共查询到19条相似文献,搜索用时 93 毫秒
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魔角旋转核磁共振波谱学 总被引:2,自引:2,他引:0
样品绕与外加恒定磁场方向成魔角βM=cos-1(1)/√3的轴向快速旋转(MAS)可以消除固体NMR的多种谱增宽。本文首先介绍了固体中的几种主要的各向异性相互作用,即偶极-偶极,核四极,自旋-自旋或称间接偶极-偶极以及化学位移相互作用。然后用平均哈密顿理论阐述了MAS对这些相互作用的影响。现今的固体高分辨方法有四种,即多脉冲(MP),多量子(MQ),交叉极化和大功率异核去耦合(CP)以及MAS,在这些方法中MAS方法是唯一可以获得各向同性化学位移的。因而要得到类似于液体谱的固体高分辨,MAS往往是最后的手段。以上这些方法的联合运用以及极为广泛的应用研究使得固体高分辨NMR兴旺发达起来了。本文引述了大量原始和最新的文献,力图概述当前该领域中的大部分成就。评论这一领域的理论和实验技术的发展。 相似文献
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描述高自旋弱耦合系统的广义积算符 总被引:1,自引:1,他引:0
本文提出了Z算符与角动量积算符相结合的广义积算符,用于描述高自旋弱耦合系统NMR实验谱。给出了高自旋系统在自旋耦合作用下的演变公式,Z算符在脉冲作用下的变化公式。以氘(D)为例,计算了重聚INEPT,DEPT和同核COSY实验谱,并对计算方法作了讨论。 相似文献
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在本文中,我们用Bessel函数展开法从理论上分析了非均匀相互作用产生的MAS旋转边带以及消除这些旋转边带的各种方法,从而指出当相互作用强度与转速的比值大于2时,对于最常用的TOSS方法来说会产生严重的谱失真。本文还对现存的各种抑制边带的方法作了实验比较。 相似文献
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γ谱分析是一种重要的放射性核素定量分析方法. 弱峰的检测和重叠峰的分解是γ 谱分析中的难点. 为了解决这两个问题, 基于压缩感知理论, 提出了一种新的γ 谱分析方法. 这一方法从谱仪对γ 谱调制的物理机理出发, 通过数学建模, 将γ 谱分析转化为一个以真实γ 谱为解的求逆问题, 并在压缩感知理论框架下, 运用γ 谱特征峰的稀疏性, 进行逆问题的求解, 直接获得γ 谱的估计结果. 数值模拟结果和蒙特卡洛模拟结果表明: 该方法能在降低统计涨落的同时, 有效减小谱仪调制带来的能谱展宽, 从而提高γ 谱分析精度.
关键词:
γ谱分析')" href="#">γ谱分析
压缩感知
非线性
逆问题 相似文献
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脉冲梯度增强技术的初步研究 总被引:2,自引:0,他引:2
自行研制一套脉冲梯度场系统,配合Bruker公司MSL 300谱仪研究脉冲梯度增强的高分辨核磁共振,研制以PC/286为核心的梯度脉冲波形和幅度可任意调节的梯度场发生器;改装谱仪的1H液体探头、增加梯度场线图.分析了脉冲梯度场产生的涡流磁场的影响;报道了利用自制梯度场系统进行的脉冲梯度增强的高分辨COSY实验. 相似文献
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用金属有机物化学气相沉积方法在r面蓝宝石上生长了非极性a面GaN薄膜,通过采用AlGaN多量子阱插入层,得到了高质量的非极性GaN材料. 用原子力显微镜和高分辨X射线衍射仪研究了a面GaN的表面形貌和结晶质量,发现非极性材料上典型的三角坑缺陷被消除,(1120)面X射线双晶摇摆曲线的半峰宽为680″.
