Influence of a surfactant and electrolytes on adsorbed polymer layers

Solvent relaxation NMR and small-angle neutron scattering have been used to characterize adsorbed poly(ethylene oxide) (PEO) layers on silica at a range of surfactant and electrolyte concentrations. Below the critical aggregation concentration (cac), the results suggest that sodium dodecyl sulfate (SDS) interacts relatively weakly, perhaps analogously to a simple salt reducing the solvency of PEO. This is evidenced by a decrease in the adsorbed layer thickness combined with an increase in the bound fraction, although the total adsorbed amount is not greatly affected. The layer thickness goes through a minimum at the cac, after which further SDS addition results in the formation of PEO/SDS aggregates that repel each other and, hence, tend to desorb. The adsorbed amount therefore decreases, from 0.7 mg m(-2) initially to 0.2 mg m(-2) with 32 mM SDS. The aggregates that remain adsorbed also repel, and hence, there is an increase in the layer thickness and the persistence length, while the bound fraction is reduced. In comparison, the effects of electrolyte at the ionic strength studied are relatively minimal. There is, however, evidence that the repulsions between adsorbed PEO/SDS aggregates are partially screened, allowing them to approach each other more readily. This leads to a contraction of the adsorbed layer when the SDS concentration is sufficiently high.     

Hearing loss from interrupted, intermittent, and time varying Gaussian noise exposures: the applicability of the equal energy hypothesis

Eight groups of chinchillas (N=74) were exposed to various equivalent energy [100 or 106 dB(A) sound pressure level (SPL)] noise exposure paradigms. Six groups received an interrupted, intermittent, time varying (IITV) Gaussian noise exposure that lasted 8 h/d, 5 d/week for 3 weeks. The exposures modeled an idealized workweek. At each level, three different temporal patterns of Gaussian IITV noise were used. The 100 dB(A) IITV exposure had a dB range of 90-108 dB SPL while the range of the 106 dB(A) IITV exposure was 80-115 dB SPL. Two reference groups were exposed to a uniform 100 or 106 dB(A) SPL noise, 24 h/d for 5 days. Each reference group and the three corresponding IITV groups comprised a set of equivalent energy exposures. Evoked potentials were used to estimate hearing thresholds and surface preparation histology quantified sensory cell populations. All six groups exposed to the IITV noise showed threshold toughening effects of up to 40 dB. All IITV exposures produced hearing and sensory cell loss that was similar to their respective equivalent energy reference group. These results indicate that for Gaussian noise the equal energy hypothesis for noise-induced hearing loss is an acceptable unifying principle.     

磁滞回线和交流电路实验

改进磁滞回线实验,使之能观察包括工频交流电路中的一些基本现象。通过介绍微分回线的概念,使学生了解更我铁实验数据处理方法及其意义。     

类He离子的电子碰撞激发截面

利用扭曲波方法计算类He离子的电子碰撞激发截面。靶波函数采用HFS自洽场波函数,本文计算了若干元素从基态(1¹S)到2¹S,2¹P,2³S,2³P的跃迁。计算结果以碰撞强度的形式给出。入射电子能量从激发阈能开始到x=10,计算结果与已有的结果作了比较,分析表明,在大多数情况下,结果是满意的。     

化学教学导入技能初探

一、导入技能及其功能导入是引起学生注意、激发学习兴趣、形成学习动机、明确学习目标和建立知识问联系的教学活动方式。这一意图性行动广泛地应用于上课之始,或应用于开设新学科、进入新单元、新段落的教学过程。课堂教学的导入,犹如乐曲的“引子”,戏剧的“序幕”,负有酝酿情绪、集中学生注意力、渗透主题和带入情境的任务。精心设计的导入,能抓住学生的心弦,立疑激趣,促成学生情绪高涨,步入智力振奋状态,有助于学生获得良好的学习成果。     

过氧化二碳酸酯和N N-二羟烷基对甲苯胺体系引发甲基丙烯酸甲酯聚合

本文以过氧化二碳酸酯BPPD和芳叔胺DHET、DHPT、DMT、DMA组成的引发体系进行MMA聚合的研究。测定了聚合速率R_p,发现添加DHET、DHPT能促进MMA的聚合,缩短诱导期,提高R_p,其效果要比DMT、DMA为好。测定了E₃和聚合速率方程。由ESR谱和端基分析证实DHET、DHPT芳胺组分产生的自由基能引发单体聚合。     

云南怒江地区芒果香味的分析

用ＧＣ／ＭＳ方法分析测定了采自云南怒江农场的芒果属（ＭａｎｇｉｆｅｒａＬ）的３个品种三年芒、吕宋芒和马切苏芒的主要香味物质。每个品种的香味成分均在２０个以上。对主要成分进行了半定量计算,结果表明三年芒主要含有异松油烯、γ－羟辛酸内酯、３,７－二甲基－１,３,６－辛三烯、γ－羟己酸内酯、石竹烯、２,６－二叔丁基－４－甲基苯酚;吕宋芒主要含α－蒎烯、蒈烯、２,６－二叔丁基－４－甲基苯酚、石竹烯、γ－羟己酸内酯。     

气相色谱法快速测定家用气雾杀虫剂中丙烯菊酯、氯菊酯、增效醚含量

用气相色谱法定量测定了家用气雾杀虫剂中的丙烯菊酯、氯菊酯和增效醚。色谱柱为５％ＱＦ－１／Ｃｈｒｏ－ｍｏｓｏｒｂＷＨＰ,以邻苯二甲酸二苯酯为内标物,测得的回收率分别为１００％,１０２％,９９．９％;变异系数为０．１３,０．５６,０．４８,方法简便、快速、准确。     

分析非线性系统随机响应的一种等效非线性化方法*

本文提出了分析非线性系统随机响应的一种新的等效非线性化方法。文中阐述了该方法的基本思想和处理方法,并对几种常见类型的非线性系统进行了分析和计算,结果表明,利用本文提出方法所得的均方位移响应与精确解或者Monte Carlc模拟解之间具有较好的一致性,并比等效线性化方法有更高的精度。     

超临界流体萃取和气相色谱／质谱法测定中国茶中咖啡因含量

运用超临界流体萃取方法和气相色谱／质谱法联用,成功地测定了三种中国茶叶中咖啡因的含量。方法简便,灵敏度高,测定速度快。平均回收率为９８．１％。