Disordered packings of soft grains are fragile mechanical systems that lose rigidity upon lowering the external pressure toward zero. At zero pressure, we find that any infinitesimal strain impulse propagates initially as ...

We revisit the question of stability of holographic superfluids with finite super-fluid velocity. Our method is based on applying the Landau criterion to the Quasinormal Mode (QNM) spectrum. In particular we study the QNMs ...