Evaluating the mobility of toxic metals in untreated industrial wastewater sludge using a BCR sequential extraction procedure and a leaching test

The distribution and speciation of toxic metals in industrial wastewater sludge (IWS) was investigated. In this work, the modified BCR three-stage sequential extraction procedure was applied to the fractionation of Cr Pb Ni, and Cd in untreated industrial wastewater sludge from industrial sites in Hyderabad (Pakistan). The extracts were analyzed using electrothermal atomic absorption spectrometry. The procedure was evaluated using a certified reference material for soil mixed with sewage sludge BCR 483. The results from the partitioning study indicate that more easily mobilized forms (acid exchangeable) of Cd were dominant. The oxidizable fraction was dominant for all four toxic metals. Metal recovery was good, with <4% difference between the total metal recovered through the extractant steps and the total metal determined after microwave digestion. Lixiviation tests (DIN 38414-S4) were used to evaluate the leaching of toxic species from IWS, and it was observed that levels of leachable toxic metals were low compared to the amount of metal extracted in the exchangeable fraction of the BCR protocol.     

GPU引发的计算化学革命

综述了图形处理器(GPU)在计算化学中的应用和进展.首先简单介绍了GPU在科学计算中应用的发展,然后分别详细讲述了迄今几个使用GPU和CUDA(compute unified device architecture,显卡厂商Nvidia推出的计算平台)开发工具设计的量子化学计算和分子动力学(MD)模拟的算法和程序,尤其对目前唯一完全使用GPU技术开发的量子化学计算软件TeraChem做了完备的介绍,包括算法、实现的细节和程序目前的功能.此外,本文还对GPU在计算化学上将会发挥的作用做出了极为乐观的展望.     

Multiple comparisons with a control in direction-mixed families of hypothesis under heteroscedasticity

For general inferential families with a mixture of one- and two-sided inferences two procedures are proposed to compare several treatments with a control under heteroscedasticity. Critical constants required for the proposed procedures are tabulated, and a numerical example is given.     

基于BCR和HG-ICP-AES的矿区土壤重金属污染特征分析

建立了基于BCR法(连续提取法)和HG-ICP-AES技术的土壤重金属形态含量的检测方法。在选定的实验条件下,HG-ICP-AES对Hg, Pb和As的检测限分别达到0.6,1.5和0.8 ng·mL-1。对国家标准沉积物样品中Hg,Pb和As的含量进行对照测定,检测结果与推荐值一致,标准物质中Hg, Pb和As多次重复测定的RSD均<8%。应用本法实测了湘西某有色金属矿区土壤中Hg, Pb和As各形态的含量,发现矿区土壤中Hg, Pb和As均以残渣态为主,有机态和Fe-Mn氧化态次之,酸交换态含量较少;与对照区相比,矿区土壤中酸交换态、Fe-Mn氧化态、有机态、残渣态Hg, Pb和As的含量分别增加1.2, 3.0, 47, 272倍(Hg); 1.2, 4.6, 8.1, 4.5倍(Pb); 1.5, 2.9, 3.3, 2.2倍(As); 表明湘西矿区土壤同时存在Hg, Pb和As的复合污染。     

岩土材料应变局部化的有限元分析方法

采用有限单元法分析岩土材料的应变局部化时经常会遇到单元尺寸敏感性问题和网格锁定问题。自适应网格技术能够有效地解决网格锁定问题,但仍然无法克服计算结果对单元尺寸的依赖性,尽管在一维情况下被证明是可行的。复合体理论(均匀化理论)和弱非连续有限元方法可以成功地解决岩土材料的单元尺寸敏感性问题,在一维情况下两类方法实际上是一致的。本文针对岩土材料应变局部化的有限元新技术所存在的若干问题进行了详细的讨论,并给出了有关算例。     

The Influence of Synthesis Conditions on the Antioxidant Activity of Selenium Nanoparticles

Selenium nanoparticles (SeNPs) have attracted great attention in recent years due to their unique properties and potential bioactivities. While the production of SeNPs has been long reported, there is little news about the influence of reaction conditions and clean-up procedure on their physical properties (e.g., shape, size) as well as their antioxidant activity. This study takes up this issue. SeNPs were synthesized by two methods using cysteine and ascorbic acid as selenium reductants. The reactions were performed with and without the use of polyvinyl alcohol as a stabilizer. After the synthesis, SeNPs were cleaned using various procedures. The antioxidant properties of the obtained SeNPs were investigated using DPPH and hydroxyl radical scavenging assays. It was found that their antioxidant activity does not always depend only on the nanoparticles size but also on their homogeneity. Moreover, the size and morphology of selenium nanoparticles are controlled by the clean-up step.     

Asymptotic analysis of microscopic impenetrability constraints for atomistic systems

We analyze systems of atomistic interactions on a triangular lattice allowing for fracture under a geometric condition on the triangles corresponding to a microscopic impenetrability constraint. Such systems can be thought as a computational simulation of materials undergoing brittle fracture. We show that in the small-deformation regime such approximation can be validated analytically in the framework of variational models of fracture. Conversely, in a finite-deformation regime various pathologies show that the continuum approximation of such a system differs from the usual variational representations of fracture and either needs new types of formulations on the continuum, or a proper interpretation of the atomistic constraints limiting their range and adapting them to a dynamical framework.     

DFT study on H2O activation by stepped and planar Rh surfaces

In this research the effect of steps (lower coordinated surface atoms) and the presence of pre-adsorbed oxygen on the activation energy of water are studied with DFT. Without oxygen water activation is found to be structure insensitive. When oxygen is adsorbed on the surface and acts as the acceptor for the hydrogen at the step edge, the barrier will decrease significantly.     

A limited resource model of fault-tolerant capability against cascading failure of complex network

We propose a novel capacity model for complex networks against cascading failure. In this model, vertices with both higher loads and larger degrees should be paid more extra capacities, i.e. the allocation of extra capacity on vertex i will be proportional to k_i ^γ , where k_i is the degree of vertex i and γ > 0 is a free parameter. We have applied this model on Barabási-Albert network as well as two real transportation networks, and found that under the same amount of available resource, this model can achieve better network robustness than previous models.