1,720,954 research outputs found
Trattamenti Superficiali per la produzione di Idrogeno Verde
No full textIl cambiamento climatico rappresenta una delle sfide più urgenti del nostro tempo, richiedendo soluzioni sostenibili per mitigarne gli effetti. Di centrale importanza è la riduzione della dipendenza dai combustibili fossili. In questo contesto, l’idrogeno si è affermato come una soluzione promettente per decarbonizzare settori difficili da elettrificare, come trasporti, industria e produzione di energia. Tuttavia, solo l’"idrogeno verde" – prodotto tramite elettrolisi dell’acqua alimentata da fonti rinnovabili – soddisfa gli obiettivi di zero emissioni nette. Tra le tecnologie di produzione di idrogeno verde, l’elettrolisi alcalina (AWE) è una delle più mature a livello industriale. Per migliorarne ulteriormente l’efficienza, la durata e ridurne i costi, lo sviluppo di catalizzatori efficienti e privi di materie prime critiche (CRM) è fondamentale. Storicamente, infatti, i catalizzatori a base di platino hanno mostrato le migliori prestazioni rispetto alla reazione di evoluzione dell’idrogeno (HER), ma la loro scarsità e gli alti costi ne limitano l’impiego su larga scala. Essi sono stati sostituiti da elettrodi a base di nichel, sebbene abbiano un’attività elettrocatalitica inferiore. L’attività elettrocatalitica del nichel può essere migliorata alligandolo con metalli di transizione, come il molibdeno, o aumentando la sua superficie specifica. In questo contesto, gli elettrodi di tipo Raney-nichel prodotti mediante Atmospheric Plasma Spray (APS) hanno dimostrato buone proprietà elettrocatalitiche rispetto alla HER, grazie alla loro elevata superficie specifica e rugosità. Tuttavia, non è ancora chiaro come la qualità della polvere utilizzata e la sua omogeneità di deposizione durante il processo APS influenzino le prestazioni elettrocatalitiche e la stabilità meccanica degli elettrodi. Un’altra criticità è la gestione delle bolle di idrogeno che, formandosi sulla superficie degli elettrodi, ne ostacolano le prestazioni, bloccando i siti attivi e aumentando la sovratensione. Pertanto, il controllo della morfologia superficiale e l’uso di substrati adeguati sono fattori determinanti per l’ottimizzazione degli elettrodi di tipo Raney-nichel. Per affrontare queste problematiche, in questo studio sono state depositate diverse tipologie di polveri Ni-Al mediante APS su un substrato di nichel. I rivestimenti così ottenuti sono stati sottoposti a trattamento termico in atmosfera inerte e attivazione chimica per ottenere elettrodi di tipo Raney-nichel con elevata superficie specifica. Nella prima parte dello studio sono state preparate diverse miscele di Ni-Al mescolando polvere di nichel puro con quantità controllate di alluminio, introdotto come formatore di porosità. Le composizioni analizzate sono: Ni-Al 50-50%, Ni-Al 70-30% e Ni-Al 85-15% in peso. Nella seconda parte dello studio sono state depositate polveri Ni50Al e Ni37Al19Mo, prodotte mediante High Energy Ball Milling (HEBM), al fine di migliorare l’uniformità della dispersione dei diversi elementi nel rivestimento. Sono state analizzate due distribuzioni granulometriche (PSD), 10-45 μm e 45-106 μm, per ciascuna composizione, per valutarne l’effetto sull’adesione del rivestimento, sulla stabilità meccanica, e sulla microstruttura. Per migliorare la gestione delle bolle, i rivestimenti ottimizzati per ciascuna composizione sono stati depositati su un secondo substrato: una sottile rete metallica di nichel. A nostra conoscenza, questo tipo di substrato non è mai stato rivestito al fine di essere utilizzato come elettrodo. Gli elettrodi ottenuti sono stati testati in una cella elettrochimica a tre elettrodi, utilizzando curve di polarizzazione catodica con estrapolazione di Tafel, voltammetria ciclica e spettroscopia di impedenza elettrochimica per valutarne l’attività elettrocatalitica.Climate change poses one of the most significant challenges of our time, driving the need for sustainable solutions to mitigate its effects. Central to this effort is the reduction of reliance on fossil fuels. In this context, hydrogen has emerged as a promising option to decarbonize hard-to-abate sectors, such as transportation, industry, and power generation. However, only “green hydrogen” - produced via water electrolysis using renewable electricity – aligns with net-zero emissions. Among various methods for green hydrogen production, alkaline water electrolysis (AWE) is one of the most mature industrial technologies. Innovation in AWE focus on improving the efficiency, the durability and reducing the costs of the technology. One way to achieve these goals is through highly active catalysts free of critical raw materials (CRM). Historically, platinum-based catalysts have dominated as cathodes materials