Explosibility of micron- and nano-size titanium powders

Explosibility of micron- and nano-titanium was determined and compared according to explosion severity and likelihood using standard dust explosion equipment. ASTM methods were followed using a Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven. The explosibility parameters investigated for both size ranges of titanium include explosion severity (maximum explosion pressure (P_max) and size-normalized maximum rate of pressure rise (K_St)) and explosion likelihood (minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT)). Titanium particle sizes were ?100 mesh (<150 μm), ?325 mesh (<45 μm), ≤20 μm, 150 nm, 60–80 nm, and 40–60 nm. The results show a significant increase in explosion severity as the particle size decreases from ?100 mesh with an apparent plateau being reached at ?325 mesh and ≤20 μm. Micron-size explosion severity could not be compared with that for nano-titanium due to pre-ignition of the nano-powder in the 20-L chamber. The likelihood of an explosion increases significantly as the particle size decreases into the nano range. Nano-titanium is very sensitive and can self-ignite under the appropriate conditions. The explosive properties of the nano-titanium can be suppressed by adding nano-titanium dioxide to the dust mixture. Safety precautions and procedures for the nano-titanium are also discussed.     

中国城市与农村环境保护的差距比较

文章比较分析了中国城市与农村在环境保护上的主要差距,并探讨了统筹城乡环境保护的对策。结果发现：自1998年以来,中国环境污染治理投资中近52%用于城市基础设施建设;城市与农村环境卫生投资差距平均为6～10倍,东部、中部和西部地区的城乡差距逐渐扩大;城市与农村生活污水处理差距平均为35～59倍,生活垃圾处理差距为7～17倍,城乡环境保护基础设施差距基本符合东中西部逐渐扩大的趋势;此外,乡镇环境保护机构仅占环保机构总数的4%～15%,乡镇环境保护人员仅占1%～4%,其中东部、西部和中部乡镇环保机构与人员所占比例均依次减小。因此中国城乡生态环境保护存在巨大差距,亟需在城乡功能的合理定位、创新城乡环保政策、统筹城乡环境建设与管理方面采取有效措施。     

Testing of dust clouds for the electrostatic-spark ignition hazard in industry. Need for a modified approach?

Current standard test methods for electric-spark minimum ignition energies (MIEs) of dust clouds in air require that a series inductance of at least 1–2 mH be included in the electric-spark discharge circuit. The reason is to prolong the spark discharge duration and thus minimize the spark energy required for ignition. However, when assessing the minimum electrostatic energy ½CU² for dust cloud ignition by accidental electrostatic-spark discharges, current testing standards require that the series inductance of at least 1–2 mH be removed from the spark discharge circuit. No other changes of apparatus and test procedure are required. The present paper questions whether this simple approach is always adequate. The reason is that in practice in industry accidental electrostatic-spark discharge circuits may contain large ohmic resistances due to corrosion, poor electrical grounding connections, poorly electrically conducting construction materials etc. The result is increased spark discharge durations and reduced mechanical disturbance of the dust cloud by the blast wave emitted by the spark. Therefore, testing for minimum ½CU² for ignition by accidental electrostatic spark discharges may not only require removal of the series inductance of 1–2 mH from the standard MIE spark discharge circuit. Additional tests may be needed with one or more quite large series resistances R_s inserted into the spark discharge circuit. The present paper proposes a modified standard test procedure for measurement of the minimum electrostatic-spark ignition energy of dust clouds that accounts for these effects.     

印染行业水污染整治升级改造技术措施

做好印染废水的排放提标工作、提高印染废水的综合回用率,是"十二五"期间中国印染行业综合整治、污染总量控制和节能减排的重要抓手。本文简要分析了中国印染废水治理与国外的差距、单厂及集中污水处理厂提标升级的技术措施、印染废水回用的技术措施,以期对印染废水治理升级改造和中水回用实践工作有所指导。     

外界热辐射作用下木材热解和着火的预测模型

在突发的火灾过程中，可燃性固体材料的着火时间和热解特性是非常关键的参数。建立了预测木材在外界热辐射作用下热解和着火时间的数值模型，可以给出固体的质量损失速率、内部温度场随时间的变化，并根据模型计算得到的表面温度随时间的变化对着火时间进行预测。计算结果和实验测量值相符较好。     

