共查询到19条相似文献,搜索用时 156 毫秒
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在对称化乘积算符(简称SAPO)方法基础上提出了多量子积算符(简称MQCPO)方法。改进的密度算符理论对InS(I=1/2,S=1/2;n为任意正整数)自旋体系多脉冲及二维核磁共振实验的描述普遍适用。MQCPO与SAPO从不同角度反映了自旋体系的对称性,故它们之间存在简单线性关系。文中给出In(I=1/2,n=2,3)自旋体系MQCPO的SAPO表示。MQCPO有利于自由演化过程的描述,而脉冲作用的描述则是SAPO为佳;利用MQCPO与SAPO的线性关系及SAPO笛卡儿分量的坐标轮换性质,“z”表象下脉冲作用的描述变得简单而直观。对异核谱剪辑及自旋拓扑滤波(spin topology filtration)等实验脉冲序列的分析,该方法是方便的。
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提出一种描述自旋为1/2的强偶AB自旋体系多脉冲NMR实验的密度算符演化的方法,推导了自旋算符的自由演化公式,具体描述了极化转移INEPT实验和二维DQ-INADEQUATE实验。该方法物理意义直观,计算量较小。 相似文献
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提出了一种设计多量子相干激发脉冲序列的新方法,用双线旋转脉冲作为基本激发单元,按照自旋偶合网络构建脉冲序列,达到(一)满自旋数激发,Pmax=N,(二)处于最佳转移条件下的高效率激发。 相似文献
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用虚拟自旋-1/2算符理论考察了I=1的核四极共振自旋系统在其能级间隔较小时对1-2个脉冲的响应.由于核四极相互作用表象中的射频场与核自旋的相互作用(Hrf)包含时间,因而用Dyson时序算符来计算密度算符在Hrf作用下的演化. 相似文献
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采用一种密度算符方法描述弱射频场存在下弱偶合自旋体系(I=1/2)的密度算符的演化,具体分析了自旋轻扰实验和显示自旋为1/2的原子核旋量特性的实验。 相似文献
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X-波段电子自旋成象 总被引:3,自引:3,他引:0
报道了自行设计研制的X-波段ESR成象装置并用之对典型样品作了ESR成象测定;用解卷积和分析图象重建中卷积滤波法对自旋样品体系进行了二维的图象重建,获取了能反映真实自旋分布的二维自旋密度图象. 相似文献
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Bak M Rasmussen JT Nielsen NC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,147(2):296-330
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K. Schmidt-Rohr 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,131(2):209-217
A multiple-pulse technique for complete dipolar decoupling of directly bonded13C-labeled sites is described. It achieves significant spectral simplifications in a recently introduced two-dimensional double-quantum solid-state NMR experiment for determining torsion angles. Both homonuclear and heteronuclear dipolar couplings are removed by combining a13C multiple-pulse sequence with continuous-wave irradiation on the protons. The13C sequence has a fundamental 10-pulse cycle which is a significantly modified magic-sandwich-echo sequence. The crucial heteronuclear decoupling is achieved by breaking the 360° “inner” pulses in the magic sandwich into 90° pulses and spacing them by1H 360° pulse lengths. Spectral artifacts typical of multiple-pulse sequences are eliminated by phase shifts between cycles. In contrast to many other multiple-pulse decoupling sequences, the long window in the cycle is the dwell time and can be longer than the inverse dipolar coupling, which makes the sequence practical for direct detection even with long pulse ring-down times. A modification of the sequence to scale the chemical shift and increase the effective spectral width is also presented. The 1D and double-quantum 2D experiments are demonstrated on polyethylene with 4%13C–13C spin pairs. The potential of this approach for distinguishing segmental conformations is illustrated by spectral simulations of the two-dimensional ridge patterns that correlate double-quantum and single-quantum chemical-shift anisotropies. 相似文献
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Nicholas P Fushman D Ruchinsky V Cowburn D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,145(2):262-275
This paper presents a software program, the Virtual NMR Spectrometer, for computer simulation of multichannel, multidimensional NMR experiments on user-defined spin systems. The program is capable of reproducing most features of the modern NMR experiment, including homo- and heteronuclear pulse sequences, phase cycling, pulsed field gradients, and shaped pulses. Two different approaches are implemented to simulate the effect of pulsed field gradients on coherence selection, an explicit calculation of all coherence transfer pathways, and an effective approximate method using integration over multiple positions in the sample. The applications of the Virtual NMR Spectrometer are illustrated using homonuclear COSY and DQF COSY experiments with gradient selection, heteronuclear HSQC, and TROSY. The program uses an intuitive graphical user interface, which resembles the appearance and operation of a real spectrometer. A translator is used to allow the user to design pulse sequences with the same programming language used in the actual experiment on a real spectrometer. The Virtual NMR Spectrometer is designed as a useful tool for developing new NMR experiments and for tuning and adjusting the experimental setup for existing ones prior to running costly NMR experiments, in order to reduce the setup time on a real spectrometer. It will also be a useful aid for learning the general principles of magnetic resonance and contemporary innovations in NMR pulse sequence design. 相似文献
