1,721,060 research outputs found
Online Visualisierung der Elementverteilungen für Messungen mit einem Röntgenfluoreszenz-Mikroskop an PETRA III
No full textDie Röntgenfluoreszenz-Mikroskopie ist ein präzises, zerstörungsfreies und bildgebendes Verfahren zur Bestimmung der Elementverteilungen einer Probe mit einer räumlichen Auflösung im Submikrometerbereich. Röntgenstrahlung wird dafür auf einen möglichst kleinen Bereich in der Probenebene fokussiert und schrittweise oder kontinuierlich verfahren. Für jedes Pixel wird ein Röntgenfluoreszenzspektrum aufgenommen, aus dem aus den charakteristischen Röntgenlinien die chemische Zusammensetzung bestimmt werden kann. Für ein gutes Signal-Rausch-Verhältnis müssen die Messungen über einen langen Zeitraum oder bei hohen Eingangszählraten am Detektor durchgeführt werden. Letztere können bei Messungen mit brillianter Synchrotonstrahlung, wie an PETRA III am DESY in Hamburg, erreicht werden.Um einschätzen zu können, ob der abgerasterte Bereich auf der Probe uninteressant ist oder Artefakte aufweist und die Messung vorzeitig abgebrochen werden kann, sollten die groben Elementverteilungen bereits während der Messung visualisiert werden. Ziel meiner Arbeit war es, zwischen dem Messrechner und einem weiteren Rechner eine schnelle, sichere und vollständige Datenkommunikation herzustellen, sodass der anfallende binäre Datenstrom auf dem zweiten Rechner möglichst schnell interpretiert, ausgewertet und die Elementverteilung auf dem Bildschirm graphisch dargestellt werden kann. Die Kommunikation wird über ZeroMQ-Sockets realisiert und die Auswertung der Röntgenfluoreszenzspektren erfolgt über die ROI-Methode. Das während meiner Arbeit erstellte Python-Programm ermöglicht bei Zählraten bis 500 000 Signalen pro Sekunde eine Visualisierung der Elementverteilung in Echtzeit, die während der Messung fortgehend aktualisiert wird
Improved quantitative XRF analysis of industrial thin film samples by calibration using thin film RMs certified by reference-free XRF enabling traceability to the SI
No full textReference-free XRF is a SI traceable technique for the
determination of the mass deposition (mass per unit area) of elements in films on the nano- and micro scale. The method is radiometrically calibrated instrumentation (PTB@BESSY II, Germany) and based on reliable knowledge of all relevant atomic fundamental, experimental and instrumental parameters. No calibration sample or reference materials are necessary. The approach had been validated in the CCQM-P140 pilot study and the K129 key comparison by determination of mole fractions in Cu(In,Ga)Se2 thin films
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
Liquid Phase Adsorption of Sulfur on Germanium Reaction Mechanism and Atomic Geometry
No full textWe present a fundamental study of the monolayer adsorption of sulfur on Ge(100) surfaces from aqueous (NH4)2S solution. This treatment shows promising perspectives for the passivation of high-mobility semiconductor surfaces and is therefore presently of great technological importance. The adsorption mechanisms as well as the adsorption geometry are thoroughly investigated at the atomic scale, by both experiment and theory, applying X-ray absorption spectroscopy and molecular dynamics simulations. Our findings indicate that sulfidation in solution results in the formation of Ge-S-Ge bridges along the [110] direction, with no indication for -SH surface groups. A S-Ge bond length of 2.25 ± 0.05 Å was deduced, which is affected by the chemical environment of the sulfur atoms, i.e., by residual surface oxides. Our study provides novel insights into the surface termination and atomic structure of (NH4)2S-treated Ge(100) surfaces and discusses possible differences from in situ sulfur adsorption methods such as H2S or S2 exposure. © 2013 American Chemical Society.sponsorship: This work has been supported by the Research Foundation Flanders (FWO), the KU Leuven BOF research programs (GOA/09/006 and PDMK/11/150), as well as by the Odysseus program of the Flemish Government. The X-ray absorption measurements were supported by the European Commission-Research Infrastructure Action under the FP6 "European Integrated Activity of Excellence and Networking for Nano- and Micro-Electronics Analysis" - Project number 026134 (RI3) ANNA. We thank Prof. R. E. Palmer for access to the High Resolution EELS spectrometer. Useful suggestions by S. Sioncke and C. Adelmann (IMEC, Leuven, Belgium) are gratefully acknowledged. (Research Foundation Flanders (FWO), KU Leuven BOF research programs|GOA/09/006, KU Leuven BOF research programs|PDMK/11/150, Flemish Government, European Commission|026134 (RI3) ANNA)status: Publishe
