bluuebunny/crossref_metadata_2025 huggingface dataset:
UV-Visible Lasers Based on Rare-Earth Ions
Authors: Moncorgé R. , Merkle L.D. , Zandi B.
Published: August 2016

An issue on novel applications of materials doped with rare-earth (RE) ions can scarcely fail to address lasers, but it need not address all RE-based lasers. Some Nd3+ -doped lasers, particularly Nd:YAG (Y3Al5O12, yttrium aluminum garnet), emitting light with a wavelength of 1064 nm, are very well-established commercial products—by no means novelties.1 Some other near-infrared (NIR) lasers, based on Er3+ or Tm3+, are also available commercially. That wavelength region is relatively easy for RE laser ions, involving energy spacings between initial and final energy levels small enough to give large stimulated emission cross sections for useful, long upper-state life-times, yet large enough to minimize thermal deexcitation mechanisms. On the other hand, RE-doped lasers for ultraviolet (UV) and visible wavelengths are quite novel, since efficient laser operation is more difficult to achieve in these spectral ranges. Intriguing progress on such devices has been made in recent years, driven by several important applications.

In this article, we begin by noting some of the alternative ways to obtain laser light at these wavelengths, including their advantages and drawbacks. We then discuss basic properties of RE-doped laser materials and how these can be advantageous. We then review a few of the most important and recent RE-doped laser materials and techniques for obtaining UV and visible output.
The Cell's Biological Rods and Ropes
Authors: Boal David
Published: August 2016

Despite a variety of shapes and sizes, the generic mechanical structure of cells is remarkably similar from one cell type to the next. All cells are bounded by a plasma membrane, a fluid sheet that controls the passage of materials into and out of the cell. Plant cells and bacteria reinforce this membrane with a cell wall, permitting the cell to operate at an elevated osmotic pressure. Simple cells, such as the bacterium shown in Figure 1a, possess a fairly homogeneous interior containing the cell's genetic blueprint and protein workhorses, but no mechanical elements. In contrast, as can be seen in Figure 1b, plant and animal cells contain internal compartments and a filamentous cytoskeleton—a network of biological ropes, cables, and poles that helps maintain the cell's shape and organize its contents.

Four principal types of filaments are found in the cytoskeleton: spectrin, actin, microtubules, and a family of intermediate filaments. Not all filaments are present in all cells. The chemical composition of the filaments shows only limited variation from one cell to another, even in organisms as diverse as humans and yeasts. Membranes have a more variable composition, consisting of a bi-layer of dual-chain lipid molecules in which are embedded various proteins and frequently a moderate concentration of cholesterol. The similarity of the cell's mechanical elements in chemical composition and physical characteristics encourages us to search for universal strategies that have developed in nature for the engineering specifications of the cell. In this article, we concentrate on the cytoskeleton and its filaments.
Neutron Diffraction from Novel Materials
Authors: Radaelli Paolo G. , Jorgensen James D.
Published: August 2016

The discovery and development of new materials is the foundation of the science and technology “food chains.” Examples of new materials with novel properties that have stimulated new scientific questions and/or led to new technologies include liquid crystals, advanced batteries, structural ceramics, dielectrics, ferroelectrics, catalysts, high-temperature superconductors, har dmagnets, and magnetoresistive devices. Establishing the crystal structure of a newly discovered Compound is a mandatory first step, but the most important contribution of diffraction techniques is to provide an understanding of the relationships among chemical composition, crystal structure, and physical behavior. In this way, diffraction experiments provide critical Information for testing theories that explain novel behavior and guide the optimization of new materials to meet the demands of emerging technologies.

The first samples of newly discovered materials are often polycrystalline. With state-of-the-art neutron powder diffraction data and Rietveld refinement techniques, for structures of modest complexity, the precision for atom positions rivals that obtained by single-crystal diffraction. Rietveld refinement is a method of obtaining accurate values for atom positions and other structural parameters from powder diffraction data by least-squares fitting of a calculated model to the full diffraction pattern. As evidence of thi s success, the Inorganic Crystal Structure Database contains 6044 entries from neutron powder diffraction, 7096 from laboratory x-ray powder diffraction, an d 228 from Synchrotron x-ray powder diffraction. Other reasons for the rapidly growing impact of neutron diffraction include the favorable neutron-scattering cross sections for light elements, the sensitivity to magnetic moments, and the ability to penetrate special sample environments forin situstudies. These strengths are widely accepted and have been exploited for many years. Previous reviews have focused on these topics.
Neutron Scattering in Structural Biology and Biomolecular Materials
Authors: Blasie J. Kent , Timmins Peter
Published: August 2016

The substantial power of both elastic and inelastic neutron-scattering techniques for the investigation of the structure and dynamics of biological systems and related biomolecular-based materials—as with soft matter in the previous article by Lindner and Wignall—arises primarily from the essentially isomorphous nature of the substitution of deuterium for selected hydrogen atoms in these systems, coupled with the exquisite sensitivity of neutron scattering to this isotopic substitution. Since these systems are comprised of large macromolecules and supramolecular assemblies thereof, their essential structures and dynamics extend from the atomic scale up to very large length scales of the Order of 101–104 Å. Hence neutron sources and neutron-scattering spectrometers optimized for longer wavelength (or “cold”) thermal neutrons are necessary in order to most effectively address the structure and dynamics at the longer length scales inherent to these Systems.

