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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
Synthesis and characterization of partially fluorinated sulfonated poly(arylene)-ionomers for application in intermediate temperature fuel cells
No full textIn der vorliegenden Arbeit wird die Synthese und Charakterisierung von Basenüberschussblendmembranen untersucht sowie deren Anwendbarkeit in der Mitteltemperaturbrennstoffzelle getestet.
Zur Herstellung der Basenüberschussblendmembranen werden zunächst teilfluorierte sulfonierte Poly(arylen)-Ionomere hergestellt, die später als saure ionische Vernetzer dienen. Die hergestellten teilfluorierten sulfonierten Poly(arylen)-Ionomere haben die Besonderheit, dass die Sulfonsäuregruppe direkt benachbart zu F-Atomen liegt. Durch die direkte Nachbarschaft der F-Atome wird die Acidität der SO3H-Gruppe aufgrund des -I-Effektes der F-Atome deutlich erhöht, wodurch die Ausbildung der ionischen Vernetzung verbessert wird. Als Matrix für die Basenüberschussblendmembranen werden drei verschiedene Polybenzimidazole (PBI-OO (B3), PBI-HOZOL (B1) und PBI-F6 (B2)) verwendet. Um die teilfluorierten sulfonierten Poly(arylen)-Ionomere herstellen zu können, werden zwei unterschiedliche perfluorierte Monomere, OFT (Oktafluortoluol) und PFP (Pentafluorpyridin), thioliert und anschließend zur Sulfonsäure oxidiert. Bei beiden Monomeren zeigt sich anhand der 19F und 13C-NMR Spektren, dass ausschließlich das in para-Stellung befindliche F-Atom durch das Thiol bzw. die Sulfonsäure substituiert wird. Die hergestellten Monomere werden anschließend mit kommerziell erhältlichen Monomeren in einer Polykondensation umgesetzt.
Um eine mechanisch und chemisch stabile Membran zu erhalten, ist unter anderem eine hohe Molmasse der eingesetzten Polymere notwendig. Arylenhauptkettenpolymere werden üblicherweise durch eine Polykondensationsreaktion hergestellt. Die Polykondensationsreaktion wird dabei unter anderem von folgenden Faktoren beeinflusst: Reaktionstemperatur, Stöchiometrie der Monomere und Katalysatormenge. Diese Faktoren werden in dieser Arbeit sowohl in Bezug auf die erhaltene Molmasse als auch auf die thermische Stabilität der Polymere untersucht. Es ist anzunehmen, dass mit steigender Reaktionstemperatur die Reaktionsgeschwindigkeit ansteigt und höhere Molmassen erreicht werden können. Dieses Verhalten kann bei den Polymeren SPTE-TBBT-PFP, SPE-BP-PFP, SPTE-TBBT-OFT und SPE-BP-OFT beobachtet werden. Bei perfluorierten aromatischen Monomeren besteht jedoch immer die Gefahr, dass ab einer bestimmten Reaktionstemperatur die Ausbildung von dreidimensionalen Netzwerken stattfindet, da mehr als zwei nukleophil substituierbare F-Atome pro Monomer vorliegen. Die Reaktionstemperatur kann somit nur bis zu einem gewissen Grad erhöht werden. Eine Erhöhung der Katalysatormenge führt aufgrund der schnelleren Aktivierung der OH- bzw. SH-Komponente ebenfalls zu einer Erhöhung der Molmasse. Dieses Verhalten kann in dieser Arbeit bei den Polymeren SPTE-TBBT-PFP und SPE-BP-PFP beobachtet werden. Durch Nicht-Einhaltung der Stöchiometrie der Monomere kann die Molmasse der Polymere in dieser Arbeit zum Teil erhöht werden. Laut Literatur ist dies jedoch nicht möglich, da gemäß der Carothers-Gleichung nur dann hohe Molmassen erreicht werden, wenn eine 1:1 Stöchiometrie der Monomere exakt eingehalten wird. Im Fall von SPTE-TBBT-OFT und SPE-BP-OFT zeigt sich jedoch, das bei einem 1 Gew.% Überschuss des F-haltigen Monomers eine Molmasse im Bereich von 8 000 g/mol erhalten wird, während bei einem 14 Gew.% Überschuss der F-Komponente eine Molmasse von ca. 17 000 g/mol erreicht wird. Die thermischen Stabilitäten der Polymere liegen im Bereich zwischen 250-440 °C für die Abspaltungstemperatur der Sulfonsäuregruppe, was weit oberhalb der Betriebstemperatur einer Mitteltemperaturbrennstoffzelle liegt.
