低功率氩电弧加热发动机的数值模拟

采用可求解可压缩流动与传热的全速度SIMPLE算法,对低功率氩电弧加热发动机内部的传热与流动进行了数值模拟,获得了电弧加热发动机内的温度、速度、马赫数及流线分布。计算结果表明:电弧加热发动机内最高温度出现在阴极下游附近中心轴线处,这是因为电弧在阴极表面收缩形成阴极弧点,从而焦耳热成为该高温区的主要加热机制;沿着发动机中心轴线,气体温度和速度开始时随着距阴极距离的增加而迅速增加,然后在等离子体流向喷管出口的过程中,气体温度和速度逐渐下降。此外还详细考察了弧电流变化对电弧加热发动机内部传热与流动特性的影响,计算获得的发动机流量和比冲与实验结果基本一致。     

Sr2Bi4Ti5O18的压致结构相变

 使用4∶1的甲醇-乙醇混合液作传压介质，利用金刚石对顶砧装置（DAC），研究了层状铁电体Sr₂Bi₄Ti₅O₁₈的在位高压拉曼光谱和压致结构相变（0～27 GPa）。发现在8.31 GPa，Sr₂Bi₄Ti₅O₁₈经历了一次结构相交。在23.13 GPa以上，Sr₂Bi₄Ti₅O₁₈似乎出现了压致非晶相交的先兆。并使用内模方法对Sr₂Bi₄Ti₅O₁₈的内模进行了指认。     

可变不确定集约束的鲁棒自适应波束形成方法

自适应波束形成方法在存在协方差矩阵误差和导向向量误差的失配条件中性能严重下降。最差情况性能最优。(Worst-Case Performance Optimization,WCPO)方法可以显著增强失配条件下自适应波束形成的鲁棒性,但该方法存在系统性的信号功率过估计问题,并且限定协方差矩阵不确定集与导向向量不确定集的两个关键参数需要人为指定,缺乏具备明确物理意义的求解方法和数据自适应性.本文以WCPO方法为基础,给出了信号功率过估计的理论分析以及相应的改进方法,提出了基于矩阵重构的协方差矩阵不确定集参数的自适应估计方法,最终得到一种可变不确定集约束的鲁棒自适应波束形成方法(WCPO-PCVC).相比WCPO方法,该方法消除了信号功率估计的系统性偏差,且关键参数无需人为指定。数值仿真和海试数据处理结果表明,该方法在失配条件下具有良好的干扰与旁瓣抑制能力,与常规波束形成方法相比具有更好的信号到达角分辨能力,与自适应波束形成方法相比估计的信号功率更为精准。     

A bipyridyl thorium metallocene: synthesis, structure and reactivity

The synthesis, structure and reactivity of a new bipy thorium metallocene have been studied. The reduction of the thorium chloride metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThCl(2) (1) with potassium graphite in the presence of 2,2'-bipyridine gives the purple bipy metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(bipy) (2) in good yield. Complex 2 has been fully characterized by various spectroscopic techniques, elemental analysis and X-ray diffraction analysis. Complex 2 reacts cleanly with trityl chloride, silver halides and diphenyl diselenide, leading to the halide metallocenes [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThX(2) (X = Cl (1), Br (3), I (4)) and [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(F)(μ-F)(3)Th[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](F)(bipy) (5), and selenido metallocene [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th(SePh)(2) (6), in good conversions. In addition, 2 cleaves the C[double bond, length as m-dash]S bond of CS(2) to give the sulfido complex, [η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)ThS (7), which further undergoes an irreversible dimerization or nucleophilic addition with CS(2), leading to the dimeric sulfido complex {[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th}(μ-S)(2) (8) and dimeric trithiocarbonate complex {[η(5)-1,3-(Me(3)C)(2)C(5)H(3)](2)Th}(μ-CS(3))(2) (10) in good yields, respectively.     