The large majority of previous neutron-scattering experiments on biological systems have been performed with reactor neutron sources. Some of the more significant of these are briefly summarized in the following sections. They may be categorized in terms of the nature of the intermolecular order, both orientational and positional, within the System of interest and either the elastic neutron-scattering technique employed to investigate their time-averaged structures or the inelastic neutron-scattering technique employed to investigate their dynamics.
Structure of High Tc Oxide Superconductors
Authors: Schuller Ivan K. , Jorgensen J.D.
Published: August 2016

Our understanding of the superconducting mechanism in the newly discovered oxide superconductors is closely connected with a detailed knowledge of the structural properties displayed by these materials. Moreover, it is important to explore possible connections between structural and superconducting properties and to establish general structural principles which can guide our search for new compounds.

We present here a survey of the structures of the recently discovered oxide superconductors. The common feature of these structures (with the exception of cubic Ba1-x Kx BiO3-y) is the presence of one or more planes of copper atoms with four strongly bonded oxygen atom neighbors in a square planar arrangement at a distance of approximately 1.90 Å (“CuO2 planes”). In some structures these planes occur in groups, with the individual planes inside a group being separated by one Y or Ca layer and the groups being intercalated by a variable number of LaO, BaO, CuO, TIO and/or BiO layers. (The intercalated CuO layer is crystallographically distinct from the “CuO2 plane”). A natural model for superconductivity which arises from these structures is that the conductivity occurs predominantly in the Cu02 planes, while the other (intercalated) layers provide in some fashion carriers and/or the coupling mechanism necessary for the superconductivity.
Oxygen Stoichiometry and the High Tc Superconducting Oxides
Authors: Tarascon J-M. , Bagley B.G.
Published: August 2016

Oxide compounds have been extensively studied through the years because they exhibit a broad spectrum of electrical, magnetic, and optical properties providing both scientific and technological interest. Most oxides are insulators, but a few of them (e.g., LiTi2O4 or BaPb1−x BixO3 show metallic conductivity and even superconductivity at low temperatures. The discovery of superconductivity at 35 K by Bednorz and Müller in the cuprate La-Ba-Cu-O system prompted the search for other high Tc compounds among this oxide family. Superconductivity above liquid nitrogen was then rapidly achieved with the Y-Ba-Cu-O system (Tc=90 K) and subsequently, with the Bi-Sr-Ca-Bu-O and Tl-Ba-Ca-Cu-O systems, Tc was raised to 110 K and then 125 K.

A common feature of these new high Tc cuprates is that they belong to the large family of materials, termed perovskites, which have been studied over the years because of their ability to absorb or lose oxygen reversibly (i.e., for their nonstoichiometry in oxygen). It had been previously established in the field of superconductivity that Tc is extremely sensitive to compositional stoichiometry.
Mössbauer Spectroscopy as a Tool for Materials Research
Authors: Stevens John G.
Published: August 2016

In 1958 Rudolph L. Mössbauer reported his discovery of a simple, practical way of observing nuclear gamma ray resonance. One of the remarkable features of the discovery was the high precision with which energy changes can be measured: energy resolutions of one part to 1011 −1013 are possible. With this high resolution capability it is possible to measure hyperfine interactions between the nucleus of an atom and its electronic environment. These interactions affect the line shape which can be described by several experimental Mössbauer parameters. The three primary parameters are the isomer shift (δ), the quadrupole splitting (Δ), and the magnetic hyperfine interaction.

The isomer shift, determined by the position of the centroid of a set of lines in a spectrum, is proportional to the electron density at the nucleus. Since only s electrons have a probability of being at the nucleus, it is possible to obtain electronic structure information such as oxidation state and population of certain molecular orbitals.

The quadrupole splitting results when the electron environment surrounding the Mössbauer nucleus is not spherical in its charge distribution. Specifically, Δ is proportional to the imbalance in electron density between the axial and equatorial directions. When this hyperfine interaction is present, there is a quadrupole splitting; i.e., a single spectra line will split into two or more lines.
μSR: Report on the 4th International Conference at Uppsala
Authors: Crowe Kenneth M. , Portis Alan M.
Published: August 2016

“His Majesty the Spin and μSR, the Youngest Princess,”—this was the title of the keynote address of Anatole Abragam, professor in the College de France, who opened the 4th International Conference, μSR, held in Uppsala, Sweden June 23-27, 1986. With more than 100 papers and almost 150 participants, the topics discussed covered the range from the most recent level-crossing resonance (LCR) studies and the quantum diffusion of muons in metals through muons in spin glasses, semiconductors, alkali halides and oxides, to muonium-radical chemistry and reaction pion dynamics as well as channeling and other new techniques.

