Phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls

The phase behaviors in a binary mixture of diblock copolymers confined between two parallel walls are investigated by using a cell dynamics simulation of the time-dependent Ginzburg-Landau theory.The morphological dependence of the wall-block interaction and the distance between walls（confinement degree） has been systematically studied,and the effect of repulsive interactions between different monomers is also discussed.It is interesting that multiple novel morphological transitions are observed by changing these factors,and various multilayered sandwich structures are formed in the mixture.Furthermore,the parametric dependence and physical reasons for the microdomain growth and orientational order transitions are discussed.From the simulation,we find that much richer morphologies can form in a binary mixture of diblock copolymers than those in a pure diblock copolymer.Our results provide an insight into the phase behaviors under parallel wall confinement and may provide guidance for experimentalists.This model system can also give a simple way to realize orientational order transition in soft materials through confinement.

SEGMENT DENSITY PROFILES OF COMPACT POLYMER CHAINS CONFINED BETWEEN TWO PARALLEL PLANE WALLS

We use the pruned-enriched Rosenbluth method to investigate systematically the segment density profiles of compact polymer chains confined between two parallel plane walls. The non-adsorption case of adsorption interaction energy ε = 0 and the weak adsorption case of ε= -1 are considered for the compact polymer chains with different chain lengths N and different separation distances between two walls D. Several special entropy effects on the confined compact polymer chains, such as a damped oscillation in the segment density profile for the large separation distance D, are observed and discussed for different separation distances D in the non-adsorption case. In the weak adsorption case, investigations on the segment density profiles indicate that the competition between the entropy and adsorption effects results in an obvious depletion layer. Moreover, the scaling laws of the damped oscillation period Td and the depletion layer width Ld are obtained for the confined compact chains. Most of these results are obtained for the first time so far as we know, which are expected to understand the properties of the confined compact polymer chains more completely.

Upper bound seismic rotational stability analysis of gravity retaining walls considering embedment depth

Stability analysis of gravity retaining wall was currently based on the assumption that the wall had no embedment depth. The effect of earth berm was usually neglected. The present work highlighted the importance of embedment depth when assessing the seismic stability of gravity retaining walls with the pattern of pure rotation. In the framework of upper bound theorem of limit analysis, pseudo-static method was applied into two groups of parallel rigid soil slices methods in order to account for the effect of embedment depth on evaluating the critical acceleration of wall-soil system. The present analytical solution is identical to the results obtained from using limit equilibrium method, and the two methods are based on different theory backgrounds. Parameter analysis indicates that the critical acceleration increases slowly when the ratio of the embedment depth to the total height of the wall is from 0 to 0.15 and increases drastically when the ratio exceeds 0.15.

Converging Parallel Plate Flow Chambers for Studies on the Effect of the Spatial Gradient of Wall Shear Stress on Endothelial Cells

Many in vitro studies focus on effects of wall shear stress (WSS) and wall shear stress gradient (WSSG) on endothelial cells, which are linked to the initiation and progression of atherosclerosis in the arterial system. Limitation in available flow chambers with a constant WSSG in the testing region makes it difficult to quantify cellular responses to WSSG. The current study proposes and characterizes a type of converging parallel plate flow chamber (PPFC) featuring a constant gradient of WSS. A simple formula was derived for the curvature of side walls, which relates WSSG to flow rate (Q), height of the PPFC (h), length of the convergent section (L), its widths at the entrance (w0) and exit (w1). CFD simulation of flow in the chamber is carried out. Constant WSSG is observed in most regions of the top and bottom plates except those in close proximity of side walls. A change in Q or h induces equally proportional changes in WSS and WSSG whereas an alteration in the ratio between w0 and w1 results in a more significant change in WSSG than that in WSS. The current design makes possible an easy quantification of WSSG on endothelial cells in the flow chamber.

