Study on enantiomeric separation of basic drugs by NACE in methanol‐based medium using erythromycin lactobionate as a chiral selector

A wide variety of chiral selectors have been employed in CZE, and among them macrocyclic antibiotics including glycopeptides, ansamycins, aminoglycosides and polypeptides exhibited prominent enantioselective properties toward abundant racemic compounds. Compared with CZE, the use of macrocyclic antibiotics as chiral selectors in NACE has not been reported previously. In this study, an approach to the enantioseparation of basic drugs by means of NACE with erythromycin lactobionate (EL) belonging to the group of macrolide antibiotics has been investigated. Especially different from the above four classes of antibiotics, there are no reports concerned with the use of macrolides which belong to macrocyclic antibiotics as chiral selectors in CE. In this work EL is first used as a chiral selector in NACE for the enantiomeric separations of two racemic basic drugs that possess high separability consisting of propranolol and duloxetine. Furthermore, EL possesses advantages such as high solubility and low viscosity in the solvent and very weak UV absorption. The chiral separations were achieved using Tris‐boric acid as the BGE and methanol as the organic medium. In the course of this work we observed that both migration time and enantioseparation were influenced by several parameters such as the pH and composition of the BGE, EL concentration, capillary temperature and applied voltage. Consequently, these parameters were systematically optimized in order to obtain the optimum enantioseparations.     

Evaluation of the enantioseparation capability of the novel chiral selector clindamycin phosphate towards basic drugs by micellar electrokinetic chromatography

To date, a series of chiral selectors have been utilized successfully in capillary electrophoresis (CE). Among these various chiral selectors, macrocyclic antibiotics have been demonstrated to represent powerful enantioselectivity towards many chiral compounds. Differing from macrocyclic antibiotics, the use of lincosamide antibiotics as chiral selectors has not been reported previously. In our recent work, clindamycin phosphate belonging to the group of lincosamides has been first used as a chiral selector in capillary zone electrophoresis (CZE). In this paper, a micellar electrokinetic chromatography (MEKC) method has been developed for the evaluation of enantioseparation capability of this novel chiral selector towards several racemic basic drugs. As observed during the course of this work, clindamycin phosphate allowed excellent separation of the enantiomers of nefopam, citalopram, tryptophan, chlorphenamine, propranolol and metoprolol, as well as partial enantioresolution of tryptophan methyl ester and cetirizine. In this MEKC chiral separation system, different types of anionic surfactants, organic additives and background electrolytes were tested, and satisfactory enantioseparations of basic drugs above-mentioned were achieved using sodium dodecyl sulfate (SDS) as the surfactant, isopropanol as the organic additive, and phosphate as the background electrolyte. Furthermore, both migration times and enantioseparation of the analytes were influenced by several experimental parameters such as pH of the BGE, clindamycin phosphate and SDS concentrations, phosphate and isopropanol concentrations, and applied voltage. Consequently, the effects of these factors on enantioseparations of the studied basic drugs were systematically investigated in order to evaluate the stereoselectivity of clindamycin phosphate in MEKC.     

顺序相依拆卸线平衡多目标优化模型及算法研究

拆卸是产品回收过程最关键环节之一,拆卸效率直接影响再制造成本。本文在分析现有模型不足基础上,考虑最小化总拆卸时间,建立多目标顺序相依拆卸线平衡问题优化模型,并提出了一种自适应进化变邻域搜索算法。所提算法引入种群进化机制,并采用一种组合策略构建初始种群,通过锦标赛法选择个体进化;在局部搜索时,设计了邻域结构自适应选择策略,并采用基于交叉的全局学习机制加速跳出局部最优,以提高算法寻优能力。对比实验结果,证实了所提模型的合理性以及算法的高效性。     

商业信用额度下易腐品最优订货策略

运作实践中,供应商不仅会给予零售商延期付款待遇以刺激其订购量,同时也会为信用期内零售商的应付账款设置上限值(即商业信用额度),从而规避零售商的应付账款对其造成的资金机会成本和违约风险。鉴于此,本文基于商业信用额度构建了零售商关于易腐品的订购决策模型。通过分析零售商资金机会成本的不同形式,可以得到零售商关于易腐品五种不同的成本函数表达式。结合数学证明可以得到零售商五种目标函数的性质,以及在商业信用额度条款下零售商最优的订购决策。算例表明供应商可以通过设置一个合理的商业信用额度条款将零售商的订购量和信用期内的应付账款控制在一个合适范围。同时商业信用额度条款有助于缓解供应商的营运资金压力,但会在一定程度上增加零售商的运营成本。     

