bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractFor 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, andRole 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.
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).
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.