红椿凋落叶全碳释放的林窗效应

为了调整低山丘陵区低效林林分结构,探明马尾松人工林不同林窗下凋落物的全碳释放规律,论文以长江上游低山丘陵区人为采伐形成的马尾松（Pinus massoniana）人工林7种不同大小林窗（G1：100 m²,G2：225 m²,G3：400 m²,G4：625 m²,G5：900 m²,G6：1 225 m²,G7： 1 600 m²）为研究对象,以林下为对照,研究了乡土阔叶树种红椿（Toona ciliata）凋落叶近1 a的全碳释放率和全碳释放速率（每30 a）。结果表明：1）相对小型（100~200 m²）和大型（1 225~ 1 600 m²）林窗以及林下,中型（400~625 m²）林窗更能促进凋落叶全碳的释放;2）全碳释放速率表现出先快后慢的变化趋势,在分解中后期（90~270 d）,出现碳的富集现象;3）凋落物全碳的释放受林窗大小、位置、分解时间的交互作用,分解时间对红椿凋落叶的全碳释放率影响极显著（P < 0.01）,林窗大小对全碳释放有显著影响（P < 0.05）,而林窗内不同位置（中心和边缘）对凋落叶碳释放无显著影响;4）凋落物分解温度、含水率和全碳释放率、质量损失速率表现出极显著正相关（P < 0.01）。     

基于详细化学动力学的甲烷热着火影响因素分析

利用化学动力学软件CHEMKIN4.1,在不同初始温度、浓度、湿度和压强下,对甲烷热着火进行了详细化学动力学 模拟。通过对主要组分摩尔浓度分析和温度敏感性分析,得到了甲烷热着火过程的主要基元反应和引发热着火发生的主 要原因。通过对甲烷热着火的延迟时间、热着火发生后主要生成物摩尔浓度和反应后的温度的对比分析,揭示了初始浓 度、湿度和压强对甲烷热着火的影响规律。本研究可以为甲烷为主的气体如瓦斯、天然气等可燃气体的燃烧和爆炸提供 理论支撑,从而有效利用这些可燃气体,降低灾害的发生。     

Commuting patterns of Czech households exposed to flood risk from the Bečva river

Using unique data collected in October–December 2012 we estimate the link between commuting for work and level of individual exposure to floods. We find that commuters on average have higher earnings than non-commuters. Individuals affected by one flood commute by 11.2% more than unaffected individuals. We conjecture that the increase is linked to intentions to cover flood-related losses, decrease households' vulnerability to flood risk or out-migrate from the risk areas. Individuals affected by at least two floods are by 20.2% less likely to commute relative to those unaffected. We explain this non-linear effect by the fact that many households out-migrate after the first flood. Stayers commute less, because they are different from non-stayers in some underlying characteristics related to education, employment and family circumstances, which strongly affect commuting behaviour. We further find that in a commuting family an individual is by 53.8% more likely to commence commuting relative to a non-commuting family. Choice of commuting destination is often similar to that of other family members.     

煤粉燃烧性与工业分析、着火温度的相关性研究

喷吹煤粉燃烧性是生产中的一个重要参数,实时掌握原煤燃烧性的波动变化对保证喷煤的安全和稳定十分必要。直接测量煤粉燃烧性的方法成本高,时间长,操作复杂,不利于生产应用;采用测定煤的工业分析和着火温度的方法简单易行,应用范围广泛。该文针对某炼铁厂的15种原煤,进行了工业分析和着火温度的实验研究,引入了统计学中相关系数的概念对数据进行了处理分析,实验证明煤的挥发分和着火温度与煤粉的燃烧性高度线性相关,此方法为利用两参数间接分析煤粉燃烧性提供了理论基础。     

武陵山片区城乡收入差距空间格局及影响因素

运用探索性空间数据分析、空间滞后模型和空间误差模型3种方法分析了武陵山片区城乡收入差距的空间格局特征及影响因素。结果表明:①2013—2017年,武陵山片区高差距区的数量先增后减,低差距区数量呈增加趋势。②武陵山片区城乡收入差距的莫兰指数为正,表现为空间正相关集聚。③城乡收入差距的主要影响因素为经济发展水平、城镇化进程程度等,但在不同时期存在差异。在研究基础上,提出对策建议,以更好地缩小武陵山片区整体收入差距,促进社会良好与稳定发展。