1,720,964 research outputs found
Hapniku elektrokeemiline redutseerumine lämmastikuga dopeeritud rauda või koobaltit sisaldavatel mitmeseinalistel süsiniknanotorudel
Get PDFKäesolevas töös uuriti hapniku elektrokeemilist redutseerumist aluselises ja happelises keskkonnas koobaltit või rauda sisaldavatel lämmastikuga dopeeritud mitmeseinalistel süsiniknanotorudel. Nii koobaltit kui ka rauda sisaldavad lämmastikuga dopeeritud süsiniknanotorud olid aluselises keskkonnas kommertsiaalse plaatinakatalüsaatoriga ligilähedase aktiivsusega ja võrreldavad kirjanduses leiduvate andmetega mitteväärismetallkatalüsaatorite jaoks. Stabiilsuse uuringust selgus, et mõlemad katalüsaatorid on aluselises keskkonnas ka väga stabilised. Happelises keskkonnas oli materjalide aktiivsus mõnevõrra väiksem, jäädes alla kommertsiaalsele Pt katalüsaatorile. Koobaltit sisaldavat katalüsaatorit testiti anioonvahetusmembraaniga vesinikkütuseelemendis ning rauda sisaldavat katalüsaatorit anioonvahetusmembraaniga metanoolkütuseelemendis
Hapniku elektrokatalüütiline redutseerumine mitteväärismetallkatalüsaatoritel
Get PDFVäitekirja elektrooniline versioon ei sisalda publikatsiooneLoodust saastava süsinikul põhineva energiatsükli asendamine on üks kõige kriitilisemaid 21. sajandi probleeme. Paraku tuleb sisuliselt kogu transpordiks kasutatav energia endiselt fossiilsetest kütustest. Üheks alternatiiviks sisepõlemismootorile on polümeer-elektrolüüt kütuseelemendid (PEFC). Kütuseelement on olemuselt seade, milles keemiline energia (konkreetsel juhul vesiniku ja hapniku vahelisel reaktsioonil tekkiv energia) muundatakse kasulikuks tööks. PEFC puhul on lõppsaaduseks puhas vesi, mis tähendab et sisepõlemismootori asendamisel selliste kütuseelementidega on võimalik vältida CO2 teket. Põhiline probleem PEFC tehnoloogia juures on katoodil toimuva hapniku redutseerumisreaktsiooni katalüsaatorite vähene aktiivsus ja stabiilsus. Siiani kasutatakse madalatemperatuursetes kütuseelementides selle reaktsiooni katalüsaatorina plaatinal põhinevaid materjale, aga plaatina on äärmiselt kallis ning vähese levimusega metall. Selle doktoritöö käigus arendati plaatina asendamiseks süsiniknanomaterjalidest uudseid elektrokatalüsaatoreid. Grafeeni, süsiniknanotorude ja karbiidset päritolu süsiniku dopeerimisel saavutati atomaarselt jaotunud aktiivtsentritega, mis pidasid sammu või isegi suurendasid kütuseelemendi võimsustihedust võrreldes kommertsiaalsete Pt/C materjalidega. Töö käigus demonstreeriti uusi strateegiaid süsiniknanomaterjalidest komposiitide valmistamiseks ning poorse struktuuri optimeerimiseks, mis suurendas samuti kütuseelemendi võimsustihedust. Käesoleva doktoritöö tulemused näitavad, et mitte-väärismetallkatalüsaatoritega on võimalik asendada kütuseelemendis plaatina-põhiseid katoodimaterjale ning seeläbi oluliselt vähendada süsteemi maksumust.Moving on from the carbon energy cycle that is destroying our environment and deteriorating living conditions is one of the priorities for humanity in the 21st century. However, nearly all of the energy used for transportation is still being produced by burning fossil fuels. Polymer electrolyte fuel cells (PEFC) have emerged as one of the pathways towards reducing the CO2 emissions from automotive applications and have already seen wide-scale use in fuel cell electric vehicles. The main remaining problems towards replacement of internal combustion engines by PEFCs are cost and durability. These issues stem from the slow oxygen reduction reaction (ORR), which takes place at the fuel cell cathode. So far, nearly all commercially available fuel cell systems have used platinum-based catalysts on the cathode to achieve this, but it has become apparent that the long-term activity and stability targets cannot be met by Pt-based materials while keeping costs low enough. This PhD thesis focuses on developing novel electrocatalysts for this reaction by rationally designing synthesis strategies for carbon nanomaterials. By using graphene, carbon nanotubes and carbide-derived carbon (CDC) and combining them with methods such as ball-milling and pyrolysis, new catalysts with atomically dispersed catalytic centres were developed. The dispersion of catalytic sites on such a level enhanced the activity of the catalyst material and thereby the power output of the fuel cell. Composite materials from carbon nanotubes and graphene or CDC were created to optimise the porous structure of the fuel cell electrode, which further raised the power density of the cell. New strategies for the optimisation of porosity in catalyst materials are also proposed in this thesis. In the end, multiple catalysts rivalling the activity of commercially used Pt/C materials are presented in this thesis, showing a great promise of non-precious metal catalysts for replacing Pt in automotive fuel cells.https://www.ester.ee/record=b539344
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
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
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