# gst: rupture dynamics of dense granular films; from liquidlike bursting to solidlike fracturing.

<< ️(AA) investigate the bursting dynamics of dense granular films punctured at imposed controlled liquid pressure. Using high-speed imaging, (They) reveal a two-stage opening process.️ At early times, the hole expands in a liquidlike manner with a nearly circular shape and a constant velocity, though significantly lower than the Taylor-Culick speed. This velocity is modeled by a balance between surface tension and effective surface viscosity, which depends on particle size and liquid depression. >>

<< ️(AA) show that as liquid pressure decreases, the initial opening slows down progressively until it ultimately reaches a jamming state. As the opening progresses, the film undergoes a transition to a solidlike regime, where faceting occurs due to fracture propagation within the granular skeleton. >>

<< ️(AA) show that the characteristic fracture size follows a 𝑡3/4 scaling, consistent with a balance between surface energy release and viscous dissipation induced by liquid redistribution within the 2D granular network. ️These findings advance (Their) understanding of the mechanics of granular films and their transition between fluidlike and solidlike behaviors. >>

Paul Gauthier, Nabil Retailleau, Yacine Khidas, et al. Rupture dynamics of dense granular films: From liquidlike bursting to solidlike fracturing. Phys. Rev. Fluids 11, 094301. Sep 8, 2026.

https://journals.aps.org/prfluids/abstract/10.1103/c9bz-d2yg

Also: particle, fracture, crack, drop, droplet, droploid, bubble, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, particles, fracture, crack, drops, droplets, droploids, bubbles, transitions, fluid-particle interactions, granular fluids, granular films, granular network, bursting dynamics, surface tension, surface viscosity, viscous dissipations, jamming states, surface energy.

# gst: odd slip at chiral active surfaces.

<< ️Odd slip at solid-liquid interfaces, characterized by a velocity component perpendicular to the applied shear stress, introduces a novel class of odd transport phenomena with transverse momentum transfer at boundaries, distinct from odd viscosity, odd elasticity, or odd diffusivity. This effect arises on chiral active surfaces with persistent energy input and defined handedness, such as carpets of rotating biological or synthetic cilia with flexible anchoring. Although odd slip itself is dissipationless, its maintenance comes at an energetic cost, which we estimate from the microscopic model. With respect to its orientation dependence, odd slip can be classified as pseudo-scalar or pseudo-vectorial. >>

<< ️(AA) use a perturbative expansion to determine the resistance tensors of problems with different levels of broken symmetries. They reveal how the surface chirality and body asymmetry together violate the Onsager symmetry, but uphold the Onsager-Casimir reciprocity. Strikingly, suspensions of particles with odd slip embedded in a conventional Newtonian bulk fluid exhibit odd viscosity, providing a new minimal mechanism for its emergence beyond current microscopic models. >>

Yuto Hosaka, Andrej Vilfan. Odd slip at chiral active surfaces. arXiv: 2609.17005v2 [cond-mat.soft]. Sep 16, 2026. 

https://arxiv.org/abs/2609.17005

Also: particle, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, particles, solid-liquid interfaces, chiral active surfaces, surface chirality, parity-violating phenomena, shear stress, odd viscosity, odd diffusivity, odd elasticity, odd slip, broken symmetries. 

# gst: how turbulent flows grow vorticity at a point.

<< ️(AA) describe how strong vorticity fluctuations appear in three-dimensional incompressible turbulence driven by a large-scale random force. By combining analytical and numerical methods, (They) construct a vorticity instanton: the most probable force history driving the flow to a prescribed large vorticity at a given point and time. >>

<< ️(AA) show how the smooth, large-scale force produces a long vortex filament with a thin, viscous-scale core. (Their) main finding is that the standard mechanism of amplifying a vortex tube through radial compression and axial stretching is only effective up to a threshold value. Producing vorticity above the threshold requires an additional ingredient: vorticity waves propagating along the tube. >>

<< ️The final vorticity is the result of two colliding waves. This mechanism has striking similarities to the one recently suggested by OpenAI for creating infinite vorticity in finite-time Navier--Stokes blow-up. >>

Timo Schorlepp, Vladimir Rosenhaus, Gregory Falkovich. How turbulent flows grow vorticity at a point. arXiv: 2609.13056v1 [physics.flu-dyn]. Sep 11, 2026.

https://arxiv.org/abs/2609.13056

Also: vortex, turbulence, random, waves, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, vortex, turbulence, randomness, waves, vorticity instanton, vortex filaments, colliding waves.

