缓冲层对量子阱二能级系统中电子子带间跃迁光吸收的影响

由于ZnO缓冲层对纤锌矿ZnO/Mg_xZn_(1-x)O有限深单量子阱结构左垒的限制作用,导致阱和右垒的尺寸、Mg组分值等因素将影响系统中形成二能级.本文考虑内建电场、导带弯曲及材料掺杂对实际异质结势的影响,利用有限差分法数值求解Schr?dinger方程,获得电子的本征能级和波函数,探讨ZnO缓冲层对此类量子阱形成二能级系统的尺寸效应及三元混晶效应的影响;利用费米黄金法则探讨缓冲层、左垒、阱及右垒宽度和三元混晶效应对此类量子阱电子子带间跃迁光吸收的影响.计算结果显示:对于加入ZnO缓冲层的ZnO/Mg_xZn_(1-x)O有限深单量子阱二能级系统,左垒宽度临界值会随着阱宽和Mg组分值的增大而逐渐减小,随着右垒宽度和缓冲层厚度的增大而逐渐增大;量子阱中电子子带间跃迁光吸收峰会随着左垒、右垒尺寸以及Mg组分的增大发生蓝移,随着阱宽增大而发生红移.本文所得结果可为改善异质结器件的光电性能提供理论指导.     

玻璃-橡胶混合颗粒体系的弹性行为研究

废旧橡胶制品颗粒与砂土颗粒混合物作为建筑填充材料具有环保、轻质、减震效果好等特点.软硬组分的混合比例可以调制体系力学性能从而实现兼顾材料柔韧性与强度的需求,但细观层面上材料性能改变的原因尚不明确.本文主要研究玻璃-橡胶混合颗粒体系的弹性行为及其微观机制.利用飞行时间法测量混合材料等效动弹性模量,发现随着橡胶颗粒增加,体系逐渐从类玻璃刚性行为转变为类橡胶柔性行为.离散元模拟结果与实验结果类似.此外,模拟显示低橡胶颗粒占比样品内主要由玻璃颗粒构成主力链结构,而橡胶颗粒基本不参与强力链的构成.当橡胶颗粒占比较大时,玻璃颗粒和橡胶颗粒共同构成主力链网络结构,但颗粒间法向接触力分布相对更为均匀,可视为玻璃颗粒悬浮于橡胶颗粒中.基于上述结果,提出了改进的等效介质理论,用于描述混合颗粒体系的弹性行为.研究认为:橡胶颗粒占比较小时内部颗粒的变形相对均匀,材料近似满足等应变假设,视为并联弹簧模型;橡胶颗粒占比较大时混合材料近似满足等应力假设,视为串联弹簧模型.两种模型得到的结果与模拟结果一致.上述结果有利于从微观角度揭示混合颗粒材料弹性行为的变化机制.     

Uniform nonintegrability of random variables

Recently, T. K. Chandra, T. -C. Hu and A. Rosalsky [Statist. Probab. Lett., 2016, 116: 27–37] introduced the notion of a sequence of random variables being uniformly nonintegrable, and presented a list of interesting results on this uniform nonintegrability. We introduce a weaker definition on uniform nonintegrability (W-UNI) of random variables, present a necessary and sufficient condition for W-UNI, and give two equivalent characterizations of W-UNI, one of which is a W-UNI analogue of the celebrated de La Vallée Poussin criterion for uniform integrability. In addition, we give some remarks, one of which gives a negative answer to the open problem raised by Chandra et al.     

Ce3+/Ce4+电对在混酸(硫酸和甲磺酸)中的电化学行为

采用循环伏安、线性扫描、交流阻抗等技术研究了Ce³⁺/Ce⁴⁺电对在混酸(硫酸与甲磺酸)中的电化学行为,并对该体系在间接有机电合成中的应用进行了探索.结果表明：当硫酸和甲磺酸(MSA)浓度分别为0.8和1.0 mol·L^-1时,Ce³⁺/Ce⁴⁺电对具有最佳的电化学活性;在上述配比的混酸介质中,铈盐的溶解度得到了大幅提高,同时电解氧化铈(III)离子的电流效率较高（92.1%）,与纯硫酸体系中的电流效率接近（92.8%）,明显高于纯甲磺酸体系（78.5%）;该混酸介质中Ce⁴⁺在氧化茴香醚生成茴香醛这一过程中也表现出很好的氧化能力.     

