1,721,045 research outputs found
Learning as a phenomenon occurring in a critical state
No full textRecent physiological measurements have provided clear evidence
about scale-free avalanche brain activity and EEG spectra, feeding
the classical enigma of how such a chaotic system can ever learn or
respond in a controlled and reproducible way. Models for learning,
like neural networks or perceptrons, have traditionally avoided
strong fluctuations. Conversely, we propose that brain activity
having features typical of systems at a critical point represents a
crucial ingredient for learning. We present here a study that provides
unique insights toward the understanding of the problem.
Our model is able to reproduce quantitatively the experimentally
observed critical state of the brain and, at the same time, learns
and remembers logical rules including the exclusive OR, which has
posed difficulties to several previous attempts. We implement the
model on a network with topological properties close to the functionality
network in real brains. Learning occurs via plastic adaptation
of synaptic strengths and exhibits universal features. We find
that the learning performance and the average time required to
learn are controlled by the strength of plastic adaptation, in a
way independent of the specific task assigned to the system. Even
complex rules can be learned provided that the plastic adaptation
is sufficiently slow
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
Critical bursts in filtration
No full textParticle detachment bursts during the flow of suspensions through porous media are a phenomenon
that can severely affect the efficiency of deep bed filters. Despite the relevance in several industrial fields,
little is known about the statistical properties and the temporal organization of these events. We present
experiments of suspensions of deionized water carrying quartz particles pushed with a peristaltic pump
through a filter of glass beads measuring simultaneously the pressure drop, flux, and suspension solid
fraction.We find that the burst size distribution scales consistently with a power law, suggesting that we are
in the presence of a novel experimental realization of a self-organized critical system. Temporal correlations
are present in the time series, like in other phenomena such as earthquakes or neuronal activity bursts, and
also an analog to Omori’s law can be shown. The understanding of burst statistics could provide novel
insights in different fields, e.g., in the filter and petroleum industries
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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