同位素测年新发展:81Kr测定古老地下水年龄理论

自从1966年Loosli&Oeschchger测定出大气中的81Kr,就已经有人设想放射性81Kr(半衰期为(2.29±0.11)×105年)可能成为测定古老地下水年龄(105~106年)的有效工具。但一直没有付诸实践,直到2000年,Collon等人首次利用81Kr同位素确定澳大利亚大自流盆地(GAB)的古老地下水年龄。本篇文章中主要介绍了影响81Kr同位素测年的因素,81Kr的取样制样分析过程,回旋加速质谱仪分析81Kr同位素的原理。     

A tale of two cities: Price uniformity and price volatility in gasoline retailing

Retail gasoline markets have been found to exhibit either price volatility and price dispersion or price rigidity and uniformity across large metropolitan areas. The purpose of this paper is to identify a theoretical explanation for these patterns of pricing behavior, and to look for evidence consistent with the theory by examining market structure, conduct, and spatial pricing patterns in different retail gasoline markets in Canada. The study utilizes a novel source of price data: price observations reported to internet data collection sites. The firm and station specific price data are consistent with the presence of tacitly collusive behavior in one retail gasoline market and the presence of maverick retailers that prevent tacit collusion in the other retail market.The authors thank In-Touch Software Corporation for providing free of charge data collected through www.gastips.com, and Derek Tam and Glen Gower for providing free of charge data collected through www.ottawagasprices.com. The authors also wish to thank Roger Stough and anonymous referees for helpful advice, Don Schunk and participants at the 48th North American Meetings of the Regional Science Association International for their comments, and Ryan Reichl and Steven Yong for research assistance. Financial support provided by the Social Sciences and Humanities Research Council of Canada and the University of Alberta are gratefully acknowledged.     

脉冲堆燃料元件设计引论

本文总结了脉冲堆燃料元件设计经验,论述了脉冲堆工作特点、燃料性能、燃料元件设计准则和设计内容,对脉冲堆燃料元件设计提出了指导性建议。     

氟利昂体系汽液平衡二元相互作用参数的普遍化关联

用ＭＨ（８１）方程关联了十一个氟利昂体系的等温汽液平衡数据，得出其二元相互作用参数，关联结果同实验符合良好。根据分子热力学的基本原理，加上一些经验的关联，提出了一个四常数的关联式来关联氟利昂混合物的ＭＨ（８１）方程二元相互作用参数，利用关联结果推算了ＤＭＥ／Ｒ１５２ａ体系在２８３．３１Ｋ、２９３．８４Ｋ、Ｒ２３／Ｒ２２在２５８．１５Ｋ和Ｒ３２、Ｒ１５２ａ在２７３．１５Ｋ的等温汽液平衡，与实验数据进行对照吻合良好，表明此式有相当程度的预测性，在氟利昂替代物的预选和工程计算中有重要的实际应用价值。     

Formation and characterization of 1, 5-diphosphono-pentane films on polycrystalline zinc substrates

Investigation on time-dependent layer formation was performed on high purity polycrystalline zinc surface in reaction with aqueous solution of 1, 5-diphosphono-pentane (DPP) at room temperature. Film evolution was characterized by X-ray photoelectron spectroscopy, contact angle, atomic force microscopy, glow discharge optical emission spectroscopy and detailed infrared reflection absorption spectroscopy measurements. Development of a partly crystalline zinc-diphosphono-pentane conversion layer of increasing thickness with time was determined by consistent evaluation of the results. The formed layers turned the hydrophobic zinc surface to hydrophilic. The conversion-type interaction of diphosphonic acid compounds with the oxidized zinc surface resulting in zinc-diphosphonate salt was unambiguously justified by XPS and GD-OES analysis.The corrosion behaviour of the coated zinc substrate was studied using electrochemical impedance spectroscopy (EIS). The formed layers show significant protective effect in sodium-sulphate solutions. It was shown, that under the applied conditions, a 4 h treatment is necessary to obtain 75% protection efficiency after 4 h of immersion into the Na₂SO₄.     

挤压态AZ81镁合金的热压缩变形行为

在温度为320～440℃、应变率为0.001～1s-1的变形条件下,采用Gleeble-1500热模拟机对挤压态AZ81镁合金的热压缩变形行为进行研究.结果表明挤压态AZ81镁合金的流变应力随变形温度的升高而降低,随应变率的升高而升高,且随应变的增加,流动应力很快达到峰值,然后逐渐降低并趋于稳定.为评价挤压态AZ81镁合金在热模压成形过程中流动应力,结合Arrhenius方程并引入Zener-Hollomon参数,对流动应力做出相应的修正,根据修正后的流动应力构建挤压态AZ81镁合金流变应力高温变形本构模型.模拟结果表明该模型的应力预测值与试验值吻合较好,计算精度较高,为后续的模压近／净终成形工艺参数的制定提供一定的理论参考.     

Biosynthesis of poly-gamma-glutamic acid in plants: transient expression of poly-gamma-glutamate synthetase complex in tobacco leaves

Transient expression of genes coding for the poly-gamma-glutamate (gammaPGA) synthetase system (pgs) was investigated in tobacco plants. Three genes of the pgs, pgsA, pgsB and pgsC, were separately placed under the control of the CaMV 35S promoter and introduced into tobacco leaves via Agrobacterium infection. Synthesized gammaPGA in plant tissues was detected immunologically with mouse anti-gammaPGA antiserum which specifically reacts with gammaPGA on a nitrocellulose membrane. Confirmation of gammaPGA biosynthesis in the transient expression analysis in tobacco tissue indicates that subunits of pgs complex were expressed and reassembled in a functional form.