1,720,991 research outputs found
Narrow-escape time and sorting of active particles in circular domains
No full textIt is now well established that microswimmers can be sorted or segregated fabricating suitable microfluidic devices or using external fields. A natural question is how these techniques can be employed for dividing swimmers of different motility. In this paper, using numerical simulations in the dilute limit, we investigate how motility parameters (time of persistence and velocity) impact the narrow-escape time of active particles from circular domains. We show that the escape time undergoes a crossover between two asymptotic regimes. The control parameters of the crossover is the ratio between the persistence length of the active motion and the typical length scale of the circular domain. We explore the possibility of taking advantage of this finding for sorting active particles by motility parameters
The most probable path of Active Ornstein-Uhlenbeck particles
Full text linkUsing the path integral representation of the non-equilibrium dynamics, we
compute the most probable path between arbitrary starting and final points,
followed by an active particle driven by persistent noise. We focus our
attention on the case of active particles immersed in harmonic potentials,
where the trajectory can be computed analytically. Once we consider the
extended Markovian dynamics where the self-propulsive drive evolves according
to an Ornstein-Uhlenbeck process, we can compute the trajectory analytically
with arbitrary conditions on position and self-propulsion velocity. We test the
analytical predictions against numerical simulations and we compare the
analytical results with those obtained within approximated equilibrium-like
dynamics
Shape and displacement fluctuations in soft vesicles filled by active particles
No full textActive granular particles can harness unbiased mechanical vibrations in the environment to generate directed motion. We provide a theoretical framework that connects the geometrical shape of a three dimensional object to its self-propulsion characteristics over a vertically vibrated plate. We find that a maximally efficient propulsion is achieved for structures having tilted flexible legs forming a characteristic angle with the vertical. Our predictions are verified by experimental observations on a class of 3D printed structures with smoothly varying geometrical features
Relation between Heterogeneous Frozen Regions in Supercooled Liquids and Non-Debye Spectrum in the Corresponding Glasses
No full textRecent numerical studies on glassy systems provide evidence for a population of non-Goldstone modes (NGMs) in the low-frequency spectrum of the vibrational density of states D(ω). Similarly to Goldstone modes (GMs), i.e., phonons in solids, NGMs are soft low-energy excitations. However, differently from GMs, NGMs are localized excitations. Here we first show that the parental temperature T* modifies the GM/NGM ratio in D(ω). In particular, the phonon attenuation is reflected in a parental temperature dependency of the exponent s(T*) in the low-frequency power law D(ω)∼ωs(T*), with 2≤s(T*)≤4. Second, by comparing s(T*) with s(p), i.e., the same quantity obtained by pinning a p particle fraction, we suggest that s(T*) reflects the presence of dynamical heterogeneous regions of size ξ3∝p. Finally, we provide an estimate of ξ as a function of T*, finding a mild power law divergence, ξ∼(T*−Td)−α/3, with Td the dynamical crossover temperature and α falling in the range α∈[0.8,1.0]
Critical active dynamics is captured by a colored-noise driven field theory
No full textActive particles can display a critical behaviour indistinguishable from an equilibrium one. The authors numerically study an active particles system close to the motility-induced critical point, and demonstrate that a nonequilibrium coloured noise field captures the coarse-grained behaviour of the system.Active matter may sometimes behave almost indistinguishably from equilibrium matter. This is particularly evident for some particle-based models and active field-theories close to a critical point which falls in the Ising universality class. Here we show however that, even when critical, active particles strongly violate the equilibrium fluctuation-dissipation in the high-wave-vector and high-frequency regime. Conversely, at larger spatiotemporal scales the theorem is progressively restored and the critical dynamics is in effective equilibrium. We develop a field-theoretical description of this scenario employing a space-time correlated noise field finding that the theory qualitatively captures the numerical results already at the Gaussian level. Moreover a dynamic renormalization group analysis shows that the correlated noise does not change the equilibrium critical exponents. Our results demonstrate that a correlated noise field is a fundamental ingredient to describe critical active matter at the coarse-grained level
Dynamical arrest with zero complexity: The unusual behavior of the spherical Blume-Emery-Griffiths disordered model
No full textThe short- and long-time dynamics of model systems undergoing a glass transition with apparent inversion of Kauzmann and dynamical arrest glass transition lines is investigated. These models belong to the class of the spherical mean-field approximation of a spin-1 model with p-body quenched disordered interaction, with p>2, termed spherical Blume-Emery-Griffiths models. Depending on temperature and chemical potential the system is found in a paramagnetic or in a glassy phase and the transition between these phases can be of a different nature. In specific regions of the phase diagram coexistence of low-density and high-density paramagnets can occur, as well as the coexistence of spin-glass and paramagnetic phases. The exact static solution for the glassy phase is known to be obtained by the one-step replica symmetry breaking ansatz. Different scenarios arise for both the dynamic and the thermodynamic transitions. These include: (i) the usual random first-order transition (Kauzmann-like) for mean-field glasses preceded by a dynamic transition, (ii) a thermodynamic first-order transition with phase coexistence and latent heat, and (iii) a regime of apparent inversion of static transition line and dynamic transition lines, the latter defined as a nonzero complexity line. The latter inversion, though, turns out to be preceded by a dynamical arrest line at higher temperature. Crossover between different regimes is analyzed by solving mode-coupling-theory equations near the boundaries of paramagnetic solutions and the relationship with the underlying statics is discussed
Probing the non-Debye low-frequency excitations in glasses through random pinning
No full textWe investigate the properties of the low-frequency spectrum in the density of states D(ω) of a 3D model glass former. To magnify the non-Debye sector of the spectrum, we introduce a random pinning field that freezes a finite particle fraction to break the translational invariance and shifts all of the vibrational frequencies of the extended modes toward higher frequencies. We show that non-Debye soft localized modes progressively emerge as the fraction p of pinned particles increases. Moreover, the low-frequency tail of D(ω) goes to zero as a power law ωδ(p), with 2 ≤ δ(p) ≤ 4 and δ = 4 above a threshold fraction pth
Noise-Induced phase separation and time reversal symmetry breaking in active field theories driven by persistent noise
No full textWithin the Landau-Ginzburg picture of phase transitions, scalar field theories develop phase separation because of a spontaneous symmetry-breaking mechanism. This picture works in thermodynamics but also in the dynamics of phase separation. Here we show that scalar nonequilibrium field theories undergo phase separation just because of nonequilibrium fluctuations driven by a persistent noise. The mechanism is similar to what happens in motility-induced phase separation where persistent motion introduces an effective attractive force. We observe that noise-induced phase separation occurs in a region of the phase diagram where disordered field configurations would otherwise be stable at equilibrium. Measuring the local entropy production rate to quantify the time-reversal symmetry breaking, we find that such breaking is concentrated on the boundary between the two phases
Entropy Production of Run-and-Tumble Particles
Full text linkWe analyze the entropy production in run-and-tumble models. After presenting the general formalism in the framework of the Fokker–Planck equations in one space dimension, we derive some known exact results in simple physical situations (free run-and-tumble particles and harmonic confinement). We then extend the calculation to the case of anisotropic motion (different speeds and tumbling rates for right- and left-oriented particles), obtaining exact expressions of the entropy production rate. We conclude by discussing the general case of heterogeneous run-and-tumble motion described by space-dependent parameters and extending the analysis to the case of d-dimensional motions
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