Telescopes and Techniques has proved itself in its first edition, having become probably one of the most widely used astronomy texts, both for numerate amateur astronomers and for astronomy and astrophysics undergraduates. The first and second editions of the book were widely used as set texts for introductory practical astronomy courses in many universities.
This book guides the reader through the mathematics, physics and practical techniques needed to use telescopes (from small amateur models to the larger instruments installed in many colleges) and to observe objects in the sky. Mathematics to around Advanced Placement standard (US) or A level (UK) is assumed, although High School Diploma (US) or GCSE-level (UK) mathematics plus some basic trigonometry will suffice most of the time. Most of the physics and engineering involved is described fully and requires no prior knowledge or experience.
This is a how to book that provides the knowledge and background required to understand how and why telescopes work. Equipped with the techniques discussed in this book, the observer will be able to operate with confidence his or her telescope and to optimize its performance for a particular purpose. In principle the observer could calculate his or her own predictions of planetary positions (ephemerides), but more realistically the observer will be able to understand the published data lists properly instead of just treating them as recipes. When the observer has obtained measurements, he/she will be able to analyze them in a scientific manner and to understand the significance and meaning of the results.
Telescopes and Techniques, 3rd Edition fills a niche at the start of an undergraduate astronomer s university studies, as shown by it having been widely adopted as a set textbook. This third edition is now needed to update its material with the many new observing developments and study areas that have come into prominence since it was published. The book concentrates on the knowledge needed to understand how small(ish) optical telescopes function, their main designs and how to set them up, plus introducing the reader to the many ways in which objects in the sky change their positions and how they may be observed. Both visual and electronic imaging techniques are covered, together with an introduction to how data (measurements) should be processed and analyzed. A simple introduction to radio telescopes is also included. Brief coverage of the most advanced topics of photometry and spectroscopy are included, but mainly to enable the reader to see some of the developments possible from the basic observing techniques covered in the main parts of the book."

This volume is a collection of papers presented at the Ninth International Symposium on "Ultrafast Processes in Spectroscopy" (UPS '95) held at the International Centre for Theo retical Physics (ICTP), Trieste (Italy), October 30 -November 3, 1995. These meetings have become recognized as the major forum in Europe for discussion of new work in this rapidly moving field. The UPS'95 Conference in Trieste brought together a multidisciplinary group of researchers sharing common interests in the generation of ultrashort optical pulses and their application to studies of ultrafast phenomena in physics, chemistry, material science, electronics, and biology. It was attended by approximately 250 participants from 20 countries and the five-day program comprises more than 200 papers. The progress of both technology and applications in the field of ultrafast processes during these last years is truly remarkable. The advent of all solid state femtosecond lasers and the extension of laser wavelengths by frequency conversion techniques provide a large variety of high-performance light sources for ultrashort pulses. With these sources ultrafast phenomena in physical, chemical and biological systems and in electronic de vi(:es are now studied extensively. Ultrafast technology is becoming one of the basic and common tools presently entering a wide variety of scientific fields not only for basic re search but also for promoting new applications in various areas. We feel that these pro ceedings vividly reflect the present status of the field.

The workshop on "Optical Properties of Low Dimensional Silicon sL Structures" was held in Meylan, France on March, I yd, 1993. The workshop took place inside the facilities of France Telecom- CNET. Around 45 leading scientists working on this rapidly moving field were in attendance. Principal support was provided by the Advanced Research Workshop Program of the North Atlantic Treaty Organisation (NATO). French Delegation a l'Armement and CNET gave also a small financial grant, the organisational part being undertaken by the SEE and CNET. There is currently intense research activity worldwide devoted to the optical properties of low dimensional silicon structures. This follow the recent discovery of efficient visible photoluminescence (PL) from highly porous silicon. This workshop was intended to bring together all the leading European scientists and laboratories in order to reveal the state of the art and to open new research fields on this subject. A large number of invited talks took place (12) together with regular contribution (20). The speakers were asked to leave nearly 1/3 of the time to the discussion with the audience, and that promoted both formal and informal discussions between the participants.

