碳纤维与复合材料的回顾(第一部分)

在论文将分为两部分,目的是要回顾碳纤维及其原丝的生产技术、纤维结构及其主要性能(第一部分).并总结目前树脂基或水泥基碳纤维复合材料的现状(第二部分)。     

侧流塔的最小回流比

蒸馏塔的设计需要估算最小回流比。本文指出如何计算有一股或多股侧流的蒸馏塔最小回流比。     

杀螟硫磷原药和制剂气相色谱测定法的协作研究

世界卫生组织(WHO)于1973年首次把杀螟硫磷(fenitrothion)编入农药规格手册。有效成份的分析采用滴定法,该法基于杀螟硫磷在酸性溶液中被锌还原,然后用亚硝酸钠滴定还原产物胺。方法包括原药及其可湿性粉剂的测定。这一方法并不是专一的而且费时。在WHO杀虫剂化学与规格专家委员会1977年会议上,J.W.Miles和D.L.Mount     

烯丙基氯共聚物链节对聚氯乙烯热降解的稳定作用

如果认为聚氯乙烯中出现的链岐化点是由于分子内链转移反应所致,则意味着叔氯原子是造成热不稳定性的原因。用氯乙烯与2—氯丙烯共聚而制成的典型聚合物分枝的多少与脱氯化氢难易之间的相互关系支持了这一论点。但是很明显在氯乙烯均聚物中,没有叔氯原子。现在人们公认,聚氯乙烯中的多数分枝是与主链中的—CH—基团相联的CH_2Cl基团最近的研究工作还未表示聚氯乙烯CH_2Cl含量与热不稳定性之间的相互关系。氯乙烯—烯丙基氯共聚而成的含有较多CH_2Cl基团的聚合物样品,使我们得以对聚氯乙烯热稳定性的影响做进一步的研究是有用的。     

盐水杂质对隔膜氯碱电槽性能的影响

具有沉积石棉隔膜的实验电槽使用不纯盐水来研究硬度对电槽性能的影响。氢氧化钠在隔膜中的浓度分布状态是由扩散、迁移和湍流三种因素来确定的;应该指出的是:在隔膜电槽的操作条件下,迁移流比扩散流要大得多。生产氯气和纯净烧碱用汞齐法水银电槽是最好的生产方法。可是,目前几乎没有再听到汞齐法水银新电槽的建设,尤其是日本,由于汞法污染环境的关系,倒是有许多水银电槽工厂正在转化为隔膜电槽,估计当今世界的硬度。     

Syntheses of female sex pheromone precursors of pine sawfly species and of some structurally related methyl-branched long-chain 2-alkanols

3,7-Dimethyl-2-undecanol, 3,7,9-trimethyl-2-tridecanol, and 3,7, 11-trimethyl-2-tridecanol were synthesized as racemic mixtures in moderate yields. The alcohols are known precursors of the female sex pheromones of the pine sawfly species Diprion nipponica, Macrodiprion nemoralis, and Microdiprion pallipes, respectively. Stereoisomeric mixtures of 3,8,12-trimethyl-2-tridecanol, erythro-(2R,3R,11R/S)-3,11-dimethyl-2-tetradecanol, 3,5-dimethyl-2-tetradecanol, and 5,7-dimethyl-2-tetradecanol, structurally related to sex pheromone alcohol precursors of pine sawfly species, were also synthesized in moderate yields. The key reaction in the syntheses was the ring opening of -butyrolactones by using different alkyl lithiums as nucleophiles.     

Influence of maize kernel hardness on flour hydration and cooking properties

Knowledge of the association between cooking properties and endosperm hardness may help nutritionist and processors to select raw materials for preparing maize based food products, particularly those eaten as cooked dispersions. Seven commercial maize cultivars differing in hardness were selected to evaluate endosperm hardness on the kernels and some characteristics such as composition and hydration and cooking properties on the grits obtained from those maizes. Results show that the differences in endosperm hardness (directly related to grits protein content) can explain the differences in swelling and amylographic consistencies values. Cultivars with the hardest endosperm show the lowest values at high temperature. They also show the lowest amylographic consistencies. On the other hand softer endosperms present the highest swelling power and the highest amylographic consistencies. These differences are attributed to the restriction for starch swelling caused by the protein matrix. Endosperm hardness measurements and swelling power at 95 degrees C, can be useful to select cultivars that are going to be used to prepare maize based foods like atoles, polenta, etc.     

Guanine and plasmid DNA binding of mono- and trinuclear fac-[Re(CO)3]+ complexes with amino acid ligands

We have synthesized and fully characterized four new complexes comprising the fac-[Re(CO)3]+ moiety and the ligands NH3, L-proline (Pro), or N,N-dimethylglycine (dmGly). The reaction of [Re(H2O)3(CO)3]+ with the two amino acids gives trinuclear complexes of general formula [Re(L)(CO)3]3 (where L = amino acid). We have studied the in vitro behavior of these compounds with guanine and DNA in order to understand whether the cytotoxicity exhibited by certain rhenium complexes based on the fac-[Re(CO)3]+ core is due to the formation of nucleobase complexes and inter- or intrastrand links between DNA bases. We have performed model studies with guanine and studied the structural effects induced by different rhenium(I) tricarbonyl complexes on PhiX174 plasmid DNA by electrophoretic methods. Our results show that rhenium complexes with two available coordination sites interact with plasmid DNA to form a stable adduct that is likely to involve two bases.     

Positive holes in magnesium oxide. Correlation between magnetic, electric, and dielectric anomalies

Magnetic susceptibility measurements of high purity MgO single crystals (<50-wt. ppm transition metals) by means of a vibrating-sample magnetometer shows an anomaly at 800 K. At the same temperature the electric conductivity increases anomalously, the static dielectric constant epsilon increases from 9 to approximately 150, a pronounced positive surface charge appears, and Fe2+ in the MgO matrix oxidizes to Fe3+. The data are consistent with O2(2-) (peroxy) defects, representing self-trapped, spin-paired positive holes at Mg2+ vacancy sites. Diamagnetic at low temperatures, the holes start to decouple their spins > 600 K, probably forming at first V0 centers (two O- at an Mg2+ vacancy), then V- centers (single O- at an Mg2+ vacancy), and releasing mobile O- states. These O- represent itinerant charge carriers on acceptor levels near the O 2p-dominated valence band and conduct by O- /O2- valency fluctuations. The O- concentration is of the order of 8 X 10(19) cm-3.