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Analysis on background magnetic field to generate eddy current by pulsed gradient of permanent-magnet MRI

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Science china(Technological Sciences) 2010年第4期53卷 886-891页

作者： ZU DongLin,HONG LiMing,CAO XueMing & TANG Xin Institute of Heavy Ion physics,beijing City Key Laboratory of Medical physics and Engineering,school of physics,peking university,beijing 100871,china Institute of Heavy Ion physics Beijing City Key Laboratory of Medical Physics and Engineering School of Physics Peking University

In this paper the analytical expressions for the magnetic field H and induction B in iron-pole plates generated by MRI gradient coil are given using line-current and the multilayer dielectric plate model with the mirror-image *** current emanates from the magnetic flux in the iron-pole *** order to fully suppress the eddy current,this magnetic flux should be fully *** research results indicate the magnetic permeability of the resist-eddy plate must be bigger than that of magnetic pole material,*** iron,and that the resist-eddy plate should be thick enough to be far away from its magnetic saturation.

关键词： MRI suppress eddy current gradient coil resist-eddy plate mirror-image method

Finite Groups in Which Sylow Normalizers Admit Supplements

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Acta Mathematica Sinica,English Series 2007年第3期23卷 417-422页

作者： Tian Ze LI school of Mathematical Sciences,peking university,beijing 100871,P.R.china school of Mathematical Sciences Peking University Beijing 100871 P. R. China

For a group G and a subgroup M of G,we say that a subgroup A of G is a supplement toM in G,if G=*** prove that a finite group in which every Sylow normalizer admits a nilpotentsupplement is *** particular we confirm a... 详细信息

关键词： Sylow normalizer Supplement Wreath product

The lifting scheme of 4-channel orthogonal wavelet transforms

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Progress in Natural Science:Materials International 2006年第1期16卷 100-104页

作者： PENG Lizhong and CHU Xiaoyong (LMAM, school of Mathematical Sciences, peking university, beijing 100871, china) LMAM School of Mathematical Sciences Peking University Beijing 100871 China

The 4-channel smooth wavelets with linear phase and orthogonality are designed from the 2-channel orthogonal wavelets with high transfer vanishing moments. Reversely, for simple lifting scheme of such 4-channel orthogonal wavelet transforms, a new 2-channel orthogonal wavelet associated with this 4-channel wavelet is constructed. The new 2-channel wavelet has at least the same number of vanishing moments as the associated 4-channel one. Finally, by combining the two such 2-channel wavelet systems, the lifting scheme of 4-channel orthogonal wavelet transform, which has simple structure and is easy to apply, is presented.

关键词： lifting scheme 4-channel orthogonal wavelet 2-channel orthogonal wavelet vanishing moment transfer vanishing moment linear phase.

The localization of 1-cohomology of transitive Lie algebroids

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Science china Mathematics 2006年第2期49卷 277-288页

作者： CHEN Zhuo & LIU Zhangju Department of Mathematics, Capital Normal university, beijing 100037, china school of Mathematical Science, peking university, beijing 100871, china Department of Mathematics Capital Normal University Beijing China school of Mathematical Science Peking University Beijing China

For a transitive Lie algebroid A on a connected manifold M and its representation on a vector bundle F, we define a morphism of cohomology groups rk: Hk(A,F) → Hk(Lx,Fx), called the localization map, where Lx is the adjoint algebra at x ∈ M. The main result in this paper is that if M is simply connected, or H (LX,FX) is trivial, then T is injective. This means that the Lie algebroid 1-cohomology is totally determined by the 1-cohomology of its adjoint Lie algebra in the above two cases.

关键词： transitive Lie algebroid representation cohomology localization.

OBLIQUE DERIVATIVE PROBLEMS FOR SECOND ORDER NONLINEAR MIXED EQUATIONS WITH DEGENERATE LINE

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Acta Mathematica Scientia 2008年第3期28卷 604-612页

作者：闻国椿 school of Mathematical Sciences Peking University

The present article deals with oblique derivative problems for some nonlinear mixed equations with parabolic degeneracy, which include the Tricomi problem as a special case. First, the formulation of the problems for the equations is given; next, the representation and estimates of solutions for the above problems are obtained; finally, the existence of solutions for the problems is proved by the successive iteration and the compactness principle of solutions of the problems. In this article, the author uses the complex method, namely, the complex functions in the elliptic domain and the hyperbolic complex functions in hyperbolic domain are used.

