1,721,081 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
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
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
Mise en évidence des schémas de dégradation des batteries Li-ion grâce à des procédures d'analyse électrochimique
No full textLa chimie des électrodes positives dans les batteries Li-ion gravitent depuis ces vingt dernières années autour d’une famille d’oxydes lamellaire à base de nickel, manganèse et cobalt, aussi appelé phases NMC. La part belle étant faite à l’autonomie des batteries, les recherches visent à accroitre la densité énergétique de ces matériaux en augmentant leur fraction de nickel ainsi que leur tension de fonctionnement. Cependant, à des teneurs en nickel supérieure de 80% et tension de 4.2 V, les phases NMC sont sujettes à une série de dégradations physico-chimiques impliquant le matériau ainsi son interface avec électrolyte. Dégradations structurales, oxydation de l’électrolyte ou dissolution des métaux de transitions sont autant d’exemples illustrant la variété des mécanismes en jeu. Pire encore, les dégradations peuvent en déclencher d’autres et au final c’est toute la cellule qui se retrouve impactée, ce qui peut conduire à une chute brutale de la capacité de la batterie appelé « emballement ». Imprédictible et soudain, les emballements sont difficiles à expliquer avec les descripteurs classiques de performance comme la capacité en décharge (QD) ou l’efficacité coulombique. L’objectif de cette thèse est de développer des protocoles d’analyses combinant des techniques électrochimiques afin d’expliquer la chimie des dégradations en jeu, c’est-à-dire, le type de dégradation, leur localisation, et le tout, de façon quantitative. Ces techniques se basent principalement sur le glissement de capacités en fin de charge et décharge, ainsi que les dérivées dV/dQ et dQ/dV. Afin de mettre place ces techniques, le premier travail était de s’assurer de la qualité des mesures électrochimiques, grâce à la standardisation des méthodes d’assemblage et de test. Une fois les données répétables et de qualité, les protocoles ont permis d’étudier les effets de la dissolution du nickel sur l’électrode de graphite et de mettre en évidence des dégradations inattendues lors de l’utilisation d’un électrolyte super concentré, bien que reconnu pour sa haute stabilité. Les compostions d’électrolyte ont donc pu être adaptées afin de réduire les dégradations et augmenter la durée de vie de la batterie. En résumé, ces protocoles améliore la compréhension des dégradations et ainsi d’optimiser au mieux les conditions de fonctionnement des batteries Li-ion. Cela ouvre la voie vers la stabilisation interfaces et matériaux et le développement de nouvelles chimies.For the past twenty years, the chemistry of positive electrodes in Li-ion batteries has predominantly focused on a group of layered oxides composed of nickel, manganese, and cobalt, commonly referred to as NMC phases. The primary goal of research has been to enhance the energy density of these materials by increasing their nickel content and operating voltage. However, once the nickel content surpasses 80% and the voltage reaches 4.2 V, the NMC phases become susceptible to a range of physicochemical degradations involving both the material itself and its interaction with the electrolyte. Structural degradation, electrolyte oxidation, and the dissolution of transition metals exemplify the various mechanisms at play. Furthermore, these deteriorations can trigger additional ones, ultimately affecting the entire battery cell and causing a sudden decline in battery capacity referred to as “rollover”. The unpredictable and abrupt nature of rollover poses challenges for conventional performance indicators like discharge capacity (QD) or coulombic efficiency in explaining them. The objective of this thesis is to develop analysis protocols that combine electrochemical techniques to comprehensively elucidate the chemistry underlying these deteriorations. This includes understanding the nature of the deterioration, its localization within the battery, and most importantly, quantifying its impact. These techniques primarily rely on observing the capacity slippages, as well as analyzing the derivatives dV/dQ and dQ/dV. To implement these techniques, the