bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neutrons as a Probe of Magnetization on Atomic to Mesoscopic Scales
Authors: Aeppli G. , Hayden S.M. 
Published: August 2016

The neutron is a spin 1/2 particle with a well-specified magnetic dipole moment which interacts with magnetic fields in solids. Because typical neutron wavelengths are comparable to interatomic distances in solids, the fields that can be probed range from the dipoles of individual electron spins to those associated with flux lines in superconductors. In this article, we give a brief introduction to the use of magnetic neutron scattering in materials science.Progress in materials science typically involves new materials or the improved fabrication of previously known materials, followed by measuring quantities such as electrical resistivity, magnetic susceptibility, or specific heat, typically as a function of variables such as temperature, magnetic field, chemical composition, or pressure. A material is deemed interesting if a simply defined bulk characteristic either undergoes a spectacular evolution as a function of one of the variables—superconductivity comes to mind—or has a range of values that makes it uniquely suited for some predetermined application. Once the material is thought to be interesting, there are natural drives to understand the origin of its interesting properties as well as to improve them. At this point, a microscopic tool such as magnetic neutron scattering provides valuable insights that bulk measurements cannot yield.
Superconductivity and Magnetism in the La2 CuO4-Based Compounds
Authors: Fisk Z. , Cheong S-W. , Johnston D.C. 
Published: August 2016

La2CuO4, crystallizes in an orthorhombic distortion of the tetragonal K2NiF4 structure, a so-called layered perovskite. The important question here concerns the stoichiometry of La2CuO4 prepared by various techniques. Regarding the La and Cu sites, recent neutron diffraction studies of powders have shown that the La:Cu ratio can vary from 2:1 by ≳1% in various preparations., Single crystals have been grown variously from CuO, PbO and Li2O-B2O3 fluxes. The last two fluxes incorporate some Pb and Li, respectively, into the crystals, but the cation ratio is found to be 2:1 within the accuracy of x-ray refinement.It is also known that the oxygen stoichiometry corresponds to La2CuO4 within ≃ 1%. Extensive and precise magnetic susceptibility (χ) and other studies of powder samples showed, however, that the physical properties are extremely sensitive to < 1% changes in the oxygen content. A clear indication from electric and magnetic measurements is that the oxygen stoichiometry is always that, or richer than that, corresponding to a Mott insulator with an exactly half-filled band. Consistent with this, the stoichiometry is more properly written La2-z CuO4-y with small, positive y and z.Several groups found that bulk superconductivity above 30 K can be produced in La2CuO4 by annealing powders or single crystals at high oxygen pressure. The weight gain in this process corresponds to producing La2CuO4.13, and these authors believe the excess oxygens go in as O-2, based on iodometric titration measurements giving the amount of [Cu-O]⊥ in the sample. Jorgensen et al. found that there is a phase separation below 320 K of La2CuO4 and the O2-loaded phase in oxygen-rich samples; the latter structure is also orthorhombic, but the position of the excess oxygens could not be determined unambiguously.
High Tc Bismuth and Thallium Copper Oxide Superconductors
Authors: Sleight A.W. , Subramanian M.A. , Torardi C.C. 
Published: August 2016

The first report of a superconductor in this family came from the laboratory of B. Raveau. The system was Bi/Sr/Cu/O. The Tc's were in the range 10-20 K, and this system therefore did not attract much attention when there was intense effort on 90 K superconductors. Neither the structure nor the composition of the superconductor in the Bi/Sr/Cu/O system was known at the time of the first publication, a common feature with all discoveries of new high Tc superconductors in the past couple of years. We now know that the first discovered member of this new family of superconductors can be represented as Bi2Sr2CuO6. However, the composition and structure of this phase are still not precisely established.Subsequent to the French work, the Bi/Sr/Ca/Cu/O system was studied in Germany, and higher Tc's were obtained. Although patents were filed; this work was not publicly announced. In January 1988, Maeda announced high Tc in the Bi/Sr/Ca/Cu/O system and Hermann announced high Tc in the Tl/Ba/Ca/Cu/O system.It is now known that there exists a very large family of compounds of the type (AO)mM2Can-1CunO2n+2. The A cation can be Tl, Pb, Bi or mixtures of these elements. The value of m may be one or two but is only two when A is Bi. The M cation is Ba or Sr, and substitution of Ca by Sr is frequently observed. The number of consecutively stacked CuO2 layers is indicated by n. The highest temperature at which zero resistivity has been obtained in this family is 122 K, and this has been obtained for several distinctly different compositions (Table I).
Science for Art's Sake
Authors: Brunetta Leslie 
Published: August 2016

