Experimental measurement of polyethylene chain modulus by scanning force microscopy

Nanoindentation technique and scanning force microscopy have been used to measure directly the polyethylene modulus along the chain axis. Single crystals of polyethylene were employed in order to obtain well-aligned chain segments. To minimize effects of scanner creep, a Z scan rate of 3 Hz was employed. The "X Rotate" value of 25 degrees was selected to eliminate effects of lateral tip motion. The results were analyzed by the Oliver -Pharr method for which direct observation and measurement of the contact area are not required. Considering the influence of tip roundness on the projected contact area, the nanoindentation results were analyzed by the Sawa method. The chain modulus obtained from the thinner polyethylene single crystal sample was 204 +/- 21 GPa by the Oliver-Pharr method and 168 +/- 17 GPa by the Sawa method. The lower values than expected were due to substrate effects and anisotropy of chain deformation during nanoindentation. An extrapolation of the chain modulus obtained by various strains to zero nanoindentation eliminated the effect of substrate and anisotropy of chain deformation. The corresponding chain modulus obtained from the thicker sample was 278 GPa by the Oliver-Pharr method and 267 GPa by the Sawa method, respectively, in better agreement with the value of 340 Cpa determined theoretically. (C) 2001 Elsevier Science Ltd. All rights reserved.

Hydrothermal synthesis and crystal structure of sandwich-like heteropolymolybdophosphates

Sandwich-like heteropoly molybdochromophosphates of supermolecular compound [NH3(CH2)(6)NH3](2)H-3{Cr[Mo6O15(HPO4)(H2PO4)(3)](2)}. 4H(2)O has been hydrothermally synthesized and the single crystal structure has been determined by X-ray diffraction. The crystal data are has follows: triclinic, space group P (1) over bar a=12.156(2), b=12.809(3), c=13.530(3) Angstrom, alpha=102.46(3)degrees, beta=93.67(3)degrees, gamma=93.46(3)degrees, V=2046.9(7) Angstrom(3), Z=1, M-r=2768.69, D-c=2.246 g/cm(-3), F(000)=1337, mu=2.162 mm(-1). The structure has been refined to R=0.0666 and wR=0.1745 by full-matrix least-squares method. The title compound is composed of 1, 6-diaminohexane, water molecules, and {Cr[Mo6O15(HPO4)(H2PO4)(3)](2)}(7-) anion which consists of six oxygen atoms from two [Mo6P4] units with a sandwich-like transition metal atom Cr located at the center of symmetry.

Cure processing modeling and cure cycle simulation of epoxy-terminated poly(phenylene ether ketone) .3. Determination of the time of pressure application

The curing temperature, pressure, and curing time have significant influence on finished thermosetting composite products. The time of pressure application is one of the most important processing parameters in the manufacture of a thermosetting composite. The determination of the time of pressure application relies on analysis of the viscosity variation of the polymer, associated with curing temperature and curing time. To determine it, the influence of the time of pressure application on the physical properties of epoxy-terminated poly(phenylene ether ketone) (E-PEK)-based continuous carbon fiber composite was studied. It was found that a stepwise temperature cure cycle is more suitable for manufacture of this composite. There are two viscosity valleys, in the case of the E-PEK system, associated with temperature during a stepwise cure cycle. The analysis on the effects of reinforcement fraction and defect content on the composite sheet quality indicates that the width-adjustable second viscosity valley provides a suitable pressing window. The viscosity, ranging from 400 to 1200 Pa . s at the second viscosity valley, is the optimal viscosity range for applying pressure to ensure appropriate resin flow during curing process, which enables one to get a finished composite with optimal fiber volume fraction and low void content. (C) 1997 John Wiley & Sons, Inc.

An ultramicroelectrode study of ferrocene diffusion and heterogeneous electron transfer rate in polyelectrolyte

Steady-state voltammograms at a microdisk electrode are used to measure the diffusion coefficient (D) and standard heterogeneous rate constant (k(s)) of ferrocene in polyelectrolyte PEG.MClO(4). The diffusion coefficient and standard heterogeneous rate constant of ferrocene are both smaller in polymer solvents than in monomeric solvents. The D and k(s) of ferrocene have been estimated in PEG containing different concentrations and cations of supporting electrolytes, and the dependencies of D and k(s) on temperature have been observed. These results show that the D and k(s) of ferrocene increase with increasing temperature in polyelectrolyte, and with increasing cation radius of supporting electrolyte, eg D and k(s) increase in the order Bu(4)NClO(4) > NaClO4 > LiClO4. On the other hand, D and k(s) increase with decreasing concentration of supporting electrolyte. The dependence of the half-wave potential (E(1/2)) on the concentration of the supporting electrolyte is also observed. E(1/2) shifts in the negative direction as the concentration of supporting electrolyte increases. (C) 1997 Elsevier Science Ltd.

