917 research outputs found
Sequential visibility-graph motifs
Visibility algorithms transform time series into graphs and encode dynamical
information in their topology, paving the way for graph-theoretical time series
analysis as well as building a bridge between nonlinear dynamics and network
science. In this work we introduce and study the concept of sequential
visibility graph motifs, smaller substructures of n consecutive nodes that
appear with characteristic frequencies. We develop a theory to compute in an
exact way the motif profiles associated to general classes of deterministic and
stochastic dynamics. We find that this simple property is indeed a highly
informative and computationally efficient feature capable to distinguish among
different dynamics and robust against noise contamination. We finally confirm
that it can be used in practice to perform unsupervised learning, by extracting
motif profiles from experimental heart-rate series and being able, accordingly,
to disentangle meditative from other relaxation states. Applications of this
general theory include the automatic classification and description of
physical, biological, and financial time series
Study of RPC gas mixtures for the ARGO-YBJ experiment
The ARGO-YBJ experiment consists of a RPC carpet to be operated at the
Yangbajing laboratory (Tibet, P.R. China), 4300 m a.s.l., and devoted to the
detection of showers initiated by photon primaries in the energy range 100 GeV
- 20 TeV. The measurement technique, namely the timing on the shower front with
a few tens of particles, requires RPC operation with 1 ns time resolution, low
strip multiplicity, high efficiency and low single counting rate. We have
tested RPCs with many gas mixtures, at sea level, in order to optimize these
parameters. The results of this study are reported.Comment: 6 pages, 3 figures. To be published in Nucl. Instr. Meth. A, talk
given at the "5th International Workshop on RPCs and Related Detectors", Bari
(Italy) 199
Functional Multiplex PageRank
(7 pages, 5 figures)(7 pages, 5 figures)(7 pages, 5 figures
Urinary Bladder Volume Reconstruction Based on Bioimpedance Measurements: Ex Vivo and In Vivo Validation Through Implanted Patch and Needle Electrodes
Restoring bladder sensation in patients with bladder dysfunctions by performing urinary volume monitoring is an ambitious goal. The bioimpedance technique has shown promising results in wearable solutions but long-term validation and implantable systems are not available, yet. In this work, we propose to implant commercial bioimpedance sensors on bladder walls to perform bladder volume estimation. Two commercial sensor types (Ag/AgCl patch and needle electrodes) were selected to this purpose. Injected current frequency of 1.337 MHz and electrodes pair on the same face of the bladder allowed to correlate the changes in impedance with increasing volumes. Two volume reconstruction algorithms have been proposed, based on the direct correlation between bioimpedance readings and bladder volume (Algorithm A) or bioimpedance readings and inter-electrode distance (Algorithm B, bladder shape approximated to a sphere). For both algorithms, a better fit with a second-degree fitting polynomial was obtained. Algorithm A obtained lower estimation errors with an average of 20.35% and 21.98% (volumes greater than 150 ml) for patch and needle electrodes, respectively. The variations in ions concentration led to a slight deterioration of volume estimation, however the presence of tissues surrounding the bladder did not influence the performance. Although Algorithm B was less affected by the experimental conditions and inter-subject biological variability, it featured higher estimation errors. In vivo validation on suine model showed average errors of 29.36% (volumes greater than 100 ml), demonstrating the potential of the proposed solution and paving the way towards a novel implantable volume monitoring system
Triadic closure as a basic generating mechanism of communities in complex networks
R.K.D. and S.F. gratefully acknowledge MULTIPLEX, Grant No. 317532 of the European Commission
A general estimator of the primary cosmic ray energy with the ARGO-YBJ experiment
The determination of the primary cosmic ray all-particle spectrum with ground-based air shower
experiments usually depends on the assumed elemental composition and hadronic interaction
model. Here we show that an energy estimator independent of the primary mass composition
can be defined by means of shower parameters measured in the core region, as carried out in
the ARGO-YBJ experiment. The energy resolution is <10% above 100 TeV and gets better with
energy increasing. Being insensitive to the number of muons, this energy determination has only
a weak dependence on the hadronic interaction model. The features of this energy estimator have
been validated by extensive MC simulations and used in the analysis of the ARGO-YBJ data
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