改进的远程C—H化学位移相关谱脉冲序列

本文在实验上比较了COLOC和近期发表的几个改进的远程C-H化学位移相关谱脉冲序列,综合各脉冲序列优点提出了一个改进的COLOCH序列。用一键(~1J_ch)相关峰压制率和远程相关峰成功率作为判断脉冲序列的依据。研究结果表明,Martin,COLOCS和COLOCH是较成功的脉冲序列,而且实验参数设置对实验的成功十分重要。     

相关光谱法检测甲烷浓度的研究

提出了一种基于相关光谱法的甲烷检测方案,在传统相关光谱法和差分吸收技术的检测理论的基础上,综合两者的优点提出了一种新的实现方案.合理的选择实验器材,构建了一个新的光纤甲烷检测系统.该系统不仅消除了待测气体中干扰气体引起的光强波动,而且也消除了周围环境的影响和光源光谱波动引起的干扰.     

基于Matlab仿真的联合变换相关器实验

利用Matlab软件平台对JTC进行了图像识别仿真实验,得到了二维及三维相关输出图像,显示出尖锐的相关峰.仿真实验表明:联合变换进行图像识别中存在强烈的零级干扰,干扰信号是有用信号的7.14倍,输出结果不理想;采用功率谱相减法可以消除零级强干扰,进而提高了图像的识别能力.     

网络远程控制实验的教学设计与管理

网络远程控制实验是实验走出实验室的重要方式.网络远程实验在技术层面已经得到了基本实现,与之相配套的教学设计与管理,也引起了很多学者的关注.笔者将从支持学习者学习的角度结合远程控制实验的具体特点对其教学设计和管理提出一些看法和建议.     

光纤光栅径向受力检测技术

对光纤布喇格光栅径向受力特性进行了理论与实验研究,给出了光纤布喇格光栅的径向受力灵敏度,并利用可调F-P标准具设计了一套解调光纤布喇格光栅反射峰劈裂值的实验系统.此系统消除了外界环境对F-P标准具初始腔长的干扰所引起的误差,系统的准确度达到了0.02 nm.     

匹配滤波识别相关峰的分析与实验判别

能否输出相关峰是相关器判定目标真伪的主要方式,但其元件调节精准度不高时,容易对相关峰产生误判。基于匹配滤波相关识别器,从理论上分析了相关峰产生误判的3种可能,重点对相关信号的强度判别进行了理论和实验研究,针对这3种可能产生误判的情况,分别从实验结果的相关峰阈值强度、形态、输入图像旋转方面探讨真伪相关峰的判别,为相关峰的判别提供实验参考。     

一种新颖的温度补偿光纤光栅应力传感测量技术

分析了光纤Bragg光栅的应变响应原理,通过实验观察光纤光栅粘贴在厚度不均的悬臂梁上产生的双峰响应,证明悬臂梁结构的不均匀会使整个光纤光栅受到不同的应力而产生两个反射峰,并且两个反射峰之间的距离随着应力的增加呈线性变化。实验中,当载荷为200g时,两个反射峰之间距离达到0.16nm,而温度变化不会引起两个反射峰之间的变化。利用这种结构的封装,可以克服光纤光栅对温度和应力交叉敏感的问题,消除温度变化引起的应力测量误差,实现一个光纤光栅对应力单参量的测量。     

胰腺癌和慢性胰腺炎的胰液核磁共振1H谱分析

运用核磁共振波谱技术对临床慢性胰腺炎和胰腺癌患者的胰液样品进行体外波谱学分析,观察和鉴别胰腺癌和慢性胰腺炎的特征代谢物变化,从而为胰腺癌以及相关胰腺疾病的病理研究提供基础数据和实验方法. 本文利用胰液样品在室温下能长时间稳定的特性,对其进行了质子的1D、TOCSY和J-resolved等多种NMR实验,并对其主要特征峰进行了指认. 实验结果显示在δ 1.19的三重峰是这两种病变在胰液中的主要区别：只在慢性胰腺炎图谱中观察到,而在胰腺癌图谱中未见. D实验结果表明此特征峰为乙氧基中的甲基峰,而乙氧基可能与胰腺中乙醇的代谢有关     

皮秒脉冲在零平均色散光纤链中传输的数值模拟

基于一种二阶和三阶色散都作了完全补偿(路径平均色散为零)的光纤级联系统模型,用数值法对1ps脉宽的高斯光脉冲长距离传输作了数值模拟.结果表明:这种完全补偿的高阶色散控制系统消除了三阶色散引起的脉冲边沿部的振荡,减弱了脉冲峰的时间移动.在不同的入上分别给输入脉冲附加以最佳的频率啁啾,可使得光脉冲的宽度`啁啾及振都围绕在初始值附近波动,在每个补偿端末基本恢复到初值,从而形成光脉冲的推稳定传输.功率增大,稳定传输的距离减小.预啁啾和零平均色散传输并不能完全消除脉冲峰的时间移动。累积的脉冲峰移与预啁啾无关,随功率增大而增大。脉宽的变化与功率和预啁啾都相关。另外,我们也考察了掺饵光纤放大器EDFA的噪声在该系统中引起的时间抖动特性。     

