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Chinese Science Bulletin 2003年第17期48卷 1853-1856页

作者： LIU Hongyan, TIAN Yuhong & DING Deng department of Ecology, College of Environmental Sciences, peking university, beijing 100871, china department of Ecology College of Environmental Sciences Peking University Beijing 100871 China

Different land cover types in Otindag Sandy Land and Bashang area of Hebei Province are linked to a material source of sand stormy weather in beijing based on results of field vegetation and soil survey and laboratory works. Results of grain size analysis show that dust release potential in per unit area of moving sandy land is small, while lowland meadow and meadow steppe in stony hills have high potential of releasing dusts in per unit area during sand stormy weather occurrence. Further considering the effects of vegetation, it is inferred that the moving sandy land served as a material source of past dust storm and the possi-bility of dust release in per unit area is low in current time. Typical steppe in stony hills is undergoing desertification and its dust release possibility in per unit area is high. Farmland has strong potential of release dusts when they are ploughed in spring, but a large amount of therophytes grow and thus prevent dusts from release when cultivation was terminated. Potentials of dust release in per unit area in fixed sand dunes, stony mountain meadow steppe and lowland meadow are low due to high cover of perennials. Sand dune reactivation and desiccation of lakes and lowlands under estimated future climatic change will make them serve as a future material source of sand stormy weather.

关键词：河北北京沙暴土地覆盖砂地坝上地区材料源

On the evolution and histology of some Cambrian protoconodonts, paraconodonts and primitive euconodonts

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Science china Earth Sciences 2004年第7期47卷 577-584页

作者： DONG Xiping department of Geology, peking university, beijing 100871, china Laboratory of Palaeobiology & Stratigraphy, Nanjing Institute of Ge-ology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, china 1. department of Geology Peking University 100871 Beijing China 2. Laboratory of Palaeobiology & Stratigraphy Nanjing Institute of Geology and Palaeontology Chinese Academy of Sciences 210008 Nanjing China

Previous reports on the morphological evolution of protoconodonts and paraconodonts are reviewed. The evolutionary trends exhibited by species of the protoconodont genus Gapparodus and the paraconodont genus Westergaadodina are discussed. Based on the present study on histology, genus Paibiconus is protoconodont, while genus Yongshunella is paraconodont (fig. 1 (a)). However, the nature of Huayuanodontus has not been fully understood so far. Recently, the transitional form New Gen. Sensu Miller, 1980 of late Late Cambrian has been found in Hunan Province, South china. It is considered as the Sister-Group of Proconodontus. Moreover, another kind of transitional form of middle Late Cambrian and late Late Cambrian between Prooneotodus notundatus and Pnoconodontus, which looks like Prooneotodus notundatus in gross morphology, but has anterior and posterior costae, has also been found in Hunan, South china. This kind of transitional form is believed to be probably the real intermediate link between Prooneotodus rotundatus and Pnoconodontus, and Prooneotodus rotundatus is most probably the ancestor of Proconodontus. The two transitional forms noted above are all euconodonts by the study of their histology. Unlike the euconodonts of Post-Cambrian, the evolutionary relationships among the species of protoconodonts, paraconodonts and the primitive euconodonts could not be made clear without the histological study on them.

关键词： protoconodonts, paraconodonts, evolution, histology, Cambrian.

User-experience-based availability analysis model and its application in P2P storage systems

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Science china(Information Sciences) 2011年第8期54卷 1585-1595页

作者： WU Yu, YANG Zhi,QU Zhi, XIAO Zhen & DAI YaFei department of Computer Science,peking university,beijing {4.,china 1. department of Computer Science Peking University Beijing 100871 China

