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1. Robust Molecular Communications: DFE-SPRTs and Synchronisation

   https://doi.org/10.1109/ICC.2019.8761054  

   Tung, Tze-Yang; Mitra, Urbashi (May 2019, Proceedings of IEEE International Conference on Communications)

   Precise synchronisation of transmitters and receivers is particularly challenging in diffusive molecular communication environments. To this end, a point-to-point molecular communication system is examined wherein the design of the transceiver offers resilience to synchronisation errors. In particular, the development of a sequential probability ratio test-based detector, which allows for additional observations in the presence of uncertainty due to mis-synchronisation at the receiver, and a modulation design which is optimised for this receiver strategy, is considered. The structure of the probability of molecules hitting a receiver within a particular time slot is exploited. An approximate maximum log-likelihood estimator for the synchronisation error is derived and the Cramér-Rao bound (CRB) computed, to show that the performance of the proposed estimator is close to the CRB at low transmission rates. The proposed receiver and modulation designs achieve strongly improved asynchronous detection performance for the same data rate as a decision feedback based receiver by a factor of 3 to 5 on average. 

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2. Emergence of the London Millennium Bridge instability without synchronisation

   https://doi.org/10.1038/s41467-021-27568-y  

   Belykh, Igor; Bocian, Mateusz; Champneys, Alan R.; Daley, Kevin; Jeter, Russell; Macdonald, John H. G.; McRobie, Allan (December 2021, Nature Communications)

   Abstract The pedestrian-induced instability of the London Millennium Bridge is a widely used example of Kuramoto synchronisation. Yet, reviewing observational, experimental, and modelling evidence, we argue that increased coherence of pedestrians’ foot placement is a consequence of, not a cause of the instability. Instead, uncorrelated pedestrians produce positive feedback, through negative damping on average, that can initiate significant lateral bridge vibration over a wide range of natural frequencies. We present a simple general formula that quantifies this effect, and illustrate it through simulation of three mathematical models, including one with strong propensity for synchronisation. Despite subtle effects of gait strategies in determining precise instability thresholds, our results show that average negative damping is always the trigger. More broadly, we describe an alternative to Kuramoto theory for emergence of coherent oscillations in nature; collective contributions from incoherent agents need not cancel, but can provide positive feedback on average, leading to global limit-cycle motion. 

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3. Increasing Robustness to Synchronisation Errors in Molecular Communications

   https://doi.org/10.1109/ISTC.2018.8625364  

   Tung, Tze-Yang; Mitra, Urbashi (December 2018, Proceedings of the IEEE 10th International Symposium on Turbo Codes & Iterative Information Processing (ISTC))

   Achieving precise synchronisation between transmitters and receivers is particularly challenging in diffusive molecular communication environments. To this end, pointto-point molecular communication system design is examined wherein synchronisation errors are explicitly considered. Two transceiver design questions are considered: the development of a sequential probability ratio test-based detector which allows for additional observations in the presence of uncertainty due to miss-ynchronisation at the receiver, and a modulation design which is optimised for this receiver strategy. The modulation is based on optimising an approximation for the probability of error for the detection strategy and directly exploits the structure of the probability of molecules hitting a receiver within a particular time slot. The proposed receiver and modulation designs achieve strongly improved asynchronous detection performance for the same data rate as a decision feedback based receiver by a factor of 1/2. 

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4. Influence of three-dimensionality on wake synchronisation of an oscillatory cylinder

   https://doi.org/10.1017/jfm.2024.1079  

   Kim, Youngjae; Godavarthi, Vedasri; Rolandi, Laura Victoria; Klamo, Joseph T; Taira, Kunihiko (December 2024, Journal of Fluid Mechanics)

   We investigate the effect of three-dimensionality on the synchronisation characteristics of the wake behind an oscillating circular cylinder at$${\textit {Re}} = 300$$. Cylinder oscillations in rotation, transverse translation and streamwise translation are considered. We utilise phase-reduction analysis, which quantifies the phase-sensitivity function of periodic flows, to examine the synchronisation properties. Here, we present an ensemble-based framework for phase-reduction analysis to handle three-dimensional wakes that are not perfectly time-periodic. Based on the phase-sensitivity functions, synchronisability to three types of cylinder oscillations is evaluated. In spite of similar trends, we find that phase-sensitivity functions involving three-dimensional wakes are lower in magnitude compared with those of two-dimensional wakes, which leads to narrower conditions for synchronisation to weak cylinder oscillations. We unveil that the difference between the phase-sensitivity functions of two- and three-dimensional flows is strongly correlated to the amplitude variation of the three-dimensional flow by the cylinder motions. This finding reveals that the cylinder motion modifies the three-dimensionality of the wake as well as the phase of vortex shedding, which leads to reduced phase modulation. The synchronisation conditions of three-dimensional wakes, predicted by phase-reduction analysis, agree with the identification by parametric studies using direct numerical simulations for forced oscillations with small amplitudes. This study presents the potential capability of phase-reduction to study synchronisation characteristics of complex flows. 

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5. A measurement of the equation of state of carbon envelopes of white dwarfs

   https://doi.org/10.1038/s41586-020-2535-y  

   Kritcher, Andrea L.; Swift, Damian C.; Döppner, Tilo; Bachmann, Benjamin; Benedict, Lorin X.; Collins, Gilbert W.; DuBois, Jonathan L.; Elsner, Fred; Fontaine, Gilles; Gaffney, Jim A.; et al (August 2020, Nature)

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