1,721,002 research outputs found
High-field electron paramagnetic resonance study of the polymerization in Na2Rb1-xCsxC60
No full textWe report on the study of the magnetic properties of the low-temperature polymer phases in Na2Rb1-xCsxC60
at 110 GHz microwave frequency with x varying between 0 and 1. The magnetic and structural properties of the polymer
phase strongly depend on the Cs content and its electronic structure progressively becomes quasi-one-dimensional as x is
increased. While the electronic properties of the polymeric Na2RbC60 appear to be close to three-dimensional metal,
Na2Rb0.3Cs0.7C60 shows characteristics of quasi-one-dimensional metal where instability in the electronic structure was
found as detected by the sudden disappearance of the ESR intensity due to the opening of the gap at the Fermi surface.
The observation of an additional resonance line below 15 K, which could be attributed to antiferromagnetic resonance,
suggests that the low-temperature polymeric phase in Na2Rb0.3Cs0.7C60 has a well-defined magnetic ground state
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
Electron spin resonance study of the polymeric phase of Na2RbC60
No full textThe structural and electronic properties of the polymeric phase of Na2RbC60 which comprises of C-C bridged
C-60(3-) chains have been studied between 410 and 4 K with the electron spin resonance (ESR) technique. On cooling,
the polymeric phase starts growing below similar to 250 K. Its fraction reaches a maximum at similar to 190 K, where
around 55% of the monomeric cubic phase have transformed to the polymer. The temperature dependence of the ESR
susceptibility suggests that the Na2RbC60 polymer is conducting down to 3 K. The ESR results exclude the possibility of
the existence of a ground-state instability and the formation of either a spin-density-wave (SDW) or a charge-densitywave
(CDW) sta
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
A tyrosil radical in an irradiated single crystal of N-acetyl-L-tyrosine studied by X-band cw-EPR, high-frequency EPR, and ENDOR spectroscopies
No full textGamma-ray irradiation of an N-acetyl-L-tyrosine single crystal produces three stable radicals (A-C) which have been identified and characterized in their hyperfine coupling (hfc) tensors by using conventional and high-frequency electron paramagnetic resonance (HF-EPR) and X-band electron nuclear double resonance (ENDOR). Radical A is a neutral phenoxyl radical of which the g-tensor principal value corresponding with a good approximation to the C-O(H) direction is g(x) = 2.0094 +/- 0.0002. The comparison with the corresponding values obtained for the similar tyrosyl radicals playing a role in different biological systems supports the idea of using the g, value as a probe to find the presence of a hydrogen-bond interaction involving the phenoxyl oxygen. Radical B is a neutral cyclohexadienyl radical obtained by hydrogen atom addition at a position ortho to the phenolic group of the tyrosine moiety. Its hfc tensors have been fully characterized and found to be in agreement with present theories. Radical C is found to be produced by reduction of the carboxylic group of the parent tyrosine derivativ
High field ESR study of TDAE-C60 powder at different Larmor frequencies
No full textSQUID magnetization measurements at low magnetic fields were performed on a freshly prepared and an aged
sample of TDAE-C-60. The ferromagnetic phase transition temperature T-c was 16 K in the freshly prepared sample,
confirming previous results, whereas T-c = 5 K was measured for the aged sample. ESR spectra of the same samples
were recorded between room temperature and 5 K at Larmor frequencies of about 110, 180, 280, 380 GHz. For both
samples below 60 K the spectrum shows a selective downshift of the resonant fields which is more pronounced in the
lower part of the spectrum profile. The results were qualitatively explained by the theory developed to account for the
one-dimensional short-range order effects between spins with inequivalent g tensors. Specifically, the observed negative
field-shifts have been attributed to short-range correlation effects induced by anisotropic exchange and dipolar interaction
fluctuations between inequivalent spins on TDAE(+) and C-60(-) centers
High-Field EMR, recent CW developments at 25 Tesla and next millenium challenges
No full textAfter a brief review of the motivations to perform electron magnetic resonance at very high-field/highfrequency
(VHF-EMR), we describe the spectrometers operational at the National High Magnetic Field Laboratory
(NHMFL), Tallahassee, Florida: a 17 and a 25 Tesla instrument. We present measurements performed with the 25 Tesla
machine that can operate up to 700 GHz for a g-Lande factor = 2 system. First we document the need of VHF-EMR to
resolve all the three components of the g-tensor and thus better characterize the electronic structure of radicals involved
in photosynthesis. We then report on the potential of VHF-EMR to address key questions concerning the fundamental
mechanisms of the glass-formation process. As a third example we show the interest of VHF-EMR to accurately
determine the zero-field splitting parameters of a large-zero-field-splitting system and consequently unequivocally decide
upon the structure of the system. The current developments underway at the NHMFL are presented. In the conclusion
we conjecture upon the developments of modern EMR
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
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