Um den Einfluss der hergestellten Poly(arylen)-Ionomeren in Basenüberschussblendmembranen zu untersuchen, werden verschiedene Mischungsverhältnisse von PBI und den Poly(arylen)-Ionomeren hergestellt. Die erhaltenen Membranen werden anschließend sowohl auf ihre oxidativen und thermischen Eigenschaften als auch auf ihre Anwendbarkeit in der Brennstoffzelle untersucht. Die ionische Vernetzung in der Basenüberschussblendmembran bewirkt, dass die Abspaltungstemperatur der Sulfonsäuregruppen bei B1S4 auf 430 °C erhöht werden kann, während das reine Polymer SPE-BP-OFT eine Abspaltungstemperatur der Sulfonsäuregruppen von 380 °C aufweist. Die oxidative Stabilität der Membranen wird durch den Fenton Test (FT) untersucht. Die Membranen aus B1 und S3 bzw. S4 weisen nach dem FT eine leichte Abnahme der thermischen Stabilität auf. Auch anhand der REM-Bilder zeigt sich, dass nach 144 h die Membranen kleine Löcher im Größenbereich von 5 μm aufweisen. Die Membranen aus B1 und S1 bzw. S2 besitzen nach dem FT eine sehr inhomogene und poröse Oberfläche, was durch Degradation der Polymere zu Stande kommt. Durch GPC-Messungen vor und nach dem FT zeigt sich, dass während des FT ein Molmassenabbau stattgefunden hat. Die Membranen aus B2 und B3 zeigen hingegen beim FT bessere Ergebnisse. Die Massenabnahme liegt in diesem Fall bei max. 10 Gew.%, während bei B1 der Massenverlust nach 144 h einen Wert von ca. 30 Gew.% erreicht. Die deutlich höhere Molmasse von B2 führt dazu, dass diese Membranen bessere Ergebnisse zeigen als die Membranen aus B3. Aufgrund der hohen Molmasse von B2 werden bei den GPC-Messungen bimodale Kurven erhalten, wodurch erste Rückschlüsse gezogen werden können, welches Polymer zuerst von den Radikalen angegriffen wird. Die Membranen aus B3 und den sauren Polymeren können mittels GPC-Messungen nicht aufgetrennt werden, da sie ähnliche Molmassen besitzen. Bei den untersuchten Membranen hat sich unabhängig vom eingesetzten PBI gezeigt, dass die Stabilität nach folgender Reihenfolge abnimmt: B2S9 > B2S8 > B2S4 > B2S6 > B2S3.
Die hergestellten Basenüberschussblendmembranen werden in eine Brennstoffzelle eingebaut und unter realen Bedingungen vermessen. Jedoch müssen die Membranen vor dem Einbau in die Brennstoffzelle mit Phosphorsäure dotiert werden, um eine protonenleitfähige Membran zu erhalten. Der Dotierungsgrad wird auf 400 Gew.% festgelegt, da hier die mechanische Stabilität der Membranen noch ausreichend ist, um diese in einer Brennstoffzelle betreiben zu können. Laut Theorie sollten die Membranen mit dem geringsten Anteil des sauren Polymers die besten Ergebnisse zeigen, was in dieser Arbeit zum Teil bestätigt werden kann. Wird der Anteil des sauren Polymers zu groß, wirkt sich das negativ auf die Leistung der Zelle aus. Bei einigen Membranen kann kein stabiles Spannungssignal eingestellt werden, da die Phosphorsäure sich nur an der Oberfläche der Membran angelagert hat und durch den Gasstrom wieder von der Membranoberfläche entfernt wird. Um die Leistung der Membran zu verbessern, wird der Dotierungsgrad erhöht, was jedoch dazu führt, dass die mechanische Stabilität der Membran abnimmt. Eine weitere Möglichkeit die Leistung der Brennstoffzelle zu verbessern, besteht darin, den Platingehalt in den Elektroden zu erhöhen. So kann bei B3S8-b durch den Einsatz von 3 mg Pt/cm² die Stromdichte um den Faktor zwei auf 360 mA/cm² erhöht werden. Obwohl die Membranen mit B2 im FT bessere Ergebnisse zeigen, können sie im Brennstoffzellentest nicht überzeugen, da sie deutlich schlechtere Strom- und Leistungsdichten aufweisen als die Membranen mit B3. Die untersuchten Membranen zeigen zum Teil bessere Ergebnisse als die Membranen in der Literatur. In der Literatur wird ein Platingehalt von mindestens 1 mg Pt/cm² verwendet, während in dieser Arbeit ein Platingehalt von 0,3 mg Pt/cm² eingesetzt wird. Somit kann in dieser Arbeit gezeigt werden, dass selbst mit einem niedrigen Platingehalt relativ hohe Stromdichten in der Brennstoffzelle erreicht werden können.In the present work the synthesis and characterization of base-excess-blend membranes are studied and also their applicability will be tested in intermediate temperature fuel cells.
To produce base-excess-blend membranes partially fluorinated sulfonated poly(arylene)-ionomers are prepared which are used as ionic cross-linker in the membrane. The prepared partially fluorinated sulfonated poly(arylene)-ionomers have the peculiarity that the sulfonic acid group is located directly neighbored to F-atoms. Because of the close proximity of the F-atoms, the acidity is increased significantly due to the -I-effect of the F-atoms, so that the formation of ionic crosslinks is improved. As a matrix for the base-excess-blend membranes three different polybenzimidazoles (PBI-OO, PBI-F6 and PBI HOZOL) are used. In order to produce the partially fluorinated sulfonated poly(arylene)ionomers, two different perfluori-nated monomers, OFT (octafluorotoluene) and PFP (pentafluoropyridine), are thiolated, and then oxidized to the sulfonic acid. The 19F- and 13C-NMR spectra indicate that only the F-atom in the para-position is substituted.
