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We study the velocity autocorrelations in an experimental configuration of confined two-dimensional active rotors (disks). We report persistent small scale oscillations in both rotational and translational velocity autocorrelations, with their characteristic frequency increasing as rotational activity increases. While these small oscillations are qualitatively similar in all experiments, we found that, at strong particle rotational activity, the large scale particle spin fluctuations tend to vanish, with the small oscillations around zero persisting in this case, and spins remain predominantly and strongly anti-correlated at longer times. For weaker rotational activity, however, spin fluctuations become increasingly larger, and angular velocities remain de-correlated at longer times. We discuss in detail how the autocorrelation oscillations are related to the rotational activity and why this feature is, generically, a signal of the emergence of chirality in the dynamics of a particulate system. [ABSTRACT FROM AUTHOR]

Diffusion is a fundamental aspect of transport processes in biological systems, and thus, in the development of life itself. And yet, the diffusive dynamics of active fluids with directed rotation, known as chiral fluids, has not been analyzed in detail so far. Here, we describe the diffusive regimes of a two-dimensional chiral fluid, composed in this case of a set of identical disk-shaped rotors. We found strong experimental evidence of odd diffusion. This odd diffusion emerges in the form of a two-dimensional tensor with an antisymmetric part. In particular, we show that chiral diffusion is complex, featuring transitions between super, quasi-normal, and sub diffusion, and very slowly aging. Moreover, we show that the diffusion tensor elements, including off-diagonal elements; i.e., odd diffusion coefficient, change sign according to flow vorticity. Therefore, the chiral fluid has a self regulated diffusion, controlled by its vorticity. Chiral fluids, whose constituent particles are chiral have attracted recent attention, particularly from diffusion behaviour. The authors provide experimental evidence of a rich and complex diffusive behaviour by studying a system composed of a set of identical disks-shaped particles. [ABSTRACT FROM AUTHOR]

The vapor-liquid coexistence curve at equilibrium of parabolic-well (PW) fluids is computed by means of Monte Carlo simulations, for a selection of well-widths. The outcome is compared with results for corresponding curves of triangle-well (TW) and square-well (SW) fluids with the same range. It is found that, for a given width, the shape of the vapor-liquid coexistence curve in the case of the parabolic-well fluid is rather similar to the one of the triangular-well fluid and a little bit different to the one of the square-well fluid. It is also found that such vapor-liquid coexistence curve shifts towards higher temperatures as the width of the parabolic-well potential increases, always falling, for the same range in all cases, between the vapor-liquid coexistence curves corresponding to the other two potentials. In addition, it was observed that the reduced critical temperature matches the theoretical prediction of the Vliegenthart and Lekkerkerker (V-L) criterion only for the smaller well-width, the accuracy of such criterion decreasing substantially as the range increases. • Coexistence curves and critical points for parabolic-well fluid with widths λ = 5 / 4 , 3/2, and 7/4. • Parabolic-well fluid is compared with square-well and triangular-well fluids. • Gibbs Ensemble Monte Carlo simulation method was employed. • Theoretical prediction of the Vliegenthart and Lekkerkerker (V-L) criterion was employed. [ABSTRACT FROM AUTHOR]