Online purchasing under uncertainty

Suppose there is a collection of independent uniform random variables, and a hypergraph of target structures on the vertex set . We would like to purchase a target structure at small cost, but we do not know all the costs x_i ahead of time. Instead, we inspect the random variables x_i one at a time, and after each inspection, choose to either keep the vertex i at cost x_i, or reject vertex i forever. In the present paper, we consider the case where is the edge‐set of a complete graph (or digraph), and the target structures are the spanning trees of a graph, spanning arborescences of a digraph, the paths between a fixed pair of vertices, perfect matchings, Hamilton cycles or the cliques of some fixed size.     

基于信用额度和外生违约概率的出口海陆仓融资质押率优化

质押率优化是出口海陆仓融资决策的核心内容。针对出口商信用、出口商与进口商外生违约以及质押物价值波动三重叠加风险下的出口海陆仓融资决策问题,在设定出口商信用额度,且给定出口商和进口商外生违约概率的前提下,依据双重Stackelberg博弈原理,以供应链协同均衡下的出口商、进口商和船公司的期望利润最大化为目标,建立了质押率与订货量及货物价格联动优化模型,设计了微分法和逆向归纳法求解模型。算例验证了模型和方法的适用性和有效性。敏感性分析结果表明质押率与出口商信用额度呈负相关关系,对出口商和进口商外生违约概率不敏感。研究结论可为出口海陆仓融资优化决策提供科学参考。     

On properties of the set of invariant lines of a Brouwer homeomorphism

Abstract

We present properties of sets of invariant lines for Brouwer homeomorphisms which are not necessarily embeddable in a flow. Using such lines we describe the structure of equivalence classes of the codivergency relation. We also obtain a result concerning the set of regular points.     

电偶极子位于均匀介质球中时球外电场的研究

采用分离变量法求解了电偶极子位于均匀介质球中时复连通域的拉普拉斯方程和泊松方程,求出了球内外两种不同介质的电势分布和球面上的极化电荷分布;通过求解二阶非线性微分方程得到了球外的电场线函数;利用计算软件Math-ematica 5.0,作出了相应的相互正交的等势线簇图形和电场线簇图形,并且进行了必要的讨论.     

A consensus line search algorithm for molecular potential energy functions

Force field based energy minimization of molecular structures is a central task in computational chemistry and biology. Solving this problem usually requires efficient local minimization techniques, i.e., iterative two‐step methods that search first for a descent direction and then try to estimate the step width. The second step, the so called line search, typically uses polynomial interpolation schemes to estimate the next trial step. However, dependent on local properties of the objective function alternative schemes may be more appropriate especially if the objective function shows singularities or exponential behavior. As the choice of the best interpolation scheme cannot be made a priori, we propose a new consensus line search approach that performs several different interpolation schemes at each step and then decides which one is the most reliable at the current position. Although a naive consensus approach would lead to severe performance impacts, our method does not require additional evaluations of the energy function, imposing only negligible computational overhead. Additionally, our method can be easily adapted to the local behavior of other objective functions by incorporating suitable interpolation schemes or omitting non‐fitting schemes. The performance of our consensus line search approach has been evaluated and compared to established standard line search algorithms by minimizing the structures of a large set of molecules using different force fields. The proposed algorithm shows better performance in almost all test cases, i.e., it reduces the number of iterations and function and gradient evaluations, leading to significantly reduced run times. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009     

全能近似分析简介

根据无限的“无有终了”的事实，应当把无尽小数看作无穷数列简写，采用这种观点就可以得到实数的运算法则；如果用康托（Cantor，G）的“无限是现实的、完成了的、存在着的整体”的“实无限”观点就得不到这个法则．点是针对误差界的足够小，其中没有大小的点叫做理想点，有大小的点叫做近似点．理想点具有无法点出的性质．近似点的集合能够组成线段，但理想点的集合不能组成线段．绝对准确地讨论没有大小的理想瞬时上的速度没有实际意义，理想的瞬时速度依赖于近似瞬时的速度．对于点、线、面、实数、函数、导数、积分、积分变换、实数集等数学名词都需要提出近似、理想、全能近似三类技术术语，应用对立统一法则去阐述数学理论．