DJJ's site navigation page


List of papers etc, with links

Research Interests

Historically, DJJ's research interests have encompassed microwave acoustics; (PhD thesis was on the microwave acoustic properties of ferroelectrics and ferroelectric semiconductors); X-ray and neutron scattering experiments from phonons in solids; frequency-crossing phonon spectrometer experiments; non-linear acoustic propagation and chaos in piezoelectric ferroelectrics; chaos in electronic circuits and telecommunications applications; chaos in computer data networks; chaos in power electronic systems. The underlying theme is the behaviour of systems having strong non-linearity and either feedback or wave propagation. Recently he has become interested in parallel computer systems where there are problems of arbitration produced by asynchronous communications which are similar to the arbitrations due to "folding" in a classic chaotic system. DJJ has also written reports on the telecommunications applications of high temperature superconducting materials, and radar absorber advanced materials construction using a photonic band-structure arrangement. At present his research interests are:

Some Postscript papers (several are large)

DJJ is interested in naturally occurring catastrophic events in complex systems. A paper which shows how these can arise as a consequence of very simple non-linear chaotic dynamics has been written for the conference COMPLEX96 in Australia, July 1996. The paper title is

The work has application to reliability in distributed parallel computing networks.

There is a follow-up paper which was presented at ECCTD97 in Budapest in September 1997. The paper title is

This work shows that noise-driven traps and snags can be almost indistinguishable from a class of chaotic intermittency.

A previous paper at COMPLEX94 entitled

discusses the problem caused by arbitration errors in asynchronous distributed computing.

Another paper at COMPLEX96 is concerned with non-linear signal processing and propagation. See

This shows that the global behaviour of a collection of coupled non-linear processes is surprising and not intuitively obvious.

Chaos and self-similarity may also occur in computer data networks. There is some debate about this in the community, but a simple model is reported in

presented at ECCTD95 in Istanbul in August 1995.

An earlier report of this work found chaotic states in computer data networks and was reported at the conference COMPLEX94

Self-similarity is also observed in the traffic on networks. There is a paper on

which can be due to both the statistics of traffic demand, and also to the chaotic dynamics of the protocol under conditions of regular demand.

There is a speculation on the applicability of the work on networks and on trapping systems to the wider worlds of software engineering, economics, and ecology, in the unpublished paper on

One of the interesting things about electronic chaotic circuits containing traps is that the trapping gives no advance warning that it is about to happen. The only thing one can be quite certain about is that if one waits long enough the circuit will trap. This is also seen in the commonplace software used on PCs, where apparent stability is always followed by a system crash. This is because the operating system is a VSS; saving different bit patterns to hard disk every time it is shut down that determine its behaviour subsequently. In fact, this software has the interesting property that trapping ( in this case a system crash) becomes more likely as the installation is used, or "ages". We see this also in the living world, as the probability of death for an individual rises with age. Yet another very interesting and significant trap is the presence of the potent nuclear arsenal on the planet. There is no doubt that this trap will be entered at some point; like in the electronic system there may be no forewarning and no chance of avoidance. It is indeed fortunate that living systems have demonstrated survivability in a high radiation environment.

Two papers presented at Complex 98 are available here.

A paper, for a meeting in Seville, Spain, in June 1996 NDES96 on electronic analogue models of two-centre and impacting systems ties in the work above on complex systems with very simple chaotic circuits. The paper title is

In 2000 DJJ has been interested in emergent fractal fixed point structures as a result of approximate image-processing computations. These structures are artefacts of the discrete nature of the computation and have no basis in reality.

He has also been investigating chaotic itinerancy in a one-dimensional lattice of harmonic potential wells. A particle traverses the lattice in an irregular way which is not a random walk, but shows strong propensities to continue to make progress to the right or to the left ("short term memory") even though there is no intrinsic bias in the direction.

He has also been investigating the chaotic motions of a Newton's Cage simulation.

He has recently been interested in the limitations of the predictive (as opposed to post-dictive) powers of the fashionable technique of "agent-based modelling". It is likely that agent based models of complex systems provide very poor foundations for policy decisions.

Research opportunities for students and visitors

Initial approaches from prospective research students, visiting research fellows, and collaborators are welcome. See the pages

D.Jefferies email
19th August 2002.