1,720,975 research outputs found
Reconstructing the free energy landscape of a mechanically unfolded model protein
No full textThe equilibrium free-energy landscape of an off-lattice model protein as a function of an internal
(reaction) coordinate is reconstructed from out-of-equilibrium mechanical unfolding manipulations. This
task is accomplished via two independent methods: by employing an extended version of the Jarzynski
equality (EJE) and the protein inherent structures (ISs). In a range of temperatures around the ‘‘folding
transition’’ we find a good quantitative agreement between the free energies obtained via EJE and IS
approaches. This indicates that the two methodologies are consistent and able to reproduce equilibrium
properties of the examined system. Moreover, for the studied model the structural transitions induced by
pulling can be related to thermodynamical aspects of folding
Front propagation in chaotic and noisy reaction-diffusion systems: a discrete-time map approach
No full textWe study the front propagation in reaction-diffusion systems whose
reaction dynamics exhibits an unstable fixed point and chaotic or noisy
behaviour. We have examined the influence of chaos and noise on
the front propagation speed and on the wandering of the front
around its average position. Assuming that the reaction
term acts periodically in an impulsive way, the dynamical evolution of
the system can be written as the convolution between a spatial propagator and
a discrete-time map acting locally. This approach allows us to perform
accurate numerical analysis. They reveal that in the pulled regime
the front speed is basically determined by the shape of the map
around the unstable fixed point, while its chaotic or noisy features
play a marginal role. In contrast, in the pushed regime the presence
of chaos or noise is more relevant.
In particular the front speed decreases when the degree of chaoticity
is increased, but it is not straightforward to derive
a direct connection between the chaotic
properties (e.g. the Lyapunov exponent) and the behaviour
of the front. As for the fluctuations of the front position,
we observe for the noisy maps that the associated mean square
displacement grows in time as in the pushed case and
as in the pulled one, in agreement with recent findings
obtained for continuous models with multiplicative noise.
Moreover we show that the same quantity saturates when a
chaotic deterministic dynamics is considered for both pushed and
pulled regimes
First and second order clustering transitions for a system with infinite-range attractive interactions
No full textAsymptotic and effective coarsening exponents in surface growth models
No full textWe consider a class of unstable surface growth models, , developing a mound structure of size λ and displaying a perpetual coarsening process, i.e. an endless increase in time of λ. The coarsening exponents n, defined by the growth law of the mound size λ with time, λ∼t n, were previously found by numerical integration of the growth equations [A. Torcini, P. Politi, Eur. Phys. J. B 25, 519 (2002)]. Recent analytical work now allows to interpret such findings as finite time effective exponents. The asymptotic exponents are shown to appear at so large time that cannot be reached by direct integration of the growth equations. The reason for the appearance of effective exponents is clearly identified. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200681.10.Aj Theory and models of crystal growth; physics of crystal growth, crystal morphology, and orientation, 02.30.Jr Partial differential equations,
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
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