The impact of property price on construction output

The interaction between the construction market and the overall economy has attracted much attention, but few studies have investigated the influence of the property market on the construction market in terms of property price. The disaggregated data of Hong Kong’s housing and retail construction sectors are collected to investigate the impact of property price on construction output. The newly developed autoregressive distributed lag (ARDL) bounds testing approach and the error correction (EC)-based Granger causality test are employed. The bounds testing results suggest that there exist stable long-run relationships between construction output and property price for both housing and retail construction sectors. Specifically, a 1.00% increase in the housing price and retail price lead to a 0.55% and 0.42% increase in construction outputs for the two sectors respectively. In addition, the Granger causality tests confirm a distinct long-run causal flow from property price to construction output. Furthermore, the proposed ARDL approach provides an effective method for forecasting construction output.     

A modelling study for moisture diffusivities and moisture transfer coefficients in drying of solid objects

This article presents an effective analytical model for determining the moisture diffusivities and moisture transfer coefficients for solid objects (namely, infinite slab, infinite cylinder, sphere; and also for irregularly shaped objects, by using a shape factor) subject to drying applications in a medium. The unsteady-state moisture diffusion analysis is used on the basis of two important criteria: 0·1 <Bi < 100 and Bi > 100. The drying coefficients and lag factors were employed. The analytical models are then verified using available experimental data taken from the literature. The results show that the method presented here can be used to determine the moisture diffusion coefficients and moisture transfer coefficients for such solid objects in a simple and accurate manner for a variety of drying applications.     

依据规范设计的钢板剪力墙的抗震性能

目前美国钢结构协会(AISC)抗震设计规范纳入了钢板剪力墙(SPSWs)的设计要求。钢板剪力墙由薄钢板中夹着被称为水平边界单元(HBEs)的钢梁和被称为竖直边界单元(VBEs)的钢柱组成。无加劲薄钢板在较低剪力作用下屈曲并发展变形,通过屈服变形达到延性和耗能的目的。HBEs的作用是加劲和提高整体强度,并将屈服局限于薄钢板内。VBEs的作用是促进梁端塑性铰的形成。研究依据规范设计的钢板剪力墙的性能,设计了一系列钢板剪力墙试件,采用不同震级的地面震动反应谱的非线性时程分析对其进行性能研究。研究发现,依据现行规范设计的试件能满足各种地震烈度下最大层间位移的要求,并且在最高地震烈度下最大层间位移比小于5%。由于高阶振型对反应的影响,低层钢板剪力墙的延性要求比高层钢板剪力墙要高。由钢板承担的楼层剪力与由边界框架承担的楼层剪力之比为60%～80%,此比值与板的长宽比和地震烈度无关,而与板的厚度有关。9层或以上钢板剪力墙在低烈度地震下对VBEs的需求比规范计算方法要小很多。     

类骨纳米结构生物材料的细观力学分析

根据贝壳、 骨骼等生物材料在纳米尺度的微结构特征, 采用剪滞模型, 分别推导了蛋白质材料为线弹性和弹塑性时类骨材料的等效模量和总体应力应变曲线。通过与有限元以及Gao等人的拉剪链模型结果的比较, 分析了线性剪滞模型和拉剪链模型在研究类骨材料等效模量时的有效性。结果显示, 剪滞模型与二维有限元结果符合较好, 拉剪链模型在长细比较大时与有限元结果偏离较大。进一步将弹塑性剪滞模型预测的应力-应变曲线与实验测量结果进行了比较, 两者符合较好。从模拟结果中可以看出, 在刚度发生明显降低之前, 已经有部分蛋白质进入塑性变形, 从而反映了生物材料的能耗与增韧特征。      

键合技术中键合胶残余应力检测的实验研究

通过检测受到键合胶残余应力影响的芯片表面的翘曲特征和力学特性,运用泰曼-格林干涉仪与力学实验机相结合,成功地分析了在采用粘胶键合中,粘胶硬化后残余应力对芯片的影响以及产生的原因,对键合胶的选择提出了科学的依据。本文对这种方法进行了理论分析和实验验证。     

Nucleation and growth behavior of β-nucleated iPP during shear induced crystallization investigated by in-situ synchrotron WAXS and SAXS