SimWall:a practical user-friendly stereo tiled display wall system

SimWall is a user-friendly, stereo tiled display wall system composed of 18 commodity projectors operated by a Linux graphics cluster. Collaborating together, these projectors work as a single logical display capable of giving a high-resolution show, large-scale, and passive stereo scene. In order to avoid tedious system setup and maintenance, software-based automatic geometry and photometric calibration are used. The software calibration is integrated to the system seamlessly by an on-card transform method and is transparent to users. To end-users, SimWall works just as a common PC, but provides super computing, rendering and displaying ability. In addition, SimWall has stereoscopic function that gives users a semi-immersive experience in polarized passive way. This paper presents system architecture, implementation, and other technical issues such as hardware constraints, projectors alignment, geometry and photometric calibration, implementation of passive stereo, and development of overall soft- ware environment.

Local receptivity in non-parallel boundary layer

The research on boundary-layer receptivity is the key issue for the laminarturbulent transition prediction in fluid mechanics. Many of the previous studies for local receptivity are on the basis of the parallel flow assumption which cannot accurately reflect the real physics. To overcome this disadvantage, local receptivity in the non-parallel boundary layer is studied in this paper by the direct numerical simulation （DNS）. The difference between the non-parallel and parallel boundary layers on local receptivity is investigated. In addition, the effects of the disturbance frequency, the roughness location, and the multiple roughness elements on receptivity are also determined. Besides, the relations of receptivity with the amplitude of free-stream turbulence （FST）, with the roughness height, and with the roughness length are ascertained as well. The Tollmien- Schlichting （T-S） wave packets are excited in the non-parallel boundary layer under the interaction of the FST and the localized wall roughness. A group of T-S waves are separated by the fast Fourier transform. The obtained results are in accordance with Dietz＇s measurements, Wu＇s theoretical calculations, and the linear stability theory （LST）.

薄壁墙式墩结构装配式方案及其抗震性能分析

针对既有柱式墩预制拼装技术难以应用于截面横纵比大的薄壁墙式墩的问题,提出了一种节段水平并联的新型装配式桥墩结构方案,预制节段采用双向无黏结预应力筋、灌浆套筒及混凝土剪力榫混合连接.依托某国际机场飞机荷载宽幅桥梁工程实例,基于ABAQUS平台分别建立了新型装配式桥墩和现浇桥墩的精细化有限元模型,通过拟静力分析对比研究了2种桥墩抗震性能的差异,并讨论了预应力筋配筋率以及剪力榫埋深对新型装配式桥墩抗震性能的影响规律.结果表明:新型装配式桥墩与现浇桥墩在纵向水平荷载作用下呈现墩底塑性铰充分发展的弯曲破坏形态,而在横向水平荷载作用下则呈现弯剪破坏形态;相较于现浇桥墩,装配式桥墩纵桥向与横桥向水平承载力分别提高68.5%和43.0%,但残余位移分别降低49.2%和67.8%;增大竖向预应力筋配筋率可显著提升装配式桥墩的水平承载力,而增加水平向预应力筋配筋率和剪力榫埋深则对限制节段接缝处的相对变形作用明显.

挡墙平动墙后被动土压力研究

墙后土压力分布形式是挡土墙设计与施工的重要参考依据。本研究开展了单一硬土、硬土-软土-硬土、软土-硬土-软土和单一软土4组挡墙平动室内模型试验,分析了墙后实测侧向水平土压力分布规律。结果表明,挡墙平动,对于成层土,被动土压力均在土层交界处土应力发生突变,墙后被动土压力图呈锯齿梯形台阶分布;在侧向水平荷载作用下,水平分层地基软硬土层界面处,无应力集中与应力扩散,与竖向荷载作用下分层地基应力集中和应力扩散存在显著区别。

近距离平行既有车站地下连续墙施工技术研究

随着城市发展速度加快,围护结构的施工效率已经成为制约地下工程施工效率的一个关键因素。研究以广州地铁11号线中山八站深基坑围护结构为工程依托,针对地下连续墙主筋连接、双轮铣地下连续墙铣洗缝问题开展研究,形成了双轮铣+锁口管的组合式地下连续墙接头形式施工技术,有效保证了地下连续墙接缝质量,提高了双轮铣整体成槽施工工效,为今后类似工程案例提供参考。

