In May 1986 a two-day workshop on Physical Processes in Comets, Stars and Active Galaxies was held at the Ringberg Castle near Lake Tegernsee, and this rather unusml. l collection of topics needs a few words of explanation. When we first thought of organizing a workshop on such a large variety of astrophysical objects our main motivation was to honor Rudolf Kippenhahn and Hermann Ulrich Schmidt on the occasion of their 60th birthdays, and we planned to cover at least a fraction of their fields of active research. We then realized immediately that despite the fact that the objects are so different, the physical processes involved are very much the same, and that it is this aspect of astrophysics which governed the scientific lives of both of our distinguished colleagues and friends and allowed them to make major contributions to all those fields. Apparently this viewpoint was shared by many colleagues and it was therefore not surprising that in response to our invitation everybody who had been invited agreed to come and to present a talk. The workshop then turned out to be a real success. In contrast to highly specialized conferences, fundamental problems as well as very recent devel opments were discussed and the participants appreciated the opportunity to exchange ideas."

This book is a translation, by Mr. S. Dunlop, FRAS, of the second German edition of Veranderliche Sterne published by Johann Ambrosius Barth Ver lag, Leipzig, DDR, and Springer-Verlag, Berlin Heidelberg New York Tokyo. We have used the opportunity to make improvements and changes in a few places and to add details of new results and discoveries. The foreword to the second German edition remains no less valid for this one, including the changes. We would like to express our thanks to Mr. Dunlop for his expert and sympathetic translation and for the many improvements he suggested. December 1984 G. RICHTER and W. WENZEL Preface to the Second German Edition The suggestion that a second edition of this book should be prepared came equally from the readers, the publishers, and from the editors of the first edition. By a lucky coincidence the completion of the manuscript and the composition of these lines comes at the time of the 90th anniversary of the birth of Cuno Hoffmeister, the author of the first edition, and consequently this current work may be dedicated to his memory."

For the last few years astrophysicists and elementary particle physicists have been working jointly on the following fascinating phenomena: 1. The solar neutrino puzzle and the question: What happens to the neutrinos on their way from the sun to the earth? 2. The growing evidence that our universe is filled with about 10 times more matter than is visible and the question: What is dark matter made of? 3. The supernovae explosions and the question: What do neutrinos tell us about such explosions and vice versa? The experimental investigation of these phenomena is difficult and involves unconventional techniques. These are presently under development, and bring together such seemingly disparate disciplines as astrophysics and elementary particle physics on the one hand and superconductivity and solid-state physics on the other. This book contains the proceedings of a workshop held in March 1987 at which the above subjects and their experimental investigation were discussed. The proposed experimental methods are very new. They involve frontier developments in low temperature and solid-state physics. The book should be useful to researchers and students who actively work on these subjects or plan to enter the field. It also offers the non-expert reader with some physics background a good survey of the activities in this field.

A physicist and an inventor, Jules Janssen (1824-1907) devoted his life to astronomical research. He spent many years traveling around the world to observe total Solar eclipses, demonstrating that a new era of science had just come thanks to the use of both spectroscopy and photography, and persuading the French Government of the necessity of founding a new observatory near Paris. He became its director in 1875. There, at Meudon, he began routine photographic recordings of the Sun surface and had a big refractor and a big reflector built. Meanwhile, he also succeeded in building an Observatory at the summit of Mont-Blanc. The story of this untiring and stubborn globe-trotter is enriched by extracts of the unpublished correspondence with his wife. One can thus understand why Henriette often complained of the solitude in which she was left by her peripatetic husband: "There are men who leave their wives for mistresses; you do it for journeys!" ... Basking in the glow of his success, Janssen was able to undertake the construction of the great astrophysical observatory of which he had dreamed. It was at Meudon that he had it built.

Interest world-wide in the provision of new observational astro nomical facilities in the form of ground-based optical telescopes of large aperture has never been higher than exists at present. The benefits to be gained from increased aperture size, however, are only utilised effectively if efficient instrumentation is also available. There have been significant improvements recently in this area, part icularly in detector technology and data handling as well as in optical design, so that systems which are currently being developed have the capability of being vastly more powerful in terms of the efficient use of photons than those which existed only 5 years ago. The rationale for the decision by Commission 9 of the International Astronomical Union to hold IAU Colloquium 67, therefore, was to obtain reports on these developments with the emphasis placed upon overall efficiency of the complete observational system - from telescope aperture right through to detector output. A fitting venue for the meeting was the site of the 6 metre BTA (Bolshoi Azimuth Telescope) at Zelenchukskaya in the Caucasus mount ains, USSR. The BTA is operated by the Special Astrophysical Observatory located at Nizhnij Arkhyz, a few kilometres from the telescope itself."

