In this volume a survey of the most relevant nonlinear crack models is provided, with the purpose of analyzing the nonlinear mechanical effects occurring at the tip of macrocracks in quasi-brittle materials - such as concrete, rocks, ceramics, polymers, high-strength metallic alloys - and in brittle-matrix fibre-reinforced composites. Such local effects, as, for example, plastic deformation, yielding, strain-hardening, strain-softening, mechanical damage, matrix microcracking, aggregate debonding, fibre bridging, fibre slippage, crazing, and so on, are properly described through different simplified models, representing the peculiarities of the phenomena involved. The models are introduced and described separately and then compared in the last part of the book. This volume will be of interest to students, professionals and researchers in the field of nonlinear fracture mechanics.

CONJUGATED POLYMERS: THE IMTERPLAY BETWEEN SYNTHESIS, 1 STRUCTURE, AND PROPERTIES C. B. GORMAN and R. H. GRUBBS 1. Introduction 2 2. Structural Features of Conjuqated. Polyaers 3 3. Polymer Synthesis: Basic Methods 4 3. 1 Step-Growth Polymerization 5 3. 2 Chain-Growth Polymerization 6 3. 3 Rinq-Openinq Polymerization 8 4. Direct Synthetic Methods 8 4. 1 Electrochemical Synthesis 9 4. 2 Synthesis by Step-Growth Polymerization 11 4. 2. 1 Polyaniline (PAN) 11 4. 2. 2 Poly(Phenylene Sulfide) 12 4. 2. 3 Poly thiophene and its Derivatives 13 4. 2. 4 Other 5-membered Heterocyclic 16 Derivatives 4. 2. 5 Polyparaphenylene (PPP) 17 4. 2. 6 Polysilanes 18 4. 2. 7 Polymers of Phthalocyanines 19 4. 2. 8 Other Conjugated Metal Coordination 20 Polymers 4. 2. 9 Ladder Polymers 21 4. 3 The Unusual Topochemical Polymerization to 23 form Polydiacetylenes 4. 4 Chain-Growth Polymerizations 24 4. 4. 1 Polyacetylene via Ziegler-Natta 24 Polymerization 4. 4. 2 Ring-Opening Metathesis Polymerization 26 Routes to Polyacetylenes 5. Polymers fro. precursors 27 5. 1 Polyparaphenylene (PPP) 27 5. 2 Poly(Phenylene Vinylene) (PPV) and Other 28 Vinylene Polymers 5. 3 Precursors to Polyacetylene 29 6. Extentions of these Methods in the Synthesis of 31 *saall-Bandqap* Pplymers 7. Conjuqated. Polymer Matrices 33 8. Conclusions and Caveats 35 Acknowled. qements 36 References 36 vi TABLE OF CONTENTS PROPERTIES OF HIGHLY CONDUCTIHG POLYACETYLEHE 49 Th. SCHIMMEL, D. GLASER, M. SCHWOERER AND H. NAARMANN 1. Introduction 50 2. SBIlpie Synthesis, lIorphology and Properties 52 2.

It has been ten years since I presented the paper entitled "A new model and theory on yield and failure of materials under the complex stress state" at the Sixth Conference on Mechanical Behaviour of Materials held at Kyoto, Japan in 1991. The proceedings edited by Jono and Inoue were published by Pergamon Press in 1991. At that conference Professor Murakami and I were invited to act as the chairperson and co-chairperson of a session, and I presented the paper at another session. Few days before the conference, I had given a seminar regarding the tw- shear strength theory and the unified strength theory at Nagoya Technological University. These were the first two presentations of the unified strength theory, although I had completed the research of the unified strength theory in 1990. The paper "Twin-shear strength theory and its generalization" was published in the English edition of Sciences in China, the top journal in China, in 1985. The th original generalized twin-shear strength theory was presented at the 16 International Theoretical and Applied Mechanics Congress held at Copenhagen in Denmark and MPA (MaterialPrufungsAnstalt) at Stuttgart University, Germany in 1984. After this Congress I visited the MPA and School of Civil Engineering of Stuttgart University, and gave a seminar regarding the generalized twin-shear strength theory at MPA of Stuttgart University. Professor Otto Mohr (1835-1918) has had worked at the Stuttgart University. He was a very good professor, his lectures aroused great interest in his students."

