Anomalous Rotational Resonance Spectra in Magic-Angle Spinning NMR

Magic-angle spinning NMR spectra of samples containing dilute spin-1/2 pairs display broadenings or splittings when a rotational resonance condition is satisfied, meaning that a small integer multiple of the spinning frequency matches the difference in the two isotropic shift frequencies. We show experimental rotational resonance NMR spectra of a 13C2-labeled retinal which are in qualitative disagreement with existing theory. We propose an explanation of these anomalous rotational spectra involving residual heteronuclear couplings between the 13C nuclei and the neighboring 1H nuclei. These couplings strongly influence the rotational resonance 13C spectrum, despite the presence of a strong radiofrequency decoupling field at the 1H Larmor frequency. We model the residual heteronuclear couplings by differential transverse relaxation of the 13C single-quantum coherences. We present a superoperator theory of the phenomenon and describe a numerical algorithm for rapid Liouville space simulations in periodic systems. Good agreement with experimental results is obtained by using a biexponential transverse relaxation model for each spin site.     

质子化学位移各向异性的测量

测量质子化学位移各向异性（CSA）有助于表征分子结构与其动力学,但由于¹H-¹H同核偶极耦合相互作用很强及质子各向异性化学位移较小,测量质子化学位移各向异性仍具有巨大挑战,特别是对含有多种质子的生物大分子,如蛋白质.本文简要综述了测量质子化学位移各向异性的方法,包括同核去耦慢速魔角旋转方法、超快魔角旋转方法、对称重耦（RN_n^v）方法、xCSA方法以及量子化学计算方法.我们重点介绍了在高速魔角旋转条件下蛋白质氨基质子化学位移各向异性的测量及它们与氢键长度、蛋白质二级结构之间的关系.     

固体核磁共振中膜蛋白双交叉极化效率与动力学参数相关的定量分析

固体核磁共振（NMR）中双交叉极化（DCP）是用于膜蛋白信号指认的多维异核相关实验的基本技术模块.DCP的效率在很大程度上决定了多维异核相关实验的效率.本文分析了3种典型的膜环境中的膜蛋白（AQPZ、DAGK和EV71 2B）的DCP效率及其影响因素.结果显示,在相同的实验条件下,3种蛋白样品的DCP效率存在明显差异：其中AQPZ的DCP效率最高（31%）,DAGK的效率次之（23%）,EV71 2B的效率最低（14%）.通过测量它们在旋转坐标下的自旋-晶格弛豫时间（T_1ρ）和偶极耦合常数（D_HN）,发现膜蛋白的运动会明显缩短T_1ρ,但对D_HN的影响较小.在实验的基础上,建立了T_1ρ与DCP效率相关的模型,并基于DCP动力学的定量分析,证明了运动导致的T_1ρ缩短是降低DCP效率的主要原因.因此,可以通过定量分析未知样品的T_1ρ来预测其DCP的最优效率,为DCP实验的优化提供依据.     

Application of Rotor-Synchronized Amplitude-Modulated Cross-Polarization in aC–H Spin Pair under Fast Magic-Angle Spinning

Rotor-synchronized amplitude-modulated Hartmann–Hahn cross-polarization has been applied under fast magic-angle spinning to a powder sample of ferrocene. The influence on the cross-polarization process of the heteronuclear double quantum (flop–flop) transitions induced by the amplitude modulation for low ratios of the radiofrequency-field strength to the spinning speed is studied in details. The experimental data are in good agreement with theoretical calculations for a two-spinsystem, although the intensity of the double quantum transitions is observed to be significantly smaller than expected. Moreover, it is shown that an efficient polarization transfer at the Hartmann–Hahn centerband matching condition as well as a broadening of the matching conditions is obtained by an appropriate partial scaling of the effective radiofrequency fields which minimizes the destructive effect of double quantum cross-polarization.     