关键词:
GaN
原子力显微镜
高分辨X射线衍射仪
非极性 相似文献
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富马酸单乙酯(FAME)的单脉冲1H MAS谱由-高分辨成分与-宽线谱成分组成.高分辨成分可由Hahn回波脉冲序列单独获得.文中通过变温1H MAS与CRAMPS实验对两组分的性质进行了系统的研究.发现当温度趋于样品的熔点时,其1H CRAMPS谱可观察到化学位移明显区别的两套谱,它们分别对应于1H MAS谱的高分辨与宽线组分.实验表明:高分辨成分来自FAME样品的-塑性相,而宽线组分来自通常的刚性相.文中所给出的实验事实充分说明1H MAS与CRAMPS技术是研究有机塑性固体的强有力的工具. 相似文献
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Fast magic-angle spinning (MAS) holds promise for new approaches to pulsed high-resolution NMR in solids where homogeneous interactions dominate. Prerequisite for developing new pulse methods is the understanding of signal encoding by spin interactions under MAS conditions and of interferences between MAS and pulses. This review discusses corresponding strategies and techniques in a coherent way with particular concentration on homonuclear decoupling techniques for line-narrowing in solids. 相似文献
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In this article we present a new approach to high resolution NMR combining the concepts of magic angle hopping (MAH)/magic angle turning (MAT) and dipolar based NMR methods such as SEDOR, REDOR or cross polarization (CP). Employing aluminophosphates as model systems we demonstrate that No MAS needed (NOMAS) is capable of supplying high resolution dipolar information without the need of fast MAS. 相似文献
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HR/MAS高分辨魔角微量探头用于天然橡胶固体1H、13C NMR测试及其与液体BBO探头、固体CP/MAS探头测试的比较 总被引:5,自引:0,他引:5
采用BRUKER高分辨魔角微量探头(HR/MAS),液相宽带BBO探头和固体CP/MAS探头,对天然橡胶固体、乳液以及天然橡胶溶于氘代苯的溶液进行了1H、13C 1D和2D NMR谱的测试和比较. 发现HR/MAS探头用于天然橡胶固体和乳液时可以得到高分辨的1H、13C谱,克服了CP/MAS探头测试固体13C NMR谱或者是固体1H NMR谱时,谱图存在S/N值可能较小、谱峰可能宽化的弱点. 相似文献
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Ernst M 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,162(1):1-34
Achieving high spectral resolution is an important prerequisite for the application of solid-state NMR to biological molecules. Higher spectral resolution allows to resolve a larger number of resonances and leads to higher sensitivity. Among other things, heteronuclear spin decoupling is one of the important factors which determine the resolution of a spectrum. The process of heteronuclear spin decoupling under magic-angle sample spinning is analyzed in detail. Continuous-wave RF irradiation leads only in a zeroth-order approximation to a full decoupling of heteronuclear spin systems in solids under magic-angle spinning (MAS). In a higher-order approximation, a cross-term between the dipolar-coupling tensor and the chemical-shielding tensor is reintroduced, providing a scaled coupling term between the heteronuclear spins. In strongly coupled spin systems this second-order recoupling term is partially averaged out by the proton spin-diffusion process, which leads to exchange-type narrowing of the line by proton spin flips. This process can be described by a spin-diffusion type superoperator, allowing the efficient simulation of strongly coupled spin systems under heteronuclear spin decoupling. Low-power continuous-wave decoupling at fast MAS frequencies offers an alternative to high-power irradiation by reversing the order of the averaging processes. At fast MAS frequencies low-power continuous-wave decoupling leads to significantly narrower lines than high-power continuous-wave decoupling while at the same time reducing the power dissipated in the sample by several orders of magnitude. The best decoupling is achieved by multiple-pulse sequences at high RF fields and under fast MAS. Two such sequences, two-pulse phase-modulated decoupling (TPPM) and X-inverse-X decoupling (XiX), are discussed and their properties analyzed and compared. 相似文献
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Brouwer DH Ripmeester JA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,185(1):173-178
A two-dimensional NMR experiment for estimating proton chemical shift anisotropies (CSAs) in solid powders under magic-angle spinning conditions is demonstrated in which 1H CSAs are reintroduced with a symmetry-based recoupling sequence while the individual proton sites are resolved according to their isotropic chemical shifts by magic-angle spinning (MAS) or combined rotation and multiple pulse (CRAMPS) homonuclear decoupling. The experiments where carried out on an ultrahigh-field solid-state NMR instrument (900 MHz 1H frequency) which leads to increased resolution and reliability of the measured 1H CSAs. The experiment is expected to be important for investigating hydrogen bonding in solids. 相似文献
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介绍了自行研制的用于动态核极化实验的固体高分辨CP/MAS探头,给出了典型含自由基固体样品的DNP增强高分辨NMR谱.并对动态核极化实验中的技术问题进行了讨论,提出了相应的解决方法. 相似文献
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Two-dimensional indirectly detected through-space and through-bond 1H{15N} solid-state NMR experiments utilizing fast magic angle spinning (MAS) and homonuclear multipulse 1H decoupling are evaluated. Remarkable efficiency of polarization transfer can be achieved at a MAS rate of 40 kHz by both cross-polarization and INEPT, which makes these methods applicable for routine characterizations of natural abundance solids. The first measurement of 2D 1H{15N} HETCOR spectrum of natural abundance surface species is also reported. 相似文献
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Nishiyama Y Endo Y Nemoto T Utsumi H Yamauchi K Hioka K Asakura T 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,208(1):44-48
Substantial resolution and sensitivity enhancements of solid-state (1)H detected (14)N HMQC NMR spectra at very fast MAS rates up to 80 kHz, in a 1mm MAS rotor, are presented. Very fast MAS enhances the (1)H transverse relaxation time and efficiently decouples the (1)H-(14)N interactions, both effects leading to resolution enhancement. The micro-coil contributes to the sensitivity increase via strong (14)N rf fields and high sensitivity per unit volume. (1)H-(14)N HMQC 2D spectra of glycine and glycyl-L-alanine at 70 kHz MAS at 11.7 T are observed in a few minutes with a sample volume of 0.8 μL. 相似文献