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101.
Nicholas J. Curro Charles P. Slichter 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,130(2):186-194
Measurement ofT2G, the Gaussian component of the spin-echo envelope of planar Cu nuclei in high-temperature superconductors, gives important information about the real part of the Cu electron spin susceptibility. In the traditional picture of the planar Cu echo decay, the internuclear coupling is assumed to remain static with respect to spin–lattice relaxation and mutual exchange fluctuations. In some circumstances, however, this assumption breaks down. We calculate the internuclear corrections arising from spin–lattice relaxation to the conventional theory ofT2Gand show thatT2Gcan be easily corrected for these effects. We argue that mutual exchanges due to the perpendicular indirect couplings are suppressed in these materials. For YBa2Cu4O8, we find a correction on the order of 10% inT2Gand using the corrected values we find that the isotope ratio63T2G/65T2Gagrees with theory. 相似文献
102.
Tony Shardlow 《BIT Numerical Mathematics》2006,46(1):111-125
We describe a backward error analysis for stochastic differential equations with respect to weak convergence. Modified equations are provided for forward and backward Euler approximations to Itô SDEs with additive noise, and extensions to other types of equation and approximation are discussed. 相似文献
103.
104.
N. B. Brusnikina A. V. Lotov 《Computational Mathematics and Mathematical Physics》2007,47(11):1779-1787
A method is proposed for approximating the reachable set of a dynamic system with a state space dimension no higher than six-eight considered on a finite time interval. The system is governed by linear differential equations with piecewise constant coefficients and impulse actions specified at prescribed times. The method is based on guaranteed-accuracy polyhedral approximations of reachable sets at researcher-specified times. Every approximation is constructed using the preceding one. A procedure is described for choosing parameters of the method that ensure the required accuracy with close-to-minimal time costs. 相似文献
105.
106.
为了精确计算束流在离子光学系统中的传输,用Visual FORTRAN 6.5语言编写了一个计算程序,长约13000行. 此程序可以计算由三圆筒单透镜、三膜片单透镜、双元筒透镜、均匀场静电加速管、磁四极透镜、六极磁铁、静电四极透镜、偏转磁铁、螺线管透镜、ExB~正交电磁场分析器、静电偏转器、漂浮管、QWR(Quarter Wave Resonators)和SLR(Split Loop Resonators)射频加速元件等元件任意组成的离子光学系统. 粒子轨迹的计算可精确到三级近似. 粒子的分布类型也可以有多种选择. 程序具有最优化计算功能,即可以自动调整元件的参数,以实现所需要的光学条件. 各元件之后的横向和纵向相图以及系统的束流包络线以图形方式显示在屏幕上. 相似文献
107.
The aim of this article is to discuss an asymptotic approximation model and its convergence for the minimax semi-infinite programming problem. An asymptotic surrogate constraints method for the minimax semi-infinite programming problem is presented by making use of two general discrete approximation methods. Simultaneously, the consistence and the epi-convergence of the asymptotic approximation problem are discussed. 相似文献
108.
我们定义了(H,λ)求和法,它含有(N,pn),(R^rn)和(Vmn)求和法。讨论了函数f(x)∈C^r[-1,1](r∈N0)以及f(x)∈W^rH^a(r∈N0,0<a<1)的切比晓夫-富里埃级数的逼近阶。 相似文献
109.
Yang Jing Wen Xiang Lin Yang 《International Journal of Infrared and Millimeter Waves》1998,19(7):963-975
The modified quantum nonlinear Schrodinger equation of ultra-short pulse propagating in fiber is derived using dispersion relation and the Hamiltonian of the transmission system. The derived equation is solved with linearization approximation, and modulation instability is analyzed. The equation is also solved with Hartree approximation. The results indicate that pulse power, loss and self-steeping effect change the critical frequency, the maximum gain and the gain spectrum range, but the third order dispersion has no effect on modulation instability. The expectation value of optical field is average of a set of modified classical solitons, and higher order terms change the amplitude, pulse position and phase of soliton. 相似文献
110.
For one-dimensional expanding mapsT with an invariant measure we consider, in a parameter space, the envelope
n
of the real lines associated to any couple of points of the orbit, connected byn iterations ofT. If the map hass inverses and is piecewise linear, then the sets
n
are just the union ofs
n
points and converge to the invariant Cantor set ofT. A correspondence between all the sets and their measures is established and allows one to associate the atomic measure on 1 to the completly continuous measure on the Cantor set. If the map is nonlinear, hyperbolic, and hass inverses, the sets
n
are homeomorphic to the Cantor set; they converge to the Cantor set ofT and their measures converge to the measure of the Cantor set whenn. The correspondence between the sets
n
allows one to define converging approximation schemes for the map an its measure: one replaces each of thes
n
disjoint sets with a point in a convenient neighborhood and a probability equal to its measure and transforms it back to the original set 1. All the approximations with linear Cantor systems previously proposed are recovered, the converging proprties being straightforward in the present scheme. Moreover, extensions to higher dimensionality and to nondisconnected repellers arte possible and are briefly examined. 相似文献