1,720,997 research outputs found
Butterfly hysteresis loop and dissipative spin reversal in the S = 1/2, V-15 molecular complex
No full textChiorescu I, Wernsdorfer W, Müller A, Bögge H, Barbara B. Butterfly hysteresis loop and dissipative spin reversal in the S = 1/2, V-15 molecular complex. PHYSICAL REVIEW LETTERS. 2000;84(15):3454-3457.Time resolved magnetization measurements have been performed on a spin 1/2 molecular complex, so-called V-15. Despite the absence of a barrier, magnetic hysteresis is observed over a time scale of several seconds. A detailed analysis in terms of a dissipative two-level model is given, in which fluctuations and splittings are of the same energy. Spin-phonon coupling leads to long relaxation times and to a particular "butterfly" hysteresis loop
Adiabatic Landau-Zener-Stuckelberg transition with or without dissipation in the low-spin molecular system V-15
No full textChiorescu I, Wernsdorfer W, Müller A, Miyashita S, Barbara B. Adiabatic Landau-Zener-Stuckelberg transition with or without dissipation in the low-spin molecular system V-15. PHYSICAL REVIEW B. 2003;67(2): 020402.The spin-1/2 molecular system V-15 shows no barrier against spin reversal. This makes possible direct phonon activation between the two levels. By tuning the field sweeping rate and the thermal coupling between the sample and the thermal reservoir we have control over the phonon-bottleneck phenomena previously reported in this system. We demonstrate adiabatic motion of molecule spins in time dependent magnetic fields and with different thermal coupling to the cryostat bath. We also discuss the origin of the zero-field tunneling splitting for a half-integer spin
Environmental effects on big molecule with spin 1/2
No full textChiorescu I, Wernsdorfer W, Barbara B, Müller A, Bögge H. Environmental effects on big molecule with spin 1/2. JOURNAL OF APPLIED PHYSICS. 2000;87(9):5496-5498.The V-15 polyoxovanadate molecule is made of 15 spins 1/2 with antiferromagnetic couplings. It is a low spin/big molecule with spin S=1/2. Contrary to large spins/big molecules of the Mn-12-ac type, V-15 has no energy barrier against spin rotation. Nevertheless, it shows magnetic hysteresis. This new phenomenon characterized by a "butterfly" hysteresis loop is due to the effect of the environment on the quantum rotation of the entangled 15 spins of the molecule, in which the phonon density of states is not at its equilibrium (phonon bottleneck). This behavior is very likely specific to big molecules with low spin. (C) 2000 American Institute of Physics. [S0021-8979(00)31908-9]
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
The V-15 molecule, a multi-spin two-level system: Adiabatic LZS transition with or without dissipation and Kramers theorem
No full textBarbara B, Chiorescu I, Wernsdorfer W, Bögge H, Müller A. The V-15 molecule, a multi-spin two-level system: Adiabatic LZS transition with or without dissipation and Kramers theorem. PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT. 2002;(145):357-369.The so-called V-15 compound, of formula K-6[(V15As6O42)-As-IV(H2O)]8H(2)O, is formed of 15 spins 1 antiferromagnetically coupled. The resultant spin is equal to 1/2. Contrary to what is expected at first sight, this half-integer spin is gapped. We show that this is a consequence of the multi-spin character of the molecule. Time reversal symmetry (Kramers theorem) is preserved due to the existence of a groundstate degeneracy larger than 2. Magnetization experiments have been performed at different temperatures, sweeping-field rates and couplings with the cryostat. Their interpretation in terms of the Landau-Zener-Stuckelberg model gives evidence for adiabatic LZS spin reversal with and without dissipation
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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