The symbiosis between particle physics and cosmology has virtually become a conjugal relationship. Hence the 9th biennial Course of the International School of Cosmic-Ray Astrophysics was designed to bridge these formerly dispa- rate disciplines. This NATO Advanced Study Institute (ASI) took place at the Ettore Majorana Centre in Erice, Italy, June 20-30, 1992. Seventy participants from 17 countries enjoyed the opportunities for lively interactions as much as they benefitted from the stimulating lectures. This volume is based on a selection of lectures and shorter talks presented at the sessions. Warm thanks are due to my co-director, Prof. J. P. Wefel and to co-editor Dr. Rein Silberberg for their co- operation. The support of NATO's Scientific Affairs Di- vision and of Dr. L. V. da Cunha, Director of its ASI Pro- gramme, was invaluable. We also acknowledge important con- tributions by the following: Prof. A. Zichichi, Director of the Majorana Centre and its dedicated staff; the Italian Ministry of Education; the Italian Ministry of Scientific Research; the Sicilian Regional Government; the National Science Foundation of the USA, the European Physical Soci- ety, and Mrs. Shirley Ratner of Bethesda, Maryland. The Scientific Advisory Committee consisted of Profs. P. V. Auger, G. P. S. Occhialini, B. Rossi, M. M. Shapiro, R. Silberberg, J. A. Simpson, J. A. Van Allen, J. P. Wefel, and A. Zichichi. All of the foregoing persons and agencies helped make this ASI a memorable experience for the parti- cipants.

The Galactic cosmic rays have far-reaching effects on the interstellar medium, and they are, in turn, profoundly affected by the particles and fields in space. Supernova remnants and their expanding shock fronts pervade the Galaxy, heating the interstellar medium, and accelerating the cosmic rays. The interplay among the cosmic rays, the interstellar medium in which they propagate, and supernovae has been investigated for decades; yet these studies have generated as many enigmas as they have resolved. These puzzles continue to challenge observers and theorists alike. th This volume is devoted to selected lectures presented in the 7 Course of the International School of Cosmic-Ray Astrophysics in Erice, Italy in July-August, 1990. Alltogether, some 400 participants have attended the biennial sessions of this School since its inception in 1978. As its name implies, the School deals with cosmic-ray phenomena viewed in the broader context of astrophysics. Students and Lecturers are attracted from many astrophysical disciplines. Like earlier courses in this series, the present one was organized under the aegis of the Ettore Majorana Centre as a NATO Advanced Study Institute. Given the diverse scientific backgrounds of the students, it was deemed useful to include lectures at the introductory level. Other lectures and contributed talks were at a more advanced level, featuring new developments. If this collection is useful pedagogically, and if it provides some stimulus and information for the mature research worker, then the editors will feel well rewarded.

This volume comprises selected lectures presented in the Ninth Course of the International School ofCosmic-Ray Astrophysics held at the Ettore Majorana Centre in Erice, Sicily, May 7-18,1994. Director ofthe Centre is A. Zichichi, assisted by M. Zaini. Director ofthe School is M. M. Shapiro. 1. P. Wefel was co-director of the Ninth Course, which was also a NATO Advanced Study Institute (ASI), and NATO support is gratefully acknowledged. Devoted to problems and prospects in high-energy astrophysics and cosmology, the major areas explored in this course were: gamma-ray, X-ray, and neutrino astronomies; cosmic rays; pulsars and supernova remnants; and cosmology, as well as cosmogony. Among the principal developments in gamma-ray astrophysics were those generated by the Compton Gamma Ray Observatory. Cosmic neutrinos at MeV energies, i.e., those from the sun and from Supernova 1987a, were discussed, as well as neutrino masses in astrophysics. The source composition ofcosmic rays, and extensive air shower experiments, received special attention. The early universe according to COBE data, and as viewed by theorists ofcosmology, was reviewed. Finally, the connections with particle physics occasioned a timely description ofthe Standard Model ofelementary particles.

The symbiosis between particles physics and cosmology has virtually become a conjugal relationship. Hence the 9th Biennial Course of the International School of Cosmic-Ray Astrophysics was designed to bridge these formerly disparate disciplines. This NATO Advanced Study Institute took place at the Ettore Majorana Centre in Erice, Italy, June 20-30, 1992. Seventy participants from 17 countries participated in lively interactions and enjoyed the stimulating lectures that form the basis for this volume. The book includes current advances in both astrophysics (cosmic gamma ravs, X-rays, cosmic rays) and cosmology (an introduction to inflation in big-bang theory, the age of the universe, nucleosynthesis in the early universe). It is suitable for reading and study by all interested physical scientists, especially those having a limited specialized background in astrophysics and cosmology.

I. Cosmic Rays and the Interstellar Medium.- A Brief Introduction to the Cosmic Radiation.- The Composition of the Cosmic Rays: An Update.- Interstellar Dust-Gas Relationships.- Dust, Gas and Cosmic Rays in the Interstellar Medium.- Comparison Between Greenberg and Mathis Models of Grains for the H2 Formation Induced by Cosmic Rays.- II. Supernovae, Acceleration, Propagation and Source Composition.- Shock Acceleration of Cosmic Rays.- Source Composition, Sites of Origin And Acceleration of Cosmic Rays.- Cosmic-Ray Age and the Interstellar Medium.- The Production of Antiprotons in the Interstellar Gas by Propagating Cosmic Rays.- The Source Composition of Galactic Cosmic Rays and the Condensation Process of the Elements in Circumstellar and Interstellar Gases.- The Distribution of Supernova Remnants in the Galaxy.- Gamma Rays from Supernova 1987A.- Acceleration of Cosmic Rays at Young Supernova Remnants.- The Effect of Relativistic Particle Beams on the Evolution of Supernova Envelopes: Self-Consistent Solutions.- Radio Spectral Variations in the Cygnus Loop.- III. Gamma Rays and Their Role as Cosmic Ray Tracers.- Gamma Ray Astrophysics at Energies up to 10 Gev.- Vhe and UHE Gamma Ray Sources.- Gamma-Rays from Electron, Proton Beam Interactions with Matter and/or Radiation: Application to Cygx-L, Geminga, and 3C273.- Gamma Rays and Neutrinos from Accretion Processes onto Collapsed Objects: Application to 3C273.- Nearby Galaxies in Highenergy Gamma Rays.- IV. Ultra-Energetic Cosmic Nuclei.- Cosmic Rays at the Highest Energies.- Participants.- Author Index.