//------------------ materials define--------------------------
air       3 14.0067 15.9994 39.948  7. 8. 18. 1.205e-5 .755 .231 .014
          0 1 30. .001
          0
silicon   1 28.0855 14. 2.33
          1 1 20. .001
          0
iron      1 55.874 26. 7.87
          1 1 20. .001
          0