基于差分进化算法的核磁共振T2谱多指数反演

提出了一种基于差分进化(DE)算法的核磁共振弛豫信号多指数反演新方法.将核磁共振T2谱反演问题转化为带非负约束的非线性优化问题,不需要预先给定横向弛豫时间T2分布,直接利用差分进化算法进行反演计算.在测量信号低信噪比的情况下,计算机模拟和实验数据反演鄙表明了该方法在分析处理NMR弛豫信号中的有效性.     

基于差分进化算法的核磁共振T2谱多指数反演

提出了一种基于差分进化(DE)算法的核磁共振弛豫信号多指数反演新方法. 将核磁共振T₂谱反演问题转化为带非负约束的非线性优化问题,不需要预先给定横向弛豫时间T_{2分布,直接利用差分进化算法进行反演计算. 在测量信号低信噪比的情况下,计算机模拟和实验数据反演都表明了该方法在分析处理NMR弛豫信号中的有效性. 关键词： 核磁共振 多指数反演 差分进化 岩心分析}     

基于改进非线性拟合的核磁共振T2谱多指数反演

核磁共振T₂谱多指数反演算法是开展复杂体系样品核磁共振(NMR)弛豫研究最重要的数学工具. 常用的T₂谱多指数反演算法一般都是事先给出弛豫时间T₂分布的布点, 然后转化为线性拟合问题进行求解. 在求解的T₂谱较为分散的时候, 反演得到的T₂谱精确度不高, 分辨率较低. 非线性拟合是解决这个问题的有效办法. 本文针对分散T₂谱反演利用非线性拟合时遇到的初值依赖及运算复杂问题, 利用线性回归最小二乘方法, 改进了其中的带非负约束非线性优化模型, 将搜索的反演参数从T₂, f 减少为T₂, 加快了收敛速度, 减少了对初值的依赖, 提高了反演精度, 使算法更加稳健. 通过用改进的Levenberg-Marquardt算法和差分进化算法进行计算机模拟反演及实验数据反演, 验证了改进方法在核磁共振T₂ 谱反演中的有效性.     

一种基于组分补偿的二维核磁共振测井数据高精度处理方法

二维核磁共振技术能够对储层中各类含氢流体进行无损、快速、定量的测量和表征，但受限于采集方式和参数，核磁共振设备在对页岩油等致密储层中的有机质、沥青等超快弛豫组分进行检测时，经常出现由于信号采集不完整所导致的二维谱中流体组分缺失或不准的问题.本文提出了基于超快弛豫组分补偿技术的T₂-T₁二维谱高精度反演方法，该方法将一维核磁共振前端信号补偿技术进行推广，通过在二维核磁数据反演前对回波数据进行组分补偿，能够有效解决二维核磁共振测井前端信号漏失的问题.实验及测井数据的应用表明，该方法在页岩油等富含快弛豫组分信号的储层中，可以得到更加精准和完整的储层信息.     

氧分子离子第一负带系（b^4∑g^——α^4Пu）（2，6）带的光谱测量与分析

采用光外差-速度调制分子离子吸收光谱技术，在近红外波段13170-13500cm^-1范围内，对氧分子离子第一负带（b^4∑g^--α^4Пu）（2，6）带进行测量和分析，有关第一负带（2,6）带光谱测量尚未见文献报道．本文简述了光外差-速度调制光谱技术的特点，同时给出了对复杂四重态跃迁谱带的分析，运用非线性最小二乘拟合获得了该跃迁上下态精确的分子常数。     

回波间隔对核磁共振表观孔隙度的影响及矫正方法

本文对具有特定横向弛豫时间（T₂）的硫酸铜溶液进行了多回波间隔（T_E）的核磁共振（NMR）实验,并利用数值模拟对32组具有不同弛豫分量的模型进行了变T_E模拟实验,定量研究了T_E对致密油气、页岩气等低孔低渗储层NMR孔隙度的影响规律.实验结果表明,随着T_E的增大,各T₂弛豫组分NMR孔隙度先维持在100%左右,然后迅速衰减,当T_E增加到一定数值时,趋近于0;不同T₂弛豫组分NMR孔隙度开始迅速衰减及最后变为0的T_E值存在显著差异.根据不同T₂弛豫组分NMR孔隙度与T_E的关系,将整个NMR测量分为无损测量区、快速衰减区、无效参数区和仪器盲区4个区域.对特定弛豫组分而言,在快速衰减区弛豫组分损失量与T_E呈对数关系,本文还给出了该区域NMR孔隙度的校正公式及方法.     