Although μSR studies began in 1957, the first real advances in the field were not made until the mid 1970s when muon trapping sites in solids were first unambiguously identified. These last ten years have seen materials scientists join with nuclear and particle physicists at the meson facilities: LAMPF at Los Alamos, TRIUMF at Vancouver, CERN at Geneva, SIN at Zurich, and KEK at Tokyo. U.S. federal support of visiting materials science user groups at these facilities has recently been examined by a National Academy of Science Panel.

For the materials scientist, the muon offers a new, light, hydrogen-like probe of great sensitivity with which to investigate internal magnetic fields. This report will examine just a few current problems in order that workers outside the field might catch a glimpse of the present excitement of the subject and obtain a brief introduction to current techniques.

μSR is based on the following sequence of events: pions produced by high-intensity proton accelerators decay to muons, which are highly polarised along their momenta, and to neutrinos.
Modeling of the Solidification Process—Historical Survey
Authors: Âgren John
Published: August 2016

The modeling of solidification processes is a broad field covering many different types of activities. On one level, technical aspects of casting processes are investigated by computer simulations. The modeling is then a tool for the designer and the calculations may even be integrated with a CAD/CAM system. A more fundamental level may consider how the microstructure develops during solidification and how it can be controlled. This article gives a brief historical survey of the modeling of solidification processes.

A well-known rule of thumb, often given in textbooks, states that the solidification time for a simple casting is proportional to its squared volume-to-area ratio. This rule is named after Chovrinov, who verified it experimentally in 1940. The mathematical treatment of solidification, however, has a much older tradition started more than 100 year s earlier in 1831 when Lamé and Clapeyron analyzed the growth of a solid crust generated by cooling a liquid. Their analysis showed that the thickness of the solid is proportional to the square root of time, which is also the essence of Chovrinov's rule. Their basic idea was that the solidification rate was controlled by the removal of latent heat. That idea may seem quite obvious to us, but a necessary pre-equisite for it is the concept of heat as quantifiable and transportable. Actually, Fourier had made his mathematical analysis of heat propagation only 20 years earlier and had won the prize of the French Academy of Sciences in 1811 for his contribution.
Materials for SDI
Authors: Yonas Gerold
Published: August 2016

Al the plenary session held December 4, 1985 during the annual MRS Fall Meeting in Boston, Dr. Gerold Yonas was the keynote speaker. He was introduced to the packed ballroom by 1985 MRS President Elton N. Kauftnann.

Kaufmann: To introduce our plenary address this evening, I would like to make a few remarks on the context in which it is being presented. Iam sure you are all aware that materials research, as most fields of science, is a field where it is rare indeed that one can cleanly separate the technical aspects of a program from the social, economic, and political aspects. This evening's topic is certainly no exception. It involves the U.S. government's Strategic Defense Initiative, or SDI for short. It has broad technical and political implications and has raised highly contentious issues of both technical feasibility and political appropriateness. It is in every source of news available today. This evening we want to focus on those technical aspects of SDI which involve materials and which should therefore be of interest to this audience.

Recently, in Space Business News, John McTague, Acting Director of OSTP (Office of Science and Technology Policy), indicated that “the technology of Swords and the technology of Plowshares have much in common.” Of course the degree of commonality between the Swords and the Plowshares becomes greateras one goes to more fundamental research. In the same article Gerold Yonas indicated that “several aspects of SDI are likely to have enormous implications in the private sector with spinoffs directed into every part of the economy.” In addition to the technical materials aspect of the program those larger issues will certainly impact our lives. In that spirit we want to make this presentation so you can evaluate the program with a maximum amount of information. Of course, because this is a publicly controversial issue, I need to stress that the Society is not endorsing one particular view or another. But, we are strongly advocating the wide dissemination of information on a topic such as this.
Formation of Amorphous Metallic Alloys by Solid-State Reactions
Authors: Schwarz Ricardo B.
Published: August 2016

For the last 25 years, amorphous metallic alloys have been prepared by the rapid quenching of melts. Recently, new methods of synthesis based on isothermal solid-state reactions have been developed. It has further been shown that the reaction products can be predicted from free energy diagrams that treat the amorphous alloy as an undercooled liquid. These discoveries have opened new windows to the synthesis of novel metastable materials, both amorphous and crystalline. This paper reviews the basic concepts behind amorphization by solid-state reactions and discusses our current understanding of the nucleation and growth of the amorphous alloy.
Research in China on High TcSuperconductors
Authors: Jiajiong Xiong , Binglin Gu , Yusheng He
Published: August 2016

Since the discovery by Karl Alex Muller and Johannes Georg Bednorz (IBM Zurich) in January 1986 that an oxide of barium, lanthanum and copper might be superconducting at temperatures up to 35 K, the superconducting transition temperature has jumped to 125 K in only two years. A great tide of high Tcsuperconductor exploration has swept across the world. Like their counterparts in other countries, Chinese scientists also stood in the frontline of this revolution.