This volume contains papers presented at IAU Colloquium No. 90. at the Crimean Astrophysical Observatory in May of 1985. A few additional contributions are included from authors who for various reasons were unable to attend the meeting. Four years have passed since the last major international conference on chemically peculiar stars of the upper main sequence was held in Liege. Belgium in 1981. Previous conferences were held in 1975 (Vienna. Austria) and in 1965 (Greenbelt. Maryland. USA). As the proceedings of this Colloquium show. the recent availability of ultraviolet spectra of large numbers of normal and chemically peculiar A and B stars is having a major impact on the way we study these objects. and has led to many new. exciting and unanticipated results. Simultaneously. the more traditional study of optical spectra has been advanced through the increasing use of very high spectral resolution with high signal-to-noise detectors. The chemically peculiar (CP) stars on the upper main sequence belong in the standard framework within which we understand stellar evolution and the history of matter. Recent work has made it clear that the unusual chemistry and magnetic structure of these objects is of relevance across the broad domain of stellar astronomy. from the upper main sequence to horizontal branch stars and white dwarfs. Metal poor (J>. Boo) as well as metal rich (Ap. Am) stars are an integral part of the picture.

Infrared Astronomy is a relatively new subject but it has already radically altered our ideas about astronomical sources. Recent progress in this subject is the result of improved detection techniques, particularly the use of detectors at liquid helium temperatures. Unfortunately, the terrestrial atmosphere greatly restricts Infrared astronomers by allowing them to detect radiation only in narrow transmission win dows and by presenting a foreground emission which limits the faintness of observable sources. It is only from aircraft or balloon altitudes that we can begin to observe faint sources over the complete range of wavelengths between the visible and the radio regions. Few such observations have yet been made and none from satellites, although the latter vehicle will offer complete freedom from atmospheric effects. New developments and intermediate steps will be required before the ultimate aim of flying in space can be achieved. It is not surprising therefore that the Fifth Eslab/Esrin Symposium should deal with this problem. This book contains the proceedings of the Symposium and faithfully records all discussions. The Symposium covered the present situation and future perspectives of IR techniques. International leaders in the field reviewed the results to date and the possible developments in telescope systems, detectors, cryogenics, filters, and interferometers. Individual con tributions were made by European and U. S. scientists in each of these fields."

This work deals with some of the most typical complexes of interstellar matter and is intended to serve both as a reference book for the specialist and as an introduction for the newcomer to the field. It is hoped to meet the first aim by presenting a holistic view of the well studied complexes in Orion, built on information derived from various branches of modern Astrophysics. The wealth of published data is presented in the form of photographs, contour maps, diagrams and numerous heavily annotated tables. The second aim is pursued by providing an outline of the complexes, the physical problems associated with them, the empirical models describing their be haviour and, in addition, by including an extended Appendix section summarizing the numerous methods employed to derive the physical parameters of an H II region and the dust and molecular cloud physically associated with it. The book consists of five chapters and four Appendix sections. Chapter 1, which is concerned with the large scale view of the Orion region, outlines the morphology of the area and examines in particular the nature of Barnard's Loop and the associated filamentary structure in addition to the origin of the I Orion OB association. Chapter 2 focuses on the ionized gas of the Orion H II/molecular complex i. e."

Planet Earth is part of our Galactic environment, not just the product of it, and it is still today influenced by phenomena related to Galactic forces. Specifically, our planet is affected by its near environment, in particular the small bodies in the Solar System. This book reviews the processes which cause the collisions of these small bodies with the Earth as well as the consequences of such collisions. The various articles take the reader through the Galaxy-Solar System connection to the orbital dynamics of the small bodies and to their number and distribution in near-Earth space. The hazards of the impacts of small bodies on Earth are evaluated, and the geophysical records of such impacts are discussed. The book takes the reader to the forefront of research on both impact cratering and the origin and evolution of small bodies in the Solar System. Thus it brings together two subjects, geophysics and astronomy, which are usually discussed in separate volumes but are closely knit together in this particular area of research.