Data availability is one of the most important properties of peer-to-peer (P2P) storage *** analysis model and data placement are two key design *** in P2P storage system are both providers and *** characteristic determines that the availability analysis must be user-centric,and thereby enhance the quality of service and decrease the system *** popular approach in recent studies is simple random placement with steady-state model,which has the following drawbacks:1) It ignores the up/down patterns of nodes,whose availability is over-estimated or under-estimated at different periods of time.2) It ignores the access patterns of users,so the availability perceived by users is hard to evaluate precisely.3) It ignores the huge difference of nodes’ availability, thus leading to the absence of incentive. This paper proposes a novel user-experience-based availability model, which evaluates the availability of P2P storage system in terms of user experience,which can degenerate to traditional availability analysis model. Based on the new model,this paper proposes decentralized data placement algorithms for two typical P2P storage applications:"data sharing"and"personal backup".By the trace-driven simulation, we prove that our methods can enhance the availability perceived by users greatly,reduce the variance of the availability dramatically and eliminate the nodes with low availability in data-sharing applications;meanwhile,it can provide different-level service to encourage users according to their contributions.

关键词： P2P storage user experience availability data replacement

Representation of Integers by Ternary Quadratic Forms

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Acta Mathematica Sinica,English Series 2001年第4期17卷 715-720页

作者： De Lang LI Chun Lai ZHAO department of Mathematics, Sichuan university, Chengdu 610064. P. R. china department of Mathematics,{4., beijing 100871, P. R. china 四川大学数学系四川成都北京大学数学系北京

In this paper we give a formula for the number of representations of some square-free integers by certain ternary quadratic forms and estimate the lower bound of the 2-power appearing in this number.

关键词： Congruent elliptic curve Tate-Shafarevich group Modular form Class number

Improvement of Selectivity with Boric Acid in Separating Phenolic Acids by Capillary Zone Electrophoresis

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Chinese Chemical Letters 1998年第1期9卷 87-91页

作者： Hong LONG Ai Jin HUANG Yi Liang SUN(department of Chemistry, peking university, beijing 100871) peking Univ Dept Chem Beijing 100871 Peoples R China

It was shown that in capillary electrophoresis (CE) the addition of boric acid as a complexing agent in phosphate buffer can modulate the separation selectivity of phenolic acids.

关键词： capillary electrophoresis boric acid separation phenolic acid

The Middle Devonian Bimodal Association of Volcanic Rocks in the Northern Area of East Junggar, Xinjiang

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Acta Geologica Sinica(English Edition) 1992年第2期66卷 141-153页

作者： Han Baofu department of Geology, peking university, beijing department of Geology Peking University Beijing

The Middle Devonian volcanic rocks in the northern area of East Junggar, located between the Ertix andUlungur rivers of northern Xinjiang, may be divided into basic and acid ones. It is evident that a compositionalgap exists between the two groups so that the volcanic rocks are not in line with a calc-alkaline series becausethe intermediate rocks are absent in the area. The fact shows that the volcanic rocks are a typical bimodal asso-ciation. The formation of the bimodal association of volcanic rocks in the area was closely related to continen-tal rifting or continental extension in the Middle Devonian. In such a tectonic setting, magmas were first pro-duced by partial melting of the mantle. Where crustal thinning was greater, the magmas ascended and eruptedon the surface directly so that the basic volcanic rocks formed, but olivine and/or partial pyroxenefractionation occurred in the magmas during their ascent through the thinning crust. On the other hand, wherecrustal thinning was less, ascending mantle-derived magmas reached the lower crust and accumulated there, re-sulting in partial melting of the lower crust and thus giving rise to the contaminated magma which was consoli-dated as acid volcanic rocks on the surface.

关键词： rock REE area The Middle Devonian Bimodal Association of Volcanic Rocks in the Northern Area of East Junggar Xinjiang

Study of Photostimulable Luminescence Materials Sr_9Ca(PO_4._6Cl_2:Eu

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Rare Metals 1989年第4期9卷 49-53页

作者： Song Qingfang china Criminal Police Institute,Shenyang 110035Wang Yanji Zhao Wei Su Mianzeng department of Chemistry,peking university,{4. 100871 china Criminal Police Institute 辽宁沈阳北京大学北京

The polycrystalline Sr_9Ca(PO_4._6Cl_2:Eu has been synthesized by solid state *** reaction condition,the appropriate raw materials and their quantity used,which may affect the photostimulable luminescence (PSL),have been systematically inves- *** properties of this PSL phosphor as a material for storing and reproducing the X-ray image in computer-aided radiography have been reported briefly.

