Synthesis, characteristic and theoretical investigation of the structure, electronic properties and second-order nonlinearity of salicylaldehyde Schiff base and their derivatives

A series of asymmetric donor-acceptor substituted salen-type Schiff-bases have been synthesized and their structures, electronic properties and second order nonlinearities were investigated by DFT methods. In order to verify the stable of these Schiff-base derivates, the IR spectrum of these Schiff-base derivates were calculated, the result showed that these compounds are stable. The results of TD-DFT calculation indicate that the derivatives with the electron-donating group (CH3, OCH3 or N(C2H5)2) have a red shift absorption compared to derivatives with the electron-withdrawing group (NO2). The analysis of MOS indicates that the CN group has contribution to the LUMO orbital while the groups of OCH3, N(C2H5)2 and NO2 have contribution to the HOMO orbital. OCH3, N(C2H5)2 as electron rich groups, made the derivates have a larger first static hyperpolarizability. However, the compound (II) with a NO2 substituent, also has a large first static hyperpolarizability. This is probably because of the special transition model, namely the values of two oscillator strength f (fHOMO-1-LUMO=0.405, fHOMO-LUMO=0.321) are almost equal. In order to understand the influence of the energy gap (ΔE) between the HOMO and the LUMO orbitals on the first static hyperpolarizability, we calculated the energy gap (ΔE) of all Schiff-base compounds. The results show that the smaller the HOMO-LUMO energy gap is, the larger the first static hyperpolarizability is.     

弱非线性热声理论模型的建立及简化

本文指出非零的周期平均热声效应在本质上是非线性的,应保留到二阶精度。在小振幅条件下,利用摄动方法,以无限大平板流道为例,建立了二阶精度的弱非线性热声理论模型,并在不同条件下对模型做了进一步简化。这一理论为理解热声系统的工作机制以及设计优化热声系统提供了强有力的理论工具。     

KClO3-甲基紫催化光度法测定痕量溴的研究

在稀H2SO4介质中,以抗坏血酸为活化剂,痕量溴可强烈催化KClO3氧化甲基紫的反应,研究了反应的最佳条件及动力学参数,建立了测定痕量溴的新方法.方法的线性范围为0.0012～0.18 μg/mL,检出限为8.92×10-10g/mL.方法可用于大米、小麦及海带样品中痕量溴的测定.     

助剂含量对CuLi/AC 催化剂结构及甲醇氧化羰基化反应性能的影响

采用微波辐射法制备出不同助剂含量的CuLi/AC(活性炭)催化剂, 考察了其在甲醇气相氧化羰基化合成碳酸二甲酯(DMC)反应中的催化性能, 使用X射线衍射、 扫描电子显微镜、 比表面积、 H₂程序升温还原、 X射线光电子能谱和CO程序升温脱附对催化剂的结构进行了表征. 研究结果表明, 添加适量的Li有助于铜物种还原为低价态的Cu⁰, 形成颗粒尺寸更小、 分布更加均匀的铜纳米颗粒, 并高度分散在活性炭载体表面. 催化剂活性与表面单质铜的含量有关, 即Cu⁰是催化剂的主要活性物种, 并且Cu⁰的晶粒尺寸越小, 催化剂活性越好. 添加Li后增加了催化剂表面的CO弱吸附位, 有利于CO对Cu-OCH₃的插入反应, 因此提高了催化活性. 随着Li含量的增加, DMC的时空收率逐渐升高, 当Li添加质量分数达到0.15%时, DMC的时空收率达到最高值540.6 mg·g^-1·h^-1, 甲醇转化率为4.5%, DMC选择性为81.4%.     

基于聚乙烯醇离子液体负载HRP修饰石墨烯/纳米金复合膜的过氧化氢生物传感器

以石墨烯/纳米金修饰玻碳电极为基底, 用聚乙烯醇与离子液体复合物将辣根过氧化物酶固定于电极表面, 制备了过氧化氢生物传感器. 结果表明, 在0.1 mol/L HAc-NaAc+0.1mol/L KCl(pH=6.5)中, H₂O₂的氧化峰电流与其浓度在9.55×10^-6~6.01×10^-3 mol/L间呈良好线性关系, 检出限(3S/N)为3.3×10^-7 mol/L. 用标准加入法做回收实验, 回收率在93.4%~100.5%之间. 该传感器对H₂O₂具有较高的灵敏度和较低的检测限, 稳定性和重现性良好, 使用寿命较长, 且制作成本低, 可多次重复使用.     

Physical meaning of conductivity spectra for ZnO ceramics

With the help of broadband dielectric spectroscopy in a wide temperature and frequency range, the conductivity spectra of ZnO polycrystalline ceramics are measured and the direct-current-like (DC-like) conductivity and relaxation polarization conductivity are observed successively along the frequency axis. According to the classical Debye theory and Cole-Cole equation, the physical meanings of the two conductivities are discussed. It is found that the DC-like conductivity corresponds to electron transportation over the Schottky barrier at the grainboundary. The relaxation polarization conductivity corresponds to electronic trap relaxation of intrinsic point defects (zinc interstitial and oxygen vacancy). When in the high frequency region, the relaxation conductivity obeys the universal law with the index n equal to the index α in the Cole-Cole equation as an indictor of disorder degree.     

改进型驻波热声发动机的实验研究

压比是热声发动机性能的一个重要衡量参数。驻波发动机由于自身热力过程的不可逆性,使得目前所能获得的压比通常都比较低。笔者认为除了发动机各部件的尺寸参数之外,换热器的换热性能也是影响发动机压比的一个重要参数。因此本文对驻波热声发动机的换热器进行了改进设计,增强了加热器与工作介质的换热效果,系统的工作压比有了较大的提高。采用氦气、氮气和二氧化碳作为工质,其压比分别达到了1.15、1.22和1.215。     

Perturbative Treatment for Stationary State of Local Master Equation

The local approach to construct master equation for a composite open system with a weak internal coupling is simple and seems reasonable. However, it is thermodynamic consistent only when the subsystems are resonantly coupled. Efforts are being made to understand the inconsistency and test the validity of the local master equation. We present a perturbative method to solve the steady-state solutions of linear local master equations, which are demonstrated by two simple models. The solving process shows the stationary state as the result of competition between incoherent operations and the unitary creating quantum coherence, and consequently relate quantum coherence with thermodynamic consistency.     

双向进气与惯性管功能的研究

基于线性热声理论,本文对斯特林型脉冲管制冷机的调相机构一双向进气和惯性管进行了系统的数值模拟,研究结果表明:在惯性管结构能够为脉冲管制冷机提供所需要的最佳阻抗时,双向进气模式不能提高脉冲管制冷机性能;但是因为惯性管调相能力有限,不能为小功率脉冲管制冷机提供所需要的最佳阻抗,此时双向进气仍然能够为提高脉冲管制冷机性能发挥积极的作用.另外,本文还总结了脉冲管制冷机调相机构实验中出现的现象,对其进行了理论解释,这也是对本文结论的有力佐证.     

Effect of Tunneling Current on Schottky Barrier Height in ZnO Varistors at Low Temperature

On the basis of the Schottky barrier and thermionic emission models, the temperature dependence of barrier height in ZnO varistors is investigated by the I - V characteristics in a wide temperature range from 93 K to 373 K. The obtained barrier height decreases with reducing temperature, which is ascribed to the contribution of tunneling current in measured current. From the proposed equivalent circuit, it is suggested that two current components coexist. One is thermionic emission current, which reflects the thermionic emission barrier height. The other is tunneling current, which appears even at low voltage, especially in low temperature ranges, and thus makes the barrier height obtained from measured current vary with temperature.