bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Tc Oxide Superconductors
Authors: Maple M. Brian 
Published: August 2016

The recent revolution in high temperature superconducting materials has generated a wave of intense excitement and activity that has swept through the scientific community, attracting the attention of the news media and general public as well. The reason for this is twofold: the unexpected occurrence of superconductivity at such high temperatures is of immense scientific interest, and the new high temperature oxide superconductors may have important technological applications.Based on a large amount of experimental information and (presumed!) theoretical understanding, the prevailing view prior to 1986, when high temperature superconductivity in oxides was discovered, was that the maximum value of the superconducting transition temperature Tc of any material would not increase much above ˜23 K, the high Tc record held since 1973 by the A15 compound Nb3Ge. In fact, between 1911 (the year H. Kammerlingh Onnes discovered superconductivity) and 1986, Tc only increased at an average rate of ˜0.25 K per year. However, within the last two years the maximum Tc value of the new copper oxide super-conductors has risen at an average rate of ˜50 K per year to its present value of ˜125 K! Thus, superconductivity near or above room temperature no longer seems out of the question, as it did a few short years ago! Moreover, the oxides were generally regarded as the least likely candidates for high Tc superconductivity due to their low concentrations of charge carriers. An understanding of the origin and nature of high Tc superconductivity in the new oxide compounds constitutes one of the most important and challenging scientific problems that has emerged in recent years.
Novel Preparation Methods for High TcOxide Superconductors
Authors: Nellis W.J. , Woolf L.D. 
Published: August 2016

High Tc oxide superconductors can be prepared by a variety of novel metallurgical or ceramic processing techniques. For example, forming metallic precursors of YBa2Cu3 or REBa2Cu3, where RE is a rare earth element, followed by oxidation has yielded the corresponding ceramic oxide in pellet, wire, and thin film forms. Ceramic fabrication techniques (which often involve incorporating fine particles of the ceramic in a suitable vehicle) such as doctor-blade tape casting and screen printing have been utilized to synthesize both tapes and thin films. Due to intense worldwide effort to develop these ceramics into useable forms, many unique fabrication techniques have been employed, such as the melt-textured growth method of Jin et al. and dynamic compaction. In addition, it is likely that numerous laboratories, particularly industrial, are developing proprietary methods to fabricate wire and other forms but have not published these results due to the intensely competitive nature of this area. In this article, we review some of the methods reported so far for preparing high Tc ceramic superconductors, and we discuss one example of a proprietary method being developed at one of the author's (LDW) laboratories.Tapes of YBa2cu3O7-x fabricated using the doctor-blade tape casting technique were first displayed by AT&T Bell Laboratories scientists at the 1987 March meeting of the American Physical Society. This method involves mixing ceramic powder, a binder to provide green (unfired ceramic) strength, a plasticizer to provide flexibility, a dispersant to prevent particle agglomeration and a solvent. After mixing all these components together, the solution is poured into a “doctor blade” device which allows a controlled thickness of material to be deposited on a plastic film carrier that passes underneath the doctor blade.
Perspectives on the Theory of the New High Tc Superconducting Oxides
Authors: Emery V.J. 
Published: August 2016

There is a widespread feeling that the discovery of high temperature superconductors will force us to change our way of thinking about superconductivity in solids. It has steadily emerged that the simple free-electron picture is inadequate, that a new mechanism of superconductivity is most likely at work, and that modifications (if not outright revisions of the many-body theory) are needed. The situation is not entirely without precedent: much the same could have been said of superfluidity in liquid He. That, however, did not cause such a stir: it had been anticipated some 12 years before its eventual discovery, and the transition temperature of liquid He is so low that experiments have been confined to the few laboratories around the world with a milli-kelvin capability. Finally, the normal state of He was already wellunderstood, so that theorists were poised and ready to tackle the problems posed by the superfluid.Contrast the oxides. Even the rather extensive earlier studies of Ba1-x PbxBiO3 and other superconducting oxides did not prepare us for the advances of the past two years. Laboratories all over the world have been able to prepare and study the new superconductors rather easily, although well-characterized samples and incisive experiments have not been so easy to come by. The flood of new information poses a particular challenge for condensed matter theory — to distil the essence of these complicated multicomponent materials and to explain how the genie of high temperature superconductivity has escaped after so many years. Despite the existing understanding of the properties of oxides, much work remains to be done before we have a good grip on the many-body theory of these strongly correlated systems.
Up Close: The Center for Laser Studies University of Southern California
Authors: Allen Susan 
Published: August 2016

