检索结果-南通市图书馆

Progress and review of the studies on the end-Triassic mass extinction event

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{1. Earth sciences 2005年第12期48卷 2049-2060页

作者： DENG Shenghui1,2. LU Yuanzheng1,2.3 & XU Daoyi4.1. Research institute of Petroleum Exploration and Development, {1. 100083,{2. 2. Key Laboratory of Oil and Gas Reservoir of Petrochina, {1. 100083,{2. 3.{2. University of Geosciences, {1. 100083,{2. 4. institute of Geology,{2. Earthquake Administration, {1. 10002.,{2. 1. Research institute of Petroleum Exploration and Development 100083 Beijing China 2. Key Laboratory of Oil and Gas Reservoir of Petro{1. 100083 Beijing China 3. china University of Geo{1.s 100083 Beijing China 4. {1. of Geology China Earthquake Administration 100029 Beijing China

The mass extinction at the end-Triassic is one of the five biggest in the Phanerozoic. However,it is the least well understood among these five events, and only till last decade it became a great academic interesting subject to geologists. The evidences for this event come obviously from bivalves, brachiopods, ammonites, corals, radiolaria, ostracods and foraminifera of marine habitats, and plants and tetrapods of terrestrial realm. By contrast, for some of other groups, such as marine gastropods and marine vertebrates, no mass extinction has been recog-nized yet. The extinction event is strongly marked at specific level but shown a complicated situa-tion at generic and family levels. Dramatic changing of the environment, such as the temperature raise due to the greenhouse effect, the marine anoxic habitats caused by a sudden transgression after the regression at the end of Triassic, has been claimed to be the main cause of the extinction. Many hypotheses have been suggested to demonstrate the mechanisms of the environment changing, among which two popular ones are the bolide impact and volcanic eruption. The Triassic-Jurassic (Tr-J) boundary mass extinction event is still poorly understood because no enough data have been obtained from the Tr-J boundary successional sections of both marine and terrestrial sediments, and most of these studies were regionally restricted. The basic aspects of the event and its associated environmental conditions remain poorly characterized and the causal mechanism or mechanisms are equivocal. Some authors even doubt its occurrence. china has many successionally developed terrestrial and marine Tr-J sections. Detailed studies of these sections may be important and significant for well understanding of the event.

关键词： progress, review, end-Triassic, mass extinction, mechanism, Tr-J boundary.

Calculating soil moisture by remote sensing and analyzing hydrologic cycle process in the Yellow River basin

在线全文

学校读者我要写书评

暂无评论

science{1.(Technological sciences) 2004年第z1期47卷 1-13页

作者： YANG Shengtian1.& LIU Changming1. 2.1. School of Environmental {1.s, {1. Normal University, {1. 1.0875,{4. 2. institute of Geographic {1. and Natural Resources Research, {1. 1.01.1.{4. beijing Normal Univ Sch Environm Sci Beijing 100875 Peoples R China Inst Geog Sci & Nat Resources Beijing 100101 Peoples R China

Based on the AVHRR pathfinder remote sensing data, soil moisture, precipitation and evaporation during the period of 1.82.1.98, soil moisture of all layers of soil-profile (0—1.m) in the Yellow River basin over the 1. years are calculated by the remote sensing model of calculating soil water. The Yellow River basin is divided into seven subcatchments as control sections at the location of six hydrologic stations (Lanzhou, Toudaoguai, Longmen, Sanmenxia, Huayuankou and Lijin). After calculating soil moisture and obtaining runoff data and precipitation data, the dynamical features of hydrological cycle in the Yellow River basin are analyzed for the period from 1.82.to 1.88 using water balance method. The conclusions are as follows: It is feasible to calculate the soil water on the macro-scale, in the soil profile with temporal continuity by means of remote sensing and survey in land. Some values of the key water cycle factors in the Yellow River are obtained, which include the annual precipitation of 4.00 km3, the evapotranspiration of 3000-3500 km3, and the soil moisture transformation of ?500- 500 km3. Consequently, we analyzed the process of the water cycle in the Yellow River over the 1. years, and the results show that the segment upstream of Lanzhou city is a relatively humid region, and the area of internal waters and the reaches of Shanshan is the most desiccated region. Therefore, the runoff in the depth process is intensive and the runoff-generating process is weak in more arid regions.

关键词： the Yellow River, soil moisture, remote sensing, hydrologic cycle.

