Analogy Sandpile

Consider how a sand pile behaves. A sand pile is a simple system whose components interact by exchanging forces or information. Gravity drives the sand pile system externally. The grains represent flowing molecules. Piled sand grains display unique behaviors as we add grains to bring the pile into unstable, non-equilibrium 'avalanche' conditions. The changes grains undergo as they move in an avalanche models the solid to liquid transition because the avalanche recruits surrounding grains. Temperature plays no role in the dynamic transitions between phases, as the system responds with its own nonlinear dynamics to applied forces (Ref: Self-organized Criticality).

Self-organized criticality (SOC) embodies the idea that complex behaviors develop spontaneously in certain many-body systems whose dynamics change rapidly. Self-organized critical-ity in some basic way may influence the development of structure in biological systems. What are the properties of systems that lend themselves to similar sand-pile like cascades? These systems require events to occur on separated time scales for one. What constitutes the external driving of the system must occur slower than the time for the system to relax. An example would be the shaking of hemolymph from the movements of flying and walking and the imparting of the energy of body movements to moving the hemolymph (Chapter 9). Signals of any form traverse the system as long as a signal encounters a connected path of above threshold regions for its propagation. Making analogous granular models even of some of a hemocoel's dynamics, might suggest how information might circulate. Investigating the consequences of the inherently inhomogeneous distributions of forces inside piles of granules might allow particles of a system to explore phase space as well as other aspects of aggregation. Looking at the phenomena of aggregation and the spontaneous formation of structure together with changing instabilities under applied stresses suggests how energy and momentum might propagate through highly dissipative materials. One might use video, magnetic resonance imaging (MRI), and X-ray tomography to record a model system.

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