检索结果-南通市图书馆

Environmental characteristics of Mid-Holocene recorded by lacustrine sediments from Lake Daihai, north environment sensitive zone, 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 2006年第9期49卷 968-981页

作者： SUN Qianli1,2, ZHOU Jie1, SHEN Ji3, CHEN Peng1,2, WU Feng1,2 & XIE Xiuping1,2 1. State Key Lab of Loess and Quaternary Geology, Institute of Earth Environment, chinese academy of sciences, Xi’an 710075, China 2. graduate university of chinese academy of sciences, Beijing 100039, China 3. Nanjing Institute of Geography and Limnology, chinese academy of sciences, Nanjing 210008, China State Key Lab of Loess and Quaternary Geology Institute of Earth Environment Chinese Academy of Sciences Xi’an China graduate university of chinese academy of sciences Beijing China Nanjing Institute of Geography and Limnology Chinese Academy of Sciences Nanjing China

Climate proxies, such as total organic carbon and nitrogen (TOC, TN), carbonate content (CaCO3), grain-size and pollen of the sediment core retrieved from enclosed Lake Daihai which lies in the north China environment sensitive zone are analyzed to reconstruct the environment evolution of the area based on high-resolution radiocarbon chronology. The results reveal that the TOC and TN contents of the sediments correlate well with pollen percentage and pollen flux variations during the Holocene, and both reach their peak values simultaneously at 6.7―3.5 ka BP (calendar age, 7.6―3.6 ka BP). Since 6.7 ka BP, both the CaCO3 and organic matter contents of the core have simultaneous variations, and their high values also occur during 6.7―3.5 ka BP. While during 9.0―6.7 ka BP (calendar age, 10―7.6 ka BP) relatively lower level of organic matter content and pollen flux corre- spond to the higher level of carbonate content. The above relations suggest that during 6.7―3.5 ka BP, the productivity and effective precipitation were greatly improved in the lake drainage area, and this would probably strengthen the hydrodynamic conditions, enhancing organic matter, pollen and carbonate inputs from terrestrial sources. Such processes would account for the enrichment of both organic matter and carbonate in the sediments. While during 9.0―6.7 ka BP, the lower level of or- ganic matter, pollen flux but high carbonate content show depressed productivity and declined vege- tation coverage. The higher carbonate content at this stage would have probably resulted from the higher evaporation ratio of the lake water under relatively drier climate conditions. Therefore, it is in- ferred that during 6.7―3.5 ka BP, the climate was more humid with abundant rainfalls and vegetation was more flourishing in the Lake Daihai area. This can be seen as Holocene Climate Optimum (HCO). As a result, this has evident discrepancies with the traditional notion that the HCO occurs at Early Holocene or early Mid

关键词： Lake Daihai, Mid-Holocene, lacustrine sediments, environmental characteristics.

Thermal analysis of the baffle structure of the Solar Space Telescope

在线全文

学校读者我要写书评

暂无评论

science China(Physics,Mechanics & Astronomy) 2010年第9期53卷 1755-1764页

作者： LI Rong1,2,3 & WANG Sen1,3 1 National Astronomical Observatories,chinese academy of sciences,Beijing 100012,China 2 graduate university of chinese academy of sciences,Beijing 100049,China 3 Key Laboratory of Solar Activity,National Astronomical Observatories of chinese academy of sciences,Beijing 100012,China National Astronomical Observatories Chinese Academy of Sciences Beijing China graduate university of chinese academy of sciences Beijing China Key Laboratory of Solar Activity National Astronomical Observatories of Chinese Academy of Sciences Beijing China

