1,721,147 research outputs found
Oxygen Selective Barium Bismuth based Perovskite Membranes
No full textThis thesis focused on the research and development of novel dense perovskite membranes for oxygen separation from air. Owing to the mixed ionic-electronic conducting (MIEC) properties of perovskite materials, oxygen ionic transport takes place at high temperatures generally in excess of 600oC, resulting in the production of pure oxygen. Despite the attractiveness of this technology, the oxygen fluxes are still limited at temperatures below 850oC, mainly attributed to low oxygen ionic diffusion. To address this problem, the research community has worked intensively on the compositional tailoring of perovskite materials with ABO3-d structure. These perovskite materials have the capability to incorporate different cation types namely A/A’ and/or B/B’ in their A-site and B-site leading to different A1-xA’xB1-xB’xO3-d compounds with specific structures and properties. Examples include (La,Sr)(Co,Fe)O3-d parent compounds and a large array of doping using various different cations, e.g. Ba, Ca, Sr, Na, La onto A-site of LaCo0.8Fe0.2O3-d; Cu, Ni, Co, Fe, Mn, Cr onto B-site of La0.6Sr0.4CoO3-d; Ba onto A-site of SrCo0.8Fe0.2O3-d; La, Nd, Sm, Gd onto A-site of SrCoO3-d and Ti and Bi onto B-site and A-site of SrFeO3-d. In this thesis, barium was selected as the base material for A-site cation in the perovskite lattices due to its fixed valence cation, Ba2+ and large ionic radius, 1.60Å which favours the creation of large lattice spacing and higher freedom of oxygen ionic movements. To complement barium, bismuth was chosen as a cation dopant since it has ionic radius variability at different valence states (Bi3+ and Bi5+) and coordination numbers which allowed flexible incorporation of bismuth in A-site and/or B-site. Hence, this work takes the advantage of these combined features of barium and bismuth to manipulate the perovskite structure towards favourable oxygen transport properties. This can be achieved through the fixed placement of barium in A-site in conjunction with flexible bismuth position in perovskite lattices. The first postulation of this thesis relates to the bismuth incorporation into perovskite lattice of barium-based perovskite oxides aiming at improving the ionic transport and oxygen fluxes at intermediate temperatures (650-850oC). This postulation is based on the superior ionic transport properties of bismuth. To test the first postulation, barium-bismuth perovskite oxides with different molar ratios of BiO1.5 to BaO (z), where z varied between 0.5-3, were investigated. It was found that barium-rich perovskite oxide of z=0.86, BaBi0.86O2.29 with slight deviation from z=1 showed the optimised oxygen fluxes of 1.2 ml cm-2 min-1. This was attributed to a higher sintering temperature of 1080oC for a compound of z=0.86 instead of 1000oC for a compound of z=1. Nevertheless, due to the insufficient amount of defects for high ionic diffusion, barium-bismuth perovskite oxides did not achieve optimum performance below 850oC. To that end, incorporating complementary metal oxides were deemed necessary to improve the membrane performance. The second postulation in this thesis was that iron addition onto barium-bismuth perovskite oxides provides better structural stability for barium-bismuth-iron perovskite oxides due to iron’s reduction tolerant properties. This postulation was verified by investigating barium-bismuth-iron perovskite oxides within the family of [Ba2−3xBi3x−1][Fe2xBi1−2x]O2+3x/2 with x between 0.17-0.60. It was found that upon increasing x from 0.33 to 0.60, the structure of these compounds changed from cubic to tetragonal and then to hexagonal. Compounds with x=0.33-0.40 exhibited the highest oxygen fluxes attributed to the cubic structure formation. While barium-bismuth-iron perovskite oxides delivered better structural stability with respect to barium-bismuth perovskite oxides, the optimised compound (x=0.33, [Ba][Fe0.67Bi0.33]O2.5) delivered low oxygen fluxes of 0.59 ml cm-2 min-1. Hence, the incorporation of iron decreased the oxygen flux by 50.83% as compared to the best composition of barium-bismuth perovskite oxides. In other words, the incorporation of iron in the barium-bismuth perovskite lattice reduced oxygen ionic transport, though relatively better structural stability was obtained. In addition, structure transition phenomena were found for compounds of x=0.55 and 0.66. The third postulation in this thesis was that bismuth doped barium-scandium-cobalt perovskite oxides enhanced the oxygen fluxes below 850oC. This postulation was envisaged based on the partial substitution of barium or cobalt on a perovskite compound BaSc0.1Co0.9O3-d with bismuth. This work aimed at using bismuth to reduce the ionic radius discrepancy between Ba and Sc/Co and thus ensuring the attainment of cubic structure below 850oC. Cobalt was utilized as the main component in the B-site cation to boost the oxygen permeation properties of the resultant perovskite oxides while scandium was added in small proportions to enhance the crystal structural stability and electrical conductivity as well as to counteract cobalt’s reducibility. A notable point discovered here is that a low amount of bismuth doping, e.g. less than or equal to 10 mole % stabilised the cubic structure. As a result, oxygen fluxes in these compounds increased up to two orders of magnitude between 650-850oC when compared to a non-doped compound. It was further demonstrated that nominal B-site doping was more beneficial to oxygen permeability with respect to nominal A-site doping. In particular, the optimised composition of BaBi0.05Sc0.1Co0.85O3-d delivered very high fluxes of 2.17 ml cm-2 min-1 at 950oC. Structure transition phenomena from non-cubic to cubic structure were also observed for non-doped compound (BaSc0.1Co0.9O3-d) and A-site doped compounds with 20 and 30 mole % of bismuth. A final contribution of this thesis was the development of the hollow fibre membranes with the optimised composition of barium-bismuth-scandium-cobalt perovskite oxide, BaBi0.05Sc0.1Co0.85O3-d, using a combined phase inversion and sintering technique. The hollow fibre membranes showed for the first time the achievement of very high oxygen fluxes e.g. 11.34 ml cm-2 min-1 at 950oC, in excess of target values for air separation units of 10 ml cm-2 min-1. This work further showed the effect of sweep gas flow rate on the oxygen permeances of BBSC hollow fibres, particularly above 800oC. This finding demonstrates that high oxygen fluxes were achieved only at high sweep gas flow rates of 150 ml min-1. For temperatures at or below 800oC, the oxygen flux was independent of the sweep gas flow rate, thus indicating the limitations imposed by oxygen ionic bulk diffusion and surface reaction. Through a compositional tailoring approach, this thesis has demonstrated the potential of barium-bismuth based perovskite oxides in advancing oxygen transport membrane technologies
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
Oxygen reduction reaction activity and structure of La-based perovskite oxides
No full text1706 files in 35 folders, containing 388MB. Comprises plots, figures, and manuscripts. The data contains x-ray diffraction patterns and electrochemical data of lanthanum based perovskite oxides (e.g. 9 different perovskite compositions e.g. LaNiO3, LaCoO3, LaFeO3, LaMnO3, LaCrO3, LaNi0.5Co0.5O3 and LaNi0.5Fe0.5O3, LaNi0.5Mn0.5O3 and LaNi0.5Cr0.5O3) characterized using rotating ring disk electrodes.</p
A new graphical method to target carbon dioxide emission reductions by simultaneously aligning fuel switching, energy saving, investment cost, carbon credit, and payback time
No full textkoamabayili/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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