If Zdenek Kopal Department of Astronomy University of Manchester Your Magnificences, my Lord Mayor, ladies and gentlemen! It is a great pleasure for me to respond, on behalf of your foreign guests, to your gracious words of welcome; and to thank you for the wonderful reception which you nave extended to us. The city of Bamberg and its Remeis Sternwarte nas indeed been renowned allover the world for a great many years - as the place where your Observatory's first director, Professor Ernst Hartwig (1851-1923) - in addition to his other titles to fame - collaborated (with Gustav Muller of Potsdam) on the construc- tion of the monumental Geschichte und Literatur des Lirhtwechsels der Veranderlichen Sterne, which since 1918 has (together with its sub- sequent continuation) been a veritable vade-mecum of a1l students of variable stars; where the second director, Professor Ernst Zinner (1886-19]~ prepared his valuable Katalog der Verdachtigen Veranderlichen Sterne (192@ which safeguarded many an astronomer (including the present speaker in the days of his innocence) from premature discovery claims; and whose third director, Professor Wolfgang Strohmeier, initiated in 1959 the tradition of the international colloquia of which ours is the latest successor. It is indeed a great pleasure to welcome Professor Strohmeier - now Emeritus - among us; and to congratulate him on the grace with which he is carrying his years.

..".The Multiversal book series is equally unique, providing book-length extensions of the lectures with enough additional depth for those who truly want to explore these fields, while also providing thekind of clarity that is appropriate for interested lay people to grasp the general principles involved." - Lawrence M. Krauss

Cosmic Update Covers: A novel approach to uncover the dark faces of the Standard Model of cosmology.The possibility that Dark Energy and Dark Matter are manifestations of the inhomogeneous geometry of our Universe.On the history of cosmological model building and the general architecture of cosmological modes.Illustrations on the Large Scale Structure of the Universe.A new perspective on the classical static Einstein Cosmos.Global properties of World Models including their Topology.The Arrow of Time in a Universe with a Positive Cosmological Constant.Exploring the consequences of a fundamental Cosmological Constant for our Universe. Exploring why the current observed acceleration of the Universe may not be its final destiny.Demonstrating that nature forbids the existence of a pure Cosmological Constant.Our current understanding of the long term (in time scales that greatly exceed the current age of the Universe) future of the Universe.The long term fate and eventual destruction of the astrophysical objects that populate the universe --including clusters, galaxies, stars, planets, and black holes.

The material is presented in a layperson-friendly language followed by addition technical sections that explain the basic equations and principles. This feature is very attractive to readers who want to learn more about the theories involved beyond the basic description.

"Multiversal Journeys is a trademark of Farzad Nekoogar and Multiversal Journeys, a 501 (c) (3) nonprofit organization.""

This volume contains a series of lectures presented at the 4th Course of the International School of Astrophysics, held in Erice (Sicily) from July 9 - July 20, 1977 at the "E. Majorana" Centre for Scientific Culture. The course was fully supported by a grant from the NATO Advanced Study Institute Programme. It was attended by 82 participants from 15 countries. Even though the infrared portion of the electromagnetic spectrum covers an extensive interval from the red region of the optical spectrum (10,000 A) to the microwave radio region (1 mm), its role in astronomy has been minimal until the last two decades. Until very recently, the only objects observed were the sun, the moon and the planets. A primary reason for this late development was the lack of sensitive detectors and the necessary cryogenic technology that must accompany their use. Recent progress in this technology has been paralleled by an ever increasing interest of astronomers in infrared observations, leading to a number of ex tremely important results in different branches of astronomy. This becomes evident when one realizes that in many astrophysical conditions most of the energy is found to be channeled into the infrared portion of the electromagnetic spectrum. Stars were detected that yield most of their radiation in the infrared; these objects present a new view of stellar evolution, both in the birth and death stages."

