单扫描快速采样方法及其在NMR中的应用

单扫描快速采样方法利用空间编码技术,只需单次扫描就能获得二维及多维核磁共振(NMR)谱数据,极大地缩短了二维和多维核磁共振谱的采样时间,有望在NMR领域得到广泛的应用. 该文以离散编码单扫描快速采样方法为例阐明了单扫描快速采样方法的原理,介绍了连续幅度调制、连续相位调制等各种单扫描快速采样新方法及其在NMR领域中的应用, 指出了单扫描快速采样方法的局限性,并对其未来发展进行了展望.     

基于相关序列脉冲的布里渊光时域反射测量系统解码方法研究

布里渊光时域反射测量(BOTDR)系统空间分辨率和传感距离存在相互制约的关系.相关序列脉冲编码技术可用于解决这一矛盾,但直接对编码脉冲的布里渊散射采样信号进行解码,会因采样时间间隔小于编码单位脉冲宽度而导致解码信号的失真,从而降低了系统空间分辨率和测量精度.分析了直接互相关解码对BOTDR系统空间分辨率的影响,提出一种...     

Varian系统所有通道上的整形脉冲

本文介绍了Varian系统所有通道上的整形脉冲;整形脉冲的形状;波形发生器的功率适中的脉冲整形以及应用"Tophat"的选择激发;整形脉冲与选择性反转;选择性反转或宽带反转,整形脉冲的宽带激发;以及多频率激发的移层式脉冲等.     

NMR碳谱谱峰检索系统

介绍了核磁共振(NMR)碳谱谱峰检索系统的程序设计原理、系统流程框图、检索比较算法和主要显示界面．系统数据库包含化合物核磁共振碳谱4万多张,能够根据未知物¹³C NMR波谱的谱峰个数及其化学位移值进行检索．结果得到未知化合物的有关信息及其标准波谱图．系统还允许用户将本专业的一些常用化合物的标准谱的信息以及图谱添加进数据库以供日后查询．     

用于测量J偶合常数的同时多层选择性恒时J分解谱的方法(英文)

标量偶合是核磁共振(NMR)波谱的一个重要参数.其中氢-氢偶合能提供关于分子结构的有用信息.但是,在复杂的偶合网络中解析出氢-氢偶合常数(J_(H-H))较为困难.本文提出了一种基于空间编码选择性恒时演化的测量J_(H-H)的方法,利用一次实验就能解析分子中所有氢核的偶合网络,并测量J_(H-H).该方法被称为同时多层选择性恒时J分解谱(SMS-SECTJRES).它结合空间编码梯度和选择性恒时演化,并利用平面回波谱成像(EPSI)采样模块,从不同的空间位置提取出对应不同氢核偶合网络的J分解谱,促进了NMR技术在分子结构解析中的进一步应用.     

采用单工循环编码解码的分布式光纤喇曼温度传感器

针对连续脉冲编码解码技术在分布式光纤喇曼温度传感器应用中出现被测光纤非线性峰值阀值光功率变低、编码过程较复杂等问题,提出了一种将光脉冲码均匀分布在整条被测光纤的单工循环编码解码技术和应用方案,并在27km单模系统中与传统单脉冲技术系统做了对比实验.结果表明:相比连续编码解码技术,单工循环编码解码技术不仅保持了编码解码技术相对于传统单脉冲技术的信噪比改善能力,而且有效地提高了光纤的非线性峰值阀值光功率.在编码时只需循环发送一组码,就可使系统的信噪比和测量距离获得极大的提高.采用211位循环编码解码技术的多模系统经16万次重复测量后,可在25km处获得±1.5℃的温度不确定度,空间分辨率为3m.     

