1.961 Life at low Reynolds numbersIntroduction to the class Brownian motion

1.961 Life at low Reynolds numbersRandom walkers: a toy model for diffusion The diffusion coefficient and Einstein s formula

1.961 Life at low Reynolds numbersDiffusion-limited uptake: nutrient flux to a sphere When does nutrient uptake occur only by diffusion: The Peclet number Diffusion vs. locomotion: how do you escape from your boundary layer? Diffusion and metabolism: limits to size Following the scent: concentration and gradient around a sphere Other shapes: peanuts, M s, disks

1.961 Life at low Reynolds numbersSolving the diffusion equation A fundamental property of diffusion: rapid smearing of fine-scale heterogeneities

1.961 Life at low Reynolds numbersThe capillary assay: testing what microorganisms like Diffusion in a pipe Insect tracheae: limits to respiration Diffusion of momentum: an analogy The porosity of eggs and the gas exchange in leaves (handouts only)

1.961 Life at low Reynolds numbers Receptors on cell surfaces: how many do you need? Other forms of diffusion Diffusion with drift

1.961 Life at low Reynolds numbersPoiseuille flow The advection-diffusion equation Stretching the mixing zone: enhancing diffusion via shear

1.961 Life at low Reynolds numbersBrownian rotational diffusion A bacterial random walk: E. coli s run-and-tumble swimming Other bacterial swimming modes Brownian constraints on swimming The distribution of tumbling angles

1.961 Life at low Reynolds numbersTumbling intervals: a Poisson process Diffusion of a bacterial population Motility mutants

1.961 Life at low Reynolds numbersMany taxis: chemo-, photo-, pH-, magneto-, rheo-, geo-, aero-, thermo-, gyro-taxis. A computer model of chemotaxis: a sensing random walker with memory Deriving an advection-diffusion equation for bacteria

1.961 Life at low Reynolds numbersWhen inertia doesn t matter: low Reynolds number Counterintuitive fluid mechanics (GI Taylor s movie) Deriving the Stokes equations The curious phenomena of low-Reynolds number flow (GI Taylor movie)

1.961 Life at low Reynolds numbersStrouhal and Knudsen numbers A world with no inertia The instantaneous diffusion of momentum Linearity: breaking down a problem into simpler ones