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C P Malta

Publications and source records attributed to C P Malta.

7 recordsLinked to original sources
PubMed2002

Comment on "Dynamics of some neural network models with delay".

Based upon numerical evidence, Ruan et al. [J. Ruan, L. Li, and W. Lin, Phys. Rev. E 63, 051906 (2001)] suggest that the delay differential equation dx/dt(t)=-x(t)+A tanh[x(t)]+B tanh[x(t-tau)] may display chaotic dynamics. As mentioned by Pakdaman and Malta [IEEE Trans. Neural Netw. 9, 231 (1998)], this equation presents a monotonic delayed feedback, so that it satisfies a Poincaré-Bendixson-like theorem, ruling out the existence of complex aperiodic dynamics.

Comment↗
PubMed2002

Effect of symmetry breaking on level curvature distributions.

We derive an exact general formalism that expresses the eigenvector and the eigenvalue dynamics as a set of coupled equations of motion in terms of the matrix elements dynamics. Combined with an appropriate model Hamiltonian, these equations are used to investigate the effect of the presence of a discrete symmetry in the level curvature distribution. An explanation of the unexpected behavior of the data regarding frequencies of acoustic vibrations of quartz block is provided.

Journal Article↗
PubMed2002

Chaos in two-loop negative feedback systems.

Multiloop delayed negative feedback systems, with each feedback loop having its own characteristic time lag (delay), are used to describe a great variety of systems: optical systems, neural networks, physiological control systems, etc. Previous investigations have shown that if the number of delayed feedback loops is greater than two, the system can exhibit complex dynamics and chaos, but in the case of two delayed loops only periodic solutions were found. Here we show that a period-doubling cascade and chaotic dynamics are also found in systems with two coupled delayed negative feedback loops.

Biophysics↗
PubMed1999

Metastability for delayed differential equations.

In systems at phase transitions, two phases of the same substance may coexist for a long time before one of them dominates. We show that a similar phenomenon occurs in systems with delayed feedback, where short-term stable oscillatory patterns can also have very long lifetimes before vanishing into constant or periodic steady states.

Journal Article↗
PubMed1997

Effect of delay on the boundary of the basin of attraction in a self-excited single graded-response neuron.

Little attention has been paid in the past to the effects of interunit transmission delays (representing axonal and synaptic delays) on the boundary of the basin of attraction of stable equilibrium points in neural networks. As a first step toward a better understanding of the influence of delay, we study the dynamics of a single graded-response neuron with a delayed excitatory self-connection. The behavior of this system is representative of that of a family of networks composed of graded-response neurons in which most trajectories converge to stable equilibrium points for any delay value. It is shown that changing the delay modifies the "location" of the boundary of the basin of attraction of the stable equilibrium points without affecting the stability of the equilibria. The dynamics of trajectories on the boundary are also delay dependent and influence the transient regime of trajectories within the adjacent basins. Our results suggest that when dealing with networks with delay, it is important to study not only the effect of the delay on the asymptotic convergence of the system but also on the boundary of the basins of attraction of the equilibria.

Animals↗
PubMed1990

Chaos in multi-looped negative feedback systems.

Non-linear control systems with multiple negative feedback loops display periodicity, quasiperiodicity and period-doubling bifurcations leading to chaos. The possibility that normal fluctuations in physiological control may result from deterministic chaos in multi-looped negative feedback systems is discussed.

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