and Natural Resources Research, chinese academy of {2., beijing 100101, China Institute of Mountain Hazards and Environment Chinese Academy of Sciences Chengdu 610041 Sichuan China ***

Seven factors, including the maximum volume of once flow , occurrence frequency of debris flow , watershed area , main channel length , watershed relative height difference , valley incision density and the length ratio of sediment supplement are chosen as evaluation factors of debris flow hazard degree. Using support vector machine （SVM） theory, we selected 2.9 basic data of 37 debris flow channels in Yunnan Province as learning samples in this study. We create a debris flow hazard assessment model based on SVM. The model was validated though instance applications and showed encouraging results.

关键词： debris flow hazard assessment support vector machine (SVM)

Formal analysis and design of multi-party fair exchange protocols

在线全文

学校读者我要写书评

暂无评论

Science in China(Series F) 2006年第2期49卷 155-174页

作者： QING Sihan1,2.3 & LI Gaicheng1,3 1. Engineering Research Center for Information Security Technology, Institute of Software, chinese academy of {2., beijing 100080, China 2. beijing Zhongke Ansheng Corporation of Information Technology, beijing 100080, China 3. graduate school of the chinese academy of {2., beijing 100039, China Engineering Research Center for Information Security Technology Institute of Software Chinese Academy of Sciences beijing Zhongke Ansheng Corporation of Information Technology graduate school of the {2. academy of sciences

Based on the origin of message items and channel combination between transacting parties, and events and relations among events, this paper presents a concise, precise, and hierarchical model for general fair exchange protocols, formally specifies various security requirements which are able to reflect inherent requirements for fair exchange protocols more rigorously, and partition these security requirements with fine granularity. This work helps analyze, debug, and design multi-party fair exchange protocols more effectively and elaborately,

关键词： fair exchange logical protocol formal model security requirement.

Identification of novel SINEs from Cyprinidae and their evolutionary significance

在线全文

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2007年第3期17卷 270-279页

作者： HAN Yawei, HE Slumping and CHEN Yiyu ( Institute of Hydrobiology, chinese academy of {2., Wuhan 430072. China. graduate school, chinese academy of {2., beijing 100039, China) Institute of Hydrobiology Chinese Academy of Sciences Wuhan 430072 China

Short interspersed nuclear elements (SINEs) are widespread among eukaryotic genomes. They are repetitive DNA sequences that have been amplified by retrotransposition. In this study, a class of SINEs were isolated from the Opsariichthys bidens genome, and named Opsar. Sequence analysis confirmed that Opsar is a new class of typical SINEs derived from tRNA molecules. With the tRNA-derived region of Opsar and through BLASTN search, we further identified Zb-SINEs from the zebrafish genome, which includes two groups: Zb-SINE-A and Zb-SINE-B. The Zb-SINE-A. group comprises subfamilies of -Al--A5, and the Zb-SINE-B group is a dimer of the tRNA -derived region and shares a similar dimeric composition to Alu. Zb-SINEs are composed of three distinct regions: a 5’ end tRNA-derived region, a tRNA-unrelated region and a 3’ end AT-rich region. The flanking regions are AT rich. The average length of Zb-SINEs elements is about 340 bp. Zb-SINEs account for as much as 0.1 % of the whole zebrafish genome. About 70% of the Zb-SINEs are on chromosomes 11, 18, and 19. These Zb-SINEs were characterized by PCR and dot hybridization. The distribution pattern of Zb-SINEs in genome strongly supports the master genes model. The tRNA-derived regions of Opsar and Zb-SINEs were compared with the tRNAAla gene, and they showed 76% similarity, indicating that Opsar and Zb-SINEs originated from an inactive tRNA sequence or a tRNA -like sequence. In view of the evolutionary status of zebrafish in the Cyprinidae, we deduced that Zb-SINEs were a very old class of interspersed sequences.

关键词： short interspersed nuclear elements (SINEs) master gene model Opsar Zb-SINEs and Cyprinidae.

Spatial heterogeneity of the driving forces of cropland change in China

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Science China Earth sciences 2005年第12期48卷 2231-2240页

作者： LIU Xuhua1,2. WANG Jinfeng1, LIU Mingliang4,1 & MENG Bin1,2.3 1. Institute of Geographic sciences and Natural Resources Research, chinese {2. of sciences, beijing 100101, China 2. graduate school of the chinese academy of sciences, beijing 100039, China 3. College of Arts and sciences of beijing Union University, beijing 100083, China 4. school of Forestry and Wildlife sciences, Auburn University, Auburn, Alabama, AL36849, USA Institute of Geographic sciences and Natural Resources Research Chinese Academy of Sciences Beijing China graduate school of the {2. academy of sciences Beijing China school of Forestry and Wildlife sciences Auburn University Auburn Alabama USA College of Arts and sciences of beijing Union University Beijing China

