772 research outputs found
Rapid detection and quantification of features such as damage or flaws in composite and metallic structures
An apparatus, system, and method for non-destructible evaluation (NDE) of a material use thermography to rapidly detect and/or generally locate a feature such as, for example, damage or a defect in the material. The apparatus, system, and method also use ultrasound to specifically locate the feature in the material for quantification and/or evaluation either by an operator or by an external device suited for such purpose. Accordingly, the apparatus, system and method are particularly useful for NDE in applications such as the analysis of the structure of an aircraft, for example, in which the scale of the material to be analyzed is large, thus requiring the rapid NDE afforded by thermography, and in which quantification and/or evaluation of a feature must be performed with precision, thus requiring the relatively high-resolution NDE afforded by ultrasound
Delay Induced Excitability
We analyse the stochastic dynamics of a bistable system under the influence
of time-delayed feedback. Assuming an asymmetric potential, we show the
existence of a regime in which the systems dynamic displays excitability by
calculating the relevant residence time distributions and correlation times.
Experimentally we then observe this behaviour in the polarization dynamics of a
vertical cavity surface emitting laser with opto-electronic feedback. Extending
these observations to two-dimensional systems with dispersive coupling we
finally show numerically that delay induced excitability can lead to the
appearance of propagating wave-fronts and spirals.Comment: 5 pages, 6 figure
Self-replication and evolution of DNA crystals
Is it possible to create a simple physical system that is capable of replicating itself? Can such a system evolve interesting behaviors, thus allowing it to adapt to a wide range of environments? This paper presents a design for such a replicator constructed exclusively from synthetic DNA. The basis for the replicator is crystal growth: information is stored in the spatial arrangement of monomers and copied from layer to layer by templating. Replication is achieved by fragmentation of crystals, which produces new crystals that carry the same information. Crystal replication avoids intrinsic problems associated with template-directed mechanisms for replication of one-dimensional polymers. A key innovation of our work is that by using programmable DNA tiles as the crystal monomers, we can design crystal growth processes that apply interesting selective pressures to the evolving sequences. While evolution requires that copying occur with high accuracy, we show how to adapt error-correction techniques from algorithmic self-assembly to lower the replication error rate as much as is required
Robustness of the noise-induced phase synchronization in a general class of limit cycle oscillators
We show that a wide class of uncoupled limit cycle oscillators can be
in-phase synchronized by common weak additive noise. An expression of the
Lyapunov exponent is analytically derived to study the stability of the
noise-driven synchronizing state. The result shows that such a synchronization
can be achieved in a broad class of oscillators with little constraint on their
intrinsic property. On the other hand, the leaky integrate-and-fire neuron
oscillators do not belong to this class, generating intermittent phase slips
according to a power low distribution of their intervals.Comment: 10 pages, 3 figure
Synchronization of networks with variable local properties
We study the synchronization transition of Kuramoto oscillators in scale-free
networks that are characterized by tunable local properties. Specifically, we
perform a detailed finite size scaling analysis and inspect how the critical
properties of the dynamics change when the clustering coefficient and the
average shortest path length are varied. The results show that the onset of
synchronization does depend on these properties, though the dependence is
smooth. On the contrary, the appearance of complete synchronization is
radically affected by the structure of the networks. Our study highlights the
need of exploring the whole phase diagram and not only the stability of the
fully synchronized state, where most studies have been done up to now.Comment: 5 pages and 3 figures. APS style. Paper to be published in IJBC
(special issue on Complex Networks' Structure and Dynamics
Existence of hysteresis in the Kuramoto model with bimodal frequency distributions
We investigate the transition to synchronization in the Kuramoto model with
bimodal distributions of the natural frequencies. Previous studies have
concluded that the model exhibits a hysteretic phase transition if the bimodal
distribution is close to a unimodal one, due to the shallowness the central
dip. Here we show that proximity to the unimodal-bimodal border does not
necessarily imply hysteresis when the width, but not the depth, of the central
dip tends to zero. We draw this conclusion from a detailed study of the
Kuramoto model with a suitable family of bimodal distributions.Comment: 9 pages, 5 figures, to appear in Physical Review
Modeling rhythmic patterns in the hippocampus
We investigate different dynamical regimes of neuronal network in the CA3
area of the hippocampus. The proposed neuronal circuit includes two fast- and
two slowly-spiking cells which are interconnected by means of dynamical
synapses. On the individual level, each neuron is modeled by FitzHugh-Nagumo
equations. Three basic rhythmic patterns are observed: gamma-rhythm in which
the fast neurons are uniformly spiking, theta-rhythm in which the individual
spikes are separated by quiet epochs, and theta/gamma rhythm with repeated
patches of spikes. We analyze the influence of asymmetry of synaptic strengths
on the synchronization in the network and demonstrate that strong asymmetry
reduces the variety of available dynamical states. The model network exhibits
multistability; this results in occurrence of hysteresis in dependence on the
conductances of individual connections. We show that switching between
different rhythmic patterns in the network depends on the degree of
synchronization between the slow cells.Comment: 10 pages, 9 figure
To synchronize or not to synchronize, that is the question: finite-size scaling and fluctuation effects in the Kuramoto model
The entrainment transition of coupled random frequency oscillators presents a
long-standing problem in nonlinear physics. The onset of entrainment in
populations of large but finite size exhibits strong sensitivity to
fluctuations in the oscillator density at the synchronizing frequency. This is
the source for the unusual values assumed by the correlation size exponent
. Locally coupled oscillators on a -dimensional lattice exhibit two
types of frequency entrainment: symmetry-breaking at , and aggregation
of compact synchronized domains in three and four dimensions. Various critical
properties of the transition are well captured by finite-size scaling relations
with simple yet unconventional exponent values.Comment: 9 pages, 1 figure, to appear in a special issue of JSTAT dedicated to
Statphys2
Phase shifts of synchronized oscillators and the systolic/diastolic blood pressure relation
We study the phase-synchronization properties of systolic and diastolic
arterial pressure in healthy subjects. We find that delays in the oscillatory
components of the time series depend on the frequency bands that are
considered, in particular we find a change of sign in the phase shift going
from the Very Low Frequency band to the High Frequency band. This behavior
should reflect a collective behavior of a system of nonlinear interacting
elementary oscillators. We prove that some models describing such systems, e.g.
the Winfree and the Kuramoto models offer a clue to this phenomenon. For these
theoretical models there is a linear relationship between phase shifts and the
difference of natural frequencies of oscillators and a change of sign in the
phase shift naturally emerges.Comment: 8 figures, 9 page
Collective synchronization in spatially extended systems of coupled oscillators with random frequencies
We study collective behavior of locally coupled limit-cycle oscillators with
random intrinsic frequencies, spatially extended over -dimensional
hypercubic lattices. Phase synchronization as well as frequency entrainment are
explored analytically in the linear (strong-coupling) regime and numerically in
the nonlinear (weak-coupling) regime. Our analysis shows that the oscillator
phases are always desynchronized up to , which implies the lower critical
dimension for phase synchronization. On the other hand, the
oscillators behave collectively in frequency (phase velocity) even in three
dimensions (), indicating that the lower critical dimension for frequency
entrainment is . Nonlinear effects due to periodic nature of
limit-cycle oscillators are found to become significant in the weak-coupling
regime: So-called {\em runaway oscillators} destroy the synchronized (ordered)
phase and there emerges a fully random (disordered) phase. Critical behavior
near the synchronization transition into the fully random phase is unveiled via
numerical investigation. Collective behavior of globally-coupled oscillators is
also examined and compared with that of locally coupled oscillators.Comment: 18 pages, 18 figure
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