Victorian men placed fig leaves over those parts of classical statues they didn't want their wives and children to see. Yet it's easy for someone looking at those statues today to assume that the leaves play some part in the Roman and Greek concepts of physical beauty.A fig leaf may be the most blatant breach of an artist's original inspiration you'll encounter in a museum, but it's not likely to be the only one. Other more subtle transgressions are displayed in nearly every gallery and museum in the country—but unmasking them takes more than just a discerning eye. For instance, did the 17th-century painter see the world as quiet and subdued, or have his bright colors been muted by a 19th-century varnish? Did the classical sculptor intend his work to have an even, green patina, or has the Renaissance infatuation with antiquity allowed this corrosion to hide his varying shades of burnished bronze? Did Leonardo conceive the face of the Christ of “The Last Supper” as speaking, or silent, as his overpainters would have it?“Modern conservators really make us think about objects, says Carol Faill, administrator of college collections at Franklin & Marshall College. “There's been a consciousness raising about objects' own integrity.” Art and science are being used together as never before to gain an understanding of the physical and chemical properties of materials and their role in the fine arts.
Development of Direct Drive, High-Gain Capsules for Inertial Fusion: A Materials Challenge
Authors: Campbell J. H. 
Published: August 2016

Abstract:The application of Inertial Confinement Fusion to power production requires the development of a high-yield fusion capsule. Theoretical design calculations suggest that a single shell capsule with a uniformly distributed deuterium-tritium (DT) fuel layer on the inside surface could give the desired high-gain performance when directly driven with 0.35 μm laser light. This design requires operation at cryogenic temperatures necessary to condense DT (20-30 K) and a means of levitating the fuel layer inside the capsule. On e recently suggested method for making this capsule is to use a rigid foam matrix to support the condensed DT in a spherical shell configuration. For such a capsule to be successfully fielded, a number of critical materials problems must be solved.
Damage Mechanisms in Optical Materials For High-Power, Short-Wavelength Laser Systems
Authors: Haglund Richard F. 
Published: August 2016

Damage to optical materials under intense photon irradiation has always been a major problem in the design and operation of high-energy and high-average-power lasers. In short-wavelength lasers, operating at visible and ultraviolet wavelengths, the problem appears to be especially acute; presently attainable damage thresholds seriously compromise the engineering design of laser windows and mirrors, pulsed power trains and oscillator-amplifier systems architecture. Given the present interest in ultraviolet excimer lasers and in short-pulse, high-power free-electron lasers operating at visible and shorter wavelengths, the “optical damage problem” poses a scientific and technological challenge of significantdimensions. The solution of this problem even has significant implications outside the realm of lasers, for example, in large space-borne systems (such as the Hubble Telescope) exposed to intense ultraviolet radiation.The dimensions of the problem are illustrated by the Large-Aperture krypton-fluoride laser amplifier Module (LAM) shown schematically in Figure 1. This device, now operating at the Los Alamos National Laboratory, is typical of current and planned large excimer lasers for fusion applications. The LAM has an active volume of some 2 m3, and optical surfaces (resonator mirror and windows) exceeding 1 m2 in size; the fabrication of these optical elements was the most expensive and time-consuming single item in the construction of the laser. During laser operation, a population inversion in an Ar-Kr-F2 mix ture is created through electron-beam excitation of the laser gas by two 400 kA beams of 650 keV electrons from a cold cathode discharge. The electron trajectories in the gas are constrained by a 4 kG magnetic field transverse to the optical axis produced by a pair of large Helmholtzcoils.
Defect Engineering
Authors: Kimerling Lionel C. 
Published: August 2016

The pervasive role of defects in determining the thermal, mechanical, electrical, optical, and magnetic properties of materials is biblical. Thermodynamic control of imperfection under equilibrium conditions dictates, for instance, the high temperatures needed to raise defect content for diffusion processes. Nonequilibrium treatments, such as work hardening, are used to control dislocation and grain boundary density and morphology to enhance mechanical properties. Both approaches represent the practice of defect engineering. Both are examples of a synergistic interaction between science and engineering in which an existing knowledge base is applied to its limits, stirring the development of new knowledge and new applications.The purpose of this article is to convey the flavor of the defect engineering culture. The invention of the transistor can be traced to a triumph of defect engineering. Original explorations of semiconductor materials had the goal of controlling surface rectification properties to devise rectifiers, oscillators, and amplifier substitutes for vacuum tube counterparts. Schottky barriers, p-n junctions and metal-oxide-semiconductor capacitors—the products of the endeavor—are now the building blocks of today's microcircuits. The commercial success of these applications has fueled a boom in materials physics research during the last two decades. The work-hardening knowledge base can be traced from the Japanese swordmaking ritual to the discovery of dislocations (in theory first, and then by direct observation). Expansion of the dislocation knowledge base was a dominating concern in materials science prior to the transistor. As shown in this article, these two disparate areas are essential components of the defect engineer's tool kit.
Point Defects in Materials Part I: Behavior and Characteristics in Different Material Classes
Authors: Seidman David N. , Shi Donglu 
Published: August 2016

