Knots are everywhere — from tangled headphones to DNA strands packed inside viruses — but how an isolated filament can knot itself without collisions or external agitation has remained a longstanding puzzle in soft-matter physics.

Now, a team of researchers at Rice University, Georgetown University and the University of Trento in Italy has uncovered a surprising physical mechanism that explains how a single filament, even one too short or too stiff to easily wrap around itself, can form a knot while sinking through a fluid under strong gravitational forces. The discovery, published in Physical Review Letters, provides new insight into the physics of polymer dynamics, with implications ranging from understanding how DNA behaves under confinement to designing next-generation soft materials and nanostructures.

Soil is one of Earth’s largest carbon sinks, second to the ocean. New study discovers a key iron mineral in soil has a nanoscale mosaic of positive and negative charges. Varied charges, hydrogen bonding and strong chemical bonds enable mineral to trap carbon. Findings help explain why some carbon is locked in soils for centuries.

Snow and ice can damage paved surfaces, leading to frost heaves and potholes. These become potential hazards for drivers and pedestrians and are expensive to fix. Now, researchers propose in ACS Sustainable Chemistry & Engineering a figurative and literal green solution to improve the durability of roads and sidewalks: an algae-derived asphalt binder. For temperatures below freezing, results indicated that the algae binder reduced asphalt cracks when compared to a conventional, petroleum-based binder.