Bismuth embrittlement of copper is an atomic size effect

Embrittlement by the segregation of impurity elements to grain boundaries is one of a small number of phenomena that can lead to metallurgical failure by fast fracture. Here we settle a question that has been debated for over a hundred years: how can minute traces of bismuth in copper cause this ductile metal to fail in a brittle manner? Three hypotheses for Bi embrittlement of Cu exist: two assign an electronic effect to either a strengthening or weakening of bonds, the third postulates a simple atomic size effect. Here we report first principles quantum mechanical calculations that allow us to reject the electronic hypotheses, while supporting a size effect. We show that upon segregation to the grain boundary, the large Bi atoms weaken the interatomic bonding by pushing apart the Cu atoms at the interface. The resolution of the mechanism underlying grain boundary weakening should be relevant for all cases of embrittlement by oversize impurities.     

Rocket UV flash spectra from the solar eclipse of March 7, 1970

Flash spectra of the total solar eclipse throughout all its phases have been obtained in the extreme ultraviolet for the first time.     

耐水脱硫石膏、粉煤灰胶结材的研究

本文较深入地研究了脱硫石膏粉煤灰化学成分、杂质、颗粒特征和激发剂等对脱硫石膏、粉煤灰胶结材性能的影响 研究表明 ,激发剂是影响脱硫石膏、粉煤灰胶结材性能的主要因素 这为脱硫石膏、粉煤灰资源化利用打下良好理论基础 经实际应用表明 ,研究结果与实际情况能很好相符     

Quaternary ammonium bases in the tomato plant

Zusammenfassung Im Hinblick auf die Untersuchung der Wirkung von Chlorcholinchlorid im Stoffwechsel der Quartärammoniumverbindungen in Pflanzen wurden deren natürlich vorhandene Substanzen in wässrigen Extrakten von Tomatenpflanzen papierchromatographisch in vier Lösungsmitteln untersucht.In den Extrakten überwog eine Substanz, die sich von Cholin chromatographisch unterscheidet, die aber dieselbe Farbreaktion mit einem modifizierten Dragendorffschen Reagens gibt. Während der Papierelektrophorese bei pH 6 wird diese Substanz in zwei andere umgewandelt. Eine von diesen entspricht chromatographisch Cholin. Keine von den unbekannten Substanzen aber scheint ein phosphoryliertes Derivat von Cholin zu sein.     

正弦稳态扫频信号的产生与输出

介绍用计算机软件产生正弦稳态扫频信号的编程方法。通过对Ｄ／Ａ变换与Ａ／Ｄ采集的同步输出可以获得不同频率量程和设定电压的扫频输出     

Room-temperature ferroelectricity in supramolecular networks of charge-transfer complexes

Materials exhibiting a spontaneous electrical polarization that can be switched easily between antiparallel orientations are of potential value for sensors, photonics and energy-efficient memories. In this context, organic ferroelectrics are of particular interest because they promise to be lightweight, inexpensive and easily processed into devices. A recently identified family of organic ferroelectric structures is based on intermolecular charge transfer, where donor and acceptor molecules co-crystallize in an alternating fashion known as a mixed stack: in the crystalline lattice, a collective transfer of electrons from donor to acceptor molecules results in the formation of dipoles that can be realigned by an external field as molecules switch partners in the mixed stack. Although mixed stacks have been investigated extensively, only three systems are known to show ferroelectric switching, all below 71 kelvin. Here we describe supramolecular charge-transfer networks that undergo ferroelectric polarization switching with a ferroelectric Curie temperature above room temperature. These polar and switchable systems utilize a structural synergy between a hydrogen-bonded network and charge-transfer complexation of donor and acceptor molecules in a mixed stack. This supramolecular motif could help guide the development of other functional organic systems that can switch polarization under the influence of electric fields at ambient temperatures.     

一类高阶非线性系统的零解稳定性

由Барбащин公式得到的四阶常系数线性系统的Ляпунов函数出发，通过类比法构造了一类四阶非线性系统的Ляпунов函数，并由此得到了这些系统零解的全局渐近稳定性的充分条件