initial step involved ensuring the accuracy of the electrochemical measurements by standardizing the assembly and testing methods. Once reliable and high-quality data were obtained, the protocols facilitated the examination of the effects of nickel dissolution on the graphite electrode, revealing unforeseen deteriorations that occurred when using a highly concentrated electrolyte, despite its recognized high stability. Consequently, adjustments to the electrolyte compositions could be made to mitigate deteriorations and extend the battery's lifespan. In summary, these protocols significantly contribute to our understanding of deteriorations and enable the optimization of operating conditions for Li-ion batteries. This advancement allows for stabilizing interfaces and materials, as well as fostering the development of novel chemical approaches in battery technology
Ingénierie des électrolytes via de nouveaux sels et additifs pour les solutions aqueuses de stockage d'énergie
No full textLes batteries Li-ion sont essentielles pour les appareils électroniques portables et les véhicules électriques, offrant une densité d'énergie élevée jusqu'à 400 Wh kg−1. Cependant, leurs électrolytes organiques inflammables et toxiques posent des défis de durabilité. La recherche se tourne donc vers des batteries alternatives avec des matériaux abondants et économiques. Les batteries aqueuses à base de métaux alcalins et à ions zinc apparaissent comme des options plus sûres et durables. L'eau, non inflammable et économique, offre des avantages, mais sa réactivité et sa fenêtre de stabilité électrochimique (FSE) étroite de 1,23 V posent des défis. L'ingénierie des électrolytes, avec des stratégies comme la super-concentration, la dilution avec des solvants organiques et les additifs, est cruciale pour relever ces défis. Cependant, la réactivité de l'eau reste problématique, surtout à l'anode où elle concurrence l'intercalation des ions (lithium) ou le stripping et le plating du métal (zinc). Les acides aminés ont été étudiés comme additifs pour moduler les liaisons hydrogène de l'eau et affecter la cinétique de la dissociation de l'eau. Certains électrolytes prometteurs ont montré de faibles performances de cyclage dans les cellules Li-ion complètes. Cependant, certains acides aminés, comme l'acide aspartique (Asp) et l'acide glutamique (Glu), tamponnent efficacement la dynamique acide/base et maintiennent la réduction de H3O+ à des densités de courant élevées. Cette étude met en évidence l'interaction entre le pH, le pKa et la cinétique de la réaction d'évolution de l'hydrogène (HER), montrant le potentiel des acides aminés pour explorer cette relation. Une nouvelle approche pour concevoir des sels pour les électrolytes de batteries aqueuses combine des ions chaotropes tels que les cations guanidinium (Gdm+) avec les anions bis(trifluorométhanesulfonyl)imide (TFSI-). Le nouveau sel GdmTFSI perturbe les liaisons hydrogène de l'eau, augmentant la FSE de 0,25 V par rapport aux solutions de LiTFSI aux mêmes concentrations. Pour résoudre les problèmes des électrolytes aqueux, des sels d'oligoéthers de zinc avec des longueurs de chaîne variables ont été synthétisés et utilisés comme additifs dans les batteries à ions zinc. Ces sels, ajoutés à une solution de 2 M ZnSO4(aq), ont augmenté le temps de cycle des cellules symétriques Zn de 200 à plus de 1000 heures en améliorant la morphologie de l'électrodéposition de Zn et en empêchant la croissance des dendrites. L'additif le plus performant, Zn(MEEA)2, ajouté à un électrolyte breveté contenant de l'urée pour les cellules Zn || MnO2 complètes, a triplé la durée de vie des cycles par rapport à l'électrolyte sans l'additif. L'acide perylène-3,4,9,10-tétracarboxylique diimide (PTCDI) a été évalué comme matériau organique redox-actif (ROM) pour les batteries Li-ion aqueuses (ALIB). Malgré sa haute conductivité et sa faible solubilité dans l'eau, le PTCDI n'avait pas été utilisé dans les électrolytes aqueux pour les batteries Li-ion. En utilisant diverses techniques telles que l'IR ex-situ, la DRX ex-situ et l'EQCM, le mécanisme de compensation de charge a été déterminé. La concentration du sel et le choix de l'anion se sont révélés cruciaux pour la stabilité à long terme, où une solution de 1 mol/kg de LiTFSI(aq) a conservé 90 % de sa capacité