FROM ONE SWIMMER TO COLLECTIVE FLOW
Active matter from swimming particles to moving defects
A grain that swims can join a crowd without an attractive force. A pattern of rods can carry a moving defect and push fluid. Start with a short path, then build the models that connect these scenes.
Particle branch · Chapters 1–4
How motion creates a crowd
Follow one swimmer, calculate its spreading, then let crowding slow it down. The density-instability calculation gives a first quantitative prediction.
Start with a single path →Orientation branch · Chapters 5–8
How a defect moves fluid
Start with rods that have no preferred head. Count their half-turn defects, calculate active flow and test a local alignment pattern before reading research figures.
Start with a half-turn →Eight chapters, with examples and experiments
01 L1
A swimming particle remembers its direction
What changes when a tiny particle propels itself?
Read and try →02 L2
Two ways for a swimmer to lose its heading
When do gradual turns and sudden tumbles give the same spreading?
Read and try →03 L2
A crowd can grow without anyone pulling
Why can swimmers form a dense crowd without attracting one another?
Read and try →04 L3
Calculate when a density ripple grows
How steeply must swimming slow for a uniform density to become unstable?
Read and try →05 L2
Why a liquid-crystal defect can turn only halfway
How can going around a defect rotate the orientation by only half a turn?
Read and try →06 L3
Turn an orientation field into a flow
How does a bent pattern of rods push the surrounding fluid?
Read and try →07 L3
Guide defects by choosing where rods prefer to point
Can a local preference for orientation redirect a defect and its flow?
Read and try →08 L4
Read active turbulence through a spectrum and a material path
What can a spectrum or a tracer path tell us about an active fluid?
Read and try →