食品中化学性有害物的质谱软电离裂解规律及筛查技术研究进展

食品中化学性有害物是导致食品安全问题的重要原因，质谱是对食品中化学性有害物进行定性定量分析的有效方法。该文按照化合物结构类别，综述了食品中重要化学性有害物的质谱软电离裂解机理，包括农药、兽药、真菌毒素，以及其他化学污染物。对于每类化合物，重点综述化合物质谱裂解产生的特征碎片、中性丢失等，以及这些质谱软电离裂解机理在食品中化学性有害物筛查及发现中的应用。研究化合物的质谱裂解机理可以帮助研究者对化合物进行结构解析和结构确证，为食品中同类结构新型化学性有害物的发掘提供理论依据。     

Some exact expressions for the mean and higher moments of functions of sample moments

Examples of exact expressions for the moments (mainly of the mean) of functions of sample moments are given. These provide checks on alternative developments such as asymptotic series for n, and simulation processes. Exact expressions are given for the mean of the square of the sample coefficient of variation, particularly in uniform sampling; Frullani integrals studied by G. H. Hardy arise. It should be kept in mind that exact results for (joint) moment generating functions (mgfs) are of interest as they produce a means of obtaining exact results for (cross) moments—including moments with negative indices. Thus an exact expression for the joint mgf of the 1st two noncentral moments can be used to obtain the mean of the (c.v.)² (but not for the mean of the c..). A general expression is given for the moment generating function of the sample variance. The limitations of Fisher's symbolic formula for the characteristic function of sample moments (or more general statistics) are noted.This research was sponsored by the Applied Mathematical Sciences Research program, Office of Energy Research, U. S. Department of Energy under contract DE-AC0584OR21400 with the Martin Marietta Energy Systems. Inc.     

A note on differentiability of the cluster density for independent percolation in high dimensions

The cluster density function of independent percolation in ad-dimensional lattice is considered. For eachn, it is shown that(p) has finitenth leftderivative at critical probabilityp _c ifd is sufficiently large. This result agrees with the Bethe lattice approximation, where thenth one-sided derivative of(p) is bounded atp _c for alln.     

Graph theoretical procedure for obtaining analytical expressions of eigenspectra of linear chains and cycles with alternant vertex weights and same edge weight: Application to some complicated graphs

A graph theoretical procedure for obtaining eigenvalues of linear chains and cycles having alternant vertex weights (h₁, h₂, h₁, h₂, h₁, h₂, …) and the same edge weight (k) have been developed. The eigenvalues of some complicated graphs, such as graphs of linear polyacenes, methylene‐substituted linear polyacenes and cylindrical polyacene strips, stack graphs, and reciprocal graphs have been shown to be generated in closed analytical forms by this procedure. Many such graphs represent chemically important molecules or radicals. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Method and algorithm of obtaining the molecular intrinsic characteristic contours (MICCs) of organic molecules

The molecular intrinsic characteristic contour (MICC) is defined as the set of all the classical turning points of electron movement in a molecule. Studies on the MICCs of some medium organic molecules, such as dimethylether, acetone, and some homologues of alkanes, alkenes, and alkynes, as well as the electron density distributions on the MICCs, are shown for the first time. Results show that the MICC is an intrinsic approach to shape and size of a molecule. Unlike the van der Waals hard-sphere model, the MICC is a smooth contour, and it has a clear physical meaning. Detailed investigations on the cross-sections of MICCs have provided a kind of important information about atomic size changing in the process of forming molecules. Studies on electron density distribution on the MICC not only provide a new insight into molecular shape, but also show that the electron density distribution on the boundary surface relates closely with molecular properties and reactivities. For the homologues of alkanes, Rout(H), Dmin, and Dmax (the minimum and maximum of electron density on the MICC), all have very good linear relationships with minus of the molecular ionization potential. This work may serve as a basis for exploring a new reactivity indicator of chemical reactions and for studying molecular shape properties of large organic and biological molecules.     

Theory on the molecular characteristic contour (II)--Molecular intrinsic characteristic contours of several typical organic molecules

The molecular intrinsic characteristic contour (MICC) is defined based on the classical turning point of electron movement in a molecule. Three typical organic molecules, I.e. Methane, methanol and formic acid, were employed as examples for detailed introduction of our method. Investigations on the cross-sections of MICC provide important information about atomic size changing in the process of forming molecules. The electron density distributions on the MICCs of these molecules were calculated and shown for the first time. Results showed that the electron density distribution on the MICC correlates closely with molecular chemical properties, and it provides a new insight into molecular boundary.     

μs级负充电时不同体积分数去离子水与乙二醇混合液电性能的实验研究

 以去离子水与乙二醇的混合液（体积分数分别为36.5%,48.7%,59.0%及71.2%，以下简称混合液）作为同轴传输线的绝缘介质，进行了μs级高电压负充电条件下的正电极击穿实验，研究了混合液的击穿电压、击穿时间、相对介电常数及电阻率与体积分数的关系。实验结果表明：在充电电压为20kV时，71.2%的混合液比36.5%的混合液的平均击穿电压提高25.1%，平均击穿时间延长10.49%，而相对介电常数减小868%。同时，随着充电时间的缩短，混合液的击穿电压提高。     

也谈《高分子化学》课程教学的工科特色

《高分子化学》课程是大部分工科化工、材料类专业的必修课程,如何在工科专业高分子化学课程教学中体现工科特色,成为大家关注的热点.针对什么是工科特色,提出了本人的见解.并就如何在教学过程中体现工科特色介绍了本人的探索与尝试.     

Optimal feedback gains of a delayed proportional-derivative (PD) control for balancing an inverted pendulum

In the dynamics analysis and synthesis of a con-trolled system, it is important to know for what feedback gains can the controlled system decay to the demanded steady state as fast as possible. This article presents a sys-tematic method for finding the optimal feedback gains by taking the stability of an inverted pendulum system with a delayed proportional-derivative controller as an example. First, the condition for the existence and uniqueness of the stable region in the gain plane is obtained by using the D-subdivision method and the method of stability switch. Then the same procedure is used repeatedly to shrink the stable region by decreasing the real part of the rightmost charac-teristic root. Finally, the optimal feedback gains within the stable region that minimizes the real part of the rightmost root are expressed by an explicit formula. With the optimal feedback gains, the controlled inverted pendulum decays to its trivial equilibrium at the fastest speed when the initial val-ues around the origin are fixed. The main results are checked by numerical simulation.     

The Ablowitz–Ladik hierarchy integrability analysis revisited: the vertex operator solution representation structure

A regular gradient-holonomic approach to studying the Lax type integrability of the Ablowitz–Ladik hierarchy of nonlinear Lax type integrable discrete dynamical systems in the vertex operator representation is presented. The relationship to the Lie-algebraic integrability scheme is analyzed and the connection with the τ-function representation is discussed.