Following the biannual meetings in MUnster (1977) and Stanford (1979) the Third International Conference on Secondary Ion Mass Spectroscopy was held in Budapest from August 31 to September 5, 1981. The Conference was attended by about 250 participants. The success of the 1981 Conference in Budapest was especially due to the excellent preparation and organization by the Local Organizing Committee. We would also like to acknowledge the generous hospitality and cooperation of the Hungarian Academy of Sciences. Japan was chosen to be the location for the next conference in 1983. SIMS conferences are devoted to two main issues: improving the application of SIMS in different and especially new fields, and understanding the ion formation process. Needless to say, there is a very strong interaction be tween these two issues. The major reason for the rapid increase in SIMS activities in the last few years is the fact that SIMS is a powerful tool for bulk, thin-film, and surface analysis. Today it is extensively and successfully applied in such different fields as depth profiling and imaging of semiconductor devices, in isotope analysis of minerals, in imaging biological tissues, in the study of catalysts and catalytic reactions, in oxide-layer analysis on metals in drug detection, and in the analysis of body fluids.

Powders have been studied extensively because they arise in a wide variety of fields, ranging from soil mechanics to manufacture of pharmaceuticals. Only recently, however, with the deepening understanding of fractals, chaos, 1/f noise, and self-organization, has it been useful to study the mechanical properties of powders from a fundamental physical perspective. This book collects articles by some of the foremost researchers in the field, including chapters on: the role of entropy in the specification of a powder, by S.F. Edwards (Cambridge); discrete mechanics, by P.K. Haff (Duke); computer simulations of granular materials, by G.C. Barker (Norwich); pattern formation and complexity in granular flow, by R.P. Behringer and G.W. Baxter (Duke); avalanches in real sand piles, by A. Mehta (Birmingham); micromechanical models of failure, by M.J. Adams (Unilever) and B.J. Briscoe (Imperial College); mixing and segregation in particle flows, by J. Bridgwater (Birmingham); and hard-sphere colloidal suspensions, by P. Bartlett (Bristol) and W. van Megen (Melbourne).

The history of low dimensional conductors goes back to the prediction, more than forty years ago, by Peierls, of the instability of a one dimensional metallic chain, leading to what is known now as the charge density wave state. At the same time, Frohlich suggested that an "ideal" conductivity could be associated to the sliding of this charge density wave. Since then, several classes of compounds, including layered transition metal dichalcogenides, quasi one-dimensional organic conduc tors and transition metal tri- and tretrachalcogenides have been extensively studied. The molybdenum bronzes or oxides have been discovered or rediscovered as low dimensional conductors in this last decade. A considerable amount of work has now been performed on this subject and it was time to collect some review papers in a single book. Although this book is focused on the molybdenum bronzes and oxides, it has a far more general interest in the field of low dimensional conductors, since several of the molybdenum compounds provide, from our point of view, model systems. This is the case for the quasi one-dimensional blue bronze, especially due to the availability of good quality large single crystals. This book is intended for scientists belonging to the fields of solid state physics and chemistry as well as materials science. It should especially be useful to many graduate students involved in low dimensional oxides. It has been written by recognized specialists of low dimensional systems."

This book represents a collection of lectures presented at the NATO Advanced study Institute(ASI) on "Chemistry & Physics of the Molecular Processes in Energetic Materials," held at Hotel Torre Normanna, Altavilla Milicia, Sicily, Italy, September 3 to 15, 1989. The institute was attended by seventy participants including twenty lecturers, drawn from thirteen countries. The purpose of the institute was to review the major ad vances made in recent years in the theoretical and experi mental aspects of explosives and propellants. In accordance with the format of the NATO ASI, it was arranged to have a relatively small number of speakers to present in depth, re view type lectures emphasizing the basic research aspects of the subject, over a two week period. Most of the speakers gave two lectures, each in excess of one hour with addition al time for discussions. The scope of the meeting was limit ed to molecular and spectroscopic studies since the hydro dynamic aspects of detonation and various performance crite ria of energetic materials are often covered adequately in other international meetings. An attempt was made to have a coherent presentation of various theoretical, computational and spectroscopic approaches to help a better understanding of energetic materials from a molecular point of view. The progress already made in these areas is such that structure property (e. g."

