Field and pressure response of Yb compounds close to a quantum critical point

YbCu_5−x Al _x provides the possibility to tune ground state properties by a change of the valence due to the Cu/Al substitution, by pressure as well as by the application of a magnetic field. Near to the critical concentration x _cr≈1.5 non-Fermi-liquid properties (NFL) are obvious, obeying hyperscaling. If magnetic order sets in for x>1.5, the application of moderate magnetic fields quenches order and again NFL features become evident. Hyperscaling in this case indicates strongly interacting spin fluctuations.     

介电高弹聚合物理论

软材料受刺激会发生变形, 该变形会引起相应的功能, 这种材料称为活性软材料(soft active material, SAM). 本综述主要讨论介电高弹聚合物这一类活性软材料. 当介电高弹聚合物薄膜受到厚度方向的电压作用时, 薄膜厚度减小同时面积增大, 可导致超过100{\%}的应变. 介电高弹聚合物作为转换器被广泛应用, 包括柔性机器人、智能光学器件、盲文显示屏、发电机等. 本文综述了建立在连续介质力学和热力学框架内的、并且基于分子理论描述和经验观测的介电高弹聚合物理论. 该理论耦合了大变形和电势, 描述了非线性和非平衡行为, 如力电失稳和黏弹性. 采用该理论能够通过有限元方法模拟实际构型的转换器, 计算力电能量转换的效率, 给出电致大变形的可行途径. 该理论有助于材料和器件设计.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

应用数学的拓展——用一篇关于蛋白质分子的结构和功能的动理论发展的论文来说明

近来,人们喜欢从历史的角度来探讨数学在生物学中的应用问题.这种趋势似乎可以看作是应用数学范围逐渐拓展的一种自然现象.但它所用到的数学概念和方法与以往应用数学所用的概念和方法并无本质区别.例如,我们在本文中简单描述了如何将耗散系统中的动理学原理用于研究蛋白质分子的结构和功能.在这些研究中,传统统计物理学的概念和方法可以用来成功地建立与经验数据相对应的假设及理论.