1,720,959 research outputs found
Tides and dumbbell dynamics
Full text linkWe discuss a model describing the effects of tidal dissipation on satellite's
orbits. Tidal bulges are described in terms of a dumbbell, coupled to the
rotation by a dissipative interaction. The assumptions on this dissipative
coupling turns out to be crucial in the evolution of the system.Comment: 2 figure
Shaken Dynamics on the 3-D Cubic Lattice
Full text linkOn the space of spin configurations on the 3-square lattice, we
consider the \emph{shaken dynamics}, a parallel Markovian dynamics that can be
interpreted in terms of Probabilistic Cellular Automata. The transition
probabilities are defined in terms of pair ferromagnetic Ising-type
Hamiltonians with nearest neighbor interaction , depending on an additional
parameter , measuring the tendency of the system to remain locally in the
same state. Odd times and even times have different transition probabilities.
We compute the stationary measure of the shaken dynamics and we investigate its
relation with the Gibbs measure for the 3 Ising model. It turns out that the
two parameters and tune the geometry of the underlying lattice. We
conjecture the existence of unique line of critical points in plane. By a
judicious use of perturbative methods we delimit the region where such curve
must lie and we perform numerical simulation to determine it. Our method allows
us to find in a unified way the critical values of for Ising model with
first neighbors interaction, defined on a whole class of lattices, intermediate
between the two-dimensional hexagonal and the three-dimensional cubic one, such
as, for example, the tetrahedral lattice. Finally we estimate the critical
exponents of the magnetic susceptibility and show that our model captures a
dimensional transition in the geometry of the system at
Shaken Dynamics: An Easy Way to Parallel Markov Chain Monte Carlo
Full text linkWe define a class of Markovian parallel dynamics for spin systems on arbitrary graphs with nearest neighbor interaction described by a Hamiltonian function H(σ). These dynamics turn out to be reversible and their stationary measure is explicitly determined. Convergence to equilibrium and relation of the stationary measure to the usual Gibbs measure are discussed when the dynamics is defined on Z2. Further it is shown how these dynamics can be used to define natively parallel algorithms to face problems in the context of combinatorial optimization
Metastability for the Ising model on the hexagonal lattice
Full text linkWe consider the Ising model on the hexagonal lattice evolving according to Metropolis dynamics. We study its metastable behavior in the limit of vanishing temperature when the system is immersed in a small external magnetic field. We determine the asymptotic properties of the transition time from the metastable to the stable state up to a multiplicative factor and study the mixing time and the spectral gap of the Markov process. We give a geometrical description of the critical configurations and show how not only their size but their shape varies depending on the thermodynamical parameters. Finally we provide some results concerning polyiamonds of maximal area and minimal perimeter
Gaussian Mean Field Lattice Gas
No full textWe study rigorously a lattice gas version of the Sherrington-Kirckpatrick spin glass model. In discrete optimization literature this problem is known as unconstrained binary quadratic programming and it belongs to the class NP-hard. We prove that the fluctuations of the ground state energy tend to vanish in the thermodynamic limit, and we give a lower bound of such ground state energy. Then we present a heuristic algorithm, based on a probabilistic cellular automaton, which seems to be able to find configurations with energy very close to the minimum, even for quite large instances
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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