The SST(Space Solar Telescope) is an astronomical telescope with a primary mirror of 1 m in *** observes the sun with a small view field to ensure that its high spatial resolution imaging has 0.1″-0.15″ and high SNR(signal to noise ratio).Surrounding the small view field is still the sun,which is an intense source of both heat and stray *** baffles(the main baffle,the aperture,and the outer baffle),which are used to eliminate the stray light,will change the thermal flux in the SST and will weaken the effect of the thermal control *** this study,the compatibility analysis of the thermal effect of baffle structures in SST is *** GCF(Geometry Composing Function) and BRDF(Bidirectional Reflectance Distribution Function),which are two inherent related parameters in the compatibility analysis,are *** objective and method of the compatibility analysis are *** the thermal analysis software,the temperature fields are calculated for different lengths of the main baffle,different radii of apertures,different lengths of the outer baffle with a 3' tilt angle and 16' tilt angle,and different tilt angles of the outer baffle with a 200 mm length.A series of configurations and sizes of the baffles are studied with the goals of both thermal control and elimination of stray *** design of the baffle structure of SST is achieved:the main baffle of length 4100 mm,the internal shield of radius 494 mm,the outer baffle of length 200 mm,and the outer baffle of tilt angle 3' are successfully *** paper presents the relationship between the thermal control design and stray light elimination plan in the *** aims of the optimal design of the baffle structure of SST are *** thoughts and methods of the optimal analysis are also useful for similar optical telescopes designed for solar observation.

关键词： baffle the main baffle the outer baffle GCF BRDF

Estimating possible impact of human activity on the warm season temperature in Beijing since the industrial era

在线全文

学校读者我要写书评

暂无评论

chinese science Bulletin 2010年第16期55卷 1590-1593页

作者： QIN Li1,2 & ZHOU Xin1,2 1 Institute of Geology and Geophysics,chinese academy of sciences,Beijing 100029,China 2 graduate university of chinese academy of sciences,Beijing 100049,China Institute of Geology and Geophysics Chinese Academy of Sciences Beijing China graduate university of chinese academy of sciences Beijing China

Global surface temperature shows an increasing trend over the past 100 *** and natural factors have been invoked to explain this warming, but their relative contribution and the spatial variability remain *** on a 2650-year temperature record from a stalagmite near Beijing, we explore the possible impacts of human activity on the warm season temperature in Beijing since the industrial era using the method of singular spectrum analysis (SSA).The results suggest that the warm season temperature in Beijing under the natural forcing should have an overall decreasing trend for the past 13. years (1870 to 2000 AD) with an amplitude of 0.45±0.84°C, while the instrumental record and stalagmite data show an increase of 1.08°*** imply that human activity would have caused an increase in the warm season temperature of Beijing for about 1.53±0.84°C compared to its natural trends, from 1870 AD to 2000 *** results also suggest that anthropogenic forcing began to significantly influence the temperature since 1870 AD, and the effect further intensified since 1915 AD.

关键词：人类活动北京温度工业时代季节温暖估计地表气温

Eclogites in the interior of the Tibetan Plateau and their geodynamic implications

在线全文

学校读者我要写书评

暂无评论

chinese science Bulletin 2009年第15期54卷 2556-2567页

作者： ZHANG KaiJun1,2 & TANG XianChun2,3 1 Department of Earth sciences, Nanjing university, Nanjing 210093, China 2 Guangzhou Institute of Geochemistry, chinese academy of sciences, Guangzhou 510640, China 3 graduate university of chinese academy of sciences, Beijing 100049, China Department of Earth sciences Nanjing University Nanjing China Guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou China graduate university of chinese academy of sciences Beijing China

Eclogites have been recently reported in the interior of the Tibetan Plateau, including in the central Qiangtang metamorphic belt, in the Basu metamorphic massif of the eastern Bangong-Nujiang suture zone, and at Songdo and Pengco in the eastern Lhasa terrane. Some typical ultrahigh-pressure (UHP) metamorphic phenomena, e.g., garnet exsolution from clinopyroxene, were documented in the Basu and Pengco eclogites. The UHP metamorphism in the interior of the Tibetan Plateau marked by these eclogites generally took place in the Early Mesozoic. Along with exhumation of these eclogites, (post-) collision-related magmatism extensively occurred around the central Qiangtang belt, the eastern Ban-gong-Nujiang suture zone, and the eastern Lhasa terrane. The occurrence of these Early Mesozoic ec-logites manifests an out-of-sequence evolution of the Tethys, and they could be a product of diachro-nous collision between the eastern Qiangtang terrane and the irregular continental margin of the united western Qiangtang-Lhasa plate, along the linked eastern Bangong-Nujiang-central Qiangtang zone. The collision-related magmatic rocks could have been originated from lithospheric thickening, melting, or detachment due to the collision. The presence of UHP metamorphic rocks in central Qiangtang and Basu implies likely continental deep-subduction, and the denudation of these two metamorphic zones could have served as the source of the Triassic turbidites in the Songpan-Garzê complex and the Ju-rassic turbidites in the western Bangong-Nujiang zone, respectively. However, studies of the eclogites in the interior of the Tibetan Plateau just began, and many principal aspects still remain to be explored, such as their distributions, typical lithologies and minerals, temperature-pressure conditions, timing of formation and exhumation, protoliths and tectonic setting, and relationship with the evolution of the Tethys and large-scale basins in Tibet.

