It is known that there are thermodynamic states for which the Gaussian-core (GC) fluid displays anomalous properties such as expansion upon isobaric cooling (density anomaly) and increased single-particle mobility upon isothermal compression (self-diffusivity anomaly). We investigate how temperature and density affect its short-range translational structural order, as characterized by the two-body excess entropy. We find that there is a wide range of conditions for which the short-range translational order of the GC fluid decreases upon isothermal compression (structural order anomaly). The origin of the structural anomaly is qualitatively similar to that of other anomalous fluids and is connected to how compression affects static correlations at different length scales. We find that the self-diffusivity of the GC fluid obeys a scaling relationship with the two-body excess entropy that is very similar to the one observed for a variety of simple liquids. One consequence of this relationship is that the state points for which structural, self-diffusivity, and density anomalies of the Gaussian-core fluid occur appear as cascading regions on the temperature-density plane, a phenomenon observed earlier for models of waterlike fluids. There are, however, key differences between the anomalies of GC and waterlike fluids, and we discuss how those can be qualitatively understood by considering the respective interparticle potentials of these models. Finally, we note that the self-diffusivity of the Gaussian-core fluid obeys different scaling laws depending on whether the two-body or total excess entropy is considered. This finding, which deserves more comprehensive future study, appears to underscore the significance of higher-body correlations for the behavior of fluids with bounded interactions.
Giant number fluctuations (GNF) are an anomaly universally observed in active fluids with polar or nematic order. In this paper, we show that GNF arise in the fluid phase of active Brownian particles (ABP), where the polar order is absent. GNF in ABP extends over a large but finite length which characterizes the growing velocity correlations. To suppress unwanted phase separation and allow ones to explore the disordered fluid phase at large activities, we impart the inertia, or the mass, to the ABP. A linearized hydrodynamic theory captures our findings, but only qualitatively. We find numeric…
Anomalous statistics in the Langevin equation with fluctuating diffusivity: from Brownian yet non-Gaussian diffusion to anomalous diffusion and ergodicity breaking
Tokyo University of Science（东京科学大学）；Pohang University of Science and Technology（浦项科技大学）；Asia Pacific Centre for Theoretical Physics（亚太理论物理中心）；University of Potsdam（波茨坦大学）；Wakayama University（和歌山大学）；Nagoya University（名古屋大学）；Keio University（庆应义塾大学）
Anomalous short- and long-time self-diffusion of non-overlapping fractal particles on a percolation cluster with spreading dimension $1.67(2)$ is studied by dynamic Monte Carlo simulations. As reported in Phys. Rev. Lett. 115, 097801 (2015), the disordered phase formed by these particles is that of an unconfined, homogeneous and monodisperse fluid in fractal space. During particle diffusion in thermodynamic equilibrium, the mean squared chemical displacement increases as a nonlinear power of time, with an exponent of $0.96(1)$ at short times and $0.63(1)$ at long times. At finite packing fract…
We investigate the swim pressure exerted by non-chiral and chiral active particles on convex or concave circular boundaries. Active particles are modeled as non-interacting and non-aligning self-propelled Brownian particles. The convex and concave circular boundaries are used as models representing a fixed inclusion immersed in an active bath and a cavity (or container) enclosing the active particles, respectively. We first present a detailed analysis of the role of convex versus concave boundary curvature and of the chirality of active particles on their spatial distribution, chirality-induce…