Iron-phthalocyanine molecular junction with high spin filter efficiency and negative differential resistance

We investigate the spin transport properties of iron-phthalocyanine (FePc) molecule sandwiched between two N-doped graphene nanoribbons (GNRs) based on the density functional theory and nonequilibrium Green's function methods. Our calculated results clearly reveal that the FePc molecular junction has high spin-filter efficiency as well as negative differential resistance (NDR). The zero-bias conductance through FePc molecule is dominated by the spin-down electrons, and the observed NDR originates from the bias-dependent effective coupling between the FePc molecular orbitals and the narrow density of states of electrodes. The remarkable high spin-filter efficiency and NDR are robust regardless of the edge shape and the width of GNRs, and the N-doping site in GNRs. These predictions indicate that FePc junction holds great promise in molecular electronics and spintronics applications.     

自动微分的原理和方法

从计算一阶和二阶各种导数形式的角度,讨论了自动微分的基本原理和方法,给出了一阶和二阶各种微分模式最简单而最直观的表述形式,分别讨论了用不同微分模式计算不同导数形式的计算代价,讨论并给出了非线性问题求解中常用数值算法的计算代价.讨论了断点存储、正向积分和反向积分方法.     

All-fiberized Tm-doped fiber MOPA with 30-W output power

We demonstrate a 30-W all-fiberized laser in a master oscillator power amplifier(MOPA) structure with a central wavelength of 1 950 nm.The laser is a continuous-wave(CW) operation with double-clad Tm-doped silica fiber pumped by pigtailed laser diodes with a central wavelength of 793 nm.The optical-to-optical efficiency of the MOPA system is 37.5% with respect to the total 80-W pump power.The maximal slope efficiency of the system is approximately 43%,which belongs to the main amplifier and exceeds the Stoke limit.No obvious amplified spontaneous emitting(ASE) is observed in the experiment,and the power can be scaled straightforwardly by improving the pump power.     

物理开放性问题的质性评价——SOLO分类理论的应用

1对物理开放性问题的认识 传统物理教学主要采用封闭性问题对学生进行训练和考核．所谓封闭性问题是指习题条件完备，结论明确，解题方法和策略单一的习题．同时，教师多采用封闭性问题进行测验，并给出具体量化的分数，然后以此为依据对学生的学习能力进行评价．这种评价对学生学习量的考核多于对学习质的评价，重学习结果，轻学习过程，教师难于通过此种评价掌握学生的思维能力发展水平．     

Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO_2?x) powders and CeO_2?x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce³⁺ species to hydrogen, which results in the formation of Ce⁴⁺, and thus in oxidation of ceria.     

高效液相色谱-串联质谱法测定荔枝花粉和花蜜中腈菌唑和苯醚甲环唑残留

采用改良的QuEChERS-高效液相色谱-串联质谱（HPLC-MS/MS）技术,建立了荔枝花粉和花蜜中2种主要杀菌剂腈菌唑和苯醚甲环唑的测定方法。花粉和花蜜样品均由乙腈提取,花粉样品经0.9 g无水硫酸镁、0.15 g N-丙基乙二胺（PSA）和0.15 g十八烷基键合硅胶（C₁₈）吸附剂净化,花蜜样品由0.9 g无水硫酸镁和0.15 g PSA净化。采用Poroshell-120 EC-C₁₈色谱柱分离,以0.1%（v/v）甲酸水溶液-乙腈（25∶75,v/v）为流动相等度洗脱,在电喷雾离子（ESI）源、正离子扫描和选择离子监测模式下进行检测,基质匹配标准溶液法定量。结果显示：腈菌唑和苯醚甲环唑在1~100 μg/L范围内线性关系良好,相关系数（r²）均大于0.9990;腈菌唑和苯醚甲环唑的检出限（LOD）分别为0.25 μg/kg和0.50 μg/kg,定量限（LOQ）分别为0.83 μg/kg和1.7 μg/kg;腈菌唑和苯醚甲环唑在荔枝花粉和花蜜样品中的平均加标回收率分别为87.0%~95.2%和90.1%~96.4%,相对标准偏差（RSD）分别为1.2%~3.6%和0.7%~4.1%。该法快速、简便、灵敏,可用于荔枝花粉和花蜜样品中腈菌唑和苯醚甲环唑的痕量测定,可为蜜蜂等授粉昆虫的暴露性风险评估提供技术支持。