Die Erhöhung der Grundfrequenz und der Beullast von Kreisplatten durch geeignete plastische Verformung

Zusammenfassung Eine M?glichkeit, ohne Mehraufwand an Material oder Verwendung teurerer Werkstoffe das dynamische Verhalten oder die Tragf?higkeit von Bauteilen zu verbessern, wird am Beispiel der Grundfrequenz- und Beullaststeigerung von Kreisplatten durch das Einpr?gen von geeigneten Eigenspannungszust?nden dargelegt. Die Ergebnisse einer Optimierung solcher Eigenspannungsfelder werden dargestellt, und die M?glichkeit der Erzeugung geeigneter Eigenspannungszust?nde wird an Hand eines Experiments nachgewiesen.     

Experimental activation energies for evolution of oxygen and chlorine on oxide electrodes

The chlorine and oxygen overpotential in dependence on the current density i (A cm^?2) and on the temperature in the range of 15–75°C was measured at γ-MnO₂ and β-PbO₂ electrodes in concentrated water solutions of sodium chloride and perchlorate. From the measured values the experimental activation energy in dependence on overpotential was calculated and, for the temperature of 25°C, the constants of Tafel's equation (a,b) (α, i_o respectively) were evaluated.     

Gearless Drive for a Finish-Grind Mill with a Capacity of 160 t/h

The principle of the gearless drive has already been applied to some large mills. A synchronous motor is ``wrapped' directly around the mill cylinder and supplied by a thyristor frequency converter at approximately 10-percent system frequency. The drive thus operates at the low mill speed and dispenses with interposed gearing.     

液相色谱质谱联用测定多种兽药残留方法中标准品稳定性的挑战（网络首发、推荐阅读）

采用等时测量法对可用于食品和饲料链中兽药检测的标准品混合溶液和中间混合液进行了短期和长期稳定性研究。其中短期稳定性实验考察了混合标准曲线在–20（作为基线）、4和23 ℃（避光和不避光保存）条件下存储1、2、4和7 d的稳定性,而长期稳定性实验考察了中间混合液在–20、4、23 ℃（避光和不避光保存）和–80 ℃储存条件下2、4、8和12周的稳定性。结果表明,使用不含酸溶剂配制的混合标准曲线在4 ℃下建议储存1~2 d,中性储存条件即使在室温也可短期储存1~2 d。对于含有ß-内酰胺和头孢菌素类标准品的中间混合液在4 ℃和室温下储存超过1个月会损失近90%。对于含有青霉素V和G的混和标准品中间储备液,在–20 ℃不含酸的条件下可储存2周。其他类别的兽药标准品对长期储存条件要求较少。整体而言,兽药标准品中间混合液长期储存的最佳储存条件为–20 ℃。     

Copolymers—A refined way to tailor intrinsically conducting polymers

An overview is given on electrochemically prepared intrinsically conducting copolymers, their preparation, their properties, potential applications and significant differences from the respective homopolymers. Particular attention is paid to verification of the formation of true copolymers and their characteristic features in comparison to mixtures of homopolymers.     

Halogen-free polyisobutylene by in situ methylation of living polyisobutylene using dimethylzinc

Summary Halogen-free polyisobutylene (PIB) was synthesized by in situ methylation of living PIB using dimethylzinc. Quantitative methylation of living PIB was achieved within 60 min using a ratio of [(CH₃)₂Zn]/[TiCl₄]₀= 1 without any side reactions. Under similar conditions, living PIB capped with 1,1-diphenylethylene (PIB-DPE⁺) yielded close to 1:1 mixture of methoxy- and methyl-functionality. By using the ratio of [(CH₃)₂Zn]/[TiCl₄]₀≥ 3, however, quantitative methylation of PIB-DPE⁺ could be achieved in 120 min without any side reactions as confirmed by spectroscopic and chromatographic analyses. Received: 1 February 2000/Revised version: 23 April 2000/Accepted: 23 April 2000