激光烧蚀-多接收电感耦合等离子体质谱测定铀颗粒物中铀全同位素比值

建立了铀颗粒物中铀全同位素比值的分析方法,采用双面胶带装载铀颗粒物样品,优化激光烧蚀-多接收电感耦合等离子体质谱的运行参数,用标准样品交叉法校正质量分馏和探测器检测效率,测定了粒径几十微米的铀标准物质CRM124-1、GBW04234和GBW04238中铀全同位素比值.本方法对铀颗粒物中235U/238U、234 U/235U和236 U/235U测量的相对实验标准不确定度分别小于0.050％,1.7％和1.8％,测量结果与参考值在不确定度范围内符合.研究表明,本方法可快速、准确、高精度地测定铀颗粒物中铀全同位素比值.     

New insights into the impact toughness of ASA (acrylonitrile-styrene-acrylate) with controllable core–shell structure synthesized by three-stage seeded emulsion polymerization

Acrylonitrile-styrene-acrylate (ASA) with controllable core–shell structure was prepared through three-stage seeded emulsion polymerization. A series of characterizations had been performed to study the effect of different core–shell ratios on the properties of ASA. The most interesting was that the impact strength of ASA exhibited a “wave” variation instead of a linear variation with the increasing loading content of poly(butyl acrylate) (PBA) core. Moreover, the threshold of impact strength appeared at 49.725?wt% PBA content, nearly 33 kJ/m². To explain this unusual variation, an impact schematic was proposed.     

High‐performance liquid chromatography thermodynamic study of new potential antiepileptic compounds on a cholesterol column using isocratic elution with methanol/water and acetonitrile/water eluent systems

Basic thermodynamic functions responsible for retention of new 1,2,4‐triazole derivatives exhibiting varied antiepileptic activity on cholesterol‐based stationary phase were determined. Evaluation of the Gibbs energy change, the change in enthalpy and the change in entropy was based on the van't Hoff relationship representing lnk versus 1/T . A detailed discussion of the van't Hoff equation, exploring the influence of the phase ratio on deviations from linearity in a van't Hoff plot is presented. We show chromatographic evidence to the question of how a varied mobile phase composition may cause different thermodynamic phase ratios. The analysis of data from a differential scanning calorimetry excluded any phase transitions of either the individual solutes or cholesterol stationary phase suspended in the mobile phase components within the studied temperature range.     

Sediment records of Sb and Pb stable isotopic ratios in Lake Qinghai

A sediment core in Lake Qinghai in northwest China was collected in 2006. ¹³⁷Cs and ²¹⁰Pb activities were analyzed to investigate the chronology of the sediment core. Sb and Pb concentrations, and Pb stable isotopic ratios were analyzed to study the historical atmospheric deposition records and sources of Sb over the past 15 centuries. The Sb concentration was 4.21 ± 1.52 μg/g in the sediments, its vertical distribution of Sb shows three large peaks in the recent two centuries, 1799, 1896 and 1944, coincided with Sb contamination from large wars, respectively. The peak in 1920 responded the large earthquake that happened in northern China, which was not far away from Lake Qinghai. The Sb/Pb ratio, ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb results suggest that Sb and Pb were probably from the ores in South China and coals in North China before 1965, but obviously from uses of leaded gasoline after 1965.     

边界条件含特征参数的Sturm-Liouville问题的特征值比率

给出修正Prfer变换的几何意义以及相关性质,并利用上述性质讨论Sturm-Liouville问题-(py′)′+gy=λωy,x∈[0,1],参数边界条件为y(0)=0与((py′)(1))/(y(1))=aλ+b,得到了当a>0,q≥0的特征值比率上界,这把Ashbaugh等人的结果推广到边界条件含参数的情形.     

On the origin of the Epps effect

The Epps effect, the decrease of correlations between stock returns for short time windows, was traced back to the trading asynchronicity and to the occasional lead-lag relation between the prices. We study pairs of stocks where the latter is negligible and confirm the importance of asynchronicity but point out that alone these aspects are insufficient to give account for the whole effect.     

我国上市公司财务状况的非线性主成分分析研究

文章通过对我国上市公司的财务指标进行综合分析 ,构建了我国上市公司财务状况综合分析的非线性主成分分析模型 ,并应用该模型对上市公司财务状况进行了合理的评价 .     

Triangular arbitrage as an interaction among foreign exchange rates

We first show that there are in fact triangular arbitrage opportunities in the spot foreign exchange markets, analyzing the time dependence of the yen–dollar rate, the dollar–euro rate and the yen–euro rate. Next, we propose a model of foreign exchange rates with an interaction. The model includes effects of triangular arbitrage transactions as an interaction among three rates. The model explains the actual data of the multiple foreign exchange rates well.