Distinct element modeling of laser assisted milling of silicon nitride ceramics

Laser assisted milling (LAMill) of ceramics shows some complicated characteristics such as discontinuous chips, crack formation, propagation and coalescence. In this paper, numerical simulation is conducted to explore the machining mechanism of LAMill. The distinct element method (or discrete element method, DEM) is applied to model the microstructure of a β-type silicon nitride ceramic. Clusters are used to simulate the real grain shape of the silicon nitride ceramic and parallel bonds are employed to represent the connections between intergranular glass phase and grains. Numerical tests (compression, bending and fracture toughness tests) are performed to evaluate the macroproperties of the synthetic material, thus matching the corresponding physical properties of the real silicon nitride. Moreover, a temperature-dependent synthetic DEM specimen is created and then used in simulations of LAMill. The DEM model is validated through comparing the simulation results with the experimental ones in terms of the cutting forces and subsurface damage under different depths of cut. It is shown that the model can successfully predict the subsurface damage in LAMill.     

川西北高寒草甸两种蚯蚓的互作及其对土壤养分的影响

以川西北高寒草甸中普遍存在的两种蚯蚓(微小双胸蚓Bimastus parvus和威廉腔蚓Metaphire guillemi)为研究对象,采用野外微宇宙实验方法比较单独接种和混合接种时两种蚯蚓的数量、分布和繁殖状况,以及牛粪分解率和土壤养分含量的变化,探讨不同蚯蚓种群间的相互作用及其对土壤养分的影响.结果发现:1)两种蚯蚓混合接种加快了牛粪分解,增加了下层(10~20 cm)土壤可溶性氮含量,但对牛粪分解速率和土壤可溶性氮含量均不存在交互作用;2)在混合接种处理中,微小双胸蚓的死亡比率显著高于威廉腔蚓的死亡比率;3)两种蚯蚓混合接种处理时,威廉腔蚓的繁殖明显受到抑制,而微小双胸蚓的幼蚓数量有所增加.研究表明,威廉腔蚓和微小双胸蚓共存能够发生竞争性相互作用,加快地面上的牛粪分解,增加土壤可溶性氮含量,从而可能提高高寒草甸的初级生产力.     

温度对芦苇不同部位分解动态的影响

研究温度对芦苇不同部位分解动态的影响,结果表明,温度促进了各部分分解速度,在5、15和25℃下,7个月后叶片干物质剩余率为75%、64%和55%,茎秆为80%、68%和61%,茎鞘为83%、80%和74%.从5℃到25℃,叶片、叶鞘和茎秆分别多分解了20%、19%和9%,表明温度对各部分分解的影响存在差异.进一步由Q10可以看出,从5℃到15℃再到25℃,叶片、茎鞘和茎秆的Q10分别为1.3860和1.3059,1.5582和1.2602,1.141 2和1.2746.成分不同可能是引起这种差异的重要原因,此结果对于预测未来生态系统中C循环等生态过程具有重要意义.     

黔西南汞铊矿废弃物中污染物释放的联合调控研究

为评价植生改良与先锋植物联合调控作用对矿产采冶废弃物中污染物迁移的控制情况,以黔西南兴仁市滥木厂大量露天堆存的汞铊矿废弃物(采冶废渣、尾矿、废石等混合物)为研究对象,选择当地广泛存在的碳酸盐岩、腐熟牛粪作为植生改良剂,并种植三叶草和黑麦草作为先锋植物进行联合调控,通过淋滤实验评价其对废弃物中高毒性污染物Hg、Tl、As...     

地下水除铁除锰技术研究进展

对地下水铁锰污染现状及危害进行了介绍,概述了地下水铁锰去除技术方法:主要包括自然氧化法、接触氧化法、生物氧化法等。重点综述了生物法除铁锰的研究进展,从滤料、微生物筛选及驯化、运行条件等方面进行强化以提高除铁除锰效率,是该研究方向的重点。     

Investigating into composition,distribution, sources and health risk of phthalic acid esters in street dust of Xi’an City,Northwest China

Phthalic acid esters (PAEs) are widely used as plasticizers and in consumer products, which may enter the environment and present risks to human health. U.S. EPA classifies six PAEs as priority pollutants, which could be accumulated in street dust at the interface of atmosphere, biosphere and geosphere. This study collected a total of 58 street dust samples from Xi’an City in Northwest China and analyzed for concentrations of the priority PAEs. Composition, distribution, sources and health risk of the PAEs were further examined. All the priority PAEs were detected in the street dust. The concentrations of individual PAEs varied between not detected and 183.19 mg/kg. The sum of the 6 priority PAEs (∑6PAEs) ranged from 0.87 to 250.30 mg/kg with a mean of 40.48 mg/kg. The most abundant PAEs in the street dust were di-n-butyl phthalate and di (2-ethylhexyl) phthalate (DEHP). Higher concentrations of ∑6PAEs in the street dust were found in the south and west parts of Xi’an City as well as its urban center, which were possibly attributed to the prevailing northerly Asian winter monsoon. The PAEs in the street dust originated mainly from wide application of plasticizers as well as cosmetics and personal care products. The main pathways of human exposure to PAEs in the street dust were ingestion and dermal adsorption of dust particles. The non-cancer risk of human exposure to PAEs in the street dust was relatively low, while the risk to children was higher than that to adults. The cancer risk of human exposure to DEHP in the street dust was lower than the standard limit value of 10^?6.     