A circum-earth shear zone at low-latitudes and episodic large earthquakes in it and the circum-Pacific seismic zone

在线全文

学校读者我要写书评

暂无评论

science{1. Earth sciences 2006年第9期49卷 897-903页

作者： MA Zongjin1, DU Pinren1, REN Jinwei2.& GAO Xianglin1 1. institute of Geology,{1. Earthquake Administration, {2. 10002.,{1. 2. institute of Earthquake science,{1. Earthquake Administration, beijing 1.0036,{1. 1. institute of Geology China Earthquake Administration Beijing 100029 China 2. {1. of Earthquake {1. China Earthquake Administration Beijing 100036 China

Because of the differential motions between the Northern and Southern Hemispheres of the Earth, there exists a motion discordant zone between them. On the surface this zone consists of 1. large faults dominant with strike-slip. We call it a global shear zone at low-latitudes (E system). By statistical analysis of temporal distribution of earthquakes Mw≥7.5 in the E system and the circum-Pacific (P system) during 1.00―2.03, we find that there exist quasi-episodic and alternative activities in and between these two systems. This phenomenon is likely associated with the half-sphere oscillation in dilation and contraction and the change of the Earth’s rotation rate.

关键词： shear zone, circum-Pacific zone, great earthquake, quasi-episode.

Research progress in synthesis and catalysis of polyoxometalates

在线全文

学校读者我要写书评

暂无评论

Progress in Natural science:Materials International 2005年第5期15卷 385-394页

作者： GONG Yun1. HU Changwen1.* and LIANG Hong2.1. Department of Chemistry, School of {1., the {1. for Chemical Physics, {2. {1. of Technology, {2. 1.0081. china 2. Chemical Industry Press, {2. 1.002., china) Department of Chemistry School of Science the Institute for Chemical Physics Beijing Institute of Technology Beijing 100081 China Chemical Industry Press Beijing 100029 China

Recent progress in the synthetic chemistry and catalysis of polyoxometalates (POMs) is reviewed. The novel POMs and their derivatives emerging in nearly three years (2.02.2.04. are introduced, including POMs with novel structure, POMs-organic hybrid compounds and host-guest complexes. Our review is focused on the elaboration of POMs' supramolecular chemistry.

关键词： polyoxometalates hybrid host-guest structure supramolecule catalysis.

The numerical method for three-dimensional impact with friction of multi-rigid-body system

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{1.(Physics,Mechanics & Astronomy) 2006年第1期49卷 102-118页

作者： ZHAO Zhen1.2. LIU Caishan2.& CHEN Bin2.1. beijing {4. of Graphic Communication, beijing 1.2.00, china 2. Department of Mechanics & Engineering science, Peking University, beijing 1.0871. china beijing {1. of Graphic Communication Beijing 102600 China Department of Mechanics & Engineering science Peking University Beijing 100871 China

The differential equations for planar impacts reduce to an algebraic form, and can be easily solved. For three dimensional impacts with friction, there is no closed-form solution, and numerical integration is required due to the swerve behavior of tangential impulse during collisions. The dynamic governing equations in the impact process are built up in impulse space based on the Lagrangian equation in this paper. The coefficient of restitution defined by Poisson is used as the condition of impact termination. A valid nu- merical method for solving three-dimensional frictional impact of multi-rigid body system is established. The singular cases of tangential movement in sticking point are especially noticed and analyzed. Several examples are present to reveal the different kinds of tan- gential movement modes varied with the normal impulse during collision.

关键词： multi-rigid body, impact, friction.

Pattern phenomena in an rf discharge dusty plasma system

在线全文

学校读者我要写书评

暂无评论

science{1.(Physics,Mechanics & Astronomy) 2006年第5期49卷 588-596页

作者： HUANG Feng1.2. YE Maofu2.& WANG Long2.1. College of science,{4. Agricultural University, {2. 1.0083,{4. 2. institute of Physics, Chinese Academy of sciences, {2. 1.0080,{4. 1. College of science China Agricultural University Beijing 100083 China 2. {1. of Physics Chinese Academy of Sciences Beijing 100080 China

Various dust patterns are observed in an rf discharge dusty plasma system. According to the dust growth process from small to large in size, the formation of different dust patterns can be divided into two stages: the small-particle stage (or dust cloud stage), and the large-particle stage (or dust crystal stage). The evolution relations between different dust patterns with gas pressure changing are investigated. Dust voids, dust acoustic waves and strong turbulence modes are presented at the small-particle stage. The self-organized dust lattices and dust clusters are investigated at the large-particle stage. The static structure of a dust lattice is characterized by means of the pair correlation function. Dust clusters formed by particles with different numbers and the regular evolution of the clusters with gas pressure are also investigated. The packing sequences of dust clusters are verified through two-dimensional confined molecular dynamics simulations.

