1,721,367 research outputs found
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
Investigation and implementation of improved and degradation-tolerant fuel electrodes for solid oxide cells
No full textNi- yttria-stabilized zirconia is commonly used as a fuel electrode cermet in solid oxide cells due to its compelling combination of conductivity, stability, and material compatibility. However, it faces significant degradation when exposed to hydrocarbon-rich fuels, such as tar-containing biogas. Carbon adsorption poisons the Ni component, leading to a decrease in catalytic activity, while the formation of carbon fibers ultimately results in nickel dusting. To address the issue of fuel electrode degradation without the need for fuel pre-treatment, this study investigates two alternative fuel electrode materials. The first material is gadolinia-doped ceria (Gd0.1Ce0.9O2-δ) as a replacement for yttria-stabilized zirconia. Gadolinia-doped ceria possesses mixed electronic and ionic conductivity, allowing it to maintain catalytic activity even when Ni is poisoned. Moreover, it exhibits oxygen storage capacity, potentially aiding in carbon removal. The second candidate is a Ni-exsolution perovskite material, Sr1-x(Ti0.3Fe0.7-yNiy)O3-δ. Upon reduction, Ni migrates to the surface, forming nanoparticles that offer a high catalytic surface area. These nanoparticles might be more stable against carbon degradation as they are socketed in the host lattice and can potentially be regenerated through redox-cycling. One major challenge arises when considering the replacement of the fuel electrode in a specific type of solid oxide cell, namely, the fuel electrode-supported cell. The half cell of this configuration consists of a substrate providing mechanical stability, onto which the fuel electrode and electrolyte are sequentially screen printed and then sintered together at 1400 °C to achieve the desired microstructure and gas-tightness. In state-of-the-art cells, the substrate is composed of NiO- yttria-stabilized zirconia, and the electrolyte is made of yttria-stabilized zirconia. Therefore, high sintering temperatures do not cause interface, structural, or functional degradation. However, if the fuel electrode is modified, interdiffusion can occur. As the sintering temperature cannot be adjusted due to the need for electrolyte gas-tightness, interdiffusion was investigated in symmetrical model cells. The dopant in ceria was changed with the intention of suppressing interdiffusion, resulting in significant but minor changes in the interdiffusion behavior. Additionally, novel sintering techniques and their impact on interdiffusion were explored using compacted powder mixtures. The presence of Ni in the cermet was found to enhance interdiffusion, leading to the formation of Kirkendall voids. These are the primary cause of cell performance degradation, rather than the formation of a mixed phase of ceria and zirconia at the interface. To mitigate porosity, a barrier layer was introduced between the Nigadolinia- doped ceria fuel electrode and yttria-stabilized zirconia electrolyte, thereby improving cell performance. Fuel electrode-supported cells with Ni- gadolinia-doped ceria fuel electrodes, with and without the barrier layer, were fabricated and delivered to the Technical University of Munich to assess their performance and degradation tolerance in artificial biogas. The Ni-exsolution material was successfully self-synthesized and investigated in terms of its exsolution behavior, phase stability and carbon degradation tolerance. Although exsolution of nanoparticles was observed, the materials undergo phase transitions at harsher reducing conditions, leading to mechanical instability in compacted pellets. This instability may be attributed to chemical expansion or contraction and secondary phase formation in the presence of H2O. Remarkably, when compared to Ni- yttria-stabilized zirconia,Sr1-x(Ti0.3Fe0.7-yNiy)O3-δ exhibited no degradation in terms of carbon deposition or nickel dusting after exposure to tar-containing biogas
Entwicklung alternativer Brenngaselektroden für die Hochtemperatur-Elektrolyse
No full textThe production of hydrogen is vital for a CO2-neutral, hydrogen-based energy system, essential for achieving national and international climate goals. Solid oxide electrolysis cells (SOECs) powered by renewable energy are key to producing green hydrogen and can achieve electrical efficiencies over 100% when coupled with waste heat. However, there are challenges concerning long-term stability and cost efficiency. Current materials used in these cells degrade significantly under SOEC conditions, leading to reduced performance. In particular, the commonly used Ni-YSZ fuel electrode shows considerable degradation due to Ni agglomeration and migration. A potential solution is using alternative fuel electrodes. This study aimed to develop alternative perovskite-based fuel electrodes for steam electrolysis in SOECs. Five alternative perovskite materials were synthesized and characterized: La0.6Sr0.38Fe0.8Mn0.2O3-δ – LSFM, La0.35Sr0.63TiO3-δ – LST, Sr0.98Ti0.7Fe0.3O3-δ – STF30, Sr0.98Ti0.5Fe0.5O3-δ – STF50 and Sr1.98FeNbO6-δ – SFN. In particular, the stability under reducing conditions and the compatibility of the perovskites with 8YSZ under the production conditions of fuel electrode-supported SOECs were investigated. It was found that SFN exhibits the highest stability in a reducing atmosphere as well as low reactivity with 8YSZ under the tested conditions. Based on the results of the characterizations, SFN