Halperin and Nelson developed a theory of one type of this process that is mediated by dislocations. One occurrence of this process happens when a particular parameter is equal to pi over two times the spin stiffness and occurs when vortexes unbind. One way of describing these processes is based on 
Halperin and Nelson developed a theory of one type of this process that is mediated by dislocations. One occurrence of this process happens when a particular parameter is equal to pi over two times the spin stiffness and occurs when vortexes unbind. One way of describing these processes is based on a Taylor series of free energy where each term has a power of the order parameter. Another way for classifying them is to find which order derivative of a thermodynamic variable is required for there to be a discontinuity. They are classified by Ehrenfest and Landau schemes. The Clausius-Clapeyron relation gives the slope of a curve representing one of these occurrences. For 10 points, name this phenomenon, in which one state of matter is transformed into another.
Halperin and Nelson developed a theory of one type of this process that is mediated by dislocations.
phase transitions (also accept phase changes;)