吸气式管道尺寸及温差对烟颗粒输运的影响

在火灾标准燃烧室中,用扫描电迁移粒谱仪测量单孔采样的吸气管道内5种标准试验火烟雾颗粒浓度和粒径分布的变化,分析管道输运中管道参数对烟颗粒数目浓度损耗和中位径的影响.结果表明,在管道输运中,平均粒径相对较小的热解和阴燃烟雾颗粒.其小于0.1μm的超细颗粒部分的浓度损耗随管道长度的增加而增大,且烟颗粒平均粒径随管道增长而增大.而明火烟雾在管道输运中,由于管道与高温烟雾的温差增大,导致0.1～1 μm颗粒的管壁沉积损耗增大,使烟颗粒数浓度下降,中位径减小了几个纳米.火灾早期,火灾阴燃和热解期间小于0.1 μm的烟颗粒数目浓度占15%以上,因此,用较短的管道或者管道分级预警的方式可以减少滞留时间,提高极早期感烟探测的灵敏度.     

Effect of shock strength on dust entrainment behind a moving shock wave

Secondary dust explosion is a serious industrial issue because it occurs under conditions corresponding to an increased quantity and concentration of dispersed, combustible dust when compared with the primary explosion. The problems of lifting and dispersion of a dust layer behind a propagating shock wave must therefore be understood to ensure safety regarding secondary dust explosion hazards. Using a new shock-tube facility for studying shock propagation over dust layers, limestone dust was subjected to Mach numbers ranging from 1.10 to 1.60. A shadowgraph technique was applied by using a high-speed camera (15,000 fps) for visualization of the dust-layer height change behind the moving shock wave. Also, the effect of dust-layer thickness on the entrainment process was observed by performing tests with two different layer depths, namely 3.2- and 12.7-mm thicknesses. New correlations were developed between the shock strength and the dust entrainment height as a function of time for each layer depth. In general, the results herein are in agreement with trends found in previous work, where there is a linear relationship between dust growth rate and shock Mach number at early times after shock passage. Also, new data were collected for image analyses over longer periods, where the longer observation time and higher camera framing rates led to the discovery of trends not previously observed by earlier studies, namely a clear transition time between the early, linear growth regime and a much-slower average growth regime. This second regime is however accompanied by surface instabilities that can lead to a much larger variation in the edge of the dust layer than seen in the early growth regime. In addition, for the linear growth regime, there was no significant difference in the dust-layer height growth between the two layer thicknesses; however, the larger thickness led to higher growth rates and much larger surface instabilities at later times.     

Development of the vertebrate central nervous system: formation of the neural tube

The developmental process of neurulation involves a series of coordinated morphological events, which result in conversion of the flat neural plate into the neural tube, the primordium of the entire central nervous system (CNS). Failure of neurulation results in neural tube defects (NTDs), severe abnormalities of the CNS, which are among the commonest of congenital malformations in humans. In order to gain insight into the embryological basis of NTDs, such as spina bifida and anencephaly, it is necessary to understand the morphogenetic processes and molecular mechanisms underlying neural tube closure. The mouse is the most extensively studied mammalian experimental model for studies of neurulation, while considerable insight into underlying developmental mechanisms has also arisen from studies in other model systems, particularly birds and amphibians. We describe the process of neural tube formation, discuss the cellular mechanisms involved and highlight recent findings that provide links between molecular signaling pathways and morphogenetic tissue movements. Copyright © 2009 John Wiley & Sons, Ltd.     

软岩隧道自旋锚管抗拔力的计算理论

在软岩隧道支护中,大多数情况下需要向上钻孔打锚杆,目前应用较多的中空注浆锚杆和砂浆锚杆在向上打锚杆的情况下,均存在注浆不饱满及不能形成快速初锚力的问题,影响支护效果和工程安全。自旋注浆锚管能比较好的解决上述工程中存在的技术缺陷。在软岩隧道支护中,自旋注浆锚管的抗拔力是至关重要的技术参数,关系到锚固体系的安全。本文根据自旋注浆锚管的结构特点和作用机理,对其抗拔力的计算理论进行了探讨,对实际支护工程有一定的参考作用。     

家具企业喷涂过程呼吸防护技术应用研究

随着家具行业持续高速发展和从业人数的不断增加,家具企业职业危害的严峻性也日益突显,职业危害预防、控制也越来越受重视。喷涂作为家具表面处理的重要工艺,其作业过程产生的漆雾和挥发性有机化合物更是直接威胁到职工的健康安全。基于对家具企业喷漆作业场所的有毒、有害因素分析研究的基础上,从个体职业危害防护的角度,提出适用于家具企业喷漆过程的固定式长管呼吸装置防护技术,加强对家具企业职工喷漆作业的劳动保护,实现职业危害的预防控制。     

Attenuation of a point blast shock wave in the dusty air

The behavior of the blast impulse initiated by a point blast in the dusty air is investigated theoretically. It is shown that the jumps of parameters at the shock front in the dusty air follow other regularities in comparison with the case of an ideal gas, beginning from the distance of three dynamic radii, so at ten dynamic radii the difference in overpressure exceeds 60%. When the air heterogeneity is taken into account, substantial gradual changes of wave profile come over and the total blast wave impulse can't be determined by the front overpressure only. The known far asymptotic law takes no place in the point blast flow at the volume dust densities ρ₂₀ > 3·10^?3 kg/m³. In contrast to the ideal gas, the shock front discontinuity vanishes in the dusty air at a finite distance from its origin and the blast wave eventually turns into a dispersive wave without discontinuity. The wave structure changing is studied in the process of the shock wave transformation into the dispersive wave.     

火灾后配筋圆钢管混凝土柱剩余承载力数值分析

研究配筋圆钢管混凝土轴压短柱火灾后剩余承载力。利用ABAQUS有限元分析软件建立了ISO-834标准升温曲线升温作用下配筋圆钢管混凝土短柱温度场模型,基于温度场分析结果建立了配筋圆钢管混凝土轴压短柱力学分析模型,利用以往试验结果对模型进行了验证,计算结果与实验结果吻合良好。在此基础上进行了火灾后配筋圆钢管混凝土轴压短柱剩余承载力参数分析,选用的参数包括：升温时间、混凝土强度、钢管强度、钢筋强度、含钢率、配筋率、构件截面尺寸等。研究结果表明：在本次参数范围内,在其它条件相同的情况下,与常温下的承载力相比,受火时间越长,截面尺寸越小,构件火灾后剩余承载力的损失越高。结果可供有关钢管混凝土工程火灾后修复加固参考。