混合的记忆

<正>春节少不了同学聚会,而今年恰是我的母校——百年名校雅礼中学的新建教学楼落成后的第一个春节。在大家漫不经心的回忆里,仍旧是斑驳的红砖房与房子后面的那个院子。席间,有人感叹,真是找不到那旧时的影子了。我知道改变一个建筑行为的最终目的大概是将一个平衡改变为另一个平衡。日子的飞奔也大抵是与遗忘成正比的,当多年后的今天,我们能掏出时间来回忆往事,是我们的日子总算开始慢了下来的证据。因为新教学楼大部分是自己的手笔,带着对孩     

港口防波堤的损坏及原因分析

随着港口建设规模的不断扩大,深水防波堤建设项目也逐年增多,防波堤在抵御海浪侵袭等方面具有重要的作用。但近年来不断出现的防波堤损坏事件,给港口水工工程建设造成了一定的困扰。本文就港口防波堤的损坏情况及损坏的原因进行了分析。     

城市交通拥挤收费技术及其应用案例

交通拥挤问题是目前大中城市普遍面临的问题,是城市交通需求系统与交通供给系统发生矛盾的突出表现。而实行交通拥挤收费,是一个缓解城市交通堵塞较为有效的经济手段。从四个方向分别对交通拥挤收费技术进行探讨,分别为基于博弈论的交通拥挤收费分析、最优拥挤收费模型分析、基于自由流时间的交通拥挤收费研究、弹性需求下多类型用户拥挤收费模型研究。并对实施交通拥挤收费的典型案例作简要分析。     

电梯层门耐火性能研究（2）

笔者在《电梯层门耐火性能研究（1）》（刊登于《中国电梯》杂志2013年第24卷第23期）中主要阐述了高层建筑火灾蔓延路径、建筑物构件耐火要求及国内常用电梯层门的耐火试验结果。本文将接续上文继续探讨电梯层门材料、厚度及制作结构等因素对层门耐火性能的影响,继续研究高层住宅电梯候梯厅（前室）防火阻隔及电梯层门耐火性能的技术要求,与广大读者交流和讨论。     

某地下人防商业建筑防火设计分析

为保障战时人员与物资掩蔽、人民防空指挥、医疗救护及经济发展,某市拟建设某地下人商业项目。由于《人民防空工程设计防火规范》与《建筑设计防火规范》对地下商业的消防设计的有关规定存在一定的差距,本着安全、经济的原则,针对某地下人防商业建筑的特点,运用FDS、EVACNET4等软件,从火灾控制、防火分隔、人员疏散及消防系统等方面分析了其消防设计的难点及解决方案。     

城市不平衡发展的分析与探讨

文章在阐述城市空间发展理论的基础上，分析了城市空间不平衡发展的规律，对我国西部大开发战略进行了反思，提出了发展我国不发达地区的思路。     

Kinetic modeling of simultaneous polycondensation and free radical polymerization for polyurethane/poly(methyl methacrylate) interpenetrating polymer network

A comprehensive kinetic Monte Carlo algorithm has been developed to investigate the formation process of a polyurethane/poly(methyl methacrylate) (PU/PMMA) interpenetrating polymer network (IPN), in which a component independent strategy is proposed to perform the simulation of simultaneous polycondensation and free radical polymerization. An empiric diffusion model based on the mass fraction of polymer is used to quantify the effect of diffusional limitations on MMA polymerization. Results show that the presence of acrylic monomers has little impact on the formation rate of PU, but the presence of the PU network can accelerate the polymerization of MMA. In addition, the effects of component mass ratio, acrylic cross-linker concentration, and [NCO]/[OH] ratio on the IPN formation kinetics are investigated based on the kinetic model. It is believed that the as-developed modeling strategy can be extended to other IPN systems and provide a better understanding of the interactions between chemically independent networks.     

A New Ferroelectric Phase of YMnO3 Induced by Oxygen‐Vacancy Ordering

Manganese oxides are good candidates of strongly correlated electron materials due to the uniqueness of electronic structure of manganese and the mobility of oxygen among lattice sites under external impacts. Here, we used electron beam as the excitation source to explore the structural evolution of YMnO₃ and identified a new phase under the radiation of electron beam in the transmission electron microscope. Analyses of the electron energy‐loss spectra reveal that this phase originates from ordered oxygen vacancy. We applied the first principles calculation to pick out the optimized stable structure with a lower polarization, and verified its correctness by electron diffraction and image simulations. Analyses of density of states indicate that weak Y–O covalence is favorable for the existence of ferroelectricity, supporting the electrostatic nature of ferroelectricity in the YMnO₃.     

A physical strategy for the preparation of isotactic polypropylene spheres with microsphere and bead–string spherulite morphologies

This study mainly focuses on the formation of isotactic polypropylene (iPP) blend morphologies with microspheres and distinct bead–string spherulites. iPP microspheres have been prepared by a simple and convenient strategy through either an isothermal or a nonisothermal crystallization process based on the macrophase‐separated structure in molten state of iPP/olefin block copolymer (OBC) blend. The dimension of the iPP spheres can be adjusted easily from about 1 µm to >10 µm by controlling the compatibility and annealing conditions. It was found that any of the following three parameters, the molecular structure of OBC (particularly the octene content), molecular weight of iPP, and annealing condition can be rescaled with others in controlling the dimension of the iPP microspheres. The mechanism of the formation of iPP microspheres was studied in detail. Surprisingly, the typical spinodal decomposition morphology with interconnected or thin sheet structure is the precursor of these microspheres. During the subsequent annealing process, it breaks up and further coarsens into spherical structure. In addition, distinct spherulites with a bead–string substructure have been obtained during the isothermal crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40863.     

集中式提纯器的设置与具有中间等级氢气网络的优化

氢气系统的集成与优化对于炼厂合理配置氢气资源和降低生产成本具有重要意义。针对具有中间等级氢气分配网络系统,本文提出了先确定中间等级状态再设置集中式提纯器的氢气网络分步优化模型,分析了在具有中间等级氢气网络中优化设置集中式提纯器的策略,并通过实例阐明了本文所提出方法的有效性。研究表明:对于具有中间等级的氢气网络系统,集中式提纯器应设置在氢源与中间等级之间,本文所提出的优化方法不仅使氢气网络结构具有可扩充性,而且可降低氢气公用工程的用量,减少炼厂的用氢费用。