Advanced composite materials have been a major research focus for the past forty years. As a reinforcement for conventional materials including glass, ceramics and polymers, carbon has proved to be the most successful. Carbon gives these materials flexibility so that they may be produced in bulk form with a wide variety of properties. Whereas carbon/carbon composites are the most effective materials in extreme temperature conditions. Application ranges from brakes to missile nose cones. Carbon Reinforcements and Carbon/Carbon Composites gives the present state on this subject in comprehensive form, as well as projections for other "High Tech" materials and their application.

Luminescence of Solids gathers together much of the latest work on luminescent inorganic materials and new physical phenomena. The volume includes chapters covering -- the achievements that have led to the establishment of the fundamental laws of luminescence -- light sources, light-dispersing elements, detectors, and other experimental techniques -- models and mechanisms -- materials preparation, and -- future trends. This international collection of cutting-edge luminescence research is complemented by over 170 illustrations that bring to life the text's many vital concepts.

Materials and Processes for Surface and Interface Engineering, which has been written by experts in the fields of deposition technology and surface modification techniques, offers up to date tutorial papers on the latest advances in surface and interface engineering. The emphasis is on fundamental aspects, principles and applications of plasma and ion beam processing technology. A handbook for the engineer and scientist as well as an introduction for students in several branches of materials science and surface engineering.

This volume contains papers presented at the NATO Advanced Research Workshop (ARW) on Photons and Local Probes. The workshop had two predecessors. The first was the NATO ARW on Near Field Optics, held in October 1992 at Arc et Senans and was organized by Daniel Courjon and Dieter Pohl. The other predecessor was a workshop on Photons and Scanning Probe Microscopies held at the University of Konstanz in July 1992. The workshop on Photons and Local Probes was held at the Loechnerhaus on the Reichenau Island at the Lake of Constance, from September 11 to 17, 1994. The Reichenau Island was an important place in Europe in the middle age. Even the tomb of one of the carolingian emperors, Charles the Fat, is located there. At this workshop more than 60 scientists from Europe and the United States met to communicate their latest results in the field of local probes in combination with optical techniques. In eight sessions 31 talks as well as 9 posters were presented. Among those 31 publications were submitted for publication in the NATO proceedings. They were accepted after a strict, but constructive refereeing process.

This volume is based on the proceedings of the NATO-sponsored Advanced Studies Institute (ASn on The New Superconducting Electronics (held 9-20 August 1992 in Waterville Valley, New Hampshire USA). The contents herein are intended to provide an update to an earlier volume on the same subject (based on a NATO ASI held in 1988). Four years seems a relatively short time interval, and our title itself, featuring The New Superconducting Electronics, may appear somewhat pretentious. Nevertheless, we feel strongly that the ASI fostered a timely reexamination of the technical progress and application potential of this rapid-paced field. There are, indeed, many new avenues for technological innovation which were not envisioned or considered possible four years ago. The greatest advances by far have occurred with regard to oxide superconductors, the so-called high transition-temperature superconductors, known in short as HTS. These advances are mainly in the ability to fabricate both (1) high-quality, relatively large-area films for microwave filters and (2) multilayer device structures, principally superconducting-normal-superconducting (SNS) Josephson junctions, for superconducting-quantum-interference-device (SQUID) magnetometers. Additionally, we have seen the invention and development of the flux-flow transistor, a planar three-terminal device. During the earlier ASI only the very first HTS films with adequate critical-current density had just been fabricated, and these were of limited area and had high resistance for microwave current."