The Center for Laser Studies (CLS) is a research organization within the School of Engineering at the University of Southern California. Since its founding in 1973, CLS has grown to about a dozen full-time research scientists working with about 35 graduate students on projects funded by a wide range of government and industrial agencies. Because studies of and research with lasers are frequently interdisciplinary ventures, close ties are maintained with academic departments within the University such as Electrical Engineering, Physics, Materials Science, Chemistry, Mechanical Engineering and Chemical Engineering. The need to cross traditional university department lines was one of the reasons for establishing CLS. The CLS researchers share an extensive equipment and knowledge base, which also serves as a resource facility for cooperative research with industry. This approach has led to over 200 publications in major journals and has given the Center national prominence.Six faculty members conduct a majority of their research at CLS and an approximately equal number have experiments in residence. Examples of some of the current research projects of the primary faculty are given below:1. Professor Elsa Garmire, Director, is studying nonlinear optical devices in a variety of materials with particular emphasis on using semiconductor nonlinearities in optically bistable devices and in optical phase conjugation. This group first demonstrated mid-infrared bistability in In As with a 3 mW threshold, the lowest threshold for any bistability reported at that time. Optical bistability occurs when a semiconductor etalon is illuminated near its bandgap. The nonlinear refractive index combined with reflection feedback causes the transmission or reflection to have two stable outputs at a single value of the input, depending on the device irradiation history. Typical results are shown in Figure 1. Currently under investigation is optical phase conjugation by means of degenerate four wave mixing with two wave mixing recently observed in Cr-doped GaAs.
Theory of Solid-State Defects
Authors: Stoneham A. M. 
Published: August 2016

Serious studies of materials are often serious studies of defects, for control of properties of materials implies control of defects or impurities. Understanding defect phenomena is crucial, and both theoretical ideas and modeling are enhancing key areas of materials properties and processing. I shall review some of the ways theory contributes. Theory enters into all aspects of materials science, even if you don't always realize you are using it.Even self-styled practical people, for whom theory is a luxury, use theory routinely in its first main role, as a framework for the data they lovingly collect. Elasticity theory, electromagnetic theory, and thermodynamics are normal tools for working engineers. The simplest ideas about electronic and atomic structures of solids are now so standard that one can forget their original impact, just as one forgets those within living memory who objected even to the idea of atoms. It was theory which gave clear guidelines for solids to be metals or insulators, when the real-space ideas of crystal structures based on interacting atoms were complemented by the reciprocal space notions from band theory. Such rules had been far from obvious. The behavior of amorphous solids has forced analogous theory-led upheavals in understanding.
Workshop Identifies Scientific, Commercial Opportunities for Future Thin Film Research and Technology
Authors: Chang R.P.H. , Poate J.M. 
Published: August 2016

The first International Workshop on the Science and Technology of Thin Films for the 21st Century, held this past summer at Northwestern University, assembled the world's leading experts to assess the trends and opportunities in one of the most fruitful areas of materials research. A complex field, thin film science touches virtually all areas of technology and has had a major economic impact as well. Silicon integrated circuits, for example, form the basis of the computing and telecommunications industries, both noted economic cornerstones.The diverse, highly qualified group of 150 invited speakers and registered participants came to several conclusions:∎ The scientific, technological, and commercial opportunities in this field have never been more exciting. The panel chairs have articulated their findings, and they are presented here in separate reports.∎ Although the thin film field is huge, complex, and interdisciplinary, there are common scientific linkages or driving forces in how the field has developed and is practiced. The discovery of new deposition and fabrication techniques has historically led to new thin film materials. Analysis of the basis molecules of these materials has led to the discovery of new physical and chemical phenomena. And the practitioners of thin film science have traditionally had a lively, realistic interest in applying their work.∎ The funding situation and lack of a coherent national policy in the United States were causes for concern among U.S. workshop participants.
Molecular Tribology
Authors: Granick Steve 
Published: August 2016

Molecular tribology—the study of tribology at atomic and molecular scales—constitutes a new frontier of tribology research. In a major surge of activity, experimental methods have recently been developed to measure dynamic interfacial forces in shear. Building partly on earlier, somewhat neglected friction studies, striking new findings have been obtained. The new methods include the surface forces apparatus for measuring adhesion and static interfacial forces as a function of surface separation, new molecular tribometers for measuring friction in shear, atomic force microscopy, use of UHV tribometers, and the quartz-crystal microbalance. Theoretical calculations and molecular dynamics simulations are also emerging for friction in dry and lubricated sliding.On the scientific side, appreciation is growing that scientific understanding of these systems, so complex and so far from equilibrium, is possible. Tribology is becoming recognized as an area with many exciting and useful surface science opportunities.The engineering significance is that while tribology design and tribology-based applications are rooted in our economic life, too often the technologies and formulations are empirically derived. One tends to take friction, wear, and tear for granted. A scientific understanding is needed so that better design can emerge by rational extension.This review seeks to bring out the excitement of new developments. The reader is referred to the original literature for full accounts.
Adhesion, Friction, and Wear
Authors: Landheer D. , de Gee A.W.J. 
Published: August 2016

