Exercises

1. Try the sandpile applet at Ref.[7], varying the parameters and the conditions, and compare what you see with what has been described above.
2. (a) Explain where dissipation occurs in the sand-pile model.
   (b) Explain why the sand must be added slowly to the sandpile. What would happen otherwise ?
   (c) In actual simulations, the straight line fit on a log-log plot does not hold for very large avalanche sizes. Explain why.
3. Read the article [3] and discuss the applications of the self-organised criticality concept.
4. Read the article [8] and compare the forest-fire phenomena with that of conflicts and wars.
5. Take a look at http://sps.nus.edu.sg/ wongjian/sp2174/$\char93$1 for a student project on SOC.
6. Check out the websites below of Zipf's law.
   (a) Find other situations where Zipf's law applies.
   (b) Discuss possible human factors that could be the drving force behind the laws.
   (c) Is Zips's law an example of self-organised criticality ?
7. Read the article [13].
   (a) What evidence is there that forest fires are an example of a self-organised critical system?
   (b) What similarities are there between forest fires and wars ?
   (c) What in your opinion is the best way to prevent conflicts from getting very large and destructive ? (d) Can you justify your answer in (c) in the face of claims of self-organised criticality of the system ? (e) Check out Ref.[14] and others similar in spirit.