鋁的晶粒边界本性对蠕变的影响

一、引言大多数金属材料是在多晶状态下使用的.此时金属的性貭包括两个部分:晶粒内部的性质和晶粒边界的性貭。在许多文献中都研究了晶粒大小对金属性质的影响.晶粒愈大则晶界的相对影响愈小.在低温下细晶粒金属具有较好的力学性质,细晶粒金属的弹性性能较好,例如拉伸试验时比例极限随着晶粒变细而增加.晶粒边界对范性的影响比对强度的影响大.的工作(1957)指出,只有当样品截面中晶粒数小于20的时候(实验是用锡做的)晶粒大小对强度和范性才会有明显的影响.我们在研究低碳钢的范性时(莫洛卓夫和王煜明,1957)也得到相似的结论. 这样,就可以得出一个结论:在晶粒边界上有着很大的晶格畸变. 曾经观察到,随着金属纯度的增高,晶界对金属强度的影响减小.这说明杂质原子     

二氧化硫在含鉀、鈉盐助催化剂的釩催化剂上的氧化动力学

早在1926年已知将硷金属盐加入钒催化剂中可显然增加其对二氧化硫氧化的催化活性.关于硷金属盐的助催化作用已有不少的研究工作.Frazer及Kirkpatrick发现K_2S_2O_7在钒催化剂的工作温度能溶解V_2O_5而生成熔盐.等对V_2O_5—K_2SO_4,V_2O_5—K_2S_2O_7体系的研究,等对V_2O_5—Na_2SO_4体系的研究,及Topsoe等对Rb,Cs,K,Na的焦硫酸盐与V_2O_5体系的研究都说明在工作温度时V_2O_5与以上盐类的体系已处于熔融状态.Topsoe等且认为其熔点降低是催化活性提高的原因。另一方面Neu mann等认为硷金属盐的作用是防止V_2O_5被SO_2还原为VOSO_4以致活性降低.发现钒钾催化剂在工作条件下可被SO_2还原.并认为这是钒钾催化剂的活性在450°突然降低,而使Arrhenius綫在450°左右发生破折的     

《种子的信仰》

《种子的信仰》是梭罗的遗作,一如既往着他特有的文风:明澈和优雅。梭罗在《种子的信仰》中描述了各种植物通过种子的传播,进行着生命延续。他接受了当时还不被广泛认同的达尔文的自然选择理论,写就了这本现在看来依然新奇的19世纪中期的著作。内容精选:秋冬时节的蓟花启人深思     

The specific contribution of object''''s origin on artifacts categorization

Gelman and Bloom found that adults and children's object naming was sensitive to how an object was created (man-made or not), but they did not reveal on which specific level of conceptual system this effect was. Using a free-naming task and a force-choice task, two experiments were conducted to test a hypothesis that this effect was specifically on domain level ("artifact/non-artifact" distinction). In Experiment 1, participants were asked to name shortly-depicted objects, rate their confidence, and report their reasons for each naming response. Results showed that most of the naming responses in "man-made" condition were in artifact domain, and most in "natural" condition were in non-artifact domain, although in both conditions names were very divergent on basic level. In Experiment 2, another group of participants were asked to choose one from two names (one in artifact domain and the other in non-artifact domain) to match the same shortly-depicted objects presented in the first experiment. Re-sults of Experiment 1 on domain level were replicated in Experiment 2. These convergent findings supported the hypothesis that the effect of object's origin is specifically on domain level of conceptual system of objects. Reasons explicitly reported for naming responses in Experiment 1 suggested that participants might automatically infer objects' functions in "man-made" condition but not in "natural" condition. Here the function-based hypothesis of artifacts classification is discussed.     

学无止境

把思想或语言直接转化成物质的机器,称之为"物化机".现在,这部机器终于制造成功了.     

Synthesis and Crystal Structure of New Supramolecular Adducts of[PtCl_6]~(2-) with Cucurbit [7] uril:[(H_3O)_2 [PtCl_6]_3 [C_(42)H_(42)N_(28)O_ (14)_2·H_2O

0　IntroductionCucurbit [n]urils (Qn ,Fig .1.)arecyclicoligomersofnunitsofglycolurillinkedby 2nmethylenebridgesderivedfromformaldehyde.Theypossessacharacteristicannularshape,withtwoidenticalcarbonyl fringedportals[1 ,2 ] .Themostcom moncucurbituril,Q6 ,wasreportedtoaccommodatedifferentguestssuchaswater[3] ,THF[4 6] ,xenon[7] ,pyridium[8] andp xylyenediammonium[3] ionsandsoon .ThealkyldiaminesthreadthroughtheQ6 ,andformtherotaxanestructures[9 1 3] .Metalions[1 ,3 6 ,1 4 ,1 5] andclusters[8,…     

卡桑德拉

烈火熊熊. 这里越来越难以忍受. 艾黎摸到了公寓门,感觉门很牢固.她也能感觉到烈焰中冷金属的把手……穿过外面的滚滚浓烟,看到了隐蔽的楼梯,甚至能看清下面的路,这使她更加确信地面可以承载她的重量. 发疯的艾黎.她不紧不慢.     

自然管理与持续发展

自从1987年世界环境与发展委员会布伦特兰报告——《我们共同的未来》出版后,它已唤起若干次国际会议的召开.格罗宁根代表大会的目的是优先考虑并详尽阐述以往国际会议没有解决的一个关键性论题,该主题为《自然管理与持续发展》,主要解决如下9个议题:     

斯蒂芬·罗森伯格——继承性免疫疗法的先驱

《研究与开发》杂志1990年度科学家的桂冠授予了一名癌症研究前沿的科学家。美国每年死于癌症的人近50万。马里兰贝塞斯达美国国立癌症研究所的外科主任斯蒂芬·A·罗森伯格(Steven.A.Rosenberg)把他在手术室的技能与富有想象力、创造性以及偶尔引起争论的研究结合在了一起。罗森伯格曾是一种新疗法——继承性免疫疗法,亦称细胞转移疗法的先驱。从这种疗法的含意看,它包括从患者体内的免疫系统中取出细胞,改良它们使之更有效地对付患者的特定病症,而后把它们重新注入患者的免疫系统,攻击引起疾病的那部分细胞。     

Applications of Atomic and Molecular Theory to Calculations in Space Science and Engineering

A systematic elaboration is given on atomic and molecular theory problems encountered in dealing with space science and engineering. Three sections are presented in the paper on calculations for gas thermodynamic and transfer properties, characteristics of the optical radiation from the reentry' bodies, and the interaction between surfaces of man-made satellites and incident particles. Researches on them are much related to the fundamental problems regarding the atomic and molecular theory.