Degradation of Polylactic Acid (PLA) Plastic in Costa Rican Soil and Iowa State University Compost Rows

In this study the degradation of polylactic acid (PLA) plastic films in Costa Rican soil and in a leaf composting environment was investigated. Three types of PLA films were used: Ch-I, (PLA monolayer plastic films from Chronopol, Golden, CO), GII (PLA trilayer plastic films from Cargill Dow Polymers LLC, Minnetonka, MN), and Ca-I (PLA monolayer plastic films from Cargill Dow Polymers LLC). The average soil temperature and moisture content in Costa Rica were 27°C and 80%, respectively. The average degradation rate of PLA plastic films in the soil of the banana field was 7675 M _w/week. Two compost rows were set up at the Iowa State University (ISU) (Ames) compost site. Temperature and relative humidity of the compost rows were kept at 55 ± 5°C and 50 ± 10% RH, respectively. The degradation rates of GII and Ca-I in the compost rows were 113,290 and 71,283 M _w/week, respectively. Therefore, it was estimated that in Costa Rican soil and in compost rows, PLA would be visibly degraded in 6 months and in 3 weeks, respectively.     

Charity hazard—A real hazard to natural disaster insurance?

After the flooding in 2002 European governments provided billions of Euros of financial assistance to their citizens. Although there is no doubt that solidarity and some sort of assistance are reasonable, the question arises why these damages were not sufficiently insured. One explanation why individuals reject to obtain insurance cover against natural hazards is that they anticipate governmental and private aid. This problem became to be known as “charity hazard”. The present paper gives an economic analysis of the institutional arrangements on the market for natural disaster insurances focusing on imperfections caused by governmental financial relief. It provides a theoretical explanation why charity hazard is a problem on the market for natural disaster insurances, in the way that it acts as an obstacle for the proper diffusion and therefore the establishment of natural hazard insurances. This paper provides a review of the scientific discussion on charity hazard, provides a theoretical analysis and points out the existing empirical problems regarding this issue.     

基于风险的检验(RBI)在国内合成氨装置中的应用

利用API581基于风险的检验原理,采用RISKWISE分析软件对九江石化合成氨装置中的设备和管道进行了风险评估;并在装置采用的工艺、不同装置的设备和管道的失效机理和计算出的风险分布这3方面,将其风险评估结果与国内兄弟单位完成的其他合成氨装置的风险评估结果进行了比对;其结果体现了我国目前合成氨装置的设备和管道风险的大致分布,可供我国其他合成氨装置的风险评估参考,也为制定我国合成氨装置基于风险检验的法规标准提供了相关数据;同时,对国内采用针对装置的基于风险的检验的新模式进行了探讨。     

内排压脚与边坡稳定性的关系

为了研究边坡角及边坡形状与边坡稳定性的关系,采用有限元软件ANSYS模拟了不同边坡角对应的稳定系数,以及不同平盘宽度和压脚高度所形成的等储备强度边坡的稳定系数。模拟中假设材料符合相关联的理想弹塑性本构关系,强度准则符合Drucker-Prager准则,用计算收敛性作为边坡稳定性的准则,用强度折减法得出边坡的稳定系数。为了形成等储备强度边坡,由下到上分步骤进行压脚。先在平面边坡最下台阶压脚,这样提高了边坡稳定系数,在边坡进入临界状态时,最下两台阶的塑性状态相同,则压脚停止;再在最下两台阶同时压脚,在边坡进入临界状态时,最下3个台阶的塑性状态相同,则压脚停止;以此类推,在最下边n个台阶同时压脚,在边坡进入临界状态时,压到与第n+1个台阶的塑性状态相同为止。结果表明,边坡总是从坡脚开始形成塑性区,在重力加载过程中,塑性区以弧形条带向坡顶扩展,形成滑带。最有效的内排压脚是从最下台阶开始形成等储备强度边坡的压脚。     

火灾探测报警系统失效风险评估

火灾探测报警系统的可靠程度,直接影响消防系统控制火灾蔓延和保护人民生命财产安全的能力,对系统进行失效风险评估是检验火灾探测报警系统可靠性的有效方法。先采用故障树分析法对火灾探测报警系统的失效风险进行分析,得出影响火灾探测报警系统失效的底事件;再利用模糊综合评价法和重要度算法得到各底事件的失效概率和权重,并给出火灾探测报警系统失效风险计算步骤;以沈阳航空航天大学图书馆火灾探测报警系统为例,评价该系统不失效的概率为0.795 0,不易失效的概率为0.144 1,较易失效的概率为0.0608,易失效的概率为0,然后根据模糊评价的最大隶属度原则,确定评估结果为该系统不失效。     

