顶空气相色谱-质谱法测定婴幼儿食品中的呋喃

通过顶空装置将样品中的呋喃提取出来,以D4-呋喃作为内标物,HP-PLOT Q石英毛细管柱作为分析柱,采用气相色谱分离,质谱定性定量,建立了婴幼儿食品中呋喃的顶空气相色谱-质谱联用分析方法。方法的低浓度工作曲线的线性范围为10～70 ng,高浓度工作曲线的线性范围为50.0～400.0 ng,两条曲线的相关系数均为0.997。方法的定性检出限（S/N≥3）为3.8 ng/g,定量检出限（S/N≥10）为10.0 ng/g。不同基底样品中高低添加浓度的加标回收率为90.0%～98.4%,相对标准偏差均小于10%。     

聚醚砜酮涂层纤维顶空固相微萃取-气相色谱法分析水中痕量的酚类化合物

应用自制的聚醚砜酮(PPESK,30 μm)涂层纤维,采用顶空固相微萃取-气相色谱法测定水中痕量的酚类化合物。优化了固相微萃取温度、萃取时间、pH值和离子强度。方法的检出限为0.003～0.041 μg/L,相对标准偏差低于16%(n=5)。将PPESK涂层纤维与商品化的聚丙烯酸酯涂层纤维对比,结果表明PPESK萃取酚类化合物有较高的萃取富集倍数。用所制备的PPESK萃取头分析自来水、海水等实际水样,20 μg/L添加水平下的回收率分别为100.5%～111.8%和94.8%～117.3%。     

机械系统中摩擦模型的研究进展

摩擦现象在机械系统中的作用日益突出, 合理地解决机械系统中摩擦环节尤其是非线性摩擦环节的制约问题 已成为当前研究的重点. 由于摩擦的复杂性, 很难从机理上获得其准确唯一的数学模型, 迄今已提出的摩擦模 型有数十种. 鉴于目前机械系统中摩擦建模的发展状况, 首先描述了几种重要的摩擦现象, 如库仑摩擦、黏性 摩擦、Stribeck效应、预滑动摩擦、可变的静态摩擦力和摩擦记忆效应等. 其次, 系统地介绍了几种较为重要的、 常用的摩擦模型, 包括6种静态摩擦模型和7种动态摩擦模型, 并对每一种模型的构成, 特点和适用范围等 进行了较为详细地论述. 比较而言, 静态摩擦模型结构简单, 参数辨识容易, 但是无法描述摩擦的动态特性, 动态摩擦模型能够比较全面的描述摩擦现象, 但结构复杂, 参数辨识难度较大. 再次, 简要概述了摩擦建模 对机械系统动力学行为的影响, 以及在高精度定位系统的控制中的作用. 最后, 针对当前机械系统中摩擦建 模方面存在的一些不足提出了几点展望. 为今后摩擦模型的选用和新摩擦模型的建立提供了参考.     

Conformal Ricci Collineations of Static Spherically Symmetric Spacetimes

Conformal Ricei collineations of static spherically symmetric spacetimes are studied. The general form of the vector fields generating eonformal Rieei eollineations is found when the Rieei tensor is non-degenerate, in which ease the number of independent eonformal Rieei eollineations is 15, the maximum number for four-dimensional manifolds. In the degenerate ease it is found that the static spherically symmetric spaeetimes always have an infinite number of eonformal Rieei eollineations. Some examples are provided which admit non-trivial eonformal Rieei eollineations, and perfect fluid source of the matter.     

基于三维Hopkinson杆的混凝土动态力学性能研究

混凝土、岩石类材料在复杂应力状态下的动态力学性能研究一直备受关注,但鉴于动态实验的复杂性,对真三轴应力状态下材料的动态加载一直未曾实现。本文中研制了一套真三轴静载作用下混凝土、岩石类材料的“三维Hopkinson杆”动态力学实验系统,为冲击载荷作用下材料动态各向异性特性的研究提供了一种有效的实验测试技术。该系统采用液压伺服控制对立方体试件施加三向独立的0~100 MPa真三轴静载,再利用分离式Hopkinson压杆对试件施加冲击动载,具体研究了C30混凝土材料在不同真三轴静载条件下的动态压缩性能,得到了不同条件下X、Y、Z方向上的动态应力应变关系。     

基于持续集成的软件度量

软件度量是针对软件开发项目、过程及产品进行数据定义、收集和分析的持续度量化过程;持续集成工具上的的构建工程每天自动完成从版本库更新代码、静态检查、编译、出包、自动化用例测试等任务,在进行集成构建的过程中可以为软件度量提供多种相关的度量数据;结合工作实践,叙述了基于持续集成的软件度量的原理;软件度量管理涉及到的角色;软件度量实现过程;叙述了基于持续集成的两种类型的软件度量指标的定义以及提取方法;最后详细叙述了在软件度量过程中遇到的几个典型案例;工作实践表明在软件的开发过程中做好软件度量工作有助于软件开发部门控制、预测、和改进软件产品的质量与软件开发过程;从而提高软件质量和软件开发效率,降低软件开发成本。     

