1,720,957 research outputs found
Simulating real molecules with tensor network techniques
Get PDFDie Beschreibung quantenmechanischer Systeme, wie großer Moleküle, aus der Grundlagenperspektive ist, dank des Fortschritts numerischer Verfahren und der enormen Rechenleistung moderner Computer, in greifbare Nähe gerückt. In dieser Arbeit implementieren wir einen Rahmen zur Erweiterung des Matrix-Produkt-Zustand-Ansatzes zu höheren Topologien und zeigen, wie mit diesen Zuständen physikalische Eigenschaften großer Systeme berechnet werden können. Wir diskutieren diverse mögliche Anwendungen, die zumeist über den ursprünglichen, eindimensionalen Einsatzbereich von MPS hinaus gehen. Dies führt zu neuen Fragestellungen, wie der Notwendigkeit, sich mit Systemen ohne konkreten Dimensionlitätsbegriff zu befassen, sowie der Implementierung neuer Algorithmen zur Berechnung von Observablen. Wir besprechen sowohl statische, als auch dynamische Tensornetzwerkanwendungen und beschäftigen uns ausgiebig mit der Frage der dynamischen Adaptierung der Einteilchenorbitale. Anschließend verwenden wir eine neue Methodik zur Behandlung großer, lokaler Hilberträume mit gebrochener U(1) Teilchenzahlerhaltung, um Fermi-Bose-Gemische effizient zu beschreiben. Dies ermächtigt uns, im Folgenden, zu zweierlei Untersuchungen.
Zuerst behandeln wir das statische, eindimensionale Hubbard-Holstein-Modell erneut und berechnen ein Phasendiagramm mit hoher numerischer Güte. Auch wenn es sich hierbei nicht um eine Grundlagenrechnung handelt, so ist sie doch von hohem Interesse für die theoretische Deutung realistischer Systeme, wie wir im entsprechenden Teil argumentieren werden. Zusätzlich zu der antiferromagnetischen und der Peierls Phase, die bereits in früheren Untersuchungen gefunden worden sind, können wir auch die Existenz einer metallischen Phase dazwischen bestätigen. Des Weiteren finden wir ein zuvor nicht beschriebenes Signal in der metallischen Phase. Dieses wird gekennzeichnet durch eine breitere Phononenverteilung und das Erscheinen von nur einer Anregung ohne Energiedifferenz, welche höchst wahrscheinlich ein Spin-Gap hat, jedoch kein Charge-Gap.
Im Folgenden wenden wir uns der ab-initio Behandlung großer organischer Moleküle außerhalb des Gleichgewichts, in Abwesenheit der Gültigkeit der Born-Oppenheimer Näherung, zu. Wir nutzen unsere Methoden zur Simulation der Dynamik der zwei niedrig-liegenden Anregungen des Pyrazin-Moleküls S_1 und S_2 und stellen eine Übereinstimmung mit vorherigen Arbeiten fest. Des Weiteren erkennen wir, dass die Dynamik größtenteils durch die klassische, reduzierte Dichtematrix korrekt wiedergegeben wird. Dann wenden wir uns dem Thema unseres Hauptinteresses zu, der Singulett-Spaltung in großen, organischen Molekülen. Singulett-Spaltung ist ein spinerlaubter, photo-physikalischer Prozess, bei dem ein Singulett Exciton in zwei Triplett Excitone zerfällt. Es wird angenommen, dass dadurch ein Verschieben der theoretischen Grenze für die Effizienz von Solarzellen erreicht werden kann, und daher wird diesem Prozess eine Schlüsselrolle bei der Entwicklung neuer Photovoltaikgeräte zugesprochen. Wir finden eine hervorragende Übereinstimmung mit experimentellen Messungen in dem von uns untersuchten 1,4-bis(11-phenyltetracen-5-yl)Benzol Molekül und können des Weiteren diejenigen Moden feststellen, die für den Energietransfer zwischen den Systemen verantwortlich sind. Weiterhin berechnen wir den Ertrag an Triplett Elektronen für verschiedene, im Experiment einstellbare, Parameter und finden auch hier eine Übereinstimmung mit den Messungen. Eine charakteristische Zeitskala gibt sich zu erkennen, die unabhängig von den elektronischen Parametern ist. Daher untersuchen wir deren Ursprung, im Zuge dessen unsere Analyse zeigt, dass es sich hierbei um einen durch Kohärenzen getriebenen Prozess handelt. Des Weiteren wird der Ursprung des Zusammenbruchs der Kohärenzen, durch ein Kombinationsvorgehen aus Analytik und Numerik, untersucht. Dies ermöglicht uns nicht nur, den exakten Wert dieser Zeitskala anzugeben, sondern verbindet auch den Grund für den Zeitpunkt des Zusammenbruchs der Kohärenzen mit dem Ausbilden von Quasiteilchen und der Renormierung derer effektiver Tunnelamplituden.Describing quantum mechanical systems, like large molecules, from first principles has come within reach of numerical techniques due to the progress in method development and the enormous computational power of modern day computers. In this thesis we establish a framework in order to extend the matrix product state ansatz to higher topologies and demonstrate how to compute physical properties of large systems with these states. We discuss various possible applications mostly going further than the original domain of applicability for one-dimensional systems. This introduces additional issues like the necessity to deal with systems without a notion of dimensionality, as well as implementing new algorithms in order to be able to compute observables. We discuss static and dynamic applications of tensor networks and deal extensively with the question of single particle orbitals and their optimization on the fly. We then use a new method for the treatment of large local Hilbert spaces with broken U(1) particle number symmetry in order to describe efficiently Fermi-Bose mixtures. This enables us to do investigations of two systems.
First, we revisit the static one-dimensional Hubbard-Holstein model and map out its phase diagram faithfully. Even though not a first principles model, it is still of high interest in the theoretical clarification of realistic systems, as we shall argue. In addition to the antiferromagnetic phase and the Peierls phase known from previous investigations, we can also confirm the existence of an intermediate metallic phase. Furthermore, we find new features within the metallic phase which were not described before. These include the existence of a broader phonon distribution and the emergence of a single gapless mode which is most likely spin gapped but does not have a charge gap.
Second, we turn to the ab-initio out-of-equilibrium investigation of the dynamics of large organic molecules in the vicinity of a breakdown of the Born-Oppenheimer approximation. We benchmark our methods with the pyrazine molecule and its two low lying excitations S_1 and S_2 and find agreement to previous works. Furthermore, we find the main part of the dynamics to be captured by the classical reduced density matrix. Then we turn to our main topic of interest, the singlet fission in large organic molecules. Singlet fission is a spin-allowed photo physical process in which a singlet exciton decays into two triplets excitons. It is widely believed to be able to shift the theoretical bounds of solar cells and therefore might be key to the development of new photo voltaic devices. In addition to an excellent agreement to experimental data, we investigate the modes which dominate the energy transfer in 1,4-bis(11-phenyltetracen-5-yl)benzene and compute the triplet electron yield for various experimentally tuneable parameters. This, as well, is in good agreement with experimental measurements. A characteristic time-scale arises, which is independent of the chosen electronic parameters. Therefore, we investigate its origin where our analysis shows that it is a coherence-driven process. Furthermore, the origin of the breakdown of coherence is investigated with a hybrid approach between analytics and numerics. This not only enables us to give an exact numerical value for this time-scale, but also attaches the reason for the particular value to quasi particle formation and the renormalization of their effective hopping elements
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
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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