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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 h3a 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.

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 h3a 2k6, canada School of Applied Sciences University of Science and Technology Beijing School of Materials Science and Engineering Nankai university

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

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

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.

ON MAXIMUM NORM ESTIMATES FOR RITZ-VOLTERRAPROJECTION WITh APPLICATIONS TO SOME TIME DEPENDENT PROBLEMS

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Journal of Computational mathematics 1997年第2期15卷 159-178页

作者： Y.P. Lin(department of mathematics university of Alberta Edmonton, Alberta T6G 2G1 canada) Univerisity of Alberta Edmonton 加拿大

The stability in L∞-norm is considered for the Ritz-Volterra projection and some applications are presented in this paper. As a result, point-wise error estimates are established for the finite element approximation for the parabolic integrodifferential equation, Sobolev equations, and a diffusion equation with non-local boundary value problem.

关键词： Math ON MAXIMUM NORM ESTIMATES FOR RITZ-VOLTERRAPROJECTION WITh APPLICATIONS TO SOME TIME DEPENDENT PROBLEMS

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.

Numerical modeling of the transmission dynamics of drug-sensitive and drug-resistant hSV-2

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Communications in Nonlinear Science and Numerical Simulation 2001年第1期6卷 23-27页

作者： A. B. GUMEL(department of mathematics, university of Manitoba, Winnipeg, Manitoba, R3T 2N2, canada ) department of mathematics University of Manitoba Winnipeg Manitoba R3T 2N2 Canada

A competitive finite-difference method will be constructed and used to solve a modified deterministic model for the spread of herpes simplex virus type-2 (hSV-2) within a given population. The model monitors the transmission dynamics and control of drug-sensitive and drug-resistant hSV-2. Unlike the fourth-order Runge-kutta method (Rk4), which fails when the discretization parameters exceed certain values, the novel numerical method to be developed in this paper gives convergent results for all parameter values.

关键词： hSV-2 finite-difference initial-value problem numerical instabilities positivity

hierarchical linear regression models for conditional quantiles

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Science China mathematics 2006年第12期49卷 1800-1815页

作者： TIAN Maozai & ChEN Gemai School of statistics, Renmin university of China, Beijing 100872, China and Center for Applied statistics, Renmin university of China, Beijing 100872, China department of mathematics and statistics, university of Calgary, canada School of statistics Renmin University of China Beijing China Center for Applied statistics Renmin University of China Beijing China department of mathematics and statistics University of Calgary Canada

The quantile regression has several useful features and therefore is gradually developing into a comprehensive approach to the statistical analysis of linear and nonlinear response models,but it cannot deal effectively with the data with a hierarchical *** practice,the existence of such data hierarchies is neither accidental nor ignorable,it is a common *** ignore this hierarchical data structure risks overlooking the importance of group effects,and may also render many of the traditional statistical analysis techniques used for studying data relationships *** the other hand,the hierarchical models take a hierarchical data structure into account and have also many applications in statistics,ranging from overdispersion to constructing min-max ***,the hierarchical models are virtually the mean regression,therefore,they cannot be used to characterize the entire conditional distribution of a dependent variable given high-dimensional ***,the estimated coefficient vector (marginal effects)is sensitive to an outlier observation on the dependent *** this article,a new approach,which is based on the Gauss-Seidel iteration and taking a full advantage of the quantile regression and hierarchical models,is *** the theoretical front,we also consider the asymptotic properties of the new method,obtaining the simple conditions for an n1/2-convergence and an asymptotic *** also illustrate the use of the technique with the real educational data which is hierarchical and how the results can be explained.

关键词： hierarchical quantile regression models,EQ algorithm,fixed effects,random effects,regression quantile.