This book presents an account of the NATO Advanced Study Institute on "Energy Transfer Processes in Condensed Matter," held in Erice, Italy, from June 16 to June 30, 1983. This meeting was organized by the International School of Atomic and Molecular Spectroscopy of the "Ettore Majorana" Centre for Scientific Culture. The objective of the Institute was to present a comprehensive treatment of the basic mechanisms by which electronic excitation energy, initially localized in a particular constituent or region of a condensed material, transfers itself to the other parts of the system. Energy transfer processes are important to such varied .fields as spectroscopy, lasers, phosphor technology, artificial solar energy conversion, and photobiology. This meeting was the first encounter of this sort entirely dedicated to this important topic. A total of 65 participants came from 47 laboratories and 16 nations (Belgium, Czechoslovakia, F.R. of Germany, France, Greece, India, Ireland, Israel, Italy, The Netherlands, Poland, Portugal, Switzerland, Turkey, United Kingdom, and the United States of A America). The secretaries of the course were: Ms. Aliki Karipidou for the scientific aspects and Mr. Massimo Minella for the admini strative aspects of the meeting."

One of the ultimate goals of materials research is to develop a fun damental and predictive understanding of the physical and metallurgical properties of metals and alloys. Such an understanding can then be used in the design of materials having novel properties or combinations of proper ties designed to meet specific engineering applications. The development of new and useful alloy systems and the elucidation of their properties are the domain of metallurgy. Traditionally, the search for new alloy systems has been conducted largely on a trial and error basis, guided by the skill and intuition of the metallurgist, large volumes of experimental data, the principles of 19th century thermodynamics and ad hoc semi-phenomenological models. Recently, the situation has begun to change. For the first time, it is possible to understand the underlying mechanisms that control the formation of alloys and determine their properties. Today theory can begin to offer guidance in predicting the properties of alloys and in developing new alloy systems. Historically, attempts directed toward understanding phase stability and phase transitions have proceeded along distinct and seemingly diverse lines. Roughly, we can divide these approaches into the following broad categories. 1. Experimental determination of phase diagrams and related properties, 2. Thermodynamic/statistical mechanical approaches based on semi phenomenological models, and 3. Ab initio quantum mechanical methods. Metallurgists have traditionally concentrated their efforts in cate gories 1 and 2, while theoretical physicists have been preoccupied with 2 and 3."

Relaxation phenomena of excited molecular states are abundant in all nature. They mediate such key processes as photochemical reactions or even the pathways of ordinary chemical reactions. However, for a long time the main research in electronic relaxation processes was concerned with anorganic solids, in part because of their great technological importance (photography, semiconductors ... ) in part also because these compounds were the "workhorses" of the solid state physicists. In the last 30 years, there was a steadily increasing interest in organic molecular systems, first in molecular crystals and later in all forms of molecular solids (glasses, polymers, membranes, ... ). The present volume combines papers on quite different types of relaxation phenomena: the type of solid studied, the electronic states involved, the physical processes responsible for the relaxations are all different. Nevertheless, after reading this book, a more clear and complete picture of the phenomenon "relaxa tion" emerges that proves that this volume is more than just a collection of individual articles. The volume starts with the paper "Spin-lattice and spin-spin relaxation in photo-excited triplet states in molecular crystals" by Jan Schmidt. Even in these seemingly simple systems of isolated guest molecules in a single crystal host, the relaxation phenomena are quite involved and a very thorough investigation is necessary to find the key relaxation processes. The end of the article provides a bridge to the following paper: it treats interactions of two molecules (dimers), where resonant interactions become important and lead to new, characteristic relaxation processes."

The Fourth American Physical Society Topical Conference on Shock Waves in Condensed Matter was held in Spokane, Washington, July 22-25, 1985. Two hundred and fifty scientists and engineers representing thirteen countries registered at the conference. The countries represented included the United States of America, Australia, Canada, The People's Repub lic of China, France, India, Israel, Japan, Republic of China (Taiwan), United Kingdom, U. S. S. R, Switzerland and West Germany. One hundred and sixty-two technical papers, cov ering recent developments in shock wave and high pressure physics, were presented. All of the abstracts have been published in the September 1985 issue of the Bulletin of the American Physical Society. The topical conferences, held every two years since 1979, have become the principal forum for shock wave studies in condensed materials. Both formal and informal technical discussions regarding recent developments conveyed a sense of excitement. Consistent with the past conferences, the purpose of this conference was to bring together scientists and engineers studying the response of condensed matter to dynamic high pressures and temperatures. Papers covering experimental, theoretical, and numerical studies of con densed matter properties were presented. A noteworthy feature of this conference was the participation by several leading scientists engaged in static high pressure research. Donald Curran served as the Master of Ceremonies at the conference banquet, which was at tended by two hundred and seventy-five conference participants and guests including Dr. Samuel Smith, the new President of Washington State University. Dr.

