bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Feedback Control on Flexural Toughness of Fiber Reinforced Concrete in ASTM C1399 Tests
Authors: Banthia Nemkumar , Mindess Sidney , Jiang Zhengwu
Published: February 2011

The influence of feedback control on the measured flexural toughness of fiber reinforced concrete (FRC) remains elusive. Some tests such as ASTM C1609/C1609M-07 require closed-loop control, while others such as ASTM C1399/C1399M-10 are considered control independent, and hence open-loop testing is allowed. Recent field experience has indicated that results from even ASTM C1399/C1399M-10 tests may be test control dependent. Towards this end, a test program was initiated to understand the influence of feedback control in ASTM C1399/C1399M-10 tests. Tests were performed on specimens of two different concrete strengths and one dosage of a polymeric fiber under both open-loop and closed-loop environments. In addition to performing the analysis using the ASTM C1399/C1399M-10 approach, Ri values as per the Canadian Highway Bridge Design Code (CHBDC-S06-16) were calculated. Ri values are derived from the Average Residual Strength (ARS) values obtained from ASTM C1399/C1399M-10 tests. The results indicate that while the influence of feedback control on the measured ARS values in the case of normal strength FRC is only marginal, its influence on high strength FRC is significant. The same applies to the Ri values calculated in CHBDC-S06-16, where the results indicate that based on the published minimum acceptance criteria, the choice of feedback control may in fact govern the acceptance or rejection of a given FRC material. In the context of these findings, it is recommended that beyond a certain compressive strength, ASTM C1399/C1399M-10 tests should only be performed in a closed-loop environment.
Arrestin in Ciliary Invertebrate Photoreceptors: Molecular Identification and Functional AnalysisIn Vivo
Authors: Gomez Maria del Pilar , Espinosa Lady , Ramirez Nelson , Nasi Enrico
Published: February 2011

Arrestin was identified in ciliary photoreceptors ofPecten irradians, and its role in terminating the light response was established electrophysiologically. Downstream effectors in these unusual visual cells diverge from both microvillar photoreceptors and rods and cones; the finding that key regulatory mechanisms of the early steps of visual excitation are conserved across such distant lineages of photoreceptors underscores that a common blueprint for phototransduction exists across metazoa. Arrestin was detected by Western blot analysis of retinal lysates, and localized in ciliary photoreceptors by immunostaining of whole-eye cryosections and dissociated cells. Two arrestin isoforms were molecularly identified by PCR; these present the canonical N- and C-arrestin domains, and are identical at the nucleotide level over much of their sequence. A high degree of homology to various β-arrestins (up to 70% amino acid identity) was found.In situhybridization localized the two transcripts within the retina, but failed to reveal finer spatial segregation, possibly because of insufficient differences between the riboprobes. Intracellular dialysis of anti arrestin antibodies into voltage-clamped ciliary photoreceptors produced a gradual slow-down of the photocurrent falling phase, leaving a tail that decayed over many seconds after light termination. The antibodies also caused spectrally neutral flashes to elicit prolonged aftercurrents in the absence of large metarhodopsin accumulation; such aftercurrents could be quenched by chromatic illumination that photoconverts metarhodopsin back to rhodopsin. These observations indicate that the antibodies depleted functionally available arrestin, and implicate this molecule in the deactivation of the photoresponse at the rhodopsin level.
Posterior Medial Frontal Cortex Activity Predicts Post-Error Adaptations in Task-Related Visual and Motor Areas
Authors: Danielmeier Claudia , Eichele Tom , Forstmann Birte U. , Tittgemeyer Marc , Ullsperger Markus
Published: February 2011