魔角旋转固体核磁共振探头中转子的研制

转子作为魔角旋转（MAS）探头一个至关重要的部件,是固体样品高速旋转的载体,被广泛应用于各种固体核磁共振（NMR）实验.但国内关于MAS转子的研究极少,以至其长期被国外市场垄断.本文通过对MAS转子的深入研究,设计了常规的4 mm MAS转子;并对MAS转子进行了流固耦合仿真,分析其应力应变大小;同时进行了模态仿真,确定了MAS转子的各阶振型及临界转速;最后制作了转子,进行了转速测试和固体NMR实验.结果表明,本文设计和制作的转子能在14 kHz转速下正常运行,并在4 kHz及12.5 kHz转速下采集了金刚烷标样的¹H NMR信号,结果表明该转子能满足常规固体NMR实验的需求.     

氘核破裂效应对质子出射能谱的贡献(英文)

基于连续离散化耦合道理论（CDCC）, 并在假设剩余核不仅可处于束缚态而且可处于一系列的激发态的基础上, 本工作论述了氘核破裂效应对质子出射能谱的贡献。计算结果可以基本解释质子出射能谱在大约氘核入射能量一半处出现峰值结构的实验现象。本工作的计算结果与C.Kalbach的经验公式基本保持一致。Based on the continuum discretized coupled channels(CDCC) theory, and the hypothesis that the residual nucleus locates not only in bound state but also in a series of excited states, the contribution of deuteron breakup effect in outgoing proton energy spectra are studied in the present work. And the results can basically explain the experimental results that a peak structure is appeared in the outgoing proton energy spectra at about half of the incident energy. The results of present calculation generally agree with those obtained from C. Kalbach’s empirical formulaum.     

High-Speed Magic-Angle SpinningC MAS NMR Spectra of Adamantane: Self-Decoupling of the Heteronuclear Scalar Interaction and Proton Spin Diffusion

We have investigated the carbon line shape of solid adamantane under high-speed magic-angle sample spinning (MAS) acquired without proton decoupling. The CH-group shows a spinning-speed-dependent line broadening while the CH₂-group consists of a spinning-speed-independent sharp component and a spinning-speed-dependent broader part. These phenomena can be explained by self-decoupling of theJ-interaction due to proton spin diffusion. Such a self-decoupling process can be described by a magnetization exchange process between the multiplet lines. Changing the spin-diffusion rate constant by off-resonance irradiation of the protons allows us to observe the full range from slow exchange to coalescence to fast exchange of the carbon spectra. One of the multiplet components in the CH₂-group corresponds to a group spin of the protons of zero and therefore does not couple to the other protons. This gives rise to the sharp central line. The magnetization exchange rate constant between the different multiplet lines can be determined from the spectra and is a measure for the spinning-speed-dependent proton spin-diffusion rate constant. Even at an MAS speed of 30 kHz, proton spin diffusion is still observable despite the relatively weak intermolecular proton dipolar-coupling network in adamantane which results in a static proton line width of only 14 kHz (full width at half height).     

Measurement of Cross Correlation between Dipolar Coupling and Chemical Shift Anisotropy in the Spin Relaxation ofC,N-Labeled Proteins

We present a simple method for extracting interference effects between chemical shift anisotropy (CSA) and dipolar coupling from spin relaxation measurements in macromolecules, and we apply this method to extracting cross-correlation rates involving interference of amide¹⁵N CSA and¹⁵N–¹H dipolar coupling and interference of carbonyl¹³C′ CSA and¹⁵N–¹³C′ dipolar coupling, in a small protein. A theoretical basis for the interpretation of these rates is presented. While it proves difficult to quantitatively separate the structural and dynamic contributions to these cross-correlation rates in the presence of anisotropic overall tumbling and a nonaxially symmetric chemical shift tensor, some useful qualitative correlations of data with protein structure can be seen when simplifying assumptions are made.     