Simultaneous impacts of MHD and variable wall temperature on transient mixed Casson nanofluid flow in the stagnation point of rotating sphere

A numerical analysis is provided to scrutinize time-dependent magnetohydrodynamics(MHD) free and forced convection of an electrically conducting non-Newtonian Casson nanofluid flow in the forward stagnation point region of an impulsively rotating sphere with variable wall temperature. A single-phase flow of nanofluid model is reflected with a number of experimental formulae for both effective viscosity and thermal conductivity of nanofluid. Exceedingly nonlinear governing partial differential equations(PDEs)subject to their compatible boundary conditions are mutated into a system of nonlinear ordinary differential equations(ODEs). The derived nonlinear system is solved numerically with implementation of an implicit finite difference procedure merging with a technique of quasi-linearization. The controlled parameter impacts are clarified by a parametric study of the entire flow regime. It is depicted that from all the exhibited nanoparticles,Cu possesses the best convection. The surface heat transfer and surface shear stresses in the x-and z-directions are boosted with maximizing the values of nanoparticle solid volume fraction ? and rotation λ. Besides, as both the surface temperature exponent n and the Casson parameter γ upgrade, an enhancement of the Nusselt number is given.     

二维相关光谱的猪肉TVB-N特征变量优选研究

为了探讨利用二维相关可见/近红外光谱法优选猪肉挥发性盐基氮(TVB-N)特征变量的可行性,以贮藏时间为外扰,研究了不同新鲜程度猪肉样本的二维相关光谱特性。首先,获取56个猪肉样本在贮藏1～14 d的400~1 000 nm范围的可见/近红外反射光谱,经过标准正态变量变换(SNV)处理后,基于全波段光谱建立TVB-N的偏最小二乘回归(PLSR)模型。然后,依据TVB-N实测值,从中挑选出10个具有一定浓度梯度的样本(贮藏时间分别为0,36,72,108,144,180,216,252,288和324 h),利用一阶导数对光谱进行预处理后,根据不同样本之间的光谱差异,选取7个波段用于二维相关光谱解析。分析各个波段的二维相关同步谱和自相关谱,从7个波段范围内共选取23个变量作为不同贮藏时间下与TVB-N相关的敏感波长,并建立简化的PLSR模型。相较于全波段光谱数据所建模型,模型效果有所改善,预测集决定系数R2_p由0.792 1上升至0.865 8,误差从3.658 2 mg·(100 g)-1下降至3.246 0 mg·(100 g)-1。表明基于二维相关光谱对猪肉TVB-N特征变量进行优选的思路是可行的,该方法能够从全光谱数据中筛选出与目标物质相关的敏感变量,这也为近红外光谱特征波长选择提供了一个新的方法。     

Modeling based on subspace orthogonal projections for QSAR and QSPR research

A novel projection modeling method for quantitative structure activity relationship (QSAR) and quantitative structure property relationship (QSPR) is developed in this paper. Orthogonalization of block variables is introduced to deal with the problem of variable selection. Projections based on least squares are used to construct the modeling space in order to search for the best regression directions for chemical modeling. A suitable prediction space for such a model is further defined to confine the usage range of the model. Three real data sets were analyzed to check the performance of the proposed modeling method. The results obtained from Monte‐Carlo cross‐validation (MCCV) showed that the proposed modeling method might provide better results for QSAR and QSPR modeling than PCR and PLS with respect to both fitting and prediction abilities. Copyright © 2007 John Wiley & Sons, Ltd.     

Comparisons of mixed systems with decreasing failure rate component lifetimes using dispersive order

Because lifetimes of systems are not deterministic, partially, orders are used for comparison purposes which lead us to provide optimal system configurations. This paper deals with a signature‐based dispersive ordering of mixed systems. It is assumed that component lifetimes are independent and identically distributed, and the common distribution has a decreasing failure rate function. Some illustrative examples are also given.     

十四烷基三甲基氯化铵/十二烷基苯磺酸钠混合表面活性剂双水相体系的萃取性能

研究了十四烷基三甲基氯化铵(TTAC)与十二烷基苯磺酸钠(SDBS)混合表面活性剂水溶液双水相体系的分相情况、萃取性能及两相的微观结构.结果表明,TTAC/SDBS混合表面活性剂水溶液在30℃下能够形成稳定的双水相体系;该双水相体系对亚甲基蓝、靛红都具有一定的萃取分离作用.其上、下两相的微观结构明显不同,这是其能够形成稳定双水相体系且具有萃取作用的重要原因.     

Peak shape analysis of Ag 3d core‐level X‐ray photoelectron spectra of Au@Ag core‐shell nanoparticles using an asymmetric Gaussian–Lorentzian mixed function

This article reports on the peak shape analysis of X‐ray photoelectron spectra of gold‐silver core‐shell (Au@Ag) nanoparticles (NPs) using an asymmetric Gaussian–Lorentzian mixed function. Unlike Ag NPs, Au@Ag NPs have no oxide peak and show asymmetric line shape with a high energy tail in Ag 3d core‐level spectra. A monotonic increase in the Ag 3d binding energy and a decrease in the degree of asymmetry with increasing the Ag shell thickness were observed supporting the occurrence of charge transfer from Au core to Ag shell. Copyright © 2012 John Wiley & Sons, Ltd.