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

The Singapore Flyer and design of giant observation wheels, Singapore

Some of the engineering principles conceived behind the design of Singapore Flyer, the giant observation Wheel (GOW), built by Arup, are discussed. The wheel is 150 m in diameter, and features access gantries to allow the passenger boarding and loading platforms having two stories above ground in the terminal building located at the base of the wheel. A tropical rainforest attraction has been built into the courtyard space immediately below the wheel to attract the visitor's experience. The 2D ladder truss helps reduce wind load on the Flyer rim. The Flyer also uses cable spokes that need to be prestressed to resist compression. The structural team used purpose-written software to study rim buckling. The GOW represents one lineage of a family of visitor attractions known as ionic viewing platforms, and the engineering design process has recognized several geometric effects on the efficiency of the structure