# gst: extreme events in an active fluid medium.

<< ️(AA) observe the emergence of extreme events in an active fluid involving two distinct chemical species that regulate active stress. One species is slow diffusing and the other is fast diffusing, and the growth of the fast-diffusing species is modelled using a nonlinear logistic term. >>

<< ️(AA) demonstrate the presence of extreme events in the temporal evolution of the concentrations, as well as in the spatial profile of the system,in regimes of merging-emerging soliton-like dynamics and spatio-temporal chaos, through analysis of the time-series, bifurcation diagrams, probability distribution functions of the concentration of the two species, return maps and distributions of inter-event intervals. >>

<< ️Interestingly, (They) also find evidence of pronounced bunching of extreme events and super-extreme events in the slow chemical species in the soliton-like regime. (They) go on to systematically explore the dependence of the extreme event occurrences on the Péclet number and the strength of the nonlinear growth term, and find that the probability of extreme events increases after a critical Péclet number, while increasing the nonlinearity suppresses extreme events. >>

<< ️Lastly, in order to gain further insight, (AA) investigate a modified mode-truncated reduced order model comprising of coupled differential equations mimicking this active fluid system. (They) find that this reduced order model also exhibits extreme events whose emergence is correlated with a sudden expansion in attractor size due to a crisis arising from attractor collision. >>

<< ️So these results demonstrate the existence of extreme events in an active fluid system, and are of potential relevance to biological phenomena where active transport plays an important role. >>

Joydeep Das, Abhishek Chaudhuri, Sudeshna Sinha. Extreme Events in an Active Fluid Medium. arXiv: 2609.14334v1 [nlin.PS]. Sep 13, 2026.

https://arxiv.org/abs/2609.14334

Also: chaos, soliton, attractor, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, chaos, solitons, attractors, extreme events, merging-emerging soliton-like dynamics, soliton-like regimes, criticality, active transport.

# gst: permeability of deforming soft particle packs.

<< ️The permeability of the fluid between packs of particles is an important parameter for a range of natural and industrial applications. Here, (AA) start from experiments in which soft spherical particles—“soft balls”—are compressed uniaxially, resulting in particle-particle flattening and an overall decrease in interstitial volume fraction 𝜙 down to very low values. >>

<< ️During deformation, the soft particle packs were scanned in three dimensions using x-ray tomography; (AA) segment these data to isolate the fraction between the particles. (They) then run lattice Boltzmann fluid flow simulations through the domains to determine the permeability. >>

<< ️Additionally, (AA) determine the specific surface area 𝑠 and 𝜙. Together, (They) use these parameters to test and validate a semiempirical extension to a theoretical percolation model, to propose a framework for predicting permeability in deforming soft particle systems. >>

<< ️Once validated, (AA) compare this model to the permeability of the fluid in packs of hard particles and during particle sintering; (They) conclude that this model is applicable to a wide range of initially particulate systems with all the geometric information encoded in 𝑠. >>

Jérémie Vasseur, Fabian B. Wadsworth, Jingwei Zhang, et al. Permeability of deforming soft particle packs. Phys. Rev. E 114, 035424. Sep 18, 2026.

https://journals.aps.org/pre/abstract/10.1103/zpm1-lp4n

Also: particle, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, particles, percolation, permeability, flows in porous media, granular compaction, laminar flows, mechanical deformation, granular materials.