This volume contains the proceedings of a five-day NATO Advanced Research Workshop "On Three Levels, the mathematical physics of micro-, meso-, and macro phenomena," conducted from July 19 to 23 in Leuven, Belgium. The main purpose of the workshop was to bring together and to confront where relevant, classical and quantum approaches in the rigorous study of the relation between the various levels of physical description. The reader will find here discussions on a variety of topics involving a broad range of scales. For the micro-level, contributions are presented on models of reaction-diffusion pro cesses, quantum groups and quantum spin systems. The reports on quantum disorder, the quantum Hall effect, semi-classical approaches of wave mechanics and the random Schrodinger equation can be situated on the meso-level. Discussions on macroscopic quantum effects and large scale fluctuations are dealing with the macroscopic level of description. These three levels are however not independent and emphasis is put on relating these scales of description. This is especially the case for the contributions on kinetic and hydrodynamicallimits, the discussions on large deviations and the strong and weak coupling limits. The advisory board was composed of J.L. Lebowitz, J.T. Lewis and E.H. Lieb. The organizing committee was formed by Ph.A. Martin, G.L. Sewell, E.R. Speer and A.

This volume contains the proceedings of the University of Miami Workshop on the subject of "Electronic Structure and Mechanisms for High Temperature Super conductivity". The workshop was held at the James L. Knight Physics Building on the campus of the University of Miami, Coral Gables, 3-9 January 1991. Some 106 scientists from 12 countries attended this workshop, most of whom presented either invited or contributed papers. The reader will find in this volume a series of papers discussing the most im portant experimental and theoretical developments as of winter/spring 1990/1991. Despite more than four years of intensive research on high-T materials, there has c been considerable controversy both with respect to the interpretation of experiment and even more so in connection with the construction of an appropriate theory. In this regard, workshops such as this, gathering scientists with many viewpoints, and varying specialization, and fostering constructive discussions, are important in the de velopment of a common ground. Of major concern in the present context were the basic physical processes involved in high-temperature superconductivity.

This Festschrift is an outgrowth of a collection of papers presented as a conference in honor of Professor Heinz K. Henisch on his sixty-fifth birthday held at the Institute for Amorphous Studies. Bloomfield Hills. Michigan. It is our great pleasure to be editors of the Festschrift volume to honor Heinz and his work. Professor Henisch has a long and distinguished career and has many accomplishments in semiconductor materials and devices. He has made seminal contributions to the understanding of semiconductor switching devices and contact properties. He has an outstandin~ reputation as an expositor of science. His seminars and lectures are always deep. lucid and witty. He received his doctorate in Physics from the University of Reading and then joined the faculty. In 1963. he accepted a position in the Department of Physics at Pennsylvania State University. While at Penn State. Dr. Henisch broadened his research interest to include the History of Photography. At the present time. Dr. Henisch holds parallel appointments as a Professor of Physics and a Professor of the History of Photography at Pennsylvania State University. He is a Fellow of the American Physical Society. the Institute of Physics. London. the Royal Photographic society and is a Corresponding Member of the Deutsche Gesellschaft fur Photographie. In addition to his considerable publication in the fields of physics and the history of photography. Dr. Henisch is the founder and editor of the Journal of the History of Photography published quarterly by Taylor and Francis. Ltd .. London.

Techniques for the preparation of condensed matter systems have advanced considerably in the last decade, principally due to the developments in microfabrication technologies. The widespread availability of millikelvin temperature facilities also led to the discovery of a large number of new quantum phenomena. Simultaneously, the quantum theory of small condensed matter systems has matured, allowing quantitative predictions. The effects discussed in Quantum Dynamics of Submicron Structures include typical quantum interference phenomena, such as the Aharonov-Bohm-like oscillations of the magnetoresistance of thin metallic cylinders and rings, transport through chaotic billiards, and such quantization effects as the integer and fractional quantum Hall effect and the quantization of the conductance of point contacts in integer multiples of the `conductance quantum'. Transport properties and tunnelling processes in various types of normal metal and superconductor tunnelling systems are treated. The statistical properties of the quantum states of electrons in spatially inhomogeneous systems, such as a random, inhomogeneous magnetic field, are investigated. Interacting systems, like the Luttinger liquid or electrons in a quantum dot, are also considered. Reviews are given of quantum blockade mechanisms for electrons that tunnel through small junctions, like the Coulomb blockade and spin blockade, the influence of dissipative coupling of charge carriers to an environment, and Andreev scattering. Coulomb interactions and quantization effects in transport through quantum dots and in double-well potentials, as well as quantum effects in the motion of vortices, as in the Aharonov-Casher effect, are discussed. The status of the theory of the metal-insulator and superconductor-insulator phase transitions in ordered and disordered granular systems are reviewed as examples in which such quantum effects are of great importance.

