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- Volume 40, 2010
Annual Review of Materials Research - Volume 40, 2010
Volume 40, 2010
- Preface
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Biological Composites
Vol. 40 (2010), pp. 1–24More LessMost natural materials are composites based on biopolymers and some minerals. Despite the relative paucity of these constituents, their combination yields materials with outstanding properties and a great variation in functionality. A particular characteristic of biological composites is their multifunctionality. The basis for achieving this property is usually a complex hierarchical architecture in which an adaptation to the function(s) is possible at different structural levels. Only a few biological composites have been thoroughly studied from a materials science perspective; nacre is a prominent example. Fueled by the increasing interest in bioinspired materials research, biological composites are now studied more widely, and it has become apparent that Nature often solves materials problems in an unexpected way. This review discusses some striking examples. Many more are likely to emerge in the near future.
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On the Mechanistic Origins of Toughness in Bone
Vol. 40 (2010), pp. 25–53More LessOne of the most intriguing protein materials found in nature is bone, a material composed of assemblies of tropocollagen molecules and tiny hydroxyapatite mineral crystals that form an extremely tough, yet lightweight, adaptive and multifunctional material. Bone has evolved to provide structural support to organisms, and therefore its mechanical properties are of great physiological relevance. In this article, we review the structure and properties of bone, focusing on mechanical deformation and fracture behavior from the perspective of the multidimensional hierarchical nature of its structure. In fact, bone derives its resistance to fracture with a multitude of deformation and toughening mechanisms at many size scales ranging from the nanoscale structure of its protein molecules to the macroscopic physiological scale.
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Teeth: Among Nature's Most Durable Biocomposites
Vol. 40 (2010), pp. 55–75More LessThis paper addresses the durability of natural teeth from a materials perspective. Teeth are depicted as smart biocomposites, highly resistant to cumulative deformation and fracture. Favorable morphological features of teeth at both macroscopic and microscopic levels contribute to an innate damage tolerance. Damage modes are activated readily within the brittle enamel coat but are contained from spreading catastrophically into the vulnerable tooth interior in sustained occlusal loading. Although tooth enamel contains a multitude of microstructural defects that can act as sources of fracture, substantial overloads are required to drive any developing cracks to ultimate failure—nature's strategy is to contain damage rather than avoid it. Tests on model glass-shell systems simulating the basic elements of the tooth enamel/dentin layer structure help to identify important damage modes. Fracture and deformation mechanics provide a basis for analyzing critical conditions for each mode, in terms of characteristic tooth dimensions and materials properties. Comparative tests on extracted human and animal teeth confirm the validity of the model test approach and point to new research directions. Implications in biomechanics, especially as they relate to dentistry and anthropology, are outlined.
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Mechanical Principles of Biological Nanocomposites
Baohua Ji, and Huajian GaoVol. 40 (2010), pp. 77–100More LessBiological nanocomposites, such as bone, tooth, shell, and wood, exhibit exceptional mechanical properties. Much recent effort has been directed at exploring the basic mechanical principles behind the microstructures of these natural materials to provide guidelines for the development of novel man-made nanocomposites. This article reviews some of the recent studies on mechanical properties of biological nanocomposites, including their stiffness, strength, toughness, interface properties, and elastic stability. The discussion is focused on the mechanical principles of biological nanocomposites, including the generic nanostructure of hard-mineral crystals embedded in a soft protein matrix, the flaw-tolerant design of the hard phase, the role of the soft matrix, the hybrid interface between protein and mineral, and the structural hierarchy. The review concludes with some discussion of and outlook on the development of biomimicking synthetic materials guided by the principles found in biological nanocomposites.
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Optimal Design of Heterogeneous Materials
Vol. 40 (2010), pp. 101–129More LessThis article reviews recent inverse techniques that we have devised to optimize the structure and macroscopic properties of heterogeneous materials such as composite materials, porous media, colloidal dispersions, and polymer blends. Optimization methods provide a systematic means of designing materials with tailored properties and microstructures for a specific application. This article focuses on two inverse problems that are solved via optimization techniques: (a) the topology optimization procedure used to design heterogeneous materials and (b) stochastic optimization methods employed to reconstruct or construct microstructures.
