Short Conduction Delays Cause Inhibition Rather than Excitation to Favor Synchrony in Hybrid Neuronal Networks of the Entorhinal Cortex

How stable synchrony in neuronal networks is sustained in the presence of conduction delays is an open question. The Dynamic Clamp was used to measure phase resetting curves (PRCs) for entorhinal cortical cells, and then to construct networks of two such neurons. PRCs were in general Type I (all advances or all delays) or weakly type II with a small region at early phases with the opposite type of resetting. We used previously developed theoretical methods based on PRCs under the assumption of pulsatile coupling to predict the delays that synchronize these hybrid circuits. For excitatory coupling, synchrony was predicted and observed only with no delay and for delays greater than half a network period that cause each neuron to receive an input late in its firing cycle and almost immediately fire an action potential. Synchronization for these long delays was surprisingly tight and robust to the noise and heterogeneity inherent in a biological system. In contrast to excitatory coupling, inhibitory coupling led to antiphase for no delay, very short delays and delays close to a network period, but to near-synchrony for a wide range of relatively short delays. PRC-based methods show that conduction delays can stabilize synchrony in several ways, including neutralizing a discontinuity introduced by strong inhibition, favoring synchrony in the case of noisy bistability, and avoiding an initial destabilizing region of a weakly type II PRC. PRCs can identify optimal conduction delays favoring synchronization at a given frequency, and also predict robustness to noise and heterogeneity

Chimera states: Coexistence of coherence and incoherence in networks of coupled oscillators

A chimera state is a spatio-temporal pattern in a network of identical coupled oscillators in which synchronous and asynchronous oscillation coexist. This state of broken symmetry, which usually coexists with a stable spatially symmetric state, has intrigued the nonlinear dynamics community since its discovery in the early 2000s. Recent experiments have led to increasing interest in the origin and dynamics of these states. Here we review the history of research on chimera states and highlight major advances in understanding their behaviour.Comment: 26 pages, 3 figure

Efficient Synchronous Byzantine Consensus

We present new protocols for Byzantine state machine replication and Byzantine agreement in the synchronous and authenticated setting. The celebrated PBFT state machine replication protocol tolerates $f$ Byzantine faults in an asynchronous setting using $3f+1$ replicas, and has since been studied or deployed by numerous works. In this work, we improve the Byzantine fault tolerance threshold to $n=2f+1$ by utilizing a relaxed synchrony assumption. We present a synchronous state machine replication protocol that commits a decision every 3 rounds in the common case. The key challenge is to ensure quorum intersection at one honest replica. Our solution is to rely on the synchrony assumption to form a post-commit quorum of size $2f+1$, which intersects at $f+1$ replicas with any pre-commit quorums of size $f+1$. Our protocol also solves synchronous authenticated Byzantine agreement in expected 8 rounds. The best previous solution (Katz and Koo, 2006) requires expected 24 rounds. Our protocols may be applied to build Byzantine fault tolerant systems or improve cryptographic protocols such as cryptocurrencies when synchrony can be assumed

Maintaining consistency in distributed systems

In systems designed as assemblies of independently developed components, concurrent access to data or data structures normally arises within individual programs, and is controlled using mutual exclusion constructs, such as semaphores and monitors. Where data is persistent and/or sets of operation are related to one another, transactions or linearizability may be more appropriate. Systems that incorporate cooperative styles of distributed execution often replicate or distribute data within groups of components. In these cases, group oriented consistency properties must be maintained, and tools based on the virtual synchrony execution model greatly simplify the task confronting an application developer. All three styles of distributed computing are likely to be seen in future systems - often, within the same application. This leads us to propose an integrated approach that permits applications that use virtual synchrony with concurrent objects that respect a linearizability constraint, and vice versa. Transactional subsystems are treated as a special case of linearizability

Synthesis: Works of Sarah Weaver and Collaborations (2020-2022)

Synthesis Series is a set of contemplative contemporary network arts works for solo, chamber, and large ensemble performance. The works are my compositions and collaborations from the years 2020 to 2022. The concept of synthesis is conceived as an activation of synchrony. Synthesis Series follows my prior works in Synchrony Series and Source Series as sequences of compositions since 1998 proliferating into a networked system of artistic realization. In Synchrony Series I defined synchrony as the perceptual alignment of distributed time and space components. Synthesis builds on this to activate the alignment as a networked state of composite resultants, networked synchrony across realities, transformation of distance, and synthesis activation for healing and transcendence. Synthesis is expressed through the pieces “Integral Infinity” (2021) for large ensemble, “At the Intersection of Eternity and Time” (2021) for solo percussion (collaborative composition with Gerry Hemingway), “Isomorphic Now” (2021) and “Interpolation Space” (2021) for chamber ensembles, and “Duplexity State” (2020) for audiovisual duo (collaborative composition with Daniel Pinheiro). The artistic and technological strategies for Synthesis Series utilize network arts in concept and in practice. Artistically, the pieces apply composition, improvisation, gestures, and individual performer artistic languages for virtual, hybrid, and in-person settings. The technology strategies for network performance, streaming, and recording include usages of open source technologies JackTrip, Pretty Good JackTrip Toolkit (PGJTT), and Open Broadcaster Software (OBS), together with commercial technologies Zoom, Vimeo, and Squarespace. This essay outlines the Synthesis Series technological context, artistic strategies for the series, details and excerpts for each piece, and new directions for the work, from my perspective as a composer