The extensive use of low-energy accelerators in non-nuclear physics has now reached the stage where these activities are recognized as a natural field of investigation. Many other areas in physics and chemistry have undergone similarly spectacular development: beam foil spectroscopy in atomic physics, studies in atomic collisions, materials implantation, defects creation, nuclear microanalysis, and so on. Now, this most recent activity by itself and in its evident connec tion with the others has brought a new impetus to both the funda mental and the applied aspects of materials science. A summer school on "Material Characterization Using Ion Beams" has resulted from these developments and the realization that the use of ion beams is not restricted to accelerators but covers a wide energy range in the developing technology. The idea of the ion beam as a common denominator of many act1v1t1es dealing with surface and near-surface characterization was enthu siastically received by many scientists and a school on this subject received the positive endorsement of NATO. The Advanced Study Institute on Materials Science has assumed for us the status of an "institution" leading to better contact among the many laboratories engaged in this field. The fourth Institute in this series was held in Aleria, Corsica, between August 22 and September 12, 1976."

After an introduction by J.G. Bednorz, describing the discovery of high Tc superconductivity and its consequences, the book goes on to describe modern research, dealing with general problems, new materials and structures, phase separation, electronic homogeneities and related problems, and applications. Specific systems dealt with include the La-cuprates. the Bi-cuprates and the Y-cuprates and related compounds.

There have been many books published on scanning tunneling microscopy (STM), atomic force microscopy (AFM) and related subjects since Dr. Cerd Binnig and Dr. Heinrich Rohrer invented STM in 1982 and AFM in 1986 at IBM Research Center in Zurich, Switzerland. These two techniques, STM and AFM, now form the core of what has come to be called the 'scanning probe microscopy (SPM)' family. SPM is not just the most powerful microscope for scientists to image atoms on surfaces, but is also becoming an indispensable tool for manipulating atoms and molecules to construct man-made materials and devices. Its impact has been felt in various fields, from surface physics and chemistry to nano-mechanics, nano-electronics and medical science. Its influence will surely extend further as the years go by, beyond the reach of our present imagination, and new research applications will continue to emerge. This book, therefore, is not intended to be a comprehensive review or textbook on SPM. Its aim is to cover only a selected part of the active re search fields of SPM and related topics in which I have been directly involved over the years. These include the basic principles of STM and AFM, and their applications to fullerene film growth, SiC surface reconstructions, MBE (molecular beam epitaxy) growth of CaAs, atomic scale manipulation of Si surfaces and meso scopic work function."

When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the debate of critical issues in this still developing field. In this matter, I have been assisted greatly by the excellent series of articles provided by the different authors, who are widely recognized as some of the leaders in this vital area of research.

One of the major challenges of science in the last few years of the second millennium is learning how to design materials which can fulfill specific tasks. Ambitious as it may be, the possibilities of success are not ne li ble provided that all the different expertises merge to overcome the limits of eXIsting disciplines and forming new paradigms science. The NATO Advanced Research Workshop on "Magnetic Molecular Materials" was organized with the above considerations in mind in order to determine which are the most appropriate synthetic strategies, experimental techniques of investigation, and theoretical models which are needed in order to develop new classes of magnetic materials which are based on molecules rather than on metallic or ionic lattices. Why molecules? The answer may be obvious: molecular chemistry in principle fine can tune the structures and the properties of complex aggregates, and nature already provides a large number of molecular aggregates which can perform the most disparate functions. The contributions collected in this book provide a rather complete view of the current research accomplishments of magnetic molecular materials. There are several different synthetic approaches which are followed ranging from purely organic to inorganic materials. Some encouraging successes have already been achieved, even if the critical temperatures below which magnetic order is observed still are in the range requiring liquid helium.

