The influence of F doping on the activity of PbO2 film electrodes in oxygen evolution reaction

The PbO₂ and F⁻-doped PbO₂ (F-PbO₂) film electrodes have been prepared by an electrodeposition process onto platinum substrate. The changes of their electrochemical activity for oxygen evolution (OE) reaction with accelerated electrolysis time have been studied. The results show that the activity of the electrodes decreases with increasing electrolysis time. This can be attributed to the conductivity variations, which are caused by the decrease of the oxygen vacancy concentration in PbO₂ films during OE. The mechanism of the decrease of the oxygen vacancies has been investigated. For F-PbO₂ film electrodes, though its electrochemical activity is somewhat lower than that of undoped one, its activity stability is much higher in comparison with that of PbO₂. The influence of F⁻ doping on the activity of PbO₂ film electrodes has been also discussed.     

Photocatalytic H2 evolution under visible light irradiation on Zn1-x Cu x S solid solution

The H₂ evolution reaction from an aqueous Na₂SO₃ solution proceeded with 3.7% quantum yield under visible light irradiation (λ > 420 nm) on a Zn_0.957Cu_0.043S solid solution photocatalyst without co‐catalysts such as Pt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cinétique de dégagement des matières volatiles lors de la pyrolyse d'électrodes de carbone industrielles

In aluminium plants, the anode baking process is associated with an important release of volatile combustible matter. It is the purpose of this study to investigate the kinetics of the evolution of these volatiles. A large thermogravimetry set-up has been designed in such a way that it could simulate real plant conditions. Samples of two distinct masses have been subjected to pyrolysis at different heating regimes. The loss of weight together with the concentrations of the released gases were recorded on a continuous basis during the temperature rise. Kinetic results were found for methane, hydrogen and tar. No variation of the order of reaction with the heating rate was observed, whereas the activation energy and the pre-exponential factor increased. Furthermore, for the range of sample dimensions studied, it was found that the mass of the solid had no significant influence on the kinetic parameters.     

有向动态网络中基于模体演化的链路预测方法

以往传统的链路预测方法大多数针对无向网络,而实际上大多数社交网络是有向的,并且没有考虑网络中同一节点对之间的重复边以及微观演化信息,因此不能较好地解决有向动态网络中的链路预测问题。针对有向网络,将节点对之间的重复边信息转换为该节点对之间连边的权值;接着采用了基于三元组模体的演化模型,对滑动窗口中相邻时间片的模体转换概率进行统计后,采用指数加权滑动平均法对其进行时序分析得到不同模体转换概率的预测矩阵,进而使用该矩阵对网络中的链边进行预测。这不仅充分利用了网络微观演化信息,而且解决了动态网络中重复边的问题。最后对实验结果进行分析发现,在高全局聚类系数高平均度的网络中AUC相比Triad Transition Matrix方法提高了近0.01,而相比Common Neighbor方法提高更多。因此,所提方法能够较好地应用网络微观演化信息进行链路预测。     

城市雨洪放大效应驱动因子时空演变规律分析

城市雨洪具有复杂的放大效应,引起该现象较直接的原因包括大暴雨的频繁出现、可渗透地表面积的骤减以及排蓄水能力的改变和排水管网的扩张等。以武汉市为例,选择降雨强度、不透水面积比例、排水管道密度作为洪水放大效应的驱动因子进行趋势分析和演变规律分析,计算表明:从20世纪80年代开始,暴雨雨量和历时明显增加;不透水面在20世纪90年代初增加较快;排水管道在1990~2006年间缓慢增长,2007年跳跃式增长。降雨量和历时的增加使城市洪量增大,排水压力随之上升,在一定程度上增加了内涝几率;不透水面积的逐年增多以及水体等天然蓄水区的减少,不但增加了产流量,也使汇流时间更短,且雨水管渠的建设缩短了天然汇流路径,导致城市洪水呈现峰高量大,洪峰提前的放大效应。研究成果可用于城市雨洪放大效应对其驱动因子的定量响应研究,为进一步量化城市内涝风险与驱动因子间的关系提供依据,从而为内涝风险调控措施提供技术支撑。     

Understanding aluminum behaviour in aqueous alkaline solution using coupled techniques: Part I. Rotating ring-disk study

Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) measurements have been undertaken to study the behaviour of pure aluminum electrodes in alkaline media. The measurements did consist of linear sweep voltammetry from anodic to cathodic potentials on 4N, 5N or 5N5-aluminum samples in 4 M aqueous potassium hydroxide solution. In the potential range studied (−0.7 V versus NHE to −2.5 V versus NHE) the aluminum undergoes oxidation/dissolution into aluminates anions at high electrode potential while it yields strong hydrogen evolution at low potentials. Thanks to the RRDE technique, we show that hydrogen starts to evolve from the aluminum electrode even above the open circuit potential. Also, the oxidation state of superficial aluminum varies according to the electrode potential: whereas non-conducting aluminum oxides are present above the open-circuit potential hindering hydrogen evolution reaction (HER), they tend to disappear below the ocp, due to the strong hydrogen evolution, following the probable porous oxide layer blow up induced by the hydrogen bubbles formation. In consequence at very low potential, HER occurs on bare aluminum, HER kinetics being much faster than on oxide-covered aluminum.     

过度开采对地下水水化学特征的影响研究

为探究过度开采对地下水水化学特征的影响,通过对比分析研究区1997年和2010年的地下水水位与水质资料,研究了过度开采条件下地下水水位与水化学特征的动态规律及两者之间的联系。研究结果表明:1997年和2010年研究区地下水水位与水化学特征的空间变化规律具有很高的一致性,表现为地下水水位降幅较大的区域对应的镁离子、硫酸盐含量增幅也相对较大,地下水水化学特征受地下水水位变化的影响较大。空间叠加分析结果表明:镁离子、硫酸盐与地下水水位变化较大的区域空间重合率分别为72.2%,53.1%。过度开采通过改变地下水补径排条件及饱和带、非饱和带的水环境变化对地下水水化学特征产生影响,因此对于地下水不可盲目、过度开采。     

拆坝对河流生态系统的影响及评估方法综述

为研究拆坝对河流生态系统造成的影响,从短期和长期两个时间尺度综合分析了河流水文情势、地形地貌、岸边带植物、鱼类和底栖动物等关键生态因子对拆坝的响应,并总结了目前拆坝对生态系统影响的两种主要评估方法。认为根据实际拆坝情况进行评估和基于数值模型进行预测两种评估方法中,实地观测是最直接、最有说服力的研究方法,但受成本和一些不可控因素限制;数值模拟具有速度快、费用低、无比尺影响等优点,可对拆坝影响进行预测,为管理者提供参考,但精度和准确性有待提高。指出后续研究中应综合考虑拆坝过程中各生态因子间的耦合效应,需对不同拆坝时机和分阶段拆坝方式对河流生态系统的影响进行深入研究。     

山西省孝义市近40年气候变化特征分析

为了深入研究山西省孝义市气候变化特征,采用Mann-Kendall检验、滑动T检验及Morlet小波变换等方法对孝义市1975-2015年气候要素进行趋势估计、突变检验、周期分析及发展趋势预测。结果表明:近40年来,孝义市年平均气温呈显著上升趋势,突变年份为1996年,存在32、9 a长周期;年降雨量呈不显著下降趋势,突变年份为1990年,存在32、6 a长周期;年蒸发量呈显著性上升趋势,突变年份为1997年,存在32、10 a长周期;年平均相对湿度呈显著下降趋势,突变年份为1982、2003年,存在15、32 a长周期。孝义市1975-2015年年代际气候经历了"冷湿-暖湿-暖干"的变化过程,预测全境2017-2030年年代际气候将经历"冷湿-暖干"的变化过程。     

Effects of hydrological changes on cooperation in transnational catchments: the case of the Syr Darya

Water allocation along the Syr Darya River may be affected by climate change. Here we statistically model cooperation strategies, country profits, and sensitivity of cooperation, showing that the hydrological regime affects transboundary cooperation. Climate change in the twenty-first century may reduce glacial cover, and reducing stream flows, decreasing chances of cooperation and potentially raising conflicts. Comparison with other transboundary catchments in Central Asia indicates moderate-to-high risk of conflicts for the Syr Darya. A template is provided for assessment of the stability of cooperation in the Syr Darya basin, and in catchments similarly dependent on water availability.