基于薄壁齿轮车工夹具设计及应用

在实际加工中遇到薄壁齿轮在加工车工端面平行度超差问题,加工时如果采用数控车床的液压动力卡盘夹外圆加工,卡爪夹紧力使得薄壁齿轮端面发生轻微变形,导致车削后薄壁齿轮端面平行度偏大,过程能力不稳定,有超上限现象发生,导致尺寸不合格。经过统计分析,齿轮端面平行度过程能力CPK值最高0.97,低于目标值1.67。通过人、机、料、法各环分析后,发现机床与薄壁齿轮接触的定位面和夹紧力是端面平行度大小的至关因素。因此迫切需要改善现有加工方式,设计一套薄壁齿轮车工夹具,既能保证薄壁齿轮端面平行度,又能方便操作人员使用。

非平行双墙施工缝液压联动撑合模板的设计与施工

为解决非平行双墙施工缝支设传统做法存在的施工烦琐、材料不可周转使用且不符合绿色环保要求、施工质量不易控制的问题,创新了一种低成本、高质量、可周转、施工简便的施工方法。在结合以往施工经验的基础上,通过方案比选,最终选择借鉴雨伞撑合的方式实现模板联动撑合。介绍了撑合式模板的设计思路,并对施工关键技术进行了总结,以期为类似工程提供参考。

电磁波穿透墙体的衰减特性

应用平面电磁波理论和菲涅耳公式分析了电磁波穿透不同介质的衰减特性,对不同的极化方式、入射角、介电常数、电导率、损耗角正切和频率下,电磁波在介质间的透射性能及介质中的传输衰减特性进行了分析,对常见的普通混凝土墙、37砖墙、24砖墙、石膏空心板、水泥泡沫板、木板和玻璃与频率的衰减特性进行了数值仿真,比较了新砌混凝土墙、实心粘土砖墙和多孔粘土砖墙的损耗特点,将仿真结果与实际测量及参考文献测量结果进行了比较,结果表明仿真的墙体频率衰减趋势与实际测量结果一致,衰减数值接近并略低于实测结果。

并联机器人开槽薄壁柔顺关节设计与实验

针对传统柔顺关节运动范围小、易产生轴向漂移的不足,依据3RRR并联机器人运动范围,以关节的移动范围及所需刚度作为条件,对关节的几何尺寸进行了设计计算,并用ANSYS软件进行强度分析,设计了一种新型开槽式薄壁柔顺关节。利用扭转作为主要变形方式时,该柔顺关节具有扭转角度可达到36°及轴线相对固定不易漂移的优点。根据关节设计尺寸选择65Mn为材料进行了加工,在三自由度并联机器人实验平台上进行了片簧式与开槽式两种柔顺关节的实验对比,实验结果表明设计的开槽式薄壁柔顺关节能够完成轨迹跟踪任务,且最大相对误差为6.05%,对比片簧式柔顺关节具有一定优越性。

基于AFT-Delaunay的二维解耦并行网格生成算法

面向平面任意几何区域网格生成,提出了一种将波前法AFT(Advancing Front Technique)与Delaunay法相结合的解耦并行网格生成算法。算法主要思想是沿着求解几何区域惯性轴,采用扩展的AFT-Delaunay算法生成高质量三角形网格墙,递归地将几何区域动态划分成多个彼此解耦的子区域;采用OpenMP多线程并行技术,将子区域分配给多个CPU并行生成子区域网格;子区域内部的网格生成复用AFT-Delaunay算法,保证了生成网格的质量、效率和一致性要求。本算法优先生成几何边界与交界面网格,有利于提高有限元计算精度;各个子区域的网格生成彼此完全解耦,因此并行网格生成过程无需通信。该方法克服了并行交界面网格质量恶化难题,且具有良好的并行加速比,能够全自动、高效率地并行生成高质量的三角网格。

钻墙高效截流瓦斯抽放技术在寺河煤矿的应用

为了提高厚煤层煤巷掘进工作面的瓦斯抽放率,探讨了钻墙高效截流边掘边抽技术的原理,并将该技术应用于寺河煤矿X13014瓦斯抽放试验巷,试验结果表明:钻墙的瓦斯抽放率可达80%以上,能够有效截流煤壁瓦斯涌出、避免巷道瓦斯超限。

