Separation of five diketopiperazines from the marine fungus Alternaria alternate HK‐25 by high‐speed counter‐current chromatography

High‐speed counter‐current chromatography was applied to the separation of five diketoperazines from the marine Alternaria alternate HK‐25 for the first time using one‐step elution method with a pair of two‐phase solvent systems composed of petroleum ether/ethyl acetate/methanol/water (5.5:11:5:7, v/v). Where 151.6 mg of crude sample yielded five diketoperazines, 12,13‐dihydroxy‐fumitremorgin C ( 1 ), gliotoxin ( 2 ), demethoxyfum itremorgin C ( 3 ), bisdethiobis(methylthio)gliotoxin ( 4 ), fumitremorgin C ( 5 ), and the purities of all compounds were above 94% as determined by high‐performance liquid chromatography. The structures of these compounds were identified by ¹H and ¹³C NMR spectroscopy. These results showed that high‐speed counter‐current chromatography can provide a feasible way for highly effective preparation of marine natural products, which ensured the supple of numerous samples for drug development.     

9,9-二辛基聚芴-苯并噻二唑交替共聚物的绿光偏振电致发光

通过缩聚法合成了绿光9,9-二辛基聚芴-苯并噻二唑交替共聚物（PFBT）.该聚合物在一定温度范围内形成向列液晶态,利用其在定向层上的有序排列,实现了峰值发光波长为550 nm的偏振电致发光.采用摩擦后的空穴注入层聚（3,4-乙撑二氧噻吩）∶聚（苯乙烯磺酸）（PEDOT:PSS）作为定向层,通过偏振紫外可见吸收光谱和偏振光致发光谱,研究了聚合物分子在薄膜平面内的单轴取向特性,计算得到薄膜的有序参数为075.制备了结构为ITO/PEDOT:PSS/PFBT/LiF/Al的聚合物电致发光器件,工作电压为15 V时,电致发光偏振率达到4,亮度和流明效率分别为450 cd/m²和021 cd/A. 关键词： 偏振发光 交替共聚物 聚合物电致发光器件     

线性增长条件下一类非线性梁方程解的存在性

考察了一类非线性四阶两点边值问题的解的存在性.通过构造适当的Banach空间并且利用积分方程建立了一个存在定理.主要工具是Leray-Schauder非线性抉择.本文表明,如果非线性项在其定义域的某个有界子集上的增长速度是线性的,该问题可能存在解.     

利用有限域上交错矩阵构造Cartesian认证码

设Fq是q元有限域,q是素数的幂.令信源集S为Fq上所有的n×n交错矩阵的合同标准形,编码规则集E为Fq上所有的n×n非奇异矩阵,信息集M为Fq上所有的n×n交错矩阵,构造映射f:S×E→M,(K'(v,n),g)→gK'(v,n)gT.证明了该四元组(S,E,M;f)是一个Cartesian认证码,并计算了它的参数.进而,假定编码规则按照均匀的概率分布所选取,计算出了该码的成功模仿攻击概率PI和替换攻击概率Ps.     

一维交替型脉冲微分系统

讨论一维空间中超前型与滞后型交替的脉冲微分系统.首先考虑具常系数的脉冲微分系统平凡解稳定的充分条件;其次研究了具变系数的脉冲微分系统的振动性,并给出了其解的表示式.     

Numerical Integration of Reaction–Diffusion Systems

Approximating numerically the solutions of a reaction–diffusion system in an efficient manner requires the application of implicit methods, since the Courant–Friedrichs–Lewy condition on explicit methods imposes a time step of the order of the square of the space step. In this article, we review two types of strategies which are expected to yield reasonably precise solutions within a reasonable computing time. The first examines methods for solving the linear step necessary in any resolution procedure; estimates of CPU time in terms of the error are given in the non preconditioned and in the preconditioned case – provided that it is possible to define an efficient preconditioner. The second strategy is based on splitting, with or without extrapolation. The respective faults and qualities of both strategies are examined; they lead to a list of difficult analytical and numerical problems with possible hints as to their solution.     

作为一般性反例的Hamilton图

文［２］对文［１］中的定理３，就ｐ＝２的特殊情况给一个反例．本文则对ｐ〉３的一般情况给出一类反例     

离散信道容量的迭代算法

引入信息量偏差概念，给出平均交互信息量关于输入概率的增量公式，设计出离散信道容量线性乘法迭代和线性常系数迭代算法，它们都优于现有的指数迭代算法．并证明在所有单步迭代算法中它们几乎是最好的算法.     

喀纳斯湖区的土壤

本文从喀纳斯湖区的自然条件、土壤形成过程、属性和化学性质等方面,论述了由山地冰沼土、高山草甸土、亚高山草甸土、棕色针叶林土、山地黑钙土五种土类,组成的新疆特有的冷湿型高山湖区(除基带棕钙土之外)的土壤垂直带谱。     

电桥法测电阻综述

本文对测量电阻的多种电桥法进行了介绍，并分析了各种方法的使用范围及改进方法。