毛细管气相色谱法测定中药中有机氯农药残留量

建立了江西省两种中药中有机氯农药残留量的气相色谱分析方法。样品以丙酮提取,在NaCl存在下,以正已烷进行液—液分配,提取液用H2SO4净化,采用DB—1701毛细管柱,GC—ECD检测有机氯农药残留量。最低检测限为1.0×10-3-5.0×10-3mg/kg,添加回收率为85.7%-115.2%,应用于实际样品中有机氯农药残留量的检测,获得了较为满意结果。     

Tribute to Endre Csáki and Pál Révész

Summary This article provides a glimpse of some of the highlights of the joint work of Endre Csáki and Pál Révész since 1979. The topics of this short exploration of the rich stochastic milieu of this inspiring collaboration revolve around Brownian motion, random walks and their long excursions, local times and additive functionals, iterated processes, almost sure local and global central limit theorems, integral functionals of geometric stochastic processes, favourite sites--favourite values and jump sizes for random walk and Brownian motion, random walking in a random scenery, and large void zones and occupation times for coalescing random walks.     

Bounds to optimal burn‐in and optimal work size

Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd.     

Fractional Brownian Heavy Traffic Approximations of Multiclass Feedforward Queueing Networks

We consider multiclass feedforward queueing networks under first in first out and priority service disciplines driven by long-range dependent arrival and service time processes. We show that in critical loading the normalized workload, queue length and sojourn time processes can converge to a multi-dimensional reflected fractional Brownian motion. This weak heavy traffic approximation is deduced from a deterministic pathwise approximation of the network behavior close to constant critical load in terms of the solution of a Skorokhod problem. Since we model the doubly infinite time interval, our results directly cover the stationary case.AMS subject classification: primary 90B15, secondary 60K25, 68M20     

Negative luminescence in semiconductors: a retrospective view

Twenty-five years ago, we introduced the phenomenon of negative luminescence (NL) into semiconductor physics. This paper provides an overview of work conducted to develop this fundamental concept. Initially, we consider the first-principle approach to radiation interaction with basic matter and the major properties of NL. Then we describe the problems of NL direct measurements in homogeneous materials and structures. Finally, we emphasize the use of NL approach in applications involving devices for infrared (IR) wavelength (3–12 μm) high-temperature (300–400 K) optoelectronics. Our subjects will include NL IR emitting diodes, radiative coolers, IR dynamic scene simulators, light up-conversion devices, and the Stealth effect in IR.     

Two‐stage copolycondensation of preformed oligomers with bisphenols by tosyl chloride/dimethylformamide/pyridine from distributions of resulting oligomers determined by a combination of gel permeation chromatography and NMR

A two‐stage co‐oligomerization of the oligomers initially formed from an equimolar mixture of isophthalic acid (IPA) and terephthalic acid (TPA) and 2,2‐bis(4‐hydroxyphenyl)propane (BPA, 50 mol %) with bisphenols (BPs, 20 mol %) was carried out using a tosyl chloride/dimethylformamide/pyridine condensing agent. The distributions of the resulting oligomers (n_x‐mers), which were quenched with methanol, were determined by a combination of gel permeation chromatography (GPC) and NMR. These distributions (presented by molar percentage) were conveniently calculated with the equation n_x (mol %) = n_x (% mol by GPC) × n₀ (mol % by NMR)/n₀ (% mol by GPC), where n_x (% mol) = n_x (wt % by GPC)/its molecular weight. The results showed the distributions of the preformed IPA/TPA‐BPA oligomers to be in fairly good accord with those obtained directly from GPC and to be supported by the NMR results. The calculation was applied to the co‐oligomers prepared up to a reaction of 0.7, at which there was an increase in the number of higher oligomers indivisible by GPC and the distributions could no longer be determined by molar percentage. The calculated distributions are discussed in relation to the results of copolycondensation. The sequence distributions in the resulting co‐oligomers, which were also examined by NMR, are compared with those in the copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 44–51, 2004     