The Influence of Solvent Viscosity on the Fluorescence Decay and Time-Resolved Anisotropy of Green Fluorescent Protein

This report describes fluorescence decay and time-resolved anisotropy studies of green fluorescent protein (GFP) in various environments. The addition of glucose and fructose, NaCl, or polyethylene glycol changes the viscosity of the medium surrounding the GFP. Both the time-resolved anisotropy and the fluorescence decay of GFP are measured and it is shown that only the time-resolved anisotropy of GFP is affected by the viscosity, but not its fluorescence decay.     

Influence of Light Scattering on Transmission Spectra of Photonic Crystals of Anodized Alumina

The light scattering is found to have a great influence on the transmission spectra of photonic crystal of anodic alumina. The incident light is diffracted by a regular array of branched channels or pores obeying the Bragg law. The intensity of transmission light decreases with the increasing etching time because of the increasing porosity or enlarging scatterers. The variation of intensity and widths of dips in transmission spectra of the porous alumina membrane versus the incidence angle shows the quite different characteristics from the other photonic crystal such as colloidal photonic crystal.     

应力各向异性对铁磁/反铁磁双层薄膜磁性质的影响

 采用铁磁共振方法,研究了交换各向异性和应力各向异性对铁磁/反铁磁双层薄膜性质的影响。结果表明：界面交换作用导致单向各向异性,应力各向异性对材料的磁化难易程度有较大影响。在外磁场方向接近应力场方向时,共振频率向高值方向移动,其它区域共振频率则向低值方向移动。对频率线宽而言,接近应力场方向,频率线宽加宽,其它区域频率线宽则变窄。此外,当磁场变化时,应力的存在使得共振频率向低值方向移动,尤其在β＝π方向情况较为复杂,在弱场范围出现了两个区域：即在某磁场范围内,共振频率向高值方向移动,且频率线宽加宽;而其它范围的共振频率（线宽）是向高值方向移动（加宽）还是向低值方向移动（变窄）,取决于外磁场的相对强弱。     

Molecular-orientation analysis based on alignment-induced TROSY chemical shift changes

We present a new NMR technique for determining the alignment tensor of a weakly aligned protein using only alignment-induced ¹⁵N transverse relaxation optimized spectroscopy (TROSY) chemical shift changes. Alignment-induced TROSY chemical shift changes reflect the combined contributions from two different anisotropic spin interactions including the residual dipolar couplings (RDCs) and the residual chemical shift anisotropy effects (RCSAs). We show here that these two residual anisotropic spin interactions’ values, encoded in the TROSY chemical shift changes, can be used to determine a weakly aligned protein’s alignment tensor. To prove the significance of this method, we show that our TROSY-based analysis gives the consistent alignment angles with those determined using RDCs for ¹⁵N-labeled ubiquitin (8.6 kDa) in an aligned medium, within an uncertainty range estimated by considering experimental and structural noises, being 5° at most. Because our approach requires a pre-determined ¹⁵N CSA tensor value, we also estimated the uncertainties associated with the resultant alignment tensor values caused by variation in ¹⁵N CSA tensors. In spite of the significant variations in literature-reported ¹⁵N CSA tensors, they gave consistent orientation angles within an uncertainty range. These results ensure that our TROSY-based approach is a useful alternative to the RDC-based method to determine the alignment angles especially for large proteins in a weakly aligned state.     

质子直线加速器设计研究

当前质子直线加速器发展的两个重要方向是强流质子直线加速器和小型质子直线加速器.前者主要用于核能领域,后者主要用于质子治疗.两类加速器有着共同的特点:1.采用一些新型加速结构,它们是传统结构的组合和发展;2.加速小发射度的质子束;3.加速器应有高度的可靠性.但前者的建造难度远大于后者,它还要求具有很低的束流损失率和尽可能高的能量利用效率.研究了两类加速器设计中的一些重要问题,提出了一些设计方案.     

Influence of Thermal Cycling on the Optical Spectra of TlInS2 Crystals Having an Incommensurate Phase

The crystals of TlInS₂ are investigated by the methods of optical absorption and second-harmonic generation. It is found that after a crystal is cooled for the first time an additional band appears in the absorption spectrum and the intensity of the second harmonic is greatest at temperatures 170–201 K. The characteristic features of the spectra and their dependence on the process of thermal cycling are explained by the formation of clusters and regions of an incommensurate phase in a commensurate one.     

