Dear colleagues, We would like to invite you to the following SPASS seminar, jointly organized by UniPi, SNS, UniFi (abstract below): *Effective Lagrangian regularity and the uniqueness threshold for random Hölder velocity fields* by *Keefer Rowan* (EPFL Lausanne) The seminar will take place on *Tuesday, 10.11.2026* at *14:00 CET* in Aula Seminari, Dipartimento di Matematica, UNIPI and streamed online at this link <https://meet.google.com/wfg-cyqy-ewv>. Abstract: We discuss the behavior of the ordinary differential equations, flow maps, and continuity equations associated to autonomous random velocity fields that admit a natural multiscale finite range decomposition. The velocity fields we consider are only Hölder regular in space, and thus the associated ODE and continuity equation are not a priori well-posed. However, above the critical threshold of 1/2, due to multiscale stochastic cancellations, we show well-posedness is almost surely restored away from the zero level set of the velocity field. This threshold marks a genuine transition, as demonstrated by examples lying below the threshold that exhibit robust ill-posedness. Best regards Mario Maurelli https://sites.google.com/unipi.it/spass <https://www.google.com/url?q=https://sites.google.com/unipi.it/spass&source=gmail-imap&ust=1665669490000000&usg=AOvVaw07o0tKOUGmZjDDF2Ta7pQY>