As Seneca the Younger put it, “To err is human, but to persist is diabolical.” To prevent repetition of errors, human performance monitoring often triggers adaptations such as general slowing and/or attentional focusing. The posterior medial frontal cortex (pMFC) is assumed to monitor performance problems and to interact with other brain areas that implement the necessary adaptations. Whereas previous research showed interactions between pMFC and lateral-prefrontal regions, here we demonstrate that upon the occurrence of errors the pMFC selectively interacts with perceptual and motor regions and thereby drives attentional focusing toward task-relevant information and induces motor adaptation observed as post-error slowing. Functional magnetic resonance imaging data from an interference task reveal that error-related pMFC activity predicts the following: (1) subsequent activity enhancement in perceptual areas encoding task-relevant stimulus features; (2) activity suppression in perceptual areas encoding distracting stimulus features; and (3) post-error slowing-related activity decrease in the motor system. Additionally, diffusion-weighted imaging revealed a correlation of individual post-error slowing and white matter integrity beneath pMFC regions that are connected to the motor inhibition system, encompassing right inferior frontal gyrus and subthalamic nucleus. Thus, disturbances in task performance are remedied by functional interactions of the pMFC with multiple task-related brain regions beyond prefrontal cortex that result in a broad repertoire of adaptive processes at perceptual as well as motor levels.
Memory Retrieval and the Passage of Time: From Reconsolidation and Strengthening to Extinction
Authors: Inda Maria Carmen , Muravieva Elizaveta V. , Alberini Cristina M.
Published: February 2011

An established memory can be made transiently labile if retrieved or reactivated. Over time, it becomes again resistant to disruption and this process that renders the memory stable is termed reconsolidation. The reasons why a memory becomes labile after retrieval and reconsolidates still remains debated. Here, using inhibitory avoidance learning in rats, we provide evidence that retrievals of a young memory, which are accompanied by its reconsolidation, result in memory strengthening and contribute to its overall consolidation. This function associated to reconsolidation is temporally limited. With the passage of time, the stored memory undergoes important changes, as revealed by the behavioral outcomes of its retrieval. Over time, without explicit retrievals, memory first strengthens and becomes refractory to both retrieval-dependent interference and strengthening. At later times, the same retrievals that lead to reconsolidation of a young memory extinguish an older memory. We conclude that the storage of information is very dynamic and that its temporal evolution regulates behavioral outcomes. These results are important for potential clinical applications.
Separate Visual Signals for Saccade Initiation during Target Selection in the Primate Superior Colliculus
Authors: White Brian J. , Munoz Douglas P.
Published: February 2011

The primary function of the superior colliculus (SC) is to orient the visual system toward behaviorally relevant stimuli defined by features such as color. However, a longstanding view has held that visual activity in the SC arises exclusively from achromatic pathways. Recently, we reported evidence that the primate SC is highly sensitive to signals originating from chromatic pathways, but these signals are delayed relative to luminance signals (White et al., 2009). Here, we describe a functional consequence of this difference in visual arrival time on the processes leading to target selection and saccade initiation. Two rhesus monkeys performed a simple color-singleton selection task in which stimuli carried a chromatic component only (target and distractors were isoluminant with the background, but differed in chromaticity) or a combined chromatic–achromatic component (36% luminance contrast added equally to all stimuli). Although visual responses were delayed in the chromatic-only relative to the combined chromatic–achromatic condition, SC neurons discriminated the target from distractors at approximately the same time provided stimulus chromaticity was held constant. However, saccades were triggered sooner, and with more errors, with the chromatic–achromatic condition, suggesting that luminance signals associated with these stimuli increased the probability of triggering a saccade before the target color was adequately discriminated. These results suggest that separate mechanisms may independently influence the saccadic command in the SC, one linked to the arrival time of pertinent visual signals, and another linked to the output of the visual selection process.
Vision Screening for Children 1 to 5 Years of Age: US Preventive Services Task Force Recommendation Statement
Authors:   US Preventive Services Task Force
Published: February 2011

OBJECTIVE:

The goal was to provide an update of the 2004 US Preventive Services Task Force (USPSTF) statement about screening for visual impairment in children <5 years of age.

METHODS:

The USPSTF examined evidence on the association of screening for visual impairment in children 1 to 5 years of age with improved health outcomes, the accuracy of risk factor assessment and screening tests, the effectiveness of early detection and treatment, and the harms of screening and treatment.

