外光注入半导体激光器实现时钟分频

从理论和实验上研究了利用光注入半导体激光器对高重复速率光脉冲产生的周期振荡和时钟分频现象.结果表明，光注入半导体激光器引起的二倍周期振荡是使注入脉冲重复频率分频的直接原因.通过耦合速率方程，数值模拟了半导体激光器在外光注入时输出光的时间序列和功率谱，并且分析了激光腔内各种周期振荡的特征.研究表明，当注入光使半导体激光器出现稳定的二倍周期振荡，且注入光的重复频率为此振荡频率的二倍时，时钟分频即可产生实验中，采用重复频率为6.32GHz的光脉冲注入Fabry-Perot激光器，实现了3.16GHz时钟分频信号 关键词： 周期振荡 时钟分频 光谱侧带 光注入     

Bifunctional cinchona alkaloids-catalyzed asymmetric [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones

A highly enantioselective [4+2] cycloaddition reaction of β,γ-unsaturated α-keto esters with oxazolones was realized with readily available cinchona alkaloids as the catalysts. Using this reaction, a series of highly functionalized δ-lactones with adjacent α-quaternary-β-tertiary stereocenters were obtained in high yields (up to 97%) and with good-to-excellent enantioselectivities (up to 97% ee).     

Stereoselective construction of a 5-aza-spiro[2,4]heptane motif via catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides and ethyl cyclopropylidene acetate

A direct and facile synthesis of highly functional 5-aza-spiro[2,4]heptanes, a valuable structural motif for drug discovery, is developed via catalytic asymmetric 1,3-dipolar cycloaddition of cyclopropylidene acetate and azomethine ylides for the first time.     

Synthesis and Characterization of Bis(methyl-2-pyridylmethylidenedrazinecarbodithioate)manganese(II)

Abstract  Brown crystals of title compound, bis(methyl-2-pyridylmethylidene-drazinecarbodithioate)manganese(II), was formed by reaction of methyl-2-pyridylmethylidenehydrazinecarbodithioate(HNNS) with manganese perchlorate at 323 K temperature and recrystallized from ethanol at room temperature, crystallizing in the monoclinic system, space group P2(1)/n, with a = 11.631(2), b = 14.010(3), c = 13.128(3) ?, β = 105.791(11)°; V = 2058.6(7)  ?³, D _c  = 1.533 g/cm³, Z = 4, C₁₆H₁₆N₆MnS₄, M _r  = 475.53, μ(M₀ K _α ) = 1.060 mm⁻¹, F (000) = 972. The structure was refined to R = 0.0441, wR = 0.1196 for 3,682 (I > 2σ(I)) reflections and S = 1.110. In title complex the coordination geometry about manganese is distorted octahedral and the two ligands in the mer configuration (S and tertiary N atom cis to each other and the iminic N atoms trans). Furthermore, the neutral molecule units Mn^II(NNS)₂ are connected by hydrogen bonds C–H···N and C–H···S and form a three dimensional ordered network structure. Graphical Abstract  The title compound, Mn(NNS)₂, exists as discrete molecules in which the central MnII atom is coordinated by two S atoms and four N atoms from two ligands NNS- molecules in a mer-octahedral configuration. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

等价电子数组元Heusler合金Fe_2RuSi中的原子占位

对等价电子数组元Heusler合金Fe_2RuSi的原子占位、电子结构与磁性进行了理论与实验研究.第一性原理计算表明,虽然Fe_2RuSi中Fe,Ru均有8个价电子,但是Ru仍表现出强烈的占据A,C晶位倾向.基态总能最低的是Fe与Ru分别占据A,C晶位的XA结构,次低的是Fe,Ru在A,C位混乱占位的L2_1B结构,且两者能量差很小.这说明决定Heusler合金中过渡族原子占位的因素除价电子数以外还可能有原子半径和共价杂化作用等.态密度和差分电荷密度计算表明Heusler合金中主族元素与最近邻过渡族元素之间的p-d共价杂化对Heusler合金的占位有明显影响,在XA结构中Ru与Si和Fe(B)之间都存在明显的杂化作用,而在高能的L2_1结构中,Si与最近邻的Fe杂化作用相当弱.XRD测试表明在室温Fe_2RuSi存在A,C位之间的Fe-Ru反占位,形成了能量次高的L21B结构,这主要来自于混合熵对自由能的贡献及其引起的原子自发混乱占位.在5 K下Fe_2RuSi的饱和磁矩为4.87μB/f.u.,与计算值符合得相当好.     

