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The evolution and morphological stability of a spherical crystal

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Science China(Technological Sciences) 2008年第3期51卷 225-243页

作者： ChEN MingWen1,2, WANG ZiDong2 & XU JianJun3,4 1 School of Applied Sciences, university of Science and Technology Beijing, Beijing 100083, China 2 School of Materials Science and Engineering, university of Science and Technology Beijing, Beijing 100083, China 3 School of Mathematical Sciences, Nankai university, Tianjin 300071, China 4.department of mathematics and statistics, mcgill university, montreal h3. 2k6, canada School of Applied Sciences University of Science and Technology Beijing Beijing China School of Materials Science and Engineering University of Science and Technology Beijing Beijing China School of Mathematical Sciences Nankai University Tianjin China department of mathematics and statistics McGill University Montreal Canada

The growth model of a spherical crystal in the undercooled melt including the surface energy, interfacial kinetics and convective flow is established. The effect of the convective flow induced by a small far field flow on the evolution and morphological stability of the interface of the spherical crystal is studied. The interface shape of the spherical crystal, which is affected by the far field flow, and the dispersion relation of the growth rate of amplitude of the perturbed interface are derived. It is shown that the convection induced by the far field flow makes the interface of the growing spherical crystal further grow in the upstream direction of the far field flow and inhibit growth in the downstream direction; the interface of the decaying spherical crystal further decays in the upstream direction and inhibits decay in the downstream direction. The theoretical result suggests that both the growth of the sphere in the upstream direction and the decay of the sphere in the downstream direction make the spherical crystal tend to evolve into an oval; the morphological stability of the interface depends on a certain radius R c such that the spherical crystal is unstable when its radius is greater than R c and stable when its radius is less than R c . The surface energy and interfacial kinetics have strong stabilizing effects on the growth of the spherical crystal. In the meantime interfacial kinetics is a table factor of the interface when the interface of the sphere is growing; it is an unstable factor of the interface when the interface is decaying.

关键词： solid-liquid interface spherical crystal convective flow crystal growth morphological stability

Study on the alkylation reaction of guanine and N-acetylguanine and the synthesis of 1'-C alkylated carba-DhPG analogues

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Chinese Journal of Chemistry 1994年第1期12卷 85-94页

作者： LIU, Yu-Gang FEI, Chang-PeiInstitute of Chemistry, Chinese Academy of Sciences, Beijing 100080, ChinaChAN, Tak-hangdepartment of Chemistry, mcgill university, montreal, PQ, canada h3. 2k6 Institute of Chemistry Chinese Academy of Sciences Beijing 100080 China department of Chemistry McGill University Montreal PQ Canada H3A 2K6

The alkylation reaction of guanine and N-acetylguanine with model compounds such as isopropyl bromide or 4-heptyl tosylate were studied. The reaction conditions such as temperature, solvent, base, and catalyst were examined for their effects on the reaction rate, and the yield and regioselectivity of the coupling reaction. The highest yield was obtained by using DMSO as the solvent. The reaction proceeded in a homogenous manner to give higher yield of 9-N and 7-N substituted product in a mole ratio of 1:1. The ratio could be raised to 2:1 if dibenzo-18-crown-6 was used as a catalyst. Using the above procedure, three carba-DhPG analogues bearing different 1'-C alkyl side chains were synthesized.

关键词： Acyclonucleoside alkylation N-acetylguanine carba-DhPG.

