Synchronization of Coupled Boolean Phase Oscillators

We design, characterize, and couple Boolean phase oscillators that include state-dependent feedback delay. The state-dependent delay allows us to realize an adjustable coupling strength, even though only Boolean signals are exchanged. Specifically, increasing the coupling strength via the range of state-dependent delay leads to larger locking ranges in uni- and bi-directional coupling of oscillators in both experiment and numerical simulation with a piecewise switching model. In the unidirectional coupling scheme, we unveil asymmetric triangular-shaped locking regions (Arnold tongues) that appear at multiples of the natural frequency of the oscillators. This extends observations of a single locking region reported in previous studies. In the bidirectional coupling scheme, we map out a symmetric locking region in the parameter space of frequency detuning and coupling strength. Because of large scalability of our setup, our observations constitute a first step towards realizing large-scale networks of coupled oscillators to address fundamental questions on the dynamical properties of networks in a new experimental setting.Comment: 8 pages, 8 figure

Multirhythmicity in an optoelectronic oscillator with large delay

An optoelectronic oscillator exhibiting a large delay in its feedback loop is studied both experimentally and theoretically. We show that multiple square-wave oscillations may coexist for the same values of the parameters (multirhythmicity). Depending on the sign of the phase shift, these regimes admit either periods close to an integer fraction of the delay or periods close to an odd integer fraction of twice the delay. These periodic solutions emerge from successive Hopf bifurcation points and stabilize at a finite amplitude following a scenario similar to Eckhaus instability in spatially extended systems. We find quantitative agreements between experiments and numerical simulations. The linear stability of the square-waves is substantiated analytically by determining stable fixed points of a map.Comment: 14 pages, 7 figure

Transient scaling and resurgence of chimera states in networks of Boolean phase oscillators

We study networks of non-locally coupled electronic oscillators that can be described approximately by a Kuramoto-like model. The experimental networks show long complex transients from random initial conditions on the route to network synchronization. The transients display complex behaviors, including resurgence of chimera states, which are network dynamics where order and disorder coexists. The spatial domain of the chimera state moves around the network and alternates with desynchronized dynamics. The fast timescale of our oscillators (on the order of $100\;\mathrm{ns}$) allows us to study the scaling of the transient time of large networks of more than a hundred nodes, which has not yet been confirmed previously in an experiment and could potentially be important in many natural networks. We find that the average transient time increases exponentially with the network size and can be modeled as a Poisson process in experiment and simulation. This exponential scaling is a result of a synchronization rate that follows a power law of the phase-space volume.Comment: http://journals.aps.org/pre/abstract/10.1103/PhysRevE.90.03090

Reservoir computing with a single time-delay autonomous Boolean node

We demonstrate reservoir computing with a physical system using a single autonomous Boolean logic element with time-delay feedback. The system generates a chaotic transient with a window of consistency lasting between 30 and 300 ns, which we show is sufficient for reservoir computing. We then characterize the dependence of computational performance on system parameters to find the best operating point of the reservoir. When the best parameters are chosen, the reservoir is able to classify short input patterns with performance that decreases over time. In particular, we show that four distinct input patterns can be classified for 70 ns, even though the inputs are only provided to the reservoir for 7.5 ns.Comment: 5 pages, 5 figure

Excitability in autonomous Boolean networks

We demonstrate theoretically and experimentally that excitable systems can be built with autonomous Boolean networks. Their experimental implementation is realized with asynchronous logic gates on a reconfigurabe chip. When these excitable systems are assembled into time-delay networks, their dynamics display nanosecond time-scale spike synchronization patterns that are controllable in period and phase.Comment: 6 pages, 5 figures, accepted in Europhysics Letters (epljournal.edpsciences.org

Drought increases heat tolerance of leaf respiration in Eucalyptus globulus saplings grown under both ambient and elevated atmospheric [CO₂] and temperature

