基于1085 km实地光纤链路的双波长光纤时间同步研究

在长距离高精度光纤时间同步系统中,为了减少后向反射光与光纤色散对传输精度的影响,本文在双波长光纤时间同步传输方法之上,提出了一种具有色散误差修正功能的双波长光纤时间同步传输方法.以自行研制的工程样机在长度约为800 km的实验室光纤链路上和1085 km的实地光纤链路上进行了实验测试,也是国内首次实现千公里级实地光纤时间同步传输.在实验室光纤链路上,测得传输链路色散补偿后的色散时延误差为10 ps,时间同步标准差为5.7 ps,稳定度为1.12 ps@105 s,不确定度为18.4 ps.在实地光纤链路上,测得传输链路色散补偿后的色散时延误差为60 ps,时间同步标准差为18 ps,稳定度为5.4 ps@4×10⁴ s,不确定度为63.5 ps.     

Transition to chaos in lid-driven square cavity flow

To date, there are very few studies on the transition beyond second Hopf bifurcation in a lid-driven square cavity, due to the difficulties in theoretical analysis and numerical simulations. In this paper, we study the characteristics of the third Hopf bifurcation in a driven square cavity by applying a consistent fourth-order compact finite difference scheme rectently developed by us. We numerically identify the critical Reynolds number of the third Hopf bifurcation located in the interval of (13944.7021,13946.5333) by the method of bisection. Through Fourier analysis, it is discovered that the flow becomes chaotic with a characteristic of period-doubling bifurcation when the Reynolds number is beyond the third bifurcation critical interval. Nonlinear time series analysis further ascertains the flow chaotic behaviors via the phase diagram, Kolmogorov entropy and maximal Lyapunov exponent. The phase diagram changes interestingly from a closed curve with self-intersection to an unclosed curve and the attractor eventually becomes strange when the flow becomes chaotic.     

原位低场核磁共振弛豫法定量监测光催化Cr(Ⅵ)还原反应

本文利用原位低场核磁共振（LF-NMR）技术在真实固液反应环境中对光催化还原Cr（Ⅵ）反应进行了定量研究,并对Ag纳米颗粒负载量不同的Ag担载石墨相氮化碳复合光催化剂（Ag/g-C₃N₄）在可见光照射下催化Cr（Ⅵ）还原为Cr（Ⅲ）的性能进行了研究.研究发现,Ag纳米颗粒负载（负载量分别为1 wt.%、2 wt.%、5 wt.%和10 wt.%）可以有效提高g-C₃N₄的光催化性能;且负载量为5 wt.%时光催化性能最优,为无Ag负载的g-C₃N₄的4倍.此外,本文还通过横向弛豫时间（T₂）定量分析了反应体系中顺磁性Cr（Ⅲ）离子的浓度,证实了采用LF-NMR弛豫法评价光催化Cr（Ⅵ）还原反应性能的可行性.     

Characterization of Gasoline by 1H Nuclear Magnetic Resonance and Chemometrics

Automotive fuel adulteration is an old and significant problem. One common type of fuel adulteration is the addition of diesel to gasoline. Unsupervised models were developed through hierarchical cluster and principal component analysis models. Supervised models through partial least square discriminant analysis using ¹H nuclear magnetic resonance spectra as the input were used to classify samples as adulterated or unadulterated. Quantitative models were developed using partial least squares to determine the gasoline and diesel concentrations in the samples. This set contained samples composed of pure gasoline and anhydrous ethanol reproducing commercial gasoline and other samples treated with diesel. Hierarchical cluster and principal component analysis did not distinguish between adulterated and unadulterated samples except for the most adulterated materials. However, partial least square discriminant analysis classified 100% of the samples correctly. The partial least square algorithm provided excellent regression models for the gasoline and diesel content. The determination coefficient was 0.9920 for both models, whereas the root mean square error of cross-validation and root mean square error of prediction for the diesel model were 2.32 and 1.42%, respectively, and 2.40 and 1.38% for the gasoline model.     