氧化降解壳聚糖铜配合物制备低聚壳聚糖

氧化降解壳聚糖铜配合物制备低聚壳聚糖;壳聚糖铜配合物;壳聚糖;氧化降解;催化     

镉－硫氰酸根与铵－苯并15－冠－5配合物的合成与结构研究

用凝胶法生长了标题配合物［ＮＨ_４（Ｂ１５Ｃ５）_２］［Ｃｄ（ＳＣＮ）_３］的晶体，并对其进行了红外光谱，元素分析等各项物理性质的测试。经Ｘ射线单晶结构分析得到了配合物的全部晶体学数据：Ｍ_ｒ＝８４１．３１，正交晶系，空间群Ｐ２_１２_１２_１，晶胞常数ａ＝１０．９７０（３），ｂ＝２１．８３４（３），ｃ＝１５．５６３（４），Ｖ＝３７２７（３），Ｚ＝４，Ｄ_ｘ＝１．５０ｇ／ｃｍ￣３，Ｆ（０００）＝１７３６，μ＝７．０９ｃｍ￣（－１），Ｒ＝０．０７０，Ｒ_ｗ＝０．０６３。结构分析结果表明，配阳离子［ＮＨ_４（Ｂ１５Ｃ５）_２］￣＋和配阴离子［Ｃｄ（ＳＣＮ）_３］￣－间靠静电力结合成配合物。     

Highly enantioselective synthesis of α-fluoro-α-nitro esters via organocatalyzed asymmetric Michael addition

Primary amines catalyzed the asymmetric Michael addition of ethyl 2-fluoro-2-nitroacetate to enones to provide chiral α-fluoro-α-nitro ester ketones with two contiguous stereogenic centers, one of which is a fluorinated quaternary chiral center, with excellent enantioselectivities and in moderate to good yields.     

Synthesis and characterization of zinc(II) and cobalt(III) Schiff base complexes

Two mononuclear complexes with the Schiff base ligand 2-((2-(dimethylamino)ethylimino)methyl)phenol (HL), namely ZnL₂ and CoL₂(N₃), have been synthesized and characterized using single-crystal X-ray diffraction and spectroscopy (IR, ¹H NMR, UV–Vis, MS and EA). Both complexes are mononuclear. The coordination geometry in the Zn(II) complex is distorted square-pyramidal with a weak Zn···N interaction. The Co(III) complex is distorted octahedral, and the neutral molecule unit [Co^IIIL₂(N₃)] is connected by C–H···N hydrogen bonds to form a one-dimensional infinite chain. The luminescence of the zinc compound has been investigated. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Application of regularization technique to variational adjoint method: A case for nonlinear convection-diffusion problem

A discrete assimilation system for a one-dimensional variable coefficient convection-diffusion equation is constructed. The variational adjoint method combined with the regularization technique is employed to retrieve the initial condition and diffusion coefficient with the aid of a set of simulated observations. Several numerical experiments are performed: (a) retrieving both the initial condition and diffusion coefficient jointly (Experiment JR), (b) retrieving either of them separately (Experiment SR), (c) retrieving only the diffusion coefficient with the iteration count increased to 800 (Experiment NoR-SR), and (d) retrieving only the diffusion coefficient with the consideration of a regularization term based on the Experiment NoR-SR (Experiment AdR-SR). The results indicate that within the limit of 100 iterations, the retrieval quality of the Experiment SR is better than those from the Experiment JR. Compared with the initial condition, the diffusion coefficient is a little difficult to retrieve, whereas we still achieve the desired result by increasing the iterations or integrating the regularization term into the cost functional for the improvement with respect to the diffusion coefficient. Further comparisons between the Experiment NoR-SR and AdR-SR show that the regularization term can really help not only improve the precision of retrieval to a large extent, but also speed up the convergence of solution, even if some perturbations are imposed on those observations.