磁共振波谱及成像技术在纳米尺度物质生物效应研究中的应用

纳米尺度物质的生物效应研究是近年来在纳米科技发展过程中派生出来的一个崭新的、发展很快的且多学科高度交叉的领域，需要把纳米科学、物理学、化学以及生物医学等多学科的研究手段结合起来，进行综合研究．核磁共振波谱与成像，作为一种原位、无损、动态、实时、多信息的检测手段，在此领域的研究中将发挥不可或缺的重要作用．文章分3个方面简要介绍核磁共振波谱与成像技术在纳米尺度物质生物效应研究中的应用：（1）纳米尺度物质在生物组织及个体内的检测与分析；（2）纳米尺度物质与生物大分子相互作用的核磁共振波谱研究；（3）纳米尺度物质生物效应的核磁共振代谢组学研究．     

用于测量J偶合常数的同时多层选择性恒时J分解谱的方法

标量偶合是核磁共振（NMR）波谱的一个重要参数.其中氢-氢偶合能提供关于分子结构的有用信息.但是,在复杂的偶合网络中解析出氢-氢偶合常数（J_H-H）较为困难.本文提出了一种基于空间编码选择性恒时演化的测量J_H-H的方法,利用一次实验就能解析分子中所有氢核的偶合网络,并测量J_H-H.该方法被称为同时多层选择性恒时J分解谱（SMS-SECTJRES）.它结合空间编码梯度和选择性恒时演化,并利用平面回波谱成像（EPSI）采样模块,从不同的空间位置提取出对应不同氢核偶合网络的J分解谱,促进了NMR技术在分子结构解析中的进一步应用.     

迭代软阈值法压缩感知重建谱峰较宽的二维固体谱

压缩感知技术可以打破传统奈奎斯特采样定理的限制,利用优化算法对欠采数据进行重建,并获得高质量的结果,因此在核磁共振领域得到了广泛的关注．但是当核磁共振谱的谱峰很宽时,基于共轭梯度方法的压缩感知重建却难以得到令人满意的谱图．因此,该文采用凸优化非线性重建算法,使用基于谱图域软阈值的压缩感知算法重建固体二维宽谱（¹H双量子-单量子谱或MQMAS谱）,有效地解决了宽峰在重建时变弱的问题．     

不均匀场下空间编码超快速高分辨NMR研究进展

二维核磁共振(2D NMR)的提出和发展,为NMR技术的研究和应用提供了广阔的空间. 然而当样品或磁场本身不均匀时,高分辨的2D NMR谱难以获得. 此外,常规2D NMR实验通常需要长的采样时间. 空间编码超快速采样方法利用空间编码技术,只需单次扫描即可获得2D甚至多维NMR谱,极大地缩短了采样时间. 目前相位补偿、相干转移和分子间多量子相干等技术与空间编码技术相结合,已成功实现不均匀场下超快速获得高分辨NMR谱. 该文对不均匀场下空间编码超快速NMR方法进行了介绍,对其未来发展进行了展望.     

Improving spectral resolution in spatial encoding dimension of single-scan nuclear magnetic resonance 2D spin echo correlated spectroscopy

The spatial encoding technique can be used to accelerate the acquisition of multi-dimensional nuclear magnetic resonance spectra. However, with this technique, we have to make trade-offs between the spectral width and the resolution in the spatial encoding dimension (F1 dimension), resulting in the difficulty of covering large spectral widths while preserving acceptable resolutions for spatial encoding spectra. In this study, a selective shifting method is proposed to overcome the aforementioned drawback. This method is capable of narrowing spectral widths and improving spectral resolutions in spatial encoding dimensions by selectively shifting certain peaks in spectra of the ultrafast version of spin echo correlated spectroscopy (UFSECSY). This method can also serve as a powerful tool to obtain high-resolution correlated spectra in inhomogeneous magnetic fields for its resistance to any inhomogeneity in the F1 dimension inherited from UFSECSY. Theoretical derivations and experiments have been carried out to demonstrate performances of the proposed method. Results show that the spectral width in spatial encoding dimension can be reduced by shortening distances between cross peaks and axial peaks with the proposed method and the expected resolution improvement can be achieved. Finally, the shifting-absent spectrum can be recovered readily by post-processing.     

