一种空气中14C监测技术

本文主要介绍用于监测空气中^14C的^CO2碱液吸收-CaCO3悬浮液闪计数法”的原理、条件实验和最小可探测水平,在采样2m^3空气,测量时间300min的条件下,按通常的方法计算的空气中^14C活度浓度最小可探测水平约为0．017Bq／m^3(空气)[或0．09Bq／g(碳)],约是实测的环境本底的2／5。     

芜湖长江大桥用14MnNbq钢性能的分析研究

通过收集芜湖长江大桥采用的14MnNbq钢4万余吨钢材的质保书,采用数理统计的方法对其主要化学成分、机械性能进行了分析研究,同时与其他桥梁采用的日本和韩国生产的SM490C桥梁钢进行了比较、分析,表明14MnNbq钢的综合性能是优异的。     

锂离子电池Na_2Li_2Ti_6O_(14)负极材料的合成与电化学性能

采用高温固相法成功合成了新型钛基负极材料Na_2Li_2Ti_6O_(14),并研究了其结构及电化学性能。利用高分辨透明电镜(HRTEM)、X射线衍射(XRD)及其Rietveld精修、扫描电子显微镜(SEM)及能谱分析(EDS)表征分析了材料的物相和显微结构。结果表明,合成的Na_2Li_2Ti_6O_(14)负极材料为纯相,具有Fmmm空间群结构;Na_2Li_2Ti_6O_(14)颗粒约为500~800 nm,Na、Ti和O三种元素分布均匀。循环伏安(CV)、充放电及电化学阻抗谱(EIS)测试表明,材料具有较好的锂离子脱嵌可逆性,较好的倍率性能和循环稳定性。钛电流密度为500 m A/g充放电时,Na_2Li_2Ti_6O_(14)材料的首次脱锂(充电)容量为180 m A·h/g,100次循环后可逆容量为136 m A·h/g;100次循环后,Na_2Li_2Ti_6O_(14)材料的电荷转移电阻增加,锂离子扩散系数略有下降,表明Na_2Li_2Ti_6O_(14)材料在循环后SEI膜的生成,降低了材料的电化学活性。     

聚1,10-癸二酮二苯并-14-冠-4的合成方法改进

以KOH／LiCI催化合成二苯并-14-冠-4,再经过适当比例混酸催化,与癸二酸缩聚合成聚1,10-癸二酮二苯并-14-冠-4,有效地缩短了反应时间,降低了生产成本．明显提高了收率。     

14Ni3CrMoV锻钢的回火脆性研究

对14Ni3CrMoV锻钢的回火脆性进行研究的结果表明,回火脆性可以通过对冲击试样断口观察、晶界腐蚀、透射电镜分析和俄歇电子能谱分析等方法来判断,该锻钢的回火脆性与磷在晶界的偏聚和连续第二相在晶界的析出有关。     

用有机相还原法制备钴纳米颗粒

硼氢化钠在乙二醇的碱性溶液中比在水溶液中更稳定,使还原醋酸钴制备金属Co纳米颗粒的反应平稳进行,制备出六方晶型的Co纳米颗粒,平均粒径为50.2 nm.原子力显微镜和激光散射分析表明,Co纳米粒子为类球形.制备Co纳米粒子的最佳温度为60℃,最佳pH为11～12.用不同种类的表面活性剂对Co纳米颗粒进行表面修饰,能减少其在正己烷中的软团聚,以吸附作用为主的非离子表面活性剂的效果最佳,可以使团聚体的平均尺寸由80.0 nm降低至50.2 nm.     

铝合金U型模锻件锻造工艺研究

介绍了2A14铝合金U型模锻件的生产工艺,针对该模锻件的材料特性、锻件的结构特点和技术要求,确定了锻造工艺。经过生产验证,制定的锻造工艺是合理的,成功地生产出了外形尺寸、组织和性能均合格的2A14铝合金U型模锻件。     

Nuisance zoning,the labor market and capital gain

Setting a two-generation model of current and new residents in a simple linear city, this paper analyzed the effects of nuisance zoning on urban system. In the model, decisive agents of zoning regulation (current residents) behave not only as consumers of land service affected by nuisance externality, but as investors of land for capital gain. We emphasize that this paper analyzed the zoning effect on labor market and thus on the wage level as well as on land market. It is shown that under the optimal zoning to maximize the welfare of current residents, the sum of the value of marginal disutility due to expanded industry-operation district for both current and new residents is just equal to the increased total wage income for new residents.The original version of this paper was presented at the annual meeting of Applied Regional Science Conference and at the Urban Economies Workshop of Kyoto University. We thank the participants of both meetings, and the editor and two anonymous referees of this journal for their useful comments. This research was supported in part by Grant-in-Aid for Scientific Research (C), which is gratefully acknowledged.Received: January 2003/Accepted: September 2003     

Minimal rational parametrizations of canal surfaces

It is well known that canal surfaces defined by a rational spine curve and a rational radius function are rational. The aim of the present paper is to construct a rational parameterization of low degree. The author uses the generalized stereographic projection in order to transform the problem to a parameterization problem for ruled surfaces. Two problems are discussed: parameterization with boundary conditions (design of canal surfaces with two curves on it, as is the case for rolling ball blends) and parameterization without boundary conditions.     

Biosynthetic (14)C-labelling of xanthohumol in hop cones

Xanthohumol (Xn) has well-established chemopreventive potential in vitro. In order to carry out in vivo bioavailability and tissue distribution studies,( 14)C-labelled Xn was produced by biolabelling. Supplying hop sprouts with 5 mCi [U-(14)C]glucose led to incorporation of (14)C into Xn. Delivering the radioactive precursor at once resulted in Xn with a specific activity of 318 microCi.mmol(-1); if however the amount was supplied in aliquots over 4 days a specific activity of only 53.1 microCi.mmol(-1) Xn was obtained.