新型含能化合物的热危险性计算预测

简要介绍了含能材料的热危险性评价,进而提出了一套用于计算预测热危险性的方法,并对高能量密度化合物、有机叠氮化合物、笼形多硝基烷烃化合物进行了热危险性预测.结果表明,目前常见高能量密度化合物的热危险性均小于NG.在选取的有机叠氮化合物中叠氮乙酰的热危险性较大,对甲基叠氮苯热危险性相对较小.立方烷和金刚烷上引人硝基后,热危险性增大,并随硝基数量的增多而增大.该计算方法和预测结果对评估含能材料热危险性有一定的参考意义.     

不同空间尺度的景观结构对袁河浮游细菌群落的影响

为分析不同空间尺度的土地利用与浮游细菌群落的关系以及土地利用对细菌群落的影响机制.于2019年8月(丰水期)和2020年1月(枯水期)在袁河14条支流采集表层水样,基于高通量测序技术确定浮游细菌群落的特征,采用Bioenv和方差分解(VPA)等统计方法分析了不同空间尺度的景观结构(景观组成与景观格局)、水化学特征和浮游...     

Green Chemistry - Views and Strategies * (5 pp)

Background and Goal The object of Green Chemistry is the reduction of chemical pollutants flowing to the environment. The Chemistry and the Environment Division of EuCheMS has assumed Green Chemistry as one of its areas of interest, but one question to solve is where Green Chemistry should be placed within the context of Chemistry and the Environment. The concept of Green Chemistry, as primarily conceived by Paul Anastas and John Warner, is commonly presented through the Twelve Principles of Green Chemistry. However, these Twelve Principles, though fruit of a great intuition and common sense, do not provide a clear connection between aims, concepts, and related research areas of Green Chemistry. These two unsolved questions are the object of the present article.Discussion Green Chemistry is here placed as a part of Chemistry for the Environment, concerning the still non-existent pollutants. Indeed, the object of Green Chemistry is the reduction of pollution and risks by chemicals by avoiding their generation or their introduction into the biosphere. The distinction between pollutant chemicals and dangerous chemicals, along with the consideration of the exhaustion of fossil resources and the acknowledgement of the harmful effects of the chemicals employed in a great variety of activities, leads to the recognition of four general objectives for Green Chemistry. In order to accomplish these general objectives, a number of strategies, or secondary objectives and some fundamental concepts, namely, atomic economy, selectivity, potential harm or historical harm can be visualized. A connection is finally established between the strategies and current and future research areas of Green Chemistry.Conclusion The ultimate aim of green chemistry is to entirely cut down the stream of chemicals pouring into the environment. This aim seems unattainable at present, but progress in the green chemical research areas and their application through successive approaches will certainly provide safer specialty chemicals and much more satisfactory processes for the chemical industry.- * The basis of this peer-reviewed paper is a presentation at the 9th FECS Conference on ‘Chemistry and Environment’, 29 August to 1 September 2004, Bordeaux, France.     

Numerical study of the effect of obstacles on the spontaneous ignition of high-pressure hydrogen

A numerical simulation of the spontaneous ignition of high-pressure hydrogen in a duct with two obstacles on the walls is conducted to explore the spontaneous ignition mechanisms. Two-dimensional rectangular ducts are adopted, and the Navier–Stokes equations with a detailed chemical kinetic mechanism are solved by using direct numerical simulations. In this study, we focus on the effects of the initial pressure of hydrogen and the position of the obstacles on the ignition mechanisms. Our results demonstrate that the presence of obstacles significantly changes the spontaneous ignition mechanisms producing three distinct ignition mechanisms. In addition, the position of the obstacles drastically changes the interaction of shock waves with the contact surface, and spontaneous ignition may take place at a relatively low pressure in some obstacle positions, which is attributed to the propagation direction and interaction timing of two reflected shock waves.     

地铁站火灾时空气幕防烟的数值模拟与分析

随着国内地铁的迅速发展,地铁火灾的防范及应急处理成为重要的研究课题。笔者根据地铁站建筑结构特点及火灾烟气的扩散规律,首次提出将空气幕用于地铁站楼梯口防烟,以保障火灾时人员的安全疏散。并用CFD方法模拟分析一列地铁列车着火时,防烟空气幕对烟气扩散的控制。结果表明,在楼梯口设置防烟空气幕不仅可以保证人员在6分钟以上的安全疏散时间,而且减少了比传统方式所需的新鲜空气量,有效阻止火灾的进一步扩大和控制烟气扩散。     

Optimization of dilution ventilation layout design in confined environments using Computational Fluid Dynamics (CFD)

