An update on thoron exposure in Canada with simultaneous ²²²Rn and ²²⁰Rn measurements in Fredericton and Halifax

Naturally occurring isotopes of radon in indoor air are identified as the second leading cause of lung cancer after tobacco smoking. Radon-222 (radon gas) and radon-220 (thoron gas) are the most common isotopes of radon. While extensive radon surveys have been conducted, indoor thoron data are very limited. To better assess thoron exposure in Canada, radon/thoron discriminating detectors were deployed in 45 homes in Fredericton and 65 homes in Halifax for a period of 3 months. In this study, radon concentrations ranged from 16 to 1374 Bq m(-3) with a geometric mean (GM) of 82 Bq m(-3) and a geometric standard deviation (GSD) of 2.56 in Fredericton, and from 4 to 2341 Bq m(-3) with a GM of 107 Bq m(-3) and a GSD of 3.67 in Halifax. It is estimated that 18 % of Fredericton homes and 32 % of Halifax homes could have radon concentrations above the Canadian indoor radon guideline of 200 Bq m(-3). This conclusion is significantly higher than the previous estimates made 30 y ago with short-term radon measurements. Thoron concentrations were below the detection limit in 62 % of homes in both cities. Among the homes with detectable thoron concentrations, the values varied from 12 to 1977 Bq m(-3) in Fredericton and from 6 to 206 Bq m(-3) in Halifax. The GM and GSD were 86 Bq m(-3) and 3.19 for Fredericton, and 35 Bq m(-3) and 2.35 for Halifax, respectively. On the basis of these results, together with previous measurements in Ottawa, Winnipeg and the Mont-Laurier region of Quebec, it is estimated that thoron contributes ～8 % of the radiation dose due to indoor radon exposure in Canada.     

Prospective safety performance evaluation on construction sites

This paper presents a systematic Structural Equation Modeling (SEM) based approach for Prospective Safety Performance Evaluation (PSPE) on construction sites, with causal relationships and interactions between enablers and the goals of PSPE taken into account. According to a sample of 450 valid questionnaire surveys from 30 Chinese construction enterprises, a SEM model with 26 items included for PSPE in the context of Chinese construction industry is established and then verified through the goodness-of-fit test. Three typical types of construction enterprises, namely the state-owned enterprise, private enterprise and Sino-foreign joint venture, are selected as samples to measure the level of safety performance given the enterprise scale, ownership and business strategy are different. Results provide a full understanding of safety performance practice in the construction industry, and indicate that the level of overall safety performance situation on working sites is rated at least a level of III (Fair) or above. This phenomenon can be explained that the construction industry has gradually matured with the norms, and construction enterprises should improve the level of safety performance as not to be eliminated from the government-led construction industry. The differences existing in the safety performance practice regarding different construction enterprise categories are compared and analyzed according to evaluation results. This research provides insights into cause–effect relationships among safety performance factors and goals, which, in turn, can facilitate the improvement of high safety performance in the construction industry.     

An ergonomic analysis framework for construction tasks

This paper presents a new methodology for obtaining a quantitative measure of human task performance complexity and effort on the construction site. An example application of the developed methodology to the analysis of concrete placement tasks is provided. The developed method can be used to aid construction equipment manufacturers in understanding and assessing the automation potential for a variety of construction work tasks.     

Decision support analysis for safety control in complex project environments based on Bayesian Networks

This paper presents a novel and systemic decision support model based on Bayesian Networks (BN) for safety control in dynamic complex project environments, which should go through the following three sections. At first, priori expert knowledge is integrated with training data in model design, aiming to improve the adaptability and practicability of model outcome. Then two indicators, Model Bias and Model Accuracy, are proposed to assess the effectiveness of BN in model validation, ensuring the model predictions are not significantly different from the actual observations. Finally we extend the safety control process to the entire life cycle of risk-prone events in model application, rather than restricted to pre-accident control, but during-construction continuous and post-accident control are included. Adapting its reasoning features, including forward reasoning, importance analysis and background reasoning, decision makers are provided with systematic and effective support for safety control in the overall work process. A frequent safety problem, ground settlement during Wuhan Changjiang Metro Shield Tunnel Construction (WCMSTC), is taken as a case study. Results demonstrate the feasibility of BN model, as well as its application potential. The proposed model can be used by practitioners in the industry as a decision support tool to increase the likelihood of a successful project in complex environments.     