关键词：地球动力学意义青藏高原榴辉岩

Floral organogenesis of Delavaya toxocarpa (Sapindaceae;Sapindales)

在线全文

学校读者我要写书评

暂无评论

Journal of Systematics and Evolution 2009年第3期47卷 237-244页

作者： 1,2,3Li-Min CAO 1Nian-He XIA 1(Institute of Economic Botany, South China Botanical Garden, chinese academy of sciences, Guangzhou 510650, China) 2(Department of Life sciences, Hengyang Normal university, Hengyang 421008, China) 3(graduate university of chinese academy of sciences, Beijing 100049, China) (Institute of Economic Botany South China Botanical Garden Chinese Academy of Sciences Guangzhou 510650 China) (Department of Life sciences Hengyang Normal University Hengyang 421008 China) (graduate university of chinese academy of sciences Beijing 100049 China)

The floral organogenesis and development of Delavaya toxocarpa Franch. (Sapindaceae) were studied under scanning electron microscope and light microscope to determine its systematic position within Sapindaceae. Flowers arise in terminal thyrses. The sepal primordia initiate in a spiral (2/5) sequence, which are not synchronous. The flve petal primordia initiate almost synchronously and alternate with sepal primordia. Eight stamens initiate almost simultaneously and their differentiation precedes that of the petals. The last formed petal and one stamen initiate from a common primordium. Mature stamens curve inwards and cover the ovary in bud. The gynoecium begins as a hemispheric primordium on which two carpellary lobes arise simultaneously. Later in development a single gynocium is formed with two locules and two ovules per locule. Floral morphology suggests a closer affinity with Sapindaceae, although certain features of floral ontogenesis are similar to those observed in certain members of the former Hippocastanaceae, such as Handeliodendron.

关键词： Delavaya toxocarpa Franch. floral organogenesis Hippocastanaceae Sapindaceae.

A NUMERICAL STUDY ON A SIMPLIFIED TAIL MODEL FOR TURNING FISH IN C-START

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Hydrodynamics 2006年第2期18卷 135-142页

作者： YANG Yan TONG Bing-gang The Laboratory for Biomechanics of Animal Locomotion Graduate University of Chinese Academy of SciencesBeijing 100049 China Department of Mechanics and Mechanical Engineering University of Science and Technology of China Hefei230026 China

Most freshwater fish are good at turning manoeuvres. A simulated fish tail model was numerically investigated and discussed in detail. This study deals with unsteady forces and moment exerted on the fish tail-fin in an initial sideways stroke and a subsequent return stroke motion, and visualizes the flow fields and vortex structures, in order to explore the flow control mechanism of the typical turning motion of fish. Further discussion on fluid dynamic consequences corresponding to two different bending forms of fish tail-fins in its C-start is given. The two-dimensional unsteady incompressible Navier-Stokes equations are solved with a developed pseudo-compressibility method to simulate the flow around the fish tail-fin. The computed results and the comparison with experiments indicate that （1） fish performs a turning motion of its body using the impulsive moment produced by the to-and-fro stroke, and each stage of the process exhibits its specific hydrodynamic characteristic, （2） fishes adopt two forms of tail-tip bend （single bend and double bend） to accomplish a C-start turning manoeuvre, in dependence of their physical situations and natural environments, （3） fish can control its turning motion by modulating some key kinematic parameters.