Improved sensitivity of headspace gas chromatography for organic aromatic compounds

Summary The effect of adding an electrolyte and increasing the temperature on the preconcentration of volatile compounds in headspace analysis has been investigated. Quantification of the interactive effects of temperature and addition of salt on the vapor concentration is of interest for the determination of trace organic impurities in pharmaceutical base materials. This study was undertaken to investigate the quantitative effects of the addition of salts alcohols, and acetone, and of increasing the temperature on the vapor concentrations and distribution coefficients of volatile aromatic compounds (benzene, toluene, ando-xylene). It was found that the concentration of aromatic compound residues in the headspace could be increased by adding an inert salt to the water, but this effect was not very significant because of the low orginal solubility of the aromatic compounds in water. The reverse effect can be achieved by use of polar organic additives; this can be explained by the high polarizability of aromatic compounds and their greater solubility in the presence of these solvents. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999.     

Susceptibilities of the antiferromagnet REM model

The linear and non-linear susceptibilities of the two sub-lattices Random Energy Model (REM) allowing antiferromagnetic order is studied as a function of the external field (h) and temperature (T). Due to the competition between external field and the internal exchange field acting on the spins there is a drastic change of the system's behavior as the parameters (h,T) are varied. The behavior of the susceptibilities in low and high fields is very different in that the latter may grow as the temperature decreases. Moreover, the critical region undergoes a substantial enlargement as the external field increases. Received: 29 May 1998     

A quark model based on QCD scale anomaly

We consider a quark model based on QCD scale anomaly in which the quarks move in the field of an effective glueball field. Hadrons correspond to solitonic bags of higher energy density in a nonperturbative sea of condensed gluons. We calculate the static properties of nucleon in this model and find that the nucleon mass is far too large (2.4–4 GeV) and the proton charge radius (0.37–0.54 fm) is low. The proton gyromagnetic ratio and g_A/g_v are in reasonable agreement with the experimental numbers.     

On some aspects of the dynamics of a monoatomic Lennard-Jones liquid

Summary On the basis of the results obtained by methods of molecular dynamics by Rahman on liquid Ar, it is empirically shown that the harmonic spectrum of the atomic motion can be interpreted as a sum of two contributions. A ?preliminary? frequency spectrum, obtained by considering every possible (practically harmonic) motion of an atom in the field of its nearest neighbours, duly transformed to take account of the very short duration of the single monochromatic oscillations, constitutes one of the contributions interpretable as a superposition of disordered ?local oscillations?. The other contribution, interpretable as a superposition of travelling waves, is given by a sum of two bands having some analogy with Rayleigh-Debye bands, but having the customary cut replaced by a factor of the form exp [−(ω/ω₀)²] whose physical meaning is that only oscillations having an amplitude larger than a minimal value appear as travelling waves. These bands come into evidence when the spectrum of the local oscillations is subtracted from the harmonic spectrum. The lower frequency band is quite small (area about 2% of the total area of the spectrum) and suggests the existence of transverse waves (in the field of 10¹² Hz.)

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Riassunto Sulla base dei risultati ottenuti con metodi di dinamica molecolare applicati da Rahman al caso dell’argon liquido, si mostra empiricamente che lo spettro armonico dei moti atomici in questo liquido si può interpretare come somma di due contributi. Uno spettro di frequenza ?preliminare? ottenuto considerando tutti i possibili moti di un atomo nel campo dei suoi vicini piú prossimi, debitamente transformato per tener conto della brevissima durata delle singole oscillazioni, costituisce uno dei contributi, interpretabile come sovrapposizione disordinata di ?oscillazioni locali?. L’altro contributo, interpretabile come sovrapposizione di onde viaggianti, risulta formato da due bande aventi una certa analogia con le bande di Rayleigh-Debye nelle quali però l’abituale taglio discontinuon è sostituito da un fattore exp [−(ω/ω₀)²] il cui significato fisico è che soltanto oscillazioni con un’ampiezza superiore ad un minimo (legato al valore di ω₀) appaiono come onde viaggianti. Queste bande di onde viaggianti si evidenziano quando lo spettro delle oscillazioni locali è sottratto dallo spettro atomico. La banda di frequenza minore è molto piccola (area di circa il 2% dell’area totale dello spettro) e suggerisce l’esistenza di onde trasversali (nel campo di 10¹² Hz).