长壁综采工作面覆岩采动变形破坏时空演化规律研究

回采工作面煤层被采出以后,上覆岩层产生离层、断裂、垮落等运动,形成的冒落带和裂隙带范围对煤矿安全生产影响极大.以顾桥煤矿1116(1)综采工作面为工程背景,采用数值模拟和井下电法测试技术,研究了淮南矿区11-2煤层开采时覆岩移动破坏的规律.结果表明:在垂直方向上,采空区上方覆岩破坏分区特征明显,由下而上依次为双拉应力破坏区、拉伸裂隙区、剪切破坏区和未破坏区域;冒落带最大高度11.5～14.5 m,裂隙带最大高度45～47.5 m;覆岩破坏最终形态类似于马鞍形,破坏在水平方向的范围要比开采区域大.     

基于灰色模糊集理论的船舶搁浅概率分析

为深入分析船舶搁浅概率,在随机性和模糊性的基础上,考虑了系统的灰色性,建立灰色模糊集,模部为正态模糊数,灰部以系统的灰度熵来表示。建立了船舶航行计划失效造成船舶搁浅的事件树,构造了船舶搁浅概率的灰色模糊隶属度函数,根据各基本事件的失效概率来分析因航行计划失效造成船舶搁浅事故的灰色模糊概率分布情况。结果表明,与经典概率论和模糊概率相比,采用灰色模糊概率更能全面地反映船舶搁浅概率的可能性与不确定性。并采用RRW法和RAW法对基本事件的重要度进行了分析,找出了事故主要诱因及对降低事故风险价值最大的基本事件。     

地表载荷对硬岩区埋地管道应力应变影响分析

为研究地表载荷对硬岩区埋地管道力学性能的影响,建立了管-土耦合三维数值模型,分析了地表载荷大小、作用面积、管道压力、管道径厚比及回填土弹性模量对管道应力分布、塑性应变、椭圆度的影响。结果表明:地表压载作用下,高应力区首先出现在管道顶部且呈椭圆形;随着地表载荷及其作用面积的增大,管道高应力区逐渐扩大,管道截面左右两侧也出现应力集中;随着回填土弹性模量、管道壁厚及内压的增加,管道顶部高应力区及最大等效应力均减小。塑性应变首先出现在管顶,且塑性区随地表载荷、载荷作用长度增加而增大,随回填土体弹性模量及管道壁厚增大而逐渐减小;当内压为0~4MPa时,管道塑性应变及塑性区随内压的增大而减小。管道椭圆度随回填土体弹性模量、管道内压、壁厚增加而逐渐减小,随地表压载增大而增大。     

Climate change,adaptation and Eco-Art in Singapore

Eco-Art has recently emerged as a potential means to place emphasis on environmental issues such as climate change, recycling and the metabolism of the city experienced both materially and conceptually within local, regional and global contexts. Such art presents the possibility of shaping civic practices in arenas beyond those of traditional planning domains. Adopting a pragmatic approach, which recognises the contextual pluralism that exists in debates regarding climate change, this paper is interested in how Eco-Art projects encourage the re-imagining of urban spaces within the context of sustainability, and flows of materials and the recycling of plastic in art specifically.     

长期覆膜条件下农田土壤微生物群落的响应特征

地膜覆盖是农业生产中保障粮食增产增收的重要措施.为明确长期地膜覆盖对农田土壤微生物群落结构特征的影响,采集4个不同覆膜年限的农田土壤,利用高通量测序技术分析土壤细菌和真菌群落结构变化,探讨长期覆膜农田土壤中微生物群落的变化及其对微生物生态环境效应的影响.结果表明,长期覆膜对土壤细菌多样性无显著影响,但降低真菌多样性;长期覆膜使土壤细菌酸杆菌（Acidobacteriota）和真菌被孢霉菌（Mortierellomycetes）物种丰度降低,增加土壤放线菌（Actinobacteriota）物种丰度.长期覆膜可以使土壤富集细菌中的芽孢杆菌（Bacillus）和类诺卡氏菌（Nocardioidaceae）,及真菌中的肉座菌目（Hypocreales）和曲霉菌（Aspergillus）等有益微生物菌群.然而长期覆膜使土壤真菌共生网络变得简单而脆弱,其关键物种仅有子囊菌门中的粪壳菌目（Sordariales）中的未知菌属一种,因此对农田土壤生态环境带来潜在风险.本研究为深化了解长期覆膜对农田微生物生态环境效应的影响提供理论依据.