关键词： dusty plasma dust patterns

Mineralogy and crystal structure determination of Mg-fillowite

在线全文

学校读者我要写书评

暂无评论

science{1. Earth sciences 2005年第5期48卷 635-646页

作者： MA Zhesheng 1., SHI Nicheng 1.& YE Danian 2.1.{1. University of Geo{1.s, {2. 1.0083,{1. 2. institute of Geology, Chinese Academy of {1.s, {2. 1.002.,{1. 1. china University of Geo{1.s 100083 Beijing China 2. {1. of Geology Chinese Academy of Sciences 100029 Beijing China

Accurate crystal structure determination of complex phosphate Mg-fillowite ? Na2.a(Mn{1.g2.e)7[PO{1.6 has been finished. Mg-fillowite occurs in muscovite-pegmatite in the Altay area, Xinjiang, china. It is of the trigonal lattice, with space group R-3, unit cell a=1.51.1.(3) nm, c={1.31.1.2. nm, V=8.5736 nm3, Z = 1.. The R-factor of the determination accuracy is R (I > 2. ( I )) = 0.0776. The cationic polyhedra consist of two kinds of structural units: compound col- umn and screw column. In three-dimensional space, they are linked with each other through corner sharing or edge sharing to build the entire structure. There are {1. atoms in an asymmetric unit and 72. atoms in a unit cell. In terms of types and connection manners of the coordination polyhedra, the degree of complicity is rarely seen in all mineral crystal structures. Study of such a structure is significant for the classification of phosphate and the building rule of coordination polyhedra in a complex crystal structure.

关键词： Mg-fillowite, complex phosphate, crystal structure, coordination polyhedron.

The crustal structure under Sanjiang and its dynamic implications:Revealed by seismic reflection/refraction profile between Zhefang and Binchuan,Yunnan

在线全文

学校读者我要写书评

暂无评论

science{1. Earth sciences 2005年第9期48卷 1329-1336页

作者： ZHANG Zhongjie1. BAI Zhiming1. WANG Chunyong2. TENG Jiwen1. Lü Qingtian3, LI Jiliang1. LIU Yifeng1.& LIU Zhenkuan{1.1. institute of Geology and Geophysics, Chinese Academy of {1.s, {2. 1.002., china 2. institute of Geophysics, china Seismological Bureau, {2. 1.0085, china 3. institute of Deposition Resource, Chinese Academy of Geo{1.s, {2. 1.0037, china {1. School of Exploration and Information, china University of Geo{1.s, {2. 1.0083, china 1. institute of Geology and Geophysics Chinese Academy of Sciences 100029 Beijing China 2. {1. of Geophysics China Seismological Bureau 100085 Beijing China 3. institute of Deposition Resource Chinese Academy of Geosciences 100037 Beijing China 4. School of Exploration and Information China University of Geosciences 100083 Beijing China

The fault belts in Sanjiang mainly include Jinshajiang-Honghe fault, Lancangjiang fault and Nujiang fault (called Sanjiang faults) in western Yunnan Province, china. By interpreting the wide-angle seismic reflection/refraction profile between Zhefang and Binchuan, which crosses Tengchong and Baoshan blocks in Dianxi (western Yunnan) tectonic zone, we recon- struct the crustal structure with seismic traveltime tomography for crustal P-wave velocity and the seismic scattering image for crustal seismic reflection structure. In this paper, we firstly present the crustal structure images of P-wave velocity and seismic reflection under the wide-angle seismic profile. These results demonstrate that, the crustal velocity structure and seismic reflec- tion structure along the profile can be divided into 3 segments, and there is an obvious difference of crustal structure among the eastern, the western and the middle segment. Generally, crustal P-wave velocities in the Baoshan segment are 0.1.0.{1.km/s slower and seismic reflection am- plitudes from Moho discontinuity are stronger than the other {1.segments. In the studied area, crustal thickness is about 4. km, and shows the thickening tendency from west to east along the profile. Additionally, it can be seen that there is one strong-amplitude seismic reflection event as bright points at the depths of 8―1. km, along the segment of 80―1.5 km of the profile (south- ward of Tengchong); and seismic reflection wave-field from Moho discontinuity varies obviously along the lateral direction. Finally, we make some discussions on the crustal thickening pattern in the Sanjiang fault belt, structural environment of earthquake development and the contact rela- tionship between the Tengchong block, Banshan block and Luxi trough.

关键词： Sanjiang area wide-angle seismic profile crustal structure.

Randomization of protein encoding gene during species evolution

在线全文

学校读者我要写书评

暂无评论

Chinese science Bulletin 1998年第4期43卷 299-303页

作者： GE Weiwen 1.and HE Fuchu 2.1. {1. of Hygiene and Environment Medicine, Tianjin 300050,{1. 2. {1. of Radiation Medicine, beijing 1.0850,{1. institute of Hygiene and Environment Medicine Tianjin China institute of Radiation Medicine Beijing China

Employing chi_square test, the authors observed the bias of 4.kinds of bases’ locating in 3 codon positions in gene sequence, and proved that there is a positive correlation between higher chi_square value and protein coding structure. By this, the observation that genes undergo progressive reduction in chi_values along evolution direction will reflect the progressive randomization of gene structures and the loss of the characteristics of protein coding sequences. The result proposed that during the evolution of life, genes are unexpectedly degenerating.

关键词： chi_square test gene sequence randomization evolution.