1,287 research outputs found
Chaotic Jets
The problem of characterizing the origin of the non-Gaussian properties of
transport resulting from Hamiltonian dynamics is addressed. For this purpose
the notion of chaotic jet is revisited and leads to the definition of a
diagnostic able to capture some singular properties of the dynamics. This
diagnostic is applied successfully to the problem of advection of passive
tracers in a flow generated by point vortices. We present and discuss this
diagnostic as a result of which clues on the origin of anomalous transport in
these systems emerge.Comment: Proceedings of the workshop Chaotic transport and complexity in
classical and quantum dynamics, Carry le rouet France (2002
Reducing or enhancing chaos using periodic orbits
A method to reduce or enhance chaos in Hamiltonian flows with two degrees of
freedom is discussed. This method is based on finding a suitable perturbation
of the system such that the stability of a set of periodic orbits changes
(local bifurcations). Depending on the values of the residues, reflecting their
linear stability properties, a set of invariant tori is destroyed or created in
the neighborhood of the chosen periodic orbits. An application on a
paradigmatic system, a forced pendulum, illustrates the method
An Algorithm to Predict E-Bike Power Consumption Based on Planned Routes
E-bikes, i.e., bikes equipped with a small electrical engine, are becoming increasingly widespread, thanks to their positive contribution to mobility and sustainability. A key component of an e-bike is the battery that feeds the drive unit: clearly, the higher the capacity of the battery, the longer the distances that the biker will cover under engine support. On the negative side, the additional weight incurred by the electric components is likely to ruin the riding experience in case the battery runs out of power. For this reason, an integrated hardware-software system that provides accurate information about the remaining range is essential, especially for older or “not-in-shape” bikers. Many e-bikes systems are already equipped with a small control unit that displays useful information, such as speed, instantaneous power consumption, and estimated range as well. Existing approaches rely on machine learning techniques applied to collected data, or even on the remaining battery capacity and the assistance level required by the drive unit. They do not consider crucial aspects of the planned route, in particular the difference in altitude, the combined weight of bike and biker, and road conditions. In this paper, we propose a mathematical model implemented in an application to compute battery consumption, and hence the presumed remaining range, in a more accurate way. Our application relies on external sources to compute the route and the elevation data of a number of intermediate points. We present the mathematical model on which our application is based, we show the implemented application in shape of an app, and we report the results of the experiments
Emergence of a non trivial fluctuating phase in the XY model on regular networks
We study an XY-rotor model on regular one dimensional lattices by varying the
number of neighbours. The parameter is defined.
corresponds to mean field and to nearest neighbours coupling. We
find that for the system does not exhibit a phase transition,
while for the mean field second order transition is recovered.
For the critical value , the systems can be in a non
trivial fluctuating phase for whichthe magnetisation shows important
fluctuations in a given temperature range, implying an infinite susceptibility.
For all values of the magnetisation is computed analytically in the
low temperatures range and the magnetised versus non-magnetised state which
depends on the value of is recovered, confirming the critical value
Phase Ordering Dynamics of Theory with Hamiltonian Equations of Motion
Phase ordering dynamics of the (2+1)- and (3+1)-dimensional theory
with Hamiltonian equations of motion is investigated numerically. Dynamic
scaling is confirmed. The dynamic exponent is different from that of the
Ising model with dynamics of model A, while the exponent is the same.Comment: to appear in Int. J. Mod. Phys.
Unveiling the nature of out-of-equilibrium phase transitions in a system with long-range interactions
Recently, there has been some vigorous interest in the out-of-equilibrium
quasistationary states (QSSs), with lifetimes diverging with the number N of
degrees of freedom, emerging from numerical simulations of the ferromagnetic XY
Hamiltonian Mean Field (HMF) starting from some special initial conditions.
Phase transitions have been reported between low-energy magnetized QSSs and
large-energy unexpected, antiferromagnetic-like, QSSs with low magnetization.
This issue is addressed here in the Vlasov N \rightarrow \infty limit. It is
argued that the time-asymptotic states emerging in the Vlasov limit can be
related to simple generic time-asymptotic forms for the force field. The
proposed picture unveils the nature of the out-of-equilibrium phase transitions
reported for the ferromagnetic HMF: this is a bifurcation point connecting an
effective integrable Vlasov one-particle time-asymptotic dynamics to a partly
ergodic one which means a brutal open-up of the Vlasov one-particle phase
space. Illustration is given by investigating the time-asymptotic value of the
magnetization at the phase transition, under the assumption of a sufficiently
rapid time-asymptotic decay of the transient force field
Anomalous transport in Charney-Hasegawa-Mima flows
Transport properties of particles evolving in a system governed by the
Charney-Hasegawa-Mima equation are investigated. Transport is found to be
anomalous with a non linear evolution of the second moments with time. The
origin of this anomaly is traced back to the presence of chaotic jets within
the flow. All characteristic transport exponents have a similar value around
, which is also the one found for simple point vortex flows in the
literature, indicating some kind of universality. Moreover the law
linking the trapping time exponent within jets to the transport
exponent is confirmed and an accumulation towards zero of the spectrum of
finite time Lyapunov exponent is observed. The localization of a jet is
performed, and its structure is analyzed. It is clearly shown that despite a
regular coarse grained picture of the jet, motion within the jet appears as
chaotic but chaos is bounded on successive small scales.Comment: revised versio
Targeted mixing in an array of alternating vortices
Transport and mixing properties of passive particles advected by an array of
vortices are investigated. Starting from the integrable case, it is shown that
a special class of perturbations allows one to preserve separatrices which act
as effective transport barriers, while triggering chaotic advection. In this
setting, mixing within the two dynamical barriers is enhanced while long range
transport is prevented. A numerical analysis of mixing properties depending on
parameter values is performed; regions for which optimal mixing is achieved are
proposed. Robustness of the targeted mixing properties regarding errors in the
applied perturbation are considered, as well as slip/no-slip boundary
conditions for the flow
Passive Tracer Dynamics in 4 Point-Vortex Flow
The advection of passive tracers in a system of 4 identical point vortices is
studied when the motion of the vortices is chaotic. The phenomenon of
vortex-pairing has been observed and statistics of the pairing time is
computed. The distribution exhibits a power-law tail with exponent
implying finite average pairing time. This exponents is in agreement with its
computed analytical estimate of 3.5. Tracer motion is studied for a chosen
initial condition of the vortex system. Accessible phase space is investigated.
The size of the cores around the vortices is well approximated by the minimum
inter-vortex distance and stickiness to these cores is observed. We investigate
the origin of stickiness which we link to the phenomenon of vortex pairing and
jumps of tracers between cores. Motion within the core is considered and
fluctuations are shown to scale with tracer-vortex distance as . No
outward or inward diffusion of tracers are observed. This investigation allows
the separation of the accessible phase space in four distinct regions, each
with its own specific properties: the region within the cores, the reunion of
the periphery of all cores, the region where vortex motion is restricted and
finally the far-field region. We speculate that the stickiness to the cores
induced by vortex-pairings influences the long-time behavior of tracers and
their anomalous diffusion.Comment: 18 pages, 15 figure
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