>>47 つづき

1 . Introduction

The definition of long-range order which we adopt arises naturally in the case of a
solid from the dislocation theory of melting (Nabarro 1967). In this theory, it is supposed
that a liquid close to its freezing point has a local structure similar to that of a solid,
but that in its equilibrium configurations there is some concentration of dislocations
which can move to the surface under the influence of an arbitrarily small shear stress,
and so produce viscous flow. In the solid state there are no free dislocations in equilibrium,
and so the system is rigid. This theory is much easier to apply in two dimensions
than in three since a dislocation is associated with a point rather than a line.
Although isolated dislocations cannot occur at low temperatures in a large system
(except near the boundary) since their energy increases logarithmically with the size of
the system, pairs of dislocations with equal and opposite Burgers vector have finite
energy and must occur because of thermal excitation. Such pairs can respond to an
applied stress and so reduce the rigidity modulus. At sufficiently high temperatures, the
largest pairs become unstable under an applied shear stress and produce a viscous
response to the shear.
The presence or absence of free dislocations can be determined in the following
manner. We suppose that the system has a fair degree of short-range order so that a
local crystal structure can be identified.
つづく

dislocation theory （転位）ね。普通の人はしらんだろう