Immigration and Construction: The Makeup of the Workforce in the Washington, D.C., Metropolitan Area

There are an estimated 11 million illegal immigrants currently residing in the United States. Of this population, research shows that approximately 19% work in the construction industry, comprising around 14% of all construction workforces. The Washington, D.C. metropolitan region has a unique makeup of workforces within the construction industry. Between September 2006 and February 2007, 896 construction workers from several projects in the Washington, D.C. metropolitan area participated in a survey. The study targeted the low-skilled, immigrant-saturated trades in construction. The most compelling finding in this study was that illegal immigrants make up a far greater proportion of the construction workers in low-skilled trades than indicated by national averages, 55% as compared to between 20 and 36% nationally. This will increase the impact of immigration and immigration reform substantially for the Washington, D.C. metropolitan.     

建筑施工中裂缝的成因与防治措施

从设计、施工、原材料等方面入手，针对现在混凝土易出现裂缝的原因进行研究与探讨，提出了一些解决方法，并分别作了具体阐述，从而尽量减少混凝土裂缝给我们生活所带来的不便和我们对安全的担心。     

Invited review: Modelling quality changes of fruits and vegetables during drying: a review

Fruits and vegetables have received much attention as these materials have been reported to contain various phytochemicals, which are claimed to exert many health benefits. When extraction of bioactive compounds cannot be performed on fresh fruits and vegetables, drying needs to be conducted to keep the materials for later use. Dried fruits and vegetables have also been regarded as alternative fat‐free snacks and received more attention from the food industry during the past decade. This implies that not only nutritional changes, but also other changes including physical and microstructural changes are of importance and need to be optimised, preferably through the use of various modelling approaches. The objective of this article is to provide a brief review of some advances in modelling quality changes of fruits and vegetables during drying. These include modelling of nutritional, colour and selected physical changes. Approaches to monitoring and modelling microstructural changes are also mentioned.     

沈阳地铁和超长地下室结构混凝土规程对膨胀剂及补偿收缩混凝土的控制

本文基于部分调研、实验研究工作,对膨胀剂在当今混凝土工程中的问题进行了初步分析,在此基础上分析了抗裂防水剂比膨胀剂的优势所在;介绍了沈阳市地方标准《地铁混凝土技术规范》、沈阳市建设标准《超长地下室混凝土结构防裂技术规定》对膨胀剂和抗裂防水剂以及补偿收缩混凝土的控制。     

某机组高压外缸开裂原因分析

采用残余应力测试、力学性能测试、断口分析和金相检验等方法分析了某机组ZG15Cr1Mo1V-B2钢高压外缸在泵水时开裂的原因。结果表明:开裂始于高压外缸内表面的补焊区,该区为缩松缺陷密集区,材料塑性指标不符合技术条件要求,导致缺陷处的承载能力下降,应力集中加剧;另高压外缸补焊区的残余应力较大,硬度与基体之间的差异也较大;可见,汽缸在补焊过程中未能将铸造缺陷彻底清除干净,焊接质量不高和焊后去应力处理不充分是造成该高压外缸在泵水时开裂的主要原因。     

Natural Vibrations of Open-Variable Thickness Circular Cylindrical Shells in High Temperature Field

The feasibility of using the transfer matrix method (TMM) to analyze open-variable thickness circular cylindrical shells exposed to a high-temperature field is explored theoretically. In the approach to the problem, the thermal degradation (TG) of thermoelastic characteristics of the material is considered. Natural frequencies and mode shapes for the cylindrical shells are investigated in detail by combining the vibration theory with the TMM. The governing equations of vibration for this system are expressed by the matrix differential equations, and the coefficient matrices are derived. After the relationship between the transfer matrix and the coefficient matrix is established, the fourth-order Runge-Kutta method is used numerically to solve the matrix equation. Once the transfer matrix of single component has been obtained, the product of each component matrix can compose the matrix of the entire structure. The frequency equations and mode shape are formulated in terms of the elements of the structural matrices. Finite-element numerical simulation has validated the present formulas of natural frequencies. Numerical illustrations, supplying pertinent information on the implications of the TG, are presented for various curvatures, aspect ratios, boundary conditions, and thickness ratios, and the pertinent conclusions are outlined.     

Application of a SOM-Based Optimization Algorithm in Minimizing Construction Time for Secant Pile Wall

Construction time matters for activities where rental equipment must be used. The building of a secant pile wall requires the rental of equipment and finding the optimal sequence to minimize the construction time is one way to lower construction costs. In this study we develop an effective and efficient optimization algorithm, which we call self-organizing feature map (SOM)-based optimization (SOMO), to minimize the construction time. The algorithm is applied to a case study to obtain the optimal sequences for both primary and secondary bored piles for a secant pile wall. The new SOMO algorithm is developed based on the ability of the human brain to produce topologically ordered mapping, so as to exploit better solutions via updating the weighting vectors of the neurons in a self-organizing topological way that occurs in the evolution of the feature map for optimization. Given detailed building time of the 16 activities of each bored pile, we find that 143.92 h or 27.21% of the original construction can be saved. The optimal sequences for both primary and secondary bored piles are also determined. The practicability of the SOMO algorithm is substantiated.     

Inclusion of fatigue effects in human reliability analysis

The effect of fatigue on human performance has been observed to be an important factor in many industrial accidents. However, defining and measuring fatigue is not easily accomplished. This creates difficulties in including fatigue effects in probabilistic risk assessments (PRA) of complex engineering systems that seek to include human reliability analysis (HRA). Thus the objectives of this paper are to discuss (1) the importance of the effects of fatigue on performance, (2) the difficulties associated with defining and measuring fatigue, (3) the current status of inclusion of fatigue in HRA methods, and (4) the future directions and challenges for the inclusion of fatigue, specifically sleep deprivation, in HRA.     

Shrinkage, density, porosity and shape changes during dehydration of pumpkin (Cucurbita pepo L.) fruits

The aim of this work was to study the changes in volume, density, porosity and shape factors of pumpkin tissue during osmotic dehydration (OD) and air drying (AD). Pumpkin cylinders with length/diameter ratio of 5/3 were used. OD experiments were carried out with solutions of sucrose, sodium chloride and mixtures of both solutes at different temperatures. AD experiments were conducted at 70 °C. Volume of samples decreased linearly with weight reduction (WR). Bulk density varied in a restricted range (5-13%) during dehydration and for all the methods maximum values were found. Particle density increased during both processes. Porosity increased at advanced degrees of dehydration, showing a minimum value at the beginning of OD and AD. The proposed models to evaluate shrinkage, bulk and particle densities and porosity from WR were satisfactorily applied. Image analysis showed that shrinkage of samples during OD was isotropic. Pumpkin cylinders increased elongation and decreased roundness and compactness during osmotic dehydration.     

山西省电力营销走势及其影响因素分析——以用电量为依据全省前三季度电力营销情况分析

2013年以来,受国内外经济下行压力增大、工业用电减缓特别是高耗能行业用电减少等因素影响,山西全省电力营销增速呈现低速平稳增长趋势.进入三季度,煤炭、焦化等传统行业产销回暖,拉动当月用电增速连续回升,电力营销呈现企稳向好的态势.