Dilution ventilation systems have been widely used to control the airborne toxic and explosive material in confined spaces. Layout design of dilution ventilation is critical to industrial hygiene control and ventilation efficiency. A properly designed dilution ventilation system can significantly improve the safety of confined workshops and maintain a comfortable work condition. In this work, Computational Fluid Dynamics (CFD) has been used to analyze the performance of dilution ventilation system in the confined workshop environment. Seven different ventilation layouts are proposed to evaluate ventilation performance of different installation layouts. Carbon monoxide (CO), which has the similar density as air, is selected as the sample contaminant to conduct steady-state CFD simulations. The simulation results of different layouts are examined and compared to get the optimal layout design for the best contaminant control. Results have shown that the layout with two opposite inlets has the highest ventilation efficiency among seven proposed layouts. This work can serve as a reference to increase dilution ventilation efficiency and minimize the energy cost in general confined areas.     

A method for double-sided friction stir spot welding

A rotating anvil similar to a pinless friction stir welding (FSW) tool can be applied to friction stir spot welding (FSSW) of thin metal plates. FSSW is a solid-state joining process that is currently being used by automotive manufacturers as an alternative to rivets and traditional resistance spot welding. The principal detractor of this process is the keyhole left by pin extraction, which can be detrimental to the weld strength. A pinless tool can be used to eliminate the keyhole. However, this approach is limited to joining thin sheet (≤1 mm). Using a rotating anvil with the FSSW process permits the joining of thicker cross sections, improves the mechanical strength of the spot weld and reduces the reaction forces on the spot welding frame. A numerical model of the process, tensile shear tests and macrosection analysis are used to evaluate the spot welds.Macrosection and numerical analysis reveals that the material flow between the pinless tool and rotating anvil is complex and unique to this process. It has been found that the use of a rotating anvil for FSSW is a viable means to create quality spot welds in thicker weldments.     

中国降水酸度和离子浓度的时空分布

1991～1995年在全国进行了酸雨观测,建立了覆盖全国的具有区域代表性的酸沉降监测网,含271个测站?降水的pH值和电导率在现场采样后立即测量,降水样品的化学分析则在实验室里进行?主要离子SO2-₄,NO-₃,NH+₄,Ca2+浓度的加权均值分别为125.86,19.96,67.89和80.41μeq/L?由离子浓度地理分布图看出,这些离子浓度地理分布状况因离子而异?值得注意的是降水中SO2-₄和NO-₃浓度,北方非酸雨区甚高于南方酸雨区,这说明降水的酸度并不简单地决定于降水中SO2-₄和NO-₃的绝对浓度,而决定于这些离子对于Ca2+和NH+₄的相对浓度?发现了降水年均pH值低至4的一些地区,此值可能是目前世界年降水酸性最强的地区?文中还对代表性地区1986～1993年降水化学特征进行了分析,结果表明降水的酸度仍在升高?      

3D geometric structures and biological activity: Application to microbial soil organic matter decomposition in pore space

During the past 10 years, soil scientists have started to use 3D Computed Tomography in order to gain a clearer understanding of the geometry of soil structure and its relationships with soil properties. We propose a geometric model for the 3D representation of pore space and a practical method for its computation. Our basic idea consists in representing pore space using a minimal set of maximal balls (Delaunay spheres) recovering the shape skeleton. In this representation, each ball could be considered as a maximal local cavity corresponding to the “intuitive” notion of a pore as described in the literature. The space segmentation induced by the network of balls (pores) was then used to spatialize biological dynamics. Organic matter and microbial decomposers were distributed within the balls (pores). A valuated graph representing the pore network, organic matter and distribution of micro-organisms was then defined. Microbial soil organic matter decomposition was simulated by updating this valuated graph. The method was implemented and tested using real CT images. The model produced realistic simulated results when compared with data in the literature in terms of the water retention curve and carbon mineralization. A decrease in water pressure decreased carbon mineralization, which is also in accordance with findings in the literature. From our results we showed that the influence of water pressure on decomposition is a function of organic matter distribution in the pore space. As far as we know, this is the approach to have linked pore space geometry and biological dynamics in a formal way. Our next goal will be to compare the model with experimental data of decomposition using different soil structures, and to define geometric typologies of pore space shape that can be attached to specific biological and dynamic properties.     

燃煤痕量元素转化、排放及控制的研究进展

综述了煤燃烧过程中痕量元素转化、排放规律及实用的控制技术,重点介绍了当前最受关注的汞排放控制技术,并反映了量子化学在燃煤痕量元素研究中的最新应用。分析了燃煤痕量元素研究存在问题及发展方向。