Crystalline behavior and critical crystalline sequence length of propylene/alpha-olefin copolymer

The melting points(T-m), crystalline temperature(T-c) and crystallinity(chi(c)) of propylene/alpha-olefin (pentene-l, octene-1 and decene-1) copolymers have been investigated, The results show that the T-m, T-c and chi(c) of the copolymers are lower than those of propylene homopolymer, indicating that lower alpha-olefin incorporation in copolymer has strongly hampered the crystallization of propylene, From critical crystalline sequence length of several propylene/alpha-olefin copolymers, it can be seen that a long chain alpha-olefin has much stronger effect on crystallization of PP than a short alpha-olefin does.

丙烯／α－烯烃共聚物的结晶行为及临界结晶序列长度研究

丙烯／α－烯烃共聚物的结晶行为及临界结晶序列长度研究陈辉，王建国，张学全，庞德仁，黄葆同（中国科学院长春应用化学研究所，长春，１３００２２）关键词丙烯／α－烯烃共聚物，结晶行为，临界结晶序列长度聚丙烯（ＰＰ）是最重要的通用塑料之一，但其低温抗冲性能差...

UNSTEADY DIFFUSION KINETICS OF ZIEGLER-NATTA HETEROGENEOUS CATALYST POLYMERIZATION .4. PREDICTION OF EXPERIMENTAL RESULTS OF PROPYLENE ETHYLENE 1-HEXADECENE TERPOLYMERIZATION

The prediction, based on unsteady diffusion kinetics, of the enhancement of reactivity and incorporation of 1-hexadecene in its copolymerization with propylene on adding a small amount of ethylene (increase from 5,2 mol-% to 10,8 mol-% when 2% of ethylene was added, and to 16,1 mol-% when 5% was added) was verified in the terpolymerization of propylene/1-hexadecene/ethylene on a commercial Solvay-type delta-TiCl3 catalyst. The catalyst efficiency was thus also increased. These augmentations originate from the increase in diffusion coefficient of 1-hexadecene at the catalyst surface when the PP crystallinity decreases on introduction of ethylene. Calculation based on unsteady diffusion kinetics showed that the order of diffusion coefficients ethylene > propylene > 1-hexadecene is reversed as the monomer concentration increases when the monomers are not at their equilibrium concentration. Sequence distribution as determined by means of C-13 NMR revealed a tendency of blocky structure rather than a Bernoullian one. The terpolymer compositions obtained by means of an IR method developed in this work conform rather well with the NMR results. Results in this work not only support the unsteady diffusion kinetics but also provide a new route to prepare olefinic copolymer rubbers with heterogeneous titanium catalysts.

Effects of buoyancy on Langmuir circulation

Based on the Navier-Stokes equation, an equation describing the Langmuir circulation is derived by a perturbation method when the influences of Coriolis force and buoyancy force are both considered. The approach used in the analysis is similar to the works carried out by Craik and Leibovich [J. Fluid Mech. 73 (1976) 401], Leibovich [J. Fluid Mech. 79 (1977) 715] and Huang [J. Fluid Mech. 91 (1979) 191]. Potential applications of the equation proposed are discussed in the area of Antarctic circumpolar current.

