Optimisation in ‘Self-modelling’ Complex Adaptive Systems

When a dynamical system with multiple point attractors is released from an arbitrary initial condition it will relax into a configuration that locally resolves the constraints or opposing forces between interdependent state variables. However, when there are many conflicting interdependencies between variables, finding a configuration that globally optimises these constraints by this method is unlikely, or may take many attempts. Here we show that a simple distributed mechanism can incrementally alter a dynamical system such that it finds lower energy configurations, more reliably and more quickly. Specifically, when Hebbian learning is applied to the connections of a simple dynamical system undergoing repeated relaxation, the system will develop an associative memory that amplifies a subset of its own attractor states. This modifies the dynamics of the system such that its ability to find configurations that minimise total system energy, and globally resolve conflicts between interdependent variables, is enhanced. Moreover, we show that the system is not merely ‘recalling’ low energy states that have been previously visited but ‘predicting’ their location by generalising over local attractor states that have already been visited. This ‘self-modelling’ framework, i.e. a system that augments its behaviour with an associative memory of its own attractors, helps us better-understand the conditions under which a simple locally-mediated mechanism of self-organisation can promote significantly enhanced global resolution of conflicts between the components of a complex adaptive system. We illustrate this process in random and modular network constraint problems equivalent to graph colouring and distributed task allocation problems

Transformations in the Scale of Behaviour and the Global Optimisation of Constraints in Adaptive Networks

The natural energy minimisation behaviour of a dynamical system can be interpreted as a simple optimisation process, finding a locally optimal resolution of problem constraints. In human problem solving, high-dimensional problems are often made much easier by inferring a low-dimensional model of the system in which search is more effective. But this is an approach that seems to require top-down domain knowledge; not one amenable to the spontaneous energy minimisation behaviour of a natural dynamical system. However, in this paper we investigate the ability of distributed dynamical systems to improve their constraint resolution ability over time by self-organisation. We use a ‘self-modelling’ Hopfield network with a novel type of associative connection to illustrate how slowly changing relationships between system components can result in a transformation into a new system which is a low-dimensional caricature of the original system. The energy minimisation behaviour of this new system is significantly more effective at globally resolving the original system constraints. This model uses only very simple, and fully-distributed positive feedback mechanisms that are relevant to other ‘active linking’ and adaptive networks. We discuss how this neural network model helps us to understand transformations and emergent collective behaviour in various non-neural adaptive networks such as social, genetic and ecological networks

Neutron Stars as Type-I Superconductors

In a recent paper by Link, it was pointed out that the standard picture of the neutron star core composed of a mixture of a neutron superfluid and a proton type-II superconductor is inconsistent with observations of a long period precession in isolated pulsars. In the following we will show that an appropriate treatment of the interacting two-component superfluid (made of neutron and proton Cooper pairs), when the structure of proton vortices is strongly modified, may dramatically change the standard picture, resulting in a type-I superconductor. In this case the magnetic field is expelled from the superconducting regions of the neutron star leading to the formation of the intermediate state when alternating domains of superconducting matter and normal matter coexist.Comment: 4 page

Pfaffian representations of cubic surfaces

Let K be a field of characteristic zero. We describe an algorithm which requires a homogeneous polynomial F of degree three in K[x_0,x_1,x_2,x_3] and a zero A of F in P^3_K and ensures a linear pfaffian representation of V(F) with entries in K[x_0,x_1,x_2,x_3], under mild assumptions on F and A. We use this result to give an explicit construction of (and to prove the existence of) a linear pfaffian representation of V(F), with entries in K'[x_0,x_1,x_2,x_3], being K' an algebraic extension of K of degree at most six. An explicit example of such a construction is given.Comment: 17 pages. Expanded with some remarks. Published with minor corrections in Geom. Dedicat

The crux of the matter: did the ABC's Catalyst program change statin use in Australia?

This article argues that the ABC’s Catalyst program criticising statins affected people’s willingness to take these drugs. Abstract Objectives: To examine the impact of a two-part special edition of the Australian Broadcasting Corporation\u27s science journalism program Catalyst (titled Heart of the matter), aired in October 2013, that was critical of HMG-CoA reductase inhibitors (“statins”). Design, setting and participants: Population-based interrupted time-series analysis of a 10% sample of Australian long-term concessional beneficiaries who were dispensed statins under the Pharmaceutical Benefits Scheme (about 51% of all people who were dispensed a statin between 1 July 2009 and 30 June 2014); dispensing of proton pump inhibitors (PPIs) was used as a comparator. Main outcome measures: Change in weekly dispensings and discontinuation of use of statins and PPIs, adjusting for seasonal and long-term trends, overall and (for statins only) stratified by the use of cardiovascular and diabetes medicines. Results: In our sample, 191 833 people were dispensed an average of 26 946 statins weekly. Following the Catalyst program, there was a 2.60% (95% CI, 1.40%–3.77%; P < 0.001) reduction in statin dispensing, equivalent to 14 005 fewer dispensings Australia-wide every week. Dispensing decreased by 6.03% (95% CI, 3.73%–8.28%; P < 0.001) for people not dispensed other cardiovascular and diabetes medicines and 1.94% (0.42%–3.45%; P = 0.01) for those dispensed diabetes medicines. In the week the Catalyst program aired, there was a 28.8% (95% CI, 15.4%–43.7%; P < 0.001) increase in discontinuation of statin use, which decayed by 9% per week. An estimated 28 784 additional Australians ceased statin treatment. Discontinuation occurred regardless of the use of other cardiovascular and diabetes medicines. There were no significant changes in PPI use after the Catalyst program. Conclusions: Following airing of the Catalyst program, there was a temporary increase in discontinuation and a sustained decrease in overall statin dispensing. Up until 30 June 2014, there were 504 180 fewer dispensings of statins, and we estimate this to have affected 60 897 people

