Burgers vector, Burgers circuit, line direction in RH/SF convention (See Hirth & Lothe)

RHS : right-handed screw

Burgers vector (b) and the line direction (\xi) are parallel.

LHS : left-handed screw

Burgers vector (b) and the line direction (\xi) are anti-parallel.

+E : positive edge

The extra-half plane above the slip plane. (\xi \times b >0)

-E : negative edge

The extra-half plane below the slip plane. (\xi \times b <0)

Dislocations of opposite sign attract each other, and the dislocation loop will annihilate unless we apply shear stress.

Hand Rule (See Prof. Nix's Lecture Notes)

In order to expand the loop, we apply the stress \sigma such that shear stress goes along the +b direction above the slip plane and along the -b direction below the slip plane. The hand rule tells which direction the dislocation moves to. For example, the thumb of right hand, when its fingers pointing the stress direction, directs RHS move left in top-view.