Polymer crystallization under flow was investigated because final properties of polymers strongly depend on the crystalline structure and morphology formed during processing. In-situ synchrotron WAXS and SAXS were used to investigate the structure formation and morphological developments during quiescent and shear-induced crystallization of iPP with 3 different concentrations (0.01, 0.03 and 0.1 wt%) of β-nucleating agent. Under quiescent conditions, a high β-content was obtained at all those concentrations indicating the high β-nucleating efficiency of the nucleating agent. After application of shear, the β-nucleating ability at small concentration was retained, while at larger concentrations it was strongly retarded. Furthermore, the addition of β-nucleating agent was beneficial for the molecular alignment during processing, the anisotropic particles of β-nucleating agent were much more effective to align the molecular chains in the flow direction compared to isotropic ones. A crystallization scheme for the iPP β-nucleating agent under shear was proposed.     

Effect of shear deformation on interfacial stresses in plated beams subjected to arbitrary loading

Bonding a fibre reinforced polymer (FRP) composite or metallic plate to the soffit of a reinforced concrete (RC), timber or metallic beam can significantly increase its strength and other aspects of structural performance. These hybrid beams are often found to fail due to premature debonding of the plate from the original beam in a brittle manner. This has led to the development of many analytical solutions over the last two decades to quantify the interfacial shear and normal stresses between the adherends. The adherends are subjected to axial, bending and shear deformations. However, most analytical solutions have neglected the influence of shear deformation of the adherends. For the few solutions which consider this effect in an approximate manner, their applicability is limited to one or two specific load cases. This paper presents a general analytical solution for the interfacial stresses in plated beams under an arbitrary loading with the shear deformation of the adherends duly considered. The shear stress distribution is assumed to be parabolic through the depth of the adherends in predicting the interfacial shear stress and Timoshenko's beam theory is adopted in predicting interfacial normal stress to account for the shear deformation. The solution is applicable to a beam of arbitrary prismatic cross-section bonded symmetrically or asymmetrically with a thin or thick plate, both having linear elastic material properties. The effect of shear deformation is illustrated through an example beam. The influence of material and geometric parameters of the adherends and adhesive on the interfacial stress concentrations at the plate end is discussed.     

Applying dry powder coatings to pharmaceutical powders using a comil for improving powder flow and bulk density

A method for applying nano-sized silicon dioxide guest particles onto host pharmaceutical particles (a.k.a. “dry-coating” or “nanocoating”) has been developed using conventional pharmaceutical processing equipment. It has been demonstrated that under selected conditions, a comil can be used to induce sufficient shear to disperse silicon dioxide particles onto the surfaces of host particles such as active pharmaceutical ingredients (API) without significant host particle attrition. In accordance with previous studies on dry coating, the dispersed silicon dioxide adheres to the host particle surface through van der Waals attractions, and reduces bulk powder cohesion. In this work, laboratory and pilot scale comils were used to dry coat pharmaceutical API and excipient powders with 1% w/w silicon dioxide by passing them through the mill with an appropriate combination of screen and impeller. In general, the uncoated powders exhibited poor flow and/or low bulk density. After dry coating with a comil, the powders exhibited a considerable and in some cases outstanding improvement in flow performance and bulk density. This coating process was successful at both the laboratory and pilot scale with similar improvements in flow. The superior performance of the coated powders translated to subsequent formulated blends, demonstrating the benefit of using nanocoated powders over uncoated powders. This particle engineering work describes the first successful demonstration of using a traditional pharmaceutical unit operation that can be run continuously to produce uniform nanocoating and highlights the substantial improvements to powder flow properties when this approach is used.     

A simple scaling derivation of the shear thinning power-law exponent in entangled polymer melts

By suggesting that the polymer dynamics in entangled polymer melts possesses the property of dynamical self-similarity, we argue that the power-law exponent of the Carreau-Yasuda law, which empirically describes the shear thinning effect of the polymer melt viscosity, is inversely proportional to the exponent of the molecular mass dependence of the terminal relaxation time. This finding is obtained in cases where the shear rate dependence of the segmental relaxation time is negligible. If such dependence is essential, the Carreau-Yasuda law is slightly modified at high shear rates: instead of a power-law dependence with a small shear rate independent exponent, a weaker logarithmic dependence is found both for shear rate and molecular mass dependence, which resembles the approach to zero of an effective shear rate and molecular mass dependent power-law exponents at sufficiently high shear rates.