间二甲苯分子在不同外电场下结构和解离特性研究

间二甲苯是挥发性有机物(VOCs, Volatile Organic Compounds)的关键活性成分,研究其在外电场下的性质十分重要.采用密度泛函理论(DFT),在B3LYP/6-311G++基组水平上对间二甲苯分子进行优化,从分子结构研究了不同外电场(-0.025 a.u.～0.025 a.u.)作用下,间二甲苯分子的总能量,键长,电偶极矩,前线轨道,红外光谱和解离势能面.计算结果表明,沿两甲基中C原子连线方向的电场(-0.025 a.u.～0.025 a.u.)增加时,分子总能量和能隙先增大后减小,电偶极矩先减小后增加.通过计算发现外电场对间二甲苯分子不同键长和不同振动模式的红外光谱的影响均有所不同.间二甲苯分子的解离特性表现为:沿两甲基中C原子连线方向施加强度超过0.047 a. u.的电场时,位于电场增加方向的甲基与苯环之间起连接作用的C-C键断裂.以上计算结果可为利用电场降解间二甲苯提供重要理论参考.     

Solid-phase extraction techniques based on nanomaterials for mycotoxin analysis: An overview for food and agricultural products

Mycotoxin contamination is a globally concerned problem for food and agricultural products since it may directly or indirectly induce severe threats to human health. Sensitive and selective screening is an efficient strategy to prevent or reduce human and animal exposure to mycotoxins. However, enormous challenges exist in the determination of mycotoxins, arising from complex sample matrices, trace-level analytes, and the co-occurrence of diverse mycotoxins. Appropriate sample preparation is essential to isolate, purify, and enrich mycotoxins from complicated matrices, thus decreasing sample matrix effects and lowering detection limits. With the cross-disciplinary development, new solid-phase extraction strategies have been exploited and integrated with nanotechnology to meet the challenges of mycotoxin analysis. This review summarizes the advance and progress of solid-phase extraction techniques as the methodological solutions for mycotoxin analysis. Emphases are paid on nanomaterials fabricated as trapping media of solid-phase extraction techniques, including carbonaceous nanoparticles, metal/metal oxide-based nanoparticles, and nanoporous materials. Advantages and limitations are discussed, along with the potential prospects.     

CRITICAL EXTINCTION EXPONENTS FOR POLYTROPIC FILTRATION EQUATIONS WITH NONLOCAL SOURCE AND ABSORPTION

In this article,by applying the super-solution and sub-solution methods,instead of energy estimate methods,the authors investigate the critical extinction exponents for a polytropic filtration equation with a nonlocal source and an absorption term,and give a classification of the exponents and coefficients for the solutions to vanish in finite time or not,which improve one of our results(Applicable Analysis,92(2013),636-650) and the results of Zheng et al(Math.Meth.Appl.Sci.,36(2013),730-743).     

Loading of cold ~(87)Rb atom with diffuse light in an integrating sphere

<正>Cold ~(87)Rb atom's loading in an integrating sphere with diffuse light is analyzed theoretically and experimentally. The experimental results show that diffuse light cooling has the greatest efficiency to cool the most atoms when the red detuning between the frequencies of cooling light and atom transition is about 3.3r(Γis the natural linewidth,6.065 MHz).Theoretical analysis using rate equation and numerical calculations on the cold atom number and loading time agree with the experimental results.This integrating sphere cooling would be a novel method for cooling atoms and lead to a new and robust cold atom source for atomic clock.     

REGULARITY CRITERIA FOR WEAK SOLUTION TO THE 3D MAGNETOHYDRODYNAMIC EQUATIONS＊

In this article,regularity criteria for the 3D magnetohydrodynamic equations are investigated.Some sufficient integrability conditions on two components or the gradient of two components of u + B and u...     

基于荧光树状聚合物的高灵敏化学反应型汞离子传感器

以2,4-二氯苯硫酚为单体, 通过“一步法”合成了平均分子量为10.910 kD的荧光树状超支化聚苯硫醚(HPPS). 通过亲核取代和水解反应对HPPS进行了外围氨基修饰, 通过偶氮共价键使HPPS与氨基硫脲小分子相连, 制备出了高灵敏度树状聚合物基多位点反应型汞离子传感器. 基于汞离子与氨基硫脲脱硫关环反应和超支化聚苯硫醚对光信号的放大传递作用, 传感器对汞离子有灵敏的荧光响应信号, 线性范围为2.5～100 nmol/L, 检出限为0.46 nmol/L. 并利用分子模拟计算对反应识别机理进行了讨论.     

Preparation of TiO2-carbon surface composites with high photoactivity by supercritical pretreatment and sol-gel processing

TiO₂-carbon surface (TCS) composites were prepared by pretreatment of a sealing substrate in supercritical carbon dioxide using paraffin as a plugging agent, and sol-gel processing using tetrabutyl orthotitanate as a precursor. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS), optical absorption spectroscopy and nitrogen absorption. The photoactivity of TCS was checked by monitoring the decomposition of methylene blue (MB) in aqueous solution under UV irradiation. The results indicated that compared with TC prepared only by the sol-gel method, the small nanosize TiO₂ particles are well dispersed on carbon surface with large amount of micropores and high Eg values, meanwhile TCS have high Ti³⁺ concentration due to supercritical pretreatment providing a amount of carbon on the composite surface with interfacial energy effects, which controls the growth of TiO₂ nanoparticles, baffles the agglomeration of TiO₂ nanoparticles and easily produces Ti³⁺ ions. These are reasons why TCS has a higher efficiency of decomposing MB than TiO₂-carbon (TC) composites and pure TiO₂. Additional, it is also attributed to the fact that TCS produce a high concentration of organic compounds near TiO₂ in comparison with TC and pure TiO₂, because their surface area are greater than that of TC and pure TiO₂.     

外电场作用下BrCl分子的物理特性与光谱

采用HF （Hartree-Fock）方法,在6-31+G（d,p）基组水平上优化不同外电场（0~0.035 a.u.）下氯化溴分子的基态稳定构型,在此基础上计算氯化溴分子的分子结构、偶极矩、分子总能量、分子键长、分子电荷分布、分子能隙、红外光谱及解离势能面等.结果表明：随着Z轴（平行于Br-Cl连线）方向外电场的增加（0~0.035 a.u.）,分子总能量先小幅度增加后又降低,键长先减小后增大,分子偶极矩先减小后单调增加,原子电荷分布递增,分子能隙逐渐减小,分子红外光谱先蓝移后红移.通过对解离势能面的计算分析发现,强度为0.045 a.u.的外电场使得Br-Cl键断裂而降解,该结果对氯化溴进行电场降解提供参考依据.     

基于重要样本法的结构动力学系统的首次穿越

基于Gisranov定理, 提出一种估计稳态高斯白噪声激励的结构动力学系统首穿失效概率的重要样本法. 文章重点是构造控制函数, 控制函数促使随机响应尽量集中在样本空间中最易导致首次穿越发生的部分. 利用设计点构造控制函数, 在线性系统场合, 结合时不变系统的结构可靠性理论, 通过解有约束的优化问题得到设计点; 在非线性系统场合, 利用Heonsang Koo提出的设计点激励, 通过镜像法得到设计点. 最后给出例子, 将所提方法与原始蒙特卡罗法相比较, 模拟结果显示方法的正确性与有效性.     

测量中的最佳值及标准误差的数学研究

本文对间接测量量的最可信赖值及误差进行推导 ,方法简明 ,计算公式简单 ,学生易接受。