Synthesis and characterization of alt‐bipyridinylene‐phenylene copolymers containing ruthenium(II) complexes

Poly{bis(4,4′‐tert‐butyl‐2,2′‐bipyridine)–(2,2′‐bipyridine‐5,5′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3a ), poly{bis(4,4′‐tert‐butyl‐2,2′‐bipyridine)–(2,2′‐bipyridine‐4,4′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3b ), and poly{bis(2,2′‐bipyridine)–(2,2′‐bipyridine‐5,5′‐diyl‐[1,4‐phenylene])–ruthenium(II)bishexafluorophosphate} ( 3c ) were synthesized by the Suzuki coupling reaction. The alternating structure of the copolymers was confirmed by ¹H and ¹³C NMR and elemental analysis. The polymers showed, by ultraviolet–visible, the π–π* absorption of the polymer backbone (320–380 nm) and at a lower energy attributed to the d–π* metal‐to‐ligand charge‐transfer absorption (450 nm for linear 3a and 480 nm for angular 3b ). The polymers were characterized by a monomodal molecular weight distribution. The degree of polymerization was approximately 8 for polymer 3b and 28 for polymer 3d . © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2911–2919, 2004     

Novel dinitroxide mediating agent for stable free‐radical polymerization

A novel dinitroxide mediating agent that was suitable for stable free‐radical polymerization was synthesized and used in the block copolymerization of styrene and t‐butyl styrene. Quantitative yields of a novel dinitroxide based on 1,6‐hexamethylene diisocyanate and 4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy were obtained. Various experimental parameters, including the nitroxide‐to‐initiator molar ratio, were examined, and it was determined that the polymerization was most controlled under conditions similar to those of conventional 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated stable free‐radical polymerization. Moreover, the dinitroxide mediator proved to be a viable route for the facile two‐step synthesis of triblock copolymers of styrene and t‐butyl styrene. However, the dinitroxide mediation process resulted in a higher than expected level of nitroxide decomposition, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine rather than a preferred internal bisalkoxyamine. This decomposition resulted in the formation of diblock copolymer species during the triblock copolymer synthesis. Gel permeation chromatography was used to monitor the chain‐end decomposition kinetics, and the determined observed rate constant (5.89 × 10^?5 s^?1) for decomposition agreed well with previous studies for other dinitroxide mediating agents. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1547–1556, 2004     

Polyesterification of aromatic dicarboxylic acids and bisphenols with tosyl chloride/dimethylformamide/pyridine promoted by the improvement of the difficult solubility of the activated diacids with lithium chloride

The solution polyesterification of dicarboxylic acids in pyridine, the activated intermediates of which were difficult to dissolve in tosyl chloride/dimethylformamide/pyridine, was investigated in the presence of lithium chloride. The solubility of the activated dicarboxylic acids was largely improved by the presence of the salt, and the polycondensation with bisphenols was greatly facilitated. The salt was more effectively added to a pyridine solution of dicarboxylic acids than to the activated dicarboxylic acids in pyridine. The favorable additive effect on the improved solubility was attributed to a lowered degree of association of the activated dicarboxylic acids, which led to distributions of the resulting oligomers from bisphenols at an earlier stage closer to the theoretical ones and yielded better polycondensation results. The reaction, which proceeded through favorable distributions of the co‐oligomers, produced copolymers of higher inherent viscosities and slightly block sequence distributions determined by NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2725–2733, 2004     

X波段六腔渡越管振荡器的高频特性研究

 从麦克斯韦方程出发，采用时域有限差分法（FDTD）和离散傅里叶变换（DFFT）相结合的方法，通过数值计算得出了六腔开放式谐振腔中前四个谐振频率和场分布，计算出的谐振频率与实验测量结果基本相同。比较了开放腔和封闭腔谐振频率，验证了TEM波吸收边界条件，并在实际编程计算中得以应用。计算结果为六腔渡越管振荡器的机理研究提供了依据。