Limits of thermoluminescence dosimetry using quartz extracted from recent building materials in urban settlements

The luminescence of quartz extracted from recently fired building material is known to detect doses of few mGy and can be successfully employed in the case of large scale radiation exposures due to nuclear accidents or terrorist acts. One brick and two tiles (50-80 years range) collected from an urban settlement were used to test the realistic minimum detectable dose limits of retrospective luminescence dosimetry. Independent methods like alpha counting, beta dosimetry, gamma spectrometry and flame photometry were used for the annual dose assessment. Two approaches were employed for the evaluation of the total accrued dose: regenerative dose and additive dose. The former allows the assessment of doses due to anthropogenic sources of radiation as low as approximately 12 mGy by using 10-year-old samples, but it can be applied only in samples showing no sensitisation. The latter can be applied to any sample, however, the related uncertainty is higher and minimum detectable anthropogenic dose in young samples amounts to 20 mGy.     

Uptake of deuterium by dead leaves exposed to deuterated water vapor in a greenhouse at daytime and nighttime

Dead leaves were exposed to deuterated water vapor (D(2)O) as a substitute of tritiated water (HTO) in a greenhouse at daytime and nighttime to examine uptake and release of tritium by dead leaves because they cover a wide area of the forest floor and are therefore a major target material to be exposed when HTO is atmospherically derived to the forest. The dead cedar needles showed faster uptake and faster release rates during and after the exposure than the fresh ones, and the equilibrium concentration of the dead cedar needles was about two times higher than the fresh ones, indicating a quick response and a high buffering potential of dead leaves. The relation between uptake of D(2)O and number of stoma was examined for dead deciduous leaves; the species with larger number of stoma accumulated more D(2)O at the daytime and nighttime exposures. However, drying of the dead leaves suppressed D(2)O uptake greatly at daytime, suggesting stomata's opening and closing controls the D(2)O uptake of dead leaves.     

Anthropogenic radionuclides in sediment in the Japan Sea: distribution and transport processes of particulate radionuclides

Distributions of anthropogenic radionuclides ((90)Sr, (137)Cs and (239+240)Pu) in seabed sediment in the Japan Sea were collected during the period 1998-2002. Concentration of (90)Sr, (137)Cs and (239+240)Pu in seabed sediment was 0.07-1.6 Bq kg(-1), 0.4-9.1 Bq kg(-1) and 0.002-1.9 Bq kg(-1), respectively. In the northern basin of the sea (Japan Basin), (239+240)Pu/(137)Cs ratios in seabed sediment were higher and their variation was smaller compared to that in the southeastern regions of the sea. The higher (239+240)Pu/(137)Cs ratios throughout the Japan Basin were considered to reflect production of Pu-enriched particles in the surface layer and substantial sinking of particulate materials in this region. In the southern regions of the Japan Sea (<38 degrees N), both inventories and (239+240)Pu/(137)Cs ratios in sediment were larger than those in the other regions. In the southern Japan Sea, observations suggested that supply of particulate radionuclides by the Tsushima Warm Current mainly enhanced accumulation of the radionuclides in this region.     

Joint analysis of process and operator performance in chemical process operational safety

Independent studies of case histories by the Health and Safety Commission in the UK and by a Honeywell led industrial consortium world-wide showed that human errors represent the major cause of failure in process plant operation. In contrast to this discovery the majority of previous studies on computer aided systems for fault detection and diagnosis has focused on the process side. This paper presents a methodology, which can involve human factors into the development of systems for automatic identification and diagnosis of abnormal operations and develops methods and techniques that can be used to simultaneously capture, characterise and assess the performance of operators as well as of the process. A joint process–operator simulation platform is developed which is used as a test-bed for carrying out the study. The process part is a simulator, which simulates in high fidelity the dynamic behaviour of the process that is subject to the influence of various disturbances and operators’ interventions. The operator module is developed as a real-time expert system, which emulates operator’s behaviour in interpretation of received signals, and planning and execution of decisions. The interaction between the two modules is managed through an interaction module, which handles the real-time exchange of data using Dynamic Data Exchange. The interaction module also contains the toolkits for analysing the dynamic behaviour of the joint process–operator system. The method and system are illustrated using a simulated case study.     

造船用双角钢式脚手架的危险点电测

对角钢式脚手架进行应力测试和理论计算研究.采用电测法测试了危险截面的应力大小及分布规律.结果表明,2、4测点是危险点;采用斜弯曲理论进行理论计算,所得结论与实验测试是一致的,其中2点受拉应力作用.上述分析为脚手架的设计、制作和安全使用提供了强度分析依据.同时还对脚手架其他安全问题进行了讨论.     

