两位置交换问题魔角旋转核磁共振时域信号的准确解

已知两位置交换分子运动速率对于静态¹³CNMR谱的影响是由一简单代数关系决定,它已成为分析固体中分子运动的常规方法.慢速的魔角旋转可以保留边带,所产生的边带型原则上也可用来分析分子运动,只是缺乏象静态谱那样的简单的关系,以至于在实际应用上是不可行的.本文给出作者所发现的存在分子运动时魔角旋转核磁共振自由诱导衰减信号的解析表达式的理论推导,提供分析固体分子运动的理论谱计算公式.我们选择二甲矾(dimethylsulfone)作为模型化合物,记录其不同温度下¹³CNMR谱,又计算了两个甲基做两位置交换运动的理论谱.理论谱与实验谱定性一致.定量上,边带强度存在一些差别,但边带宽度符合很好.通过理论谱与实验谱的比较,得到交换速率与温度的对应关系.虽然本文限于化学位移各向异性相互作用两位置交换问题,但容易推广到偶极作用多位置交换问题.     

Determination of Multiple φ-Torsion Angles in Proteins by Selective and Extensive C Labeling and Two-Dimensional Solid-State NMR

We describe an approach to efficiently determine the backbone conformation of solid proteins that utilizes selective and extensive ¹³C labeling in conjunction with two-dimensional magic-angle-spinning NMR. The selective ¹³C labeling approach aims to reduce line broadening and other multispin complications encountered in solid-state NMR of uniformly labeled proteins while still enhancing the sensitivity of NMR spectra. It is achieved by using specifically labeled glucose or glycerol as the sole carbon source in the protein expression medium. For amino acids synthesized in the linear part of the biosynthetic pathways, [1-¹³C]glucose preferentially labels the ends of the side chains, while [2-¹³C]glycerol labels the C^α of these residues. Amino acids produced from the citric-acid cycle are labeled in a more complex manner. Information on the secondary structure of such a labeled protein was obtained by measuring multiple backbone torsion angles φ simultaneously, using an isotropic–anisotropic 2D correlation technique, the HNCH experiment. Initial experiments for resonance assignment of a selectively ¹³C labeled protein were performed using ¹⁵N–¹³C 2D correlation spectroscopy. From the time dependence of the ¹⁵N–¹³C dipolar coherence transfer, both intraresidue and interresidue connectivities can be observed, thus yielding partial sequential assignment. We demonstrate the selective ¹³C labeling and these 2D NMR experiments on a 8.5-kDa model protein, ubiquitin. This isotope-edited NMR approach is expected to facilitate the structure determination of proteins in the solid state.     

熔融侧面泵浦耦合器光纤夹角对耦合效率的影响

泵浦耦合器是高功率光纤激光器的关键无源光器件,其制作工艺是采用泵浦光纤和主光纤侧面熔融的方法,该方法可以保持主光纤中信号光的低插入损耗,但泵浦光纤和主光纤之间的夹角对耦合效率影响较大。为解决这一问题,根据熔融侧面泵浦耦合器的结构特点,建立了物理模型,推导出各光纤中光功率与夹角关系的方程组,进行了数值仿真和实验论证,结果是随着泵浦光纤和主光纤之间夹角的减小,耦合效率会逐渐增大,但存在临界值,NA值小的泵浦光纤耦合效率高且临界角大,NA为0.22的泵浦光纤,夹角小于9.7时耦合效率最大值为96.9%,NA为0.15的泵浦光纤,夹角小于11.5时耦合效率最大值为97.8%。     

沟渠内杨木三合板架空燃烧的火灾行为的研究

建立了缩尺寸沟渠火灾试验模型,测量了沟渠以及平台入口附近的温度分布,研究了沟渠内杨木三合板架空燃烧的位置和沟渠的倾斜角度对火蔓延行为的影响,分析了火焰传播特征和火蔓延速率.试验结果表明:在沟渠效应和烟囱效应的综合作用下,火焰先从杨木三合板与沟渠底板之间的狭长空间传播到沟渠顶部,在入口处形成喷射状火焰;狭长空间内的温度先...     

