EFFECT OF NONSOLVENT ADDITIVES ON THE PORE SIZE AND THE PORE SIZE DISTRIBUTION OF AROMATIC POLYAMIDE RO MEMBRANES

In this paper discussions are made on the effect of nonsolvent swelling agents on the average pore size and pore size distributions at the surface of polyamide membranes which result from casting solutions involving above nonsolvent swelling agents.

The size of the polymer aggregate in the film casting solution and the size of polymer network pores are correlated to physicochemical data of ions which constitute the electrolytes used as nonsolvent swelling agents. As such ionic properties the charge density and the free energy of transition of ions from polyamide phase to water phase were considered. The validity of the correlation is limited in a range of casting solution composition where the polymer concentration in the casting solution is close to the limiting concentration of polymer at the phase boundary and the molar ratio of the nonsolvent swelling agent to the amide group involved in the polyamide polymer is equal to or slightly more than 0.7.     

Radial density distribution of fractal clusters

The radial density distributions of fractal clusters generated in both DLCA and RLCA conditions by Monte-Carlo off-lattice cluster-cluster aggregation have been investigated. It has been computed by averaging a large number of clusters of same mass to form an average cluster, which is then considered as spherically symmetric. It is found that the radial density distribution, calculated using the mass center of the cluster as the center point, does not follow the fractal scaling, as sometimes assumed in the literature. An empirical model has been proposed to describe the dependence of the radial density distribution on the number of particles in the cluster. The obtained radial density distribution is used to compute permeability profile of the fractal cluster using several literature models, which is then applied to estimate the cluster hydrodynamic radius, R_h, by considering the cluster as a porous permeable object and using the solution of Brinkman equations for the fluid flow inside the cluster. The so obtained R_h values are compared to those in the literature, computed using the Kirkwood-Riseman (KR) theory. It has been found that, among the five permeability models examined, only the model proposed by Davis (Proceedings of the Institution of Mechanical Engineers Part B 1, 185) provides results in good agreement with those obtained using the KR model. Furthermore, it has been verified that the R_h values are insensitive to the model used for the density distribution.     

再生混凝土力学性能提升技术与应用

针对大量混凝土废弃物造成生态环境日益恶化及天然骨料资源日益缺乏的问题,通过配制不同强度等级和不同再生骨料掺量的再生混凝土,并结合锡澄运河三级航道整治工程对再生混凝土力学性能及其提升技术进行试验研究。结果表明:再生骨料的掺量对C35及以下中低强度混凝土力学性能影响较小,而对C40及以上中高强度混凝土有较大影响,随再生骨料掺量的增加,再生混凝土力学性能降低;通过合理选用再生骨料级配、与天然骨料复掺、对再生骨料进行强化以及优化配合比参数等措施能提升混凝土力学性能;锡澄运河三级航道整治工程实际应用取得了很好的技术经济效益。     

再生骨料的基本物理力学性能试验研究

再生骨料的物理力学性质是影响其运用范围、再生混凝土性能的本质因素。通过对公路废弃混凝土所制成的再生骨料和天然骨料同时进行物理力学性能试验研究,获得了骨料的表观密度、吸水率、压碎值、磨耗损失和针片状颗粒含量值。通过对再生骨料和天然骨料的试验结果进行对比分析发现,再生骨料除了针片状颗粒含量值会略优于天然骨料,其他四种物理力学性质均比天然骨料差,但两者的差异性不大。     

后掺粗骨料工艺对高性能泵送混凝土性能影响研究

为解决建筑工程中高性能泵送混凝土的环境问题、成本问题,基于粗骨料嵌锁效应和界面水灰比强度理论,在保证高性能和泵送要求的条件下,提出了后掺骨料工艺,并对不同粗骨料后掺比例下的混凝土进行了力学性能和抗冻性能的研究。结果表明,随着粗骨料后掺比例的增大,7 d、28 d混凝土抗压强度持续增大,而28 d混凝土劈裂抗拉强度和抗折强度均呈先增大后减小的趋势;在冻融循环作用下,质量损失率的上升速率呈先减小后增大的趋势,而抗压、抗拉、抗折强度、动弹性模量以及超声波速的下降速率均呈先减小后增大的趋势。据此建议本C30高性能泵送混凝土的粗骨料最佳后掺比例为20%。     

