6,196 research outputs found
Characterization and modeling of aperiodic pressure oscillations in combustion chambers
Classification of the long-term dynamical
behavior of pressure oscillations in a
laboratory combustion chamber has been
performed using methods of modern dynamical
systems theory. The method involves the
construction of a phase-space representation
from a single pressure record or time series using
the time-delay embedding method. The
pointwise correlation dimension of the resulting
attractor in phase-space provides a lower
bound on the number of modes that participate
in the oscillations. The results show that the
oscillations are quasiperiodic with a dimension
near two over an order of magnitude of
amplitudes. Quasiperiodicity is a result of the
incommensurate frequencies of the system
acoustic modes. A model for the dynamics is
constructed by converting the governing
equations to a kicked-oscillator model. When
compared with the experimental data, the
model results have similar pressure and
velocity spectra and the attractor dimension
verifies that quasiperiodic oscillations are
present
Self-generated and externally driven current oscillations in n-GaAs
Experimental investigations of self-generated and externally driven non-linear current oscillations due to impact ionization of shallow impurities in n-type GaAs at low temperatures are presented. The regular relaxation oscillations which appear at the onset of breakdown are destabilized by a magnetic field normal to the epitaxial layer and multifrequency oscillations and chaotic fluctuations following the Ruelle-Takens-Newhouse scenario can be found. Driving the self-generated oscillations with an external periodic bias voltage quasiperiodicity, mode locking, interaction and overlap of mode locked resonances and period doubling can be observed depending on frequency and amplitude of the external force. The reconstructed return maps, recorded phase diagrams and Devil's staircase agree with theoretical predictions based on the circle map and give new evidence of the universality of the transition from quasiperiodicity to chaos
Bose-Einstein Condensates in Optical Quasicrystal Lattices
We analyze the physics of Bose-Einstein condensates confined in 2D
quasi-periodic optical lattices, which offer an intermediate situation between
ordered and disordered systems. First, we analyze the time-of-flight
interference pattern that reveals quasi-periodic long-range order. Second, we
demonstrate localization effects associated with quasi-disorder as well as
quasiperiodic Bloch oscillations associated with the extended nature of the
wavefunction of a Bose-Einstein condensate in an optical quasicrystal. In
addition, we discuss in detail the crossover between diffusive and localized
regimes when the quasi-periodic potential is switched on, as well as the
effects of interactions
Quasiperiodic Envelope Solitons
We analyse nonlinear wave propagation and cascaded self-focusing due to
second-harmonic generation in Fibbonacci optical superlattices and introduce a
novel concept of nonlinear physics, the quasiperiodic soliton, which describes
spatially localized self-trapping of a quasiperiodic wave. We point out a link
between the quasiperiodic soliton and partially incoherent spatial solitary
waves recently generated experimentally.Comment: Submitted to PRL. 4 pages with 5 figure
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