In this issue of the MRS Bulletin we present five papers that involve point defect phenomena in a wide variety of materials—metals, conducting ceramic oxides, semiconductors, amorphous alloys, and high Tc superconducting oxides. The unifying theme of this issue is point defects—zero-dimensional defects. Even for the high Tc oxides, where planar defects are discussed, it is the ordering of oxygen/vacancy chains that ultimately gives rise to twins in the famous YBa2Cu3O7.δ (1:2:3) oxide superconductor.Hillard Huntington, professor emeritus of physics at Rensselaer Polytechnic Institute, is an early and important pioneer in the study of point defects in metals. A theorist, he has also performed many experiments over the years; for example, he performed key early experiments on electromigration effects. Huntington's article presents a historical review of the research on vacancies and self-interstitial atoms in metals during the period that stretches from the mid-1930s to the mid-1960s. He played a crucial role in this field as a result of his seminal theoretical calculations, with Fred Seitz in 1942, on the enthalpies of formation and migration of vacancies or self-interstitial atoms in pure copper. Huntington's and Seitz's calculations indicated that diffusion occurs predominantly by a monovacancy mechanism since the enthalpy of formation of a self-interstitial atom, the [100] split form, also called the dumbbell form, is too large to be compatible with the activation enthalpy for self-diffusion in copper. It is now well established that the latter is given by the sum of the enthalpy of formation and the enthalpy of migration of a monovacancy in many face-centered-cubic (fcc), body-centered-cubic (bec), and hexagonal-close-packed (hcp) metals.
Biomaterials in an Emerging National Materials Science Agenda
Authors: Mueller E.P. , Barenberg S.A 
Published: August 2016

In 1988 a biomaterials industry panel was chartered by the National Academy of Sciences and the National Academy of Engineering to address needs and opportunities in materials science and engineering as perceived by the biomaterials industry. This report was subsequently consolidated with similar reports from panels in the other materials science areas into a comprehensive National Research Council (NRC) report, Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Materials, issued by the National Academy Press in late 1989.After reading the NRC report, D. Alan Bromley, science adviser to President Bush, decided that materials science would be one of five priorities for research in the current aclministration. In a letter to Frank Press, January 1990, Bromley praised this report and encouraged the Academy to have regional meetings to stimulate action on the local level. It was felt that these regional meetings would offer materials scientists and engineers the opportunity to organize themselves and, cooperating with industry and federal laboratories, take the initiative to address the needs identified in the NRC report. Bromley encouraged structuring these meetings, to the extent possible, to produce items that could be considered for the Office of Science and Technology Policy (OSTP) agenda.
Genetic Engineering of Polymeric Materials
Authors: Tirrell David A. , Fournier Maurille J. , Mason Thomas L. 
Published: August 2016

Polymerization reactions are generally divided into two broad classes: step growth or polycondensation reactions (examples would include the synthesis of polyamides and polyesters), and chain growth processes such as those used to prepare polyethylene or polystyrene. These processes are illustrated schematically in Figure 1.The statistical nature of step and chain growth polymerization processes ensures that the products of such reactions must be heterogeneous. Conventional polymeric materials thus consist of mixtures of chains, often characterized by relatively broad distributions of chain length or composition. In many materials applications, this kind of molecular heterogeneity is advantageous since it suppresses crystallization and helps to preserve desirable properties such as optical clarity or elasticity. On the other hand, synthetic developments that afford improved control of macromolecular architecture have had profound impact on materials science and technology. As examples, one can cite the discovery of Ziegler-Natta polymerization, now used to prepare billions of pounds per year of crystalline polyolefins, or the development of living anionic polymerization of olefins, which led directly to block copolymers and the commercially important thermoplastic elastomers.The advent of recombinant DNA methods has provided a basis for developing polymeric materials characterized by essentially absolute uniformity of chain length, sequence, and stereochemistry. This article outlines the principles governing the cloning and expression of artificial genes, and examines the potential role of artificial proteins in polymer materials science.
A Materials Scientist in Space: 1990 MRS Fall Meeting Plenary Address
Authors: Dunbar Bonnie J. 
Published: August 2016