黄东海胶质浮游动物水母类研究

近年来，胶质类浮游动物尤其是水母类在近岸高生产力的海洋生态系统中的作用越来越受到全球科学家们的关注。这种关注很大程度上是由于近年来很多海域或海湾出现水母类大量繁殖的现象而引起的，这种现象与过度捕捞、气候变化、富营养化以及生物入侵等因素有着内在的联系，给人们带来经济，社会和生态等各方面的损失。这种损失包括：当水母大量出现时，由于它们与鱼类存在食物和捕食竞争，使渔业资源和渔业生产锐减；由于它们会堵塞和撕破渔业生产网，干扰了人们的渔业生产活动；另外水母增多增加了海滨游泳爱好者被蛰伤甚至死亡事件发生的频率，对旅游者们的娱乐行为造成不便。到目前为止全球范围内报道了许多水母大量繁殖并对经济社会或海洋生态系统造成负面影响的事件。在北海水母数量爆发的频率与气候相关的事实表明了该海域将要面临一个更多的胶质类浮游动物的未来。所有这些都表明海洋中水母的生态学问题仍旧是全球的一个研究热点。到目前为止，在世界上许多海湾和海区有关水母生态学问题的研究上，均已取得方方面面有意义的进展。但在我国，由于对水母功能群的研究缺乏足够的重视，对于大型水母来讲它们被认为是渔业生产的副产品或者‘垃圾’，在渔业拖网捕获后把它们直接扔入海中并不去研究；对于小型水母来讲，因为它们为非饵料生物，并且有易碎，粘糊糊等难操作的特点，对浮游生物网同步采集到的水母的研究力度远不如对其他浮游动物类群的研究力度，因此我国对水母功能群生态学的研究基础相当薄弱。 本论文基于以上背景对黄东海大型和小型水母类的生物地理分布格局进行了研究，对其生物量或丰度等生态学指标进行了定量研究。（1）利用浮游生物网样品对黄海小型水母类的种类组成及其丰度的时空变化进行了研究，表明黄海测区内小型水母整体丰度很低，且主要分布在50 m等深线以浅海域，各水母类群以及优势种类的季节更替非常明显。比较不同海区的小型水母的丰度水平及其占浮游动物丰度的比例，发现黄海的小型水母丰度水平最低，为0.8（0.04–1.3）ind. m-3，只占浮游动物丰度的 < 0.5 %，表明小型水母在黄海海域并非占优势的功能群。（2）在中国黄东海采集的沙海蜇和在日本采集的越前水母的COI基因序列差异（0.2%）处于种内水平，从分子水平上证明两者为同一个种类，基于形态学和分子生物学的证据，我国大型水母沙海蜇的分类地位可初步订正为：Nemopilema nomurai Kishinouye, 1922（Scyphozoa：Rhizostomeae：Rhizostomatidae）。（3）利用渔业底层拖网的方法对黄东海大型水母的种类组成，总生物量及各优势种类生物量的时空分布进行了半定量研究。结果共鉴定到11个种（类），其中沙海蜇（Nemopilema nomurai），洋须水母（Ulmaridae genus sp.）以及多管水母（Aequorea spp.）为黄海的优势种（类），沙海蜇（只在东海北部）和霞水母（Cyanea spp.）为东海的优势种（类）；这四个种（类）的湿重随着伞径的增大成冪增长的方式。大型水母平均总生物量的季节变化模式为：3月份水母总生物量最低，为4.6 ± 9.4 kg km–2，春夏季随着海水表层温度的升高，大型水母的生物量逐渐增加，9月初水母的总生物量达到最高值，为22891 ± 25888 kg km–2，随后随着海水的温度下降，生物量也逐渐下降。洋须水母的生物量在10月份达到最高值（2780 ind. km–2，1807 kg km–2），主要在黄海中部出现。多管水母在5月份丰度最高，为8262 kg km–2，且主要分布在30N以北海域。 聚焦大量爆发的水母种（类）沙海蜇和霞水母，基于实测的拖网资料，提供了该种可见的浮游阶段1周年的地理发生和生物量数据；结果表明，这两个种（类）表现了不同的季节出现和生物量格局：首先是黄海出现的沙海蜇（5–12月在黄海出现），5月份少量幼水母体在黄东海的交界处出现，6月它们的分布范围在南黄海扩大，到8月末及9月初沙海蜇几乎遍布黄海，其生物量和丰度以压倒其他大型水母类的优势形成“bloom”（生物量占所有大型水母的96.7%，丰度占93%，在南黄海平均生物量20446 kg km-2，平均占渔获物生物量的86.1 %），10月份至12月，沙海蜇的生物量逐渐减少甚至为零，其分布区域也向北回缩。其次为东海出现的霞水母（5月–10月）：霞水母在5月初达到生物量的高值（平均生物量为380 kg km-2），其伞径随纬度的升高而变小，8月至10月其生物量骤然下降。这两个种类的生物量高值分布在温度或潮汐锋区。结合水文条件及沙海蜇和霞水母关键的生活史策略推测了黄东海该种浮游阶段的生活史模型。 最后，通过对黄海8、9月份沙海蜇生物量的最高峰或暴发时期的呼吸率，摄食率进行估算，获得其每天对浮游动物现存量及生产力的潜在摄食压力，结果表明2006年9月在对沙海蜇最大捕获率的情况下，沙海蜇的摄食率为8.37（0.12–37.83）mg C m-2d-1，假设都以浮游动物为食，这时每天对浮游动物现存量及生产力的摄食压力分别为11.2%（0.17–50.6%），134.1%（1.98–605.7%）。因此在沙海蜇暴发期间对浮游动物的潜在的消耗非常大，甚至为毁灭性的。