By using digital satellite remote sensing data acquired in 1987―1989 and 1999―2.00 and GIS combined with the natural and socio-economic data, this paper drew an integrated zonation of the cropland change and its driving forces in China. The results indicated that the cropland change in the study period was constrained by geographical factors and driven by cli-mate change as well as socio-economic system. Moreover, the regional differences of the drivers for cropland change were significant. In the midwest of China, natural condition changes and geographical background were the main constraints and drivers, while in Eastern China, social and economic changes and economic policies were the main driving forces. The cropland loss was nationwide. The dominant factors to cause this decrease included buildup of developing area to attract foreign capital and technologies, changes of industry structure due to urban in-fluence, the change of employment notions thanks to living standard improvement, rapid ur-banization due to the expansion of cities and towns, the diminished farming net income partly because of the global warming effects, and the rapid economic growth stimulated by the con-venient transportation system. These factors interact and interdepend with each other to cause the cropland loss in China recently. The reasons for the increase of cropland were primarily the cultivation and deforestation by the farmers who want to increase income. This study on the mechnism of LUCC relied on the cropland change integrated classification considering the natural or human factors both inside and outside the region, which provides a new approach to study the integrated regionalization and LUCC mechanism.

关键词： land use change, driving force, integrated classification, spatial statistics, cropland, China.

A Facile Synthetic Method for (3Z,6Z,9S,10R)-9,10-Epoxy-3,6-heneicosadiene,Sex Pheromone Component of Hyphantria Cunea (Drug)

在线全文

学校读者我要写书评

暂无评论

chinese Chemical Letters 2005年第4期16卷 468-470页

作者： Chao CHE, Zhong Ning ZHANG StateKey Laboratory IntegratedManagementofInsectsandRodents,Institute of Zoology, chinese academy of {2., beijing 100080 graduate school of the chinese academy of {2., beijing 100039 StateKey Laboratory ofIntegratedManagementofInsectsandRodents Institute of ZoologyChinese Academy of Sciences graduate school of the {2. academy of sciences

Total synthesis of (3Z, 6Z, 9S, 10R)-9, 10-epoxy-3, 6-heneicosadiene, sex pheromone component of Hyphantria cunea (Drug), was achieved using Sharpless AE kinetic resolution and alkylative epoxide rearrangement as ke... 详细信息

关键词： Sex pheromone Hyphantria cunea (Drug) Sharpless kinetic resolution asymmeric synthesis.

Effect of rock mass structure and block size on the slope stability——Physical modeling and discrete element simulation

在线全文

学校读者我要写书评

暂无评论

Science China(Technological sciences) 2005年第z1期48卷 1-17页

作者： LI Shihai1, LIAN Zhenzhong1,2.& J. G. Wang3 1. Institute of Mechanics, chinese academy of {2., beijing 100080, China 2. graduate school, chinese academy of {2., beijing 100060, China 3. Tropical Marine Science Institute, National University of Singapore, Singapore 1192.0 Institute of Mechanics Chinese Academy of Sciences Beijing 100080 China graduate school Chinese Academy of Sciences Beijing 100060 China Tropical Marine Science Institute National University of Singapore Singapore 119260 Singapore

This paper studies the stability of jointed rock slopes by using our improved three-dimensional discrete element methods (DEM) and physical modeling. Results show that the DEM can simulate all failure modes of rock slopes with different joint configurations. The stress in each rock block is not homogeneous and blocks rotate in failure development. Failure modes depend on the configuration of joints. Toppling failure is observed for the slope with straight joints and sliding failure is observed for the slope with staged joints. The DEM results are also compared with those of limit equilibrium method (LEM). Without considering the joints in rock masses, the LEM predicts much higher factor of safety than physical modeling and DEM. The failure mode and factor of safety predicted by the DEM are in good agreement with laboratory tests for any jointed rock slope.

关键词： rock masses, slope stability, DEM simulation, block size effect, joints configuration effect, limit equilibrium method.

Properties and applications of cold supersonic gas jet

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2006年第6期49卷 709-715页

作者： ZHANG Shaofeng1,2.MA Xinwen1,2.LIU Huiping2.LI Bin1,2.& ZHU Xiaolong1,2.1. Institute of Modern Physics,chinese academy of {2.,Lanzhou 730000,China 2. graduate University of chinese academy of {2.,beijing 100049,China Institute of Modern Physics Chinese Academy of Sciences Lanzhou China graduate University of chinese {2. of sciences Beijing China

By analyzing the formation mechanism of a supersonic gas jet,a set of equations which describe the atomic beam properties were established. The influence of initial temperature,initial pressure,background gas pressure and pumping speed was discussed in detail. A simulation program was developed based on the equations,and the results under different initial conditions were obtained. The results are in good agreement with the experimental data,and suggest that,in order to get much smaller transverse momentum in collision experiments,it is necessary to lower the initial temperature and the initial pressure of the supersonic gas jet,together with increasing the pumping speed. These results are very instructive for construction of a new generation of cold supersonic gas jets.

