1,720,953 research outputs found
A Versatile New Synthesis of Carbon Rich LiFePO4 Enhancing Its Electrochemical Properties.
No full textIn this contribution we report a new reproducible synthetic route to prepare LiFePO4/C composites. As starting materials an intimate stoichiometric mixture of lithium carbonate and an hybrid organic-inorganic Fe(II) organophosphonate, i.e. Fe[(RPO3)(H2O)] (R = methyl or phenyl group) were used. The idea behind it was to provide a single source for phosphorus, iron and carbon. The hybrid organic-inorganic compounds of formula Fe[(CH3PO3)(H2O)] and Fe[(C6H5PO3)(H2O)] are easy to handle because they are stable to the air and moisture [1,2]. The mixture of Li2CO3 and Fe[(RPO3)(H2O)] (R=CH3-, C6H5) was heated in a tubular furnace under N2 gas at temperatures above 600°C for at least 16 h [3]. Nano-crystalline LiFePO4 samples were obtained. One of the most interesting aspects of this new synthetic method is the formation of elemental carbon during the decomposition of Fe(II) methyl- and phenylphosphonate. In the final LiFePO4 samples amounts of 2.5 wt. % C in the case of Fe[(CH3PO3)(H2O)] precursor and 12 wt. % C in the case of Fe[(C6H5PO3)(H2O)] precursor have been found. This means that part of the theoretical carbon content in the reaction mixtures (8.8 wt. % and 29.6 wt. % respectively) is lost during the heating process. TG measurements on the initial precursor mixtures showed in both cases the elimination of the water molecules coordinated to the Fe(II) ions at temperatures up to 200°C, while at higher temperatures (200-800°C) weight losses of 30 and 45 % have been observed. An exothermic effect at 400°C (Fe[(CH3PO3)(H2O)]) and 450°C (Fe[(C6H5PO3)(H2O)]) has been evidenced in the DTA curves and might be related to the initial formation of Li2O from the corresponding carbonate followed by the decomposition of the organophosphonate precursor and final formation of LiFePO4. The exact mechanism of the reaction is still under investigation. The crystalline LiFePO4 powders were further characterized by X-ray powder diffraction analysis (XRPD) and Scanning Electron Microscopy (SEM). Our LiFePO4 samples crystallize in the orthorhombic space group Pnma and the LiFePO4 phase consists of spherical aggregates of about 0.2 μm diameter. Composite cathode tapes were made by roll milling a mixture of 75 wt. % active material and 10 wt. % binder (Teflon, DuPont). Carbon (KJB Carbon) was added until 15 wt. % final carbon content was reached. Electrodes disks of typically diameter of 10 mm were punched and the electrode weight ranged from 7.4 to 10.7 mg. T-shaped battery cells with lithium metal as counter and reference electrode were used for electrochemical characterization. The cells, filled with a 1M solution of LiPF6 in ethylene carbonate / diethyl carbonate (1:1), were automatically cycled by means of a battery cycler (Maccor 4000). Composite cathode preparation, cell assembly, tests and storage were performed in the dry room (R.H. < 0.1 % at 20°C). To test the effect of different discharge rates, a cell was subjected to various discharge rates, i.e. C/10, 1C, 3C, 10C, 20C and 30C. The cell was always charged using the same procedure to insure identical initial conditions: a constant current step at 1C rate until the voltage reached 4.0 V, followed by a constant voltage step until the current fell below C/10 rate. Figure 1 shows the Ragone plot for the cell discharged at different rates. The specific energy and specific power are based on the weight of the active material. The specific energy calculated at C/10 rate was about 550 Wh kg-1. The specific power calculated at 30C rate was in excess at 14,000 W kg-1 while the specific energy was about 28 % of the energy delivered at C/10. The excellent electrochemical performance of the LiFePO4/C composites can be ascribed to the tailored synthesis addressed to enhance the electrochemical properties of the material. The main advantage of this synthetic route is the formation of elemental carbon from the organic constituent of the precursor. The carbon particles interact with the LiFePO4 grains just during their formation providing a good electronic contact between the grains and the carbon added for the composite electrode fabrication. The low particle size and the enhanced surface conductivity both result in the outstanding performance of the LiFePO4/C cathode. In conclusion, electrodes made of the cathode material reported here showed very high specific energy, specific power and capacity retention upon cycling. The new synthetic method is very simple and the Fe(II) organophosphonate precursors are air-stable. The good electrochemical performance of LiFePO4/C indicates that the reported method is very promising for developing high power lithium-ion batteries.
Figure 1. Ragone plot for the cell discharged at different rates. LiFePO4 was prepared starting from the Fe(II) phenylphosphonate. The cathode loading of LiFePO4 was 7.1 mg cm-2. Electrode area was 0.16 cm2.
ACKNOWLEDGEMENTS
We thank the Ministero Italiano per la Ricerca Scientifica e Tecnologica (MIUR) for financial support.
REFERENCES
1. C. Bellitto, F. Federici, M. Colapietro, G. Portalone, and D. Caschera, Inorg. Chem., 41, 709 (2002).
2. A. Altomare, C. Bellitto, S.A. Ibrahim, and M.R. Mahmoud, Inorg.Chem., 39, 1803 (2000).
3. Italian Patent no. RM2003A000048 (2003)
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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