If you can't be with the one you love, love the one you're with: How individual habituation of agent interactions improves global utility

Simple distributed strategies that modify the behaviour of selfish individuals in a manner that enhances cooperation or global efficiency have proved difficult to identify. We consider a network of selfish agents who each optimise their individual utilities by coordinating (or anti-coordinating) with their neighbours, to maximise the pay-offs from randomly weighted pair-wise games. In general, agents will opt for the behaviour that is the best compromise (for them) of the many conflicting constraints created by their neighbours, but the attractors of the system as a whole will not maximise total utility. We then consider agents that act as 'creatures of habit' by increasing their preference to coordinate (anti-coordinate) with whichever neighbours they are coordinated (anti-coordinated) with at the present moment. These preferences change slowly while the system is repeatedly perturbed such that it settles to many different local attractors. We find that under these conditions, with each perturbation there is a progressively higher chance of the system settling to a configuration with high total utility. Eventually, only one attractor remains, and that attractor is very likely to maximise (or almost maximise) global utility. This counterintutitve result can be understood using theory from computational neuroscience; we show that this simple form of habituation is equivalent to Hebbian learning, and the improved optimisation of global utility that is observed results from wellknown generalisation capabilities of associative memory acting at the network scale. This causes the system of selfish agents, each acting individually but habitually, to collectively identify configurations that maximise total utility

Multi-neuronal refractory period adapts centrally generated behaviour to reward

Oscillating neuronal circuits, known as central pattern generators (CPGs), are responsible for generating rhythmic behaviours such as walking, breathing and chewing. The CPG model alone however does not account for the ability of animals to adapt their future behaviour to changes in the sensory environment that signal reward. Here, using multi-electrode array (MEA) recording in an established experimental model of centrally generated rhythmic behaviour we show that the feeding CPG of Lymnaea stagnalis is itself associated with another, and hitherto unidentified, oscillating neuronal population. This extra-CPG oscillator is characterised by high population-wide activity alternating with population-wide quiescence. During the quiescent periods the CPG is refractory to activation by food-associated stimuli. Furthermore, the duration of the refractory period predicts the timing of the next activation of the CPG, which may be minutes into the future. Rewarding food stimuli and dopamine accelerate the frequency of the extra-CPG oscillator and reduce the duration of its quiescent periods. These findings indicate that dopamine adapts future feeding behaviour to the availability of food by significantly reducing the refractory period of the brain's feeding circuitry

Clinical audit of rectal cancer patient referrals for Papillon contact brachytherapy

AbstractBackground and purpose:Papillon treatment is a form of contact X-ray brachytherapy (CXB) which is used as an alternative to surgery for rectal cancer. This study aimed to audit patients who were referred for and treated with CXB over a 6-year period against guidelines derived from a critical review of the evidence base.Materials and methods:Patient demographics, tumour characteristics and outcome data were gathered for 31 patients referred for CXB. A critical review of the evidence identified consensus referral criteria and outcome data against which to audit patients.Results:Referral criteria were derived from six published studies. These applied to patients unfit for surgery or stoma-averse. All referred patients had a visible tumour or scar with a tumour size under 3 cm and sited less than 12 cm from the anal verge. Nodal status varied from N0 to N2, but there was no metastatic disease present. The audited cohort demonstrated demographic equivalence, while the initial clinical complete response and recurrence rates were also comparable.Conclusion:This audit confirmed the validity of referral and treatment protocols and should guide future referrals until evidence from ongoing studies becomes available. These findings should contribute to the development of robust national guidelines.</jats:sec

Spin Discrimination in Three-Body Decays

The identification of the correct model for physics beyond the Standard Model requires the determination of the spin of new particles. We investigate to which extent the spin of a new particle $X$ can be identified in scenarios where it decays dominantly in three-body decays $X\to f\bar{f} Y$. Here we assume that $Y$ is a candidate for dark matter and escapes direct detection at a high energy collider such as the LHC. We show that in the case that all intermediate particles are heavy, one can get information on the spins of $X$ and $Y$ at the LHC by exploiting the invariant mass distribution of the two standard model fermions. We develop a model-independent strategy to determine the spins without prior knowledge of the unknown couplings and test it in a series of Monte Carlo studies.Comment: 31+1 pages, 4 figures, 8 tables, JHEP.cls include