Typhoon effects on DOC dynamics in a phosphate-limited reservoir

To explore typhoon effects on dissolved organic carbon (DOC) dynamics, field investigations (tributary and dam site) and laboratory experiments (bioassay and DOC consumption) were conducted in a subtropical reservoir. A tributary survey indicated that after typhoon disruption, upstream areas were the sources of phosphate (P) but not DOC for the dam site located downstream. Bioassay experiments verified P-limitation on bacteria and phytoplankton during summer stratification, and bacteria showed a faster response than algae to added P. Experiments indicated that DOC consumption was determined by the availability of P. The 4 yr typhoon period (June-September) data of the dam site denoted that DOC concentration (27 to 270 mu M C) and its rate of change (-13 to 24 mu M C d(-1)) varied more dramatically in the weak (2006 and 2007) than in the strong (2004 and 2005) typhoon years. The negative correlation of DOC with the ratio of bacterial production (BP) to primary production (PP) in the euphotic zone (0 to 10 m) signified the interactive effects of auto- and heterotrophic processes on DOC variation. In the aphotic zone, the variation of DOC could be ascribed to the change of BP, which showed a positive correlation with P concentrations. This study documents that DOC concentration in the studied system varied at multiple time scales. Such variation can be explained by the decoupling between BP and PP, which is believed to be a function of the limiting nutrient's availability. More importantly, this study suggests that the P supply introduced by strong typhoons might have substantiated a tighter coupling between BP and PP, so that the amplitude of DOC oscillation during the summer period was effectively reduced.

高压缩比的图象压缩编码方法

本文概述了图象压缩编码的原理和方法,并提出了一种改进的基于方向分解的图象压缩编码方法,实验结果表明,对于一般的室内和室外的景物图象,当压缩比高达50 :1时,其恢复图象的视觉效果仍然较好。

异构分布式计算机网远程服务系统的设计与实现

本文阐述了自行设计的一种具有“远程变换服务”目的的简明通用的远程服务语言(RSL)的设计方法,基于 RSL 实现了对异构环境下远程服务系统(HERSS)的逻辑结构的构造.并基于 RSL 自行设计完成了SUN(UNIX)/VAX(VMS)异构分布式计算机网远程服务系统软件.RSL 语言简化了异构分布式计算机网络环境下的远程用户使用网络资源的任务,由此设计的 HERSS 具有很好的开放性与透明性.

大气活性气态汞采样和分析方法

改进了利用镀KCl扩散管采集大气活性气态汞分析方法。实验证明：在450℃条件下加热10min 被扩散管捕获的活性气态汞会被热解出。该法最低检出限为3 pg，具有成本低、分析方法简单、省时及采样管能多次使用等优点。

花江喀斯特峡谷地区石漠化成因初探

花江喀斯特峡谷区地下水埋藏深,地表干旱,存在显著的人为加速土壤侵蚀过程,植被次生性明显,生境干热特征显著,是已石漠化和半石漠化的生态系统。其中地质构造、地貌演化、岩溶形态、可开发利用的水资源、植被群落可能是石漠化过程的主要自然成因,以土地利用为表现形式的强烈人类活动是石漠化的驱动力。基于此,提出了石漠化地区的土地利用方式和生态恢复过程的建议,旨在为石漠化的演化研究及生态重建提供参考。

核磁共振波谱法在腐殖质研究中的应用

总结介绍了核磁共振波谱法在腐殖质研究中的应用情况及进展，包括^13C核磁共振波谱的应用、腐殖质的组成、腐殖质的网状结构模型及腐殖质研究的环境意义等。