Markedly apart from elementary particle physics, another current has been building up and cont i nuous ly growi ng within contemporary phys i cs for severa 1 decades, and even expanding into many other disciplines, especially chemistry, biology and, quite recently, economics. Several reasons account for this: presumably the most impor- tant one lies in the fact that, whatever the specific problem, model or material concerned, the same basic mathematical features are always involved. In this way, a general phenomenology has emerged which, unlike thermodynamics, is no longer depen- dent upon the details or specifics: what largely prevails is the nonlinear charac- ter of the underlying dynamics. Perhaps we are witnessing the emergence of a "non- linear physics" - in a way similar to the birth of "quantum physics" in the twen- ties - a physics which deals with the general behaviour of systems, whatever they are or may be. Over the past fifteen years, chemical systems evolving sufficiently far from equilibrium have proved to be particularly well fitted to experimental research on nonlinear behaviour: oscillation, multistability, birhythmicity, chaotic evolution, spatial self-organization and hysteresis are displayed by chemical reactions whose number is growing each year. In this volume are collected the lectures, communica- tions and posters (abstracts) presented at an international meeting entitled: "Non-Equilibrium Dynamics in Chemical Systems", held in Bordeaux (France), Septem- ber 3 rd-lth, 1984.

The control of optical modes in microcavities or in photonic bandgap (PBG) materials is coming of age! Although these ideas could have been developed some time ago, it is only recently that they have emerged, due to advances in both atomic physics and in fabrication techniques, be it on the high-quality dielectric mirrors required for high-finesse Fabry Perot resonators or in semiconductor multilayer deposition methods. Initially the principles of quantum electro-dynamics (QED) were demonstrated in elegant atomic physics experiments. Now solid-state implementations are being investigated, with several subtle differences from the atomic case such as those due to their continuum of electronic states or the near Boson nature of their elementary excitations, the exciton. Research into quantum optics brings us ever newer concepts with potential to improve system performance such as photon squeezing, quantum cryptography, reversible taps, photonic de Broglie waves and quantum computers. The possibility of implementing these ideas with solid-state systems gives us hope that some could indeed find their way to the market, demonstrating the continuing importance of basic research for applications, be it in a somewhat more focused way than in earlier times for funding.

We present here the transcripts of lectures and talks which were delivered at the NATO ADVANCED STUDY INSTITUTE "Electronic Structure of Complex Systems" held at the State University of Ghent, Belgium during the period July 12-23, 1982. The aim of these lectures was to highlight some of the current progress in our understanding of the electronic structure of com plex systems. A massive leap forward is obtained in bandstructure calculations with the advent of linear methods. The bandtheory also profitted tremendously from the recent developments in the density functional theories for the properties of the interacting electron gas in the presence of an external field of ions. The means of per forming fast bandstructure calculations and the confidence in the underlying potential functions have led in the past five years or so to a wealth of investigations into the electronic properties of elemental solids and compounds. The study of the trends of the electronic structure through families of materials provided invalu able insights for the prediction of new materials. The detailed study of the electronic structure of specific solids was not neglected and our present knowledge of d- and f-metals and metal hydrides was reviewed. For those systems we also investi gated the accuracy of the one electron potentials in fine detail and we complemented this with the study of small clusters of atoms where our calculations are amenable to comparison with the frontiers of quantum chemistry calculations."

Message from The Taniguchi Foundation Dr. Kanamori, Distinguished Guests and Friends: The Taniguchi Foundation wishes to welcome the participants of the nine teenth International Symposium on the Theory of Condensed Matter, who have come from within this country and from different parts of the world. The concept of the symposium is unique in that participants, both Japanese and from abroad, are limited in number to small discussion groups, and live together, although for a short period, as a close-knit community. We feel that this kind of environment will assist towards the strengthening of understanding and the fostering of friendship among the attendees. It is easy to talk about, but difficult to realize, the ideal of international friendship and understanding in a world which is steadily growing smaller. So far, the Foundation has invited a total of 149 participants in this division from 24 foreign countries and 299 participants from Japan. And we are all friends. We hope and trust that even after they have reached the heights of academic fame during the coming decades, the participants will continue to join forces and help to forge closer bonds of friendship and cooperation that will make major contributions not only to academia, but also towards world peace and the welfare of mankind. We hope that all the participants will return home with warm memories of both this symposium and the pleasant times that we have shared. Thank you."

