1,721,085 research outputs found
Nonadiabatic Landau Zener Tunneling and Quantum Phase Interference in Fe-8 Molecular Nanomagnets
No full textThe Landau-Zener method allows to measure very small tunnel splittings Δ in mol. clusters Fe8. The obsd. oscillations of Δ as a function of the magnetic field applied along the hard anisotropy axis are explained in terms of topol. quantum interference of two tunnel paths of opposite windings. Studies of the temp. dependence of the Landau-Zener transition rate P gives access to the topol. quantum interference between excited spin levels. The influence of nuclear spins is demonstrated by comparing P of the std. Fe8 sample with two isotopically substituted samples. The need of a generalized Landau-Zener transition rate theory is shown
Graphene Spintronic Devices with Molecular Nanomagnets.
No full textThe possibility to graft nano-objects directly on its surface makesgraphene particularly appealing for device and sensing applications. Here we reportthe design and the realization of a novel device made by a graphene nanoconstrictiondecorated with TbPc2 magnetic molecules (Pc = phthalocyananine), to electricallydetect the magnetization reversal of the molecules in proximity with graphene. Amagnetoconductivity signal as high as 20% is found for the spin reversal, revealing theuniaxial magnetic anisotropy of the TbPc2 quantum magnets. These results depict thebehavior of multiple-field-effect nanotransistors with sensitivity at the single-molecule level
Answer to the comment of Chudnovsky: On the square-root time relaxation in molecular nanomagnets
No full text1 pageInternational audienceAnswer to the comment of E. Chudnovsky concerning the following papers: (1) N.V. Prokofév, P.C.E. Stamp, Phys. Rev. Lett.80, 5794 (1998). (2) W. Wernsdorfer, T. Ohm, C. Sangregorio, R. Sessoli, D. Mailly, C. Paulsen, Phys. Rev. Lett. 82, 3903 (1999)
Nonadiabatic Landau–Zener Tunneling in Fe8 Molecular Nanomagnets
No full textThe Landau-Zener method allows to measure very small tunnel splittings ∆ in molecular clusters Fe8. The observed oscillations of ∆ as a function of the magnetic field applied along the hard anisotropy axis are explained in terms of topological quantum interference of two tunnel paths of opposite windings. Studies of the temperature dependence of the Landau-Zener transition rate P gives access to the topological quantum interference between excited spin levels. The influence of nuclear spins is demonstrated by comparing P of the standard Fe8 sample with two isotopically substituted samples. The need of a generalised Landau-Zener transition rate theory is shown
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
Landau-Zener Method to Study Quantum Phase Interference of Fe-8 Molecular Nanomagnets (invited)
No full textWe present details about an exptl. method based on the Landau-Zener model which allows one to measure very small tunnel splittings Δ in mol. clusters Fe8. The measurements are performed with an array of microsuperconducting quantum interference devices. The obsd. oscillations of Δ as a function of the magnetic field applied along the hard anisotropy axis are explained in terms of topol. quantum interference of two tunnel paths of opposite windings. Transitions between M=-S and (S-n), with n even or odd, revealed a parity (symmetry) effect which is analogous to the suppression of tunneling predicted for half integer spins. This observation is the first direct evidence of the topol. part of the quantum spin phase (Berry phase) in a magnetic system. The influence of intermol. dipole interactions on the measured tunnel splittings Δ is shown
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
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