1,720,995 research outputs found
Theory of excess noise of a quantum dot in the presence of a microwave field
Get PDFThe power spectrum of excess noise of a quantum dot coupled to two leads and irradiated by a microwave field of frequency Ω is derived exactly by directly solving the Heisenberg equation. We found that for Γ<ħΩ, where Γ is the linewidth of the intradot energy level, the power spectrum can be nonzero even if the averaged current is zero. This property originates from photon-assisted tunneling and is very different from the shot noise in steady state. For Γ≫ħΩ, our results are consistent with the recent experiment by Schoelkopf et al. and previous theory.published_or_final_versio
Excess Kondo resonance in a quantum dot device with normal and superconducting leads: The physics of Andreev-normal co-tunneling
No full textWe report on a novel Kondo phenomenon of interacting quantum dots coupled asymmetrically to a normal and a superconducting lead. The effects of intradot Coulomb interaction and Andreev tunneling give rise to Andreev bound resonances. As a result, a new type of co-tunneling process, which we term Andreev-normal co-tunneling, is predicted. At low temperatures, coherent superposition of these co-tunneling processes induces a Kondo effect in which Cooper pairs directly participate formation of a spin singlet, leading to four Kondo resonance peaks in the local density of states, and enhancing the tunneling current.Physics, MultidisciplinarySCI(E)50ARTICLE17null8
Theoretical study for a quantum-dot molecule irradiated by a microwave field
Get PDFMotivated by the recent experiment by Oosterkamp et al. [Nature 395, 873 (1998)] we have developed a theory to describe electron tunneling through two coupled quantum dots irradiated by a microwave field. Our results for both the weak- and strong-coupling regimes are in excellent agreement with experiment. In addition, our theory suggests several unique features in the strong-coupling regime, including Rabi oscillations, which can be verified experimentally. The main resonance and the sideband resonance of the molecular level are also calculated for the entire range of the coupling strength, and show interesting crossover behavior.published_or_final_versio
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
Photon sidebands of the ground state and the excited state of a quantum dot: A nonequilibrium Green-function approach
Get PDFThe electron tunneling through an ultrasmall quantum dot in the presence of time-dependent microwave (MW) fields is studied. In the investigation, two single electronic states (the ground state and the excited state) and the intradot Coulomb interaction are considered. Assuming the tunneling through the system as a coherent process, the time-dependent current and the average current are derived using the nonequilibrium Green-function method. Then we consider two special cases with ħω>Δε and ħω<Δε, respectively, where ω is the frequency of MW fields and Δε is the energy difference between two electronic states. Both the sidebands of the photon-assisted tunneling originated from the ground state, and, in particular, from the excited state are obtained, which is in good agreement with the recent experiment by Oosterkamp et al. [Phys. Rev. Lett. 78, 1536 (1997)]. Moreover, the dependence of the integrated average current on the intensity of MW fields is also discussed, and attributed to the many-body effect of the quantum dot.published_or_final_versio
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
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