166 research outputs found
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
Numerical oscillations for first-order nonlinear delay differential equations in a hematopoiesis model
Delay-Induced Transient Increase and Heterogeneity in Gene Expression in Negatively Auto-Regulated Gene Circuits
A generic feature in all intracellular biochemical processes is the time required to complete the whole sequence of reactions to yield any observable quantity-from gene expression to circadian rhythms. This widespread phenomenon points towards the importance of time delay in biological functions. Theoretically time delay is known to be the source of instability, and has been attributed to lead to oscillations or transient dynamics in several biological functions. Negative feedback loops, common in biochemical pathways, have been shown to provide stability and withstand considerable variations and random perturbations of biochemical parameters. The interaction of these two opposing factors-of instability and homeostasis-are features that are widespread in intracellular processes. To test the effect of these divergent forces in the dynamics of gene expression, we have designed and constructed simple negatively auto-regulated gene circuits consisting of a basic regulator and transcriptional repressor module, and compared it with one, which has delayed repression. We show, both theoretically and experimentally, that delayed repression induces transient increase and heterogeneity in gene expression before the gain of stability effected by the negative feedback. This design, therefore, seems to be suitable for conferring both stability and variability in cells required for adaptive response to a noisy environment
Troisième symposium sur les substances naturelles d'intérêt biologique de la région Pacifique-Asie = Third Pacific-Asia symposium on biologically active natural products
Machinability Investigations on High Chrome White Cast Iron Using Multi Coated Hard Carbide Tools
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