翠绿亚胺聚合物高压下芳环扭角和能隙的缩减

利用改进的Ginder-Epstein模型计算了翠绿亚胺聚合物在参数V4,0取值于1.8～35.8 eV的自洽变分基态,并通过芳环扭角的变化来估算聚合物压强,给出了V4,0,芳环扭角及能隙与理论压强之间的最小二乘拟合.结果表明随此参数的增大,芳环扭角和能隙都缩减而理论压强升高.当理论压强由零压增至3.0 GPa左右时,能隙先快后慢从2.0 eV减小至最小值0.87 eV.这理论与该聚合物的高压电导测试结果一致.     

多形性相变的分子动力学模拟

 本文利用分子动力学方法研究了KCl晶体在ρ＝ρ₀时的温度相变。面心立方（fcc）和体心立方（bcc）两种结构的径向分布函数随温度的变化的情况说明，在高压下，发生着bcc结构相fcc结构的转变，bcc结构是不稳定的。为了选取合理的势参数，利用了分子动力学程序在T＝0时的性质，计算了NaCl和KCl晶体的零温状态方程，研究了它们在压力作用下发生的多形性相变。计算表明，NaCl和KCl晶体将分别于18.8 GPa和5.9 GPa发生从fcc到bcc的多形性相变，这些值相当接近实验结果。着说明本文选用的势参数势有一定精度的。     

研究金属切削中组织变化的网格高速摄影装置

研究金属切削过程中的变化,对改进切削工艺、实现高速、自动化和精密加工具有重要意义。高速显微摄影是实现从宏观到微观、从定性到定量、从静态到动态研究的有效方法。     

Trace-matrix separations for high-purity chromium,molybdenum and tungsten with cellulose collectors

Trace metals (20 elements) in high-purity chromium, molybdenum and tungsten are collected and preconcentrated by precipitation and adsorption on cellulose collectors. The compound methods allow the application of AAS and ICP-AES as determination methods for the production control of highly pure refractory metals under routine conditions.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

使用ZFK-500型高速摄影机对液中放电现象的摄影观察

液中放电是通过放电的方式将电能高速转化为热、光、力、声等其他形式的能量。它具有一系列独特的优点,使它广泛应用于许多领域。因此,关于液中放电的研究具有重要的理论与实践意义。我们使用ZFK-500型高速摄影机对液中放电的击穿与弧道过程、冲击波的形成与传播过程,进行了比较成功的观察。大量清晰的摄影,记录了击穿时微弱光线的光导及其在整个放电阶段的情况;记录了液中放电弧道膨胀的特点 此外,不发光现象-冲击波形成与传播过程的记录,都为液中放电的理论研究,提供了十分宝贵的科学依据。     

Stress distribution in poly‐p‐phenylenebenzobisoxazole (PBO) fiber estimated from vibrational spectroscopic measurement under tension. II. Analysis of inhomogeneous stress distribution in PBO fiber

Fourier transform Raman spectra were measured for poly‐p‐phenylenebenzobisoxazole (PBO) fiber subjected to a tensile stress, and the Raman shift factor (the frequency shift caused by 1 GPa tensile stress) depended strongly on the sample‐preparation condition. To clarify the reasons of this dependency, a mechanical series parallel model was adopted that could successfully and quantitatively explain the observed Raman shift factors and gave a concreate heterogeneous stress distribution in the PBO fibers. As a result, a mechanical series model was reasonable for PBO fiber. Broadening of Raman bands, which was observed when the PBO fiber was tensioned, could also be interpreted on the basis of an idea of heterogeneous stress distribution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1281–1287, 2002     

Carbon‐based sorbents in chromatography. New achievements

The newest results in the employment of carbon‐based composites in various chromatographic techniques such as gas–liquid chromatography, high‐performance liquid chromatography and electrically driven separation techniques for the separation, quantitative determination and identification of a wide variety of compounds in complicated matrices are compiled. The results are concisely described and critically evaluated. The future trends in the application of carbon‐based compounds in the chromatographic separation methods are briefly discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Simultaneous quantification of five major constituents in stems of Dracaena plants and related medicinal preparations from China and Vietnam by HPLC–DAD

A high‐performance liquid chromatographic (HPLC) method was developed for the simultaneous quantification of five major bioactive constituents in the stems of resiniferous Dracaena plants from China and Vietnam, as well as those in the related traditional Chinese medicinal preparations. A diode array detector with the wavelength of 330 nm was used to monitor resveratrol, 7,4′‐dihydroxyflavone and pterostilbene, while loureirin A and loureirin B were monitored at 280 nm. The five constituents were separated on an Agela SB C₁₈ column by gradient elution using 0.008% (v/v) formic acid solution (A) and acetonitrile (B) as the mobile phase. The validation of the method included recovery, linearity, accuracy and precision (intra‐ and inter‐day variation). The range of recoveries of this method was 98.1–104.9%, with all the constituents showing good linearity (r² > 0.9999). The accuracy and precision were satisfactory, with the overall intra‐ and inter‐day variation being less than 4%. The present method has been successfully applied for the determination of all five constituents in 21 related herbal samples including 10 D. cochinchinensis stem samples, seven D. cambodiana stem samples and four purchased medicinal preparations. The contents of these constituents were analyzed using principal component analysis, which can efficiently identify raw herb of Dracaena from different sources. The study may be considered helpful to the quality control of Dracena plants and its medicinal preparations. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and reproducibility of a novel high‐performance liquid‐chromatography monolithic column method for the detection and quantification of trans‐indolyl‐3‐acryloylglycine in human urine

Elevated levels of trans‐indolyl‐3‐acryloylglycine (IAcrGly) have been reported in the urine of people with various conditions including pervasive developmental disorders (PDDs) such as autism and Asperger syndrome. Reversed‐phase high‐performance liquid chromatography with ultra‐violet detection using traditional particle silica‐based columns subsequent to solid‐phase extraction (SPE) has been the preferred assay method; requiring long analytical run times, high flow rates and high solvent usage. Recent developments in monolithic HPLC column technology facilitated the development of a novel analytical method, for the detection and quantification of urinary IAcrGly. The revised method eliminates the requirement for SPE pre‐treatment, reduces sample run‐time and decreases solvent volumes. Five urine samples from people diagnosed with PDD were run in quadruplicate to test the intra‐ and inter‐day reliability of the new method based on retention time, peak area and peak height for IAcrGly. Detection was by UV with IAcrGly confirmation by MS/MS‐MS. Relative standard deviations showed significant improvement with the new method for all parameters. The new method represents a major advancement in the detection and quantification of IAcrGly by reducing time and cost of analysis whilst improving detection limits and reproducibility. Copyright © 2009 John Wiley & Sons, Ltd.     

Interaction of food packaging material and selected food components under high pressure

Abstract

Interactions between ethanolic solutions of p-cymene and acetophenone and different polymer packaging materials. were studied at 500 MPa and 25° C. p-Cymene solution, filled into low-density polyethylene bags, lost 30% of its aroma concentration after 24 h at 500 MPa compared to a 60% loss at atmospheric pressure. The decrease was strongest within the first 15 min. Using LDPE/HDPE/LDPE bags, losses were 20% and 30%, resp. Applying the “bag in the bag” method, p-cymene concentrations measured inside and outside the inner bag has shown sorption by the pressurized film to be one third of that by the non-pressurized. In PET/AI/LDPE bags impermeable to p-cymene, sorption was confined to the inner LDPE layer and caused higher loss in the non-pressurized sample. Acetophenone has not been found to interact with the polymer during pressure treatment, while at atmospheric pressure sorption loss in aroma concentration was nearly 70% after 60 h.