RECOMMENDATION:

The USPSTF recommends vision screening for all children at least once between the ages of 3 and 5 years, to detect the presence of amblyopia or its risk factors (grade B recommendation). The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of vision screening for children <3 years of age (I statement).
Transparent p-Type Conducting Oxides: Design and Fabrication of p-n Heterojunctions
Authors: Kawazoe Hiroshi , Yanagi Hiroshi , Ueda Kazushige , Hosono Hideo
Published: February 2011

Inorganic solids with wide bandgaps are usually classified as electrical insulators and are used in industry as insulators, dielectrics, and optical materials. Many metallic oxides have wide bandgaps because of the significant contribution of ionic character to the chemical bonds between metallic cations and oxide ions. Their ionic nature simultaneously suppresses the formation of easily ionizable shallow donors or acceptors and enhances the localization of electrons and positive holes. Thus it is understandable that interest in these wide-gap oxides as conductive materials has not been strong.
The Synthesis of Photocatalysts Using the Polymerizable-Complex Method
Authors: Kakihana Masato , Domen Kazunari
Published: February 2011

Fine powders of semiconducting oxides loaded with deposited metal and/or metaloxide particles have been widely used as heterogeneous photocatalysts for innumerable chemical reactions. Among the many photocatalytic reactions, the splitting of water assisted by light has become one of the most active areas in heterogeneous photocatalysis, since it can be a promising chemical route for energy renewal and energy storage. The photocatalytic splitting of water on TiO2 electrodes, discovered by Fujishima and Honda in 1972, is a prototypic example of this technique, and there is a vast body of literature describing the potential application of TiO2-based photocatalysts for water decomposition. This has brought about a burst of research related to the development of many other photocatalytic systems.
Studies of Polymers with Radiation
Authors: Stein Richard S.
Published: February 2011

Research into polymers began slowly. While polymers have long been considered to be very useful materials, today they are receiving greater recognition as subjects for conducting good science.
Molecule-Based Magnets—An Overview
Authors: Miller Joel S. , Epstein Arthur J.
Published: February 2011

Molecule-based magnets are a broad, emerging class of magnetic materials that expand the materials properties typically associated with magnets to include low density, transparency, electrical insulation, and low-temperature fabrication, as well as combine magnetic ordering with other properties such as photoresponsiveness. Essentially all of the common magnetic phenomena associated with conventional transition-metal and rare-earth-based magnets can be found in molecule-based magnets. Although discovered less than two decades ago, magnets with ordering temperatures exceeding room temperature, very high (∼27.0 kOe or 2.16 MA/m) and very low (several Oe or less) coercivities, and substantial remanent and saturation magnetizations have been achieved. In addition, exotic phenomena including photoresponsiveness have been reported. The advent of molecule-based magnets offers new processing opportunities. For example, thin-film magnets can be prepared by means of low-temperature chemical vapor deposition and electrodeposition methods.
Physical Challenges Underlying Food Safety
Authors: Schroeder Peter
Published: February 2011

The safety of today' novel foods and food materials, especially those produced by means of genetic modification, has been in the news in recent times. However, the major safety problems in the food chain come from much more long-standing causes. The principal risk remains the health threat from pathogenic bacteria. Other risks include the food chain as a vector for certain serious viral infections such as hepatitis A. Food as a source of significant(and, in extremis, fatal) allergenic reactions is also a growing concern. Another significant food-safety problem is the contamination of food by potentially harmful foreign substances (pesticides, plasticizers, heavy metals, fungal micotoxins, etc.)
Scaling Transistors into the Deep-Submicron Regime
Authors: Packan Paul A.
Published: February 2011

The dominant device used in the semiconductor industry today is the silicon-based metal oxide semiconductor (MOS) transistor. The MOS transistor consists of a source, drain, channel, and gate region fabricated in single-crystal silicon (Figure 1). The source region provides a supply of mobile charge when the device is turned “on.” The source is electrically isolated from the drain by the channel region, which is oppositely charged. An insulating oxide layer between the gate and the channel region forms a capacitor. During operation, a voltage is applied to the gate. By applying the appropriate voltage, a conductive layer of charge can be attracted in the channel region at the oxide/silicon interface. This layer of charge acts as a wire that effectively connects the source and drain regions. By changing the voltage on the gate, the conducting layer of charge can be removed. Thus the transistor acts like a switch, with the gate electrode controlling the connection from the source to the drain. These individual switches can be connected to form the basic building blocks for circuit design. These building blocks are used to create the high-performance microprocessors and memory chips in today's computers.
Two- and Three-Dimensional Photonic Crystals in III–V Semiconductors
Authors: Noda Susumu
Published: February 2011