Quantitative indicator of homeostatic risk perception in car following

Driving behavior is largely affected by the risk perception of drivers. On the basis of risk homeostasis theory, we regard that drivers may adjust car movement according to the perceived risks fluctuating around a target level. However, the manner by which risk perception is quantified remains unclear. We propose assumptions on the quantitative indicators of risk perception and identify a suitable quantitative indicator of risk perception in car-following process. Three risk indicators are discussed, i.e. time-to-collision (TTC), time headway (TH), and safety margin (SM). Using homeostatic features as bases, we found that SM more suitably quantifies homeostatic risk perception than TTC or TH does. Data collected from video drive recorders installed in taxis operating in Beijing are used to analyze the target risk level of SM (desired SM, or DSM) of professional drivers during the car-following process. The data collected by Ahn et al. (2004) to verify Newell’s model are converted into DSM data to further analyze the target risk level of general drivers. The DSM histogram of professional drivers shows that the standard deviation of the DSM value is 0.115, with a mean value of 0.862 and a total distribution close to the normal distribution. For a general driver, the mean value of DSM is 0.896, which is higher than that of professional drivers. This research may shed lights on the understanding of driving behavior.     

Biohydrogen production using waste activated sludge as a substrate from fructose-processing wastewater treatment

Biohydrogen production by dark fermentation in a series of batch tests under different environmental control conditions was evaluated to determine the optimal initial cultivation pH and temperature for a continuous-flow kinetic test to validate the kinetic model system. The waste activated sludge (WAS) from fructose-processing manufacturing was used as the model substrate for biohydrogen production. The batch experiments for biohydrogen production were conducted in a 6 l bioreactor. Fifteen batch kinetic tests were investigated when pH was controlled at 6, 7, 8 and 9 as well as the temperature was controlled at 37 °C, 45 °C and 55 °C, respectively. The experimental results indicated that the optimal operational condition for hydrogen production occurred while pH was 7 and temperature was 55 °C with the highest hydrogen production of 7.8 mmol. The optimal recovery time for hydrogen was 25 h in the batch experiments. Furthermore, the kinetic test of biohydrogen production was performed by anaerobic mixed microbial culture in the continuous-flow experiment when pH and temperature was maintained at 7 and 55 °C. Approximately 60% and 7% of substrate solution was converted into acetate and hydrogen, respectively, at the steady state. Roughly only 0.77% and 2.7% of substrate solution was converted into propionate and butyrate, respectively, at a steady-state condition. The experimental and modeling approaches presented in this study could be employed for the design of pilot-scale and full-scale anaerobic biohydrogen fermentors using food-processing waste activated sludge (WAS) as a substrate solution.     

基于满意度的热风炉变论域模糊控制

针对热风炉具有参数时变、强干扰、非线性等特点,其最佳空燃比难以确定的问题,提出一种基于模糊满意度的变论域模糊控制方法。首先通过在线获得加热过程的状态参数,采用满意度函数对空燃比进行评价,并将该评价结果和炉温变化作为变论域模糊控制方法的输入来实时获取最优的空燃比值,从而保证热风炉炉温的温度控制。实际运行结果证实了该系统的有效性。     

可燃气体燃爆特性综合试验装置构建与甲烷试验

为研究半开敞空间内可燃气体爆炸过程,设计带有泄压面的气体爆炸室,并在此基础上构建一套可燃气体燃爆特性综合试验装置。运用该试验装置,研究预混塔内甲烷气体分层现象以及甲烷爆炸浓度与最小点火能之间的变化规律。甲烷分层试验结果表明:静置一段时间后,预混塔中甲烷浓度随高度的增加而增大。最小点火能试验结果显示,当甲烷的试验爆炸体积分数在10%～13%时,其浓度与点火能之间呈现比较平缓的变化关系,而当其体积分数小于10%或大于13%时,浓度稍微变化,其点火能将发生明显变化。     

基于数值模拟的城市中心区风环境研究

利用CFD软件对长沙市中心区典型区域的风环境进行了三维数值模拟研究。结果表明,城市建筑群布局不当会造成多方面不利影响:如建筑群内局部地区气流不畅,污染物难以扩散,影响市民身体健康;街道峡谷风使得行人行动不便,冬季热舒适感差;复杂的风环境可能造成建筑构件的损坏乃至脱落,对地面行人的安全造成威胁;建筑围护结构渗透风增加造成建筑能耗的增加。在城市规划和建设中,中心区风环境状况要引起足够的重视,在建设之前要进行风环境模拟与评估。