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

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 2.0008, China 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

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.

Microstructure and Mechanical Properties of Martensitic Stainless Steel 6Cr15MoV

在线全文

学校读者我要写书评

暂无评论

Journal of Iron and Steel Research International 2012年第3期19卷 56-61页

作者： MA Dang-shen1, CHI Hong-xiao1,2. ZHOU Jian1, YONG Qi-long1,2.(1. institute for Structural Materials, Central Iron and Steel Research institute, Beijing 100081, China 2. Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China) [a] institute for Structural Materials Central Iron and Steel Research Institute Beijing 100081 China [b] Faculty of Materials Science and Engineering Kunming University of Science and Technology Kunming 650093 Yunnan China

Martensitic stainless steel containing Cr of 12. to 18%（mass percent） are common utilized in quenching and tempering processes for knife and cutlery steel. The properties obtained in these materials are significantly influ- enced by matrix composition after heat treatment, especially as Cr and C content. Comprehensive considered the hardness and corrosion resistance, a new type martensitic stainless steel 6Crl5MoV has been developed. The effect of heat treatment processes on microstructure and mechanical properties of 6Crl5MoV martensitic stainless steel is emphatically researched. Thermo-Calc software has been carried out to thermodynamic calculation; OM, SEM and TEM have been carried out to microstructure observation; hardness and impact toughness test have been carried out to evaluate the mechanical properties. Results show that the equilibrium carbide in 6Cr15MoV steel is M2. C6 car- bide, and the M2. C6 carbides finely distributed in annealed microstructure. 6Crl5MoV martensitic stainless steel has a wider quenching temperature range, the hardness value of steel 6Cr15MoV can reach to HRC 60.8 to HRC 61.6 when quenched at 1 060 to 1 100 ℃. Finely distributed carbides will exist in quenched microstructure, and effectively inhabit the growth of austenite grain. With the increasing of quenching temperature, the volume fraction of undis- solved carbides will decrease. The excellent comprehensive mechanical properties can be obtained by quenched at 1 060 to 1 100℃ with tempered at 100 to 150 ℃, and it is mainly due to the high carbon martensite and fine grain size. At these temperature ranges, the hardness will retain about HRC 59.2.to HRC 61.6 and the Charpy U-notch impact toughness will retain about 17.3 to 2. J. A lot of M2.C6 carbides precipitated from martensite matrix, at the same time along the boundaries of martensite lathes which leading to the decrease of impact toughness when tempered at 500 to 540 ℃. The MaC precipitants also existed in the martensite mat

关键词： martensitic stainless steel microstructure mechanical property

The universal fuzzy logical framework of neural circuits and its application in modeling primary visual cortex

在线全文

学校读者我要写书评

暂无评论

Science China(Life Sciences) 2008年第10期51卷 902-912页

作者： HU Hong1, LI Su2. WANG YunJiu2. QI XiangLin2.& SHI ZhongZhi1 1 Key Laboratory of Intelligent Information Processing, institute of computing Technology, Chinese Academy of Sciences, Beijing 100080, China 2.Laboratory of Visual Information Processing, institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China 1. Key Laboratory of Intelligent Information Processing Institute of Computing Technology Chinese Academy of Sciences Beijing 100080 China 2. Laboratory of Visual Information Processing Institute of Biophysics Chinese Academy of Sciences Beijing 100101 China

Analytical study of large-scale nonlinear neural circuits is a difficult task. Here we analyze the function of neural systems by probing the fuzzy logical framework of the neural cells' dynamical equations. Al- though there is a close relation between the theories of fuzzy logical systems and neural systems and many papers investigate this subject, most investigations focus on finding new functions of neural systems by hybridizing fuzzy logical and neural system. In this paper, the fuzzy logical framework of neural cells is used to understand the nonlinear dynamic attributes of a common neural system by abstracting the fuzzy logical framework of a neural cell. Our analysis enables the educated design of network models for classes of computation. As an example, a recurrent network model of the primary visual cortex has been built and tested using this approach.

