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51.
Guangzhi Tu 《中国科学D辑(英文版)》1998,41(1):1-13
The new plants documented here, including a representative of the trimerophytesPsilophyton primitiuum sp. nov., a questionable rhyniophyte or trimerophyteHedeia sinica sp. nov., a prelycopodBragwanathia sp. and two species of zosterophyllophytes,Zosterophyllum australianum Lang and Cookson 1930 and2. sp. 1, from the Posongchong Formation of southeastern Yunnan, China, add to the known floral diversity of the Early Devonian
of this region. Two sections of the Posongchong Formation, Changputang section of Wenshan district and Gegu section of Mengzi
district also are introduced. After comparing the plants with those of the coeval flora of Australia and considering the data
of recent paleocontinental reconstructions, the authors suggest that there is a northeastern Gondwana phytogeographic unit
during the early Devonian comprising Australia, South China Block and perhaps Shan-Thai Block. The similarity of the floral
component between Australia and South China is discussed. Because both Australia and South China also have dominant or endemic
taxa, each might be recognized as a subunit, separately characterized byHedeia for Australia andEophyllophyton for South China.
Project supported by the National Natural Science Foundation of China (Grant Nos. 49372075 and 49742004) 相似文献
52.
We consider how the Alfven fluctuation varies as it passes through a slow MHD shock, assuming the fluctuation to originate on the Sun and such slow shocks are present between 2 and 6 solar radii. The results are 1) low latitude region in the vicinity of the neutral sheet is where the fluctuation can propagate with no or little distortion; 2) high latitude region far from the neutral sheet is a region of small distortion only for low Alfven-Mach numbers (about 0.3 or lower); 3) the observation of the Alfven fluctuations in space is consistent with, and lends support to their originating in the Sun and the existence of slow shock around the Sun. 相似文献
53.
This paper presents a boundary element method (BEM) procedure for a linear elastic fracture mechanics analysis in two‐dimensional anisotropic bimaterials. In this formulation, a displacement integral equation is only collocated on the uncracked boundary, and a traction integral equation is only collocated on one side of the crack surface. A fundamental solution (Green's function) for anisotropic bimaterials is also derived and implemented into the boundary integral formulation so that except for the interfacial crack part, the discretization along the interface can be avoided. A special crack‐tip element is introduced to capture the exact crack‐tip behavior. A computer program using FORTRAN has been developed to effectively calculate the stress intensity factors of an anisotropic bimaterial. This BEM program has been verified to have a good accuracy with previous studies. In addition, a central cracked bimaterial Brazilian specimen constituting cement and gypsum is prepared to conduct the Brazilian test under diametral loading. The result shows that the numerical analysis can predict relatively well the direction of crack initiation and the path of crack propagation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
54.
Microdiamond and graphite occur in quartzofeldspathic rocks (saidenbachites) of the central Erzgebirge in Saxony. Zircon from such rocks contains not only relatively high but also variable amounts of early formed graphite and later crystallized diamond, however no carbonate. Six purified zircon concentrates were analysed by mass spectrometry for δ13C(PDB) values which were between −24 and −33‰. The carbon inclusions resulted in C contents of the concentrates as high as 0.5 wt%. It is hypothesized that the observed δ13C signature results from organic material in the sedimentary protoliths of the saidenbachites probably deposited not earlier than Mid‐Devonian. This material was transformed to graphite during early metamorphism and subsequently to diamond after an anatectic event at great depths (>150 km). During these processes, the δ13C signature of the carbon did not (significantly) change. 相似文献
55.
Meiobenthos in estuary part of ha long bay (gulf of tonkin, south china sea, vietnam) 总被引:1,自引:0,他引:1
Olga Pavlyuk Yulia Trebukhova Nguyen Vu Thanh Nguyen Dinh Tu 《Ocean Science Journal》2008,43(3):153-160
The distribution of the taxonomical composition and the density of meiobenthos depending on some factors of environment has
been studied in bottom sediments of the northern estuary part of Ha Long Bay (Cua Luc estuary). The basic factor of influence
on meiobenthic community structure was the granulometric composition of sediment. The greatest taxonomic diversity is noted
in the silted sands, lowest — in the silty sediments. The density of meiobenthic community was higher in the silty sediments.
Slightly expressed correlation between the density of nematodes and the percentage of silty particles in the sediments is
detected (Spearman rank correlation coefficient was 0.49±0.21, p=0.035). The nematodes were dominant at all stations. In total,
representatives of 66 species of nematodes belonging to 17 families and 52 genera were identified. 相似文献
56.
57.
商丹断裂带作为扬子板块与华北板块的缝合带,在秦岭造山带中占据重要的地位。对其进行精细的构造研究,是了解扬子板块与华北板块相互作用过程的关键。研究工作在商丹断裂带东段展开,对该带进行了详细的野外观察、显微构造观察、糜棱岩化过程中温度的估算、有限应变测量、差异应力的计算以及糜棱岩化过程中运动学涡度的计算。变形温压条件指示糜棱岩形成于中-高绿片岩相到低角闪岩相变质条件。差异应力计算结果指示商丹带具备大型构造动力特征。涡度分析表明该断裂带的变形以纯剪切作用占据主导作用,但包含有简单剪切的分量,从而证明了扬子板块与华北板块之间具有以碰撞挤压为主的斜向汇聚方式。 相似文献
58.
60.
Natural Hazards - Tsunamis occur not only in marine settings but also in lacustrine environments. Most of the lacustrine tsunamis are caused by seismically- or aseismically-triggered mass... 相似文献