JAK/STAT通路抑制剂对C57BL/6小鼠血清代谢组影响的1H NMR研究

JAK/STAT通路抑制剂已被应用于多种疾病的临床试验,但其全身性用药对机体组织细胞功能活性的影响目前尚不明确.本研究运用基于核磁共振氢谱（¹H NMR）的代谢组学方法分析了JAK/STAT通路抑制剂WP1066（20 mg/kg.bw,2天一次,持续2周）对C57BL/6小鼠血清代谢组的影响.首先采用¹H NMR技术检测了WP1066处理组和对照组小鼠血清的代谢物,然后对所得的图谱数据进行了主成分分析（PCA）以及正交偏最小二乘法分析（OPLS）.研究结果表明,抑制JAK/STAT通路可明显下调小鼠血清中的N-甲基烟酰胺（N-methylnicotinamide）水平,而上调顺乌头酸（cis-aconitate）、草酰乙酸（oxaloacetate）和乙酰胺（acetamide）水平,这些代谢物改变均与能量代谢密切相关.该结果提示代谢失衡相关指标可能作为JAK/STAT通路抑制剂治疗的临床监测参考指标.     

高性能核磁共振弛豫分析仪匀场系统的设计与实现

磁场的高均匀性是高性能核磁共振弛豫分析仪实现短弛豫时间样品和微弱信号核磁共振（NMR）检测的基本保障.该文以0.45 T双极型永磁体作为设计核心部件,在大范围磁体空间-25.4 mm球空间（DSV）内,基于目标场法设计了X、Y、Z、XY、XZ、YZ、Z²共7组有源匀场线圈,根据线圈供电要求,设计了可编程恒流电源,搭建了可用于高性能核磁共振弛豫分析仪磁体的有源匀场系统,介绍了系统的基本结构、设计过程及匀场方法.实验测试结果验证了大范围磁体空间内该匀场系统的实用性.     

2D NMR技术在多季碳二萜结构确定中的应用

应用二维核磁共振技术（2D NMR：¹H-¹H COSY、HMQC、HMBC）, 尤其是HMBC谱准确归属了多季碳二萜伊丽莎白素B（Elisabatin B）的¹H,¹³C信号,并经与已报道的数据比较,进一步明确指定了11个季碳的化学位移. 以伊丽莎白素B为例,较系统阐明了几种二 维核磁共振技术在天然产物结构确定中的作用和方法.     

MAPbCl3钙钛矿中甲胺阳离子运动的固体2H NMR研究

本文利用固体²H核磁共振（²H NMR）技术探究了甲胺铅氯（MAPbCl₃）钙钛矿正交相、四方相和立方相晶体结构内甲胺阳离子（MA）的运动特征.结合²H NMR实验数据和拟合数据，本文分析和建立了不同相结构中MA阳离子的运动模型，揭示了不同相结构中MA阳离子的运动特征：正交相中MA并不处于完全静止状态，而是在围绕C-N键快速内旋转的同时局部晃动；随着温度升高，MA在钙钛矿晶格中呈现出多种不同的运动模式，MA阳离子运动在不同温度下的变化过程与该材料的相转变过程并不一致.该研究有助于加深对MAPbCl₃相结构转变分子机制的理解.     

A new method for multi-exponential inversion of NMR relaxation measurements

The NMR technique has been widely applied to petroleum well logging and rock core analysis since the 1990s when NUMAR introduced a reliable NMR logging tool to the oil industry. It has been playing an important role for prospecting and exploiting resource of oil and gas for the last ten years. In an oil well, NMR can provide parameters of reservoir and fluid properties, such as porosity, pore size distribution, bound water volume, bulk volume of free water, permeability, in-situ fluid dif…     

核磁共振弛豫时间测量数据处理方法的讨论

分析和讨论了在超小型核磁共振成像仪测量弛豫时间T1的数据处理方法中存在的问题,并提出了测量方法和数据拟合的改进方案.     

Study of activation parameters and NMR spin-lattice relaxation time in some substituted amines

The present communication reports the experimental values of NMR spin-lattice relaxation time (T₁) and dielectric relaxation time (τ) of piperidine, pyrrole, pyridine, diethylamine, triethylamine and pyrrolidine. The values of activation energy (ΔE_A) obtained using dielectric relaxation time, have been correlated with calculated values of ΔE_A obtained using Arrhenius equation of NMR relaxation time (T₁) for pyridine, diethylamine and pyrrole. Authors have also established a correlation between the experimental values of NMR spin-relaxation time (T₁) with its calculated values obtained using different equations of dielectric relaxation time (τ).     

基于二维核磁共振弛豫谱的雷四段孔隙度计算方法

基于常规测井资料的体积模型和一维核磁共振（NMR）测井资料的固定截止值法,可以计算地层孔隙度,但是扩径段孔隙度计算结果偏大.本文通过川西海相雷四段岩心样品NMR实验和实测二维NMR测井资料,开展扩径段的T₂、T₁孔隙度计算方法研究.首先总结不同孔径流体在T₂谱和T₁谱上的响应特征,分析钻井液流体峰截止值的分布范围和影响因素,建立钻井液流体弛豫时间截止值的计算模型;然后根据未扩径段和扩径段的粘土束缚水弛豫时间截止值确定原则,确立变粘土束缚水弛豫时间截止值的有效孔隙度计算方法.多口井的应用效果表明,基于T₁谱的孔隙度计算结果精度更高、定量分析误差小,能有效解决扩径段孔隙度计算结果偏大的问题,满足储层评价的要求.     