关键词： nonlinear dynamical system fuzzy logic visual cortex

在线全文

学校读者我要写书评

暂无评论

一个提高机群文件系统吞吐率的方法及其实现

计算机工程与应用 2003年第18期39卷 87-89,99页

作者：胡雨壮孟丹中国科学院计算技术研究所高性能计算机研究室北京100080

随着工作站机群系统的迅猛发展,I/O瓶颈问题也日益严重。性能优良的机群文件系统对机群系统而言至关重要。吞吐率是指在单位时间内所处理的作业数,它是评价系统性能的一个重要指标。论文提出用路径名的多成分查找来提高文件系统的创建... 详细信息

随着工作站机群系统的迅猛发展,I/O瓶颈问题也日益严重。性能优良的机群文件系统对机群系统而言至关重要。吞吐率是指在单位时间内所处理的作业数,它是评价系统性能的一个重要指标。论文提出用路径名的多成分查找来提高文件系统的创建删除吞吐率,给出并在PVFS上实现了一个路径名多成分查找方法。文章的最后对PVFS进行了优化前后的性能比较,并给出了自己的结论。

关键词：机群机群文件系统 Linux PVFS Lookup

Approaches to improving critical current density of YBCO superconducting thick films deposited by electrophoresis

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2004年第2期47卷 165-172页

作者： ZHU Yabin1,2. ZHOU Yueliang2. LIU Zhen2. WANG Shufang2. CHEN Zhenghao2. L?Huibin2. YANG Guozhen2. XIAO Ling3, REN Hongtao3, JIAO Yulei3 & ZHENG Minghui3 1. Department of Physics, College of Science, Beijing Jiaotong University, Beijing 100044, China 2. Laboratory of Optical Physics, institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences, Beijing 100080, China 3. General Research institute for Nonferrous Metals, Beijing 100088, China Correspondence should be addressed to Zhu Yabin (email: ybzhu@***) 1. Department of Physics College of Science Beijing Jiaotong University 100044 Beijing China 2. Laboratory of Optical Physics institute of Physics and Center for Condensed Matter Physics Chinese Academy of Sciences 100080 Beijing China 3. General Research institute for Nonferrous Metals 100088 Beijing China

Fabrication of YBCO superconducting thick films by electrophoresis has been widely reported. However, the value of critical current density (J c) is far from what the practical application requires. The superconducting thick films are obtained using top-seeded melt growth method with different proportional Y2.aCuO5 (Y2.1) addition. high-pressure oxygen has been used in the annealing process to improve the uniformity of the oxygen content in the superconducting thick films. When 40mol% Y2.1 powder is added to the YBa2.u3O7–5 (Y12.) powder,J c for the superconducting thick film by approaches described above reaches 7.008×103 A/cm2.(77 K, 0 T), which is greater than the value ever reported.

关键词： YBCO thick films, electrophoretic deposition, melt-textured.

Transition from platemargin to intraplate environment: Geochemistry of basalts in Paleogene Liaohe basin, northeastern China

在线全文

学校读者我要写书评

暂无评论

Science China Earth Sciences 2005年第12期48卷 2069-2080页

作者： WU Changzhi1, GU Lianxing1, REN Zuowei1,2. ZHANG Zunzhong1, CHEN Zhenyan2.& ZHAO Ming1 1. State Key Laboratory of Mineral Deposit Research (Nanjing University), Department of Earth Sciences, Nanjing University, Nanjing 2.0093, China 2. Exploration and Development Research institute of Liaohe Oilfield Branch Company, PetroChina, Panjin 12.010, China 1. State Key Laboratory of Mineral Deposit Research (Nanjing University) Department of Earth Sciences Nanjing University 210093 Nanjing China 2. Exploration and Development Research institute of Liaohe Oilfield Branch Company PetroChina 124010 Panjin China

Paleogene basalts from the Liaohe basin, northeastern China, are dominated by alkaline olivine basalts and olivine basalts. These basalts are generally enriched in high field strength elements (HFSE), depleted in large ion lithophile elements (LILE) and comparable to those of typical ocean island basalts (OIB). Positive anomalies of Ba, Sr and Zr with high Nb/U, U/Pb, Ce/Pb and Zr/Hf ratios imply that materials from an oceanic crust had been added to the mantle sources of the basalts. In addition, the basalts are generally depleted in Sr, Nd and Pb isotopes, indicating that an enriched mantle (EMI) and a depleted mantle (DM) sources were added to the OIB-like resource. Comprehensive research on lithosphere evolution and tectonic setting of the Liaohe basin and surrounding areas suggests that these basalts were derived by variable degrees of partial melt-ing from an upwelling asthenosphere mantle. Materials from an oceanic lithosphere were added to the source in company with Paleogene tectonic transition from platemargin to intraplate envi-ronment. Retreating and steepening of the subducting Pacific oceanic plate could be the main cause for the tectonic environment transition.

关键词： geochemistry, basalt, Paleogene, Liaohe basin, North China Block, eastern China.