# gst: shear v. stretching as drivers for mixing in 3-D porous media flows.

<< ️Solute mixing in porous media results from the interplay between molecular diffusion and the deformation of fluid parcels, which elongates solute elements and steepens concentration gradients in the pore space. >> 

<< ️In three-dimensional porous media, fluid deformation is asymptotically governed by exponential stretching, arising from the chaotic stretching and folding of fluid elements. However, early-time deformation may be dominated by shear, induced by no-slip boundary conditions at grain surfaces, leading to linear elongation. Yet, the persistence and relative contributions of linear shear and exponential stretching to fluid deformation and solute mixing remain poorly understood. >>

<< ️Here, (AA) address this question using numerical simulations of fluid deformation and mixing in body-centered cubic bead packs, where the rate of chaotic stretching can be varied with the direction of flow, while maintaining the same average shear rate. (They) quantify the mean deformation dynamics of elementary surfaces as a function of their initial orientation with respect to streamlines, and their consequences on mixing through Lagrangian methods. >>

<< ️(AA) show that surface elements with certain initial orientations relative to the streamline direction experience a transient phase of shear-dominated deformation at early times, leading to persistently larger deformation compared to those with initial orientations that yield purely exponential growth. By expressing the deformation components in streamline coordinates, (They) derive approximate analytical expressions linking the different components of fluid deformation to shear, helicity, and chaotic stretching. (They) discuss consequences for the mixing of solute sheets and blobs, highlighting generic behaviors as well as differences between these two representations. >>

Manuel Maeritz, Tanguy Le Borgne, Daniel R. Lester, et al. Shear versus stretching as drivers for mixing in three-dimensional porous media flows. Phys. Rev. Fluids 11, 094501. Sep 17, 2026.

https://journals.aps.org/prfluids/abstract/10.1103/4wyw-nkrb

Also: chaos, transition, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, chaotic advection, fluid deformation, flows in porous media, laminar flows, mixing enhancement, shear flows, chaotic stretching, porous media.

# gst: collective hysteresis and multistability in threshold networks.

<< ️In a mechanistic model of the dawn chorus, Kaye showed that heterogeneous activation thresholds and a shared feedback signal determined by the population's active fraction can produce abrupt collective activation and hysteresis. >>

<< ️(AA) extend this mechanism to a network of interacting agents. Each node has a continuous activation level, and a nonnegative row-stochastic matrix determines how node activities contribute to individual feedback. (They) prove that sufficiently weak feedback yields a unique globally attracting equilibrium. For all feedback strengths, the homogeneous dynamics exactly reproduce Kaye's scalar equation; consequently, network topology does not alter the folds or cusp of the homogeneous branch, and no heterogeneous mode becomes unstable before the homogeneous mode. >>

<< ️For equitable partitions, the network admits an exact quotient system in which nodes within a block receive the same aggregate input from every block. When blocks are uncoupled, the quotient reduces to independent copies of Kaye's scalar equation. (AA) show that every assignment of stable scalar equilibria to blocks persists under sufficiently weak interblock coupling, producing a combinatorial family of stable quotient equilibria that lift to stable full-network equilibria and remain under small perturbations that break exact equitability. >>

<< ️For two symmetrically coupled blocks, branches with unequal block activities terminate at a pair of symmetry-related cusp bifurcations. Near the onset of bistability, (AA) derive scaling laws for the interblock coupling at which these bifurcations occur, the activity difference between the blocks at bifurcation, and the corresponding shift of the external stimulus from the scalar cusp. Numerical continuation confirms the scaling laws for gamma, logistic, and normal threshold distributions. >>

Moses Boudourides. Collective Hysteresis and Multistability in Threshold Networks. arXiv: 2609.10580v1 [cs.SI]. Sep 5, 2026.

https://arxiv.org/abs/2609.10580

Also: network, instability, random, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, hysteresis, collective hysteresis, networks, threshold networks, stability, bistability, multistability, randomness, small perturbations, bifurcations, cusp bifurcations, Kaye's dawn chorus, stochasticity, heterogeneous activation thresholds, weak feedbacks, shared feedback signals, attracting equilibrium.