When Prof. Zhao Zhongxian obtained Bednorz and Müller's paper in September 1986, he thought their ideas were reasonable. A team at the Institute of Physics, Academia Sinica was then organized to search for high Tcmaterials. In December 1986, Zhao and his colleagues successfully obtained superconducting samples of Sr0.25La4.75Cu5Oxwith onset temperature Tcon48.6 K and Ba0.5La4.5Cu5Oxwith Tcon= 46.3 K (Figure 1). This occurred only a few days after the announcement of the confirmation of superconductivity by diamag-netic observation from Japan. These were the highest records for superconducting transition temperature Tconin the world at that time. Moreover, a sign of superconductivity with Tc0(zero resistivity) around 70 K was also observed in some La-Ba-Cu-O samples. Because these samples were unstable, however, the Tcdecreased after several days storage in air. Since then Zhao and his colleagues have searched for materials with higher Tc by using various compositions and substitutions, different sintering processes, and heat treatments.
Properties and Defects of Type II Superconductors
Authors: Shi Donglu
Published: August 2016

Three major superconducting parameters can characterize a type II superconductor: critical transition temperature, Tc, upper critical magnetic field, Hc2, and critical current density, Jc. Because of the variety of crystal structures, chemical stoichiometrics, and microstructures of the materials, these superconducting parameters differ greatly from system to system.

It has been found that the critical transition temperature is closely related to the crystal structure and stoichiometry. Previous studies have shown that compounds with a high degree of symmetry tend to be more favorable to superconductivity. Compounds with a cubic structure, such as a bcc structure, usually have higher Tc values than compounds with a hexagonal lattice. Among conventional superconductors, the so-called A-15 structure is most favorable for high transition temperatures. It is well known that many high Tc superconductors such as YBa2Cu3Ox and Bi2Sr2CaCu2Ox have an orthorhombic structure with a high degree of symmetry.

The upper critical field, Hc2, is more complicated in terms of its relationship to structural characteristics. Experimental results have indicated that Hc2 is more closely related to the chemical stoichiometry and crystal structure than to the microstructure.

However, the critical current density, Jc, can vary tremendously in a compound with a given crystal structure. The change in critical current density is associated with the so-called flux pinning that arises from the interaction between the flux lines and crystal defects. Thus, Jc is determined mostly by the microstructure of the materials.
Point Defects and Diffusion in Semiconductors
Authors: Gösele Ulrich M. , Tan Teh Y.
Published: August 2016

Semiconductor devices generally contain n- and p-doped regions. Doping is accomplished by incorporating certain impurity atoms that are substitutionally dissolved on lattice sites of the semiconductor crystal. In defect terminology, dopant atoms constitute extrinsic point defects. In this sense, the whole semiconductor industry is based on controlled introduction of specific point defects. This article addresses intrinsic point defects, ones that come from the native crystal. These defects govern the diffusion processes of dopants in semiconductors. Diffusion is the most basic process associated with the introduction of dopants into semiconductors. Since silicon and gallium arsenide are the most widely used semiconductors for microelectronic and optoelectronic device applications, this article will concentrate on these two materials and comment only briefly on other semiconductors.

A main technological driving force for dealing with intrinsic point defects stems from the necessity to simulate dopant diffusion processes accurately. Intrinsic point defects also play a role in critical integrated circuit fabrication processes such as ion-implantation or surface oxidation. In these processes, as well as during crystal growth, intrinsic point defects may agglomerate and negatively impact the performance of electronic or photovoltaic devices. If properly controlled, point defects and their agglomerates may also be used to accomplish positive goals such as enhancing device performance or processing yield.
Defects in High Tc Cuprate Superconductors
Authors: Zhu Yimei , Tafto J. , Suenaga M.
Published: August 2016

Characterization of microstructural defects in high critical temperature oxide superconductors has been very valuable in gaining an understanding of their phase transformations and insight into the relationship between defects and some superconducting properties such as critical current densities Jc. For this purpose, transmission electron microscopy (TEM) techniques have been proved powerful. In this article we will briefly summarize typical defects in the perovskite-based layered oxides, i.e., [La(1−x)(Ba,Sr)x]2CuO4, YBa2Cu3O7−δ, and (Bi,Pb)2Sr2Can−1Cun−O4+2n+δ. Then we will discuss the nature of defects in YBa2Cu3O7−δ in detail since this oxide has been most extensively studied. Among the many varieties of microstructural defects in YBa2Cu3O7−δ, we will emphasize only those we consider most important. An account of the field before 1990 is given in an excellent review by Beyers and Shaw and a more recent review of the structure of the grain boundaries in YBa2Cu3O7−δ by Babcock.

