预硬型塑料模具钢718的切削性能和夹杂物研究

对预硬型塑料模具钢ASSAB718和国产的GC718的切削加工性能进行了对比性研究，并结合Thermo-Calc软件对钢中非金属夹杂物进行了分析。结果表明，由于钢中夹杂物的影响，ASSAB718钢的切削加工性能优于GC718钢；运用Thermo-Calc软件可实现对钢中夹杂物的预测。     

已二酸交联木薯醋酸酯淀粉的制备与性能研究

以木薯淀粉为原料，用己二酸二乙烯酯做交联剂，醋酸乙烯酯做酯化剂制备了交联醋酸酯淀粉；确定了最佳反应条件；并测定了产物糊化温度、粘度、冻融稳定性等特性。结果表明，经过交联酯化的淀粉具有较高粘度和冻融稳定性。     

基于分形理论的非线性信号噪声污染程度检测

针对以傅立叶分析为代表的传统方法在非线性信号分析上的不足,提出了将分形理论应用于非线性信号含噪分析的方法,设计了具体实验的流程,并结合实际心电数据进行了相关的实验.实验结果表明:周期性非线性时间序列与随机噪声在分形指数上有明显差异,当随机噪声对原始信号的影响程度变化时,分形维数也随之变化;分形维数可以有效地描述工程数据被噪声污染的程度,因而具有良好的工程应用前景.     

第二届北京市职工职业技能大赛“首都机场博维航空杯”电梯维修工比赛圆满落幕

9月17日,随着决赛结束哨声的吹响,第二届北京市职工职业技能大赛“首都机场博维航空杯”电梯维修工比赛圆满落幕。本次共有来自32家电梯企业的711名选手参加比赛,而决赛当天,由脱颖而出的30名优秀选手进行了最后的角逐。     

裂缝宽度控制钢筋直径选用图表

钢筋混凝土构件中 ,高强度钢筋的应用使钢筋应力提高 ,应变增大 ,裂缝加宽。本文按照新的《混凝土结构设计规范》(GB5 0 0 10 2 0 0 2 )研究影响裂缝宽度的主要因素 ,找出在各种主要因素影响下满足裂缝宽度限值的最大等效钢筋直径 ,绘制成图表 ,供设计者查用     

Survival tests with Chironomus riparius exposed to spiked sediments can profit from DEBtox model

DEBtox model is a biologically based model used to analyse aquatic toxicity data (The analysis of aquatic toxicity data, VU University Press, Amsterdam, The Netherlands, 1996, 149pp.). To date, it has not been used to analyse sediment survival tests, mainly because this would require daily counting of survivors, which is difficult for benthic organisms. In the present study, we adapted survival toxicity tests with the midge Chironomus riparius to permit survival data analysis with DEBtox. To validate the adaptation proposed, we exposed organisms to two chemicals, copper and methiocarb. We exposed larvae of second, third and fourth instar to different concentrations of the tested compounds and two different diets to assess the influence of diet and instar on DEBtox parameter estimates. Daily counting of organisms did not affect survival and did not lead to much more effort when compared to usual tests. Moreover, the analysis profited much from use of the DEBtox model. It was possible, with only survival data to estimate and validate the kinetics of the compounds, to predict survival during the recovery of exposed organisms and to assess the influence of food availability on toxicity. Food availability did not influence methiocarb toxicity, but copper was more toxic to food-limited organisms when a threshold concentration was exceeded. Comparison of parameters estimate also helped in understanding the differences in toxicity responses between instars. For the two compounds we studied, the difference was entirely explained by differences in threshold values.     

Stereoselective Radical Additions using chiral 1,3-dioxolanones derived from lactic and malic acid

The hydrogen abstraction of radical intermediates yielded by radical addition to the methylene compound 6 , shows excellent facial selectivity. Conformational analyses of the radical intermediates were carried out by quantum chemical calculations and explain these results. The chiral radicals 7 and 8 , yielded from the chiral bromides 3 and 4 , lead with ethyl acrylate to the adducts 28 and 29 with more 96% de. The adduct 28 was converted to the optically active γ-valerolactone 30 . The structures of the bromides 3, 4 and 31 as well as the radical adducts 19a, 24 and 25 have been verified by X-ray diffraction analysis.