离子注入对InAs/GaAs量子点光学效质的影响

研究了低能质子注入诱导的界面混合和快速热退火对量子点发光效率的影响，对其光致发光 峰强进行了拟合计算.研究发现量子点的发光峰强度主要由载流子俘获时间和非辐射复合寿 命决定.由于后退火处理能够部分的消除因质子注入造成的缺陷，量子点中非辐射复合中心 浓度与注入剂量成亚线性关系；退火温度越高，非辐射复合中心被消除越多，亚线性程度越 高.界面混合导致的俘获效率的增加和注入损伤引起的非辐射复合是相互竞争过程，存在一 个临界的注入剂量N_C，当注入剂量N小于N_C，界面混合作 用较为明显，量子点 发光峰强随注入剂量增加而增强；当N大于N_C时，质子注入引起了大量的非 辐射复合 中心，主要表现为注入损伤，量子点的发光峰强随注入剂量增加而迅速减弱.退火温度越高 ，N_C越大. 关键词： 量子点 离子注入 峰强     

Proton dipolar recoupling in resin-bound peptides under high-resolution magic angle spinning

Rotational resonance and radiofrequency-driven dipolar recoupling (RFDR) experiments have been used to recover the weak proton dipolar interaction present in peptides bound to swollen resins spun at the magic angle. The intensity of the correlation peaks obtained using these sequences is shown to be significantly stronger than the one obtained using the classical NOESY experiment. In addition, it is found that during the relatively long mixing times required to transfer magnetization in such soft materials, the RFDR sequence also achieves magnetization transfer via the scalar J-coupling.     

HAT HMBC: a hybrid of H2BC and HMBC overcoming shortcomings of both

A new 2D NMR experiment, HAT HMBC, that is a hybrid of H2BC and HMBC aims at establishing two-bond correlations absent in H2BC spectra because of vanishing (3)J(HH) coupling constants. The basic idea is to create an additional pi phase difference in the multiplet structure in HMBC peaks with respect to the (n+1)J(HH) coupling constant between the proton(s) attached to a (13)C and a (1)H separated by n bonds. Thus HMBC peaks associated with small J(HH) will be the most attenuated in a HAT HMBC spectrum in comparison to a regular HMBC spectrum, i.e. peaks associated with (n+1)J(HH) and (n)J(CH) will for n>2 usually be strongly attenuated. The HAT HMBC pulse sequences contain the same number of pulses as regular HMBC and are only a few milliseconds longer.     

A J-multiplied HMQC (MJ-HMQC) experiment for measuring (3)J(HNHalpha) coupling constants

The J-multiplied HSQC experiment (MJ-HSQC: S. Heikkinen et al., J. Magn. Reson 137, 243 (1999)) amplifies J coupling constants m times and allows direct observation of the (3)J(HNHalpha) coupling constants of peptides and proteins (<10 kDa). The drawbacks to this method are line broadening in the f(1)-dimension and lower sensitivity. In the J-multiplied HMQC (MJ-HMQC) experiment described here, the PEP-HSQC pulse sequence is replaced by a sensitivity-enhanced HMQC section, and the total decay time for the J-coupling and the chemical shift evolution is shortened by a period of t(1). This experiment affords narrower linewidth and enhances the sensitivity by 34%, on an average of 105 well-isolated peaks, when compared with the MJ-HSQC experiment.     

Double-quantum filtered MAS NMR in the presence of chemical shielding anisotropies and direct dipolar and J couplings

Double-quantum filtered MAS NMR spectra of an isolated homonuclear spin-1/2 pair are considered, at and away from rotational resonance conditions. The pulse sequence used is the solid-state NMR equivalent of double-quantum filtered COSY, known from solution-state NMR. The 119Sn spin pair in [(chex3Sn)2S] is characterized by a difference in isotropic chemical shielding smaller than the two chemical shielding anisotropies and by direct dipolar and isotropic J-coupling constants of similar magnitudes. At rotational resonance, one-dimensional double-quantum filtered 119Sn lineshapes yield the relative orientation of the two 119Sn chemical shielding tensors. Good double-quantum filtration efficiencies are found at and away from rotational resonance conditions, despite the presence of large chemical shielding anisotropies. Numerical simulations illustrate the interplay of the direct dipolar and J-coupling pathways and identify the latter as the main pathway even at rotational resonance conditions.     

降压活性成分淫羊藿甙的HMQC和HMBC谱研究

首次对中药淫羊藿中降压活性成分淫羊藿甙的HMQC和HMBC谱进行了深入研究,结合¹H-¹H COSY谱,确切归属了全部碳氢信号,并直接从HMBC谱上确认了异戊烯基,甲氧基,鼠李糖和葡萄糖在黄酮母核上的连接位置,并修正了文献中关于该化合物某些碳信号归属的错误.显示这两种2D NMR新技术对结构复杂的黄酮甙类化合物的结构研究具有重要意义.     

