# Resources

## Publications

• ### Small Obstacle in a Large Polar Flock

Author(s): Joan Codina, Benoît Mahault, Hugues Chaté, Jure Dobnikar, Ignacio Pagonabarraga, and Xia-qing Shi We show that arbitrarily large polar flocks are susceptible to the presence of a single small obstacle. In a wide region of parameter space, the obstacle triggers counterpropagating dense bands leading to reversals of the flow. In very large systems, these bands interact, yielding a never-ending cha… [Phys. Rev. Lett. 128, 218001] Published...
• ### Continuum Field Theory for the Deformations of Planar Kirigami

Author(s): Yue Zheng, Imtiar Niloy, Paolo Celli, Ian Tobasco, and Paul Plucinsky Mechanical metamaterials exhibit exotic properties that emerge from the interactions of many nearly rigid building blocks. Determining these properties theoretically has remained an open challenge outside a few select examples. Here, for a large class of periodic and planar kirigami, we provide a co… [Phys. Rev. Lett. 128, 208003] Published Fri May 20, 2022
• ### Susceptibility of Polar Flocks to Spatial Anisotropy

Author(s): Alexandre Solon, Hugues Chaté, John Toner, and Julien Tailleur We study the effect of spatial anisotropy on polar flocks by investigating active $q$-state clock models in two dimensions. In contrast to the equilibrium case, we find that any amount of anisotropy is asymptotically relevant, drastically altering the phenomenology from that of the rotationally inva… [Phys. Rev. Lett. 128, 208004] Published Fri May 20, 2022
• ### Thermal Fluctuations of Singular Bar-Joint Mechanisms

Author(s): Manu Mannattil, J. M. Schwarz, and Christian D. Santangelo A bar-joint mechanism is a deformable assembly of freely rotating joints connected by stiff bars. Here we develop a formalism to study the equilibration of common bar-joint mechanisms with a thermal bath. When the constraints in a mechanism cease to be linearly independent, singularities can appear … [Phys. Rev. Lett. 128, 208005] Published Fri May 20, 2022
• ### Collective Drifts in Vibrated Granular Packings: The Interplay of Friction and Structure

Author(s): A. Plati and A. Puglisi We simulate vertically shaken dense granular packings with horizontal periodic boundary conditions. A coordinated translating motion of the whole medium emerges when the horizontal symmetry is broken by disorder or defects in the packing and the shaking is weak enough to conserve the structure. We a… [Phys. Rev. Lett. 128, 208001] Published Tue May 17, 2022
• ### Softening and Residual Loss Modulus of Jammed Grains under Oscillatory Shear in an Absorbing State

Author(s): Michio Otsuki and Hisao Hayakawa From a theoretical study of the mechanical response of jammed materials comprising frictionless and overdamped particles under oscillatory shear, we find that the material becomes soft, and the loss modulus remains nonzero even in an absorbing state where any irreversible plastic deformation does no… [Phys. Rev. Lett. 128, 208002] Published Tue May 17, 2022
• ### Elastohydrodynamic Synchronization of Rotating Bacterial Flagella

Author(s): Maria Tătulea-Codrean and Eric Lauga To rotate continuously without jamming, the flagellar filaments of bacteria need to be locked in phase. While several models have been proposed for eukaryotic flagella, the synchronization of bacterial flagella is less well understood. Starting from a reduced model of flexible and hydrodynamically c… [Phys. Rev. Lett. 128, 208101] Published Tue May 17, 2022