Ultrafast 2D NMR spectroscopy using a continuous spatial encoding of the spin interactions

A new protocol for acquiring multidimensional NMR spectra within a single scan is introduced and illustrated. The approach relies on applying a pair of frequency-chirped excitation and storage pulses in combination with echoing magnetic field gradients, in order to impart the kind of linear spatial encoding of the NMR interactions that is required by ultrafast 2D NMR spectroscopy. It is found that when dealing with 2D NMR experiments involving a t1 amplitude-modulation of the spin evolution, such continuous encoding scheme presents a number of advantages over alternatives employing discrete excitation pulses. From an experimental standpoint this is mainly reflected by the use of a single pair of bipolar gradients during the course of the indirect-domain encoding, as opposed to the numerous (and more intense) gradient echoes required so far. In terms of the spectral outcome, main advantages of the continuous spatial encoding scheme are the avoidance of "ghost peaks" and of "enveloping effects" associated to the discrete excitation mode. The principles underlying this new spatial encoding protocol are derived, and its applicability is demonstrated with homo- and heteronuclear 2D ultrafast NMR applications on small molecule and on protein samples.     

Use of spatial encoding in NMR photography

NMR photography has gained significant attention as a method of storing and retrieving information using NMR spectroscopy. Among the commonly practiced methods the most important is the frequency encoding by use of a multi-frequency pulse on a liquid crystal molecule. We propose and demonstrate another robust method which relies on spatial encoding. Spatial information is mapped onto the spectrum, if excited and recorded in the presence of a gradient. The encoding is performed by applying a multi-frequency pulse in the presence of a gradient. The subsequent acquisition, under a gradient, helps storing this spatial information on a one-dimensional spectrum. Series of such spectra can also store two-dimensional patterns. This procedure is described and exemplified in this paper.     

Simplifying DOSY spectra with selective TOCSY edited preparation

Diffusion-ordered NMR spectroscopy, while quite powerful, is limited by its inability to resolve signals that are severely overlapped in the proton spectrum. We present here a DOSY experiment that uses selective TOCSY as an editing/preparation period. With this method, well-resolved signals of the analytes are selectively excited and the magnetization subsequently transferred by isotropic mixing to resonances buried in the matrix background, which are then resolved by the ensuing DOSY sequence. Key to the success of our proposed method is the incorporation of a highly effective zero-quantum filter into the selective TOCSY preparation period, which prevents zero-quantum coherence from being carried into the DOSY part of the pulse sequence. Further improvement in spectral resolution can be obtained by expanding the proposed experiment into a 3D sequence and utilizing the homonuclear decoupling feature of the BASHD-TOCSY technique. Both pulse sequences were found to greatly simplify the DOSY spectrum of a 'dirty' sucrose/raffinose mixture, as the complex matrix background is no longer present to obscure or overlap with the signals of interests. Furthermore, complete resolution of the relevant signals was achieved with the 3D sequence.     

A continuous phase-modulated approach to spatial encoding in ultrafast 2D NMR spectroscopy

Ultrafast 2D NMR replaces the time-domain parametrization usually employed to monitor the indirect-domain spin evolution, with an equivalent encoding along a spatial geometry. When coupled to a gradient-assisted decoding during the acquisition, this enables the collection of complete 2D spectra within a single transient. We have presented elsewhere two strategies for carrying out the spatial encoding underlying ultrafast NMR: a discrete excitation protocol capable of imparting a phase-modulated encoding of the interactions, and a continuous protocol yielding amplitude-modulated signals. The former is general but has associated with it a number of practical complications; the latter is easier to implement but unsuitable for certain 2D NMR acquisitions. The present communication discusses a new protocol that incorporates attractive attributes from both alternatives, imparting a continuous spatial encoding of the interactions yet yielding a phase modulation of the signal. This in turn enables a number of basic experiments that have shown particularly useful in the context of in vivo 2D NMR, including 2D J-resolved and 2D H,H-COSY spectroscopies. It also provides a route to achieving sensitivity-enhanced acquisitions for other homonuclear correlation experiments, such as ultrafast 2D TOCSY. The main features underlying this new spatial encoding protocol are derived, and its potential demonstrated with a series of phase-modulated homonuclear single-scan 2D NMR examples.