Revisiting the two-stage choice model: an empirical study of consumer choice on brand website visits

In consumer choice behaviour literature, a two-stage choice model serves as a base theory where choice behaviour is decomposed into a consideration stage plus a choice stage. Yet, this default model has been increasingly challenged by the ‘limited consumer search’ school of thought because consumers do not necessarily review all products in a choice set before making decisions, but frequently draw on external information as mental short cuts. Methodologically, the choice behaviour in stage 1 has traditionally been latent because data that directly observe how consumers form their consideration sets by eliminating alternatives are lacking. This study continues the ‘limited consumer search’ line of reasoning and proposes an aided non-compensatory process in choice stage 1, where consumers reduce brand website alternatives by using online ratings to arrive at a consideration set. We use observed Web analytics data to unveil the stage 1 choice process and also the transition from stage 1 to stage 2, which is in need of further research based on extant literature. Lastly, we cross-validate our model with two types of websites (i.e. search vs. experience/credence) and find our model is contingent on the type of website content, where consumers’ inclination to use online ratings for decision-making varies.     

Alkali-silica reactivity of some frequently used lightweight aggregates

Lightweight aggregates (LWAs) are frequently used in concrete as well as in thermally insulating mortars and grouts, so that information on their alkali-silica reactivity (ASR) is very important. Four LWAs—expanded vermiculite, expanded clay, expanded glass and perlite—were studied regarding their ASR, using the following test methods: the accelerated mortar bar test (ASTM C 1260), the rapid chemical test (ASTM C 289) and the combined scanning electron microscopy-energy dispersive X-ray technique (SEM-EDX). According to these methods, neither the expanded vermiculite nor the expanded clay exhibited any potential ASR. On the other hand, in the case of the aggregates containing a glassy phase (expanded glass and perlite), the results of SEM-EDX analysis showed serious decomposition of aggregate texture due to ASR, although no deleterious expansion was observed in the accelerated mortar bar test. Therefore, suitable test criteria for ASR need to be defined for LWAs of this type when the AMBT method is used, as has already been suggested for slowly reactive aggregates in Australia.     

高温大颗粒气固流化床流化行为数值模拟

通过数值模拟,对内含直径为3 mm流化颗粒的二维高温流化床开展了研究。其中欧拉途径被用于描述气相运动,而对颗粒相描述则采用拉格朗日途径。采用离散单元法跟踪颗粒在不同时刻位置和速度。结果表明:与300K时相比,1 000 K高温床的临界流化风速有所提高,压降脉动及床层最大膨胀比明显降低。1 000 K时,流化数提高至1.67,高温床内可见到大尺寸的气泡。在气泡之外上、下2个区域中处于气泡对称轴上的颗粒,水平速度具有相反的方向;而y方向上,这二部分颗粒群的速度均向上并大致在10-1m/s范围之内。     

高黏弹火药粗碎装置的研制

为解决半溶剂法发射药双螺杆成型工艺中预混捏合后物料形状及大小的差异悬殊，导致双螺杆挤出成型机吃料困难、挤出速度不均匀问题，将民用行业适于湿固体物料用粗碎机，通过主要工作参数及安全技术措施的改进，加工出一台适于高黏弹火药用的粗碎设备CSZZ-200。通过代料和真料实验，验证了装置性能。结果表明，经该粗碎机粗碎后的粒料，外形尺寸相对均匀，粒问不黏连，经双螺杆挤出后，挤出速度均匀稳定，解决了双螺杆挤出机中的喂料和出料不均匀问题。     

骨料对透水混凝土性能的影响

试验研究了骨料品种、骨料粒径对透水混凝土主要性能的影响。试验结果表明：在相同骨料粒径的情况下,由碎石骨料配置的透水混凝土总孔隙率和透水系数明显大于卵石骨料配置的透水混凝土,碎石的强度变化幅度比卵石的变化幅度明显;随着骨料粒径的增大两种骨料配置的透水混凝土的孔隙率、透水系数均有所增大,在同一配合比情况下,随着骨料粒径的增大透水混凝土的强度呈非线性变化,且存在最佳粒径尺寸。