We present our analysis on micro-rheology of a bench-scale pulsed fluidized bed, which represents a weakly confined system. Non-linear gas-particle and particle-particle interactions resulting from pulsed flow are associated with harmonic and sub-harmonic modes. While periodic structured bubble patterns are observed at the meso-scale, particle-scale measurements reveal anomolous diffusion in the driven granular medium. We use single-particle tracks to analyze ergodicity and ageing properties at two pulsing frequencies having remarkably different meso-scale features. The scaling of ensemble-ave…
The slip of a fluid layer in contact with a solid confining surface is investigated for different temperatures and densities using molecular dynamic simulations. We show that for an anomalous water-like fluid the slip goes as follows: for low levels of shear, the defect slip appears and is related with the particle exchange between the fluid layers; at high levels of shear, the global slip occurs and is related to the homogeneous distribution of the fluid in the confining surfaces. The oscillations in the transition velocity from the defect to the global slip is shown to be associated with cha…
Activity and Competing Length Scales in an Anomalous Core-Softened Fluid
Programa de Pós-Graduação em Física, Instituto de Física e Matemática, Universidade Federal de Pelotas（佩洛塔斯联邦大学物理与数学研究所）；Departamento de Física, Centro de Ciências Exatas e Naturais, Universidade Federal de Santa Maria（圣玛丽亚联邦大学自然科学与中心物理系）；Programa de Pós-Graduação em Modelagem Matemática, Instituto de Física e Matemática, Universidade Federal de Pelotas（佩洛塔斯联邦大学物理与数学研究所数学建模研究生项目）；Centro de Ciências, Tecnologias e Saúde, Campus Araranguá, Universidade Federal de Santa Catarina（圣卡塔琳娜联邦大学阿拉兰瓜校区科学技术与健康中心）；Fachbereich Physik, Universität Konstanz（康斯坦茨大学物理学系）；Departamento de Física, Instituto de Física e Matemática, Universidade Federal de Pelotas（佩洛塔斯联邦大学物理与数学研究所物理系）
Nanoconfinement can drastically change the behavior of liquids, puzzling us with counterintuitive properties. Moreover, it is relevant in applications, including decontamination and crystallization control. It still lacks a systematic analysis for fluids with different bulk properties. Here we fill this gap. We compare, by molecular dynamics simulations, three different liquids in a graphene slit pore: (A) A simple fluid, such as argon, described by a Lennard-Jones potential; (B) An anomalous fluid, such as a liquid metal, modeled with an isotropic core-softened potential; (C) Water, the proto…
2D competitive systems shows a large variety of solid and aggregate patterns, re-entrant fluid phase, a continuous melting as predicted by the KTHNY theory and, in some cases, waterlike anomalies. In this paper, we employ Langevin Dynamics simulations of a ramp-like core-softened fluid that have two characteristic length scales and all the features mentioned above. Analyzing the fluid phase of this system, Bordin and Barbosa [Phys. Rev. E 97, 022604 (2018)] reported the existence of two waterlike anomalous region. Now, we revisit this problem focusing in the low temperature regime and a larger…
Undulation Amplitude of a Fluid Membrane in a Near-Critical Binary Fluid Mixture Calculated beyond the Gaussian Model Supposing Weak Preferential Attraction
The dynamics of self-locomotion of active particles in aligned or liquid crystalline fluids strongly deviates from that in simple isotropic media. We explore the long-time dynamics of a swimmer moving in a three-dimensional smectic liquid crystal and find that the mean-square displacement (MSD) transverse to the director exhibits a distinct logarithmic tail at long times. The scaling is distinctly different from that in an isotropic or nematic fluid and hints at the subtle but important role of the director fluctuation spectrum in governing the long-time motility of active particles. Our findi…
Dynamic heterogeneities and non-Gaussian behavior in two-dimensional randomly confined colloidal fluids
超顺磁性胶体颗粒的二元混合物被限制在玻璃板之间，使得大颗粒变得固定，并为仍然移动的小颗粒提供二维无序基质，其形成流体。通过改变流体和基质面积分数，并通过外部磁场调节超顺磁性颗粒之间的相互作用，探索了状态图的不同区域。移动粒子在小的基质面积分数下表现出离域动力学，在高的基质面积分数下表现出局域运动，并且局域化转变被软相互作用圆化[T. O. E. Skinner等人，Phys.Rev.Lett. { \bf 111}，128301（2013）]。扩展以前的工作，我们发现的动力学示踪剂是强烈的异质性，并表明，分子动力学模拟的理想气体局限在一个固定的矩阵表现出类似的行为。模拟显示了这些软相互作用如何使动力学比无序洛伦兹气体更不均匀，并导致强烈的非高斯波动。