关键词： Oblique derivative problems nonlinear mixed equations parabolic degeneracy

r-matrix and algebraic-geometric symplectic map

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Chinese Science Bulletin 1999年第2期44卷 114-118页

作者： QIAO ZhijunInstitute of Mathematics and school of Mathematical Sciences, peking university, beijing 100871, china Institute of Mathematics and school of Mathematical Sciences Peking University Beijing China

A new Lax matrix is introduced for the integrable symplectic map (ISM), and the non-dynamical(i. e. constant) r-matrix of ISM is obtained. Moreover, an effective approach is systematically presented to construct the explicit solution(here, the explicit solution means algebraic-geometric solution expressed by the Riemann-Theta function) of a soliton system or nonlinear evolution equation from Lax matrix, r-matrix, and the theory of nonlinearization through taking the Toda lattice as an example. The given algebraic-geometric solution of the Toda lattice is almost-periodic and includes the periodic and finite-band solution.

关键词： symplectic map r-matrix algebraic-geometric solution.

Magnetic moments of ^(33)Mg in the time-odd relativistic mean field approach

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Science china(physics,Mechanics & Astronomy) 2009年第10期52卷 1586-1592页

作者： LI Jian1,ZHANG Ying1,YAO JiangMing1 & MENG Jie1,2 1 school of physics,State Key Laboratory of Nuclear physics and Technology,peking university,beijing 100871,china 2 school of physics and Nuclear Energy Engineering,Beihang university,beijing 100191,china school of physics State Key Laboratory of Nuclear Physics and Technology Peking University Beijing China school of physics and Nuclear Energy Engineering Beihang University Beijing China

The configuration-fixed deformation constrained relativistic mean field approach with time-odd component has been applied to investigate the ground state properties of 33Mg with effective interaction *** ground state of 33Mg has been found to be prolate deformed,β2=0.23,with the odd neutron in 1/2[330] orbital and the energy -251.85 MeV which is close to the data -252.06 *** magnetic moment -0.9134 μN is obtained with the effective electromagnetic current which well reproduces the data -0.7456 μN self-consistently without introducing any *** energy splittings of time reversal conjugate states,the neutron current,the energy contribution from the nuclear magnetic potential,and the effect of core polarization are discussed in detail.

关键词： magnetic moment binding energy time-odd component configuration-fixed deformation constrained calculation relativistic mean field theory

Identifying the northernmost summer monsoon location in East Asia

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Progress in Natural Science:Materials International 2007年第7期17卷 812-820页

作者： Hu Haoran~1 Qian Weihong~(2**) (1.Institute of Plateau Meteorology,CMA,Chengdu 610071,china 2.Monsoon and Environment Research Group,school of physics,peking university,beijing 100871,china) Institute of Plateau Meteorology CMAChengdu 610071 China

An integrated index which can be used to indicate the advance of subtropical summer monsoon in East Asia has been proposed in this *** index was comhined by three variables including precipitation,wind and pseudo-equivalent potential tempera- *** northernmost summer monsoon location(NSML)was identified by using this index *** was found that the NSML ex- perienced an interdecadal shift in the period 1977—1979 based on the annual index analysis from 1961 to 2001.A comparison of the NSML with other four summer monsoon indices has also been *** result showed that the NSML could well represent the interan- nual and interdecadal variability of summer monsoon precipitation in North china(beyond 35°N),while other four indices could well indi- cate the precipitation anomalies of East Asian summer monsoon along the Yangtze River valley(around 30°N).

关键词： subtropical summer monsoon northernmost location index,interdecadal variability East Asia

Dynamics of DNA in vitro evolution

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Progress in Natural Science:Materials International 2009年第2期19卷 137-144页

作者： Xiaojing Yang 1,Xili Liu 1,Chunbo Lou,Qi Ouyang Center for Theoretical Biology,school of physics,peking university,beijing 100871,china Center for Theoretical Biology School of Physics Peking University Beijing 100871 China

In vitro evolution has become a very important research area in recent years. From a practical point of view,it provides a powerful and reliable tool for engineering functional molecules (DNA,RNA or proteins) in reasonably short periods of time. From a theoretical point of view,since in vitro evolution is analogous to natural evolution in many respects,the study of the dynamic details of in vitro evolution may provide some instructive insights into the process of evolution. In this review,we summarize current theoretical and exper-imental studies,including several efforts made by our group,on the dynamics of DNA in vitro evolution.

关键词： DNA-TF interaction DNA in vitro evolution Natural evolution Crossover