in AWE, exhibiting the best hydrogen evolution reaction (HER) performance. However, their scarcity and high costs hinder their large-scale application. Consequently, nickel-based electrodes are currently used in AWE, even though they show a lower electrocatalytic activity compared to platinum group materials (PGMs). The electrocatalytic activity of nickel can be enhanced by alloying it with other transition metals, such as molybdenum, or by increasing its surface area. In this regard, Raney nickel electrodes obtained by atmospheric plasma spray (APS) have shown good electrocatalytic properties towards the HER, due to their high surface area and roughness. Nevertheless, it is still not clear how the quality of the Raney nickel powder and the uniformity of powder deposition during the APS process can influence the electrodes’ performance and their mechanical stability. Another challenge is bubble management: hydrogen bubbles forming on the surface of the electrodes hinder their performance by clogging active sites, leading to increased overpotentials. For these reasons, control of the surface morphology and the application of suitable substrates are critical factors in the optimization of Raney nickel electrodes. To address those issues, in this work different types of Ni-Al powders were deposited by means of APS onto a nickel substrate and subjected to heat treatment and chemical leaching of aluminum to obtain Raney nickel electrodes. In the first part of this work, different Ni-Al feedstocks were prepared by blending pure nickel powder with controlled aluminum addition, employed as a pore-forming agent. The Ni-Al blends analyzed are the following: Ni-Al 50-50 wt.%, Ni-Al 70-30 wt.%, and Ni-Al 85-15 wt.%. In the second part of the study, Ni50Al and Ni37Al19Mo powders produced by high energy ball milling (HEBM) were prepared to improve the distribution of the two elements during coating deposition. Two different particle size distributions (PSD), 10-45 μm and 45-106 μm, were analyzed for each powder composition to understand the influence of PSD on the adhesion of the coating to the substrate, its mechanical stability, surface texture, and microstructure. To improve the bubble management of the electrodes, the optimized coatings for each feedstock system were also deposited onto a second substrate: a thin nickel wire mesh, which allows finer apertures than a perforated nickel sheet, but wider than a nickel foam. To our knowledge, this kind of substrate has never been coated and employed as an electrode before. The obtained electrodes were tested in a three-electrode electrochemical cell. Cathodic polarization curves with Tafel extrapolation, cyclic voltammetry, and electrochemical impedance spectroscopy techniques were employed to determine the electrocatalytic activity of the selected electrodes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
High temperature properties of nichrome resistant heaters – A systematic comparison of APS, suspension and filament HVOF sprayed coatings
Get PDFThis study investigates the performance of Nichrome coatings, a nickel‐chromium alloy containing 20 wt.-% chromium, applied using three thermal spray techniques: powder plasma spray, suspension HVOF, and filament HVOF. Thin, homogeneous coatings approximately 35 μm thick were deposited onto steel substrates pre-coated with an insulating Al2O3 layer. The oxide content in the coatings varied based on the spraying technique and parameters, ranging from 57 to 64 vol.-% for plasma spraying, 42 to 54 vol.-% for filament HVOF, and 9 to 43 vol.-% for suspension HVOF. The coating's heating performance was evaluated over a temperature range of room temperature (RT) to 700 °C. Analytical techniques such as X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Spectroscopy (EDS) were employed to investigate the mechanisms affecting temperature-dependent resistivity in relation to the coating microstructure. The results indicate that increased oxidation leads to a decrease in specific resistivity at RT (ρ0). In example, plasma sprayed coatings exhibited lower specific resistivity ρ0 of 0.80 Ωmm2/m. In contrast, suspension HVOF reaches values up to 2.75 Ωmm2/m. At the same time coatings with higher oxidation levels demonstrate an elevated dependence of resistivity as compared to less oxidized coatings. Both can be attributed to changes in the phase composition of the conductive phase as the dominating factor, primarily driven by the preferential oxidation of chromium during the spraying process. Notably, the results provide valuable information for adjusting the coating properties to suit specific needs, such as self-regulating or high-temperature heating applications
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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