1,721,095 research outputs found
Spinwellenberechnungen für niedrigdimensionale Magnete
No full textThe focus of this thesis is on quantum Heisenberg magnets in low dimensions. We modify the method of spin-wave theory in order to address two distinct issues. In the first part we develop a variant of spin-wave theory for low-dimensional systems, where thermodynamic observables are calculated from the Gibbs free energy for fixed order parameter. We are able to go beyond linear spin-wave theory and systematically calculate two-loop correction to the free energy. We use our method to determine the low-temperature physics of Heisenberg ferromagnets in one, two and three spatial dimensions. In the second part of the thesis, we treat a two-dimensional Heisenberg antiferromagnet in the presence of a uniform external magnetic field. We determine the low-temperature behavior of the magnetization curve within spin-wave theory by taking the absence of the spontaneous staggered magnetization into account. Additionally, we perform quantum Monte Carlo simulations and subsequently show that numerical findings are qualitatively comparable to spin-wave results. Finally, we apply our method to an experimentally motivated case of the distorted honeycomb lattice in order to determine the strength of the exchange interactions.Die vorliegende Dissertation befasst sich in zwei Teilen mit den Quanten-Heisenberg-Magneten in reduzierten Dimensionen. Zur Beantwortung physikalischer Fragestellungen wird die Methode der Spinwellenentwicklung herangezogen und weiterentwickelt. Im ersten Teil schlagen wir eine neue Spinwellen-Methode für niedrigdimensionale Spinsysteme vor; thermodynamische Observable werden aus der Gibbschen Freien Enthalpie bei konstantem Ordnungsparameter berechnet. Neben der linearen Spinwellentheorie konnten wir auch die Zwei-Schleifen-Korrektur zur Freien Energie bestimmen. Wir bestimmen mit unserem Zugang die Eigenschaften der Heisenberg-Ferromagnete in ein, zwei und drei Raumdimensionen bei tiefen Temperaturen. Im zweiten Teil der vorliegenden Arbeit widmen wir uns zweidimensionalen Heisenberg-Antiferromagneten mit Nächste-Nachbar-Wechselwirkung in Anwesenheit eines homogenen externen Magnetfeldes. Wir bestimmen die Magnetisierungskurve bei tiefen Temperaturen im Rahmen der Spinwellentheorie unter Berücksichtigung der Abwesenheit der Untergitter-Magnetisierung. Darüberhinaus führen wir Quanten-Monte-Carlo Berechnungen durch und zeigen, dass die Spinwellen-Resultate in guter Übereinstimmung mit den numerisch exakten Ergebnissen sind. Abschließend wenden wir unsere Ergebnisse auf den experimentell motivierten Fall eines neuartigen zweidimensionalen metall-organischen Heisenberg-Antiferromagneten auf einem verzerrten Wabengitter an, um die Kopplungsstärke der Austauschwechselwirkung zu bestimmen
Vom Abstrakten zum konkreten «historischen Milieu». Zur An- und Verwendbarkeit der Marxschen Analyse der kapitalistischen Produktionsweise
No full textIn diesem Buchbeitrag bin ich der Frage nach der Aktualität und dem Erklärungspotenzial der Marxschen Analyse der kapitalistischen Produktionsweise auch für die sich im Laufe des 20. Jahrhunderts stark veränderten Gestalten der kapitalistischen Gegenwartsgesellschaft nachgegangen.
Hierbei habe ich zu zeigen versucht, dass für die umfassende Erforschung eines historisch-geographisch bestimmten, konkreten kapitalistischen Landes die Marxsche Analyse der kapitalistischen Produktionsweise aus theorieimmanenten und werkgeschichtlichen Gründen nicht unmittelbar (d.h. ohne theoretische Mittelglieder) verwendet und nicht direkt (d.h. ohne Erforschung des spezifischen historischen Milieus) angewendet werden kann
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
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
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