In this volume there is set forth the text of the Pro ceedings of the Third International Conference on Sintering and Related Phenomena, which conference was held at the University of Notre Dame on June 5-7, 1972. This conference was the seventh in the series of University Conferences on Ceramic Science organized yearly by a happy "confederation" of four institutions; North Carolina State University, Raleigh, North Carolina; the University of California, Berkeley, California; Alfred University, Alfred, New York; and the University of Notre Dame, Notre Dame, Indiana. The 1972 Conference at Notre Dame was devoted to prob lems of sintering and allied phenomena. Previous gatherings at Notre Dame took place in 1954 and 1965. The proceedings of the first Notre Dame Conference were not published by reason of the conviction that a free forum similar in spirit to the Gordon Conferences should prevail. However, discus sions of the second Conference were preserved for posterity in a rather substantial volume (894 pp) published by Gordon and Breach in 1967. As the spirit of free exchange of ideas was not diminished by threat of publication of the revela tions of the second Notre Dame Conference, we deemed it just that the 1972 Proceedings be made public. Thus the present volume is a report upon progress realized in our science during the past six years.

This volume entitled "Protective Coatings and Thin Films : Synthesis, Characterization and Applications" contains the Proceedings of the NATO Advanced Research Workshop (ARW) held in Alvor, Portugal from May 30 to June 5, 1996. This NATO-ARW was an expert meeting on the surface protection and modification of solid materials subjected to interactions with the environment. The meeting attracted 10 key speakers, 40 contributing speakers and 3 observers from various countries. The existing knowledge and current status of the science and technology related to protective coatings and thin films were assessed through a series of oral presentations, key notes (titles underlined in the volume content) and contributed papers distributed over various sessions dealing with: (a) plasma-assisted physical and chemical vapor deposition processes to enhance wear and corrosion protection of materials, (b) low friction coatings operating in hostile environment (vacuum, space, extreme temperatures, . . . ), (c) polymer films for protection against mechanical damage and chemical attack, (d) characterization of the structure of films and correlations with mechanical properties, (e) wear and corrosion resistant thermal spray coatings, (f) functional gradient ceramic/metallic coatings produced by high energy laser beam and energetic deposition processes for high temperature applications, (g) protective coatings for optical systems, and (h) ion beam assisted deposition of coatings for protection of materials against aqueous corrosion.

Significant progress has been made in recent years in developing silicon nitride ceramics. The advances that have been achieved are mainly based on an increasing understanding of processing and microstructure-properties relationships. New analytical methods and high resolution transmission electron microscopy (HRTEM) coupled with extensive phase equilibria studies have provided new insights into the grain boundary region and offer the possibility to tailor the microstructure for specific applications. Because of the anticipated break-through in industrial applications there are still considerablt; research activities at industrial laboratories as well as other research centres. This volume presents the contributions to the international workshop "Tailoring ofHigh- Temperature Properties of Si3N4-Ceramics" with 60 participants from 12 countries held on 6th - 9th October 1993 at SchloB Ringberg in Germany, the conference site of the Max- Planck-Society. Additionally, it contains all invited papers of the International Conference "Silicon Nitride 93" held before the workshop on 4th - 6th October 1993 in Stuttgart/Germany. The book covers all recent research activities on silicon nitride ceramics and gives an overview with respect to recent developments.

FRANCIS W. HOLM 7102 Meadow Lane, Chevy Chase, MD 20815 The North Atlantic Treaty Organization (NATO) sponsored an Advanced Research Workshop (ARW) in Prague, Czech Republic, on 1-2 July 1996, to collect and study information on mobile alternative and supplemental demilitarization technologies and to report these fmdings. The mobile, or transportable, technologies identified for assessment at the workshop are alternatives to incineration technology for destruction of munitions, chemical warfare agent, and associated materials and debris. Although the discussion focused on the treatment of metal parts and explosive or energetic material, requirements for decontamination of other materials were discussed. The mobile alternative technologies are grouped into three categories based on process bulk operating temperature: low (0-200 C), medium (200-600 C), and high (600- 3,500 C). Reaction types considered include hydrolysis, biodegradation, electrochemical oxidation, gas-phase high-temperature reduction, stearn reforming, gasification, sulfur reactions, solvated electron chemistry, sodium reactions, supercritical water oxidation, wet air oxidation, and plasma torch technology. These categories represent a broad spectrum of processes, some of which have been studied only in the laboratory and some of which are in commercial use for destruction of hazardous and toxic wastes. Some technologies have been developed and used for specific commercial applications; however, in all cases, research, development, test, and evaluation (RDT &E) is necessary to assure that each technology application is effective for destroying chemical warfare materiel.

