Speckle statistics as a tool to distinguish collective behaviors of Zebrafish shoals Adauto J. F. de Souza, Antonio. R. de C. Romaguera, João V. A. Vasconcelos, Luis G. Negreiros-Neto, Viviane M. de Oliveira, et al. Scientific Reports, 2024 Zebrafish have become an important model animal for studying the emergence of collective behavior in nature. Here, we show how to properly analyze the polarization statistics to distinguish shoal regimes. In analogy with the statistical properties of optical speckles, we show that exponential and Rayleigh distributions emerge in shoals with many fish with uncorrelated velocity directions. In the opposite limit of just two fish, the polarization distribution peaks at high polarity, with the average value being a decreasing function of the shoal’s size, even in the absence of correlations. We also perform a set of experiments unveiling two shoaling regimes. Large shoals behave as small domains with strong intra-domain and weak inter-domain correlations. A strongly correlated regime develops for small shoals. The reported polarization statistical features shall guide future automated neuroscience, pharmacological, toxicological, and embryogenesis-motivated experiments aiming to explore the collective behavior of fish shoals.
Impact of Correlated Disorder on Surface Superconductivity: Revealing the Robustness of the Surface Ordering Effect R. H. de Bragança, L. M. T. de Moraes, A. R. de C. Romaguera, J. Albino Aguiar, M. D. Croitoru Journal of Physical Chemistry Letters, 2024 Surface superconductivity, wherein electron pairing occurs at material surfaces or interfaces, has attracted a remarkable amount of attention since its discovery. Recent theoretical predictions have unveiled increased critical temperatures, especially at the surfaces of certain compounds and/or structures. The notion of "surface ordering" has been advanced to elucidate this phenomenon. Employing the framework of self-consistent Bogoliubov-de Gennes equations and a model incorporating correlated disorder, our study demonstrates the persistence of the surface ordering effect in the presence of weak to moderate bulk disorder. Intriguingly, our findings indicate that under moderate disorder conditions the surface critical temperature can be further increased, depending on the intensity and correlation of the disorder.
Interaction between a robot and Bunimovich stadium billiards J. V. A. Vasconcelos, L. H. Miranda-Filho, A. J. F. de Souza, A. R. de C. Romaguera, A. L. R. Barbosa Scientific Reports, 2022 The robot–environment–task triad provides many opportunities to revisit physical problems with fresh eyes. Hence, we develop a simple experiment to observe chaos in classical billiards with a macroscopic 3.38-m long setup. Using a digital video camera, one records the dynamic time evolution of the interaction between a robot and Bunimovich stadium billiards with specular reflection. From the experimental time series, we calculate the Lyapunov exponent $$\\lambda$$ λ as a function of a geometric parameter. The results are in concordance with theoretical predictions. In addition, we determine the Poincaré surface of section from the experimental data and check its sensitivity to the initial conditions as a function of time.
Lyapunov exponent in the Vicsek model L. H. Miranda-Filho, T. A. Sobral, A. J. F. de Souza, Y. Elskens, Antonio R. de C. Romaguera Physical Review E, 2022 The well-known Vicsek model describes the dynamics of a flock of self-propelled particles (SPPs). Surprisingly, there is no direct measure of the chaotic behavior of such systems. Here we discuss the dynamical phase transition present in Vicsek systems in light of the largest Lyapunov exponent (LLE), which is numerically computed by following the dynamical evolution in tangent space for up to two million SPPs. As discontinuities in the neighbor weighting factor hinder the computations, we propose a smooth form of the Vicsek model. We find a chaotic regime for the collective behavior of the SPPs based on the LLE. The dependence of LLE with the applied noise, used as a control parameter, changes sensibly in the vicinity of the well-known transition points of the Vicsek model.
The spike state in type-I mesoscopic superconductor Isaias G. de Oliveira, Leonardo R. Cadorim, Antonio R. de C. Romaguera, Edson Sardella, Rodolpho R. Gomes, et al. Physics Letters Section A General Atomic and Solid State Physics, 2021
Vortex pattern in a nanoscopic cylinder Antonio R. de C. Romaguera, Mauro M. Doria, François M. Peeters Physica C Superconductivity and Its Applications, 2007