Equilibrium Shape of Copper Crystals Grown on Sapphire

The equilibrium crystal shape (ECS) of copper has been studied by scanning electron microscopy on m-sized copper crystallites supported on single-crystals of -alumina. In addition, the orientation relationships between copper crystals and the sapphire substrate were investigated by X-ray techniques. A detailed discussion of the kinetic factors that can inhibit equilibration is provided, and it is shown that only crystals ranging in radius from 3 to 4.5 m can achieve equilibrium shapes under the conditions of the experiment. The maximum anisotropy of surface energy was found to be about 1.02, which is significantly lower than that of the other two fcc metals (lead and gold) for which reliable data are available. Another distinction between copper and those other fcc metals is that its ECS displays {110} facets, and possibly {311} facets, in addition to the commonly observed {111} and {100} facets, at temperatures where equilibration is possible. The observed facets connect tangentially to the curved parts of the ECS, so that all possible surface orientations are present on the copper ECS.     

并合不变中子质子产额比值角分布各向异性与对称能关系的研究

采用ImQMD05模型分析了非对称反应体系40Ar+197Au,124Sn在中低能区（E_beam=35~100 MeV/u）的半擦边反应的条件下的反应机制,并进一步探索了不同模型参数,如对称能斜率、碰撞参数等,对轻粒子并合不变中子质子产额之比角分布各向异性的影响。通过研究发现:对于出射动能大于每核子10 MeV的动力学出射的轻粒子而言,其并合不变的中子质子产额比值角分布各向异性与对称能的软硬具有明显的关联;碰撞参数对轻粒子动力学发射各向异性的影响最弱。By using the ImQMD05 code,we simulate the 40Ar+197Au,+124Sn at beam energy of 35,50 and 100 MeV/u and semi-peripheral collisions.The reaction mechanism,symmetry potential and Coulomb potential competition around the overlapped neck region and impact parameters effects are investigated for understanding the angular distribution of isospin contents of dynamical emitted light particles.Our results show that the angular anisotropy of the coalescence invariant neutron to proton yield ratios is sensitive to the stiffness of symmetry energy,especially for the dynamical emitted light particles with E_k>10 MeV.     

Precise Measurement of Muon Capture on the Proton

The aim of the μCap experiment is a 1% measurement of the singlet capture rate Λ _S for the basic electro-weak reaction μ + p → n + ν_μ. This observable is sensitive to the weak form-factors of the nucleon, in particular to the induced pseudoscalar coupling constant g _P . It will provide a rigorous test of theoretical predictions based on the Standard Model and effective theories of QCD. The present method is based on high precision lifetime measurements of μ⁻ in hydrogen gas and the comparison with the free μ⁺ lifetime. The μ⁻ experiment will be performed in ultra-clean, deuterium-depleted H₂ gas at 10 bar. Low density compared to liquid H₂ is chosen to avoid uncertainties due to ppμ formation. A time projection chamber acts as a pure hydrogen active target. It defines the muon stop position in 3D and detects rare background reactions. Decay electrons are tracked in cylindrical wire-chambers and a scintillator array covering 75% of 4π. This revised version was published online in August 2006 with corrections to the Cover Date.     

稀土邻菲咯啉双核配合物的光谱研究

合成了 Yx Eu1-x(phen) 2 Cl3· n H2 O、Tbx Eu1-x(phen) 2 Cl3· n H2 O(x=0、0 .2 5、0 .5 0、0 .75 )固体配合物 ,并测定了红外光谱、荧光发射光谱 ,讨论了配合物的组成与发光特性     

超导质子直线加速器的分段研究

对超导直线加速器的分段进行了详细的研究.包括超导加速器的分段原则的讨论,对称性分段和非对称性分段的讨论.超导加速腔的加速单元数及设计值β_G的确定,加速器的能量增益的确定.