Over the last decade many efforts have been made to develop high angular resolution techniques in astrophysics. Combined with imaging facilities, they have rapidly proved their efficiency and have already led to major astrophysical results. During the decade to come, astronomers will be offered new, even more sophisticated high angular resolution tools, especially in the IR and optical domains, coupled with much bigger telescopes, either on the ground or in space. In such a context of rapidly evolving techniques and a growing need for higher angular resolution to test theories or discover new objects, the present book reviews both instrumental and scientific aspects. The main questions addressed are: what kind of science will benefit from high angular resolution techniques? How can they best be used? Audience: The book is accessible to students and research workers in both instrumental and astrophysical aspects.

After the same pattern as the XIII th General Assembly of the International Astronom ical Union the present Volume of the Highlights in Astronomy contains the texts of the invited discourses given at the XIVth General Assembly held in Brighton, England, August 1970. It contains further the papers and discussion remarks presented at the six joint discussions, as well as the invited papers given at the special session on the Moon. In addition this Volume contains the papers given at the joint meeting of Commissions 24, 27, 30, 33 and 37 on RR Lyrae Stars. It goes without saying that the nearly hundred papers printed in this Volume represent only a minor part of all matter dealt with at the XIVth General Assembly of the Union; the many important discussions that took place in a few hundred commission meetings are not included. For short abstracts and reviews of these the reader is referred to Transactions of the International Astronomical Union XIVB. I wish to thank those who contributed to this Volume for the speed in submitting the manuscripts of their papers. This, together with the efficiency of the Publishers allowed for a rapid publication.

It is hard to appreciate but nevertheless true that Michael John Seaton, known internationally for the enthusiasm and skill with which he pursues his research in atomic physics and astrophysics, will be sixty years old on the 16th of January 1983. To mark this occasion some of his colleagues and former students have prepared this volume. It contains articles that de scribe some of the topics that have attracted his attention since he first started his research work at University College London so many years ago. Seaton's association with University College London has now stretched over a period of some 37 years, first as an undergraduate student, then as a research student, and then, successively, as Assistant Lecturer, Lecturer, Reader, and Professor. Seaton arrived at University College London in 1946 to become an undergraduate in the Physics Department, having just left the Royal Air Force in which he had served as a navigator in the Pathfinder Force of Bomber Command. There are a number of stories of how his skill with instruments and the precision of his calcula tions, later to be so evident in his research, saved his crew from enemy action, and on one occasion, on a flight through the Alps, from a collision with Mount Blanc that at the time was shrouded in clouds."

ix List of Speakers and Participants xi Group Photograph xviii Greetings by B. Garfinkel, A. E. Roy and P. J. Message xix Introduction xxiii PART I: FUNDAMENTAL CONSIDERATIONS OF STABILITY R. BROUCKE/Simple Non-Integrable Systems with Two Degrees of Freedom 3 G. CONTOPOULOS/lnstabilities in Systems of Three Degrees of Freedom 25 R. W. EASTON/Perturbed Twist Maps, Homoclinic Points and Ergodic Zones 41 O. GUREL/Bifurcation Theory and its Applications V. SZEBEHELY/General Considerations of Stability in 49 61 Celestial Mechanics PART II: ASPECTS OF NUMERICAL ANALYSIS AND STATISTICAL MECHANICS S. J. AARSETH/An N-Body Integration Method in Co-Moving Coordinates 69 J. BAUMGARTE/The General Theory of Conservative Stabilization of the Keplerian Problem 81 C. DEWITT-MORETTE /Celestial Mechanics, Quantum Mechanics, and Path Integration 95 G. C. STEY/Statistical Viewpoint in Classical Mechanics 103 PART III: STABILITY OF PLANETARY SYSTEMS ~ C. FROESCHLE and H. SCHOLL/Evolution of Orbits in the Outer Part of the Asteroidal Belt and in the Kirkwood Gaps as Influenced by the Mass Effects of Saturn and Jupiter 115 v TABLE OF CONTENTS vi B. GARFINKEL/On the Stability of Resonant Motion in 121 the Light of the Regularizing Function 129 P. GOLDREICH/The Rings of Saturn and Uranus J. D. HADJIDEMETRIOU/Instabilities in Periodic 135 Planetary-Type Orbits P. J. MESSAGE/Bounds on Secular Terms in Celestial 165 Mechanics A. E. ROY/Empirical Stability Criteria in the 177 Many-Body Problem R. O. VICENTE/Instabilities in Planetary Systems 211 PART IV: THE PROBLEM OF THREE BODIES H.