This book is a course of lectures given for senior students at the Moscow Institute of Physics and Technology. For those who have graduated in the USSR this information should beisufficient to give an idea of the level and the manner in which the subject matter is presented. On the other hand, readers outside of this country may never have heard about this well-known Sgviet institution, and so we would like to say few words about it now. The Moscow Institute of Physics and Technology (MFTI or Fiztekh) was founded in 1947 as the result of a special directive of Stalin in order to supply the space and nuclear program with highly educated experts. The best scientists in the country were involved in the foundation process. They invented an effective and flexible educational system that includes basic education accord ing to an university program followed by specialization at lead ing scientific centers. Being organized initially as a department of Moscow State University, MFTI recently separated into an inde pendent institution. In the sixties it lost its mainly top secret and military character and became the most prestigious place in the country for an education in physics. The political changes of the last few years have opened it to contacts with other countries. The course of lectures comprising this book is dedicated to the subject of the intense resonant interaction of laser radiation. with matter and contains a significant part of the Ph. D."

Understanding the origin of spatio-temporal order in open systems far from thermal equilibrium and the selection mechanisms of spatial struc tures and their symmetries is a major theme of present day research into the structures of continuous matter. The development of methods for pro ducing spatially ordered microstructures in solids by non-equilibrium methods opens the door to many technological applications. It is also be lieved that the key to laminar/turbulence transitions in fluids lies in the achievement of spatio-temporal order. Let us also emphasize the fact that the idea of self-organization in it self is at the origin of a reconceptualisation of science. Indeed, the appear ance of order which usually has been associated with equilibrium phase transitions appears to be characteristic of systems far from thermal equi librium. This phenomenon which was considered exceptional at first now the rule in driven systems. The chemical oscillations obtained appears to be in the Belousov-Zhabotinskii reaction were initially considered to be ther modynamically impossible and were rejected by a large number of chemists. Now these oscillations and related phenomena (waves, chaos, etc. ) are the subject of intensive research and new classes of chemical oscil lators have been recently discovered. Even living organisms have long been considered as the result of chance rather than necessity. Such points of view are now abandoned under the overwhelming influence of spatio-tem poral organization phenomena in various domains ranging from physics to biology via chemistry, nonlinear optics, and materials science ."

"Granular Gases" are diluted many-particle systems in which the mean free path of the particles is much larger than the typical particle size, and where particle collisions occur dissipatively. The dissipation of kinetic energy can lead to effects such as the formation of clusters, anomalous diffusion and characteristic shock waves to name but a few. The book is organized as follows: Part I comprises the rigorous theoretical results for the dilute limit. The detailed properties of binary collisions are described in Part II. Part III contains experimental investigations of granular gases. Large-scale behaviour as found in astrophysical systems is discussed in Part IV. Part V, finally, deals with possible generalizations for dense granular systems.

The articles in this book have been selected from the lectures of a NATO Advanced Study Institute held at Bad Lauterberg (Germany) in August 1995. Internationally well-known researchers in the field of mesoscopic quantum physics provide insight into the fundamental physics underlying the mesoscopic transport phenomena in structured semiconductor inversion layers. In addition, some of the most recent achievements are reported in contributed papers. The aim of the volume is not to give an overview over the field. Instead, emphasis is on interaction and correlation phenomena that turn out to be of increasing importance for the understanding of the phenomena in the quantum Hall regime, and in the transport through quantum dots. The present status of the quantum Hall experiments and theory is reviewed. As a "key example" for non-Fermi liquid behavior the Luttinger liquid is introduced, including some of the most recent developments. It is not only of importance for the fractional quantum Hall effect, but also for the understanding of transport in quantum wires. Furthermore, the chaotic and the correlation aspects of the transport in quantum dot systems are described. The status of the experimental work in the area of persistent currents in semiconductor systems is outlined. The construction of one of the first single-electron transistors is reported. The theoretical approach to mesoscopic transport, presently a most active area, is treated, and some aspects of time-dependent transport phenomena are also discussed.