Methane Dynamics in Northern Peatlands: A Review

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Pedosphere 2009年第4期19卷 409-421页

作者： D. Y. F. LAI department of Geography McGill University

Northern peatlands store a large amount of carbon and play a significant role in the global carbon cycle. Owing to the presence of waterlogged and anaerobic conditions, peatlands are typically a source of methane (Ch4), a very potent greenhouse gas. This paper reviews the key mechanisms of peatland Ch4 production, consumption and transport and the major environmental and biotic controls on peatland Ch4 emissions. The advantages and disadvantages of micrometeorological and chamber methods in measuring Ch4 fluxes from northern peatlands are also discussed. The magnitude of Ch4 flux varies considerably among peatland types (bogs and fens) and microtopographic locations (hummocks and hollows). Some anthropogenic activities including forestry, peat harvesting and industrial emission of sulphur dioxide can cause a reduction in Ch4 release from northern peatlands. Further research should be conducted to investigate the in fluence of plant growth forms on Ch4 flux from northern peatlands, determine the water table threshold at which plant production in peatlands enhances Ch4 release, and quantify peatland Ch4 exchange at plant community level with a higher temporal resolution using automatic chambers.

关键词： global carbon cycle greenhouse gas methane oxidation methanogenesis methanotrophy

REMARk ON CRITICAL SPEED OF TRAVELING WAVEFRONTS FOR NIChOLSON'S BLOWFLIES EQUATION WITh DIFFUSION

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Acta Mathematica Scientia 2010年第5期30卷 1561-1566页

作者：危地吴教育梅铭 department of Information and Computation Nanchang Hangkong University School of Computer Engineering and Technology Guangdong Institute of Science and Technology department of mathematics Champlain College Saint-LambertSaint-Lambert department of mathematics and statistics McGill University

This note is devoted to the son＇s blowflies equation with diffusion, a critical speed of traveling waves, we give behavior with respect to the mature age study on the traveling wavefronts to the Nicholtime-delayed re... 详细信息

关键词： Nicholson's blowflies equation traveling wavefronts critical wave-speed

Minimal regular 2-graphs and applications

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Science China mathematics 2006年第2期49卷 158-172页

作者： FAN hongbing, LIU Guizhen & LIU Jiping department of Physics and Computer Science, Wilfrid Laurier university, Waterloo, ON., N2L 3C5 canada School of mathematics and System Science, Shandong university, Jinan 250100, China department of mathematics and Computer Science, university of Lethbridge, Lethbridge, AB., T1k 3M4, canada department of Physics and Computer Science Wilfrid Laurier University Waterloo Canada School of mathematics and System Science Shandong University Jinan China department of mathematics and Computer Science University of Lethbridge Lethbridge Canada

A 2-graph is a hypergraph with edge sizes of at most two. A regular 2-graph is said to be minimal if it does not contain a proper regular factor. Let f2(n) be the maximum value of degrees over all minimal regular 2-graphs of n vertices. In this paper, we provide a structure property of minimal regular 2-graphs, and consequently, prove that f2(n) = n+3-i/3, where 1 ≤ i ≤ 6, i ≡ n (mod 6) and n ≥ 7, which solves a conjecture posed by Fan, Liu, Wu and Wong. As applications in graph theory, we are able to characterize unfactorable regular graphs and provide the best possible factor existence theorem on degree conditions. Moreover, fa(n) and the minimal 2-graphs can be used in the universal switch box designs, which originally motivated this study.

关键词： graph regular factor 2-graph switch box design.

A conjecture on k-factor-critical and 3-γ-critical graphs

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Science China mathematics 2010年第5期53卷 348-354页

作者： WANG Tao1&YU QingLin2 1Institute of Applied mathematics,College of mathematics and Information Science,henan university,kaifeng 475001,China 2department of mathematics and statistics,Thompson Rivers university,kamloops,BC V2C5N3,canada Institute of Applied mathematics College of Mathematics and Information Science Henan University Kaifeng China department of mathematics and statistics Thompson Rivers University Kamloops Canada

For a graph G =(V,E),a subset VS is a dominating set if every vertex in V is either in S or is adjacent to a vertex in *** domination number γ(G) of G is the minimum order of a dominating set in G.A graph G is said to be domination vertex critical,if γ(G-v) h G is domination edge critical,if γ(G ∪ e) h G k-γ-vertex-critical(resp.k-γ-edge-critical) if it is domination vertex critical(*** edge critical) and γ(G) = *** and Plummer posed the conjecture:Let G be a k-connected graph with the minimum degree at least k+1,where k 2 and k≡|V|(mod 2).If G is 3-γ-edge-critical and claw-free,then G is *** this paper we present a proof to this conjecture,and we also discuss the properties such as connectivity and bicriticality in 3-γ-vertex-critical claw-free graph.