The principal purpose of IAU Colloquium No. 35 was to discuss those aspects of the techniques of the compilation, evaluation, and distribution of data that are common to astrometry, photometry and spectrometry of stars and stellar systems. In the announcement of the Colloquium, it was suggested that there would be special emphasis on the techniques of quality control, and on the standards for the presentation of numerical data in both printed and com puter-readable form. As the meeting progressed it became clear that the lack of a standard, unambiguous system for the identifi cation of stellar objects was a source of much confusion and inefficiency in the use of existing data files. This and other such matters were the subject of further discussions by Commission 5 at the General Assembly of the International Astronomical Union (IAU), which was held at Grenoble during the following fortnight, 24 August - 2 September 1976. The proposal for the Colloquium was prepared by J. Jung, who was then Director of the Centre des Donnees Stellaires at Stras bourg, and G. A. Wilkins, Chairman of the IAU Working Group on Numerical Data, and was accepted by the IAU Executive Committee on the recommendation of the President of Commission 5, with the support of Commissions 25, 29 and 45. The Scientific Organising Committee consisted of W. Fricke, B. Hauck, C. Jaschek, J. Jung, B. Kukarkin, P. Lacroute, A. Underhill and G. A. Wilkins (Chair man). The Local Organising Committee consisted of A."

The First Conference of the International Society for the Study of Time was held at the Mathematisches Forschungsinstitut at Oberwolfach in the Black Forest, Federal Republic of Germany from Sunday, 31 August to Saturday, 6 September, 1969. The origin of this conference and the formation of the Society goes back to a proposal due to J. T. Fraser that was discussed at a conference on "Interdisciplinary Perspectives of Time" held by the New York Academy of Sciences in January, 1966. It was unanimously agreed than that an international society should be formed on an interdisciplinary basis with the object of stimulating interest in all problems concerning 'time and that this object could best be attained by means of conferences held at regular intervals. J. T. Fraser was elected Secretary, S. Watanabe Treasurer, and I was elected President. It was agreed, at my suggestion, that the organization of the first conference of the newly formed Society be left to a committee of these three officers, on the understanding that they would invite authorities on the role of time in the various special sciences and humanities to form an Advisory Board to assist them. One of the main difficulties in seeking support for an interdisciplinary conference is that most foundations confine their interest exclusively either to the sciences or to the humanities.

Long-term measurements of field strength have been performed over a 160 km path entirely over sea in the Baltic area. For short periods the radio measurements have been combined with meteorolo- gical measurements in order to describe the structure of the re- fractive index field. The heigth of layers was continously deter- mined by remote sensing techniques and their thickness and inten- sity by airborne and balloonborne instruments. From these data, field strengths have been calculated for scatter, reflection and duct propagation. It will be shown that reflection propagation dominates at the low frequency end. Whilst at higher frequencies, very sharp layers are required for reflection propagation. At these frequencies, high signals are generally caused by duct propagation. 1.1 Instruments and plan for the experiments. The radio measurements were performed with the following equipment. 5000 MHz: Transmitted power 500 kW (pulsed). Reflector antennas. Free space field strength over the path + 15 dBm. 460 MHz: Transmitted power 10 W (CW) 8 element Yagi antennas. Free space field strength over the path - 65 dBm. 170 MHz: Transmitted power 10, W(CW). 8 element Yagi antennas. Free space field strength over the path - 60 dBm. The antenna heights for the transmitters and receivers were 100 m above sea level. The field strengths were recorded on ink recorders and simul- taneously sampled, digitized and evaluated on line in a minicom- puter. For the meteorological measurements, the following equipment were used: Airborne microwave refractometer and thermistor, flown up to 2000 m.

P. J. MESSAGE University of Liverpool The papers which comprise this volume were presented at Colloquium No. 41 of the International Astronimical Union, which was held in Cambridge, England, from the 17th to the 19th of August, 1976, and had as its subject 'Dynamics of Planets and Satellites and Theories of their Motion'. The Colloquium was held just prior to the XVIth General Assembly of the Union (which was held from 24th August to 2nd September, in Grenoble, France) to provide an opportunity for the presentation of research papers on a number of active and lively branches of Celestial Mechanics to a gathering of experts in the field, and for the stimulus of discussion of research problems of interest to participants. A number of papers testify to the progress being made in General Planetary Theory, the theories of motion of the minor planets, the Moon, and the satellites of Jupiter and Saturn, and to significant advances in both the general and restricted gravitational problems of three bodies. The Organizing Committee of the Colloquium was comprised of J. Chapront, R. L. Duncombe, J. Hadjidemetriou, Y. Kozai, B. Morando, J. Schubart, V. Szebehely, and P. J. Message (Chairman). The local Organizer was D. C. Heggie, to whose tireless efforts the success of the arrangements is due. IX LIST OF PARTICIPANTS N. Abu-el-Ata, Bureau des Longitudes, 77 Avenue Denfert Rochereau, 75014 Paris, France K. Aksnes, Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, U. S. A.