关键词： Eu PO4 Study of Photostimulable Luminescence Materials Sr9Ca Sr Cl

The effects of shock wave and quasi-traveling wave in the mechanical impact test

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Science china(Technological Sciences) 2010年第9期53卷 2535-2541页

作者： WU Mei1,5,SUN ZhongFeng2,ZHANG LuMei3,CHEN Yong1 & JI LinHong4.1 Institute of High Energy Physics,Chinese Academy of Sciences,beijing 10004.,china 2 School of Mathematical Sciences,peking university,beijing 100871,china 3 High School of Central university for Nationalities,beijing 100081,china 4.Institute of Mechanical Design,department of Precision Instruments and Mechanology,Tsinghua university,beijing 100084.china 5 Academy of Opto-electronics,Chinese Academy of Sciences,beijing 100190,china 1. Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China5. Academy of Opto-electronics Chinese Academy of Sciences Beijing 100190 China2. School of Mathematical Sciences Peking University Beijing 100871 China3. High School of Central University for Nationalities Beijing 100081 China4. Institute of Mechanical Design Department of Precision Instruments and Mechanology Tsinghua University Beijing 100084 China

It is well-known that the numerical value is always larger than the measured value,amounting to many times,if we calculate the stress of the specimen in the impulse test using the NASTRAN and ANSYS (N-A) *** believe that the impact induces shock wave or quasi-traveling wave in the specimen,which can qualitatively explain the discrepancy of the two *** order to verify it,the Lax-Friedrichs (L-F) scheme is taken to simulate the transmission of shock wave and quasi-traveling wave in *** results show that the action area of the stress wave is small and the action time is very short,so the resulting stress and actual work are not *** addition,the distribution of the impact values obtained by the numerical simulation is in accordance with the trend of the measured impact values.

关键词： aerospace environment test shock wave quasi-traveling wave

INTERACTION BETWEEN Cu AND LIQUID Sn(II)——SEM OBSERVATION OF INTERMETALLIC GROWTH

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Acta Metallurgica Sinica(English Letters) 1993年第8期6卷 81-86页

作者： ZHANG Qiyun LIU Shuqi XU Yaping peking university,beijing,china professor,department of Chemistry,{4. university,beijing,100871,china

The features of Cu_6Sn_5 growing slowly at lower temperature and growing rapidly up over 350℃,and or Cu_3Sn growing at higher temperatures,bave been detailedly observed under *** increase of Pb content seems to inhib... 详细信息

关键词： Cu liquid Sn Cu_6Sn_5 Cu_3Sn lead wire solderability

MORPHOLOGICAL TRANSITION BETWEEN VESICLES AND TUBULES FOR A GLYCOPOLYMER-CONTAINING AMPHIPHILIC DIBLOCK COPOLYMER IN AQUEOUS SOLUTIONS

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Chinese Journal of Polymer Science 2001年第3期19卷 297-301页

作者： Zi-chen Li Yue Shen Yu-zeng Liang Fu-mian Li department of Polymer Science & Engineering College of Chemistry peking university beijing 100871, china beijing Univ Coll Chem Dept Polymer Sci & Engn Beijing 100871 Peoples R China

The morphological transition of molecular assemblies in aqueous solutions for a new amphiphilic diblock copolymer induced by changing the initial solvent conditions was studied by transmission electron microscopy (TEM). The copolymer was polystyrene(77)-b-poly[2-(beta -D-glucopyranosyloxy)ethyl acrylate (6)] (PSt(77)-b-PGEA(6)) and the solvent was a mixture of DMF and THF. PSt(77)-b-PGEA(6) yields vesicles and tubules when it is initially dissolved in THF and DMF respectively. The morphological transition between vesicles and tubules can be achieved by simply varying the amounts of THF and DMF, or changing the temperature at which the aggregates were prepared.

关键词： block copolymer amphiphile glycopolymer self-assembly tubule vesicle