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Physical Properties of Composites Near Percolation
Vol. 40 (2010), pp. 131–151More LessDramatic changes in the physical properties of composites occur when filler particles form a percolating network through the composite, particularly when the difference between the properties of the constitutive phases is large. By use of electric conductivity and dielectric properties as examples, recent studies on the physical properties of composites near percolation are reviewed. The effects of geometric factors and intrinsic properties of the fillers and the matrix, and especially of the interface between fillers and matrix, on electric and dielectric properties near percolation are discussed. Contact resistivity at the interface is less desirable for enhancing electrical conductivity. By contrast, an interface with high resistivity suppresses tunneling between adjacent fillers and leads to percolative composites with higher dielectric constant but lower dielectric loss. This review concludes with an outlook on the future possibilities and scientific challenges in the field.
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Magnetoelectric Composites
Vol. 40 (2010), pp. 153–178More LessIn a composite of magnetostrictive and piezoelectric phases, mechanical strain mediates magnetoelectric (ME) coupling between the magnetic and the electric subsystems. This review discusses recent advances in the physics of ME interactions in layered composites and nanostructures and potential device applications. The ME phenomena of importance are giant low-frequency interactions and coupling when the electric and/or the magnetic subsystems show resonance, including electromechanical resonance (EMR) in the piezoelectric phase, ferromagnetic resonance (FMR) in the magnetic phase, and magnetoacoustic resonance at the overlap of EMR and FMR. Potential device applications for the composites are magnetic-field sensors, dual electric-field- and magnetic-field-tunable microwave and millimeter-wave devices, and miniature antennas.
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Self-Healing Polymers and Composites
Vol. 40 (2010), pp. 179–211More LessSelf-healing polymers and fiber-reinforced polymer composites possess the ability to heal in response to damage wherever and whenever it occurs in the material. This phenomenal material behavior is inspired by biological systems in which self-healing is commonplace. To date, self-healing has been demonstrated by three conceptual approaches: capsule-based healing systems, vascular healing systems, and intrinsic healing polymers. Self-healing can be autonomic—automatic without human intervention—or may require some external energy or pressure. All classes of polymers, from thermosets to thermoplastics to elastomers, have potential for self-healing. The majority of research to date has focused on the recovery of mechanical integrity following quasi-static fracture. This article also reviews self-healing during fatigue and in response to impact damage, puncture, and corrosion. The concepts embodied by current self-healing polymers offer a new route toward safer, longer-lasting, fault-tolerant products and components across a broad cross section of industries including coatings, electronics, transportation, and energy.
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Steel-Based Composites: Driving Forces and Classifications
Vol. 40 (2010), pp. 213–241More LessIn this overview of steel-based composites, consideration is given to conventional metal-matrix composites, in which steel is combined with another metal, ceramic, or polymer. In addition, we define fully steel composites, in which both components of the structure are developed within the steel. These approaches are integrated by discussing a series of macroscopic, mesoscopic, and microscopic examples. This review provides an integrated view of steel composites and allows modeling of the mechanical response to be considered both at the continuum level and in terms of dislocation mechanisms depending on the length scale and the degree of mechanical contrast between the constituent phases. In the context of fully steel composites, consideration is given to static systems in which the volume fraction of the strengthening phase is constant and the length scale is varied by heat treatment or imposed plastic strain. Moreover, we discuss dynamic systems in which a phase transition occurs concomitantly with plastic strain, resulting in an increase in the density of planar barriers that control the plasticity. A discussion of classical works that describe materials such as Damascus steels is used as a template to consider a variety of ways of producing ultrahigh-strength steel composites. Examples of applications are cited and linked to the important issue of developing appropriate fabrication methods for the production of current and future steel composites.