Since the types and the nature of the defects depend greatly on the crystal structure of the materials, the basic structures of the three oxides are shown in Figures la to 1c: (a) [La1−x(Sr,Ba)x]2CuO4, (2:1:4), (b) YBa2Cu3O7 (1:2:3:), and (c) Bi2Sr2CaCu2O8 (2:2:1:2). (The structure of Tl cuprates are very similar to the Bicuprate and will not be discussed here.)
What is Tribology, Anyway?
Authors: Nichols Fred A.
Published: August 2016

Several years ago, when my boss came to my office and said that he wanted me to manage the tribology program at Argonne National Laboratory, I was mystified. My first response was, “What is tribology?” In the years since, the cards have been somewhat reversed. The initial response of person after person when I mention my position as Tribology Section Manager of the Materials and Components Technology Division is to look blank and pose the same question to me. Having somewhat of a playful nature, I often simply try to drop the term very nonchalantly and continue speaking, taking great delight in the puzzled looks my approach engenders. When somone eventually injects the inevitable inquiry, I give a rather stilted answer, such as:

“Tribology is the science and art of interacting surfaces in relative motion with respect to one another.”

Since this succeeds in erasing only a portion of their curiosity, I eventually have pity on them and say, “It's really the rather mundane areas of friction, lubrication, and wear.” I have often pondered and discussed with colleagues whether we did ourselves any favor by coining the word in the first place, but it does serve a useful purpose in at least attempting to obtain a degree of helpful communication between people engaged in the various aspects of this broad area of endeavor.
Report of the Committee to Survey Needs and Opportunities for the Biomaterials Industry
Authors: Barenberg S.A.
Published: August 2016

The Biomaterials Industry Subpanel was chartered by the National Research Council (on behalf of the National Academies of Sciences and Engineering) to address the needs and opportunities in materials science and engineering as perceived by the biomaterials industry. This report represents an initial overview and should not be considered definitive.

The Committee examined the short-term, intermediate, and long-term needs of the industry and how external factors such as regulations, lack of standards, and international competition influenced the industry. The industry is heterogeneous and was subsequently defined by the following market segments: artificial organs, biosensors, biotechnology, cardiovascular/blood products, drug delivery, equipment/devices, maxillofacial, ophthalmology, orthopedics, packaging, and wound management.

Each of these market segments then addressed the:

Role of materials in the industry,

Current materials and material needs,

Material opportunities and impact,

Industrial needs/issues,

International competition/foreign initiatives, and

Role of the U.S. government.
Environmentally Sensitive Polymers and Hydrogels
Authors: Hoffman Allan S.
Published: August 2016

Environmentally sensitive polymers and hydrogels exhibit sharp changes in behavior in response to relatively small changes in conditions such as temperature or pH. Typical changes include precipitation of the polymer in water or collapse of a hydrogel with expulsion of a large fraction of the gel pore water. These changes are depicted in Figure 1. If such a polymer is grafted or adsorbed on another polymer surface or within the pores of a porous membrane, then one observes sharp changes in wettability or permeability, respectively, when the polymer is environmentally stimulated. These changes are usually reversible, although the recdissolution or reswelling processes are often slower than the precipitation or deswelling steps. Other examples of environmental stimuli and polymer system responses are listed in Tables I and II.

A large number of polymers display sharp responses to such stimuli. Many are based on vinyl monomers, such as anionic and cationic monomers for pH, specificion, solvent, or electrically responsive systems, and N-alkyl substituted acrylamides (e.g., N-isopropyl acrylamide, or NIPAAm) for temperature-sensitive systems. Other copolymer compositions may contain the responsive moiety as a pendant group on one of the monomers. Photoresponsive groups have been incorporated in such a way.

The ratio in the responsive polymer of the responsive monomeric component to the “nonresponsive” comonomer (e.g., the pH-sensitive monomer, acrylic acid, versus acrylamide or the temperature-sensitive monomer, NIPAAm versus acrylamide) will control both the sharpness and intensity of the response as well as the specific environmental conditions where it begins.
Cardiovascular Materials
Authors: Eberhart Robert C. , Huo Hsiao-Hwei , Nelson Kevin
Published: August 2016

The search for biocompatible cardiovascular materials has gone on for more a century, beginning with the metallic and glass blood vessel substitutes of Alexis Carrel. The quest has become more involved as the need for flexible polymeric materials became apparent, and as knowledge has been gained about the reactions of blood with artificial surfaces. Current materials in clinical practice are, for the most part, standard polymers that have been in incardiovascular materials is thrombosis, a combination of the coagulation of the blood proteins (which traps red cells, thus obstructing vessel channels) and the activation and deposition of blood platelets, cells that rapidly aggregate with other platelets to obstruct the channel. Coagulation and platelet aggregation are interdependent, highly volatile processes, acting like two positive feedback cascade amplification processes. Thrombosis is prevented in clinical practice by administering heparin, ity. The endothelial cell releases heparin and heparan sulfate, natural anticoagulants, in response to various external stimuli. Endothelial cells produce prostacyclin, which prevents platelet activation by surface contact and is also a powerful, shortacting vasodilator. Prostacyclin release is modulated by fluid shear stresses on the endothelial membrane, among other stimuli. Endothelial cells bind the coagulation enzyme thrombin to thrombomodulin, one of the endothelial membrane proteins, removing it from circulation but also enhancing the activation of protein C, another circulating protein which inhibits blood coagulation. Creation of a material that would precisely mimic all functions of the endothelial cell is a daunting task. Fortunately, more prosaic materials exist that may be purified or modified to elicit minimal biological responses. Progress in developing these materials will be discussed in the context of typical cardiovascular devices.
The Bone-Biomaterial Interface for Load-Bearing Implants
Authors: Pilliar R.M. , Davies J.E. , Smith D.C.
Published: August 2016