Clean HMBC: suppression of strong-coupling induced artifacts in HMBC spectra

A new experiment, clean HMBC, is introduced for suppression of strong-coupling induced artifacts in HMBC spectra. The culprits of these artifacts are an inherent shortcoming of low-pass J filters in the presence of strong coupling and the (1)H pi pulse in the middle of the evolution period aimed at suppressing evolution under heteronuclear J couplings and (1)H chemical shifts. A pi pulse causes coherence transfer in strongly coupled spin systems and, as is well known in e.g., homonuclear J spectra, this leads to peaks that would not be there in the absence of strong coupling. Similar artifacts occur in HMBC spectra, but they have apparently been overlooked, presumably because they have been assigned to inefficiency of low-pass J filters or not noticed because of a coarse digital resolution in the spectra. Clean HMBC is the HMBC technique of choice for molecules notorious for strong coupling among protons, such as carbohydrates, and the new technique is demonstrated on D-mannose. Finally, a fundamental difference between HMBC and H2BC explains why strong-coupling artifacts are much less of a problem in the latter type of spectra.     

歧化松香中树脂酸异构体的NMR研究

树脂酸是松香的主要成分,歧化松香质量的好坏,主要取决于树脂酸的组分及其含量.本文测定了五种树脂酸——枞酸、新枞酸、左旋海松酸、长叶松酸和脱氢枞酸的¹H、¹³C、DEPT谱.并通过二维HMQC以及HMBC相关谱和模型化合物分别对其谱图的归属进行了详细的探讨.     

Getting to know the nitrogen next door: HNMBC measurements of amino sugars

Long-range 1H-1?N correlations detected by the heteronuclear multiple-bond correlation (HMBC) experiment are explored for the characterization of amino sugars. The gradient-enhanced HMBC, IMPACT-HMBC, and a modified pulse sequence with the 1J-filters removed, IMPACT-HNMBC, are compared for sensitivity and resolution. 1?N chemical shifts and long-range proton correlations are reported using the IMPACT-HNMBC experiment for N-acetyl-glucosamine, N-acetyl-galactosamine, and for a series of glucosamine analogs with an N-sulfo substitution, unmodified amino group, and 6-O-sulfonation. As is common with sugars, for all the compounds examined both anomeric forms are present in solution. For each compound studied, the 1?N chemical shifts of the α anomer are downfield of the β form. For the N-acetylated sugars, the β anomer has a unique long-range 1?N correlation to the anomeric proton not observed for the α anomer. Though N-sulfonation results in a significant change in the 1?N chemical shift of the glucosamine analogs, 6-O sulfo substitution has no significant effect on the local environment of the amino nitrogen. For N-acetylated sugars in D?O solution, peaks in the 1?N projection of the HMBC spectrum appear as triplets as a result of J-modulation due to 2H-1?N coupling.     

Efficient spin-spin scalar coupling mediated C-13 homonuclear polarization transfer in biological solids without proton decoupling

We demonstrate that an efficient C′↔C polarization transfer based on J-coupling can be realized under fast magic-angle spinning (MAS) condition without ¹H decoupling. Experimental results are presented for model crystalline compounds as well as a non-crystalline 17-residue polypeptide MB(i+4)EK. Measurements on MB(i+4)EK demonstrate that 53% of the initial C′ polarization was transferred to the cross peaks at 7.05 T under 25 kHz MAS spinning.     

Spectral characteristic of high-dose high-temperature emission from LiF:Mg,Cu,P (MCP-N) TL detectors

High-temperature emission spectra of LiF:Mg,Cu,P (MCP-N) TL detectors, irradiated above the nominal saturation level, up to the hundreds of kGy, have been measured. Emission spectra integrated over the whole temperature range, as well as the spectra recorded at the temperatures corresponding to the TL peaks maxima, were analyzed. With increasing dose of γ-radiation no significant changes were observed in the short wavelength emission range (220–450 nm) of the measured spectra. For doses of 4 kGy and higher the long wavelength emission (450–800 nm) started to be visible. All recorded spectra have been expressed in a form of the sum of several Gaussian-shape bands in the energy domain, which parameters remain in a general agreement with the measurements of Mandowska et al. (2010). Spectra of the low-temperature, main, high-temperature and “B” TL peaks were investigated. In the ranges of the low-temperature and the main dosimetric peaks, that is 100–125 and 210–230 °C, respectively, the short wavelength emission disappeared with increasing dose and for the highest doses the long wavelength emission became dominant. Both the high-temperature (290–320 °C) and the “B” (370–425 °C) peaks emission spectra exhibited somewhat different behavior with increasing dose. Initially, an even growth of the whole spectrum was observed and for doses higher than 16 kGy the intensity of the spectrum decreased, but the short wavelength emission band fell significantly faster, in case of the high-temperature TL peaks. In case of the “B” peak emission spectra the long wavelength emission did not play any role in the analyzed dose range. The spectra measured at the TL peaks maxima were also fitted with several Gaussian-shape bands. Dose-intensity dependences for all Gaussian-shape bands fitted to the measured spectra are also included in this paper.