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Metal Matrix Composites
Vol. 40 (2010), pp. 243–270More LessIn metal matrix composites, a metal is combined with another, often nonmetallic, phase to produce a novel material having attractive engineering attributes of its own. A subject of much research in the 1980s and 1990s, this class of materials has, in the past decade, increased significantly in variety. Copper matrix composites, layered composites, high-conductivity composites, nanoscale composites, microcellular metals, and bio-derived composites have been added to a palette that, ten years ago, mostly comprised ceramic fiber– or particle-reinforced light metals together with some well-established engineering materials, such as WC-Co cermets. At the same time, research on composites such as particle-reinforced aluminum, aided by novel techniques such as large-cell 3-D finite element simulation or computed X-ray microtomography, has served as a potent vehicle for the elucidation of the mechanics of high-contrast two-phase elastoplastic materials, with implications that range well beyond metal matrix composites.
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The Indentation Size Effect: A Critical Examination of Experimental Observations and Mechanistic Interpretations
Vol. 40 (2010), pp. 271–292More LessThe indentation size effect is one of several size effects on strength for which “smaller is stronger.” Through use of geometrically self-similar indenters such as cones and pyramids, the size effect is manifested as an increase in hardness with decreasing depth of penetration and becomes important at depths of less than approximately 1 μm. For spherical indenters, the diameter of the sphere is the most important length scale; spheres with diameters of less than approximately 100 μm produce measurably higher hardnesses. We critically review experimental observations of the size effect, focusing on the behavior of crystalline metals, and examine prevailing ideas on the mechanisms responsible for the effect in light of recent experimental observations and computer simulations.
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Plasticity in Confined Dimensions
Vol. 40 (2010), pp. 293–317More LessThis review examines the size effects observed in the mechanical strength of thin metal films and small samples such as single-crystalline pillars, whiskers, and wires. Experimental results from mechanical testing and electron microscopy studies, as well as recent insights from discrete dislocation dynamics simulations, are presented. The size dependency of deformation may be separated into three regimes: the nanometer regime of roughly 100 nm and below, an intermediate regime between 100 nm and approximately 1 μm, and a bulk-like regime. We argue that there is no scaling law with one universal power-law exponent encompassing the entire range. Instead, there are a number of different mechanisms and underlying effects, e.g., the initial dislocation microstructure or loading conditions. The complex interaction of these mechanisms leads to the typically observed scaling behavior.
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Saturation of Fragmentation During Severe Plastic Deformation
Vol. 40 (2010), pp. 319–343More LessIn this review, we focus on the saturation microstructure that evolves during severe plastic deformation (SPD). These nanocrystalline or ultrafine-grained microstructures consist predominantly of high-angle boundaries, although low-angle boundaries are also present. Deformation temperature, alloying, and strain path are the dominant factors controlling the saturation grain size in single-phase materials. The saturation grain size decreases significantly with decreasing deformation temperature, although the dependency is stronger at medium homologous temperatures and less in the low-temperature regime. The saturation microstructure is sensitive to strain rate at medium temperatures and less so at low temperatures. The addition of alloying elements to pure metals also reduces the saturation grain size. The results indicate that grain boundary migration is the dominant process responsible for the limitation in refinement by SPD. Therefore, second-phase particles of the nanometer scale can stabilize even finer microstructures. This mechanism of stabilization of the microstructure is an effective tool for overcoming the limit in refinement of single-phase materials by SPD. The improved thermal stability of the obtained nanostructures is another benefit of the introduction of second-phase particles.
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Ultrasonic Fabrication of Metallic Nanomaterials and Nanoalloys
Vol. 40 (2010), pp. 345–362More LessThis review demonstrates the potential of sonochemistry to become a valuable tool for nanotechnology through composite fabrication if the underlying complex processes are understood and controlled. We show that control of cavitation requires control of interfaces at the microsecond timescale, and a diversity of phenomena is observed at the cavitation interface using different surfactants. Concrete examples show that it is possible to prepare nonequilibrium mono- and multicomponent metallic nanostructures that possess properties considerably different from those of nanostructures prepared by conventional methods.