Bone-interfacing surgical implants used in orthopedics and dentistry must bear the forces of normal patient activity with minimal risk of mechanical failure of the implant. This requires using appropriate materials and designs for implant fabrication. Additionally, reliable long-term implant attachment to host bone must be assured so that effective force transfer between implant and bone occurs for the patient's lifetime without the implant loosening. With recent advances in implant designs and techniques for their placement, effective implant fixation to bone can last for years (decades) either directly or through an acceptable intermediate fibrous tissue layer at the bone-implant interface. With approximately 500,000 artificial hips implanted annually worldwide and the demand for other joint replacements approaching the same order of magnitude, as well as the recent major growth in the use of dental implants (300,300 projected for insertion in North America alone in 1991), the assurance of effective implant-to-bone fixation is extremely important.

Studies of implant biocompatibility have resulted from concerns over the cumulative effects of foreign element release through implant corrosion and wear. Accumulation of this debris in tissues both local and remote to implant sites over the long term is a concern. Of equal importance, for load-bearing implants, are studies to determine the important factors for successful long-term implant fixation. Current trends in design and use of both dental and orthopedic implants reflect the trial-and-error approach that has characterized this field for decades.
Biostability of Biomedical Polymers
Authors: Anderson James M. , Zhao Q. H.
Published: August 2016

The living body is an aggressive environment for almost all types of foreign materials, devices, prostheses, and artificial organs which are in contact with the tissues or body fluids of the living body. This aggressive environment can potentially produce changes in the chemical, physical, mechanical, and structural properties of biomaterials, i.e., biodegradation. The vast majority of biomedical polymers used today as biomaterials or in prostheses, devices, or artificial organs are considered biostable and are expected to resist the influence of the in vivo environment for the lifetime of the device or patient while retaining the necessary properties that fulfill the intended functions. In contrast, biodegradable or bioresorbable biomedical polymers are designed to be degraded and eliminated from the body by normal metabolic and physiological processes without adversely affecting body fluids, tissues, and organs.

The term “biostability” commonly refers to the relative stability of biomedical polymers in the physiological environment as a function of time. It is advantageous to discuss biostability and biodegradation of biomedical polymers together. In vivo physiological mechanisms leading to changes in the properties of biomedical polymers are considered to be biodegradation phenomena, while biostable materials are considered to be those materials where physiological interactions do not lead to material property changes and loss of function during the service life of the biomedical polymer.
Materials Biotechnology and Blood Substitutes
Authors: Kossovsky Nir , Millett David
Published: August 2016

Blood is a dispersion of formed elements in an aqueous colloid. The combined mass of the formed elements of blood measure on average 30 ml per kg body weight, or about the same weight as the liver. The colloidal phase of blood contains numerous organic factors that play important primary and supporting roles in homeostasis, including immune surveillance, coagulation, and nutrient transport.

Erythrocytes (red blood cells) are the principle formed elements and provide the life-sustaining function, in conjunction with the heart, lungs, blood vessels and kidneys, of transporting and protecting the oxygen-carrying pigment, hemoglobin, to the tissues. The oxygen-binding properties of hemoglobin are sensitive to factors such as the cooperative effects of O2binding, pH and CO2levels, and the presence of other metabolic intermediates such as 2,3-diphosphoglycerate. The synergistic effects of these factors produce a well-known sigmoidal curve plot of the relationship between oxygen affinity and the partial pressure of oxygen (pO2): there is high oxygen affinity in the lung where the pO2is high, and a low oxygen affinity in the tissues, where the pO2is low. Uptake and delivery of oxygen by hemoglobin is associated with considerable spatial rearrangement of the hemoglobin molecule.

Blood is a non-Newtonian suspension. Its viscosity is a function of both the vascular diameter and the concentration of erythrocytes. At a normal hematocrit of 40%, the viscosity of blood ranges between 2 and 4 Pa s as measured in tubes ranging 10–1,500 μm diameter. The osmolality of blood serum is 275–295 mOsm/1.
Single Crystals: What They Tell About High Temperature Superconductivity
Authors: Brodsky Merwyn B.
Published: August 2016

From the beginning of the activity in high temperature superconductivity (near the end of 1986), there were efforts to grow single crystals of the compounds. The push for single crystals arose because earlier work on Chevrelphase superconductors (e.g., PbMo6S8) or re-entrant superconductors (ErRh4B4) showed that the properties of complex superconductors were easily masked by impurities, grain boundaries, imperfectly averaged properties, etc.