There has been increasing interest in photonic crystals in which the refractive index changes periodically. A photonic bandgap can be formed in the crystals, and the propagation of electromagnetic waves is prohibited for all wave vectors in this bandgap. Various important scientific and engineering applications, such as control of spontaneous emission, sharp bending of light, trapping of photons, and so on, may be realized by creating photonicbandgap crystals and engineering the defects and light-emitters. In the field of two-dimensional (2D) photonic crystals, some important contributions aiming at device applications have included Scherer et al.'s demonstration that a single defect can be utilized as a very tiny cavity for light emission, and Joannopoulos et al.'s work on 2D photonic-crystal circuits. Here, the present status of our work in III–V semiconductor-based 2D and 3D photonic crystals is briefly reviewed.
Fundamental Studies of Plutonium Aging
Authors: Wirth Brian D. , Schwartz Adam J. , Fluss Michael J. , Caturla Maria J. , Wall Mark A. , Wolfer Wilhelm G.
Published: February 2011

Plutonium metallurgy lies at the heart of science-based stockpile stewardship. One aspect is concerned with developing predictive capabilities to describe the properties of stockpile materials, including an assessment of microstructural changes with age. Yet, the complex behavior of plutonium, which results from the competition of its 5f electrons between a localized (atomic-like or bound) state and an itinerant (delocalized bonding) state, has been challenging materials scientists and physicists for the better part of five decades. Although far from quantitatively absolute, electronic-structure theory provides a description of plutonium that helps explain the unusual properties of plutonium, as recently reviewed by Hecker. (See also the article by Hecker in this issue.) The electronic structure of plutonium includes five 5f electrons with a very narrow energy width of the 5f conduction band, which results in a delicate balance between itinerant electrons (in the conduction band) or localized electrons and multiple lowenergy electronic configurations with nearly equivalent energies. These complex electronic characteristics give rise to unique macroscopic properties of plutonium that include six allotropes (at ambient pressure) with very close free energies but large (∼25%) density differences, a lowsymmetry monoclinic ground state rather than a high-symmetry close-packed cubic phase, compression upon melting (like water), low melting temperature, anomalous temperature-dependence of electrical resistance, and radioactive decay. Additionally, plutonium readily oxidizes and is toxic; therefore, the handling and fundamental research of this element is very challenging due to environmental, safety, and health concerns.
Mixed Atomistic–Continuum Models of Material Behavior: The Art of Transcending Atomistics and Informing Continua
Authors: Ortiz M. , Cuitiño A.M. , Knap J. , Koslowski M.
Published: February 2011

The recent development of microscopes that allow for the examination of defects at the atomic scale has made possible a more direct connection between the defects and the macroscopic response they engender (see, e.g., the December 1999 issue of MRS Bulletin).
Integrated MEMS Technologies
Authors: Franke Andrea E. , King Tsu-Jae , Howe Roger T.
Published: February 2011

While microelectromechanical systems (MEMS) technology has made a substantial impact over the past decade at the device or component level, it has yet to realize the “S” in its acronym, as complex microsystems consisting of sensors and actuators integrated with sense, control, and signal-processing electronics are still beyond the current state of the art. There are several incentives to co-fabricate MEMS devices and electronics on a single silicon chip, which apply to applications such as inertial sensors.
Designing for MEMS Reliability
Authors: Arney Susanne
Published: February 2011

Microelectromechanical systems (MEMS) devices are being manufactured in the hundreds of millions and are widely deployed for pressure sensor, accelerometer, display, and printing applications. This suggests customer confidence in the longterm reliability of MEMS (also known as microsystems or micromachines) under diverse stringent conditions.
Polymer Nanocomposites: Status and Opportunities
Authors: Vaia Richard A. , Giannelis Emmanuel P.
Published: February 2011

Reinforcement of polymers with a second phase, whether inorganic or organic, to produce a polymer composite is common in the production of modern plastics. Polymer nanocomposites (PNCs) represent a radical alternative to these conventional polymer composites.
A Diffusion Multiple Approach for the Accelerated Design of Structural Materials
Authors: Zhao Ji-Cheng , Jackson Melvin R. , Peluso Louis A. , Brewer Luke N.
Published: February 2011