关键词： cold supersonic gas jet,zone of silence,nozzle,skimmer.

Sequence analysis of mRNA polyadenylation signals of rice genes

在线全文

学校读者我要写书评

暂无评论

chinese Science Bulletin 2006年第9期51卷 1069-1077页

作者： LU Ying1, 2. GAO Chenxi1,2.3 & HAN Bin1,3,41. National Center for Gene Research, Shanghai Institutes for Biological sciences, chinese {2. of sciences, Shanghai 2.02.3, China 2. graduate school of the chinese academy of sciences, beijing 100039, China 3. Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological sciences, chinese {2. of sciences, Shanghai 2.0032. China National Center for Gene Research Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai 200233 China graduate school of the {2. academy of sciences Beijing 100039 China Institute of Plant Physiology and Ecology Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai 200032 China

The formation of eukaryotic mRNAs involves the cleavage and polyadenylation of pre- mRNAs. To investigate the sequence requirement of putative polyadenylation signals (PASs), poly(A) sites and downstream elements (DUEs) in 3′-end-pro- cessing in rice, we compared expressed sequences tags (ESTs) with poly(A) extremity to full-length cDNA sequences and constructed a database of 12.69 pre- mRNA sequences in ?40―+40 nt surrounding the poly(A) sites, which were from 9953 genes. The al- ternative poly(A) sites were revealed in approxi- mately 2.% of mRNAs. Nearly 80% of pre-mRNAs showed stringent requirement of the YA (CA or UA) at poly (A) sites for polyadenylation. About 7.9% had the AAUAAA signals on ?40―?1 nt upstream of the poly(A) sites. Over 60% of mRNAs probably used the one- or two-base variants of AAUAAA hexamers as their PASs in 3′ fragments. The single-base variants of AAUGAA revealed the high frequency in 11.5% of 3′ fragments. The DUEs were detected in 90% of pre- mRNAs, especially more than half of the pre-mRNAs with multi-base variants of AAUAAA had the DUEs surrounding the poly(A) site. The location of DUE is also important for defining the cleavage site. Al- though most of the rice pre-mRNAs did not contain AAUAAA signal, the existence of downstream ele- ments ensured the efficiency of cleavage-polyade-

关键词：多聚腺苷酸序列分析 mRNA 水稻基因工程

Ionization state of cosmic hydrogen by early stars and quasars

在线全文

学校读者我要写书评

暂无评论

Research in Astronomy and Astrophysics 2009年第6期9卷 665-681页

作者： Xiao-Chun Mao1,2.1 National Astronomical Observatories, chinese academy of {2., beijing 100012. China 2.graduate University of chinese academy of {2., beijing 100049, China National Astronomical Observatories Chinese Academy of Sciences graduate University of chinese {2. of sciences

Cosmic hydrogen is reionized and maintained in its highly ionized state by the ultraviolet emission attributed to an early generation of stars and quasars. The Lyα opacity observed in absorption spectra of high-redshift quasars permits more stringent constraints on the ionization state of cosmic hydrogen. Based on density perturbation and structure formation theory, we develop an analytic model to trace the evolution of the ionization state in the post-overlap epoch of reionization, in which the bias factor is taken into account. For quasars, we represent an improved luminosity function by utilizing a hybrid approach for the halo formation rate that is in reasonable agreement with the published measurements at 2.≤ z ≤ 6. Comparison with the classic Press-Schechter mass function of dark matter halos, we demonstrate that the biased mass distribution indeed enhances star formation efficiency in the overdense environment by more than 2. per cent following the overlap of ionized bubbles. In addition, an alternative way is introduced to derive robust estimates of the mean free path for ionizing photons. In our model, star-forming galaxies are likely to dominate the ionizing background radiation beyond z = 3, and quasars contribute equally above a redshift of z ～ 2.5. From 5 ≤ z ≤ 6, the lack of evolution in photoionization rate can thus be explained by the relatively flat evolution in star formation efficiency, although the mean free path of ionizing photons increases rapidly. Moreover, in the redshift interval z ～ 2.- 6, the expected mean free path and Gunn-Peterson optical depth obviously evolve by a factor of ～ 500 and ～50 respectively. We find that the relative values of critical overdensities for hydrogen ionization and collapse could be 430% at z ≈2.and 2. at z ≈6, suggesting a rapid overlap process in the overdense regions around instant quasars following reionization. We further illustrate that the absolute estimates of the fraction of neutral hydrogen computed fr

关键词： cosmology theory -- formation galaxies -- quasars general -- diffuse radiation -- intergalactic medium