après 1000 cycles à un taux de charge de 1C, ce qui est très favorable comparé à d'autres exemples de PTCDI dans la littérature. Cette thèse propose plusieurs solutions aux défis des batteries aqueuses grâce à l'ingénierie des électrolytes. Les travaux futurs peuvent approfondir les fondamentaux de la dissociation de l'eau, prévenir la formation de dendrites dans les batteries à métal zinc, et explorer le potentiel des matériaux organiques redox-actifs pour s'éloigner des électrolytes aqueux super-concentrés.Li-ion batteries are the primary power source for portable electronics and electric vehicles, offering a high energy density of up to 400 Wh kg−1. However, the use of flammable and toxic organic electrolytes in these batteries poses significant sustainability challenges. Consequently, research is now focused on developing alternative battery devices using resource-abundant and cost-efficient materials. Aqueous alkaline-metal batteries and aqueous zinc-ion batteries are emerging as safer and more sustainable options. Water, being non-flammable and cost-effective, offers several advantages over organic electrolytes, but its reactive nature and narrow electrochemical stability window (ESW) of 1.23 V present challenges. Electrolyte engineering, employing strategies such as super-concentration, dilution with organic solvents, and additives, has been crucial in addressing these challenges. However, water reactivity remains an issue, specifically at the anode where it competes with ion (lithium) intercalation or metal (zinc) striping and plating, for instance.Amino acids have been investigated as additives to modulate the hydrogen bonding network of water and thus affect the kinetics of water splitting. While some promising electrolytes were developed, they showed poor cycling performance in full Li-ion cells. However, certain amino acids, like aspartic acid (Asp) and glutamic acid (Glu), were found to effectively buffer acid/base dynamics and sustain H3O+ reduction at high current densities. This study highlights the interplay between pH, pKa, and hydrogen evolution reaction (HER) kinetics, showing the potential of amino acids as tools for exploring this relationship. Next, a new approach for designing salts for aqueous battery electrolytes is examined, by combining chaotropic ions such as guanidium cations (Gdm+) with bis(trifluoromethanesulfonyl)imide anions (TFSI-). The novel GdmTFSI salt disrupts the hydrogen bonding network of water, extending the ESW by 0.25 V compared to LiTFSI solutions at the same concentrations. Building on idea of designing new salts to solve the various issues of aqueous electrolytes, zinc oligoether salts with varying chain lengths were synthesized and used as additives in zinc-ion batteries. These salts, added to a 2 M ZnSO4(aq) solution, increased the cycle time of Zn symmetric cells from 200 to over 1000 hours by improving the morphology of Zn electrodeposition and preventing dendrite growth. The best-performing additive, Zn(MEEA)2, was added to a patented electrolyte containing urea for Zn || MnO2 full cells, increasing cycle life threefold compared to the electrolyte without the additive. Perylene-3,4,9,10-tetracarboxylic acid diimide (PTCDI) was evaluated as a redox-active organic material (ROM) for aqueous Li-ion batteries (ALIBs). Despite its high conductivity and low solubility in water, PTCDI had not been previously used in aqueous electrolytes for Li-ion batteries. Using various techniques such as ex-situ IR, ex-situ XRD, and EQCM, the charge compensation mechanism was determined. The concentration of the salt and anion choice were found to be crucial for long-term stability, where a 1 mol/kg LiTFSI(aq) was able to retain 90% capacity after 1000 cycles at a c-rate of 1C, which compares very well to other examples of PTCDI in the literature.This thesis provides multiple solutions to the challenges faced by aqueous batteries through electrolyte engineering. Future work can build on these findings to further probe the fundamentals of water splitting, prevent dendrite formation in Zn-metal batteries, and explore the potential of redox-active organic materials to move away from super-concentrated aqueous electrolytes
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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