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Solvent Suppression in Intermolecular Magnetic Resonance Spectra Multiple-Quantum Coherence Nuclear with Only z-axis Gradients 下载免费PDF全文
The solvent peak in the intermolecular multiple-quantum coherence spectra can be suppressed by either applying pulse field gradients or spinning sample along the magic angle direction (φ = 54.7). However, these two methods also suppress the signals of the solute. We design two pulse sequences with only z-axis gradients to suppress the solvent peak without reducing the intensity of solute signals. Compared to the former pulse sequence, the latter pulse sequence is insensitive to the imperfection of pulse flip angles. When the flip angles of the second pulse sequence are purposely deviated 1/10 from the optimal values, the solvent peak is still weak. Theoretical expressions, experimental observations and computer simulations demonstrate that the two methods can be used to effectively suppress solvent peak in intermolecular multiple-quantum coherence spectra. 相似文献
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本文采用EHT近似下的紧束缚能带方法,计算了NbX(X=C,N,O)的能带结构。结果表明,它们的能带结构相近,Nb—X间存在较强的成键作用,传导电子主要具有Nb的4d特征,Nb—Nb键与超导电性相关,从C到N,Nb—Nb键共价性削弱,Tc提高。尽管计算所得NbO中Nb—Nb键强度介于NbC和NbN之间,但其实际Tc却比NbC和NbN的都低,这是NbO的空位效应所致,这一结果可从我们对有序缺陷的Nb_(0.75)O_(0.75)晶体能带结构的计算得到验证。 相似文献
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Apparent diffusion behaviour of intermolecular double-quantum coherence modulated by a distant dipolar field in solution NMR 下载免费PDF全文
A modified correlated spectroscopy (COSY) revamped with
asymmetric Z-gradient echo detection sequence was designed to
investigate the influence of diffusion behaviour on intermolecular
double-quantum coherence signal attenuation during the
pre-acquisition period. Theoretical formulas were deduced and
experimental measurements and simulations were performed. It is
found that the diffusion behaviour of intermolecular double-quantum
coherence in the pre-acquisition period may be different from that of
conventional single-quantum coherence, depending on the relative
orientation of diffusion weighting gradients to coherence selection
gradients. When the orientation of the diffusion weighting gradients is
parallel or anti-parallel to the orientation of the coherence
selection gradients, the diffusion is modulated by the distant
dipolar field. This study is helpful for understanding the signal
properties in intermolecular double-quantum coherence magnetic
resonance imaging. 相似文献
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Observation of intermolecular double-quantum coherence signal dips in nuclear magnetic resonance 下载免费PDF全文
The correlated spectroscopy revamped by asymmetric Z-gradient echo detection (CRAZED) sequence is modified to investigate intermolecular double-quantum coherence nuclear magnetic resonance signal dips in highly polarized spin systems. It is found that the occurrence of intermolecular double-quantum coherence signal dips is related to sample geometry, field inhomogeneity and dipolar correlation distance. If the field inhomogeneity is refocused, the signal dip occurs at a fixed position whenever the dipolar correlation distance approaches the sample dimension. However, the position is shifted when the field inhomogeneity exists. Experiments and simulations are performed to validate our theoretic analysis. These signal features may offer a unique way to investigate porous structures and may find applications in biomedicine and material science. 相似文献
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改进了Warren所提出的CRAZED脉冲序列以研究分子间多量子相干的扩散过程 ,讨论了利用核磁共振测量分子内和分子间多量子相干表观自扩散系数的理论表述 ,采用粒子的随机行走模型模拟其扩散行为 .在短脉冲近似和长脉冲梯度场两种实验条件下 ,分别获得了因扩散引起的不同相干阶数的相对信号衰减强度随梯度场脉冲间隔时间的变化曲线 ,由此得到分子内多量子相干和分子间多量子相干的表观扩散率与溶液分子扩散系数的关系 .还将计算机模拟结果与理论预测进行分析和比较 ,发现二者能很好地吻合 .研究结果表明 ,分子间多量子相干的表观扩散率与常规的分子内多量子相干的表观扩散率明显不同 ,因此 ,分子间多量子相干的表观扩散率可能提供一种新的核磁共振成像的对比度机理 相似文献
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采用基于原子球近似下线性Mufin-Tin轨道(LMTO-ASA)的平均键能计算方法,研究了以ZnSxSe1-x为衬底,沿(001)方向外延生长的应变层异质结ZnS/ZnSe、ZnS/ZnSxSe1-x和ZnSe/ZnSxSe1-x的价带带阶值ΔEv(x).研究表明,ΔEv(x)值随衬底合金组分x单调变化。且两者的关系是非线性的。在此计算结果与其它理论计算和实验结果符合较好。 相似文献
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