In the context of this article, adhesion, friction, and wear are defined as follows: Adhesion is the resistance against separation of two bodies in a direction normal to the common interface. Friction is the resistance against motion of the contacting bodies in the direction of the common interface. Wear is the gradual change of geometry and loss of material due to the different contact processes that may occur in moving contacts.Bowden and Tabor have shown convincingly that adhesion, friction and wear are interrelated at least to some extent. This article will review some of the current arguments that support this notion.If surfaces are not separated by a viscous film, both friction and wear have their origin in the contact phenomena occurring at the roughness asperities of the sliding bodies.Within one contact cycle, three primary events can be distinguished:1. In order to obtain a (normal) load-carrying capacity, the contacting asperities must be compressed or indented (Figure 1), similar to a Brinell hardness test.2. At the beginning of the contact cycle, the asperities interfere in the direction of sliding (Figure 2). Thus during the first half of the contact cycle, frontal loading of the asperities occurs (Figure 2b).Particularly if the resulting deformation is plastic (as it will usually be for metals, see Reference 1), the net effect of this contributes to friction, the so-called “ploughing” effect.
Friction-Heating Maps and Their Applications
Authors: Kong H.S. , Ashby M.F. 
Published: August 2016

Friction is often a nuisance, but it can be useful too. Brakes, clutches, and tires rely on it, of course, though the inevitable fractional heat remains a problem. Other applications use frictional heat: friction cutting and welding, skiing, skating, and curling. The damage to magnetic disks caused by head-disk contact and the striking of matches are also examples.This article illustrates a framework where the thermal aspects of friction can be analyzed in an informative way. It uses a unified approach to the calculation of flash and bulk heating, and a helpful diagram—the frictional temperature map—to display the results. The method is approximate, but the approximations have been carefully chosen and calibrated to give precision adequate to most tasks, and the gain in simplicity is great.The symbols used in this article are defined in Table I.When two contacting solids 1 and 2, pressed together by a normal forceF, slide at a relative velocity ν and with coefficient of friction ü, heat is generated at the surface where they meet. The heat generated,q, per unit of nominal contact area,An, per second isThe heat flows into the two solids, partitioned between them in a way that depends on their geometry and thermal properties. Figure 1 shows one geometry commonly used for laboratory tests: the pin-on-disk configuration. The pin is identified by the subscript 1, the disk by subscript 2. Solid 1 can have properties which differ from those of solid 2.
Sliding Friction and Wear of Ceramics With and Without Soft Metallic Films
Authors: Erdemir Ali , Nichols Fred A. , Fenske George R. , Hsieh Jang-Hsing 
Published: August 2016

In unlubricated sliding contact, essentially all the mechanical work done to overcome friction is converted into heat produced in the vicinity of real contacts. The amount of frictional heat flux q is proportional to the friction coefficient ü, the normal force F, and the sliding velocity ν, but is inversely proportional to the nominal contact area An (e.g., q = (ü × F × ν)/An). The real areas of contact, being much smaller than the nominal contact area, give rise to much higher local heat fluxes in the vicinity of asperity contacts. Because the frictional heat flux enters the contacting bodies through these regions (or locations known as “hot spots”), their local temperatures (referred to as “flash temperature”) can be much higher than the overall or “bulk” surface temperature, as discussed in References 1-3.Previous studies have demonstrated that frictional heat can profoundly affect the friction and wear behavior of both metallic and ceramic materials. In most steels and nonoxide ceramics, frictional heat was found to foster oxidation. The occurrence of phase transformations on or near the sliding surfaces was also cited in the literature for certain steels and ZrO2-based ceramics.Except for SiC, BeO, and AlN, most ceramics have significantly lower thermal conductivity than do metals. When in sliding contact, ceramics cannot dissipate frictional heat generated at sliding interfaces as effectively as most metallic alloys. Large temperature gradients can often develop between areas of real contact and surrounding regions, thus creating high thermal stresses.
Boundary Lubrication of Materials
Authors: Hsu Stephen M. 
Published: August 2016

Lubrication may be defined as any method used to achieve control of friction and wear of interacting surfaces in relative motion under load. Gases, liquids, and solids have been used successfully as lubricants. To prevent surface contact, liquids and gases provide a film under hydrodynamic pressure to support the load.When the load is high and/or the speed is low, the hydrodynamic or hydrostatic pressure may not be sufficient and the surfaces come into close contact. The amount and the extent of the surface contact depends on many factors: surface roughness, fluid film pressure, normal load, hardness of the materials, etc. When the surfaces come into close contact, many of the asperities undergo elastic deformation. The condition is generally referred to as elasto-hydrodynamic lubrication (EHL). EHL theories are well-developed. They describe and predict the surface temperatures, fluid film thickness, and hydrodynamic pressures. Contact pressure increases beyond the EHL conditions causes asperities to deform plastically and thinning of the fluid film. When the average fluid film thickness falls below the average surface roughness, the interaction between the contacting surfaces becomes the dominant factor in supporting the load.This condition is referred to as the boundary lubrication (BL) regime. Theories for BL are not well-developed and the detailed processes are not understood. The classical view of boundary lubrication postulates the formation of a surface chemical film which is easily sheared and protects the surface.
Concentrated Colloidal Dispersions
Authors: Russel William B. 
Published: August 2016

