Ice Storm Damage and Early Recovery in an Old-Growth Forest

We quantified the damage causedby a major ice storm to individual trees in two1-ha permanent plots located at Mont St. Hilairein southwestern Québec, Canada. The storm, whichoccurred in January 1998, is the worst on recordin eastern North America; glaze ice on the orderof 80–100 mm accumulated at our study site. Allbut 3% of the trees (DBH 10 cm) lost at leastsome crown branches, and 35% lost more than halftheir crown. Damage to trees increased in the order: Tsuga canadensis, Betula alleghaniensis, Ostrya virginiana, Acer saccharum, Fagus grandifolia, Quercus rubra, Betula papyrifera, Acer rubrum, Tilia americana, and Fraxinus americana. Only 22% of the saplings and small trees (4 cm < DBH < 10 cm)escaped being broken or pinned to the ground byfalling material. Levels of damage generally weregreater in an exposed ridge top forest than in acove protected from wind. By August 1999 only53% of the trees had new shoots developing fromthe trunk or broken branches; among the moredominant canopy trees, Fagus grandifoliahad the least sprouting and Acer saccharumand Quercus rubra the most. We anticipateand will monitor both significant turnover in thetree community and some shift in composition ofthe canopy dominants.     

Oxidative capacities of size-segregated haze particles in a residential area of Beijing

The frequent haze days around the Chinese capital of Beijing in recent years have aroused great attention owing to the detrimental efects on visibility and public health. To discover the potential health efects of the haze, oxidative capacities of airborne particles collected in Beijing during haze and clear days were comparably assessed by a plasmid scission assay. Eleven water-soluble trace elements(As, Cd, Cr, Cu, Mn, Ni, Pb, V, Se, Tl, and Zn) in the size-segregated airborne particles were quantitatively analyzed by inductively coupled plasma mass spectrometry, and most of the watersoluble trace elements were found to mainly concentrate in the fine particle size of 0.56–1.0 μm. In comparison with clear days, the mass concentrations of 11 analyzed water-soluble trace elements remarkably increased during haze days, and the oxidative capacities determined by the plasmid scission assay were markedly elevated accordingly during the haze days under the same dosage of particles as for those during clear days. Water-soluble trace elements in airborne particles, such as Cu, V, and particularly Zn, were found to have significantly positive correlations with the plasmid DNA damage rates. Because Cu, V, and Zn have been considered as bioavailable elements, the evident increase of these elements during haze days may be greatly harmful to human health.     

基于疲劳损伤谱的随机振动试验方法在智能电表模拟公路运输中的研究

目的解决传统试验精确度差、仿真程度低的问题,验证智能电表在随机振动过程中的可靠性。方法将基于疲劳损伤谱的等效随机振动试验方法运用到智能电表公路运输振动试验中,首先提出疲劳载荷谱的概念及其获取方法,并对采集的振动数据进行处理,得到用于加速振动试验的功率谱密度,最后验证基于疲劳损伤谱的随机振动试验方法应用于智能电表模拟公路运输方法的可行性及优势。结果使用该方法加速试验前后的累计疲劳损伤误差为6.4%。结论该方法不但能大幅减少试验时间,同时能够节省大量人力、物力资源。     

基于FAHP与灰色聚类的航空地面电源车功能损伤状态评估

目的航空地面电源车战损情况下的功能损伤状态评估。方法以电源车的功能结构层次为基础建立指标体系,应用改进的模糊层次分析法(Fuzzy Analytical Hierarchy Process,FAHP)法确定指标权重。建立灰色聚类评估模型,并提出指标灵敏度分析方法。结果通过实例验证了方法的可行性和有效性。结论基于FAHP与灰色聚类的方法能够最大限度地利用了有效信息,对电源车功能损伤状态进行科学、合理和全面的评估。     

镧、铈、钕对小鼠肝细胞核的氧化损伤作用

轻稀土元素进入生物体后主要累积于肝脏,进入肝细胞,分布于细胞核上.为探讨轻稀土元素对小鼠肝细胞核的氧化损伤作用,选用5周龄雄性封闭群(ICR)小鼠灌喂10、20和40 mg·kg-1的稀土元素镧(La)、铈(Ce)和钕(Nd),6周后测定小鼠肝细胞核中超氧化物岐化酶(SOD)、过氧化氢酶(CAT)和谷胱甘肽过氧化物酶(...     

镉造成心血管损害毒性机制的研究进展

镉是一种极易在人体内蓄积的有毒元素,长期的生物蓄积和生物放大,会对机体产生一系列的损伤,其中,对心血管系统的损伤包括易造成动脉硬化、高血压和心肌病等.本文将镉在心血管损伤方面的毒作用的研究进展进行了总结,包括镉对心血管的氧化损伤,对心血管粘附因子的破坏,对心血管内皮细胞的功能和DNA损伤修复机制的破坏,以及对心血管内皮...     

区域二氧化硫控制优化模型研究

传统的区域二氧化硫控制优化都是基于损害函数法和环境标准化法的。本文在分析比较了传统二氧化硫污染控制战略优化中的损害函数法和环境标准化法各自的优点与局限的基础上。建立了基于时间序列决策的整数规划优化模型。这一理论模型更好地描述了控制战略实施的过程。把时间作为模型优化的一个因子。这种基于时间序列的过程充分考虑了货币的时间价值。并能分析这些时间价值对二氧化硫污染控制战略的动态过程影响。本文的模型是更加符合现实的情况。它对于区域二氧化硫控制的中长期决策优化显得更为有效和准确。     

环境因素对长航时无人机机体结构复合材料的影响

从环境因素对复合材料作用和大展弦比结构影响等方面分析了长航时无人机机体结构复合材料在服役环境中的损伤。结合目前国内外研究现状,扼要叙述了环境因素对长航时无人机机体结构复合材料的影响研究领域当前的主要需求,提出了针对未来研究工作的若干建议。包括应以长航时无人机机体结构典型碳纤维增强树脂基复合材料和涂层体系为主要研究对象,开展跟随无人机的暴露试验和实验室模拟加速试验,研究复合材料在环境和载荷耦合作用下的力学性能变化,确定机体结构典型复合材料的损伤规律等。     

硬岩竖井爆破损伤区探测及衬砌荷载*

为研究硬岩竖井受爆破开挖扰动的影响,依托米仓山公路隧道竖井工程,采用RSM-RCT（B）测试系统探测竖井爆破损伤区范围为1.1~1.4 m,并利用残余地质强度指标标定损伤区力学参数,将其纳入收敛约束法和数值分析中,以评估损伤区对竖井围岩及衬砌荷载的影响。研究结果表明,在硬岩竖井中开挖爆破是造成岩体损伤区的关键因素,地应力方向和大小对硬岩损伤区分布基本无影响。分析结果表明,爆破损伤区导致围岩变形增大,从而使得衬砌荷载增加,最大剪应力出现在损伤区与未破坏岩体之间的交界处,大小为16 MPa,同时靠近该位置的衬砌荷载也会变大,较深竖井可采用分区段支护,降低投资成本。研究结果可为硬岩竖井开挖荷载计算及设计优化提供一定参考。     

火场环境下无人机热损伤试验研究

无人机(UAV)逐步运用于火场搜救,但同时会因为火场高温而受损,为提高UAV在火场救援中的工作效率,设计一种UAV动态测试平台,开展UAV火场飞行试验;分析火场环境下UAV的热损伤情况,探究UAV在火场中的机身温度变化特征和UAV火场飞行安全距离.结果 表明:火场热辐射和热对流是造成UAV热损伤的主要形式;旋翼产生的气...