arXiv subjects

Purnendu Pathak

Publications and source records attributed to Purnendu Pathak.

3 recordsLinked to original sources

arXiv2026

Aggressive Phase Separation in Dense Mixtures of Passive and Active Particles

Using Vicsek-like self-propulsion rule, we study kinetics of liquid-liquid phase separation in mixtures of passive and active particles. For evolutions following temperature quenches of homogeneous configurations to the immiscible region of the phase diagram, we identify a remarkably strong dependence of the domain growth exponent on the choice of final state point. The singular dependence is indicative of the possibility of even an exponentially fast growth for suitable choices of system parameters. This striking observation, supported by finite-size scaling and other advanced analyses, is despite the fact that the overall mixture density is quite high that risks congestion with the prospect of slowing down particle transport. From flocking in pure biological systems to robotic swarming, these results are of much practical relevance. Theoretical pictures suitable for interpreting such high growth rates are discussed. In this regard, we discuss coarsening in the velocity field as well that describes how the density field coarsening follows the latter.

cond-mat.soft↗

arXiv2025

Quicker flocking in aligning active matters for noisier beginning

The constituents in a class of active matter systems change their directions of motion by being influenced by the velocities of the neighbors. Such systems may undergo phase transitions, with respect to ordering in the velocity field, as well as clustering in the density field, when the strength of an externally imposed noise is varied. Via computer simulations, with a well-known model, that faithfully represents these systems, we show that evolutions in both clustering and ordering exhibit certain interesting features that were hitherto unrealized. The transformations occur quicker, following quenches to a fixed final state, below the transition point, for disordered starting states that are farther away from the ``critical" noise strength. This implies earliest arrival of the farthest, at a given destination. Detailed analysis of the results, combined with the outcomes from a similar study of para- to ferromagnetic transitions, show that the variation in critical fluctuations in the initial configurations can lead to such interesting effect. We quantify this via the Ornstein-Zernike theory.

cond-mat.stat-mech↗

arXiv2024

Simulations of Mpemba Effect in WATER, Lennard-Jones and Ising Models: Metastability vs Critical Fluctuations

Via molecular dynamics simulations we study ICE formation in the TIP4P/Ice model that is known to describe structure and dynamics in various phases of WATER accurately. For this purpose well equilibrated configurations from different initial temperatures, Ts, belonging to the fluid phase, are quenched to a fixed subzero temperature. Our results on kinetics, for a wide range of Ts, following such quenches, show quicker crystallization of samples that are hotter at the beginning. This implies the presence of the puzzling Mpemba effect (ME). Via a similar study, we also identify ME in fluid to solid transitions in a Lennard-Jones (LJ) model. In the latter case, the ME appears purely as an outcome of the influence of critical fluctuations on the nonequilibrium growth process, for which we present interesting scaling results. For the TIP4P/Ice case, on the other hand, we show that delay in nucleation, due to metastability, can alone be a driving factor for the exhibition of ME. To substantiate the difference between the two cases, we also present LJ-like scaling results for ME in a magnetic transition. Our simulations indicate that in each of the systems the effect can be observed independent of the cooling rate that may vary when samples from different Ts are brought in contact with a heat reservoir working at a fixed lower temperature.

cond-mat.stat-mech↗