1,720,967 research outputs found
Stroboscopic neutron diffraction from spatially modulated systems
No full textThe combination of stroboscopic techniques and neutron diffraction can be used to study the kinetics of structural changes in condensed matter on a microscopic level. Transient states may be identified and characterized on time-scales down to the microsecond regime. Hence, valuable information about the underlying mechanisms can be obtained from time-resolved experiments. Particularly interesting subjects for this type of investigation are spatially modulated systems which undergo phase transitions or phase separation. The potential of stroboscopic neutron diffraction is demonstrated using three different examples in which samples are periodically perturbed by the variation of temperature, mechanical stress or electric field and their structural response is characterized by time-resolved diffraction. Spinodal decomposition in ionic crystals of the silver-alkali halide type is shown to be dominated by two different processes on different time-scales. The stress-induced phase transition into the incommensurate phase of quartz involves relaxation processes which are reflected by different kinetic behaviours of Bragg peaks and satellite reflections, respectively. Finally, metastable transient states are observed during the field induced lock-in transition in ferroelectric Rb2ZnCl4 which are most probably due to strain fields and pinning effects
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
Kinetics of decomposition in ionic solids II : neutron scattering study of the system AgCl-NaCl
No full textThe kinetic of decomposition in the quasi-binary ionic system AgCl-NaCl has been studied by means of time-resolved neutron diffraction and small-angle neutron scattering. The coherent critical point is estimated as 447 +/- 3 K, 24 K below the upper critical binodal temperature. The chemical decomposition is almost completed in the first 200 s irrespective of the temperature. The mechanical relaxation of the lattice, however, takes place on a much longer timescale and is dominated by coherency strains leading to metastable intermediate states
Time-evolution of phonon spectra during decomposition in AgxNa1-xBr ionic crystals
No full textReal-time inelastic neutron scattering has been used to characterise the mechanism of decomposition in AgxNa1-xBr mixed single crystals well below the critical temperature on a microscopic scale. The chemical demixing process is associated with a splitting of acoustic phonon branches, which is observed to take place within some 100 s. Interestingly, the Bragg reflections exhibit a completely different time behaviour: the adaptation of the equilibrium lattice parameters occurs on a much longer time scale. Hence, decomposition is governed by large coherency strains which persist over a long period of time. Only in a second stage does the crystal lattice relax into the final equilibrium state
Kinetics of decomposition in ionic solids: III. Time evolution of phonons during spinodal decomposition in AgCl-NaCl
No full textReal-time inelastic neutron scattering has been used to study the kinetics of the demixing process in AgCl-NaCl mixed single crystals. The variation of transverse acoustic phonon spectra provides the most direct information about the microscopic non-equilibrium behaviour. It is shown that a well defined splitting of phonon peaks corresponding to the formation of the product phases takes place on a timescale of seconds. Along with the observation of satellite reflections these findings clearly demonstrate that the phase separation is governed by the mechanism of spinodal decomposition in this ionic system. During the entire process the lattice parameter keeps almost unchanged, thus leading to a metastable state characterized by large coherency strains
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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