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  • 1Universitat de Barcelona, Departament de Física de la Matèria Condensada, Martí i Franquès 1, 08028 Barcelona, Spain and UBICS (University of Barcelona Institute of Complex Systems), Martí i Franquès 1, 08028 Barcelona, Spain.

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Even stable active nematics can transition to spontaneous flows via nonlinear instability. This discontinuous transition, where resting and flowing states coexist, is predicted for various systems, including contractile rods.

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Area of Science:

  • Soft Matter Physics
  • Nonlinear Dynamics
  • Active Matter

Background:

  • Active nematics typically exhibit spontaneous flows due to linear instability from a uniform state.
  • Understanding transitions in active matter is crucial for predicting complex behaviors like turbulence.

Purpose of the Study:

  • To investigate nonlinear instabilities in active nematics that can lead to spontaneous flows.
  • To explore the coexistence of quiescent and flowing states in active nematic systems.
  • To characterize the shift from continuous to discontinuous transitions with varying parameters.

Main Methods:

  • Weakly nonlinear analysis to study bifurcations.
  • Numerical simulations to trace the bifurcation diagram of striped patterns.
  • Analysis of flow-alignment parameter effects on system stability.

Main Results:

  • A linearly stable uniform state can undergo a nonlinear instability, causing a discontinuous transition to spontaneous flow.
  • The pitchfork bifurcation changes from supercritical (continuous) to subcritical (discontinuous) with altered flow-alignment parameters.
  • Coexistence of quiescent and flowing states is possible in these systems.

Conclusions:

  • Discontinuous spontaneous flow transitions are predicted for a broad range of active nematic parameters.
  • These findings are relevant to active nematic turbulence and applicable to systems like contractile rods.
  • The predictions offer testable hypotheses for experimental studies using cell layers or cytoskeletal suspensions.