This book represents a collection of papers presented at the NATO Advanced Research Workshop (NATO/ARW) on "Science and Technology of Rapid Solidification and Processing", held at Hotel Thayer, West Point Military Academy, New York, N. Y. , during June 21-24, 1994. The workshop was attended by over forty scientists representing several NATO member countries as well as representatives from Japan, China (PRC), Taiwan and India. The purpose of this NATO/ARW conference was to review the major advances made in most recent years in both the theoretical and experimental areas of rapid solidification technology and processing. In accordance with the NATO/ARW format, the agenda for the conference was so arranged to offer in depth presentation of the latest developments in the subject area as well as to encourage follow-up discussions by the participants. There was seven sessions each opened with a lecture by an invited guest speaker. Sessions 1-4, covered two days of the conference and focused mainly on Processing Technologies of Rapid Solidification and Thermodynamic Properties (Practical Applications). Sessions 4-6 concentrated on Thermodynamics of Metastable Alloys, Relaxation, Diffusion, Magnetic and Electric Properties (Fundamentals). Session 6 was devoted to the Structural Characterization of Supercooled Melts, Ultra Fine Polycrystalline Materials (New Innovations and Techniques). There were two equally important aspects of this NATO/ARW conference which must be mentioned. Firstly, this is the first NATO/ARW conference on Science and Technology of Rapid Solidification and Processing held in the United States.

Catalysis and catalyst is a key technology to solve the problems in energy and environment issues to sustain our human society. We believe that comprehensive understanding of the catalysis and catalyst provides us a chance to develop a new catalyst and contributes greatly to our society. However, the ?eld of heterogeneous catalyst is dif?cultto study andstill stays behindmoredeveloped?elds ofchemistry such as organic and physical chemistries. This is a dilemma to the chemists who study the catalysis and catalyst. While we can accomplish the progress in the - dustrial application, the scienti?c understandingis not complete yet. A gap between the useful application and incomplete scienti?c understanding, however, becomes smaller and smaller in recent years. Because zeolites are ?ne crystals, and the structure is clearly known, the study on the catalysis using the zeolites is easier than those encountered in other catalysts such as metals and metal oxides. Very fortunately, zeolites provide us the strong acidity with the ?ne distribution which enables various useful catalytic reactions. When some metals and cations are loaded in close to the acid sites, these loadede- ments show extraordinarycharacters, and many catalytic reactions proceed thereon.

Recent advances in our understanding of complex composite media, especially chiral media for microwave applications, suggest the feasibility of creating novel materials with unusual properties and the possibility of constructing new microwave devices using such materials. The emphasis of the book is on bi-anisotropic materials, whose most interesting feature is the magnetoelectric interaction of the fields. The materials are expected to supply useful applications in radar technology, aerospace, microwave engineering, manufacturing technology, etc., such as absorbers for low-reflectivity shields, reciprocal phase shifters, polarization transformers. The first experiments with artificial bi-anisotropic media have been successfully carried out.

A survey of the machinery and science of the nanometer scale. Its twenty-two contributing authors, drawn from many different disciplines including atomic physics, microelectronics, polymer chemistry, and biophysics, delineate the course of current research and articulate a vision for the development of the nanometer frontiers in electronics, mechanics, chemistry, magnetics, materials, and biology. They reveal a world thirty years hence where motors are smaller than the diameter of a human hair; where single-celled organisms are programmed to fabricate materials with nanometer precision; where single atoms are used for computation, and where quantum chaos is the norm. Aimed at the level of at least a junior- or senior- level undergraduate in biology, chemistry, physics, or engineering.

When this publisher offered me the opportunity to \\Tite a book, some six years ago, I did not hesitate to say yes. I had just spent the last four years of graduate school struggling to understand the physics of strained quantum well lasers, and it seemed to me the whole experience was much more difficult that it should have been. For although many of the results I needed were easy to locate, the underlying physical premises and intervening steps were not. If only I had a book providing the derivations, I could have absorbed them and gone on my way. Such a book lies before you. It provides a unified and self-contained descrip tion of the essential physics of strained quantum well lasers, starting from first principles whenever feasible. The presentation I have chosen requires only the standard introductory background in quantum mechanics, solid state physics, and electromagnetics expected of entering graduate students in physics or elec trical engineering. A single undergraduate course in each of these subjects should be more than sufficient to follow the text. :'Iore advanced material on quantum mechanics is developed and collected in the first chapter. \Vhen pos sible, I have presented the results in a general setting and have later applied them to specific cases of interest. I find this the most satisfying way to ap proach the subject, and it has the additional benefit of solving many problems once and for all.

