This NATO Advanced Study Institute was the fourth in a series devoted to the subject of phase transitions and instabilities with particular attention to structural phase transforma~ions. Beginning wi th the first Geilo institute in 19'(1 we have seen the emphasis evolve from the simple quasiharmonic soft mode description within the Landau theory, through the unexpected spectral structure re presented by the "central peak" (1973), to such subjects as melting, turbulence and hydrodynamic instabilities (1975). Sophisticated theoretical techniques such as scaling laws and renormalization group theory developed over the same period have brought to this wide range of subjects a pleasing unity. These institutes have been instrumental in placing structural transformations clearly in the mainstream of statistical physics and critical phenomena. The present Geilo institute retains some of the counter cul tural flavour of the first one by insisting whenever possible upon peeking under the skirts of even the most successful phenomenology to catch a glimpse of the underlying microscopic processes. Of course the soft mode remains a useful concept, but the major em phasis of this institute is the microscopic cause of the mode softening. The discussions given here illustrate that for certain important classes of solids the cause lies in the electron phonon interaction. Three major types of structural transitions are considered. In the case of metals and semimetals, the electron phonon interaction relie6 heavily on the topology of the Fermi surface.

Energy Modelling Studies and Conservation documents the proceedings of seminar of the United Nations Economic Commission for Europe held in Washington D.C., on 24-28 March 1980. The volume begins with a Seminar Theme Paper that identifies background policy issues that lead to modeling; discusses points of view involved in energy policy modeling; defines the context of a set of energy conservation problems or questions being analyzed; and provides a forward-looking view of the subject and its problems. This is followed by 54 papers that are organized into three main topics: (1) energy models of major interest to individual countries; (2) the interaction between energy conservation measures and the economy; and (3) the international aspects of energy conservation models. The papers on Topic 1 cover forecasting methodologies, demand and conservation studies, and electricity and supply studies. The papers on Topic 2 present the experiences in countries such as Norway, UK, the USSR, and US. The papers on Topic 3 include studies on energy conservation policies in France, Germany, and Italy; and the MARKAL multi-period linear programming model for joint research and development in the field of new energy technologies of the 17 countries of the International Energy Agency.