Consider Eq. 4.19, which gives the strain energy per unit length of a screw dislocation. Assume that one has a very large square array of long, straight, parallel screw dislocations of alternating signs, so that the effective outer radius ′ of the strain field of the dislocations 3 may be taken as √ . With the aid of a computer, determine the strain energy per unit length of a screw dislocation as a function of the dislocation density, , between = 1011 and = 1018m/m3.