The present-day semiconductor technology would be inconceivable without extensive use of Schottky barrier junctions. In spite of an excellent book by Professor E.H. Rhoderick (1978) dealing with the basic principles of metal semiconductor contacts and a few recent review articles, the need for a monograph on "Metal-Semiconductor Schottky Barrier Junctions and Their Applications" has long been felt by students, researchers, and technologists. It was in this context that the idea of publishing such a monograph by Mr. Ellis H. Rosenberg, Senior Editor, Plenum Publishing Corporation, was considered very timely. Due to the numerous and varied applications of Schottky barrier junctions, the task of bringing it out, however, looked difficult in the beginning. After discussions at various levels, it was deemed appropriate to include only those typical applications which were extremely rich in R&D and still posed many challenges so that it could be brought out in the stipulated time frame. Keeping in view the larger interest, it was also considered necessary to have the different topics of Schottky barrier junctions written by experts."

The application of magnetic resonance spectroscopy (MRS) to the cardiovascular system is a relatively new phenomenon. Its ability to noninvasively examine myocardial metabolism has led to its use to answer basic questions in animal models of normal and diseased myocardium. Extension of these investigations into the realm of human myocardial metabolism has been made possible by the advent of relatively high-field magnets with spectroscopy capabilities and sufficient bore dimensions to allow human studies. While ongoing and future studies promise to enhance our understanding of myocardial metabolism, their success will, in part, depend on a thorough understanding of the technical and biologic aspects of cardiovascular MRS, as well as the current state of research in the many areas encompassed by this discipline. It is with concept that the present monograph has been written. The organization and content should lend this book to both the beginning reader who is interested but not conversant in cardiovascular MRS, as well as to the active investigator who wishes to refer to a volume that deals with the many issues of this field in a concise but complete manner. The monograph is structured with a general overview of the field, followed by a section addressing the technical issues of cardiovascular MRS. The next section is devoted to biologic issues of both normal and abnormal myocardial metabolism, primarily devoted to investigations employing phosphorus-31. This is followed by a section dealing with more specialized issues, generally involving other nuclei such as protons, carbon, and sodium. Finally, the clinical applications of cardiovascular MRS are addressed.

The NATO Advanced Research Workshop on "Nanomagnetic Devices" was held in Miraflores de la Sierra, Madrid, Spain, from 14 to 19 September 1992. This book contains 21 invited articles related to suggestive and relevant aspects of Magnetism. The NATO Advanced Research Workshop was Co-directed by R.C. O'Handley, B. Heinrich and A. Hernando. The organisers as well as the participants are gratefully acknowledged to the NATO Science Committee. I also wish to thank the publishers for their advice and help in organizing the book. xi DESIDERATA OF STORAGE DEVICES C.E. YEACK-SCRANTON IBM Corporation, E02/005 5600 Cottle Road San Jose, CA 95139 USA ABSTRACT. Typical requirements on cost, capacity, and performance of today's magnetic storage devices and industry trends in these attributes are given. Scaling components, devices, and materials is shown to be a key factor in further improvement, Challenges to continued scaling are reviewed, particularly as they relate to magnetic nano-structures, materials, and characterization techniques.

This book is t~e fifth in aseries of scientific textbooks designed to cover advances in selected research fields from a basic and general view point. The reader is taken carefully but rapidly through the introductory material in order that t~e significance of recent developments can be understood with only limited initial knowledge. The inclusion in the Appendix of the abstracts of many of the more important papers in the field provides further assistance for the non-specialist, and acts as aspringboard to supplementary reading for those who wish to consult the original liter ature. Surface analysis has been the subject of numerous books and review articles, and the fundamental scientific principles of t~e more popular techniques are now reasonably weIl established. This book is concerned with the very powerful techniques of Auger electron and X-ray photoelectron spectroscopy (AES and XPS), with an emphasis on how they may be performed as part of a modern analytical facility. Since the development of AES and XPS in the late 1960s and early 1970s there have been great strides forward in the sensitivities and resolutions of the instrumentation. Simultaneously, these spectroscopies have undergone a veritable explosion, both in their acceptance alongside more routine ana1ytical techniques and in the range of problems and materials to which they are applied. As a result, many researchers in industry and in academia now come into contact with AES and XPS not as specialists, but as users.

