深切怀念吴大猷先生

我们在这里隆重纪念吴大猷先生诞辰100周年,深切缅怀一代物理宗师的高尚风范和杰出贡献,我很高兴,也很激动.吴大猷先生毕生献身科学研究和教育事业,为中国科学技术和教育事业的发展作出了重大贡献,在世界物理学界享有盛誉.     

自力更生 铸起核盾

<正>我于1950年春从美国回到祖国参加社会主义建设。1955年,我国决定发展原子能事业。我有幸从那时起就参加了这一事业,虽然40多年来工作岗位几经变动,但仍一直在核技术领域学习和工作。记者约我回顾这段不平常的经历,我在这里就我国发展自己的核武器     

Microscopic degradation mechanism of polyimide film caused by surface discharge under bipolar continuous square impulse voltage

Polyimide （PI） film is an important type of insulating material used in inverter-fed motors. Partial discharge （PD） under a sequence of high-frequency square impulses is one of the key factors that lead to premature failures in insulation systems of inverter-fed motors. In order to explore the damage mechanism of PI film caused by discharge, an aging system of surface discharge under bipolar continuous square impulse voltage （BCSIV） is designed based on the ASTM 2275 01 standard and the electrical aging tests of PI film samples are performed above the partial discharge inception voltage （PDIV）. The chemical bonds of PI polymer chains are analyzed through Fourier transform infrared spectroscopy （FTIR） and the dielectric properties of unaged and aged PI samples are investigated by LCR testers HIOKI 3532-50. Finally, the micro-morphology and micro-structure changes of PI film samples are observed through scanning electron microscopy （SEM）. The results show that the physical and chemical effects of discharge cut off the chemical bonds of PI polymer chains. The fractures of ether bond （C-O-C） and imide ring （C-N-C） on the backbone of a PI polymer chain leads to the decrease of molecular weight, which results in the degradation of PI polymers and the generation of new chemical groups and materials, like carboxylic acid, ketone, aldehydes, etc. The variation of microscopic structure of PI polymers can change the orientation ability of polarizable units when the samples are under an AC electric field, which would cause the dielectric constant e to increase and dielectric loss tan ~ to decrease. The SEM images show that the degradation path of PI film is initiated from the surface and then gradually extends to the interior with continuous aging. The injection charge could result in the PI macromolecular chain degradation and increase the trap density in the PI oolvmer bulk.     

学习彭桓武先生,培养创新型人才

彭桓武先生是著名物理学家，为我国理论物理和核科技事业的建立和发展做出了重大贡献，去年彭桓武先生九十华诞时，我曾作简短发言，谈了他的贡献和学术思想，今天，我想着重谈谈彭先生关于培养创新型人才的思想。