A diffusion multiple is an assembly of three or more different metal blocks, in intimate interfacial contact, that is subjected to a high temperature to allow thermal interdiffusion. The power of using a diffusion multiple approach in the efficient mapping of phase diagrams and materials properties for multicomponent alloy systems is illustrated in this article using several examples. It is now possible to map phase diagrams and materials properties at an efficiency some 3 orders of magnitude higher than the conventional one-alloy-at-a-time approach. With this high efficiency, many critical materials data that otherwise would be too time-consuming and expensive to acquire can be obtained and employed to accelerate our understanding of a system's materials physics and chemistry. It is postulated that coupling the diffusion multiple approach with the CALPHAD (calculation of phase diagrams) method will have a significant impact on the computational design of materials.
Up Close: The Department of Metallurgy and Materials in Malta: Flourishing in Spite of Difficult Times
Authors: Grech Maurice
Published: February 2011

Malta is situated almost exactly in the center of the Mediterranean Sea between Europe and Africa. Its area is just 320 square km and it lies 95 km to the south of Italy and 290 km from the nearest point on the African coast.
Vertical-Cavity Surface-Emitting Lasers
Authors: Lear Kevin L. , Jones Eric D.
Published: February 2011

This issue of MRS Bulletin presents a review of the progress that vertical-cavity surface-emitting lasers (VCSELs) have made throughout the wavelength spectrum. A VCSEL is a semiconductor laser diode in which light propagates normal to the epitaxial layers. In its older cousin, the Fabry—Pérot laser, light propagates in the plane of the epitaxial layers and reflects from mirrors formed by cleaving a crystal facet across the active layers. No cleaving is required for VCSEL mirrors, which are formed from multiple layers of epitaxially grown or otherwise-deposited thin films. The simple twist in the direction of the laser beam with respect to the epitaxial layers is responsible for most of the unique attributes of VCSELs, which arise from their short cavity length, their completely lithographically defined cross section, and their reliance on only wafer-scale processes for device fabrication. The articles in this issue cover a range of topics, including blue devices, short-wavelength communications lasers, recent advances in 1.3-μm VCSELs, fundamental materials issues related to distributed Bragg reflectors, theoretical quantum-well gain calculations, and work on quantum-dot VCSELs.
Catalyzed Complex Metal Hydrides
Authors: Bogdanović Borislav , Sandrock Gary
Published: February 2011

Complex hydrides are mixed ionic–covalent compounds that can serve as reversible H2storage media only when they are catalyzed by a transition metal such as Ti. As the prime example, the phenomenology of Ti-catalyzed sodium alanate (NaAlH4) is reviewed from a historical perspective. Dehydriding yields a theoretical 5.6 wt% H2during two-step decomposition, NaAlH4→ Na3AlH6→ NaH + Al, although 100% recovery of that H2is not currently possible. H2can be discharged and recharged at practical rates at 125°C. More work is needed on the alanates, in particular, as well as the identification and optimization of the catalytic mechanism and a broad extension of the concept to other than Na-based alanates. The possibility of an even further extension of the concept to other complex hydrides (e.g., the borohydrides and transition-metal complexes) is discussed.
Silicon in All its Forms
Authors: Chelikowsky Jim
Published: February 2011

The following article is based on an edited transcript of the Turnbull Lecture presented by Jim Chelikowsky (University of Minnesota), recipient of the 2001 Materials Research Society David Turnbull Lectureship, at the 2001 MRS Fall Meeting on November 27 in Boston. Chelikowsky was cited for “contributions to the fundamental understanding of electronic, optical, mechanical, surface, and interface properties of bulk and nanostructured semiconductors, ceramics, and metals through ab initio calculations; and for excellence in teaching, lecturing, and writing.”
Conductive Adhesives for Electronic Assemblies
Authors: Murray C. T. , Rudman R. L. , Sabade M. B. , Pocius A. V.
Published: February 2011

A number of different types of adhesives are used in the assembly of electronic components and devices. This article provides an overview of such adhesives that also have another job–they work at conducting electricity or heat. The resins or binders in these adhesives range from thermosetting to pressure-sensitive. Conductivity is obtained by the judicious choice of filler. For electrically conducting adhesives, the fillers range from silver flake to silver-coated fibers. For thermally conducting adhesives, the fillers range from aluminum oxide to boron nitride. We also discuss a specific type of electrically conducting adhesive–the z-axis film adhesive. In these adhesives, particles are oriented in such a fashion that allows conduction in the direction perpendicular to the adhesive, but not in the plane of the adhesive.
Mo-Si-B Alloys: Developing a Revolutionary Turbine-Engine Material
Authors: Dimiduk Dennis M. , Perepezko John H.
Published: February 2011

