The Memory-Function Technique for the Calculation of Pulsed-Gradient NMR Signals in Confined Geometries
The Memory-Function Technique for the Calculation of Pulsed-Gradient NMR Signals in Confined Geometries
复制标题
计算受限几何结构中脉冲梯度核磁共振信号的记忆函数技术
DOI：
10.1006/jmra.1996.0188
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发表时间：
1996
期刊：
影响因子：
--
通讯作者：
V. M. Kenkre
中科院分区：
文献类型：
--
作者：
D. Sheltraw;V. M. Kenkre
本文在记忆函数形式的基础上，介绍了一种计算有限空间中脉冲梯度核磁共振信号的近似方法，并与常用的累积展开方法进行了比较。该技术的有效性进行了研究的情况下，一个时间无关的场梯度和梯度由两个脉冲的有限持续时间。结果发现，有效性是由两个特征时间的比率：时间的自旋通过扩散和倒数的旋进频率的值之间的极端差异的限制空间的尺寸。振荡的恒定梯度的信号的时间演化，以及振荡的（梯度）场的依赖性的两个脉冲的梯度，这两个特性的确切的信号，预测的新技术，但不是由累积量技术。累积量的结果显示出现作为一个近似的结果的内存结果。
Abstract An approximation technique for the calculation of pulsed-gradient NMR signals in confined spaces is introduced on the basis of a memory-function formalism and compared to the well-known cumulant expansion technique. The validity of the technique is investigated for the cases of a time-independent field gradient and a gradient consisting of two pulses of finite duration. It is found that the validity is governed by the ratio of two characteristic times: the time for the spins to traverse the dimensions of the confining space through diffusion and the reciprocal of the extreme difference between values of the precession frequency of the spin. Oscillations in the time evolution of the signal for the constant gradient, as well as oscillations in the (gradient) field dependence for the two-pulse gradient, which are both characteristic of the exact signals, are predicted by the new technique but not by the cumulant technique. The cumulant results are shown to arise as an approximate consequence of the memory results.