627 research outputs found
From Phase Space Representation to Amplitude Equations in a Pattern Forming Experiment
We describe and demonstrate a method to reconstruct an amplitude equation
from the nonlinear relaxation dynamics in the succession of the Rosensweig
instability. A flat layer of a ferrofluid is cooled such that the liquid has a
relatively high viscosity. Consequently, the dynamics of the formation of the
Rosensweig pattern becomes very slow. By sudden switching of the magnetic
induction, the system is pushed to an arbitrary point in the phase space
spanned by the pattern amplitude and the magnetic induction. Afterwards, it is
allowed to relax to its equilibrium point. From the dynamics of this
relaxation, we reconstruct the underlying fully nonlinear equation of motion of
the pattern amplitude. The measured nonlinear dynamics serves to select the
best weakly nonlinear expansion which describes this hysteretic transition.Comment: 20 pages, 12 figure
A note on the magnetic spatial forcing of a ferrofluid layer
We report on the response of a thin layer of ferrofluid to a spatially
modulated magnetic field. This field is generated by means of a constant
current in a special arrangement of aluminum wires. The full surface profile of
the liquid layer is recorded by means of the absorption of X-rays. The outcome
is analyzed particularly with regard to the magnetic self focusing effect under
a deformable fluid layer
Growth of surface undulations at the Rosensweig instability
We investigate the growth of a pattern of liquid crests emerging in a layer
of magnetic liquid when subjected to a magnetic field oriented normally to the
fluid surface. After a steplike increase of the magnetic field, the temporal
evolution of the pattern amplitude is measured by means of a Hall-sensor array.
The extracted growth rate is compared with predictions from linear stability
analysis by taking into account the proper nonlinear magnetization curve M(H).
The remaining discrepancy can be resolved by numerical calculations via the
finite-element method. By starting with a finite surface perturbation, it can
reproduce the temporal evolution of the pattern amplitude and the growth rate.
The investigations are performed for two magnetic liquids, one with low and one
with high viscosity.Comment: 12 pages, 12 figure
Magnetic traveling-stripe-forcing: enhanced transport in the advent of the Rosensweig instability
A new kind of contactless pumping mechanism is realized in a layer of
ferrofluid via a spatio-temporally modulated magnetic field. The resulting
pressure gradient leads to a liquid ramp, which is measured by means of X-rays.
The transport mechanism works best if a resonance of the surface waves with the
driving is achieved. The behavior can be understood semi-quantitatively by
considering the magnetically influenced dispersion relation of the fluid.Comment: 6 Pages, 8 Figure
Dynamical characteristics of Rydberg electrons released by a weak electric field
The dynamics of ultra-slow electrons in the combined potential of an ionic
core and a static electric field is discussed. With state-of-the-art detection
it is possible to create such electrons through strong intense-field
photo-absorption and to detect them via high-resolution time-of-flight
spectroscopy despite their very low kinetic energy. The characteristic feature
of their momentum spectrum, which emerges at the same position for different
laser orientations, is derived and could be revealed experimentally with an
energy resolution of the order of 1meV.Comment: 5 pages, 5 figure
The growth of localized states on the surface of magnetic fluids
AbstractBy means of a local magnetic perturbation we generate localized states on the surface of a ferrofluid in the bistable regime of the Rosensweig instability. Establishing a magnetic ramp at the edge of the vessel enables us to record the growth of the localized spikes with a high speed camera. From the pictures we extract their growth rate. Under variation of the local induction we find a square-root scaling of the growth rate, which can be understood by a saddle-node bifurcation, induced by the local variation of the magnetic induction
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