As early as the so-called “Woodstock of Physics” (the American Physical Society Meeting in New York, March 1987), a single-crystal, x-ray diffraction structure was given for YBa2Cu3O7-x (YBCO-123, with Tc = 93 K), the composition of which had been announced only three weeks earlier. The sample qualified as a single crystal because a single grain had been separated out for the x-ray study, although it was too small for any other measurements.

But, single crystal studies are not infallible, and may not always be the best route. For instance, the aforementioned x-ray work on YBCO gave the wrong structure because the x-ray scattering length from oxygen atoms is too small to yield enough scattering intensity to locate them. It remained for neutron-scattering work with large powdered samples to give the correct orthorhombic structure, having Cu-O chains and warped Cu-O planes (see Figure 1).
Atomic-Scale Imaging with the Scanning Tunneling Microscope
Authors: Hamers Robert J.
Published: August 2016

Atomic-resolution techniques for surface characterization are often limited in their ability to probe individual atoms or molecules. In the last few years, scanning tunneling microscopy (STM) has emerged as a powerful probe for studying the atomic-scale structure of surfaces. One of the greatest features of STM is that it is applicable to a wide variety of problems, restricted only by the condition that the material to be studied must be a conductor. Although STM has been applied to a wide variety of materials science problems, the greatest concentration of STM work has been in the study of semiconductor surfaces. This results not only because semiconductor surfaces exhibit complicated and interesting reconstructions of the atoms in the outermost surface layers, but also because many important properties of semiconductor surfaces and interfaces are dominated by defects and other surface imperfections with atomic dimensions.
Advances in Scanning Electron Microscopy
Authors: Sujata K. , Jennings Hamlin M.
Published: August 2016

Scanning electron microscopes offer several unique advantages and they have evolved into complex integrated instruments that often incorporate several important accessories. Their principle advantage stems from the method of constructing an image from a highly focused electron beam that scans across the surface of a specimen. The beam generates backscattered electrons and excites secondary electrons and x-rays in a highly localized “spot.” These signals can be detected, and the results of the analysis are displayed as a specific intensity on a screen at a position that represents the position of the electron spot. As with a television image, after a given period, information about the entire field of view is displayed on the screen, resulting in a complete image. If the specimen is thin, the same type of information can be gathered from the transmitted electrons, and a scanning transmission image is thus constructed.

The scanning electron microscope is highly versatile and widely used. The quality of the image is related to its resolution and contrast, which, in turn, depend on the diameter of the focused beam as well as its energy and current. Because electron lenses have inherently high aberrations, the usable aperture angles are much smaller than in a light microscope and, therefore, the electron beam remains focused over a relatively large distance, giving these instruments a very large depth of focus.

Scanning electron microscopes are versatile in their ability to detect and analyze a lot of information. As a result, modern versions of these instruments are equipped with a number of detectors. Developments are sometimes related to placing the detectors in a geometrically attractive position close to the specimen.
Polymer-Dispersed Liquid Crystals: Boojums at Work
Authors: Doane J. William
Published: August 2016

The idea of dispersing micron-size birefringent particles in a polymer to selectively scatter light is not new. In the 1930s Land patented a light polarizing material in which small, oriented solid crystallites were suspended in a clear polymer. The polymer material was selected so that its refractive index matched one of the principal refractive indices of the crystallites while the other did not. The resuit was a light polarizer tha t would pass one component of polarized light but scatter the other component out of the beam path.

This idea was substantially expanded by the introduction of liquid crystals as the birefringent material. The orientation of the particles (in this case droplets), and hence the refractive index match and the scattering, could be controlled by an electric field. Such a material could be used as a light shutter for either unpolarized or polarized light. In the mid-1970s this basic concept was applied by Hilsum, but having no way to disperse droplets of liquid crystals in a polymer, he did the opposite and put optically isotropic solid particles in the birefringent liquid crystal.

Although Hilsum demonstrated the concept, no commercial device was produced, probably because the shutter contrast was limited. Since then several ways have been found to disperse droplets in a polymer: filling the pores of a microfilter; emulsifying the liquid crystal in a water soluble polymer; and using phase separation methods to create a dispersion of droplets in non-aqueous polymer materials.
Liquid Crystal Elastomers with Piezoelectric Properties
Authors: Meier Wolfgang , Finkelmann Heino
Published: August 2016

During the last few years, liquid crystalline elastomers (LCEs) have been systematically produced by cross-linking liquid crystalline side-chain polymers. In these networks, a liquid crystalline molecule is fixed at each monomeric unit. LCEs exhibit a novel combination of properties. Due to liquid crystalline groups, they show anisotropic liquid crystalline properties similar to conventional liquid crystals (LCs); but due to the three-dimensional network-structure of the polymer chains, they show typical elastomer properties, such as rubber elasticity or shape stability. One exceptional property of this combination is demonstrated when a mechanical deformation to the LCE causes macroscopically uniform orientation of the long molecular axis of the LC units (the so-called “director”).