Climate change is resulting in increasing atmospheric [CO₂], rising growth temperature (T), and greater frequency/severity of drought, with each factor having the potential to alter the respiratory metabolism of leaves. Here, the effects of elevated atmospheric [CO₂], sustained warming, and drought on leaf dark respiration (R(dark)), and the short-term T response of R(dark) were examined in Eucalyptus globulus. Comparisons were made using seedlings grown under different [CO₂], T, and drought treatments. Using high resolution T-response curves of R(dark) measured over the 15-65 °C range, it was found that elevated [CO₂], elevated growth T, and drought had little effect on rates of R(dark) measured at T <35 °C and that there was no interactive effect of [CO₂], growth T, and drought on T response of R(dark). However, drought increased R(dark) at high leaf T typical of heatwave events (35-45 °C), and increased the measuring T at which maximal rates of R(dark) occurred (Tmax) by 8 °C (from 52 °C in well-watered plants to 60 °C in drought-treated plants). Leaf starch and soluble sugars decreased under drought and elevated growth T, respectively, but no effect was found under elevated [CO₂]. Elevated [CO₂] increased the Q₁₀ of R(dark) (i.e. proportional rise in R(dark) per 10 °C) over the 15-35 °C range, while drought increased Q₁₀ values between 35 °C and 45 °C. Collectively, the study highlights the dynamic nature of the T dependence of R dark in plants experiencing future climate change scenarios, particularly with respect to drought and elevated [CO₂].This work was funded by the Australian Research Council (ARC FT0991448, DP1093759, and CE140100008, to OKA; and DP0879531, to DTT). This project is supported by funding from the Australian Government Department of Agriculture, Fisheries and Forestry under its Forest Industries Climate Change Research Fund programme. Support for the renovation of the Hawkesbury Forest Experiment tree chambers to improve T and humidity control of the WTC was provided as part of an initiative of the Australian Government through the Education Investment Fund supporting research infrastructure

Restricted feedback control of one-dimensional maps

Dynamical control of biological systems is often restricted by the practical constraint of unidirectional parameter perturbations. We show that such a restriction introduces surprising complexity to the stability of one-dimensional map systems and can actually improve controllability. We present experimental cardiac control results that support these analyses. Finally, we develop new control algorithms that exploit the structure of the restricted-control stability zones to automatically adapt the control feedback parameter and thereby achieve improved robustness to noise and drifting system parameters.Comment: 29 pages, 9 embedded figure

The logic behind entrustable professional activity frameworks: A scoping review of the literature

Introduction: Entrustable professional activities (EPAs), discrete profession-specific tasks requiring integration of multiple competencies, are increasingly used to help define and inform curricula of specialty training programmes. Although guidelines exist to help guide the developmental process, deciding what logic to use to draft a preliminary EPA framework poses a crucial but often difficult first step. The logic of an EPA framework can be defined as the perspective used by its developers to break down the practice of a profession into units of professional work. This study aimed to map dominant logics and their rationales across postgraduate medical education and fellowship programmes. Methods: A scoping review using systematic searches within five electronic databases (Medline, Embase, Google Scholar, Scopus and Web of Science) was performed. Dominant logics of included papers were identified using inductive coding and iterative analysis. Results: In total, 42 studies were included. Most studies were conducted in the United States (n = 22; 52%), Canada (n = 6; 14%) and the Netherlands (n = 4; 10%). Across the reported range of specialties, family medicine (n = 4; 10%), internal medicine (n = 4; 10%), paediatrics (n = 3; 7%) and psychiatry (n = 3; 7%) were the most common. Three dominant logics could be identified, namely, ‘service provision’, ‘procedures’ and/or ‘disease or patient categories’. The majority of papers (n = 37; 88%) used two or more logics when developing EPA frameworks (median = 3, range = 1–4). Disease or patient groups and service provision were the most common logics used (39% and 37%, respectively). Conclusions: Most programmes used a combination of logics when trying to capture the essential tasks of a profession in EPAs. For each of the three dominant logics, the authors arrived at a definition and identified benefits, limitations and examples. These findings may potentially inform best practice guidelines for EPA development