Theoretical and experimental researches on C-band three-cavity transit-time effect oscillator

在线全文

学校读者我要写书评

暂无评论

Science China(Physics,Mechanics & Astronomy) 2004年第3期47卷 310-329页

作者： FAN Zhikai1, LIU Qingxiang1, CHEN Daibing1, TAN Jie1 & ZHOU Haijing2.1. institute of Applied Electronics, Chinese Academy of Engineering Physics, Mianyang 62.900, China 2. institute of Applied Physics and Computational Mathematics, Beijing 100088, China 1. institute of Applied Electronics Chinese Academy of Engineering Physics 621900 Mianyang China 2. institute of Applied Physics and Computational Mathematics 100088 Beijing China

The C-band three-cavity transit-time effect oscillator (3C TTTO) is a novel high power microwave device based on the transit-time effect of the three-cavity (3C) resonator. The operational principle of this device is briefly expounded in this paper, and the theoretical and experimental researches on the radial insulation diode, the 3C resonator, the double-gap output cavity and the circular waveguide bevel cut radiation antenna are presented in detail. By using the analytic method, the eigen modes and their field distributions of the 3C resonator are developed, and some basic laws of the transit-time effect are obtained in non-π mode field of the 3C resonator. At last, the experimental results are given. This device generated RF peak power in excess of 400MW with 15ns FWHM, and its beam-wave power conversion efficiency is about 17%.

关键词： C-band, three-cavity (3C) resonator, transit-time effect, high power microwave, oscillator.

Manufacture of Raney Ni catalyst with metastable Ni_2.l_3 by high energy milling

在线全文

学校读者我要写书评

暂无评论

中国有色金属学会会刊：英文版 1999年第3期9卷 562-565页

作者： Teng Ronghou(滕荣厚) 1, Sun Shijie(孙世杰) 1, Liu Silin(刘思林) 1, Liu Xuequan(柳学全) 1, Ma Ruzhang(马如璋) 2.Liu Tao(刘涛) 3 1. Functional Materials institute, Central Iron & Steel Research institute, Beijing 100081, P.R.China 2. Depar Cent Iron & Steel Res Inst Funct Mat Inst Beijing 100081 Peoples R China Univ Sci & Technol Beijing Dept Mat Phys Beijing 100083 Peoples R China Chinese Acad Sci Inst High Energy Phys Beijing Synchrotron Radiat Facil Beijing 100039 Peoples R China

The Ni Al alloy containing Cr, Fe additives were prepared as Raney Ni catalyst by high energy milling. The size and surface state of Ni Al alloy powder were studied by particle size analyzer and sanning electron microscopy, the structure was analyzed by XRD and Mssbauer methods. The results showed that after a high energy milling (HEM), the Ni Al alloy transforms to a nano scale NiAl structure with rich Al. By annealing the alloy, a metastable Ni 2.l 3 phase can be obtained.

关键词： Raney nickel catalyst nano crystal high energy milling

Analysis on the decadal scale variation of the dust storm in North China

在线全文

学校读者我要写书评

暂无评论

Science China Earth Sciences 2005年第12期48卷 2260-2266页

作者： KANG Dujuan1,2.& WANG Huijun1 1. NZC/LASG, institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100871, China 2. Environmental Fluid Mechanics Laboratory, Stanford University, Stanford CA 94305, USA 1. NZC/LASG Institute of Atmospheric Physics Chinese Academy of Sciences 100871 Beijing China 2. Environmental Fluid Mechanics Laboratory Stanford University 94305 Stanford CA USA

In this paper, the temporal variation characteristics of the dust storm in North China are investigated. Based on power spectrum analysis and wavelet analysis, 1956-1970 and 1985-1999 are chosen as the high-frequency and low-frequency dust storm decades respectively. Analysis results clearly show that the spring and wintertime anomalous atmospheric circulation between these two dec-ades are significantly different. Compared with the former decade, there are a strengthened polar vortex, enhanced westerlies near 50°N, and a weak East Asian major though in the winter of the latter decade. The north and center parts of the Siberian high and the Aleutian low become weak. The southerly and easterly wind anomalies appear over the north and east parts of China, which implies the weakening of East Asian winter monsoon. Meanwhile, northern China experiences warmer winters and wetter springs, which are in favor of the weakening of dust storm intensity in North China. There are significant out-of-phase relationships between dust frequency and wintertime westerly intensity, as well as between dust frequency and Arctic Oscillation. It is also found that the frequency of dust weather is strongly re-lated to winter-springtime East Asian monsoon intensity.

关键词： dust storm, climate anomaly, decadal scale variability, East Asian monsoon, AO.