Global pollution shown by lead and cadmium contents in precipitation of polar regions and Qinghai-Tibetan Plateau

The analysis of the major ions, lead and cadmium has been performed for snow-pit samples collected from the Arctic, the Qinghai-Tibetan Plateau and the Antarctic Ice Sheet. These snow pits were excavated respectively from the snowpack in Canadian Northwest Territory (NWT) and the central Arctic, three glaciers on the Qinghai-Tibetan Plateau and surface snow along the route of the International Trans-Antarctic Expedition (ITAE). The source regions for the lead pollution of central Arctic have been identified by analyzing of stable lead isotopic ratios, meteorological and atmospheric chemistry studies. It shows that the central Arctic is still under intensive lead input, despite the fact that lead content in Greenland Ice Sheet displays a rapid decreasing since the 1970s due to US and some European countries’ campaigns to reduce lead-containing gasoline-additives. This is because there are multiple lead sources for the central Arctic, including the countries that have not performed gasoline-additives reducing. The backgrounds of atmospheric aerosol compositions, as well as the concentrations of lead and cadmium in precipitation of the early 1990s, are contrasted among the Arctic, Antarctica and Qinghai-Tibetan Plateau. The measured lead content in the snowfall at the typical sites of the three regions is divided into natural (background) and anthropogenic components. It is found that natural lead concentration (mainly crustal and/or sea-salt lead) is roughly equal among the three regions (< 3×10¹²g · g¹). However, the percentage of the natural lead to the measured lead is negligible in precipitation in the central Arctic and the Qinghai-Tibetan Plateau, while it is considerable in Antarctic precipitation. The anthropogenic component of lead (>50% in Antarctic precipitation, >97% in the Arctic and the Qinghai-Tibetan Plateau ) is mainly responsible for the lead input to both polar regions and to the Qinghai-Tibetan Plateau. Lead pollution may have spread into the whole troposphere and the most remote regions on earth.     

Simulation for the primary electronic donor of photosystem IIin vitro

Histidine coordinated to Chi a is a distinct characteristic of Chl ain vivo. By using histidine analogue of 1-methylimidazole (C₄H₆N₂2) and measuring the UV/vis absorption, CD and MCD spectra of the interaction between C₄H₆N₂ and Chl a in CCI₄, we have obtained that: (i) In pure CCl₄ solvent, Chl a molecule is in five-coordinate state, and two Chl a molecules form an asymmetric compact-dimer with strong coupling interaction. We propose that the two Chl a molecules are connected by two unequally coordinated Mg-O bonds (the two oxygen atoms come from the C=O of C13¹ keto and C17 ester, respectively); (ii) when the molar ratio of C₄H₆N₂/Chl a is 0.5 or 1 (corresponding to 2Chl a · 1C₄H₆N₂ and 2Chl a · 2C₄H₆N₂, respectively), significant changes have been observed in the absorption, CD and MCD spectra, which indicate that the Chl a remains in dimer form, but the coupling interaction between them reduces greatly. We postulate that C₄H₆N₂ replaces the ligation of C=O of C17 ester and C13¹ keto to Mg atoms sequentially. The two Chl a molecules linked by two weakly interacted Mg…O bonds form a relaxed-dimer. The structure of the model is essentially similar to that of the primary electronic donor, P₆₈₀, of photosystem II in high plants and algae.     

子长油矿4207裸眼井"压胀松动"增产技术现场试验

为了研究“压胀松动”增产技术的增产效果和施工工艺,在延长石油管理局子长油矿对４２０７裸眼井进行了现场试验．介绍了裸眼井“压胀松动”增产技术的基本原理、该井现场试验所需岩石力学参数的测定、药量的计算及装药设计．并对施工工艺和实验结果进行了分析和研究,说明“压胀松动”增产技术对此井是有效的．     

A Review of The Road Not Taken

The Road Not Taken is one of the most important poems written byAmerican famous poet Robert Frost.The poem reflects his important life experi-ence,thought and emotions.Even today this poem is significant.     

敬告作者

为适应我国科技信息化建设需要，扩大作者学术交流渠道，本刊已加入《中国学术期刊（光盘版）》和《中国知网》（http：／／www．cnki．net）、万方数据电子出版社的《万方数据数字化期刊群》（http：／／www．wan-fangdata．com．cn）、教育部科技发展中心的《中国科技论文在线》、重庆维普资讯有限公司的《中文科技期刊数据库》、华艺数位艺术股份有限公司的《CEPS 中文电子期刊》、北京书生网络技术有限公司的《书生数字期刊》、北京世纪超星公司的“域出版”平台、中教数据库等。作者著作权使用费与稿酬由本刊一次性给付。如果作者不同意将文章编入上述数据库，请在来稿时声明，本刊将做适当处理。     

分布式多传感器系统航迹关联算法评述

根据计算速度、存贮量、通讯量、正确关联率、适应环境、对局部跟踪器和参数设置要求等几个方面,采用定量与定性相结合的方法,综合比较和评价独立序贯法、相关序贯法、独立双门限法、相关双门限法、MKNN法、第一类模糊双门限法、第二类模糊双门限法和模糊综合法等8种新的航迹关联算法的优劣,并重点讨论它们的差异和特点。同时把它们与最近邻域法、加权法、修正法和KNN算法这4种经典方法进行全面比较。这些分析结果对文献[1～6]提出的十几种适合于分布式多传感器数据融合的航迹关联算法的实际应用具有重要作用     

A Class of Parallel Runge-Kutta Methods for Differential-Algebraic Systems of Index 2

1-INTHODUCTIONWeconsiderthedifferential-algebraicsystemwherefandgaresufficientIydifferentiable.Inorderthat(1a)isanindex2problemwesupposethatinaneighbourhoodoftheexactsolution.wefurtherassumethattheinitialva1uesyo,zoareconsistentwith(l),i.e.,(yo,zo)satisfies(lb)andThesolutionof(1a)isdenotedby(y(t),z(t)).Problemsoftheform(l)arefrequentlyencounteredinpractice.Forexamp1e,problem(l)hasthetypicalstructureofacontrolproblemwherethez-variableactsascontrolparameterwhichforcesthesolutionofthediffer…