Geochemical significance of the relative enrichment of pristane and the negative excursion of δ^13CPr across the Permian-Triassic Boundary at Meishan, China

Changes in the distribution of isoprenoid hydrocarbons and in δ^13Ckero or δ^13Cpr across the section from the Changxing Formation to the lower Yinkeng Formation at Meishan （the GSSP of PTB） are studied, in which a relative enrichment of pristane and a sharp shift in both δ^13Ckero and δ^13Cmole near the boundary are revealed. A possible mechanism for the abnormal accumulation of pristane near PTB is suggested： Lipids in some marine animals and their metabolites, rich in pristane, can be preserved and accumulate in some suitable depositing facies under certain special conditions, such as the catastrophic death of animals and/or developing of an anoxic water column, and thus the pristane enrichment occurs in the sediment. The occurrences of isoprenoid enrichment and high Pr/Ph ratios have been found in other typical marine anoxic sediments accompanied by mass extinction in various extent during the most important geological periods, such as Late Ordovician, end of Devonian, Early Jurassic and Late Cretaceous. These occurrences support to a certain extent the above mechanism that interprets the genesis of a high Pr/Ph ratio in some typical marine anoxic sediments. The synchronous sharp negative shifts in δ^13Cmole, δ^13Ckero and δ^13Ccarb from Beds 24 to 26 of the Meishan profile indicate that a sudden and strong variation of carbon source in the atmosphere-ocean system occurred during the quick but equable evolution from the end-Permian to Early Triassic, and the coupling between the pristane enrichment and negative shift in δ^13Ckero and δ^13CPr may well indicate the importance of the release of methane hydrates and marine anoxia in the end-Permian mass extinction.     

自熔合金粉末性能对喷焊涂层组织的影响

利用扫描电镜SEM和X射线衍射仪分析研究了自熔合金粉末颗粒内部形貌和夹杂物对涂层组织的影响.结果表明,在空心粉率相同的情况下,空心粉末中气泡在中心形成,内部壁厚均匀且较厚的粉粒比颗粒内部气泡出现偏移或开口的粉粒更易产生喷焊涂层微观缺陷(针孔);粉末颗粒内部存在着少量金属Cr夹杂,由于夹杂物表面生成了保护性氧化膜,喷焊时夹杂物不能溶解到基体中,涂层在进行磨削加工时出现剥离,形成不规则状缺陷.     

估算单辊甩带法制备镁基非晶薄带的冷却速度

临界冷却速度是表征非晶态合金非晶形成能力的一个重要参数,但是正确地测量和估算非晶态合金形成时的冷却速度却十分困难.结合热传导理论和凝固理论,单辊甩带过程的热传输可以用一维傅立叶热传导方程描述.通过对热传导方程的数学解析求解,具体计算了单辊甩带法制备镁基非晶薄带的冷却速度,得到了铜辊制备50μm厚镁薄带的自由侧在凝固结束时的冷却速度为5.84×106K/s,这与早期人们预测的单辊甩带法的冷却速度相当.     

重熔工艺对油田抽油泵柱塞涂层性能的影响

对Ni60A自熔性合金粉末在氧乙炔重熔和中频感应重熔制得的涂层,分别进行了金相组织分析、表面硬度测试及腐蚀、磨粒磨损对比的试验.试验研究结果表明,中频感应重熔涂层中的晶粒细密,表面硬度值高;涂层的耐腐蚀性和抗磨性能优于晶粒较粗大的氧乙炔火焰重熔涂层.     

Mg80-xCu10+xY10非晶态合金的DSC研究

利用单辊甩带法制备了Mg80-xCu10 xY10(x=0，5，10，15)非晶态合金薄带，用XRD分析和DSC分析显示薄带形成了非晶态结构．根据DSC曲线，确定了表示非晶形成能力的Tg、Tx、T1、Trg和△Tx等温度参数，同时提出了以晶化放热值和熔化吸热值的比值作为表示非晶形成能力的新参数——约化玻璃转变焓．定量DSC分析结果显示，新旧参数在表示该非晶薄带的非晶形成能力时，结果基本一致．     

Al_2O_3陶瓷涂层电镀和刷镀封孔机理及效果评价

本文提出了用电镀、刷镀方法对A1_2O_3陶瓷涂层封孔的规范选择原则,并研究了封孔机理,评价了封孔效果。研究表明,在足够时间的条件下,电镀封孔应选择较小的电流密度,刷镀封孔应选择较低的电压;电镀、刷镀封孔过程中当阴极反应在涂层孔洞内充分进行时,大部分贯穿性孔洞将被封闭;当阴极反应移至表面进行时,涂层表面将沉积大量金属,而涂层内孔洞却未被封闭。用铜、镍刷镀封孔的Al_2O_3涂层在NaOH20％,NaC120％溶液中的耐蚀性提高,用镍封孔的涂层的抗热冲击性能得到改善。     

Tracking maneuvering target based on neural fuzzy network with incremental neural leaning

1 .INTRODUCTIONIn mixing information battle field,it is necessaryto esti mate the targets sport characteristics for i m-proving efficiency of weapons . The military tacticsguided missile defense system and air detectionsystemneed to track andidentify thousands of tar-getsinreal ti me ,the target informationinclude notonly maneuvering target and not maneuvering tar-gets ,but also environment reverberation and falsealarm. These situations take place in accurateweapon launch system, secondary…     

浅析电力设备检修安全过程管理

健康完好的电力设备是保证设备安全运行的基础,设备检修则是保证设备健康完好的主要措施。本文根据工作实际对电力设备检修的安全过程进行了探讨,提出了检修的安全过程管理模式。     

FFT的DSP汇编算法的改进

本在循环型DIT-FFT的DSP汇编算法查表实现的基础上,用1／4周期的因子表取代原有的两个周期的因子表,并把长度为2N的实数计算序列,转化为长度为N的复数序列进行FFT变换,从而改进了原算法的时间和空间复杂度及程序存储空间。     

Strip shape control capability of hot wide strip rolling mills

The elasticity deformation of rolls was analyzed by means of two-dimensional finite element method (FEM) with variable thickness. Three typical mills were used as objects for analysis. A thorough study was done on the control capabilities of these mills on the strip shape. Then the strip shape control capabilities of the three mills was compared synthetically.