1,720,986 research outputs found
Mechanism of fast surface self-diffusion of an organic glass
No full textZhu et al. [L. Zhu, C.W. Brian, S. F. Swallen, P. T. Straus,M.D. Ediger, and L.Yu,Phys. Rev. Lett. 106, 256103 (2011)]measured the surface self-diffusion for an organic glass former, indomethacin, and found surface diffusion
is more than 106 times faster than bulk diffusion at temperatures around Tg.With the help of dielectric relaxation and differential scanning calorimetry measurements on bulk indomethacin, and analysis of the data using the
coupling model, we provide a quantitative explanation. We find the bulk α-relaxation time is longer than the
primitive relaxation time also by about six orders ofmagnitude in a range of temperature above and below the bulk Tg. Thus, the cause of the fast surface diffusion is the nearly vanishing of intermolecular coupling of relaxation
and diffusion at the surface. The results of related experimental studies of enhanced relaxation and diffusion at the
surface of other glass formers also have been analyzed and quantitatively explained. Our predictions on surface diffusion from the coupling model are compared with that given by the random first order transition theory
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
Erratum: "Thermodynamic scaling of alpha-relaxation time and viscosity stems from the Johari-Goldstein beta-relaxation or the primitive relaxation of the coupling model" [J. Chem. Phys. 137, 034511 (2012)]
No full textVariations 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
The Nature of Glass: somethings are clear
No full textThe long-standing unsolved problem of glass transition has recently been drawn attention tothe research community and general public by an article published in the New York Times, entitled “The Nature of Glass Remains Anything but Clear”. The article mainly samples current and widely different views of some theoreticians, which have led to the conclusion that the situation is anything but clear. We show this pessimistic conclusion is unwarranted because results from recent experimental investigations have not been considered. These results show clearly the importance of the effects of many-body relaxation (or its surrogate, the degree of departure from linear exponential time dependence) and the relation between the structural α-relaxation with a special secondary relaxation. Both aspects have not been taken into account by most theories. If taken into consideration, significance progress can be expected
Thermodynamic scaling of a-relaxation time and viscosity stems from the Johari-Goldstein beta-relaxation or the primitive relaxation of the coupling model
No full textBy now it is well established that the structural α-relaxation time, τ α, of non-associated small molecular
and polymeric glass-formers obey thermodynamic scaling. In other words, τ α is a function
of the product variable, ργ /T, where ρ is the density and T the temperature. The constant γ as
well as the function, τ α = (ργ /T), is material dependent. Actually this dependence of τ α on ργ /T
originates from the dependence on the same product variable of the Johari-Goldstein β-relaxation
time, τ β , or the primitive relaxation time, τ 0, of the coupling model. To support this assertion, we
give evidences from various sources itemized as follows. (1) The invariance of the relation between
τ α and τ β or τ 0 to widely different combinations of pressure and temperature. (2) Experimental
dielectric and viscosity data of glass-forming van der Waals liquids and polymer. (3) Molecular
dynamics simulations of binary Lennard-Jones (LJ) models, the Lewis–Wahnström model of orthoterphenyl,
1,4 polybutadiene, a room temperature ionic liquid, 1-ethyl-3-methylimidazolium nitrate,
and a molten salt 2Ca(NO3)2 ·3KNO3 (CKN). (4) Both diffusivity and structural relaxation time,
as well as the breakdown of Stokes-Einstein relation in CKN obey thermodynamic scaling by ργ /T
with the same γ . (5) In polymers, the chain normal mode relaxation time, τ N, is another function
of ργ /T with the same γ as segmental relaxation time τ α. (6) While the data of τ α from simulations
for the full LJ binary mixture obey very well the thermodynamic scaling, it is strongly violated
when the LJ interaction potential is truncated beyond typical inter-particle distance, although in both
cases the repulsive pair potentials coincide for some distances
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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