Hydrothermal Crystallization of Zirconia and Zirconia Solid Solutions

Zirconia as well as yttria-zirconia and calcia-zirconia solid-solution powders were crystallized under hydrothermal conditions from (co)precipitated hydroxides. The morphology of the powder particles is strongly dependent on the crystallization conditions. The powders crystallized in a water solution of Na, K, and Li hydroxides show elongated particles of much larger sizes than those which result from the process carried out in pure water or a water solution of Na, K, or Li chlorides. The shapes of the latter particles are isometric. The growth mechanism of the elongated particles is suggested.     

Position‐Force Adaptive Control for Construction Robots

Typical tasks in construction engineering that can be performed by robots include the spraying or cleaning of surfaces. Both applications require that the external force at the end effector of the manipulator be properly controlled. In this paper, the force‐control problem in spraying is analyzed. The paper shows that an unpredictable jet force causes the end effector to diverge from its desired trajectory. The interface between the end effector of the robot and the jet force is modeled as soft contact because both force error and displacement of the end effector are measurable. Therefore, the force‐control problem is simplified to the position‐control problem. The proposed control scheme, using a position‐force adaptive controller, is applied to counterbalancing a jet force. Computer simulation demonstrates that the scheme works well. The maximal position error can be controlled to within 4 mm with the new controller.     

The influence of gaseous chlorine on the chemical and catalytic properties of alumina

The influence of gaseous chlorine on the chemical and catalytic properties of alumina was investigated. Cl₂ reacts both with surface OH groups and with surface oxygen anions possessing electron-donating power, forming new surface sites. When such chlorine treatment is performed at a low temperature (293 K), both Lewis and Bronsted acid centres are formed. High temperature chlorination leads exclusively to Lewis acid sites. It is proposed that such Lewis sites are responsible for olefin isomerization reactions.     

Influence of Plasma Waves on the Photoacoustic Signal of Silicon Samples

This article presents the results of theoretical and experimental studies of the influence of plasma waves on the photoacoustic signals of Si samples. The aim of these investigations was to find and examine the sensitive measurement configurations and the configurations of the sample in the photoacoustic cell for detection and measurement of the lifetime of excess carriers. Two measurement configurations were examined: transmission and phase lag and two configurations of the sample in the photoacoustic cell. This article demonstrates that both configurations for samples with differently prepared surfaces are effective for observation and detection of plasma waves with the photoacoustic method.     

Effect of spark timing and load on a DISI engine fuelled with 2,5-dimethylfuran

Currently, bioethanol leads the automotive fuel market as the main substitute for gasoline in spark-ignition engines. However, worldwide interest has been triggered in the potential of 2,5-dimethylfuran, known as DMF, since the discovery of improved production methods. Although the energy content of DMF is comparable to that of gasoline, little is known about its combustion characteristics and emissions. Therefore, this work examines the effect of DMF in a single cylinder direct-injection spark-ignition engine. The results are compared to ethanol and gasoline using the optimized spark timings for gasoline and the respective fuel. In summary, DMF produces competitive combustion and emissions qualities to gasoline, which, in some cases surpass ethanol. The two biofuels have a higher burning rate and lower initial combustion duration than gasoline. They also produce greater combustion efficiency, which helps to lower hydrocarbon and carbon monoxide emissions. These initial results highlight how DMF, which was originally only considered as an octane improver, has the potential to become a competitive renewable gasoline alternative.