The purpose of Oxide-Based Fiber-Reinforced Ceramic-Matrix Composites is to provide comprehensive information on the most recent successful findings. The book consists of six chapters which characterize the current state of the art concerning oxide-based fiber-reinforced composites. Chapter one provides an introduction, examples of application areas and background information. Chapter two deals with the primary material properties for the areas of application and lists the possible constituent parts of the composites, depending on particular demands. Chapter three explains both the past and present fabrication methods which can affect the performance of the composites. Chapter four defines the interphase-related phenomena and describes the mechanical characteristics of the oxide-based fiber-reinforced composite, produced with different interphases. Chapter five deals with the fabrication route, functionality and mechanical characterization of the porous-matrix composites. The last chapter summarizes the present achievements and identifies requirements for reaching the goal, thereby providing a promising course for future research.

The photorefractive effect is now firmly established as one of the highest-sensitivity nonlinear optical effects, making it an attractive choice for use in many optical holographic processing applications. As with all technologies based on advanced materials, the rate of progress in the development of photorefractive applications has been principally limited by the rate at which breakthroughs in materials science have supplied better photorefractive materials. The last ten years have seen an upsurge of interest in photorefractive applications because of several advances in the synthesis and growth of new and sensitive materials. This book is a collection of many of the most important recent developments in photorefractive effects and materials. The introductory chapter, which provides the necessary tools for understanding a wide variety of photorefractive phenomena, is followed by seven contributed chapters that offer views of the state-of-the-art in several different material systems. The second chapter represents the most detailed study to date on the growth and photorefractive performance of BaTi03, one of the most important photorefractive ferroelectrlcs. The third chapter describes the process of permanently fixing holographic gratings in ferroelectrics, important for volumetric data storage with ultra-high data densities. The fourth chapter describes the discovery and theory of photorefractive spatial solitons. Photorefractive polymers are an exciting new class of photo refractive materials, described in the fifth chapter. Polymers have many advantages, primarily related to fabrication, that could promise a breakthrough to the marketplace because of ease and low-cost of manufacturing.

The discovery by J. G. Bednorz and K. A. Mtllier in 1986 that the superconducting state can exist in oxides at temperatures above 30 K stimulated research in the field of superconductivity and opened up a new field of research. Within a few years a large number of cuprate superconductors with transition temperatures well above the boiling point of liquid nitrogen have been found. The possibility of using liquid nitrogen as coolant re-stimulated interest in power applications of supercon ductivity. In this book an overview of the known high-Te superconductors and their physical properties is presented. Aspects related to conductor fabrication and high-current applications are emphasised. The material should be suitable for use in graduate level courses on superconductivity. Researchers in the field may profit from the large number of tables and references describing its status at the end of 1997. An introduction to high-To superconductivity must be based on the fundamental physical principles of normal-state electrical conductivity and the well-known characteristics of conventional superconductors. In Chapter 2 this background is provided. Crystal structures, anisotropic properties and general trends of the critical temperatures of the cuprate superconductors are described in Chapters 3 and 4. The processing of superconductor powders addressed in Chapter 5 affects considerably the current-carrying capacity of high-T. wires. In Chapter 6 several fabrication techniques for superconducting wires are described. In addition, the factors limiting the transport critical currents ofhigh-Te wires are discussed.

Advances in Materials Science and Implant Orthopedic Surgery brings together experts from major university hospitals, materials scientists specializing in bio-materials, and development engineers working for implant manufacturers to address such issues as: mechanisms of fixation; foreign-body immune response; generation and consequences of ionic and wear debris; materials selection, design and manufacturing schemes; and surgical techniques to maximize the safety and efficacy of the devices.

