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1.
Observations are reported on isotactic polypropylene (i) in a series of tensile tests with a constant strain rate on specimens annealed for 24 h at various temperatures in the range from 110 to 150 °C, (ii) in two series of creep tests in the subyield region of deformations on samples not subjected to thermal treatment and on specimens annealed at 140 °C, and (iii) in a series of tensile relaxation tests on non-annealed specimens. Constitutive equations are derived for the elastoplastic and non-linear viscoelastic responses of semicrystalline polymers. A polymer is treated as an equivalent transient network of macro-molecules bridged by junctions (physical cross-links, entanglements and lamellar blocks). The network is assumed to be highly heterogeneous, and it is thought of as an ensemble of meso-regions with different activation energies for separation of strands from temporary nodes. The elastoplastic behavior is modelled as sliding of junctions in meso-domains with respect to their reference positions driven by macro-deformation. The viscoelastic response is attributed to detachment of active strands from temporary junctions and attachment of dangling chains to the network. Constitutive equations for isothermal deformations with small strains are derived by using the laws of thermodynamics. Adjustable parameters in the stress–strain relations are found by fitting the experimental data. 相似文献
2.
Takashi Yamazaki Yoichi Takino Ryosuke Matsuoka Susumu Ito 《Electrical Engineering in Japan》1993,113(8):26-36
According to the recent analysis results of temporary ac overvoltage in the ac system connected with a frequency converter station, large-magnitude over-voltages were confirmed to occur under some special system conditions. Most of the station insulators currently used cannot withstand such overvoltages according to an evaluation based on the data obtained earlier. The necessity of tests to be done to evaluate such performance more accurately was recognized. Both power frequency and switching impulse overvoltage flashover tests were made on contaminated insulators by the method well simulating the natural wetting condition. Switching impulse flashover voltage with the waveshape having a long wavefront time of 2 ms can be well correlated with the flashover voltage characteristics of temporary ac overvoltage. Higher flashover voltage characteristics were obtained by a clean fog test method compared with those obtained by equivalent fog test method. 相似文献
3.
板深51区块存在压力敏感地层,在非目的层井段存在大段高渗低压砂岩,而目的层又属于高压低渗地层,属于难采油气田。室内进行的砂床滤失量、砂床封堵带承压能力、岩心封堵带的承压能力及油气层保护效果实验表明,在超低渗钻井液中增加固相含量,能够提高超低渗透膜结构强度,提高地层承压能力,降低砂床侵入深度,增强保护油气层效果,而且有选择性地增加有用固相效果更佳。基于这一理论,研究成功了超低渗广谱屏蔽暂堵油层保护技术,并在板深51区块长22—15井和长23—17K井进行了试验应用。该技术的关键是依据地层特性确定复配暂堵剂。长22-15井和长23-17K井射孔后未经过压裂、酸化、排液处理,获自喷高产,尤其是长22-15井形成自喷油流,创油田单井试采产量最高记录。应用结果表明,超低渗广谱保护油气层钻井液技术封堵隔层的承压能力强,很大程度地提高了漏失层的承压能力和破裂压力,较好地解决了含多套压力层系长裸眼段钻井过程中发生的漏失、井喷、卡钻、油气层保护等技术难题。 相似文献
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No authorship indicated 《Canadian Metallurgical Quarterly》2005,60(9):979
Presents the official listing of accredited internship and postdoctoral residency programs. It reflects all committee decisions through July 17, 2005. The Committee on Accreditation has accredited the doctoral internship and postdoctoral residency training programs in psychology offered by the agencies in this article. The original date of accreditation, listed for each program, is the day on which the program's accredited status became effective. Also listed for each program is the date of the next regularly scheduled site visit. Program review is governed by the "Guidelines and Principles for Accreditation of Programs in Professional Psychology" (G&P). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
7.
1 引言自组网,又称为Ad hoc网,是指一组带有无线收发装置的移动节点组成的一个多跳的临时性自治系统。自组网不需要依赖于任何预先架设的网络设施,能够实现临时快速自动组网和支持节点的移动性,并具有动态网络管理和动态网络优化的功能,主要用于在高度机动和无线通信的环境下为移动节点提供通信服务。在军事通信、抢险救灾、计算机支持协同工作(CSCW)等方面都具有广泛的应用。 相似文献
8.
Juri Matinheikki Kirsi Aaltonen Derek Walker 《International Journal of Project Management》2019,37(2):298-317
Public infrastructure projects must comply with the divergent and even conflicting demands of multiple institutional logics causing institutional complexity. Despite the increasing interest in different forms of complexities in projects, we lack empirical illustrations and rigorous theorizing of mechanisms for responding to institutional complexity. This paper demonstrates how public buyers of a tunnel construction project formed a hybrid organization of a multi-party project alliance to respond to institutional complexity. We delineate a process of temporary hybridization through which the competing logics of a bureaucratic state, corporate market, and multiple professions were combined within the temporary project alliance organization. Such temporary hybridization not only focused on selective coupling with external demands but also mitigated internal tensions. Our findings emphasize a blended organizational structure, jointly formed governance and incentive systems, and the facilitation of social interaction to build a temporary yet sustainable hybrid organization capable of combining conflicting institutional logics. 相似文献
9.
《Cities》2014
As some cities grapple with economic decline and depopulating neighborhoods, a number of academics and professionals have focused their attention on the causes, conditions and patterns of the resultant vacant land, whereas others lay out broad programmatic, institutional, fiscal and design responses to address vacancy on site or citywide scales. We find that, regardless of condition and context, most responses advocate complex, officially sanctioned, formal programs and policies that call for or depend on implementation over several multi-year phases. While laudable in scope, we question whether “permanent” solutions are appropriate given the widely varying causes, durations, contexts and patterns of vacancy and the inability of similarly scoped government-led programs to thus far achieve intended goals or improve local quality of life. We present examples that make the case for temporary, incremental, flexible and experimental responses to urban vacant land, then conclude by outlining the potential benefits and drawbacks of this temporary use model. 相似文献
10.
本文就无梁异形板桥的某些设计问题作了介绍,主要是两方面的内容:一是针对异形板的计算问题,为方便使用修改了部分计算公式,并对配筋弯矩公式做了周密的推导;二是对设计实践中的一些经验作出总结,包括:指出了异形板设计中板顶应该探讨的问题,并针对异形板桥事故如何吸取教训,以及地铁通过异形板桥时的安全对策等等进行了讨论。文章是笔者近年在审图、审稿、咨询工作中的一些体会,也是对以往同类设计的一个补充。 相似文献