中小锅炉爆炸事故规律分析与研究

为研究中小型锅炉爆炸事故的规律,对中小型锅炉爆炸案例进行调查和分析,并进行了缺水再进水试验和炉胆失稳模拟试验。研究认为,爆炸主要原因是缺水和超压,缺水造成材料性能下降明显,进水汽化造成锅内压力骤升,并给出了立式锅炉爆炸机理。从锅炉结构、水容积、安全附件等方面的爆炸事故因素考虑,对3种中小型锅炉进行安全性分析,并提出了事故预防措施。     

Effects of Two Amphibian Pathogens on the Developmental Stability of Green Frogs

Abstract: Developmental instability, measured as fluctuating asymmetry (FA), is often used as a tool to measure stress and the overall quality of organisms. Under FA, it is assumed that control of symmetry during development is costly and that under stress the trajectory of development is disturbed, resulting in asymmetric morphologies. Amphibian emergent infectious diseases (EIDs), such as Ranavirus and chytrid fungus, have been involved in several mortality events, which makes them stressors and allows for the study of FA. We analyzed nine populations of green frogs (Rana clamitans) for the presence or absence of Ranavirus and chytrid fungus. Individuals were measured to determine levels of FA in seven traits under the hypothesis that FA is more likely to be observed in individuals infected by the pathogens. Significantly higher levels of FA were found in individuals with Ranavirus compared with uninfected individuals among all populations and all traits. We did not observe FA in individuals infected with chytrid fungus for any of the traits measured. Additionally, we observed a significant association between Ranavirus infection and levels of FA in both males and females, which may indicate this viral disease is likely to affect both sexes during development. Altogether, our results indicate that some EIDs may have far‐reaching and nonlethal effects on individual development and populations harboring such diseases and that FA can be used as a conservation tool to identify populations subject to such a stress.     

CHANNEL INSTABILITY IN THE LOESS AREA OF THE MIDWESTERN UNITED STATES1

ABSTRACT: The bess area of the midwestern United States contains thousands of miles of unstable stream channels that are undergoing system‐wide channel‐adjustment processes as a result of (1) modifications to drainage basins dating back to the turn of the 20th century, including land clearing and poor soil‐conservation practices, which caused the filling of stream channels, and consequently (2) direct, human modifications to stream channels such as dredging and straightening to improve drainage conditions and reduce the frequency of out‐of‐bank flows. Today, many of these channels are still highly unstable and threaten bridges, other structures, and land adjacent to the channels. The most severe, widespread instabilities are in western Iowa where a thick cap of bess and the lack of sand‐and gravel‐sized bed sediments in many channels hinders downstream aggradation, bed‐level recovery and the consequent reduction of bank heights, and renewed bank stability. In contrast, streams draining west‐central Illinois, east‐central Iowa, and other areas, where the bess cap is relatively thin and there are ample supplies of sand‐and gravel‐sized material, are closer to recovery. Throughout the region, however, channel widening by mass‐wasting processes is the dominant adjustment process.     

Flame acceleration in unconfined hydrogen/air deflagrations using infrared photography

Flame behavior and blast waves generated during unconfined hydrogen deflagrations were experimentally studied using infrared photography. Infrared photography enables expanding spherical flame behaviors to be measured and flame acceleration exponents to be evaluated. In the present experiments, hydrogen/air mixtures of various concentrations were filled in a plastic tent of thin vinyl sheet of 1 m³ and ignited by an electric spark. The onset of accelerative dynamics on the flame propagation was analyzed by the time histories of the flame radius and the stretched flame speed. The results demonstrated that the self-acceleration of the flame, which was caused by diffusional-thermal and hydrodynamic instabilities of the blast wave, was influenced by hydrogen deflagrations in unconfined areas. In particular, it was demonstrated that the overpressure rapidly increased with time. The burning velocity acceleration was greatly enhanced with spontaneous-turbulization.     

