65 research outputs found
Crowd synchrony and quorum sensing in delay-coupled lasers
Crowd synchrony and quorum sensing arise when a large number of dynamical
elements communicate with each other via a common information pool. Previous
evidence in different fields, including chemistry, biology and civil
engineering, has shown that this type of coupling leads to synchronization,
when coupling is instantaneous and the number of coupled elements is large
enough. Here we consider a situation in which the transmission of information
between the system components and the coupling pool is not instantaneous. To
that end, we model a system of semiconductor lasers optically coupled to a
central laser with a delay. Our results show that, even though the lasers are
non-identical due to their distinct optical frequencies, zero-lag
synchronization arises. By changing a system parameter, we can switch between
two different types of synchronization transition. The dependence of the
transition with respect to the delay-coupling parameters is studied.Comment: 4 pages, 4 figure
Low Dimensional Description of Pedestrian-Induced Oscillation of the Millennium Bridge
When it opened to pedestrian traffic in the year 2000, London's Millennium
Bridge exhibited an unwanted, large, side-to-side oscillation which was
apparently due to a resonance between the stepping frequency of walkers and one
of the bridge modes. Models for this event, and similar events on other
bridges, have been proposed. The model most directly addressing the
synchronization mechanism of individual walkers and the resulting global
response of the bridge-pedestrian system is one developed by Eckhardt et al.
This model treats individual walkers with a phase oscillator description and is
inherently high dimensional with system dimensionality (N+2), where N is the
number of walkers. In the present work we use a method proposed by Ott and
Antonsen to reduce the model of Eckhardt et al. to a low dimensional dynamical
system, and we employ this reduced description to study the global dynamics of
the bridge/pedestrian interaction. More generally, this treatment serves as an
interesting example of the possibility of low dimensional macroscopic behavior
in large systems of coupled oscillators.Comment: Submitted to Chaos Journa
ASSESSMENT OF URINARY HYDROXYPYRIDINIUM CROSS-LINKS MEASUREMENT IN OSTEOARTHRITIS
The aim of this study is to re-evaluate urinary collagen cross-links, previously proposed as markers of osteoarthritis (OA). The urinary excretion of collagen cross-links, pyridinoline (PYD) and deoxypyridinoline (DPD), was measured using high-performance liquid chromatography (HPLC) in 114 patients with OA, 19 patients with rheumatoid arthritis (RA) and 40 healthy subjects. An increase in PYD and DPD, expressed per millimole of creatinine, was confirmed in RA. However, PYD and DPD in patients with hip OA, knee OA and polyOA were similar, and did not differ from controls. In patients with radiographic end-stage OA, PYD and DPD were significantly higher than in patients with an early OA, but not significantly higher than in controls. The PYD/DPD ratio did not vary with the OA stage. Thus, urinary collagen cross-links are not elevated in OA, but could reflect bone sclerosis and/or erosion in late O
Pedestrian flows in bounded domains with obstacles
In this paper we systematically apply the mathematical structures by
time-evolving measures developed in a previous work to the macroscopic modeling
of pedestrian flows. We propose a discrete-time Eulerian model, in which the
space occupancy by pedestrians is described via a sequence of Radon positive
measures generated by a push-forward recursive relation. We assume that two
fundamental aspects of pedestrian behavior rule the dynamics of the system: On
the one hand, the will to reach specific targets, which determines the main
direction of motion of the walkers; on the other hand, the tendency to avoid
crowding, which introduces interactions among the individuals. The resulting
model is able to reproduce several experimental evidences of pedestrian flows
pointed out in the specialized literature, being at the same time much easier
to handle, from both the analytical and the numerical point of view, than other
models relying on nonlinear hyperbolic conservation laws. This makes it
suitable to address two-dimensional applications of practical interest, chiefly
the motion of pedestrians in complex domains scattered with obstacles.Comment: 25 pages, 9 figure
Self-generated sounds of locomotion and ventilation and the evolution of human rhythmic abilities
Study on human-induced vibration of a cable-stayed bridge without backstays located in abrupt valley
A network for the management of genetic resources of maize populations in France
International audienc
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