Quantifying criticality, information dynamics and thermodynamics of collective motion

Active matter consists of self-propelled particles whose interactions give rise to coherent collective motion. Well-known examples include schools of fish, flocks of birds, swarms of insects and herds of ungulates. On the micro-scale, cells, enzymes and bacteria also move collectively as active matter, inspiring engineering of artificial materials and devices. These diverse systems exhibit similar collective behaviours, including gathering, alignment and quick propagation of perturbations, which emerge from relatively simple local interactions. This phenomenon is known as self-organisation and is observed in active matter as well as in many other complex collective phenomena, including urban agglomeration, financial crises, ecosystems dynamics and technological cascading failures. Some open challenges in the study of self-organisation include (a) how the information processing across the collective and over time gives rise to emergent behaviour, (b) how to identify the regimes in which different collective behaviours exist and their phase transitions, and (c) how to quantify the thermodynamics associated with these phenomena. This thesis aims to investigate these topics in the context of active matter, while building a rigorous theoretical framework. Specifically, this thesis provides three main contributions. Firstly, the question of how to formally measure information transfer across the collective is addressed and applied to a real system, i.e., a school of fish. Secondly, general relations between statistical mechanical and thermodynamical quantities are analytically derived and applied to a model of active matter, resulting in the formulation of the concept of “thermodynamic efficiency of computation during collective motion”. This concept is then extended to the domain of urban dynamics. Thirdly, this thesis provides a rigorous quantification of the non-equilibrium entropy production associated with the collective motion of active Brownian particles

Informative and misinformative interactions in a school of fish

It is generally accepted that, when moving in groups, animals process information to coordinate their motion. Recent studies have begun to apply rigorous methods based on Information Theory to quantify such distributed computation. Following this perspective, we use transfer entropy to quantify dynamic information flows locally in space and time across a school of fish during directional changes around a circular tank, i.e. U-turns. This analysis reveals peaks in information flows during collective U-turns and identifies two different flows: an informative flow (positive transfer entropy) based on fish that have already turned about fish that are turning, and a misinformative flow (negative transfer entropy) based on fish that have not turned yet about fish that are turning. We also reveal that the information flows are related to relative position and alignment between fish, and identify spatial patterns of information and misinformation cascades. This study offers several methodological contributions and we expect further application of these methodologies to reveal intricacies of self-organisation in other animal groups and active matter in general

Cohesion, order and information flow in the collective motion of mixed-species shoals

Financial support came from the Australian Research Council (grant nos. DP 160103905 and DE 160100630).Despite the frequency with which mixed-species groups are observed in nature, studies of collective behaviour typically focus on single-species groups. Here, we quantify and compare the patterns of interactions between three fish species, threespine sticklebacks (Gasterosteus aculeatus), ninespine sticklebacks (Pungitius pungitius) and roach (Rutilus rutilus) in both single- and mixed-species shoals in the laboratory. Pilot data confirmed that the three species form both single- and mixed-species shoals in the wild. In our laboratory study, we found that single-species groups were more polarized than mixed-species groups, while single-species groups of threespine sticklebacks and roach were more cohesive than mixed shoals of these species. Furthermore, while there was no difference between the inter-individual distances between threespine and ninespine sticklebacks within mixed-species groups, there was some evidence of segregation by species in mixed groups of threespine sticklebacks and roach. There were differences between treatments in mean pairwise transfer entropy, and in particular we identify species-differences in information use within the mixed-species groups, and, similarly, differences in responses to conspecifics and heterospecifics in mixed-species groups. We speculate that differences in the patterns of interactions between species in mixed-species groups may determine patterns of fission and fusion in such groups.Publisher PDFPeer reviewe

INTERMUSCULAR TWO-INCISION TECHNIQUE FOR S-ICD IMPLANTATION

Background The traditional technique for subcutaneous implantable cardioverter defibrillator (S-ICD) implantation, which involves three incisions and a subcutaneous pocket, is associated with possible complications, including inappropriate interventions. The aim of this prospective multicenter study was to evaluate the efficacy and safety of an alternative intermuscular two-incision technique for S-ICD implantation. Methods The study population included 36 consecutive patients (75% male, mean age 44 ± 12 years [range 20–69]) who underwent S-ICD implantation using the intermuscular two-incision technique. This technique avoids the superior parasternal incision for the lead placement and consists of creating an intermuscular pocket between the anterior surface of the serratus anterior and the posterior surface of the latissimus dorsi muscles instead of a subcutaneous pocket. Results All patients were successfully implanted in the absence of any procedure-related complications with a successful 65-J standard polarity defibrillation threshold testing, except in one, who received a second successful shock after pocket revision. During a mean follow-up of 10 months (range 3–30), no complications requiring surgical revision were observed. At device interrogation, stable sensing without interferences was observed in all patients. Two patients (5.5%) experienced appropriate and successful shock on ventricular fibrillation and in four patients (11%), a total of seven nonsustained self-terminated ventricular tachycardias were correctly detected. No inappropriate interventions were observed. Conclusions Our experience suggests that the two-incision intermuscular technique is a safe and efficacious alternative to the current technique for S-ICD implantation that may help reducing complications including inappropriate interventions and offer a better cosmetic outcome, especially in thin individuals

A multi-element psychosocial intervention for early psychosis (GET UP PIANO TRIAL) conducted in a catchment area of 10 million inhabitants: study protocol for a pragmatic cluster randomized controlled trial

Multi-element interventions for first-episode psychosis (FEP) are promising, but have mostly been conducted in non-epidemiologically representative samples, thereby raising the risk of underestimating the complexities involved in treating FEP in 'real-world' services