Specific features of proton NMR relaxation of hydrocarbons and water in the pore space of silicates

The relaxation of the proton magnetization of water and hydrocarbons in a model medium of glass beads and quartz sand is studied by the NMR method. The spectrum of relaxation times of fluids is one-component in the model environment and three-component in quartz sand. The surface relaxivities measured in the model medium are used to determine the pore size distribution in quartz sand. Estimates of the specific surface area of sand based on the relaxation data are consistent with the values measured by the sorption method. The EPR method is used to determine the chemical nature of the active paramagnetic centers responsible for the surface relaxation of the proton magnetization. Differences in the relaxation behavior of aqueous and hydrocarbon fluids are interpreted within the framework of a simple model of surface relaxation.     

Improvement of duty-cycle heating compensation in NMR spin relaxation experiments

To reliably measure NMR relaxation properties of macromolecules is a prerequisite for precise experiments that identify subtle variations in relaxation rates, as required for the determination of rotational diffusion anisotropy, CSA tensor determination, advanced motional modeling or entropy difference estimations. An underlying problem with current NMR relaxation measurement protocols is maintaining constant sample temperature throughout the execution of the relaxation series especially when rapid data acquisition is required. Here, it is proposed to use a combination of a heating compensation and a proton saturation sequence at the beginning of the NMR relaxation pulse scheme. This simple extension allows reproducible, robust and rapid acquisition of NMR spin relaxation data sets. The method is verified with (15)N spin relaxation measurements for human ubiquitin.     

Protein dynamics using frequency-dependent order parameters from analysis of NMR relaxation data

A novel approach is described to analyze NMR relaxation data on proteins. This method introduces the frequency-dependent order parameter, S(2)(omega), in order to estimate contributions to the generalized order parameter S(2) from different motional frequencies occurring on the picosecond to nanosecond time scales. S(2)(omega) is defined as the sum of a specified set of weighting coefficients from the Lorentzian expansion of the spectral density function. 15N NMR relaxation data (500, 600, and 800 MHz) on protein GB1 exemplify the method. Using this approach provides information on motional restrictions over specific frequency or time scale ranges and provides a normalized comparison of motional restrictions between proteins having different overall tumbling correlation times.     

In situ fluid typing and quantification with 1D and 2D NMR logging

In situ nuclear magnetic resonance (NMR) fluid typing has recently gained momentum due to data acquisition and inversion algorithm enhancement of NMR logging tools. T(2) distributions derived from NMR logging contain information on bulk fluids and pore size distributions. However, the accuracy of fluid typing is greatly overshadowed by the overlap between T(2) peaks arising from different fluids with similar apparent T(2) relaxation times. Nevertheless, the shapes of T(2) distributions from different fluid components are often different and can be predetermined. Inversion with predetermined T(2) distributions allows us to perform fluid component decomposition to yield individual fluid volume ratios. Another effective method for in situ fluid typing is two-dimensional (2D) NMR logging, which results in proton population distribution as a function of T(2) relaxation time and fluid diffusion coefficient (or T(1) relaxation time). Since diffusion coefficients (or T(1) relaxation time) for different fluid components can be very different, it is relatively easy to separate oil (especially heavy oil) from water signal in a 2D NMR map and to perform accurate fluid typing. Combining NMR logging with resistivity and/or neutron/density logs provides a third method for in situ fluid typing. We shall describe these techniques with field examples.     

Determination of the rotational diffusion tensor of macromolecules in solution from nmr relaxation data with a combination of exact and approximate methods--application to the determination of interdomain orientation in multidomain proteins

In this paper we present a method for determining the rotational diffusion tensor from NMR relaxation data using a combination of approximate and exact methods. The approximate method, which is computationally less intensive, computes values of the principal components of the diffusion tensor and estimates the Euler angles, which relate the principal axis frame of the diffusion tensor to the molecular frame. The approximate values of the principal components are then used as starting points for an exact calculation by a downhill simplex search for the principal components of the tensor over a grid of the space of Euler angles relating the diffusion tensor frame to the molecular frame. The search space of Euler angles is restricted using the tensor orientations calculated using the approximate method. The utility of this approach is demonstrated using both simulated and experimental relaxation data. A quality factor that determines the extent of the agreement between the measured and predicted relaxation data is provided. This approach is then used to estimate the relative orientation of SH3 and SH2 domains in the SH(32) dual-domain construct of Abelson kinase complexed with a consolidated ligand.