This proceedings volume is devoted to the interplay of symmetry and perturbation theory, as well as to cognate fields such as integrable systems, normal forms, n-body dynamics and choreographies, geometry and symmetry of differential equations, and finite and infinite dimensional dynamical systems. The papers collected here provide an up-to-date overview of the research in the field, and have many leading scientists in the field among their authors, including: D Alekseevsky, S Benenti, H Broer, A Degasperis, M E Fels, T Gramchev, H Hanssmann, J Krashil'shchik, B Kruglikov, D Krupka, O Krupkova, S Lombardo, P Morando, O Morozov, N N Nekhoroshev, F Oliveri, P J Olver, J A Sanders, M A Teixeira, S Terracini, F Verhulst, P Winternitz, B Zhilinskii.

The concept of phase space plays a decisive role in the study of the transition from classical to quantum physics. This is particularly the case in areas such as nonlinear dynamics and chaos, geometric quantization and the study of the various semi-classical theories, which are the setting of the present volume. Much of the content is devoted to the study of the Wigner distribution. This volume gives the first complete survey of the progress made by both mathematicians and physicists. It will serve as an excellent reference for further research.

A listing of forthcoming meetings, conventions, etc.

Boltzmann's formula S = In[W(E)] defines the microcanonical ensemble. The usual textbooks on statistical mechanics start with the microensemble but rather quickly switch to the canonical ensemble introduced by Gibbs. This has the main advantage of easier analytical calculations, but there is a price to pay — for example, phase transitions can only be defined in the thermodynamic limit of infinite system size. The question how phase transitions show up from systems with, say, 100 particles with an increasing number towards the bulk can only be answered when one finds a way to define and classify phase transitions in small systems. This is all possible within Boltzmann's original definition of the microcanonical ensemble.Starting from Boltzmann's formula, the book formulates the microcanonical thermodynamics entirely within the frame of mechanics. This way the thermodynamic limit is avoided and the formalism applies to small as well to other nonextensive systems like gravitational ones. Phase transitions of first order, continuous transitions, critical lines and multicritical points can be unambiguously defined by the curvature of the entropy S(E,N). Special attention is given to the fragmentation of nuclei and atomic clusters as a peculiar phase transition of small systems controlled, among others, by angular momentum.The dependence of the liquid-gas transition of small atomic clusters under prescribed pressure is treated. Thus the analogue to the bulk transition can be studied. The book also describes the microcanonical statistics of the collapse of a self-gravitating system under large angular momentum.

Nuclear physics is presently experiencing a thrust towards fundamental phy sics questions. Low-energy experiments help in testing beyond today's stan dard models of particle physics. The search for finite neutrino masses and neutrino oscillations, for proton decay, rare and forbidden muon and pion de cays, for an electric dipole moment of the neutron denote some of the efforts to test today's theories of grand unification (GUTs, SUSYs, Superstrings, ... ) complementary to the search for new particles and symmetries in high-energy experiments. The close connections between the laws of microphysics, astrophysics and cosmology open further perspectives. This concerns, to mention some of them, properties of exotic nuclei and nuclear matter, and star evolution; the neutrino and the dark matter in the universe; relations between grand unification and evolution of the early universe. The International Symposium on Weak and Electromagnetic Interactions in Nuclei (W.E.LN. 1986)' held in Heidelberg 1-5 July 1986, in conjunction with the 600th anniversary of the University of Heidelberg, brought together experts in the fields of nuclear and particle physics, astrophysics and cosmol ogy.