Boundary effects on localized structures in spatially extended systems

We present a general method of analyzing the influence of finite size and boundary effects on the dynamics of localized solutions of non-linear spatially extended systems. The dynamics of localized structures in infinite systems involve solvability conditions that require projection onto a Goldstone mode. Our method works by extending the solvability conditions to finite sized systems, by incorporating the finite sized modifications of the Goldstone mode and associated nonzero eigenvalue. We apply this method to the special case of non-equilibrium domain walls under the influence of Dirichlet boundary conditions in a parametrically forced complex Ginzburg Landau equation, where we examine exotic nonuniform domain wall motion due to the influence of boundary conditions.Comment: 9 pages, 5 figures, submitted to Physical Review

What is tested when experiments test that quantum dynamics is linear

Experiments that look for nonlinear quantum dynamics test the fundamental premise of physics that one of two separate systems can influence the physical behavior of the other only if there is a force between them, an interaction that involves momentum and energy. The premise is tested because it is the assumption of a proof that quantum dynamics must be linear. Here variations of a familiar example are used to show how results of nonlinear dynamics in one system can depend on correlations with the other. Effects of one system on the other, influence without interaction between separate systems, not previously considered possible, would be expected with nonlinear quantum dynamics. Whether it is possible or not is subject to experimental tests together with the linearity of quantum dynamics. Concluding comments and questions consider directions our thinking might take in response to this surprising unprecedented situation.Comment: 14 pages, Title changed, sentences adde

IT Project Management from a Systems Thinking Perspective: A Position Paper

We proposes a Systems Thinking approach to the study of IT project management and show how this approach helps project managers in controlling their projects. To illustrate our proposal, we present an example model of the dynamics of IT out-sourcing projects. The example model explains these dynamics in terms of feedback loops consisting of causal relations re-ported in the literature. The model provides insight in how coordination, trust, information exchange and possibilities for op-portunistic behaviour influence each other and together influence delivery quality, which in turn influences trust. The integra-tion of these insights provided by applying the Systems Thinking perspective helps project managers to reason about how their choices influence project outcome. The Systems Thinking perspective can serve as an additional tool in the academic study of IT project management. Applying the Systems Thinking perspective also calls for additional research in which this perspective is itself the object of study

The influence of gene expression time delays on Gierer-Meinhardt pattern formation systems

There are numerous examples of morphogen gradients controlling long range signalling in developmental and cellular systems. The prospect of two such interacting morphogens instigating long range self-organisation in biological systems via a Turing bifurcation has been explored, postulated, or implicated in the context of numerous developmental processes. However, modelling investigations of cellular systems typically neglect the influence of gene expression on such dynamics, even though transcription and translation are observed to be important in morphogenetic systems. In particular, the influence of gene expression on a large class of Turing bifurcation models, namely those with pure kinetics such as the Gierer–Meinhardt system, is unexplored. Our investigations demonstrate that the behaviour of the Gierer–Meinhardt model profoundly changes on the inclusion of gene expression dynamics and is sensitive to the sub-cellular details of gene expression. Features such as concentration blow up, morphogen oscillations and radical sensitivities to the duration of gene expression are observed and, at best, severely restrict the possible parameter spaces for feasible biological behaviour. These results also indicate that the behaviour of Turing pattern formation systems on the inclusion of gene expression time delays may provide a means of distinguishing between possible forms of interaction kinetics. Finally, this study also emphasises that sub-cellular and gene expression dynamics should not be simply neglected in models of long range biological pattern formation via morphogens

Cosmology in the Solar System: Pioneer effect is not cosmological

Does the Solar System and, more generally, a gravitationally bound system follow the cosmic expansion law ? Is there a cosmological influence on the dynamics or optics in such systems ? The general relativity theory provides an unique and unambiguous answer, as a solution of Einstein equations with a local source in addition to the cosmic fluid, and obeying the correct (cosmological) limiting conditions. This solution has no analytic expression. A Taylor development of its metric allows a complete treatment of dynamics and optics in gravitationally bound systems, up to the size of galaxy clusters, taking into account both local and cosmological effects. In the solar System, this provides an estimation of the (non zero) cosmological influence on the Pioneer probe: it fails to account for the " Pioneer effect " by about 10 orders of magnitude. We criticize contradictory claims on this topic

Spin Glasses: Model systems for non-equilibrium dynamics

Spin glasses are frustrated magnetic systems due to a random distribution of ferro- and antiferromagnetic interactions. An experimental three dimensional (3d) spin glass exhibits a second order phase transition to a low temperature spin glass phase regardless of the spin dimensionality. In addition, the low temperature phase of Ising and Heisenberg spin glasses exhibits similar non-equilibrium dynamics and an infinitely slow approach towards a thermodynamic equilibrium state. There are however significant differences in the detailed character of the dynamics as to memory and rejuvenation phenomena and the influence of critical dynamics on the behaviour. In this article, some aspects of the non-equilibrium dynamics of an Ising and a Heisenberg spin glass are briefly reviewed and some comparisons are made to other glassy systems that exhibit magnetic non-equilibrium dynamics.Comment: To appear in J. Phys.: Condens. Matter, Proceedings from HFM2003, Grenobl

Delay Induced Excitability

We analyse the stochastic dynamics of a bistable system under the influence of time-delayed feedback. Assuming an asymmetric potential, we show the existence of a regime in which the systems dynamic displays excitability by calculating the relevant residence time distributions and correlation times. Experimentally we then observe this behaviour in the polarization dynamics of a vertical cavity surface emitting laser with opto-electronic feedback. Extending these observations to two-dimensional systems with dispersive coupling we finally show numerically that delay induced excitability can lead to the appearance of propagating wave-fronts and spirals.Comment: 5 pages, 6 figure

Dynamics-Driven Evolution to Structural Heterogeneity in Complex Networks

The mutual influence of dynamics and structure is a central issue in complex systems. In this paper we study by simulation slow evolution of network under the feedback of a local-majority-rule opinion process. If performance-enhancing local mutations have higher chances of getting integrated into its structure, the system can evolve into a highly heterogeneous small-world with a global hub (whose connectivity is proportional to the network size), strong local connection correlations and power law-like degree distribution. Networks with better dynamical performance are achieved if structural evolution occurs much slower than the network dynamics. Structural heterogeneity of many biological and social dynamical systems may also be driven by various dynamics-structure coupling mechanisms.Comment: Figure 2 updated. Final version as appear in Physica