The subjects of resonance and stability are closely related to the problem of evolution of the solar system. It is a physically involving problem and the methods available to mathematics today seem unsatisfactory to produce pure non linear ways of attack. The linearization process in both subjects is clearly of doubtful significance, so that, even if very restrictive, numerical solutions are still the best and more valuable sources of informations. It is quite possible that we know now very little more of the entire problem that was known to Poincare, with the advantage that we can now compute much faster and with much more precision. We feel that the papers collected in this Symposium have contributed a step forward to the comprehension of Resonance, Periodic Orbits and Stability. In a field like this, it would be a surprise if one had gone a long way toward that comprehension, during the short time of two weeks. But we are sure that the joint efforts of all the scientists involved has produced and will produce a measurable acceleration in the process. If this is true it will be a great satisfaction to us that this has happened in Brasil. The Southern Hemisphere in America has now begun to participate actively in the Astro nomical Society and for this, we are grateful to everyone who has helped."

Spectral line formation theory is at the heart of astrophysical diagnostic. Our knowledge of abundances, in both stellar and interstellar contexts, comes almost enti rely from line analysis, as does a major fraction of our ability to model stellar atmospheres. As new facets of the universe become observable so the techniques of high reso lution spectroscopy are brought to bear, with great reward. Improved instruments, such as echelle spectrographs, employ ing detectors of high quantum efficiency, have revolutioned our ability to observe high quality line profiles, although until now this ability has been confined to the brightest stars. Fabry-Perot interferometers and their modern deriva tives are bringing new ranges of resolving power to studies of atomic and ionic interstellar lines, and of course radio techniques imply exceedingly high resolution for the cool interstellar medium of molecules and radicals. Telescopes in space are extending the spectral range of these types of observations. Already the Copernicus and IUE high resolution spectrographs have given us a tantalizing glimmer of what it will be like to obtain ultraviolet spectra with resolution and signal to noise ratio approaching those obtainable on the ground. Fairly soon Space Telescope will be producing high resolution spectroscopic data of unparal leled quali ty and distance range. As often happens in astro physics the challenge is now coming from the observers to the theorists to provide interpretational tools which are adequate to the state of the data."

IAU Symposium Number 52 on Interstellar Dust and Related Topics was held at Albany, N.Y., on the campus of the State University of New York at Albany from May 29 to June 2, 1972. The members of the Organizing Committee were: Dr A. D. Code, University of Wisconsin, Madison, Wis., U.S.A. Dr B. D. Donn, Goddard Space Flight Center, Greenbelt, Md., U.S.A. Dr A. Elvius, Stockholm Observatory, Saltsjobaden, Sweden. Dr T. Gehrels, Lunar and Planetary Laboratory, University of Arizona, Tucson, Ariz., U.S.A. Dr J. M. Greenberg (Chairman), State University of New York at Albany, Albany, N.Y., U.S.A. Dr H. C. van de Hulst, Sterrewacht, Leiden, Holland. Dr S. B. Pikel'ner, Sternberg Astronomical Institute, Moscow, U.S.S.R. Dr E. E. Sal peter, Cornell University, Ithaca, N.Y., U.S.A. Dr B. E. Turner, National Radio Astronomy Observatory, Charlottesville, Va., U.S.A. The suggestion was first made in 1971 that a symposium on interstellar grains would be timely. The response to the first preliminary announcement, which was sent out on November 29, 1971, was well beyond our expectations. The meeting was locally sponsored by the State University and by Dudley Observatory. The National Aeronautics and Space Administration and the National Science Foundation con tributed along with the JAU. There were 158 participants of whom 49 were from 15 countries outside the United States. A total of 92 papers were presented.