This is a book describing electronic structure theory and application within the framework of a methodology implemented in the computer code RSPt. In 1986, when the code that was to become RSPt was developed enough to be useful, it was one of the ?rst full-potential, all-electron, relativistic implem- tations of DFT (density functional theory). While RSPt was documented p- asitically in many publications describing the results of its application, it was many years before a publication explicitly describing aspects of the method appeared. In the meantime, several excellent all-electron, full-potential me- ods had been developed, published, and become available. So why a book about RSPt now? The code that became RSPt was initially developed as a personal research tool, rather than a collaborative e?ort or as a product. As such it required some knowledge of its inner workings to use, and as it was meant to be m- imally ?exible, the code required experience to be used e?ectively. These - tributes inhibited, but did not prevent, the spread of RSPt as a research tool. While applicable across the periodic table, the method is particularly useful in describing a wide range of materials, including heavier elements and c- pounds, and its ?exibility provides targeted accuracy and a convenient and accurate framework for implementing and assessing the e?ect of new models.

More than a decade ago, because of the phenomenal growth in the power of computer simulations, The University of Georgia formed the first institutional unit devoted to the use of simulations in research and teaching: The Center for Simulational Physics. As the simulations community expanded further, we sensed a need for a meeting place for both experienced simulators and neophytes to discuss new techniques and recent results in an environment which promoted extended discussion. As a consequence, the Center for Sim ulational Physics established an annual workshop on Recent Developments in Computer Simulation Studies in Condensed Matter Physics. This year's workshop was the twelfth in this series. It was held at The University of Geor gia, March 8-12, 1999 as an unofficial satellite conference to the Centennial Meeting of the American Physical Society in Atlanta, GA. The continued interest shown by the scientific community demonstrates quite clearly the useful purpose which the series has served. These proceedings provide a "sta tus report" on a number of important topics. This volume is published with the goal of timely dissemination of the material to a wider audience. We wish to offer special thanks to IBM Corporation for their generous support of this year's workshop. This volume contains both invited papers and contributed presentations on problems in both classical and quantum condensed matter physics. We hope that each reader will benefit from specialized results as well as profit from exposure to new algorithms, methods of analysis, and conceptual devel opments."

Oaxaca, Mexico, was the place chosen by a large international group of scientists to meet and discuss on the recent advances on the understanding of the physical prop- ties of low dimensional systems; one of the most active fields of research in condensed matter in the last years. The International Symposium on the Physics of Low Dim- sions took place in January 16-20, 2000. The group of scientists converging into the historical city of Oaxaca, in the state of the same name, had come from Argentina, Chile, Venezuela, several places in Mexico, Canada, U. S. A. , England, France, Italy, Germany, Russia, and Switzerland. The presentations at the workshop provided sta- of-art reviews of many of the most important problems, currently under study. Equally important to all the participants in the workshop was the fact that we had come to honor a friend, Hans Christoph Siegmann, on his sixty-fifth birthday. This Festschrift recognizes the intellectual leadership of Professor Siegmann in the field and as a sincere homage to his qualities as an exceptional friend, college and mentor. Those who have had the privilege to work closely with Hans Christoph have been deeply impressed by his remarkable analytic mind as well as by his out of range kindness and generosity. Hans Christoph has contributed to the understanding of the difficult and very important problem of the magnetic properties of finite systems: surfaces, thin films, heterostructures.

This book contains the proceedings of the International "Workshop on 3D Process Simulation which was held at the Campus of the University Erlangen-Nuremberg in Erlangen on September 5, 1995, in conjunction with the 6th International Conference on "Simulation of Semiconductor Devices and Processes (SISDEP 95). Whereas two-dimensional semiconductor process simulation has achieved a certain degree of maturity, three-dimensional process simulation is a newly emerging field in which most efforts are dedicated to necessary basic developments. Research in this area is promoted by the growing demand to obtain reliable information on device geometries and dopant distributions needed for three-dimensional device simulation, and challenged by the great algorithmic problems caused by moving interfaces and by the requirement to limit computation times and memory requirements. This workshop provided a forum to discuss the industrial needs, technical problems, and solutions being developed in the field of three-dimensional semiconductor process simulation. Invited presentations from leading semiconductor companies and research Centers of Excellence from Japan, the USA, and Europe outlined novel numerical algorithms, physical models, and applications in this rapidly emerging field.

This book covers the state of the art in the physics of small particles and clusters. It covers a wide range of topics from quantization of free clusters, laser spectroscopy of clusters, fullerenes, clusters on supporting surfaces and much more. The papers can also be found in Zeitschrift fur Physik D.

