377 research outputs found
Wave Propagation in a Strongly Nonlinear Locally Resonant Granular Crystal
In this work, we study the wave propagation in a recently proposed acoustic
structure, the locally resonant granular crystal. This structure is composed of
a one-dimensional granular crystal of hollow spherical particles in contact,
containing linear resonators. The relevant model is presented and examined
through a combination of analytical approximations (based on ODE and nonlinear
map analysis) and of numerical results. The generic dynamics of the system
involves a degradation of the well-known traveling pulse of the standard
Hertzian chain of elastic beads. Nevertheless, the present system is richer, in
that as the primary pulse decays, secondary ones emerge and eventually
interfere with it creating modulated wavetrains. Remarkably, upon suitable
choices of parameters, this interference "distills" a weakly nonlocal solitary
wave (a "nanopteron"). This motivates the consideration of such nonlinear
structures through a separate Fourier space technique, whose results suggest
the existence of such entities not only with a single-side tail, but also with
periodic tails on both ends. These tails are found to oscillate with the
intrinsic oscillation frequency of the out-of-phase motion between the outer
hollow bead and its internal linear attachment
Coarse Bifurcation Studies of Bubble Flow Microscopic Simulations
The parametric behavior of regular periodic arrays of rising bubbles is
investigated with the aid of 2-dimensional BGK Lattice-Boltzmann (LB)
simulators. The Recursive Projection Method is implemented and coupled to the
LB simulators, accelerating their convergence towards what we term coarse
steady states. Efficient stability/bifurcation analysis is performed by
computing the leading eigenvalues/eigenvectors of the coarse time stepper. Our
approach constitutes the basis for system-level analysis of processes modeled
through microscopic simulations.Comment: 4 pages, 3 figure
Geometric stabilization of extended S=2 vortices in two-dimensional photonic lattices: theoretical analysis, numerical computation and experimental results
In this work, we focus our studies on the subject of nonlinear discrete
self-trapping of S=2 (doubly-charged) vortices in two-dimensional photonic
lattices, including theoretical analysis, numerical computation and
experimental demonstration. We revisit earlier findings about S=2 vortices with
a discrete model, and find that S=2 vortices extended over eight lattice sites
can indeed be stable (or only weakly unstable) under certain conditions, not
only for the cubic nonlinearity previously used, but also for a saturable
nonlinearity more relevant to our experiment with a biased photorefractive
nonlinear crystal. We then use the discrete analysis as a guide towards
numerically identifying stable (and unstable) vortex solutions in a more
realistic continuum model with a periodic potential. Finally, we present our
experimental observation of such geometrically extended S=2 vortex solitons in
optically induced lattices under both self-focusing and self-defocusing
nonlinearities, and show clearly that the S=2 vortex singularities are
preserved during nonlinear propagation
Decapoda and Stomatopoda (Crustacea) of Rodos island (Greece) and the Erythrean expansion NW of the Levantine sea
The Decapoda and Stomatopoda (Crustacea) of the sublittoral zone of Rodos island were studied between 1995 and 2000. Twenty-five sites, at depths ranging from the intertidal to 119 m, were sampled. Three species of stomatopods and 52 species of decapods were identified, bringing the number of decapods known from Rodos to 83. One Stomatopode and nineteen decapods, though previously known from the Aegean Sea, are new records for Rodos. The presence of seven species of Erythrean origin testify to a trend of increasing tropicalization of the area. A remarkable number of Erythrean taxa (fish, Crustacea, Mollusca, Polychaeta) have been established in Rodos, the Dodecanese and the southern Aegean Sea, whereas few reached the northern Aegean and the Ionian Seas. The expansion of the Erythrean species NW of the Levantine Sea is discussed
Skyrmion-like excitations in dynamical lattices
We construct discrete analogs of Skyrmions in nonlinear dynamical lattices.
The Skyrmion is built as a vortex soliton of a complex field, coupled to a dark
radial soliton of a real field. Adjusting the Skyrmion ansatz to the lattice
setting allows us to construct a "baby-Skyrmion" in two dimensions (2D) and
extend it into the 3D case (1D counterparts of the Skyrmions are also found).
Stability limits for these patterns are obtained analytically and verified
numerically. The dynamics of unstable discrete Skyrmions is explored, and their
stabilization by external potentials is discussed.Comment: 4 pages, 5 figure
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