基于自主研发的500 MHz NMR谱仪的紫杉醇结构解析

中国科学院武汉物理与数学研究所（WIPM）于2010年成功研制了500 MHz（WIPM-I 500）高分辨超导核磁共振（NMR）谱仪,并将其投入实际应用中.然而,关于其二维核磁共振（2D NMR）谱图的准确性及在此基础上对复杂物质的结构解析尚无系统完整的数据报道.该文利用WIPM-I 500型NMR谱仪,对紫杉醇样品进行了1D NMR及2D NMR（包括¹H-¹H COSY、¹H-¹H TOCSY、J-Res、¹H-¹³C HMQC和¹H-¹³C HMBC）实验,将谱图分析结果与进口仪器进行了对比.结果表明：利用WIPM-I 500型NMR谱仪能够采集准确的2D NMR谱图,为紫杉醇的正确归属提供了实验基础;而且该文也纠正了文献中对紫杉醇的错误归属.     

没有磁场的核磁共振谱学

核磁共振谱学（NMR）可能是有机化学研究中最有用的技术.但是常规的NMR谱仪要求将样品放置在非常强的磁场中,这就需要使用液氦冷却的庞大而昂贵的超导磁铁.美国的一个从事交叉学科研究的小组研制成功没有磁铁的NMR谱仪.     

NMR波谱仪控制台系统的软件测试

作为保证软件质量的重要手段,软件测试多年来一直受到关注. 本文阐述了核磁共振（NMR）波谱仪研制中的软件测试方法,从软件测试的概念出发,结合波谱仪控制台系统的软件结构和核磁共振实验本身的特性,介绍了整个测试过程,分析了测试难点及其解决方法,并详细说明了软件测试的实现过程以及在提高波谱仪可靠性和稳定性上所起的积极作用.      

核磁共振谱仪超导磁体研究

对核磁共振谱仪超导磁体作了一些调研 ,并在理论的基础上对 4 0 0 MHz NMR谱仪超导磁体进行了方案设计计算     

一体化核磁共振谱仪数据交换的实现机制

核磁共振（NMR）随着其应用领域的拓展和深入,核磁共振谱仪技术得到了不断的发展和完善^[1,2]_. 针对以往谱仪存在的一些问题,本文提出了一种一体化核磁共振谱仪数据交换的实现机制,同时提出了基于ARM（Advanced RISC Machines,先进精简指令计算机）微处理器的嵌入式操作系统软件设计方案,并给出了谱仪各功能模块的实际性能测试结果,对实验结果进行了总结和讨论.      

自主研制核磁共振波谱仪的性能评估

主要介绍自主研制500 MHz核磁共振谱仪的性能评估情况,旨在建立一台功能完整的核磁共振波谱仪. 首先利用系统调试使控制台各个硬件单元在用户软件控制下实现NMR实验中的基本功能,然后通过性能测试保障功率线性度、信号稳定性和场频联锁的可靠性,实验验证了谱仪溶剂峰压制的效果,并获得良好的探头线形指标（0.43/5.46/10.73 Hz）和¹H灵敏度指标（信噪比为728∶1）,表明自主研制500 MHz核磁共振波谱仪系统能够满足常规核磁共振实验需求.     

高聚物微观结构的固体NMR研究

核磁共振波谱是研究高聚物结构和动力学的有效手段,特别是固体高分辨NMR实验方法的不断发展及谱仪技术的进步,使这方面的研究不断深入. 文中简述了若干固体高分辨NMR技术在固态高聚物结构研究中的应用和重要进展. 部分实验工作在Varian UNITYplus 400MHz NMR谱仪的固体单元上完成.     

HC-4型固体多核宽线CW-NMR波谱仪

设计和研制了一台用于检测固体中NMR宽谱线、型号为HC-4的CW-NMR波谱仪.谱仪由APPLE-Ⅱ微型计算机控制扫描、信号累加和数据处理.配备了自制的交叉线圈型和魔T型NMR探头和高温(1300K)探头,使谱仪具有较高的检测灵敏度和较强的测量功能,适用于检测固体中多种非质子核的NMR宽谱线及动态NMR测量.本文简要介绍该谱仪的基本结构、系统各部分的技术性能和测量应用的具体实例.     

Bruker AC-80核磁共振谱仪故障判断与排除

就Bruker公司AC-80核磁共振谱仪的一些常见故障做了分析和总结,并给出排除方案. 一方面,谱仪故障的及时排除能给科研节省宝贵的时间;另一方面,了解谱仪容易出故障的地方及做好相应对策,对于研究者自行对商用谱仪所不能达到创新性实验研究所要求部件进行改造、设计有着重要的意义.     

布鲁克新一代NMR自动调谐探头

所有的分析仪器总是不断追求进一步提高自动化程度,例如在有机合成和药物化学方面,为了适应大量筛选工作的需要,组合化学应运而生,对仪器自动化的要求更高.在这个领域里,NMR是个关键的分析技术,首当其冲地面对这些要求.作为主要的分析仪器生产厂家,布鲁克公司的承诺是——永远不断创新.最近,布鲁克公司推出用计算机控制的自动调谐和匹配的新一代NMR探头,就是又一个明显的例子.这种新探头,不仅满足了用户对NMR谱仪不断提高的要求,同时,使分子结构的测定和验证接近于完全自动化.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.