湍流模拟壁面距离MPI/OpenMP混合并行计算方法

针对计算流体力学在湍流数值模拟过程中壁面距离计算效率不高的问题,设计了一种基于ADT数据结构搜索的MPI/OpenMP混合并行计算方法,以大幅提高大规模网格壁面距离的计算效率,降低因内存消耗而对网格规模的限制。首先分析了壁面距离计算精度对湍流模拟的重要性,介绍了壁面距离计算的几何基础。随后基于区域分解思想,将计算域划分为不同的子分区,服务器进程收集全局壁面面元网格信息后发送给其他所有进程,各进程根据全局壁面信息,基于ADT数据结构搜索其网格分区内的单元,精确计算壁面距离。为了解决全局壁面信息内存过大的问题,采用MPI/OpenMP混合并行算法,使得各计算节点中仅有一个或少数几个壁面信息备份,这些壁面信息备份被节点内的其他各进程所共享。最后采用大规模网格进行了壁面距离计算测试,网格规模最大达到33.2亿,结果表明,该方法的计算精度和直接搜索法一致,内存耗费下降70%,计算时间减少约1个量级,能满足大规模CFD数值模拟的需求。

隐式中墙连拱隧道平行中隔壁工法设计与分析

分析连拱隧道工法研究现状和趋势,结合隐式中墙复合式连拱隧道[1-2]结构形式,提出一种新的连拱隧道施工方法—平行中隔壁法,其无需中墙临时支护,预留岩体保护中墙,减小对环境的影响,大幅提高连拱隧道的施工效率,实现连拱隧道的快捷施工。对平行中隔壁法进行详细设计与分析,并对其进行数值模拟。结果表明:平行中隔壁法可保证隐式中墙复合式连拱隧道施工安全,各上台阶步序开挖和拆撑为控制竖向变形的关键工序,左洞拱腰与中墙连接处和左洞仰拱与中墙连接处是初期支护的安全控制点。

隐式中墙连拱隧道工法探讨

为了选择合理的施工方案,针对隐式中墙复合式连拱隧道,对多种施工方案进行了数值模拟。分析结果表明:在多种施工方案条件下,隐式中墙复合式连拱隧道结构均能保证施工安全;对称中隔壁法和平行中隔壁法在结构安全和变形控制上较为有利。平行中隔壁法中的主辅洞间隔、同步并行施工方案是最经济、最快捷、最环保的方案,其综合进度指标比普通中导洞法提高107%,比三导洞法提高79%,可大幅提高连拱隧道的施工效率。上台阶开挖和拆撑为控制变形的关键工序,辅洞拱部与中墙搭接处、辅洞仰拱与中墙搭接处为结构安全控制部位。

面向薄壁多腔类结构件加工特征识别方法

针对薄壁多腔类结构件加工特征识别效率低下、相交特征识别困难的问题,提出基于规则、层与特征抑制的混合并行识别方法。该方法以腔分组和加工特征分类为基础、以腔为单元对各类加工特征进行并行识别,以提高识别效率,并及时在三维模型中抑制已识别的各特征来简化相交特征的识别。首先给出了加工特征的分类及腔分组的方法;然后详细给出了特征识别流程:利用边的属性和规则识别各个腔中的完整孔、独立筋、相交筋,将各个腔采用层与特征抑制的方法识别层特征与相交孔特征,当所有腔内的特征识别完成后回到主线程进行剩余特征的识别;最后通过实例分析了算法效率,验证了所提方法的有效性。

元宝山露天矿内排土场压脚挂帮并行建设方案

针对内排土场发展建设速度与收容量问题,以元宝山露天矿内排土场为工程背景,基于露天矿开拓开采设计理论和边坡稳定性分析理论相结合的方法,建立内排土场形态的动态控制思路及流程,分析元宝山露天煤矿内排土场边坡动态稳定性,优化设计内排土场发展过程中各工程位置的空间形态,提出一种有利于快速占据内排空间的内排土场压脚挂帮并行建设方案.研究结果表明:采场南帮到界边坡从局部到整体均能满足安全储备系数1.2的要求,可实行挂帮排土;南帮到界边坡挂帮排土至471水平,且平盘宽度为180 m时为挂帮内排的极限位置;内排土场压脚挂帮并行排土方案能够加快内排土场建设速度,且在排土初期时可排弃空间远远大于正常排土方案.