Synthesis, characterization and electrocatalytic behaviour of non-alloyed PtCr methanol tolerant nanoelectrocatalysts for the oxygen reduction reaction (ORR)

In order to point out the effect of the second metal in platinum-based catalysts, a synthesis method by colloidal route derived from that of Bönnemann was used to prepare non-alloyed Pt_1−xCr_x/C electrocatalysts active towards the oxygen reduction reaction (ORR). The non-alloyed character of the catalysts was showed by XRD analysis. The Pt/Cr electrocatalyst having an nominal atomic ratio, as determined by EDX then corresponding to bulk composition and not surface composition, close to (0.8:0.2) showed higher activity for ORR in methanol-free oxygen saturated electrolyte, whereas the catalyst having an atomic ratio of (0.7:0.3) displayed higher activity for ORR at low overpotentials in saturated oxygen electrolyte containing 0.1 M methanol.Correlation of XRD and electrochemical results allows us to point out the effect of electronic interactions in catalyst activity towards ORR. It was also shown that adding chromium to platinum does not alter the reaction mechanism of oxygen reduction, and that in presence of low methanol concentration, the ORR occurs via the four-electron process according to the same mechanism as in methanol-free solution.     

Effect of precursor concentration on structural,morphological and opto-electric properties of ZnO thin films prepared by spray pyrolysis

Sprayed ZnO films were grown on glass substrate at 400 °C using zinc chloride as precursor with different molar concentrations varying from 0.05 to 0.2 M. X-ray diffraction patterns reveal that ZnO films are polycrystalline with hexagonal wurtzite structure with preferred orientation in (002) plane. Optical measurements show that transmittance reaches a maximum value of 95% in the visible region for ZnO films prepared from precursor with 0.05 M concentration. The films obtained from the precursor with 0.1 M concentration have the highest electrical conductivity and photocurrent values.     

Correlations among soils’ features,forest plant species,and vegetable crops in Tokpli mining zone (South Togo)

ABSTRACT

Agriculture and forestry resources are central to African development. In this study, Tokpli mining zone (Togo) soils were characterised and the ones appropriate to garden crops and reforested species identified and located on a map using several database and literature. Results showed that tomato (Solanum Lycopersicum) and chilli pepper (Capsicum annuum) are suitable for slightly acidic clay soils of Ahlimegni. Abelmoschus esculentus is suitable for Assou-kondji soil. Solanum macrocarpon was found appropriate to Ziome-kondji and Anagonou-kpota soils. Forest species such as Salix babylonica, Khaya senegalensis, Eucalyptus spp., and Terminalia superba exhibited best growth on slightly acidic clay soils of Ahlimegni area, rich in organic matter. Acacia auriculiformis, Azadirachta indica, Cola gigantea, and Albizia zigya can grow better on the slightly basic sandy soils of Anagonou-kpota and Ziome-kondji. Other species like Gmelina arborea, Mangifera indica, Salix babylonica, and Morinda lucida were found not selective and could be reforested on all soil types.     

一种基于模糊综合评判的网络入侵特征描述矩阵

网络入侵检测需要综合考虑各方面的因素，这不仅会带来极大的计算开销，而且由于证据的不确定性，很难准确作出直接的判断，网络入侵行为特征的描述是设计入侵检测系统的前提和关键，而它往往又是研究入侵检测技术的难点，模糊综合评判是在证据不确定的条件下，综合考虑系统各方面的因素，来判决一个网络访问连接是为攻击，由此得出的基于模糊推理的网络入侵特征描述矩阵使得推理过程计算简单，同时也具有更强的描述能力。