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
Development of operando characterizations for high energy density batteries by means of X-Ray fluorescence analysis
No full textLithium-Schwefel-Batterien (Li/S Batterien) zählen aufgrund ihrer hohen theoretischen Energiedichte zu den Hochenergiebatteriematerialien, an denen für den Einsatz in Elektroautos und als stationärer Speicher erneuerbarer Energien geforscht wird. Die in der Batterie auftretenden, bisher nicht vollständig verstandenen Alterungsmechanismen, insbesondere die Entstehung der im Elektrolyten löslichen Polysulfide, sorgen für den Verlust von Aktivmaterial und verringern dadurch so stark die Kapazität und die Lebensdauer, dass sie derzeit noch nicht großflächig eingesetzt werden. Die vollständige Entschlüsselung der zeitabhängigen Degradationseffekte kann nur durch analytische Techniken im operando Modus (Echtzeitanalysen) erschlossen werden.
Im Rahmen dieser Arbeit konnte durch die Verwendung von Synchrotronstrahlung, kalibrierter Instrumentierung und einer Kombination aus operando Nahkanten-Absorptionsfeinstruktur-Analyse (NEXAFS) mit referenzprobenfreier Röntgenfluoreszenzanalyse erstmals die Massenbelegung von Schwefel in gelösten Polysulfiden bestimmt werden. Darüber hinaus wurde mit den entwickelten Messzellen erstmals ein Zugang zu den gelösten Polysulfiden an beiden Elektrodenseiten und somit die gleichzeitige Untersuchung von Umwandlungs- und Transportprozessen der Polysulfide ermöglicht. Der Polysulfidshuttle und die Änderung der mittleren Polysulfidlänge wurden über drei volle Entlade-Ladezyklen untersucht und damit ein besseres Verständnis der Alterungsmechanismen in den Li/S Zellen gewonnen.
Die von uns entwickelte Operandomesszelle und das Verfahren eignen sich darüber hinaus auch für die quantitative Element- und Speziesbestimmung anderer Zellchemien, z.B. von Lithium-Ionen-Batterien oder Festkörperbatterien. Außerdem können mit der Messzelle auch andere unabhängige Operandomessverfahren, z.B. Ramanspektroskopie, durchgeführt werden.Lithium sulfur batteries (Li/S batteries) are promising candidates for batteries in electric vehicles and as stationary energy storage device due to their high specific energy density. The underlying degradation mechanisms are not completely unraveled yet, but it is known that the formation of soluble polysulfides causes capacity fading and limits the cycle life, so that the Li/S battery is not widely commercially used nowadays. For the investigations of the time depended aging mechanism analytical operando methods are needed.
In the present work, the use of synchrotron radiation, calibrated instrumentation and the combination of operando NEXAFS (near edge X-ray fine structure) and traceable XRF (X-ray fluorescence analysis) measurements enables the absolute quantification of the mass deposition for sulfur in dissolved polysulfides for the first time. With our reference-free quantification method, no calibration samples have to be used. Moreover, with a new cell design we got access to polysulfides at both electrode sides which lead to the simultaneous investigation of conversion reactions and transport mechanisms and therefore the possibility to evaluate the polysulfides shuttle phenomena. The measurements have been performed over three full charge/discharge cycles. With our experimental set-up, we additionally got access to the change of the average polysulfide chain length which enables a deeper understanding of the capacity fading processes.
The presented measurement cells as well as the quantification method can be adopted for other cell chemistries, like lithium ion batteries or even all solid state batteries. Last but not least, the cell design is also applicable for different, complementary analytical methods, such as optical Raman spectroscopy
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