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Bak M Schultz R Vosegaard T Nielsen NC 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,154(1):28-45
Software facilitating numerical simulation of solid-state NMR experiments on polypeptides is presented. The Tcl-controlled SIMMOL program reads in atomic coordinates in the PDB format from which it generates typical or user-defined parameters for the chemical shift, J coupling, quadrupolar coupling, and dipolar coupling tensors. The output is a spin system file for numerical simulations, e.g., using SIMPSON (Bak, Rasmussen, and Nielsen, J. Magn. Reson. 147, 296 (2000)), as well as a 3D visualization of the molecular structure, or selected parts of this, with user-controlled representation of relevant tensors, bonds, atoms, peptide planes, and coordinate systems. The combination of SIMPSON and SIMMOL allows straightforward simulation of the response of advanced solid-state NMR experiments on typical nuclear spin interactions present in polypeptides. Thus, SIMMOL may be considered a "sample changer" to the SIMPSON "computer spectrometer" and proves to be very useful for the design and optimization of pulse sequences for application on uniformly or extensively isotope-labeled peptides where multiple-spin interactions need to be considered. These aspects are demonstrated by optimization and simulation of novel DCP and C7 based 2D N(CO)CA, N(CA)CB, and N(CA)CX MAS correlation experiments for multiple-spin clusters in ubiquitin and by simulation of PISA wheels from PISEMA spectra of uniaxially oriented bacteriorhodopsin and rhodopsin under conditions of finite RF pulses and multiple spin interactions. 相似文献
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G.N. Manjunatha Reddy T.N. Guru Row N. Suryaprakash 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,196(2):119-126
The blend of spin topological filtering and the spin state selective detection of single quantum transitions by the two dimensional multiple quantum-single quantum correlation and higher quantum resolved techniques have been employed for simplifying the complexity of scalar coupled 1H NMR spectra. The conventional two dimensional COSY and TOCSY experiments, though identify the coupled spin networks, fail to differentiate them due to severe overlap of transitions. Non-selective excitation of homonuclear higher quantum of protons results in filtering of spin systems irrespective of their spin topologies. The spin state selection by passive 19F spins provides fewer transitions in each cross section of the single quantum dimension simplifying the analyses of the complex spectra. The degenerate single quantum transitions are further discerned by spin selective double and/or triple quantum resolved experiments that mimic simultaneous heteronuclear and selective homonuclear decoupling in the higher quantum dimension. The techniques aided the determination of precise values of spectral parameters and relative signs of the couplings. 相似文献
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The experimental and theoretical NQR multiple-pulse spin locking study of cross-relaxation process in solids containing nuclei of two different sorts I?>?1/2 and S?=?1/2 coupled by the dipole–dipole interactions and influenced by an external magnetic field. Two coupled equations for the inverse spin temperatures of the both spin systems describing the mutual spin lattice relaxation and the cross-relaxation were obtained using the method of the nonequilibrium state operator. It is shown that the relaxation process is realized with non-exponential time dependence describing by a sum of two exponents. The cross relaxation time is calculated as a function of the multiple-pulse field parameters which agree with the experimental data. The calculated magnetization cross relaxation time vs the strength of the applied magnetic field agrees well with the obtained experimental data. 相似文献