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Oxide Thermoelectric Materials: A Nanostructuring Approach
Vol. 40 (2010), pp. 363–394More LessThermoelectric power generation technology is now expected to help overcome global warming and climate change issues by recovering and converting waste heat into electricity, thus improving the total efficiency of energy utilization and suppressing the consumption of fossil fuels that are supposedly the major sources of CO2 emission. Thermoelectric oxides, composed of nontoxic, naturally abundant, light, and cheap elements, are expected to play a vital role in extensive applications for waste heat recovery in an air atmosphere. This review article summarizes our previous and ongoing studies on SrTiO3-based materials and further discusses nanostructuring approaches for both SrTiO3 and CaMnO3 materials. ZnMnGaO4 is taken as a model case for constructing a self-assembled nanostructure. The present status of thermoelectric oxide module development is also introduced and discussed.
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Inkjet Printing of Functional and Structural Materials: Fluid Property Requirements, Feature Stability, and Resolution
Vol. 40 (2010), pp. 395–414More LessInkjet printing is viewed as a versatile manufacturing tool for applications in materials fabrication in addition to its traditional role in graphics output and marking. The unifying feature in all these applications is the dispensing and precise positioning of very small volumes of fluid (1–100 picoliters) on a substrate before transformation to a solid. The application of inkjet printing to the fabrication of structures for structural or functional materials applications requires an understanding as to how the physical processes that operate during inkjet printing interact with the properties of the fluid precursors used. Here we review the current state of understanding of the mechanisms of drop formation and how this defines the fluid properties that are required for a given liquid to be printable. The interactions between individual drops and the substrate as well as between adjacent drops are important in defining the resolution and accuracy of printed objects. Pattern resolution is limited by the extent to which a liquid drop spreads on a substrate and how spreading changes with the overlap of adjacent drops to form continuous features. There are clearly defined upper and lower bounds to the width of a printed continuous line, which can be defined in terms of materials and process variables. Finer-resolution features can be achieved through appropriate patterning and structuring of the substrate prior to printing, which is essential if polymeric semiconducting devices are to be fabricated. Low advancing and receding contact angles promote printed line stability but are also more prone to solute segregation or “coffee staining” on drying.
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Microfluidic Synthesis of Polymer and Inorganic Particulate Materials
Vol. 40 (2010), pp. 415–443More LessThis article reviews recent developments in the microfluidic preparation of different types of particles made of polymeric and inorganic materials. We discuss control of the particle sizes, morphologies, shapes, and structures in terms of various features of microfluidic synthesis.
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Current-Activated, Pressure-Assisted Densification of Materials
Vol. 40 (2010), pp. 445–468More LessThis review of current-activated, pressure-assisted densification (CAPAD) focuses on both fundamental and practical issues. We provide some useful background for researchers interested in the process and critically assess the state of the technique.
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Heterogeneous Integration of Compound Semiconductors
Vol. 40 (2010), pp. 469–500More LessThe ability to tailor compound semiconductors and to integrate them onto foreign substrates can lead to superior or novel functionalities with a potential impact on various areas in electronics, optoelectronics, spintronics, biosensing, and photovoltaics. This review provides a brief description of different approaches to achieve this heterogeneous integration, with an emphasis on the ion-cut process, also known commercially as the Smart-Cut™ process. This process combines semiconductor wafer bonding and undercutting using defect engineering by light ion implantation. Bulk-quality heterostructures frequently unattainable by direct epitaxial growth can be produced, provided that a list of technical criteria is fulfilled, thus offering an additional degree of freedom in the design and fabrication of heterogeneous and flexible devices. Ion cutting is a generic process that can be employed to split and transfer fine monocrystalline layers from various crystals. Materials and engineering issues as well as our current understanding of the underlying physics involved in its application to cleaving thin layers from freestanding GaN, InP, and GaAs wafers are presented.
