519 research outputs found
Percolation of randomly distributed growing clusters: Finite Size Scaling and Critical Exponents
We study the percolation properties of the growing clusters model. In this
model, a number of seeds placed on random locations on a lattice are allowed to
grow with a constant velocity to form clusters. When two or more clusters
eventually touch each other they immediately stop their growth. The model
exhibits a discontinuous transition for very low values of the seed
concentration and a second, non-trivial continuous phase transition for
intermediate values. Here we study in detail this continuous transition
that separates a phase of finite clusters from a phase characterized by the
presence of a giant component. Using finite size scaling and large scale Monte
Carlo simulations we determine the value of the percolation threshold where the
giant component first appears, and the critical exponents that characterize the
transition. We find that the transition belongs to a different universality
class from the standard percolation transition.Comment: 5 two-column pages, 6 figure
Some discussions of D. Fearnhead and D. Prangle's Read Paper "Constructing summary statistics for approximate Bayesian computation: semi-automatic approximate Bayesian computation"
This report is a collection of comments on the Read Paper of Fearnhead and Prangle (2011), to appear in the Journal of the Royal Statistical Society Series B, along with a reply from the authors
Laser-matter interactions, phase changes and diffusion phenomena during laser annealing of plasmonic AlN:Ag templates and their applications in optical encoding
Nanocomposite thin films incorporating silver nanoparticles
are emerging as photosensitive templates for optical encoding applications. However, a deep understanding of the fundamental physicochemical mechanisms occurring during laser-matter interactions is still lacking. In this work, the photosensitivity of AlN:Ag plasmonic nanocomposites is thoroughly examined and a series of UV laser annealing parameters, such as wavelength, fluence and the number of pulses are investigated. We report and study effects such as the selective crystallization of the AlN matrix, the enlargement of the Ag nanoparticle inclusions by diffusion of laser-heated Ag and the outdiffusion of Ag to the film's surface. Detailed optical calculations contribute to the
identification and understanding of the aforementioned physical mechanisms and of their dependency on the laser processing parameters. We are then able to predetermine the plasmonic response of processed AlN:Ag nanocomposites and demonstrate its potential by means of optically encoding an overt or covert cryptographic pattern
Structural properties of spatially embedded networks
We study the effects of spatial constraints on the structural properties of
networks embedded in one or two dimensional space. When nodes are embedded in
space, they have a well defined Euclidean distance between any pair. We
assume that nodes at distance have a link with probability . We study the mean topological distance and the clustering
coefficient of these networks and find that they both exhibit phase
transitions for some critical value of the control parameter depending
on the dimensionality of the embedding space. We have identified three
regimes. When , the networks are not affected at all by the spatial
constraints. They are ``small-worlds'' with zero clustering at
the thermodynamic limit. In the intermediate regime , the networks
are affected by the space and the distance increases and becomes a power of
, and have non-zero clustering. When the networks are
``large'' worlds with high clustering. Our results indicate
that spatial constrains have a significant impact on the network properties, a
fact that should be taken into account when modeling complex networks.Comment: 5 pages, To appear in Europhysics Letter
Positive words carry less information than negative words
We show that the frequency of word use is not only determined by the word
length \cite{Zipf1935} and the average information content
\cite{Piantadosi2011}, but also by its emotional content. We have analyzed
three established lexica of affective word usage in English, German, and
Spanish, to verify that these lexica have a neutral, unbiased, emotional
content. Taking into account the frequency of word usage, we find that words
with a positive emotional content are more frequently used. This lends support
to Pollyanna hypothesis \cite{Boucher1969} that there should be a positive bias
in human expression. We also find that negative words contain more information
than positive words, as the informativeness of a word increases uniformly with
its valence decrease. Our findings support earlier conjectures about (i) the
relation between word frequency and information content, and (ii) the impact of
positive emotions on communication and social links.Comment: 16 pages, 3 figures, 3 table
A Random Matrix Approach to Language Acquisition
Since language is tied to cognition, we expect the linguistic structures to
reflect patterns we encounter in nature and analyzed by physics. Within this
realm we investigate the process of protolanguage acquisition, using analytical
and tractable methods developed within physics. A protolanguage is a mapping
between sounds and objects (or concepts) of the perceived world. This mapping
is represented by a matrix and the linguistic interaction among individuals is
described by a random matrix model. There are two essential parameters in our
approach. The strength of the linguistic interaction , which following
Chomsky's tradition, we consider as a genetically determined ability, and the
number of employed sounds (the lexicon size). Our model of linguistic
interaction is analytically studied using methods of statistical physics and
simulated by Monte Carlo techniques. The analysis reveals an intricate
relationship between the innate propensity for language acquisition and
the lexicon size , . Thus a small increase of the
genetically determined may lead to an incredible lexical explosion. Our
approximate scheme offers an explanation for the biological affinity of
different species and their simultaneous linguistic disparity.Comment: 16 pages, 4 figures. Submitted to JSTA
Fatal outcome of a hypersensitivity reaction to paclitaxel: a critical review of premedication regimens
Hypersensitivity reactions (HSRs) to paclitaxel are frequently encountered in patients receiving this antitumour drug. Administration of histamine H1- and H2-receptor antagonists and corticosteroids has been shown to reduce significantly the risk of developing an HSR in patients receiving taxanes. In this case report, we describe the fatal outcome of an HSR in a patient receiving paclitaxel despite short-course premedication. The level of evidence supporting the short-course i.v. premedication schedule is challenged, as it is not compatible with the pharmacokinetic properties of dexamethasone
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