分子间多量子相干横向弛豫时间(和自扩散系数)测量的参数优化和数据处理方法

针对测量横向弛豫时间T₂的CPMG脉冲序列和我们所设计的可同时测量高极化单组份单 峰核自旋体系n阶分子间多量子相干横向弛豫时间T_2,n和自扩散系数D_n的改进的CRAZED脉冲序列,分析了影响测量T₂、T_2,n（或D_n）的各种因素,并着重从技术方面讨论了准确测量T_2,n和D_n的实验参数优化和实验数据处理方法.     

双重低通滤波的HMBC实验

利用两个低通滤波器,在反转检测的异核远程相关实验(HMBC)中消除由直接相关引起的卫星峰.消除其对远程相关峰的干扰,不仅理论上说明了其原理,而且在实验上得到证实.同时此实验不会引起灵敏度的下降.     

COLOC-S脉冲序列在天然有机化合物结构分析中的应用

本文用远程异核化学位移相关谱(COLOC-S脉冲序列)和异核化学位移相关谱研究了香茶菜属二萜类化合物冬凌草甲素和香茶菜醛的化学结构,并对这两个化合物的¹³C和¹HNMR谱线进行了归属。     

COLOC—S脉冲序列在天然有机化合物结构分析中的应用

本文用远程异核化学位移相关谱(COLOC-S脉冲序列)和异核化学位移相关谱研究了香茶菜属二萜类化合物冬凌草甲素和香茶菜醛的化学结构,并对这两个化合物的~(13)C和~1HNMR谱线进行了归属。     

改进的ROESY技术及实验方法

本文介绍了对ROESY(CAMELSPIN)技术改进的脉冲序列的原理。这种改进的技术能有效的抑制偏共振效应的影响和提高谱的灵敏度。进行了1D和2D ROESY实验。实验结果表明,改进的ROESY实验能提高谱图灵敏度40%～80%,并能有效地压制其它2D响应信号。     

基于WATERGATE的双溶剂峰抑制方法

WATERGATE（W3/W5）是NMR实验中使用较为广泛的溶剂峰抑制方法,但该方法通常仅能对一个溶剂信号进行有效抑制. 本文对WATERGATE的脉冲序列进行修饰、优化,发展了两种新的双溶剂峰抑制方法. 实验结果表明,经过修饰、优化后的WATERGATE,实验的设立非常简单,不需要复杂的优化过程就能够对双（多）溶剂峰进行有效抑制, 可用于常规1D & 2D NMR 实验、HPLC NMR实验,以及天然产物粗提取物的分析中.     

体内1H NMR中的水峰抑制

本文研究了in Vivo NMR实验中的水峰抑制问题.通过结合予饱和和1-2τ-5,4-τ-5,4-2τ-1硬脉冲序列,水峰抑制系数达到1000以上.从而为研究微量代谢产物创造了条件.     

基于Bloch方程的核磁共振数值求解

核磁共振已成为分子科学、材料科学和生命科学等领域研究物质结构、动态过程及物理特性最有效的工具之一.本文将基于Bloch方程研究核磁共振现象及相关实验参数如共振频率和弛豫时间,同时对实验中常用的脉冲序列如Single Pulse,Inversion Recovery,Spin Echo,CPMG等进行系统模拟,揭示出不同脉冲序列的物理意义.     

周期性控制液态磁共振自旋湍流的研究(英文)

辐射阻尼和远程偶极场联合作用导致的混沌自旋动态能够产生常见于高场梯度磁共振实验中不可再现的实验结果,且该现象较先前所认为的更为常见.该文发展了一种基于射频微扰的周期性控制方法,以降低Lyapunov指数并抑制在波谱中的不稳定测量结果.同时讨论了周期性控制的设计原则及如何应用在诸多脉冲序列中,用以抑制自旋湍流.     

基于PC机的脉冲序列发生器

为了降低谱仪的复杂性和成本，文中提出了基于PC机的脉冲序列发生器设计方案. 详细讨论了在Windows 98和Windows XP下通过关中断的方法来保证脉冲序列时序的精度和稳定性，通过实验给出了基于PC机的脉冲序列发生器的短期稳定度和长期稳定度，最后通过自旋回波实验直接验证了该方案的可行性.     

The equivalence between off-resonance and on-resonance pulse sequences and its application to steady-state free precession with diffusion in inhomogeneous fields

We show that the spin dynamics of any pulse sequence with off-resonant pulses is identical to that of a modified sequence with on-resonant pulses, including relaxation and diffusion effects. This equivalence applies to pulse sequences with arbitrary offset frequency deltaomega(0) which may exceed the RF field strength omega(1). Using this approach, we examine steady-state free precession (SSFP) in grossly inhomogeneous fields. We show explicitly that the magnitude of the magnetization for each mode at an offset frequency deltaomega(0) is equal to that for SSFP with on-resonance pulses of rescaled amplitude, with the same dependence on relaxation times and diffusion coefficient. The rescaling depends on offset frequency and RF field strength. The theoretical results have been tested experimentally and excellent agreement is found.     