The research of unitary concepts in solid state and molecular chemistry is of current interest for both chemist and physicist communities. It is clear that due to their relative simplicity, low dimensional materials have attracted most of the attention. Thus, many non-trivial problems were solved in chain systems, giving some insight into the behavior of real systems which would otherwise be untractable. The NATO Advanced Research Workshop on "Organic and Inorganic Low-Dimensional Crystalline Materials" was organized to review the most striking electronic properties exhibited by organic and inorganic sytems whose space dimensionality ranges from zero (Od) to one (1d), and to discuss related scientific and technological potentials. The initial objectives of this Workshop were, respectively: i) To research unitary concepts in solid state physics, in particular for one dimensional compounds, ii) To reinforce, through a close coupling between theory and experiment, the interplay between organic and inorganic chemistry, on the one hand, and solid state physics on the other, iii) To get a salient understanding of new low-dimensional materials showing "exotic" physical properties, in conjunction with structural features.

This volume contains the papers presented at the NATO Advanced Research Workshop on Localization and Propagation o[ Classical Waves in Random and Periodic Media held in Aghia Pelaghia, Heraklion, Crete, May 26- 30, 1992. The workshop's goal was to bring together theorists and experimentalists from two related areas, localization and photonic band gaps, to highlight their common interests. The objectives of the workshop were (i) to assess the state of-the-art in experimental and theoretical studies of structures exhibiting classical wave band gaps and/or localization, (ii) to discuss how such structures can be fabricated to improve technologies in different areas of physics and engineering, and (iii) to identify problems and set goals for further research. Studies of the propagation of electromagnetic (EM) waves in periodic and/or disordered dielectric structures (photonic band gap structures) have been and continue to be a dynamic area of research. Anderson localization of EM waves in disordered dielectric structures is of fundamental interest where the strong ei-ei interaction efFects entering the eIectron-localization are absent.

Semimagnetic semiconductors (SMSC) and diluted magnetic semiconductors (DMS) have in the past decade attracted considerable attention because they confer many new physical properties on both bulk materials and heterostructures. These new effects are due either to exchange interactions between magnetic moments on magnetic ions, or to exchange interactions between magnetic moments and the spin of the charge carrier. These effects vary with the transition metal (Mn, Fe, Co) or rare earth (Eu, Gd, etc) used and thus provide a range of different situations. The field is very large (zero gap, small gap, wide gap), and the magnetic properties also are very rich (paramagnetic spin glass, antiferromagnetism). These materials are very convenient for studying the magnetism (the magnetism is diluted) or the superlattices (SL) with a continuous change from type II SL to type III SL. This Course attempted to provide a complete overview of the topic. The participants of this summer school held in Erice came from ten countries and were from various backgrounds and included theoreticians, experimentalists, physicists, and chemists. Consequently, an attempt was made to make the Course as thorough as possible, but at the same time attention was devoted to basic principles. The lecturers, drawn from all the groups in the world involved in the field, were asked to be very didactic in their presentation. After two introductory lectures, Dr.

The Conference on the Science and Technology of Thin Film Superconductors was conceived in the early part of 1988 as a forum for the specialist in thin film superconductivity. The conference was held on November 14-18, 1988, in Co lorado Springs, Co lorado. Al though many excellent superconductivity conferences had been convened in the wake of the 1986-1987 discoveries in high temperature superconductivity, thin film topics were often dispersed among the sessions of a more general conference agenda. The response to the Conference on the Science and Technology of Thin Film Superconductors confirmed the need for an extended conference devoted to thin film superconductors. These proceedings are a major contribution to the technnology of thin film superconductivity because of the breadth and quality of the articles provided by leaders in the field. The proceedings are divided into articles on laser deposition, sputtering, evaporation, metal organic chemical vapor deposition, thick film, substrate studies, characterization, patterning and applications, and general properties. Most of the articles discuss scientific issues for high temperature thin film superconductors, although the conference was to be a forum for technology and scientific questions for both low and high temperature superconductivity. For the first day of the 5 day conference, Lawrence Berkeley Laboratory had organized an excellent set of short courses in superconduc t ing thin film devices.