自然崩落法顶板稳定性监测分析与预警研究*

为有效预警自然崩落法开采过程中顶板大面积崩落,确定顶板失稳预警期,基于微震、时域反射、钻孔电视等综合监测数据,研究岩体失稳过程点监测数据及微震活动性参数变化特征。结果表明:基于多源参数可有效预警顶板失稳事件,但点监测无法兼顾整个采区顶板,大尺度区域性监测主要依靠微震监测系统;根据顶板失稳事件前后b值、累积视体积、能量指数、施密特数等微震活动性参数变化特征,确定普朗铜矿顶板失稳预警期为24 d。研究结果可为后续整个采区其他区域顶板稳定性监测预警工作提供借鉴。     

基于微震监测的岩体失稳智能预报

岩体稳定性预报是微震监测工作的重要组成部分。探讨微震活动性参数变化作为岩体稳定性预测的可行性,结合用沙坝矿实际生产过程中观测到的现象,提出微震监测岩体失稳预报的一般模式。根据b值在岩体失稳前先增大后减小的趋势作为危险预警初始条件;并将能量指数、施密特数急剧下降以及累积视体积增加的时间段作为岩体失稳的预警期,将事件数的急剧下降作为危险的临界状态。用沙坝矿根据这一原理建立的岩体失稳预报模式可以达到采场失稳的智能预报,解决了人工判别预警期过程中效率低的难题,保障矿山的生产工作。     

煤层钻孔失稳机理研究进展

高瓦斯松软煤层、软硬复合煤层和突出煤层深孔钻进是公认的世界性难题,已成为制约部分高瓦斯和突出矿井瓦斯治理效果的瓶颈。尽管众多研究者在钻孔施工装备及工艺的改进方面开展了大量卓有成效的工作,但因煤层钻孔失稳机理尚未完全揭示,钻孔成孔工艺缺乏理论支撑,上述难题至今仍未破解。从煤体结构判识及分类、含流体煤力学特性、失稳机理三方面入手,系统介绍了煤层钻孔失稳机理的研究进展,探讨了该领域亟待解决的问题;最后指出,含流体煤卸载过程中,煤层钻孔在流-固-应力耦合作用下的失稳破坏机制研究,是破解煤层深孔钻进难题的重点方向之一。     

气体钻井突发性井壁失稳动力演化机理及试验研究

从致密砂岩损伤破坏的角度出发,综合考虑致密砂岩的物理力学性质、地应力、裂缝圈闭高压等因素,在分析孔隙压力、地应力、裂缝圈闭高压在突发性井壁失稳过程中所起的作用基础上,将气体钻井突发性井壁失稳具有强烈时间效应的动态力学过程分为孕育、突变、井筒运移和终止4个阶段。对裂缝圈闭高压、地应力作用下致密砂岩的加速损伤演化引起的突发性井壁失稳机理进行了阐述,裂缝圈闭高压是突发性井壁失稳的主要动力源,地应力对突发性井壁失稳起辅助作用。通过模拟实验表明,受地应力破坏后的致密砂岩岩体在有裂缝情况下,卸压初始时刻释放的能量是无裂缝时的5~10倍,且该能量与动力学失稳密切相关。     

基于H-K体的矿柱流变顶板破坏分析

为了研究空场法采空区稳定性,确定特定形态采空区稳定时间,以H-K体作为岩体本构模型,对矿柱流变引起的顶板沉降变形进行了计算分析,根据顶板边界破坏条件,将空区顶板沉降过程划分为3个阶段并分别求解了各阶段持续时间,并对尚旺庄石膏矿灾害事故进行了计算验证,结果表明,计算结果与实际失稳时间吻合良好。所得结论可为稳定空区提供稳定性评估及稳定时间预测依据,或指导老空区进行安全有效的顶板监测工作,最大化节约矿山在顶板监测工作中投入的人力、物力。     

The effect of thermal instability of intact human chorionic gonadotropin (ihcg) on the application of its free β-subunit (free βhcg) as a serum marker in down syndrome screening

The kinetics of free βhCG concentrations were measured in 30 maternal whole blood samples from second-trimester pregnancies during 72 h incubation at 3, 20, and 30°C. Dissociation of intact hCG (ihCG) was undetectable at 3°C and produced a more than 20 per cent increase of free βhCG at 20°C and a more than 100 per cent increase at 30°C. hCG dissociation at 30°C was not reduced by a protease inhibitor (sodium iodoacetate) and also occurred in purified hCG dissolved in a protease-free incubation medium. These results were reproduced under conditions of sample transport by post at different environmental temperatures. In conclusion, reliable free βhCG assessment requires that the specimen be kept cool from vene puncture until assay or completely other transport strategies have to be considered. Evaluation of free βhCG as an effective marker in prenatal Down syndrome screening must be reconsidered from this aspect.