N－（N＇，N＇－二甲氨基甲基）丙烯酰胺－过硫酸钾引发丙烯酰胺聚合的研究

Ｎ－（Ｎ＇，Ｎ＇－二甲氨基甲基）丙烯酰胺－过硫酸钾引发丙烯酰胺聚合的研究潘松汉，唐康泰，王贞，王真智中国科学院广州化学研究所，广州，５１０６５０关键词Ｎ－（Ｎ＇，Ｎ＇－二甲氨基甲基）丙烯酰胺、反应动力学、氧化还原体系、相对分子质量及分布为了制备高质量...     

轿车转向杆系的优化设计

汽车转向杆系的设计对轮胎的磨损和车辆的操纵稳定性都有一定的影响。在对轿车转向杆系进行优化设计的过程中,运用位移矩阵法对MacPherson式悬架和齿轮齿条式转向系统的转向杆系进行了空间运动学分析,给出了前轴内、外轮转角关系的计算方法。综合考虑转向速比、轮胎的磨损及车辆的操纵稳定性要求提出了优化目标函数,并采用可变容差法进行求解。开发了悬架的运动分析及转向杆系的优化设计程序。运用该程序对一例实际车型进行了计算,其结果与试验值符合较好,表明该优化设计方法具有较高的准确性及一定的工程应用价值。     

从伦理视角看哈代《还乡》中的亲情悲剧与婚姻悲剧

从伦理角度看,哈代《还乡》中主要人物悲剧的根源在于人物处理家庭伦理关系时对伦理原则的违背所导致的矛盾。姚伯太太在处理家庭关系时违背了代际伦理原则,束缚了儿子克林与侄女朵荪的自由意志,不仅导致了她与克林之间的亲情悲剧,而且对克林的婚姻悲剧起了推波助澜的作用,同时也使朵荪成为一桩悲剧婚姻的无辜受害者。游苔莎与韦狄在处理各自的家庭关系时则置婚恋伦理于不顾,双双招致了殒命之灾,从而导致了各自夫妻关系的解体,给两个家庭造成了悲剧。     

Elastic properties of poly(hydroxybutyrate) molecules

Elasticity of various poly(hydroxybutyrate) (PHB) molecules of regular and irregular conformational structure was examined by the molecular mechanics (MM) calculations. Force - distance functions and the Young's moduli E were computed by stretching of PHB molecules. Unwinding of the 2(1) helical conformation H is characterized at small deformations by the Young's modulus E = 1.8 GPa. The H form is transformed on stretching into the highly extended twisted form E, similar to the beta-structure observed earlier by X-ray fiber diffraction. The computations revealed that in contrast to paraffins, the planar all-trans structure of undeformed PHB is bent. Hence, a PHB molecule attains the maximum contour length in highly straightened, but slightly twisted conformations. A dependence of the single-chain moduli of regular and disordered conformations on the chain extension ratio x was found. The computed data were used to analyze elastic response of tie (bridging) molecules in the interlamellar (IL) region of a semi-crystalline PHB. A modification of the chain length distribution function of tie molecules tau(N) due to secondary crystallization of PHB was conjectured. The resulting narrow distribution tau(N) comprises the taut tie molecules of higher chain moduli prone to overstressing. The molecular model outlined is in line with the macroscopically observed increase in the modulus and brittleness of PHB with storage time.     

构造柱施工中应注意的几个问题

针对混凝土构造柱施工容易出现的质量问题,提出注意钢筋绑扎、“柱腔”留设、“柱腔”处理、混凝土浇注等问题,严格按照规定进行操作,从而保证质量,达到设置构造柱的目的．     

李谘生平及其对北宋榷茶制度的改革

江西新喻籍人李谘,自幼仁孝,又聪明善辩,洞察世事。在地方为官历练多年,政绩突出。回到中央任职后,以革除滥赏、抑除侥幸为己任。李谘主持实行“见钱法”和“贴射法”,改革北宋的榷茶制度,虽然最终失败,但却取得了一定的成效,仍不愧为宋初一位有所作为的财税改革家。     

Small strain behavior of polyethylene: In situ SAXS measurements

Stack lamella deformation depends on their orientation with respect to the loading axis, the intrinsic properties of the lamellae, and the mechanical coupling between crystalline and amorphous phases. The aim of this work is to investigate the influence of the stress transmitter (ST) density and the crystallinity X_c on the local deformation. A wide experimental campaign has been undertaken on several polyethylenes with controlled molecular parameters and subjected to different thermal treatments. The ST density has been evaluated by the natural draw ratio and calculated by the Brown's model. The local deformation was measured by SAXS along a tensile test by using the long period stretching of the equatorial lamella stacks. The ratio ε_local/ε_macro was found to be a constant close to 0.5. This surprising low value has highlighted that the equatorial regions could be either the stiffest zone of the spherulite or submitted to a lower stress. It is proposed that the stability of the ratio ε_local/ε_macro is the result of two opposite phenomena: On one hand, the increase of X_c leads to unload the equatorial regions due to partial percolation of the crystalline phase and so decreases the stresses. On the other hand, when increasing X_c, the ST density decreases which causes the decrease in the local equatorial modulus. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1535–1542, 2010     

Critical review of the molecular topology of semicrystalline polymers: The origin and assessment of intercrystalline tie molecules and chain entanglements

Intercrystalline molecular connections in semicrystalline polymers have been the subject of numerous discussions and controversies. Nevertheless, there is one point of agreement: such intercrystalline tie molecules have a prime role in the mechanical and use properties of the materials, notably the resistance to slow crack growth. This article is a critical review of the mechanisms of generation of the tie molecules during the stage of crystallization and of the experimental and theoretical assessment of their concentration. Polyethylene and related materials are mainly studied. The contribution of chain entanglements is also discussed in parallel with tie molecules. Particular attention is paid to Huang and Brown's statistical approach, which appears to be the most appropriate one for predictive purposes and has aroused much interest from various authors. Attempts are made to provide solutions to the shortcomings of this model. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1729–1748, 2005     

钢管混凝土拱—钢腹板PC箱型系梁组合桥梁

为减轻钢管混凝土拱梁组合体系桥的自重,提出了采用钢腹板(平钢腹板或波纹钢腹板)代替PC箱形系梁的混凝土腹板,从而形成钢腹板PC箱形系梁。以一座已建成的钢管混凝土拱梁组合体系桥为原桥,进行了钢腹板PC箱形系梁的试设计研究。结果表明,试设计桥由于减小了自重下的内力,降低了面内自振频率,从而改善了原桥的静力和抗震性能。此外,试设计桥经济性好且方便施工,说明钢管混凝土拱—钢腹板PC箱型系梁组合桥梁是可行的。     

现浇板框架抗震性能的试验研究及理论分析

以现浇板对空间框架结构抗震性能的影响为主要研究内容,开展了空间框架结构的水平低周反复抗震试验.对框架结构的破坏情况、滞回曲线,以及现浇板纵向钢筋应变、梁端弯矩和现浇板受拉有效翼缘宽度进行了分析.分析结果表明,由于现浇板参与工作,框架无法形成"强柱弱梁"的破坏机制;现浇板框架结构的耗能能力较好;现浇板纵筋应变随层间侧移角的增大而增大,表明板参与框架结构受力的程度逐步增强;现浇板的参与使得框架梁端弯矩提高.最后利用拉压杆模型对现浇板受拉有效翼缘宽度进行推导,所得公式与实际情况符合良好,能够有效反映现浇板参与结构抗震工作的情况,可以用于工程实际使用.