14 research outputs found
Comment on Y. Couder and E. Fort: "Single-Particle Diffraction and Interference at a Macroscopic Scale", Phys. Rev. Lett. (2006)
In a paper from 2006, Couder and Fort [1] describe a version of the famous
double slit experiment performed with drops bouncing on a vibrated fluid
surface, where interference in the particle statistics is found even though it
is possible to determine unambiguously which slit the "walking" drop passes. It
is one of the first papers in an impressive series, showing that such walking
drops closely resemble de Broglie waves and can reproduce typical quantum
phenomena like tunneling and quantized states [2-13]. The double slit
experiment is, however, a more stringent test of quantum mechanics, because it
relies upon superposition and phase coherence. In the present comment we first
point out that the experimental data presented in [1] are not convincing, and
secondly we argue that it is not possible in general to capture quantum
mechanical results in a system, where the trajectory of the particle is
well-defined.Comment: 4 pages, 1 figur
Model For Polygonal Hydraulic Jumps
We propose a phenomenological model for the polygonal hydraulic jumps
discovered by Ellegaard et al., based on the known flow structure for the type
II hydraulic jumps with a "roller" (separation eddy) near the free surface in
the jump region. The model consists of mass conservation and radial force
balance between hydrostatic pressure and viscous stresses on the roller
surface. In addition, we consider the azimuthal force balance, primarily
between pressure and viscosity, but also including non-hydrostatic pressure
contributions from surface tension in light of recent observations by Bush et
al. The model can be analyzed by linearization around the circular state,
resulting in a parameter relationship for nearly circular polygonal states. A
truncated, but fully nonlinear version of the model can be solved analytically.
This simpler model gives rise to polygonal shapes that are very similar to
those observed in experiments, even though surface tension is neglected, and
the condition for the existence of a polygon with N corners depends only on a
single dimensionless number {\phi}. Finally, we include time-dependent terms in
the model and study linear stability of the circular state. Instability occurs
for suffciently small Bond number and the most unstable wave length is expected
to be roughly proportional to the width of the roller as in the
Rayleigh-Plateau instability.Comment: 17 pages; Phys. Rev. E (2012
Breakdown of universality in transitions to spatiotemporal chaos
We show that the transition from laminar to active behavior in extended chaotic systems can vary from a continuous transition in the universality class of directed percolation with infinitely many absorbing states to what appears as a first-order transition. The latter occurs when finite lifetime nonchaotic structures, called "solitons," dominate the dynamics. We illustrate this scenario in an extension of the deterministic Chaté-Manneville coupled map lattice model and in a soliton including variant of the stochastic Domany-Kinzel cellular automaton
Vortex Dynamics around a solid triangle in oscillatory flow
We investigate the time-dependent flow of water around a solid triangular
profile oscillating horizontally in a narrow rectangular container.
The flow is quasi two-dimensional and using particle image velocimetry we
measure 20 snapshots of the entire velocity field during a period of
oscillation. From the velocity measurements we obtain the circulation of
the vortices and study the vortex dynamics. The time-dependence of the flow
gives rise to the formation of a jet-like flow structure which enhances the
vorticity production compared to the time-independent case. We introduce
a simple phenomenological model to describe the important
dynamical parameters of the flow, i.e., the vortex circulation and the
jet velocity. We solve the model analytically without viscous damping
and find good agreement between the model predictions and our measurements.
Our work adds to the recent effort to understand more complicated flows past
sand-ripples and insect wings
Polygon formation and surface flow on a rotating fluid surface - ERRATUM
We present a study of polygons forming on the free surface of a water flow confined to a stationary cylinder and driven by a rotating bottom plate as described by Jansson et al. (Phys. Rev. Lett., vol. 96, 2006, 174502). In particular, we study the case of a triangular structure, either completely âwetâ or with a âdryâ centre. For the dry structures, we present measurements of the surface shapes and the process of formation. We show experimental evidence that the formation can take place as a two-stage process: first the system approaches an almost stable rotationally symmetric state and from there the symmetry breaking proceeds like a low-dimensional linear instability. We show that the circular state and the unstable manifold connecting it with the polygon solution are universal in the sense that very different initial conditions lead to the same circular state and unstable manifold. For a wet triangle, we measure the surface flows by particle image velocimetry (PIV) and show that there are three vortices present, but that the strength of these vortices is far too weak to account for the rotation velocity of the polygon. We show that partial blocking of the surface flow destroys the polygons and re-establishes the rotational symmetry. For the rotationally symmetric state our theoretical analysis of the surface flow shows that it consists of two distinct regions: an inner, rigidly rotating centre and an outer annulus, where the surface flow is that of a point vortex with a weak secondary flow. This prediction is consistent with the experimentally determined surface flo