1,720,969 research outputs found
First order nucleation of charge ordered domains in La0.5Ca0.5MnO3 detected by 139La and 55Mn NMR
Full text linkThe local magnetism and charge ordering of La0.5Ca0.5MnO3, was investigated between room temperature and 1.3 K by means of La-139 and Mn-55 NMR. Antiferromagnetic and ferromagnetic domains are assigned unambiguously to the insulating charge ordered and the metallic state respectively. The phases are found to coexist at all temperatures below the first formation of a charge-ordered state. The two signal fractions display thermal and magnetic hysteresis, while their local fields and relaxations do not. These features and the absence of any critical behavior are characteristic of a first order F-AF transition, with ferromagnetic domains microscopically identical to the bulk metallic phase of the OM
Inhomogeneous electronic state of low-doped insulating manganites: NMR and μSR evidence
No full textWe report on an Mn-55 NMR investigation of calcium-doped manganite samples carried out at 4.2K. In the insulating members of the family. the localization or hole-rich Ferromagnetic clusters is revealed by the peculiar two-peaked spectra, and by distinct shifts of the resonance lines in an external field. Results are discussed in view of inelastic neutron scattering findings and combined La-139 NMR and pSR data
Field-induced segregation of ferromagnetic nanodomains in Pr0.5Sr0.5MnO3 detected by 55Mn NMR
No full textThe antiferromagnetic manganite Pr0.5Sr0.5-MnO3 was investigated at low temperature by means of magnetometry
and 55Mn NMR. A field-induced transition to a ferromagnetic state is detected by magnetization
measurements at a threshold field of a few tesla. NMR shows that the ferromagnetic phase develops from zero
field by the nucleation of microscopic ferromagnetic domains, consisting of an inhomogeneous mixture of
tilted and fully aligned parts. At the threshold the NMR spectrum changes discontinuously into that of a
homogeneous, fully aligned, ferromagnetic state, suggesting a percolative origin for the ferromagnetic
transition
Electronic phase separation in lanthanum manganites: evidence from 55Mn NMR
No full textMn-55 NMR experiments were carried out at 1.3-4.2 K on six samples of lanthanum manganites, with a hole doping concentration ranging from the antiferromagnetic-insulator to the ferromagnetic-conductor region of the phase diagram. The dependence of the resonance frequencies on external fields is either as expected for ferromagnets (FM) or for antiferromagnets (AF). No indication of a canted phase could be detected. FM and AF resonances were found to coexist in all samples and are grouped in three broad bands, whose frequencies do not depend in first order on hole concentration. Strong evidence of interaction between AF and FM regions was provided by longitudinal relaxation experiments in several samples. An explanation of this behavior is offered in terms of intrinsic phase separation of the holes into FM microdomains. We determine the Mn-55 hyperfine coupling to be isotropic in all cases, with A=6.2 T/mu(B) for the on-site term in the AF domains
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
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
- …
