Digest — 2026-09-25

Curated America/New_York (ET). Prefer arXiv / open sources. Verified via arXiv Atom API and cond-mat.soft / active-matter keyword listings.
Focus: roughly since the 2026-09-24 digest. Prior items are not re-listed as “new today.”

At a glance

Diagram: original illustration of this digest’s key idea (not from the papers).

Highlights

1. Orientational Ordering of Janus Particle Arrays as Classical Compass Spin Systems

• Authors: Zhijie Fan, Myeonggon Park, Marija Vucelja, Gia-Wei Chern
• Submitted: 2026-09-24
• Link: https://arxiv.org/abs/2609.30025 
• Why newsworthy: Classical 120° compass and Kern–Frenkel models for triangular metallodielectric Janus arrays. Monte Carlo shows sixfold order via thermal order-by-disorder, with an intermediate quasi-long-range regime consistent with two BKT transitions — matching the experimental motif of sixfold order plus vortices/antivortices.
• Beginner hook: Two-faced beads on a grid act like compass needles — heat can pick a preferred pattern from many equal-looking options.
• Caveat: Theory / Monte Carlo (experiment-motivated).

2. Speed up of passive tracers in mixtures with active chemical reactions

• Authors: Filipe C. Thewes, Chengjie Luo, David Zwicker
• Submitted: 2026-09-24
• Link: https://arxiv.org/abs/2609.29416 
• Why newsworthy: Thermodynamically consistent reactions open a relaxation pathway that suppresses interaction-induced memory drag and restores tracer diffusivity; actively driven reactions can push diffusivity beyond the empty-solvent limit (confirmed in particle simulations).
• Beginner hook: Chemistry that converts particles can make a wandering probe move faster, not slower.
• Caveat: Theory + simulation.

3. Reprogrammable origami through bistable buckled hinges

• Authors: Leon M. Kamp, Lucy Liu, Ella McRitchie, Damien Rouchouse, Orel Mazor, Davood Farhadi, L. Mahadevan, Katia Bertoldi
• Submitted: 2026-09-23
• Link: https://arxiv.org/abs/2609.28790 
• Why newsworthy: Bistable buckled shims across origami hinges create an asymmetric torque–angle preference for mountain vs valley. Flipping a shim reprograms that hinge after fabrication; self-switching hinges let global boundary inputs rewrite the folding pathway.
• Beginner hook: Flip tiny memory springs in the hinges so the same crease pattern prefers a different 3D shape.
• Caveat: Soft-matter mechanics / experiment — we propose only dry paper/card demos, not lab fabrication of buckled shims.

4. Superadiabatic Dynamical Density Functional Theory for One-Dimensional Brownian Hard-Rod Fluids

• Authors: Jens Weimar, Daniel de las Heras, Martin Oettel
• Submitted: 2026-09-24
• Link: https://arxiv.org/abs/2609.29838 
• Why newsworthy: Superadiabatic DDFT with exact equilibrium excess free energy and a three-particle adiabatic closure matches Brownian-dynamics superadiabatic response when initial ensembles align; a velocity-gradient power functional also works with a simulation memory kernel.
• Beginner hook: When hard beads rearrange, extra nonequilibrium forces appear that sleepy equilibrium recipes miss — this theory catches them in a clean 1D testbed.
• Caveat: Theory / simulation.

5. Boundary and bulk perturbations in vectorial active matter

• Authors: Giuseppe Fava
• Submitted: 2026-09-23
• Link: https://arxiv.org/abs/2609.28593 
• Why newsworthy: Thesis on how explicit rotational-symmetry breaking — global environmental anisotropy or boundary-induced local anisotropies — reshapes dry flocking relative to free bulk collective motion.
• Beginner hook: Walls and preferred “wind” directions are not decorations — they change how active flocks dance.
• Caveat: Theory thesis overview.

Stretch

• Temperament engineering for robot swarms (2026-09-24): https://arxiv.org/abs/2609.29423 
• Anthropomimetic soft robotic forearm (2026-09-24): https://arxiv.org/abs/2609.29176 
• Hydrogel particles migrating through ice (cryosuction microrheology) (2026-09-24): https://arxiv.org/abs/2609.29904 
• Charged rods in 3D varying-section channels (2026-09-24): https://arxiv.org/abs/2609.29427 
• Collocated soft-robot shape regulation (2026-09-23): https://arxiv.org/abs/2609.27469 

Safe classroom / discussion follow-ons

1. Preferred-fold origami demo: Paper/card crease with tape or a small pre-bent strip biasing mountain vs valley; flip the bias and compare which 3D fold wins (inspired by arXiv:2609.28790). Dry materials only.
2. Janus-compass grid sketch: Triangular lattice of two-tone discs/arrows; score neighbor alignments under bond-direction rules and ask whether a shared sixfold pattern emerges from random starts (inspired by arXiv:2609.30025). Pencil/paper or intro coding; no chemistry.

Corpus mirror: /workspace/self-assembly-corpus/digests/2026-09-25.md.