and STF50 were selected as fuel electrode materials for all subsequent experiments. First, the stability of the perovskites under realistic SOEC conditions was tested. The results showed that both materials can be considered chemically stable, although a small amount of Fe3O4 secondary phase formation was observed in STF50. Furthermore, the compatibility of SFN/STF50 with 8YSZ and GDC under SOEC conditions and the manufacturing conditions for electrolyte-supported cells was investigated. SFN showed no interactions with 8YSZ or GDC, while STF50 was compatible only with GDC under the tested conditions. Overall, a barrier layer between the perovskite electrode and the 8YSZ electrolyte is beneficial for preventing or reducing chemical reactions. Electrochemical measurements of cells with SFN and STF50 fuel electrodes at different temperatures (650–800 °C) and varying H2O content in the fuel gas (3–90 vol.-%) indicated that the contact layer significantly impacts resistance values. It was also observed that both the ohmic resistance (RΩ) and the polarization resistance (RPol) decrease with increasing temperature but increase with a higher water vapor content. A degradation study of a full cell with an STF50 fuel electrode and an LSCF oxygen electrode over approximately 1700 h at 800 °C in 50 vol.-% H2O + H2 and a current of i = -0.43 A∙cm-2 revealed comparatively high degradation rates of 0.195 V kh-1, 0.162 Ω∙cm2 kh-1, and 0.361 Ω∙cm2 kh-1 for voltage, RPol, and RΩ, respectively. A subsequent SEM analysis of the microstructure of the STF50 fuel electrode before and after the degradation study showed no significant changes in the electrode microstructure, except for diffused Ni particles. Whether the Ni particles that diffused from the NiO/Ni contact layer into the STF50 fuel electrode and the GDC barrier layer have an impact on the cell's performance cannot be confirmed or ruled out at the current stage. In addition to producing electrolyte-supported cells, the integration of STF50 and SFN into the manufacturing route for fuel electrode-supported cells (FESCs) was investigated. Planar half-cells with STF50 fuel electrodes were successfully produced, though they did not meet the required gas tightness. In general, integrating perovskite-based alternative fuel electrodes into the FESC manufacturing process is not feasible without modifications. In summary, this work demonstrates that STF50 and SFN have considerable potential as alternative fuel electrodes in steam SOECs. Although they exhibit a certain degree of stability and, in the case of STF50, sufficient baseline performance, further optimizations and long-term studies are necessary to establish these materials as potential replacements for Ni-YSZ fuel electrodes
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
Distribution of relaxation times for analysis of solid oxide fuel cell stacks
No full textElectrochemical Impedance Spectroscopy (EIS) is a frequently used measurement technique to investigate the electrical and structural properties of electrochemical energy converters such as fuel cells and electrolyzers. Recently the Distribution of Relaxation Times (DRT) analysis became a promising method to increase the resolution of electrochemical processes on the relaxation time scale and to support the Equivalent Circuit Modelling (ECM) approach by an a priori estimation of the number of processes contributing to the total polarization loss. Among the possibilities to calculate the DRT function, the Tikhonov approach of regularized regression is a promising way to determine the DRT numerically. However, a main drawback of this method is the fact that a suitable regularization parameter has to be chosen that has a big impact on the shape of the DRT. The aim of this thesis is to investigate the influence of constant phase element (CPE) behavior, inductive effects and EIS data structure on the accuracy and repeatability of the DRT with DRTtools. CPE behavior is observed in EIS measurements of fuel cells and leads to depressed semicircular arcs in the complex plane and a broadening of the relaxation time distribution. Inductive effects and measurement errors can originate from parasitic inductances in the test rig or the cables and lead to a disturbance of the impedance measurement especially in the high-frequency regime. For the simulation study conducted in this thesis, a theoretical impedance is calculated with an equivalent circuit model consisting of an ohmic resistor, an inductor and three parallel connections of an ideal resistor and a CPE (called RQ elements) in series to simulate three electrochemical processes in an SOFC which exhibit frequency dispersion behavior in different extents depending on the magnitude of the CPE exponent n. Additionally, simulation sets with different error structures and data point densities are simulated in varying frequency ranges to investigate their impact on the DRT calculated with DRTtools, as well as co-effects of the above mentioned parameters such as combined effects of parasitic inductances and high degrees of frequency dispersion. Subsequently, the results of the simulation study are verified on EIS measurements performed on a two-layer SOFC stack in F10 design of Forschungszentrum Jülich, highlighting the practical relevance of the simulation results. Furthermore, the numerical origin of the observed calculation artefacts is investigated and a method to remove the artefacts is proposed
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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