The following is an edited version of NASA Astronaut Bonnie J. Dunbar's Plenary Address at the 1990 MRS Fall Meeting.I've often been asked, “Why a materials scientist in space?” I hope my presentation tonight will provide a little more insight on “why.” I don't think it's unusual at all. I look at myself as a continuum between outer space and inner space. I've been equally fascinated looking at the stars as at atomic structures under scanning electron microscopes. So to me it's not an unusual experience. In addition, materials scientists and engineers are needed to operate in space.Tonight I would like to do several things. I'd like to talk to you about where we've been in space, where we are, and where we hope to go. I'll emphasize the materials aspect of it, not only in how we achieved space, but how we hope to exploit the microgravity environment of space. I have with me “home movies” of a Shuttle Mission I flew on in January 1990. You'Il share with me the experience of performing research as well as retrieving the long-duration exposure facility (LDEF) with a robotic arm.
Designing Interfaces
Authors: Cornie James A. 
Published: August 2016

During the 20 years I have been working in the field of metal matrix composites, I have always been drawn to the study of interfaces. Any problems the materials researcher or developer encounters will eventually be tied to some issue involving the interface. The interface controls the in-situ fiber strength and hence the axial strength of the composite. The transverse strength of composites is also controlled directly by the strength of the interface. It follows that in order to optimize a fiber/matrix reinforcement system, one must also optimize the interface. It is no accident, then, that so soon after the two excellent issues on interfaces edited by D. Wolf and S. Yip (MRS Bulletin, September and October 1990), we launch into the subject again. This time, we approach the interface from the point of view of integrating the fields of materials science and engineering, i.e., integrating the structure-processing-properties-materialssynthesis relationships.The concept of interface design is relatively new. Until recently, we simply controlled damage and limited fiber degradation by controlling processing variables, and contented ourselves with what nature allowed. For the most demanding applications, nature was not permitting reliable structures.Our emphasis in this issue of the MRS Bulletin is the development of the skills and strategies to design interfaces to a specifie application. In the future, we will be asking materials to perform structurally at temperatures approaching 3000°C in some propulsion applications. The success of such applications will depend on how well we design the interfaces.
In Pursuit of the Lattice Vacancy 1990 MRS Fall Meeting Von Hippel Award Address
Authors: Balluffi R.W. 
Published: August 2016

The Von Hippel Award is especially significant to me for several reasons. The name Von Hippel is legendary in the halls of Building 13 at the Massachusetts Institute of Technology, where I have worked for the last 12 years. Professor Von Hippel was one of the first to appreciate the interdisciplinary nature of materials research and engineering, and his insulation laboratory at MIT provided an early prototype for the National Science Foundation-supported system of interdisciplinary materials research laboratories in existence today. These laboratories, both at MIT and earlier at Cornell, have helped me in my research in many ways over the years.Also I have been a recent councillor of the Materials Research Society and have been privileged to witness the phenomenal growth of MRS at first hand. The stature of the Von Hippel Award must be increasing at least in proportion to this growth. I, therefore, feel very honored and grateful indeed! I would also like to add that much of my work has been done in collaboration with valued colleagues and students. They deserve a substantial share of this award.Over the years, my research has been devoted mainly to the experimental study of crystal defects and their behavior. These defects can be classified according to their dimensionality as shown in the accompanying table, and they are involved in one way, or another, with a host of phenomena in crystalline materials. Since I address a rather diverse audience, it might be appropriate to discuss some of the history of lattice vacancy research and some of the details of my personal contribution to it.
Pattern Formation in Electrohydrodynamic Convection
Authors: Zimmermann Walter 
Published: August 2016

One hundred years after their discovery, we meet liquid crystals everywhere in our daily life. Their most widely known application is the liquid crystal displays (LCDs) in watches, pocket calculators, or gasoline pumps. Applications aside, liquid crystals show many exciting properties, making them highly interesting for fundamental research. For example, electrohydrodynamic convection (EHC) in nematic liquid crystals, which is studied in cells of a configuration similar to liquid crystal displays, serves with its characteristic properties as a model System for investigating central questions of pattern formation and chaos.Today's liquid crystal displays work on the principle described in 1971 by Martin Schadt and Wolfgang Helfrich (Figure 1). In nematic liquid crystals, organic molecules orient on average along a macroscopic direction, described by the director field n(r), that has neither head nor tail (n = −n). Nematics are therefore anisotropic and for energetic reasons, n(r) orients parallel (perpendicular) to an electric field when the dielectric permittivity (ε∥) along n is larger (smaller) than the perpendicular (ε⊦ one. For positive εa = ε∥ − ε⊦, when an electric field is applied perpendicular to the direction of n, a reorientation of n takes place together with a corresponding change in the optical property of the cell. The controlled change by an electric field in the optic axis (orientation) in well-defined areas of the display then allows the representation of numbers, etc.