This response of the LC-phase structure to an applied mechanical field is similar to the effect of electric or magnetic fields on low molecular weight liquid crystals (LMLC), as illustrated in Figure 1. Figure la shows an undeformed LCE. Because of the non-uniform orientation of the director, the sample scatters light strongly so the elastomer is translucent like frosted glass. On the other hand, applying a mechanical field the director becomes uniformly aligned and the sample is transparent (Figure 1b). Such a macroscopically ordered rubber exhibits optical properties very similar to single crystals. These propertie s of LCEs offer new prospects for technical application, e.g., in nonlinear and integrated optics.
Low-Density Microcellular Materials: Introduction
Authors: LeMay J.D. , Hopper R.W. , Hrubesh L.W. , Pekala R.W.
Published: August 2016

This article is dedicated to a class of specialty materials that have come to be known as low-density microcellular materials, or LDMMs. LDMMs have been developed and studied over the last decade at several U.S. Department of Energy (DOE) National Laboratories. LDMMs are used in various high energy physics programs where they meet unusual and demanding specifications (see Table 1.1).

To set the stage for introducing LDMMs, it is instructive to contrast them with more familiar cellular materials. Examples of commercially available low-density materials are plastic “blown cell” foams, such as polyurethane cushions and polystyrene coffee cups. Asymmetric membranes and filters, on the other hand, are representative of commercially available microcellular materials. The processes used to make these products generally are not suitable for making LDMMs, however, because they are limited by a tradeoff between density and cell size. That is, they yield low densities only at the expense of increased cell size, or small cell size at the expense of increased density. The challenge to DOE materials scientists, therefore, has been to develop new methods for making materials that simultaneously have low density and microcellular morphology, and also meet other application requirements (e.g., composition, homogeneity, size, and strength).

LDMMs are used by the DOE laboratories because their low density and high homogeneity (implied from their microcellular morphology) make them ideal precursors or substrates for forming high-density gases or expanded plasmas.
From Concept to Commerce: The Challenge of Technology Transfer in Materials
Authors: Hench Larry L.
Published: August 2016

Many millions of dollars are invested annually in materials science research and development in U.S. universities. Both the universities and the sponsors, either government or private industry, have enormous incentives for the R&D efforts to become commercial. For private industry a successful development means new or improved products or processes and ultimately more profits. For the government, successful materials development can lead to improved hardware or operations efficiency and lower costs. For a university the payoff can be more than economic.

Ideally, successful commercial development leads to royalties paid to the universities in the form of the most precious of assets — Unrestricted or flexible income. Students and faculty can benefit from the additional income, both privately, depending on university policy, and through their departments. However, benefits can also accrue in the form of experience and knowledge gained while participating in the technology transfer process from university to corporation. Students who take part in such efforts gain invaluable experience in preparing and defending patent applications, designing and developing prototypes, and they are exposed to economic and legal issues that are seldom taught in the classroom. They become more valuable graduates. Taking part in a technology transfer case history is a far more effective form of learning than reading about it.

These benefits to a university are offset by a number of potentially negative factors. The space, time, personnel, equipment, and deadline pressures involved in commercialization are often beyond the capabilities of a university program. However, these limitations may not be realized until the effort has begun, and it is costly to stop in midstream, as is discussed below.
Overcoats and Lubrication for Thin Film Disks
Authors: Homola A.M. , Mate C.M. , Street G.B.
Published: August 2016

Metallic alloy thin film media and ever decreasing head-to-media spacing make severe demands on storage devices. Decreasing head-to-media separation is critical for high storage densities but it also leads to increased slider-disk interactions, which can cause slider and disk wear or even head crashes. Wear can also occur when drives start and stop when the slider contacts the disk at relatively high speeds. The reliability and durability of thin film disks, which provide much higher areal density than conventional oxide disks with particulate media, are achieved by the use of very thin overcoat materials and surface lubricants. This article summarizes the approaches taken in the industry to enhance the tribological performance of magnetic media, with special emphasis on the basic understanding of the processes occurring at the slider-disk interface.

The continuous rise in the demand for storage capacity at a competitive price is the prime motivator of the changes we have seen in the data storage industry. It is clearly stimulating the present move away from particulate media, which has long dominated all fields of data storage, i.e., tape, rigid, and flexible disks, to the thin film storage media. Particulate storage devices use magnetic media formulated by dispersing magnetic particles, usually iron oxides, in an organic binder. In thin film storage devices, the storage medium is a continuous magnetic film, usually a cobalt alloy, made either by sputtering or by electroless plating.