Activity induced delocalization and freezing in self-propelled systems

Caprini, Lorenzo; Marconi, Umberto Marini Bettolo; Puglisi, Andrea

doi:10.1038/s41598-018-36824-z

Cited by 59 publications

(66 citation statements)

References 73 publications

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“…Also, an increase of ρ 0 ∝ 1/x makes U (x) larger and leads to a decrease of v 2 . Both observations qualitatively agree with the results relative to two-dimensional (2D) interacting particles in nonharmonic potentials where a similar trend was reported [72]. Moreover, the variance of the position linearly grows with τ , as shown in Fig.…”

Section: Formation Of Velocity Domains: Spatial Velocity Correlasupporting

confidence: 91%

“…We remark that, in the model employed in this paper, the self-propulsion acts independently on each particle, at variance with Vicsektype models [67][68][69][70] or more complex dynamics where explicit couplings between velocities and self-propulsions are postulated [44,45]. A convenient method to study the AOUP is achieved by switching from (x i , f a i ) variables [63,71,72] to position x i and velocity v i =ẋ i variables. In one dimension, the equation of motion (1) can be recast as…”

Section: Modelmentioning

confidence: 99%

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Time-dependent properties of interacting active matter: Dynamical behavior of one-dimensional systems of self-propelled particles

Caprini

Marconi

2020

Phys. Rev. Research

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We study an interacting high-density one-dimensional system of self-propelled particles described by the active Ornstein-Uhlenbeck particle model where, even in the absence of alignment interactions, velocity and energy domains spontaneously form in analogy with those already observed in two dimensions. Such domains are regions where the individual velocities are spatially correlated as a result of the interplay between self-propulsion and interactions. Their typical size is controlled by a characteristic correlation length. In this work, we focus on a lesser-known aspect of the model, namely, its dynamical behavior. To this purpose, we investigate theoretically and numerically the time-dependent velocity autocorrelation and spatiotemporal velocity correlation functions. The study of these correlations provides a measure of the average lifetime and, thus, the stability in time of the velocity domains.

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Section: Formation Of Velocity Domains: Spatial Velocity Correlasupporting

confidence: 91%

Section: Modelmentioning

confidence: 99%

Time-dependent properties of interacting active matter: Dynamical behavior of one-dimensional systems of self-propelled particles

Caprini

Marconi

2020

Phys. Rev. Research

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“…To shed light on the above phenomenology we perform an exact mapping of the original ABP dynamics, Eqs. (1), in the same spirit of the Ornstein-Uhlenbeck (AOUP) model [49][50][51]. In particular, we obtain an equation of motion for the microswimmer velocity, v i =ẋ i , which is an unprecedented result for ABP.…”

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confidence: 85%

Spontaneous Velocity Alignment in Motility-Induced Phase Separation

2020

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We study a system of purely repulsive spherical self-propelled particles in the minimal set-up inducing Motility-Induced Phase Separation (MIPS). We show that, even if explicit alignment interactions are absent, a growing order in the velocities of the clustered particles accompanies MIPS. Particles arrange into aligned or vortex-like domains. Their sizes increase as the persistence of the self-propulsion grows, an effect that is quantified studying the spatial correlation function of the velocities. We explain the velocity-alignment by unveiling a hidden alignment interaction of the Vicsek-like form, induced by the interplay between steric interactions and self-propulsion. As a consequence, we argue that the MIPS transition cannot be fully understood in terms of a scalar field, the density, since the collective orientation of the velocities should be included in effective coarse-grained descriptions. Fishes [1], birds [2] or insects [3] often display fashinating collective behaviors such as flocking [2, 4] and swarming [5], where all units of a group move coherently producing intriguing dynamical patterns. A different mode of organization of living organisms is clustering, for instance in bacterial colonies [6], such as E. Coli [7], Myxococcus xanthus [8] or Thiovulum majus [9], relevant for histological cultures in several areas of medical and pharmaceutical sciences. Out of the biological realm, the occurrence of stable clusters [10-13], stable chains [14] or vortices [15] in activated colloidal particles, e.g. autophoretic colloids or Janus disks [16,17], offers an interesting challenge for the design of new materials.Even if the microscopic details differ case by case, a few classes of minimal models with common coarsegrained features have been introduced in statistical physics. Units in these models are called "active" or "selfpropelled" particles [18-20] to differentiate them from Brownian colloids which passively obey the forces of the surrounding environment. Propelling forces may be either of mechanical origin (flagella or body deformation), or of thermodynamic nature (diffusiophoresis and selfelectrophoresis) [21,22]. In some simple and effective examples, self-propulsion is modeled as a constant force with stochastic orientation, as in the case of Active Brownian Particles (ABP) [23,24]. Thermal fluctuations play only a marginal role and stochasticity is usually due to the unsteady nature of the swimming force itself.It is well-known that dumbells, rods and, in general, elongated microswimmers display a marked orientational order even in the absence of alignment interactions [25][26][27][28]. Instead, in the literature, it is believed that explicit aligning velocity-interactions are crucial to observe velocity alignment between spherical self-propelled units [29]. This kind of interaction, such as that in the seminal Vicsek model [30], consists in a short-range force that aligns the velocity of a target particle to the average of the neighboring ones. Vicsek interactions lead to long-range polar order...

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“…We remark that the AOUP model constitutes a simplification of the Active Brownian Particle model (ABP) [52][53][54][55] which is known to explain the well-known phenomenology of spherical self-propelled particles [46,[56][57][58][59]. The connection between AOUP and ABP has been shown by several authors [60,61]. In Eq.…”

Section: A Free Polymer With An Active Headmentioning

confidence: 99%

How a local active force modifies the structural properties of polymers

2020

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We study the dynamics of a polymer, described as a variant of a Rouse chain, driven by an active terminal monomer (head). The local active force induces a transition from a globule-like to an elongated state, as revealed by the study of the end-to-end distance, whose variance is analytically predicted under suitable approximations. The change in the relaxation times of the Rouse-modes produced by the local self-propulsion is consistent with the transition from globule to elongated conformations. Moreover also the bond-bond spatial correlation for the chain head results to be affected and a gradient of over-stretched bonds along the chain is observed. We compare our numerical results both with the phenomenological stiff-polymer theory and several analytical predictions in the Rouse-chain approximation. arXiv:1911.06688v2 [cond-mat.stat-mech]

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Activity induced delocalization and freezing in self-propelled systems

Cited by 59 publications

References 73 publications

Time-dependent properties of interacting active matter: Dynamical behavior of one-dimensional systems of self-propelled particles

Time-dependent properties of interacting active matter: Dynamical behavior of one-dimensional systems of self-propelled particles

Spontaneous Velocity Alignment in Motility-Induced Phase Separation

How a local active force modifies the structural properties of polymers

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