From July 20 till 31, 1981, the Advanced Study Institute on "Electron Correlations in Solids, Molecules and Atoms," sponsored by NATO, was held at the University of Antwerpen (U.I.A.), in the Conference Center Corsendonk. In the last few years, the problem of many-electron correlations has gained renewed attention, due to recent experimental and theoretic al developments. From the theoretical point of view, more sophisticated treatments of the homogeneous electron gas model evolved, including dynamical aspects of the electron correlation in the dielectric response. Furthermore, the homogeneous electron gas, which served as a model for simple metals, was extended to include spin- and charge-density waves and phasons. The concept of elementary excitations too was introduced not only in perfectly ordered metallic crystals, but also in magnetic alloys, in liquid metals and alloys, in semiconductors, and even in molecules and atoms. Fairly accurate quantitative calculations of these effects recently became possible, ranging from plasmon frequencies in atoms, over dielectric response of semiconduc tors and resistivity in magnetic alloys to electron-hole liquids and their phase separation. The recent technological evolution allowed for more accurate measurements in previously unaccessible domains, e.g. X-ray scatter ing and fast electron energy loss at large wavevector. Moreover, these new developments opened new perspectives in physics, accompany ing or even introducing the new concepts which also evolved in the theory."

This book is the third volume in an approximately annual series which comprises the proceedings of the International Workshops on Condensed Matter Theories. The first of these meetings took place in 1977 in Sao Paulo, Brazil, and successive workshops have been held in Trieste, Italy (1978), Buenos Aires, Argentina (1979), Caracas, Venezuela (1980), Mexico City, Mexico (1981), St. Louis, USA (1982), Altenberg, Federal Republic of Germany (1983), Granada, Spain (1984), San Francisco, USA (1985), and Argonne, USA (1986). The present volume contains the proceedings of the Eleventh Workshop which took place in Qulu, Finland during the period 27 July - 1 August, 1987. The original motivation and the historical evolution of the series of Workshops have been amply described in the preface to the first volume in the present series. An important objective throughout has been to work against the ever-present trend for physics to fragment into increasingly narrow fields of specialisation, between which communication is difficult. The Workshops have traditionally sought to emphasise the unity of physics. By bringing together scientists working in many different areas of condensed matter theory, for the dual purpose of fostering collaborations between them and promoting the exchange of ideas between various disciplines, a common language has been exposed and developed. The Editor of the first volume in the series, F. B.

Schafer gives a concise overview of the static equilibrium properties of polymer solutions. In the first part diagrammatic perturbation theory is derived from scratch. The second part illustrates the basic ideas of the renormalization group (RG). The crucial role of dilation invariance is stressed. The more efficient method of dimensional regularization and minimal subtractions is worked out in part three. The fourth part contains a unified evaluation of the theory to the one loop level. All the important experimental quantities are discussed in detail, and the results are compared extensively to experiment. Empirical methods of data analysis are critically discussed. The final (fifth) part is devoted to extensions of theory. The first three parts of this book may serve as the basis of a course. Parts four and five are hoped to be useful for detailed quantitative evaluations of experiments.

The 6th course of the futernational School of Solid State Physics was held in Erice, Sicily, at the Ettore Majorana Centre for Scientific Culture, 19-29 June, 1995. The course was organized as a NATO Advanced Study Institute and received generous support from NATO's Nanoscale Science Program. This volume is based on the lectures presented during the course. fudispensable for the planning of the summer school was the support of the Director of the Ettore Majorana Centre, Professor A. Zichichi. We wish to express our sincere appreciation to the center staff, Dr. Maria Zaini, Dr. Alberto Gabriele, Dr. Pinola Savalli and Dr. Jerry Pilarski for their expert assistance in all organizational matters. A special word of thanks must go to the director of the International School of Solid State Physics, Professor Giorgio Benedek, not only for his valuable advice in the planning stage, but also for his active participation in the program itself. I would like to thank my coworkers, Stefan Frank, Nikola Malinowski, Renee Stotz, Frank Tast and Kristin Wirth for their valuable assistance in preparing these proceedings of the meeting. The success of a school is, in the last analysis, determined by the inter- est and commitment of the lecturers and participants. I am very grateful to the lecturers for their carefully prepared formal presentations, to the par- ticipants for their contributions to the spontaneous evening "workshops", and to all for their inexhaustible enthusiasm.