Efficiency of Spurious Signal Cancellation under the NQR Detection of Some Explosives by the SLIME-Type Pulse Sequences

Two versions of the spin-lock inversion mid-echo pulse sequence used for the prompt nuclear quadrupole resonance detection of explosives have been studied experimentally. These sequences are modifications of the conventional multiple pulse spin-locking sequence and differ from it by additional groups of pulses which invert echo signals. It was found that spurious signals produced by some magnetic objects are suppressed by one of these sequences much stronger than by the other. The attenuation of echo signals due to their inversion by the group of the inverting pulses is measured. The number of pulses is optimized in both the sequences to obtain maximum signal-to-noise ratio, taking into account some loss in the magnitude of inverted echoes.     

Slice profile improvement for a clinical MRI system

Optimal control methods have been recently introduced to improve the design of selective radio frequency pulses and several optimized selective pulses that can produce excellent slice profiles have been reported. These pulses usually require high peak rf amplitudes to implement and thus can not be widely utilized because of the limitations of the specific absorption rate and the rf power amplifier of a clinical system. We have a Siemens 1.5 T MRI clinical system. Several pulse files which consist of the bandwith matched 90° and 180° selective pulses are provided. Some of these can produce excellent slice profiles. However, they can only be used in the pulse sequences with the pulse length of 5.12 msec. The purpose of this paper is to improve the slice profiles produced by the pulse file in the pulse sequences with the shorter 2.56 msec pulse length. A pulse file optimized by the conjugate gradient method is proposed to substitute the 2.56 msec Siemens pulse file. Our experimental results confirm that the slice profiles and images are improved by the optimized pulse file with a lower peak voltage. The proposed pulse file can also be applied in other clinical MRI systems.     

Improved J-compensated sequences based on short composite pulses

Efficient J-compensated sequences that are shorter in duration and use less RF pulses have been created from short but very efficient composite 90 degrees RF pulses. The improved J-compensation transforms in-phase into antiphase magnetization and can be incorporated in any pulse sequence that involves evolution of heteronuclear J-couplings. The compensated sequences were tested and incorporated into an HMBC sequence. J-compensated experiments referred to as HMBC-J45 + 90A and HMBC-J45 + 90B, were found to be effective over a wide range of J values.     

基于单光子脉冲时间随机性的光量子随机源

提出了一种基于单光子脉冲时间随机性的光量子随机源。利用衰减成单光子态的光强恒定光源和一个单光子探测器产生单光子随机脉冲,通过连续比较单光子随机脉冲序列中相邻两个脉冲的时间间隔来提取随机位。通过设计高速响应的微通道板单光子探测器和基于现场可编程门阵列(FPGA)的随机位提取电路,获得了超过10Mbit/s的随机位产生速率。通过采用恒比定时和对计数时钟倍频的方法提高时间间隔的测量精度,从而减小随机位序列的相关系数。当光量子随机源的随机位产生速率在10kbit/s以下时,所获得的二进制随机位序列的相关系数小于0.001。运用随机性测试程序ENT和DIEHARD对所获的随机位序列进行测试,测试结果表明序列的随机性非常好且不需要后续处理,完全满足真随机数的标准。     

Long-range interaction of picosecond solitons through excitation of acoustic waves in optical fibers

We present the theory of electrostrictional interaction of soliton pulses in optical fibers. Solitons excite acoustic waves propagating in the direction transverse to the fiber axis. Scattering of optical radiation on these waves leads to a timing jitter of the optical pulses arrival time. We consider this effect as nonlinear self-scattering of light on acoustic waves. Because of the fact that a value of acoustic lifetime can reach a value of about 100 ns self-scattering on acoustic waves can be observed for a single optical pulse as well as for an optical pulse sequence as a whole. The value of single soliton self-frequency shift due to excitation of acoustic waves as a function of soliton duration have been obtained. For soliton duration _sol > 14 ps an acoustic wave soliton self-frequency shift is larger than the Raman soliton self-frequency shift.The obtained theoretical results describe well the long-range interaction of soliton pulse trains in an optical fiber. The value of bit error rate due to electrostrictional interaction of optical pulses in high bit rate, ultra long soliton communication systems have been obtained.     

二维核磁共振谱测定植物新环肽-太子参环肽A和B中氨基酸序列

在植物新环肽[太子参环肽A(HA)和B(HB)]的结构研究中,应用COLOC谱较成功地解决了其氨基酸序列。结果表明当J值选择在6Hz-15Hz时,COLOC谱能满意地给出氮上含有活泼氢的氨基酸序列。     

Solvent suppression using phase-modulated binomial-like sequences and applications to diffusion measurements

Two phase-modulated binomial-like pi pulses have been developed by simultaneously optimizing pulse durations and phases. In combination with excitation sculpting, both of the new binomial-like sequences outperform the well-known 3-9-19 sequence in selectivity and inversion width. The new sequences provide similar selectivity and inversion width to the W5 sequence but with significantly shorter sequence durations. When used in PGSTE-WATERGATE, they afford highly selective solvent suppression in diffusion experiments.