Vesicle Cluster DepletionIn this simulation, synaptic vesicles (green) bind with synapsin protein (blue) to form a cluster attached to docking sites (red) at the active zone of a presynaptic nerve terminal. Action potentials occur every 5 seconds starting at 0:10. These action potentials disrupt the cluster, and cause vesicles to fuse with the membrane (shown as vesicles escaping the compartment). |
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The plots at the right show the number of remaining vesicles, and a measure of their distance
from the active zone at the bottom. Every 300 time units in the plots
is 5 seconds in the video.
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Presynaptic Nerve Terminal with Deformable MembraneThis video shows a simulation of a presynaptic nerve terminal with a deformable membrane. Although the particles in the membrane do not individually represent real-world objects, they collectively model the shape and dynamics of a nerve cell membrane. At 0:40, an action potential arrives and disrupts the clusters of vesicles (green) and synapsins (blue). Vesicles dock at sites in the active zone (red).Return to Homepage |
Deformable Spherical MembraneIn this video an initially-spherical membrane deforms in response to an impact. The particles in the membrane were arranged in a icosahedral grid, which is based on a 20-sided regular polyhedron. Unfortunately, the edges of the 20-sided polyhedron tend to protrude inwards or outwards as the object deforms. Deformable planar or cylindrical membranes should not have the same problem.Return to Homepage |
Deformable Square MembraneIn this video a square membrane responds first to gravity, then to an impact with a falling object. Each particle in the membrane is tethered to its four nearest neighbors to the sides, and to the particle either directly below or directly above it. Gravity is represented by impulses applied to each particle at regular intervals. Because the membrane stretches in response to gravity, "tethering collisions" occur at a very high rate. The simulation is therefore computationally inefficient.Return to Homepage |
Tethered Particle System CollisionsThis video shows the different types of collisions that occur in a tethered particle system model. At 0:00, at elastic collision is shown and the particles rebound. At 0:10, energy is lost in the collision. At 0:20, two tethered particles rebound and retract in alternation. At 0:30, energy is lost each time the particles retract. At 0:40, the particles revolve around each other. At 0:47, the particles lose energy as they revolve.Return to Homepage |
Approximation to Cope with Nearly Simultaneous CollisionsThis video demonstrates an approximation that can dramatically reduce the number of collisions that occur in an impulse-based dynamic simulation. At 0:00, three particles of equal mass undergo 2 collisions in sequence. At 0:15, the mass of the center particle is reduced to 50%, and a 3rd collision occurs. At 0:30, the mass of the center particle is reduced to 0.1%, and 70 collisions occur. Most of the 70 collisions take place in a very short amount of time, and cannot be distinguished in the video. At 0:42, an approximation is employed in which colliding particles are temporarily grouped together. A particle group acts as a single body with the combined particle mass, so only 5 collisions occur instead of 70.Return to Homepage |