Global X2A′ potential energy surface of Li2H and quantum dynamics of H + Li2 (X1Σg+) → Li + LiH (X1Σ+) reaction

A global potential energy surface (PES) for the electronic ground state of Li₂H system is constructed over a large configuration space. About 30 000 ab initio energy points have been calculated by MRCI‐F12 method with aug‐cc‐pVTZ basis set. The neural network method is applied to fit the PES and the root mean square error of the current PES is only 1.296 meV. The reaction dynamics of the title reaction has been carried out by employing time‐dependent wave packet approach with second order split operator on the new PES. The reaction probability, integral cross section and thermal rate constant are obtained from the dynamics calculation. In most of the collision energy regions, the integral cross sections are in well agreement with the results reported by Gao et al. The rate constant calculated from the new PES increases in the temperature range of present investigation.     

Dielectric relaxation of Tripropylene glycol–water mixture using time domain reflectometry

The complex permittivity spectra of tripropylene glycol and water solutions have been obtained by time domain reflectometry (TDR) technique in the frequency range from 10 MHz to 30 GHz and the temperature range 20°C–05°C. The dielectric relaxation parameters such as static dielectric constant and relaxation time were obtained by using the non-linear least square fit method. The intermolecular hydrogen bonding of tripropylene glycol–water has been discussed using the Kirkwood correlation factor and thermodynamic parameters. The activation energy decreases with increase in water content in the mixture as expected in the Arrhenius behaviour. The dielectric constant for mixtures has been fitted to the Bruggeman mixture formula in the non-linear case.     

Theoretical approaches for predicting the color of rigid dyes in solution

Aiming at developing an affordable and easily implementable computational protocol for routine prediction of spectral properties of rigid molecular dyes, density functional theory, and time‐dependent density functional theory were used in conjunction with a vibronic coupling scheme for band shape estimate. To predict the perceived color of molecules in solution, a model has been setup linking the UV‐vis spectra predicted at ab initio level to the L *a *b * colorimetric parameters. The results show that a mixed protocol, implying the use of a global hybrid functional for the prediction of adiabatic energy differences and a range separated hybrid for the prediction of potential energy curvature, allows perceived colors to be quantitatively predicted, as demonstrated by the comparison of L *a *b * colorimetric parameters obtained from computed and experimental spectra. © 2017 Wiley Periodicals, Inc.     

[Cu6(NGuaS)6]2+ and its oxidized and reduced derivatives: Confining electrons on a torus

The hexanuclear thioguanidine mixed‐valent copper complex cation [Cu₆(NGuaS)₆]⁺² (NGuaS = o‐SC₆H₄NC(NMe₂)₂) and its oxidized/reduced states are theoretically analyzed by means of density functional theory (DFT) (TPSSh + D3BJ/def2‐TZV (p)). A detailed bonding analysis using overlap populations is performed. We find that a delocalized Cu‐based ring orbital serves as an acceptor for donated S p electrons. The formed fully delocalized orbitals give rise to a confined electron cloud within the Cu₆S₆ cage which becomes larger on reduction. The resulting strong electrostatic repulsion might prevent the fully reduced state. Experimental UV/Vis spectra are explained using time‐dependent density functional theory (TD‐DFT) and analyzed with a natural transition orbital analysis. The spectra are dominated by MLCTs within the Cu₆S₆ core over a wide range but LMCTs are also found. The experimental redshift of the reduced low energy absorption band can be explained by the clustering of the frontier orbitals. © 2017 Wiley Periodicals, Inc.     

N_2-DART-Orbitrap中的特征气相离子反应及在西药快速检测中的应用

采用实时直接分析(DART)离子源串联高分辨质谱Orbitrap技术(DART-Orbitrap MS),对8种市售常见西药进行有效成分分析,建立了一种快速、简便、准确测定西药中有效成分的方法.对DART离子源的离子化温度、扫描模式、操作气体种类、辅助溶剂种类及其酸碱性等实验条件进行了优化,得到最佳实验条件.实验结果表明,正谱条件下,采用N_2气作为操作气体时,待测组分准分子离子峰[M+H]+同样具有较高的灵敏度和谱图辨识度.因此,N2气可以替代昂贵的He气作为DART离子源的操作气体用于8种药物有效成分的现场实时检测.该方法具备成本低、快速和操作简便的特点.通过分析待测组分的特征碎片离子,发现了N2-DART离子源中的特征离子反应,包括氧化反应和重排反应.根据获得的特征碎片离子对N_2-DART-MS中发生的反应机理进行推导,并结合理论计算对其进行验证.N_2-DART-MS技术有望应用于复杂基质混合物的现场快速检测中.