Environmental geochemistry study of arsenic in Western Hunan mining area,P.R. China

The geochemical characteristics of arsenic in the soil of the Western Hunan mining area of P.R. China were systematically studied. The results show that the strata of Western Hunan are rich in arsenic and that Western Hunan is a geochemically abnormal region for arsenic. The experimental study on speciation in the strata also indicates that the speciation of arsenic in the Neoproterozoic-Cambrian strata are mainly easily transferred speciation (exchangeable, carbonate-bound, sulfides-bound), which are approaching or exceed 60%. Arsenic content in the main soil of Western Hunan is in the range of 8.8–22.8 μg g⁻¹, the mean value is 16.1 μg g⁻¹, which is larger than the arsenic background value of Hunan soil. The distribution of rock with high arsenic content or high easily transferred arsenic speciation is consistent with the distribution of high arsenic content soil. In the mining region, part soils and river/brook waters were polluted by mine tailings and mining/smelting waste water. The arsenic content in polluted paddy soils and river/brook water is 46.26–496.19 μg g⁻¹, 0.3–16.5 mgL⁻¹, respectively. The positive abnormality and pollution of arsenic in the soil and water affects the arsenic content of the crop and the inhabitants’ health.     

黄河包头段水-沉积物系统中重金属的污染特征

以系统的形态分析实验研究为基础 ,结合上覆水、悬浮物、沉积物及孔隙水中重金属的分布特征 ,评价了黄河包头段水体中重金属 (Cu、Pb、Zn、Cd)的潜在危害程度 .结果表明 ,黄河包头段干流沉积物中Pb、Cd等重金属具有较大的潜在生态危害性 ,更易造成污染 ;包头市工业废水对黄河干流水体重金属污染有明显的迭加作用 .此外 ,分层位 (按深度 )计算的SQC值结果揭示 ,用表层沉积物或不同层位 (深度 )的混合沉积物所得沉积物重金属质量基准代表某一区域或河段沉积物重金属质量基准有一定的风险性 .     

基于PT-IE的区域性企业整体应急准备能力评估分析

针对传统评估方法在评价区域性企业整体应急能力的过程中未考虑评价者心理偏好与风险因素之间的关系,提出了1种基于前景理论(PT)与信息熵(IE)的评价模型,并设计了企业生产安全事故应急准备能力评价体系。首先以区属整体企业为单位构建心理损益矩阵,然后运用信息熵理论修正指标权重结构,最后依据前景理论计算得出各区、各指标的综合前景值并以此分析排序。实例表明:影响各区企业整体应急水平的共性问题在于应急组织体系不完善和应急救援力量不足,该模型对政府监管部门有针对性的分析和加强地区企业整体应急建设水平具有一定的指导意义。     

云南菊科入侵物种与本地共生物种光合特性比较

为了探求菊科入侵植物的入侵机制,了解菊科入侵植物与非入侵植物光合特性的差异,以云南省包括薇甘菊(Mikania micrantha)、紫茎泽兰(Ageratina adenophora)、飞机草(Chromolaena odorata)、三叶鬼针草(Bidens pilosa)在内的4种菊科入侵物种为研究对象,并以与其共生的菊科外来非入侵物种熊耳草(Ageratum houstonianum)为对照,研究外来入侵物种与非入侵物种叶片特性及气体交换参数等方面的区别. 结果表明:薇甘菊、紫茎泽兰、飞机草和三叶鬼针草的P_nmax(maximum net photosynthetic rate, 最大净光合速率)分别为15.92、18.69、17.15和22.78 μmol/(m2·s),分别比其共生非入侵物种熊耳草的高出21.63%、42.77%、31.02%和73.99%;4种入侵物种的LSP(light saturation point, 光饱和点)和LCP(light compensation point, 光补偿点)也显著高于熊耳草,但其AQY(apparent quantum yield, 表观量子效率)却显著低于该共生种. 4种入侵物种叶片的N_mass(leaf N content per unit mass, 单位质量N含量)和CC_mass(leaf construction cost per unit mass, 单位质量建成成本)均显著高于熊耳草,除飞机草外,其他3种入侵物种的PEUE(photosynthetic energy use efficiency, 光合能量利用效率)和PNUE(photosynthetic nitrogen use efficiency, 光合氮利用效率)均显著高于熊耳草,而飞机草和熊耳草之间差异并不显著. 5种植物叶片N_mass分别与叶片SLA(specific leaf area,比叶面积)、CC_mass呈极显著正相关,与植物P_nmax、叶片P_mass(leaf N content per unit mass, 单位质量P含量)和PEUE呈显著正相关,植物P_nmax与PNUE、PEUE呈极显著正相关,与叶片SLA呈显著正相关. 研究显示,与菊科共生外来非入侵植物相比,较高的光合特性参数、叶片特性指标和能量利用效率指标可能是外来菊科入侵物种成功入侵的原因之一.