Bounds for the global cyclicity index of a general network via weighted majorization

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Ionic Liquids Effect on the Stability of 17-Electron Cation Product of the Electrochemical Oxidation of Cymantrene

The oxidative electrochemistry of cymantrene, CpMn(CO)3 (1; Cp = [η5-C5H5]–), was examined in ionic liquids (ILs) composed of anions of varying Lewis base properties. It was observed that the cyclic voltammetric responses strongly depended on the nucleophilic properties of the IL anion. Still, all observations are consistent with the initial formation of 1+ followed by an attack from the IL anion. In bis(trifluoromethylsulfonyl)amide [NTf2]-based ILs, the process shows close to ideal electrochemical reversibility as the reaction between 1+ and [NTf2] anion is very slow. On the other hand, in tetrafluoroborate and trifluoromethanesulfonate-based IL, the oxidation of 1 shows different levels of electrochemical reversibility with a marked sign of anion attack to 1+. In contrast, 1 exhibits an irreversible oxidation process in hexafluorophosphate-based IL. The reaction rate constants for the interaction of 1+ with the different IL anions were estimated by fitting the experimental data to digital simulations of the proposed mechanism. Besides, the use of [NTf2]-based ILs as a supporting electrolyte in CH2Cl2 was also examined. The oxidation process of 1 shows a close to ideal electrochemical reversibility but low to non-chemical reversibility. This study illustrates the wide range of electrochemical environments available with ILs and demonstrates their limited utility for investigating the redox properties of metal carbonyl compounds. It also intends to warn the reader on how the IL media may influence an electrochemical study if care is not exercised

Extending assortativity: An application to weighted social networks

Assortativity by degree for complex networks is quantified by the Newman coefficient, and it describes a tendency for nodes to be connected to others with a similar degree. A generalization of the assortativity index has been proposed in the literature for undirected and unweighted networks, analysing the correlation between vertices that are not necessarily adjacent, but connected through paths, shortest paths and random walks. The aim of this study is to define a new class of higher-order assortativity measures for weighted networks. The effectiveness of these measures is evident in social networks, where both weights and connections are significant. Applications to Facebook and co-authorship networks are provided, analysing the assortativity beyond the nearest neighbours

Biohydrogen—A Green Fuel for Sustainable Energy Solutions

Energy plays a crucial role in the sustainable development of modern nations. Today, hydrogen is considered the most promising alternative fuel as it can be generated from clean and green sources. Moreover, it is an efficient energy carrier because hydrogen burning only generates water as a byproduct. Currently, it is generated from natural gas. However, it can be produced using other methods, i.e., physicochemical, thermal, and biological. The biological method is considered more environmentally friendly and pollution free. This paper aims to provide an updated review of biohydrogen production via photofermentation, dark fermentation, and microbial electrolysis cells using different waste materials as feedstocks. Besides, the role of nanotechnology in enhancing biohydrogen production is examined. Under anaerobic conditions, hydrogen is produced during the conversion of organic substrate into organic acids using fermentative bacteria and during the conversion of organic acids into hydrogen and carbon dioxide using photofermentative bacteria. Different factors that enhance the biohydrogen production of these organisms, either combined or sequentially, using dark and photofermentation processes, are examined, and the effect of each factor on biohydrogen production efficiency is reported. A comparison of hydrogen production efficiency between dark fermentation, photofermentation, and two-stage processes is also presented

Biohydrogen—A Green Fuel for Sustainable Energy Solutions

Energy plays a crucial role in the sustainable development of modern nations. Today, hydrogen is considered the most promising alternative fuel as it can be generated from clean and green sources. Moreover, it is an efficient energy carrier because hydrogen burning only generates water as a byproduct. Currently, it is generated from natural gas. However, it can be produced using other methods, i.e., physicochemical, thermal, and biological. The biological method is considered more environmentally friendly and pollution free. This paper aims to provide an updated review of biohydrogen production via photofermentation, dark fermentation, and microbial electrolysis cells using different waste materials as feedstocks. Besides, the role of nanotechnology in enhancing biohydrogen production is examined. Under anaerobic conditions, hydrogen is produced during the conversion of organic substrate into organic acids using fermentative bacteria and during the conversion of organic acids into hydrogen and carbon dioxide using photofermentative bacteria. Different factors that enhance the biohydrogen production of these organisms, either combined or sequentially, using dark and photofermentation processes, are examined, and the effect of each factor on biohydrogen production efficiency is reported. A comparison of hydrogen production efficiency between dark fermentation, photofermentation, and two-stage processes is also presented

Patterned copper sulfide thin films: A method for studying leaching behaviour

An experimental study on copper leaching from Cu1.85S thin films is presented, wherein copper extraction is quantitatively evaluated by changes in film thickness measured by white light interferometric profilometry. Changes in the film morphology and elemental composition, as assessed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, are used to confirm that the loss in film thickness is due to changes in the copper content and that the resultant film species is consistent with the mechanism of copper dissolution. The Cu1.85S thin films were synthesized by chemical bath deposition. The leaching behaviour of copper from the films was investigated in acidic ferric sulfate media at pHs 1, 2, and 3, and pH 1 at redox potentials of ∼350-650mV versus Ag/AgCl in 3M KCl. The changes in the film thickness and copper sulfur ratio were shown to reflect copper dissolution behaviour from chalcocite. Leaching of the Cu1.85S films demonstrated a greater decrease in film thickness as pH decreased. In addition comparison of the order of reaction as a function of proton concentration in non-oxidative dissolution of Cu1.85S (0.06) and as a function of iron(iii) concentration in ferric oxidation of Cu1.85S (0.40) shows that the proton dissolution reaction is negligible. Leaching of the Cu1.85S films at redox potentials of up to ∼476.4mV versus Ag/AgCl in 3M KCl produced covellite and demonstrated greater decreases in film thickness with increases in the redox potential. Leaching of the films above ∼476.4mV resulted in the formation of spionkopite and demonstrated a much lesser decrease in film thickness. These results are consistent with Eh-pH diagrams for the Cu-S-H2O system