Blends of natural rubber with speciality synthetic rubbers, such as nitrile rubber and ethylene propylene rubbers, have, in the past, failed to combine the best properties of polymers, resulting in a poor return in terms of added value from the blending process. The idea of blending synthetic rubbers with natural rubbe is certainly not a new one, but it is only now that this can be shown to be possible with consistently positive resluts, but eh use of novel techniques which this book describes, giving valuable information on the technology required and the results which can be achieved. Blends of Natural Rubber is an invaluable source of information for all those working in the area of rubber technology and polymer blend technology.

Based on chaos theory two very important points are clear: (I) random looking aperiodic behavior may be the product of determinism, and (2) nonlinear problems should be treated as nonlinear problems and not as simplified linear problems. The theoretical aspects ofchaos have been presented in great detail in several excellent books published in the last five years or so. However, while the problems associated with applications of the theory-such as dimension and Lyapunov exponentsestimation, chaosand nonlinear pre diction, and noise reduction-have been discussed in workshops and ar ticles, they have not been presented in book form. This book has been prepared to fill this gap between theory and ap plicationsand to assist studentsand scientists wishingto apply ideas from the theory ofnonlinear dynamical systems to problems from their areas of interest. The book is intended to be used as a text for an upper-level undergraduate or graduate-level course, as well as a reference source for researchers. My philosophy behind writing this book was to keep it simple and informative without compromising accuracy. I have made an effort to presentthe conceptsby usingsimplesystemsand step-by-stepderivations. Anyone with an understanding ofbasic differential equations and matrix theory should follow the text without difficulty. The book was designed to be self-contained. When applicable, examples accompany the theory. The reader will notice, however, that in the later chapters specific examples become less frequent. This is purposely done in the hope that individuals will draw on their own ideas and research projects for examples.

This seriesofbooks, which is publishedattherateofaboutoneper year, addresses fundamental problems in materialsscience.Thecontents coverabroadrangeoftopicsfromsmallclustersofatomstoengineering materials and involve chemistry, physics, materials science, and engineering,withlengthscalesrangingfromAngstromsuptomillimeters. Theemphasis is on basic scienceratherthan on applications. Each book focuses on a single areaofcurrent interest and brings together leading experts to give an up-to-date discussion oftheir work and the workof others. Each articlecontainsenough references thattheinterestedreader can access the relevant literature. Thanks are given to the Center for Fundamental Materials Research at Michigan State University for supportingthisseries. M.F.Thorpe,SeriesEditor E-mail:[email protected] EastLansing,Michigan,November2002 v PREFACE ThisvolumerecordsinvitedlecturesgivenattheNewThermoelectric(TE)Materials Workshopheld inTraverseCity,MichiganfromAugust17-21,2002.Thethemeofthe workshop was Chemistry, PhysicsandMaterials ScienceofThermoelectric Materials: Beyond Bismuth Telluride. The objective of this symposium was threefold. First, to examine and assess the ability of solid state chemistry to produce new generation materials for TE applications. Second, to rationalize and predict the charge and heat transportpropertiesofpotentialcandidatesandhypotheticalsystemsthroughsolidstate theoryandexperiment.Third,toidentifyandprioritizeresearchneededtoreachvarious levelsofrequirementsintermsofZTandtemperature.Theseobjectiveswereaddressed by a series of invited talks and discussions by leading experts from academia, governmentlaboratories,andindustry. Thereweretwenty-twoinvitedandeightposterpresentations inthe workshop.Out ofthese,sixteeninvitedpresentationsarerepresentedinthisvolume.Theycoverawide range of subjects, starting from synthesis (based on different strategies) and characterizationofnovel materials to acareful studyoftheir transport properties and electronicstructure.Topicsaddressingtheissueofmakingnew materialsare: synthetic search for new materials (di Salvo et aI.) and synthetic strategies based on phase homologies (Kanatzidis). The different classes of materials covered are: bismuth nanowires (Dresselhausetal.), unconventional high-temperaturethermoelectrics, boron carbides (Aselage et aI.) , layered cobalt oxides (Fujii et aI.), early transition metal antimonides(KleinkeetaI.),skutterudites(Uher),andclathratethermoelectrics(Nolas).

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.