To obtain a mechanically and chemically stable membrane, a high molecular weight of the polymers is necessary. Arylene main-chain polymers are typically prepared by a polyconden-sation reaction. The polycondensation reaction depends on the following factors: the reaction temperature, stoichiometry of the monomers and the catalyst amount. These factors will be examined in this work, in terms of the resulting molecular weight as well as the thermal sta-bility of the polymers. With increasing reaction temperature the reaction kinetics increase and higher molecular weights will be achieved. This can be observed for the polymers SPTE-TBBT-PFP, PES-BP-PFP, SPTE-TBBT-OFT and PES-BP-OFT. Partially fluorinated monomers have the risk that after a certain reaction temperature the formation of three-dimensional networks can take place, so that the reaction temperature can be increased only up to a certain degree. An increase of the amount of catalyst results, due to the faster activa-tion of the OH-or SH-component, in an increase of the molecular weight. This behavior can be observed for the polymers SPTE-TBBT-PFP and SPE-BP-PFP. In this work the molecular weight of the polymers can be increased although the stoichiometry of the monomers is not complied. But according to the literature, high molecular weights can only be obtained, when a stoichiometry of 1:1 of the monomers is exactly maintained as the Carothers equation shows. In the case of SPTE-TBBT-OFT and SPE-BP-OFT, a molecular weight in the range from 8 000 g/mol is obtained with an excess of 1 wt.% of the F-containing monomer, whereas with an excess of 14 wt% of the F component a molecular weight of about 17 000 g/mol is achieved. The thermal stability of the polymers lies in the range between 250-440 °C for the splitting-off temperature of the sulfonic acid group, which is well above the operating temper-ature of an intermediate temperature fuel cell. In order to investigate the influence of poly(arylene)-ionomers in base-excess-blend membranes, different mixing ratios of PBI and the poly(arylene)-ionomers are made. The membranes are examined in terms of the oxidative and thermal properties and are applied in the fuel cell. Through the ionic crosslinking in base-excess-blend membranes, the splitting off temperature of the sulfonic acid groups can be in-creased. The membrane B1S4 shows a splitting off temperature of 430 °C, while the pure polymer SPE-BP-OFT has a splitting-off temperature of 380 °C. The oxidative stabilities of the membranes are examined by the Fenton Test (FT). The membranes of B1 and S3 or S4 show a slight decrease in the thermal stability after the FT. Also the SEM images show that: after 144 h, the membranes have small holes in the range of 5 μm. The membranes of B1 and S1 or S2 have, after the FT, a very inhomogeneous and porous surface, which results from the degradation of the polymers. The GPC measurements before and after the FT shows, that dur-ing the FT the molecular weight decreases. The membranes made from B2 and B3 show better FT results. In this case the mass loss is in the range of max. 10 wt%, while the weight loss after 144 h for B1 reaches a value of about 30 wt%. The much higher molecular weight of B2 leads to better results than the membranes of B3. Due to the high molecular weight of B2, bimodal curves are obtained in the GPC measurements, so that first conclusions can be drawn which polymer is attacked by the radicals. For the membranes with B3, the two polymers cannot be separated by GPC measurements, because they have similar molecular weights. The investigated membranes show a stability decrease in the following order, which is independ-ent of the PBI: B2S9 > B2S8 > B2S4 > B2S6 > B2S3.
The base-excess-blendmembranes are operated in a fuel cell and are measured under realistic conditions. Before installation of the membrane in the fuel cell, it must be doped with phos-phoric acid (PA), to obtain a proton conductive membrane. The doping level is set to 400 wt% since the mechanical stability of the PA-doped membranes is sufficient to be incorporated into a fuel cell. According to the theory, the membranes with the smallest proportion of the acidic polymer should show the best results, which can be confirmed in this work. If the proportion of the acidic polymer is too large, it has a negative effect on the performance of the fuel cell. For some membranes no stable voltage signal could be set, because the phosphoric acid is only adsorbed on the surface of the membrane and is removed by the gas stream. To improve the performance of the membrane, the doping degree can be increased, but this leads to a decrease of the mechanical strength of the membrane. A further possibility to improve the performance of the fuel cell is to increase the platinum content in the electrode. Thus, for B3S8-b the current density can be increased by the use of 3 mg Pt/cm² as catalyst, for a factor of two to 360 mA/cm². Although the membranes with B2 show better results than B3 in the FT, they have significantly poorer current densities than the membranes with B3. The investigated membranes show even better results than the membrane which are used in the literature. In the literature, a platinum content of at least 1 mg Pt/cm² is used, while in this work, a platinum content of 0,3 mg Pt/cm² is applied. Thus in this work can be shown that sufficient per-formance can be achieved with a low platinum content in the fuel cell
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
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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