Adjuvant Depot Effect — 2D Concentration-Field Model

This is the 2D counterpart to the 3D per-particle adjuvant depot simulator. Instead of animating hundreds of individual random-walking antigen particles, it solves the same underlying physics as a continuum field: a finite-volume advection–diffusion–decay equation for antigen concentration C(x,y,t), with the adjuvant's depot effect expressed as a slower diffusion coefficient, a slower clearance rate and a stronger restoring drift back toward the injection origin. Recruited immune cells are still discrete agents, but they navigate by sampling the true, numerically solved local concentration gradient at their own position — literal gradient-ascent chemotaxis — rather than heading toward a precomputed centroid. Cells that capture enough antigen mass from the field become primed and traffic to the draining lymph node, building the same cumulative "priming signal" readout as the 3D model, so the two views can be compared side by side.