Biomedical subjects

Bruno Eckhardt

Publications and source records attributed to Bruno Eckhardt.

4 recordsLinked to original sources

PubMed2003

Traveling waves in pipe flow.

A family of three-dimensional traveling waves for flow through a pipe of circular cross section is identified. The traveling waves are dominated by pairs of downstream vortices and streaks. They originate in saddle-node bifurcations at Reynolds numbers as low as 1250. All states are immediately unstable. Their dynamical significance is that they provide a skeleton for the formation of a chaotic saddle that can explain the intermittent transition to turbulence and the sensitive dependence on initial conditions in this shear flow.

Journal Article↗

PubMed2003

Lifetimes of noisy repellors.

We study the effects of additive noise on the lifetimes of chaotic repellors. Using first-order perturbation theory, we argue that noise will increase the lifetime if the escape holes lie in regions where the unperturbed density is higher than that in the immediate vicinity and that it decreases if the density is lower. Numerical experiments support the qualitative conclusions also beyond perturbation theory.

Journal Article↗

PubMed2002

Clustering dynamics of Lagrangian tracers in free-surface flows.

We study the formation of clusters of passive Lagrangian tracers in a nonsmooth turbulent flow in a flat free-slip surface as a model for particle dynamics on free surfaces. Single particle and pair dispersion show different behavior for short and large times: on short times particles cluster exponentially rapidly until patches of the size of the divergence correlation length are depleted; on larger times the pair dispersion is dominated by almost ballistic hopping between clusters. We also find that the distribution of particle density is close to algebraic and can trace this back to the exponential distribution of the divergence field of the surface flow.

Journal Article↗

PubMed1993

Correlations in quantum time delay.

The semiclassical periodic orbit content of the form factor K(lambda ), the Fourier transform of the autocorrelation function, for the quantum time delay is analyzed. In analogy to the case of bounded systems, three regimes can be identified. For small lambda isolated periodic orbits can be identified. For intermediate lambda, there is a lambda exp(-Gammalambda) regime, where Gamma is the classical escape rate. For large lambda, this changes into an exp( - gamma(qm)lambda) law, where now gamma(qm) is related to an inverse lifetime of the resonances. The transition between the latter two regimes is determined by the density of resonances. The theoretical analysis is supported by numerical data for the three disk scattering system.

Journal Article↗