The XIV International Workshop on Condensed Matter Theories has been held at the Elba International Physics Center (EIPC), Marciana Marina, Isola d'Elba, Italy, from 18-23 June, 1990. The Workshop started in 1977 in Sao Paolo, Brazil, as the 1st Pan American Workshop on Condensed Matter Theories, with the purpose of bringing together scientists from the Western countries, working in many different topics of Condensed Matter Theories, to facilitate exchanges of ideas and technologies from different areas as well as collaborations among the scientists. The next five Workshops were held at Trieste, Italy (1978), in Buenos Aires, Argentina ( 1979), in Caracas, Venezuela (1980), in Mexico City, Mexico (1981) and in St. Louis, Missouri, U. S. A. (1982). Given the international dimension reached by the Workshop, it was decided to extend it into an International Workshop, which was held for the first time in Altenberg, Germany (1983). The next editions took place in Granada, Spain (1984), San Francisco, California, U. S. A. (1985), Argonne, Illinois, U. S. A. (1986), Oulu, Finland (1987), Taxco, Mexico (1988) and Campos do Jordao, Brasil (1989). Many scientists have contributed to the development of the various editions of the Work shop. However, a particular mention has to be made to Profs. Manuel de Llano and Angel Plastino who initially proposed the Workshop and carried it forward, and to Prof. J . W. Clark, whose efforts have been of immense help to its recent developments.

The operation of semiconductor devices depends upon the use of electrical potential barriers (such as gate depletion) in controlling the carrier densities (electrons and holes) and their transport. Although a successful device design is quite complicated and involves many aspects, the device engineering is mostly to devise a "best" device design by defIning optimal device structures and manipulating impurity profIles to obtain optimal control of the carrier flow through the device. This becomes increasingly diffIcult as the device scale becomes smaller and smaller. Since the introduction of integrated circuits, the number of individual transistors on a single chip has doubled approximately every three years. As the number of devices has grown, the critical dimension of the smallest feature, such as a gate length (which is related to the transport length defIning the channel), has consequently declined. The reduction of this design rule proceeds approximately by a factor of 1. 4 each generation, which means we will be using 0. 1-0. 15 ). lm rules for the 4 Gb chips a decade from now. If we continue this extrapolation, current technology will require 30 nm design rules, and a cell 3 2 size < 10 nm , for a 1Tb memory chip by the year 2020. New problems keep hindering the high-performance requirement. Well-known, but older, problems include hot carrier effects, short-channel effects, etc. A potential problem, which illustrates the need for quantum transport, is caused by impurity fluctuations.

Soon after the discovery of quantum mechanics, group theoretical methods were used extensively in order to exploit rotational symmetry and classify atomic spectra. And until recently it was thought that symmetries in quantum mechanics should be groups. But it is not so. There are more general algebras, equipped with suitable structure, which admit a perfectly conventional interpretation as a symmetry of a quantum mechanical system. In any case, a "trivial representation" of the algebra is defined, and a tensor product of representations. But in contrast with groups, this tensor product needs to be neither commutative nor associative. Quantum groups are special cases, in which associativity is preserved. The exploitation of such "Quantum Symmetries" was a central theme at the Ad vanced Study Institute. Introductory lectures were presented to familiarize the participants with the al gebras which can appear as symmetries and with their properties. Some models of local field theories were discussed in detail which have some such symmetries, in par ticular conformal field theories and their perturbations. Lattice models provide many examples of quantum theories with quantum symmetries. They were also covered at the school. Finally, the symmetries which are the cause of the solubility of inte grable models are also quantum symmetries of this kind. Some such models and their nonlocal conserved currents were discussed.

Distinct scientific communities are usually involved in the three fields of quasi-crystals, of liquid crystals, and of systems having modulated crystalline structures. However, in recent years, there has been a growing feeling that a number of common problems were encountered in the three fields. These comprise the need to recur to "exotic" spaces for describing the type of order of the atomic or molecular configurations of these systems (Euclidian "superspaces" of dimensions greater than 3, or 4-dimensional curved spaces); the recognition that one has to deal with geometrically frustrated systems, and also the occurence of specific excitations (static or dynamic) resulting from the continuous degeneracies of the stable structures considered. In the view of discussing these problems, aNA TO-Advance Research Workshop has assembled in Preveza (Greece), in september 1989,50 experts of the three considered fields (with an equal proportion of theorists and experimentalists). 35 hours of conferences and discussions have led to a more detailed evaluation of the similarities and of the differences in the approaches implemented in the studies of the three types of systems. The papers contained in this NATO-series book provide the substance of this workshop. The reader will find three types of papers. Some very short papers giving the main ideas stated on a subject. Papers comprising 8-10 pages which stick closely to the contents of the talks presented. Longer papers providing more extensively the background and results relative to a given topic. It is worth summarizing the principal outputs of the workshop.