The rheology of dispersions often appears to be extraordinarily complex since these materials traverse all states of matter from simple Newtonian fluids to Hookean solids. Highly nonlinear viscoplastic or viscoelastic responses, with persistent time dependence, often frustrate attempts to address the mechanics without attempting to characterize the composition or understand the thermodynamics. The difficulty lies in the sensitivity of the stresses to the microstructure, which in turn depends on the interparticle forces and the deformation history.However, combining rheological measurements with other probes of the structure can permit one to anticipate the response under different conditions and, sometimes, to elucidate the relevant forces. Even better, one may learn to manipulate the composition to obtain the rheology desired for a specific process or a particular product, such as thickeners for coatings. The key lies in linking the composition, interparticle forces, and rheology. This review illustrates the current knowledge of those relationships and identifies some sources, from which the bulk of the content comes for those who wish to pursue the subject further.This brief treatment first surveys phase behavior and interparticle forces. These concepts, combined with dimensional analysis and simple ideas from statistical mechanics, motivate correlations of data for well-characterized, stable dispersions and both weakly and strongly flocculated dispersions.
Interrelationships of Particle Structure and Flow in Concentrated Suspensions
Authors: Hoffman Richard L. 
Published: August 2016

Numerous commercial products either exist as concentrated suspensions of small particles or involve the processing of concentrated suspensions during some stage of their manufacture. Examples include foods, adhesives and glues, ceramic dispersions, paints, and polymer dispersions such as polyvinyl chloride plastisols. As a result, it is important for engineers to understand the flow behavior of these systems and how the flow behavior affects the way these materials can be processed.For mahy years, progress in understanding the flow behavior of concentrated suspensions was slow compared to progress on dilute systems, partly because of how the study of suspensions evolved. Building on Einstein's classical work for dilute suspensions of rigid spheres, many authors attempted to modify his equations to predict the flow behavior of more concentrated suspensions, but the extension of Einstein's work met with limited success, because nonhydrodynamic interactions cari be just as important as the hydrodynamic interactions considered by Einstein, and multiple particle interactions quickly complicate the problem as the particle concentration increases.
Dynamics of Sand
Authors: Bak Per , Creutz Michael 
Published: August 2016

“Sand” represents a “state of matter” to which not much attention has been paid. A sand pile can be formed into different shapes; it can exist in many stable states, almost all of which are not the flat lowest energy state. Thus, sand contains memory; one can write letters in sand. If a heap of sand is perturbed, for instance by adding more sand, by tilting the pile, or by shaking it, the system goes from one metastable state to another. In some sense, this happens by a diffusion process, but this process is very different from the process which relaxes a glass of water to equilibrium after shaking. The diffusion process in sand can stop at any of many states, and the process is a threshold process, where nothing happens before the perturbation reaches a minimum magnitude.The threshold dynamics of sand is a paradigm of many processes in nature. Earthquakes occur only when the stress somewhere on the crust of the Earth exceeds a critical value, and the earthquake takes the crust from one stable state to another. Economie systems are driven by threshold processes: the individual agents change their behavior only when certain factors reach a certain level. Biological species emerge or die when specifie conditions in the ecology are fulfilled. Neurons in a network fire when the input reaches a threshold level, etc.
Bandgap and Interface Engineering for Advanced Electronic and Photonic Devices
Authors: Capasso Federico 
Published: August 2016

During the last decade a powerful new approach for designing semiconductor structures with tailored electronic and optical properties, bandgap engineering, has spawned a new generation of electronic and photonic devices. Central to bandgap engineering is the notion that by spatially varying the composition and the doping of a semiconductor over distances ranging from a few microns down to ~2.5 Å (~1 monolayer), one can tailor the band structure of a material in a nearly arbitrary and continuous way. Thus semiconductor structures with new electronic and optical properties can be custom-designed for specific applications.The enabling technology which has made bandgap engineering an exciting reality with far reaching implications for science and technology is molecular beam epitaxy (MBE), pioneered by Cho and Arthur in the late 1960s.In the subsequent decade MBE demonstrated jts ability to create ultra-thin (10–100 Å) layers and atomically abrupt interfaces between two different semiconductors (heterojunctions).