关键词： domination critical graph factor critical bicritical

Smoothness for the collision local times of bifractional Brownian motions

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Science China mathematics 2011年第9期54卷 1859-1873页

作者： ShEN GuangJun 1,2,& YAN LiTan 3 1 department of mathematics,East China university of Science and Technology,Shanghai 200237,China 2 department of mathematics,Anhui Normal university,Wuhu 241000,China 3 department of mathematics,Donghua university,Shanghai 201620,China department of mathematics East China University of Science and Technology Shanghai China department of mathematics Anhui Normal University Wuhu China department of mathematics Donghua University Shanghai China

Let B^hi,ki ={ Bt^hi,ki, t ≥ 0}, i= 1, 2 be two independent bifractional Brownian motions with respective indices hi ∈ （0, 1） and k∈ E （0, 1]. One of the main motivations of this paper is to investigate f0^Tδ（Bs^h1 ,k1 - the smoothness of the collision local time, introduced by Jiang and Wang in 2009, IT = f0^T δ（Bs^h1,k1）ds, T 〉 0, where 6 denotes the Dirac delta function. By an elementary method, we show that iT is smooth in the sense of the Meyer-Watanabe if and only if min{h-1k1, h2k2} 〈-1/3.

关键词： bifractional Brownian motion collision local time intersection local time chaos expansion

Jackknifed random weighting for Cox proportional hazards model

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Science China mathematics 2012年第4期55卷 775-786页

作者： LI Xiao 1 ,WU Yaohua 2,& TU DongSheng 1 1 Cancer Research Institute,Queen’s university,kingston,Ontario k 7L 3N6,canada 2 department of Finance and statistics,university of Science and Technology of China,hefei 230026,China Cancer Research Institute Queen’s University Kingston Canada department of Finance and statistics University of Science and Technology of China Hefei China

The Cox proportional hazards model is the most used statistical model in the analysis of survival time ***,a random weighting method was proposed to approximate the distribution of the maximum partial likelihood estimate for the regression coefficient in the Cox *** method was shown not as sensitive to heavy censoring as the bootstrap method in simulation studies but it may not be second-order accurate as was shown for the bootstrap *** this paper,we propose an alternative random weighting method based on one-step linear jackknife pseudo values and prove the second accuracy of the proposed *** Carlo simulations are also performed to evaluate the proposed method for fixed sample sizes.

关键词： Cox proportional hazards model jackknife random weighting second-order accuracy simulations survival data

STABILITY OF INTERNATIONAL ENVIRONMENTAL AGREEMENTS IN LEADERShIP MODEL

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Journal of Systems Science & Complexity 2008年第2期21卷 184-190页

作者： Jin ZhANG Shouyang WANG Lei ZU department of Economics McGill University Montreal Quebec H3A 2T7 Canada School of Management Graduate University of Chinese Academy of Sciences Beijing 100080 China

International Environmental Agreements （IEAs） are a form of cooperation ratified by countries which can improve the management of shared environmental resources. The authors analyze the stability of International Eavironmental Agreements in leadership model. In 2006, Diamantoudi ＆ Sartzetakis found that a stable coalition consists of either 2, 3, or 4 members if the number of countries is greater than 4. Their model is reconsidered. It is shown that the size of stable IEAs decreases from 3 to 2 when the total number of countries involved increases. however, a situation that can guarantee 4 to be the size of stable IEAs could not be found.

关键词： Coalition International Environmental Agreements leadership model sequential game stable size.