基于近红外光谱的柔性基底紫外臭氧改性效果表征研究

近年来,随着纳米科技、聚合物材料和先进制造技术的发展,以柔性传感器为代表的新兴柔性电子器件在可穿戴、健康医疗、物联网终端等领域发挥着越来越重要的作用。作为柔性电子器件的载体,柔性基底对传感器的机械可靠性和电学传感性能等方面有着重要的意义。但由于其表面非极性键造成的高疏水性限制了功能性材料在其表面的沉积,常常造成柔性基底层与电极层/敏感层之间不稳定的界面结合。因此,利用紫外臭氧处理对柔性基底表面改性受到了广泛的关注。利用近红外光谱技术对柔性基底的紫外臭氧处理效果进行快速精准评估,旨在从基团分子层面探究其改性效果,在实际应用中是对传统依靠接触角测量评估方法的有效补充。具体而言,对四种常见的柔性基底材料聚二甲基硅氧烷(PDMS)、聚萘二甲酸乙二醇酯（PEN）、聚对苯二甲酸乙二醇酯（PET）和聚酰亚胺（PI）进行了1/2/5/10 min不同时长的紫外臭氧（UVO）改性处理,并利用近红外光谱对其改性效果进行表征研究,最后利用接触角测量方法对上述的表征结果进行了验证分析。近红外光谱分析表明：对于柔性PDMS基底,紫外光能量不足以切断其中的甲基（—CH₃）官能团和（—C—Si—）等化学键,无法引入羟基、羧基等亲水性基团。对于柔性PEN和PET基底而言,紫外臭氧处理的效果要优于柔性PDMS基底,且对柔性PET基底的处理效果要优于柔性PEN基底,其原因可能是PEN基底材料中萘环的双环结构具有很强的紫外光吸收能力,阻隔了380 nm以下的大部分紫外线能量。对于柔性PI基底,紫外臭氧处理可以有效引入羟基（—OH）和羧基（—COOH）等活性基团,且这些官能团的强度和数量随着处理时间的增加而增加,从而在短时间内使得PI基底表面能增大、接触角减小、湿润性提高。接触角测试结果验证：紫外臭氧处理对于柔性PDMS基底处理效果不明显（接触角下降幅度为8.4%）;对柔性PET基底处理的效果（接触角下降幅度为39.6%）要优于柔性PEN基底的处理效果（接触角下降幅度为9.4%）;紫外臭氧处理的效果对柔性PI基底处理效果最佳,接触角下降幅度达到了62.7%。     

单摆周期的系统误差分析

文章逐个分析计算了单摆的摆角、摆球的自转、摆线质量、空气浮力以及空气阻力对于单摆周期的影响,以1 m长5°小幅单摆为例,得到这5种因素带来的系统相对误差分别为+0.45‰、+0.02‰、-0.45‰、+0.07‰、-0.14‰,合计仅为-0.05‰,即这5种误差因素几乎相互抵消,小幅单摆实验在理论上的系统误差极小.文章给出了较为详细的推理、计算和分析过程,尤其空气阻力矩的推理过程以及图、表等,意在提供较为完整和准确的认识.文末,针对人们在空气阻力认识上可能存在的某些不足,文章给出了几点必要的说明.     

Bifurcation analysis of visual angle model with anticipated time and stabilizing driving behavior

In the light of the visual angle model (VAM), an improved car-following model considering driver's visual angle, anticipated time and stabilizing driving behavior is proposed so as to investigate how the driver's behavior factors affect the stability of the traffic flow. Based on the model, linear stability analysis is performed together with bifurcation analysis, whose corresponding stability condition is highly fit to the results of the linear analysis. Furthermore, the time-dependent Ginzburg-Landau (TDGL) equation and the modified Korteweg-de Vries (mKdV) equation are derived by nonlinear analysis, and we obtain the relationship of the two equations through the comparison. Finally, parameter calibration and numerical simulation are conducted to verify the validity of the theoretical analysis, whose results are highly consistent with the theoretical analysis.     

Temperature dependence of spin pumping in YIG/NiOx/W multilayer

We report the temperature dependence of the spin pumping effect for Y₃Fe₅O₁₂ (YIG, 0.9 μm)/NiO (t_NiO)/W (6 nm) (t_NiO = 0 nm, 1 nm, 2 nm, and 10 nm) heterostructures. All samples exhibit a strong temperature-dependent inverse spin Hall effect (ISHE) signal I_c and sensitivity to the NiO layer thickness. We observe a dramatic decrease of I_c with inserting thin NiO layer between YIG and W layers indicating that the inserting of NiO layer significantly suppresses the spin transport from YIG to W. In contrast to the noticeable enhancement in YIG/NiO (t_NiO ≈ 1-2 nm)/Pt, the suppression of spin transport may be closely related to the specific interface-dependent spin scattering, spin memory loss, and spin conductance at the NiO/W interface. Besides, the I_c of YIG/NiO/W exhibits a maximum near the T_N of the AF NiO layer because the spins are transported dominantly by incoherent thermal magnons.     

SO(n,1) Wigner rotation as an SL(2,R) problem

We show that the composition of not only two SO(3,1) boosts, but also that of two SO(n,1) boosts for anyn 2, is basically an SO(2,1) problem and hence can be analysed completely using SL(2,R) matrices. By computing the expression for the Thomas/Wigner angle directly using SL(2,R) matrices we show that this approach results in considerable economy of algebra.     

双连续可调偏光分束器

介绍了一种性能优良的偏光分束器。该器件由4/2波片和可调分束角棱镜组合而成,同时具备强度比和分束角连续可调的功能。文中给出了此器件的结构、原理、理论分析和性能实验研究。实验与理论相符。