1,720,958 research outputs found
Non-homogeneous random walks: from the transport properties to the statistics of occupation times
Full text linkThis dissertation details our research on random walks seen as simple mathematical models
useful to describe the complex dynamics of many physical systems. In particular, we focus on
the role of spatial inhomogeneity in determining the deviations from the standard behaviour.
In the first chapter we present a general method that can be used to obtain the continuum
limit for the evolution equations of a random walk with nearest neighbour jumps, from which
one can derive the asymptotic properties and deduce the physical interpretation of the walk
itself. Then in the following we adopt this method to discuss two particular models.
The first model, which we call Gillis random walk, is treated in the second chapter and
consists in a random walk with space-dependent drift. Although lacking translational invariance, it provides one of the very few examples of a stochastic system allowing for a number of
exact results. From the continuum limit, one deduces that this model provides a microscopical description for the problem of Brownian diffusion in a logarithmic potential, and indeed
we compare the results regarding the diffusion problem already present in the literature with
the behaviour of the Gillis random walk, finding good agreement.
The second model, which we have originally introduced in the literature and deal with
in the third chapter, is a correlated random walk closely related to the Lévy-Lorentz gas, a
stochastic system where a particle is scattered by static points arranged on a line in such
a way that the distances between first neighbour scatterers are independent and identically
distributed random variables, drawn from a heavy-tailed distribution. Our model results
from a particular procedure of average over all possible arrangements of scatterers and it
is mathematically described as a correlated random walk on the integer lattice, where at
each step the particle can be either reflected or transmitted according to a space-dependent
probability. We apply the continuum limit and derive the long-time properties of the system,
which to some extent match those of the original Lévy-Lorentz gas.
In the fourth and last chapter we consider the problem of occupation times for onedimensional random walks, showing that for a wide class of processes a single exponent
related to a local property of the system is sufficient to describe the distributions of the
variables of interests. We test our findings using the two stochastic models presented in
the previous chapters and obtain good agreement with our theory. However, our result
breaks down, for example, if we consider continuous time random walk models in which the
distribution of waiting times between steps does not possess finite mean. Nevertheless, we
show how also in this case the theory developed in the first part of the chapter is useful to
obtain the statistics of occupation times. We revise some of the results already present in the
literature in terms of our theory and test the results on a novel continuous time model based
on the dynamics of the Gillis random walk, finding good agreement with both the literature
and our theory
Non-homogeneous persistent random walks and Lévy-Lorentz gas
Full text linkWe consider transport properties for a non-homogeneous persistent random walk, that may be viewed as a mean-field version of the Lévy-Lorentz gas, namely a 1D model characterized by a fat polynomial tail of the distribution of scatterers' distance, with parameter μ. By varying the value of μ we have a transition from normal transport to superdiffusion, which we characterize by appropriate continuum limits
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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