1,721,020 research outputs found
Développement d'un résonateur de test pour l'étude des propriétés radiofréquence des matériaux supraconducteurs
No full textPushing the limits of the accelerating field and quality factor of superconducting radiofrequency (SRF) cavities beyond pure niobium requires the implementation of specific inner surface treatments and the development of alternative materials, which are yet to be studied and optimized. One of the fundamental challenges in investigating alternative materials is that only samples or cavity cut-outs can be fully characterized from a material science point of view. In contrast, complete cavities enable the SRF characterization of the inner surface, while samples can usually only be analysed using surface characterization, mechanical testing, and direct current methods. To overcome this problem, a test resonator for samples called “Quadrupole Resonator” (QPR) was designed and operated at Conseil Européen pour la Recherche Nucléaire (CERN), and another one was developed later at Helmholtz-Zentrum Berlin (HZB). In a collaborative effort between Universität Hamburg (UHH) and Deutsches Elektronen-Synchrotron (DESY), an improved QPR has been designed, successfully commissioned, and is currently being operated at DESY. This QPR allows for the full RF characterization of samples at frequencies of 0.42 GHz, 0.86 GHz, and 1.3 GHz, within a temperature range of 1.8-20 K, and at designed applied magnetic fields up to 120 mT, as will be demonstrated.
This work presents the UHH QPR design, which incorporated improvements motivated by mechanical and RF studies and experimental experience. The results from both room temperature and cryogenic commissioning are discussed as well. More importantly, the results for the RF tests conducted on a Nb sample after undergoing a series of chemical surface treatments are detailed. The RF characterization data include surface resistance as a function of temperature and applied magnetic field and frequency and thermal conductivity as a function of temperature of the sample. These results show an overall good agreement with theoretical models describing superconductivity. Furthermore, material parameters, such as London penetration depth, mean free path, superconducting gap and Dynes parameter, derived from the experimental data in general align closely with values reported in literature. Finally, an outlook of the further improvements and usage of the QPR is presented.Die Optimierung des Grenzen des Beschleunigungsfeldes und des Gütefaktors von supraleitenden Hochfrequenz (SRF) Hohlraumresonatoren über reines Niob hinaus erfordert die Umsetzung spezifischer Oberflächenbehandlungen und die Entwicklung alternativer Materialien, die noch untersucht und optimiert werden müssen. Eine der grundlegenden Herausforderungen bei der Untersuchung alternativer Materialien besteht darin, dass nur Proben oder Oberflächenausschnitte aus materialwissenschaftlicher Sicht vollständig charakterisiert werden können. Im Gegensatz dazu ermöglichen vollständige Hohlraumresonatoren die SRF-Charakterisierung der inneren Oberfläche, während Proben in der Regel nur durch Oberflächencharakterisierung, mechanischen Tests und Gleichstrom-Methoden analysiert werden können. Um dieses Problem zu überwinden, wurde ein Testresonator für Proben namens ``Quadrupolresonator” (QPR) entwickelt und am Conseil Européen pour la Recherche Nucléaire (CERN) betrieben, und später wurde ein weiterer am Helmholtz-Zentrum Berlin (HZB) entwickelt. In einer Zusammenarbeit zwischen der Universität Hamburg (UHH) und dem Deutschen Elektronen-Synchrotron (DESY) wurde ein verbesserter QPR entworfen, erfolgreich in Betrieb genommen und derzeit bei DESY betrieben. Dieser QPR ermöglicht die vollständige HF-Charakterisierung von Proben bei Frequenzen von 0,42 GHz, 0,86 GHz und 1,3 GHz, in einem Temperaturbereich von 1,8-20 K und bei geplanten angelegten Magnetfeldern von bis zu 120 mT.
Diese Arbeit präsentiert das UHH-QPR-Design, das Verbesserungen aufgrund von mechanischen und HF-Studien sowie experimentellen Erfahrungen beinhaltet. Die Ergebnisse sowohl der Raumtemperatur- als auch der kryogenen Inbetriebnahme werden ebenfalls diskutiert. Zu dem werden die Ergebnisse der HF-Tests an einer Nb-Probe nach einer Reihe von chemischen Oberflächenbehandlungen diskutiert. Die HF-Charakterisierungsdaten umfassen den Oberflächenwiderstand als Funktion von Temperatur und angelegtem Magnetfeld, sowie jeweils die Frequenz und die Wärmeleitfähigkeit als Funktion der Temperatur der Probe. Diese Ergebnisse zeigen insgesamt eine gute Übereinstimmung mit theoretischen Modellen zur Beschreibung der Supraleitfähigkeit. Darüber hinaus stimmen die aus den experimentellen Daten abgeleiteten Materialparameter wie London-Eindringtiefe, mittlere freie Weglänge, supraleitende Lücke und Dynes-Parameter im Allgemeinen eng mit in der Literatur berichteten Werten überein. Abschließend wird ein Ausblick auf weitere Verbesserungen und die Verwendung des QPR präsentiert
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
Investigations and Considerations of Oxygen Diffusion Profiles in Superconducting Mid-T RF Cavities Utilizing EXAFS Spectroscopy
No full textA screening of oxygen profiles in mid-T treated SRF cavities is crucial, in order to infer physical correlations between the microscopic cavity lattice and cavity performance – a problem concerning acceleration physicists for years. This thesis provides an analysis of oxygen diffusion profiles for three differently treated samples: Two mid-T baked and the third with the standard EuXFEL recipe. The measurement method utilizes EXAFS spectroscopy and was carried out at the DELTA facility in Dortmund. The result suffers heavily under noise, making the quantity of the result barely useable. Qualitatively, no deviations of current models regarding the profiles could be proven, and no results of previous studies were contradicted. The experimental analysis is described in precision, interpretations of the possible are undertaken and theoretical considerations regarding error estimation and possible EXAFS simulations for future attempts are provided. A repetition at the PETRA III facility is indicated
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
Automated Surface Classification of SRF Cavities for the Investigation of the Influence of Surface Properties onto the Operational Performance
No full textSuperconducting niobium radio-frequency cavities are fundamental for the European XFEL and the International Linear Collider. To use the operational advantages of superconducting cavities, the inner surface has to fulfill quite demanding requirements. The surface roughness and cleanliness improved over the last decades and with them, the achieved maximal accelerating field. Still, limitations of the maximal achieved accelerating field are observed, which are not explained by localized geometrical defects or impurities. The scope of this thesis is a better understanding of these limitations in defect free cavities based on global, rather than local, surface properties.For this goal, more than 30 cavities underwent subsequent surface treatments, cold RF tests and optical inspections within the ILC-HiGrade research program and the XFEL cavity production. An algorithm was developed which allows an automated surface characterization based on an optical inspection robot. This algorithm delivers a set of optical surface properties, which describes the inner cavity surface. These optical surface properties deliver a framework for a quality assurance of the fabrication procedures. Furthermore, they shows promising results for a better understanding of the observed limitations in defect free cavities
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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