Feedback mechanisms for global oscillations in Lure systems

The paper presents two mechanisms for global oscillations in feedback systems, based on bifurcations in absolutely stable systems. The external characterization of the oscillators provides the basis for a (energy-based) dissipativity theory for oscillators, thereby opening new possibilities for rigorous stability analysis of high-dimensional systems and interconnected oscillators. © 2004 Elsevier B.V. All rights reserved.

Modelling of jacked piles in centrifuge

Pile jacking is a common installation method for displacement piles due to the low noise and vibration involved in the installation procedure. Problems may occur when modelling jacked piles in the centrifuge, especially for friction piles, due to scaling effects which can be minimised, provided that the pile diameter is greater than fifty times the mean grain size. A series of centrifuge tests of jacked piles was performed in both dry and saturated fine sand. Piles were installed using three different methods. The effect of the installation method on the head load required is assessed. The influence of the normalised roughness was also tested by testing one rough and one smooth pile. Finally, cyclic shearing at constant depth was performed to establish the shaft load reduction due to friction fatigue. © 2014 Taylor & Francis Group.

Cell types, network homeostasis, and pathological compensation from a biologically plausible ion channel expression model.

How do neurons develop, control, and maintain their electrical signaling properties in spite of ongoing protein turnover and perturbations to activity? From generic assumptions about the molecular biology underlying channel expression, we derive a simple model and show how it encodes an "activity set point" in single neurons. The model generates diverse self-regulating cell types and relates correlations in conductance expression observed in vivo to underlying channel expression rates. Synaptic as well as intrinsic conductances can be regulated to make a self-assembling central pattern generator network; thus, network-level homeostasis can emerge from cell-autonomous regulation rules. Finally, we demonstrate that the outcome of homeostatic regulation depends on the complement of ion channels expressed in cells: in some cases, loss of specific ion channels can be compensated; in others, the homeostatic mechanism itself causes pathological loss of function.