389 research outputs found
Oscillations of delay differential equations
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N-[4-(2-Morpholinoethoxy)phenyl]acetamide monohydrate
In the title compound, C14H20N2O3·H2O, the geometry about the morpholine N atom implies sp
3 hybridization. In the crystal, symmetry-related molecules are linked by intermolecular N—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds, forming infinite chains along the b axis. The chain structure is further stabilized by intramolecular C—H⋯O interactions
Synchronization in a neuronal feedback loop through asymmetric temporal delays
We consider the effect of asymmetric temporal delays in a system of two
coupled Hopfield neurons. For couplings of opposite signs, a limit cycle
emerges via a supercritical Hopf bifurcation when the sum of the delays reaches
a critical value. We show that the angular frequency of the limit cycle is
independent of an asymmetry in the delays. However, the delay asymmetry
determines the phase difference between the periodic activities of the two
components. Specifically, when the connection with negative coupling has a
delay much larger than the delay for the positive coupling, the system
approaches in-phase synchrony between the two components. Employing variational
perturbation theory (VPT), we achieve an approximate analytical evaluation of
the phase shift, in good agreement with numerical results.Comment: 5 pages, 4 figure
Characteristics of a Delayed System with Time-dependent Delay Time
The characteristics of a time-delayed system with time-dependent delay time
is investigated. We demonstrate the nonlinearity characteristics of the
time-delayed system are significantly changed depending on the properties of
time-dependent delay time and especially that the reconstructed phase
trajectory of the system is not collapsed into simple manifold, differently
from the delayed system with fixed delay time. We discuss the possibility of a
phase space reconstruction and its applications.Comment: 4 pages, 6 figures (to be published in Phys. Rev. E
4-[2-(4-Methoxyphenyl)ethyl]-3-(thiophen-2-ylmethyl)-1H-1,2,4-triazol-5(4H)-one monohydrate
In the title compound, C16H17N3O2S·H2O, the triazole ring makes a dihedral angle of 34.63 (6)° with the benzene ring. The thiophene ring is disordered over two orientations [occupancy ratio = 0.634 (4):0.366 (4)] which make dihedral angles of 54.61 (16) and 54.57 (31)° with the triazole ring. Intermolecular N—H⋯O and O—H⋯O hydrogen bonds stabilize the crystal structure
Exact synchronization bound for coupled time-delay systems
We obtain an exact bound for synchronization in coupled time-delay systems using the generalized Halanay inequality for the general case of time-dependent delay, coupling, and coefficients. Furthermore, we show that the same analysis is applicable to both uni- and bidirectionally coupled time-delay systems with an appropriate evolution equation for their synchronization manifold, which can also be defined for different types of synchronization. The exact synchronization bound assures an exponential stabilization of the synchronization manifold which is crucial for applications. The analytical synchronization bound is independent of the nature of the modulation and can be applied to any time-delay system satisfying a Lipschitz condition. The analytical results are corroborated numerically using the Ikeda system
4-[3-(1H-Imidazol-1-yl)propyl]-3-methyl-5-(thiophen-2-ylmethyl)-4H-1,2,4-triazole monohydrate
In the title compound, C14H17N5S·H2O, the triazole ring makes dihedral angles of 48.15 (8) and 84.92 (8)° with the imidazole and thiophenyl rings, respectively. The water molecule is involved in intermolecular O—H⋯N hydrogen bonding
Dynamics of FitzHugh-Nagumo excitable systems with delayed coupling
Small lattices of nearest neighbor coupled excitable FitzHugh-Nagumo
systems, with time-delayed coupling are studied, and compared with systems of
FitzHugh-Nagumo oscillators with the same delayed coupling. Bifurcations of
equilibria in N=2 case are studied analytically, and it is then numerically
confirmed that the same bifurcations are relevant for the dynamics in the case
. Bifurcations found include inverse and direct Hopf and fold limit cycle
bifurcations. Typical dynamics for different small time-lags and coupling
intensities could be excitable with a single globally stable equilibrium,
asymptotic oscillatory with symmetric limit cycle, bi-stable with stable
equilibrium and a symmetric limit cycle, and again coherent oscillatory but
non-symmetric and phase-shifted. For an intermediate range of time-lags inverse
sub-critical Hopf and fold limit cycle bifurcations lead to the phenomenon of
oscillator death. The phenomenon does not occur in the case of FitzHugh-Nagumo
oscillators with the same type of coupling.Comment: accepted by Phys.Rev.
Delay-enhanced coherent chaotic oscillations in networks with large disorders
We study the effect of coupling delay in a regular network with a ring
topology and in a more complex network with an all-to-all (global) topology in
the presence of impurities (disorder). We find that the coupling delay is
capable of inducing phase-coherent chaotic oscillations in both types of
networks, thereby enhancing the spatiotemporal complexity even in the presence
of 50% of symmetric disorders of both fixed and random types. Furthermore, the
coupling delay increases the robustness of the networks up to 70% of disorders,
thereby preventing the network from acquiring periodic oscillations to foster
disorder-induced spatiotemporal order. We also confirm the enhancement of
coherent chaotic oscillations using snapshots of the phases and values of the
associated Kuramoto order parameter. We also explain a possible mechanism for
the phenomenon of delay-induced coherent chaotic oscillations despite the
presence of large disorders and discuss its applications.Comment: 13 pages, 20 figure
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