关键词： fish swimming turning manoeuvre C-start,tail fin locomotion 2D Navier-Stokes equations CFD physical mechanism optimal control

Structure of augmentation quotients of finite homocyclic abelian groups

在线全文

学校读者我要写书评

暂无评论

science China Mathematics 2007年第9期50卷 1280-1288页

作者： Guo-ping TANG School of Mathematical sciences,graduate university of chinese academy of sciences,Beijing 100049,China School of Mathematical sciences Graduate University of Chinese Academy of Sciences Beijing China

Let G be a finite abelian group and its Sylow p-subgroup a direct product of copies of a cyclic group of order p r , i.e., a finite homocyclic abelian group. Let Δ n (G) denote the n-th power of the augmentation ideal Δ(G) of the integral group ring ?G. The paper gives an explicit structure of the consecutive quotient group Q n (G) = Δ n (G)/Δ n+1(G) for any natural number n and as a consequence settles a problem of Karpilovsky for this particular class of finite abelian groups.

关键词： integral group ring augmentation ideal consecutive quotient of augmentation ideal 16S34 20C05

A SAR sidelobe suppression algorithm based on modified spatially variant apodization

在线全文

学校读者我要写书评

暂无评论

science China(Technological sciences) 2010年第9期53卷 2542-2551页

作者： NI Chong1,2,WANG YanFei1,XU XiangHui1,ZHOU ChangYi1 & CUI PengFei1,2 1 Institute of Electronics,chinese academy of sciences,Beijing 100190,China 2 graduate university of chinese academy of sciences,Beijing 100039,China Institute of Electronics Chinese Academy of Sciences Beijing China graduate university of chinese academy of sciences Beijing China

The existing spatially variant apodizations (SVAs) either cannot depress the sidelobes effectively or reduce the energy of the *** improve this,a modified SVA (MSVA) is put forward in this paper,which expands the traditional filter from 3-taps to 5-taps and sets relevant parameters according to different sampling rates to get the excellent result that satisfies constrained optimization theory.A method for synthetic aperture radar (SAR) sidelobe control based on MSVA is presented,which applies MSVA to range compression and azimuth compression to control *** method which is available for any Nyquist sampling rate can both depress the sidelobes effectively and keep the energy of the mainlobe and the resolution of the *** method can reduce sidelobe levels more effectively than classical amplitude weighting while maintaining the image resolution,as demonstrated by the result of the experiment.

关键词： synthetic aperture radar sidelobe suppression resolution SVA

Identification and Categorization of Horizontally Transferred Genes in Prokaryotic Genomes

在线全文

学校读者我要写书评

暂无评论

Acta Biochimica et Biophysica Sinica 2005年第8期37卷 561-566页

作者： Shuo-Yong SHI~1 Xiao-Hui CAI~1 and Da-fu DING~(1,2*) Key Laboratory of Proteomics.Institute of Biochemistry and Cell Biology.Shanghai Institutes for Biological sciences,chinese academy of sciences,graduate School of the chinese academy of sciences.Shanghai 200031,China ~2 School of Life science & Technology.Shanghai Jiaotong university.Shanghai 200030.China Key Laboratory of Proteomics Institute of Biochemistry and Cell Biology Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Graduate School of the Chinese Academy of SciencesShanghai 200031 China School of Life science & Technology Shanghai Jiaotong UniversityShanghai 200030 China

Horizontal gene transfer(HGT),a process through which genomes acquire genetic materialsfrom distantly related organisms,is believed to be one of the major forces in prokaryotic genome ***,systematic investigation is still scarce to clarify two basic issues about HGT:(1) what types ofgenes are transferred:and(2)what influence HGT events over the organization and evolution of ***-scale investigations of these two issues will advance the systematical understanding ofHGT in the context of prokaryotic genome *** investigated 82 genomes,we constructed anHGT database across broad evolutionary *** identified four function categories containing a highproportion of horizontally transferred genes:cell envelope,energy metabolism,regulatory functions,andtransport/binding *** biased function distribution indicates that HGT is not completely random;instead,it is under high selective pressure,required by function restraints in ***,wemapped the transferred genes onto the connectivity structure map of organism-specific pathways listed inKyoto Encyclopedia of Genes and Genomes(KEGG).Our results suggest that recruitment of transferredgenes into pathways is also selectively constrained because of the tuned interaction between original *** organization structures still conserve well through evolution even with the recruitment ofhorizontally transferred ***,in pathways whose organization were significantly affected byHGT events,the operon-like arrangement of transferred genes was found to be *** resultssuggest that operon plays an essential and directional role in the integration of alien genes into pathways.

关键词： genome evolution horizontal gene transfer function and pathway analysis