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Electrochemically Driven Phase Transitions in Insertion Electrodes for Lithium-Ion Batteries: Examples in Lithium Metal Phosphate Olivines
Vol. 40 (2010), pp. 501–529More LessThe thermodynamics and kinetics of phase transformations in electrochemical systems are reviewed. Phase transitions in LiMPO4 (M = Fe, Mn, Ni, Co) olivines are highlighted. The phase transformation phenomena in LiMPO4 are diverse and include thermodynamic effects of particle size and applied overpotential, the appearance of metastable phases, and the effects of defects from atomic disorder and aliovalent doping. Such phenomena also include kinetic effects such as interface motion and diffusion of Li-electron complexes. The nature of phase transitions directly influences electrode performance in battery applications. Reduced particle size and doping can reduce or eliminate room-temperature Li miscibility gaps, which in turn affect characteristics of state of charge versus voltage and the elastic energy due to volume mismatches between phases. Near the conditions for a phase transition, Li diffusion coefficients are reduced. Nucleation and growth kinetics produce a series of phase transition sequences, which can result in the accumulation of noncrystalline phases during electrochemical cycling.
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Electromigration and Thermomigration in Pb-Free Flip-Chip Solder Joints
Vol. 40 (2010), pp. 531–555More LessPb-free solders have replaced Pb-containing SnPb solders in the electronic packaging industry due to environmental concerns. Both electromigration (EM) and thermomigration (TM) have serious reliability issues for fine-pitch Pb-free solder bumps in the flip-chip technology used in consumer electronic products. We review the unique features of EM and TM in flip-chip solder bumps, emphasizing the effects of current crowding and Joule heating. In addition, the challenges to a better understanding of EM and TM in Pb-free solders are discussed. For example, the anisotropic nature of Sn microstructure in Pb-free solders can enhance the dissolution rates of Ni and Cu in solders driven by EM and TM.
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The Structure of Grain Boundaries in Strontium Titanate: Theory, Simulation, and Electron Microscopy
Vol. 40 (2010), pp. 557–599More LessWe review a combination of theoretical and experimental techniques that have been applied to the study of grain boundaries in SrTiO3, with particular attention to Σ3 and (100)-oriented grain boundaries. Electron microscopy, which includes high-resolution transmission and high-angle annular dark-field methods, is discussed, with successful applications to mapping atomic columns and testing theoretical models. Then, we compare and contrast different techniques of electron holography that may be used to map electrostatic potentials. Problems with the current methods of interpretation in holography and impedance spectroscopy are highlighted in an attempt to reconcile their respective estimates of electrostatic potentials at grain boundaries. Then, standard theoretical tools for the atomistic simulation of boundary structures are critically reviewed, which include classical potentials and density functional theory. A promising genetic algorithm for discovering low-energy grain boundary structures is described and tested. Finally, the synergy of experiment, theory, and simulation that is required to understand boundaries is demonstrated, and we identify major challenges to understanding multicomponent systems.
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Previous Volumes
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Volume 54 (2024)
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Volume 53 (2023)
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Volume 52 (2022)
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Volume 51 (2021)
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Volume 50 (2020)
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Volume 49 (2019)
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Volume 48 (2018)
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Volume 47 (2017)
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Volume 46 (2016)
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Volume 45 (2015)
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Volume 44 (2014)
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Volume 43 (2013)
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Volume 42 (2012)
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Volume 41 (2011)
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Volume 40 (2010)
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Volume 39 (2009)
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Volume 38 (2008)
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Volume 37 (2007)
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Volume 36 (2006)
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Volume 35 (2005)
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Volume 34 (2004)
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Volume 33 (2003)
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Volume 32 (2002)
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Volume 31 (2001)
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Volume 30 (2000)
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Volume 29 (1999)
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Volume 28 (1998)
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Volume 27 (1997)
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Volume 26 (1996)
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Volume 25 (1995)
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Volume 24 (1994)
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Volume 23 (1993)
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Volume 22 (1992)
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Volume 21 (1991)
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Volume 20 (1990)
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Volume 19 (1989)
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Volume 18 (1988)
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Volume 17 (1987)
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Volume 16 (1986)
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Volume 15 (1985)
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Volume 14 (1984)
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Volume 13 (1983)
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Volume 12 (1982)
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Volume 11 (1981)
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Volume 10 (1980)
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Volume 9 (1979)
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Volume 8 (1978)
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Volume 7 (1977)
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Volume 6 (1976)
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Volume 5 (1975)
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Volume 4 (1974)
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Volume 3 (1973)
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Volume 2 (1972)
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Volume 1 (1971)
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Volume 0 (1932)