This article discusses three main points. First, ultrahigh-temperature materials offer a large return to the propulsion community and to the economy, but replacing Ni-based alloys is a very difficult problem for both technical and financial reasons. Second, the oxidation resistance of selected Mo-Si-B alloys and the prospects for combining this with useful structural properties are remarkable, given the nature of conventional Mo alloys; however, there are nagging issues associated with their low-temperature (∼700°C) behavior. Third, further advances in the processing of such materials, together with assessments of their affordability and reliability, are vital for achieving a successful engineering technology.
Design and Performance of Inkjet Print Heads for Non-Graphic-Arts Applications
Authors: Creagh Linda T. , McDonald Marlene
Published: February 2011

Inkjet print heads have become the dominant printing element for home and office printers; they have been a key driver forthe digitization of wide-format graphic arts printing and other printing areas as diverse as addressing and carton coding. In the past few years, inkjet print heads have begun to have an impact in areas outside the graphics arts. In these applications, the inkjet print head may be considered a manufacturing tool; this implies that it will differ in design depending on the application. Also, standards forreliability, consistency, and dependability will differ from those in graphic arts areas. Even though non-graphic-arts applications differ widely in their details, there are general considerations in terms of the systems that are required. Each nontraditional application has specific goals for manufacturing, and a unique inkjet print head designed to meet these goals may be required. This article focuses on a specific piezo-based inkjet print head that has been engineered to meet the manufacturing requirements for flat-panel displays basedon light-emitting polymeric materials.
Nanocomposite Hard Coatings for Wear Protection
Authors: Patscheider Jörg
Published: February 2011

Nanocomposite thin films successfully promote hardness, oxidation resistance, improved wear behavior, and other properties relevant for wear-reducing coatings. Such coatings are composed of nanocrystalline grains of transition-metal nitrides or carbides surrounded by an amorphous hard matrix. The properties of nanocomposite coatings, especially hardness, are directly linked to nanostructure. The codeposition of the amorphous and nanocrystalline phases of different compositions results in different morphologies, which in turn affect the coating's properties. A maximum hardness ranging from 30 GPa to reported values above 60 GPa has been observed for most nanocomposite coatings. To obtain enhanced hardness, the domain size of the nanocrystalline phase must be below 10 nm, while the thickness of the amorphous layer separating the nanocrystals must be maintained at only a few atomic bond lengths. The prime reason for the hardness enhancement is the absence of dislocation activity.
Manufacturing Nanocomposite Parts: Present Status and Future Challenges
Authors: Seal S. , Kuiry S.C. , Georgieva P. , Agarwal A.
Published: February 2011

The promises of nanotechnology are mostly based upon the ability to produce nanostructured materials with novel properties. Nanocomposites are defined here as a class of materials that contain at least one phase with constituents in the nanometer domain. This article describes the present state of knowledge of the fabrication of nanocomposite materials, with special emphasis on plasma forming of bulk parts. Future challenges facing the development of methods for consolidating nanocomposites with retained nanostructures are also highlighted.
Scanning Probe Microscopy Measurements of Friction
Authors: Perry Scott S.
Published: February 2011

This article describes the details of scanning probe microscopy measurements of interfacial friction from an experimental perspective. In such studies, the probe tip is taken as a model of a single asperity within a tribological contact, and interfacial forces are measured as a function of the sliding contact of the probe tip with the surface. With appropriate detection schemes, friction and load forces can be monitored simultaneously and used together to describe the frictional properties of the microscopic contact. This article provides a detailed description of the procedures and protocols of friction measurements performed with scanning probe microscopy, the relevant properties of probe tips, and the influence of environment on microscopic friction measurements. In addition, the article provides a brief overview of several categories of friction studies performed with scanning probe microscopy, highlighting the type of materials characterized in these studies as well as the importance and impact of the microscopic measurements.
High-Performance YBCO-Coated Superconductor Wires
Authors: Paranthaman M. Parans , Izumi Teruo
Published: February 2011

This issue of MRS Bulletin provides an overview of the current status of research and development in the area of high-temperature superconductor (HTS) wires. High-temperature oxide superconductors, discovered in the late 1980s, are moving into the second generation of their development.The first generation relied on bismuth strontium calcium copper oxide, and the second generation is based on yttrium barium copper oxide, which has the potential to be less expensive and to perform better.The potential uses of HTS wires for electric power applications include underground transmission cables, oil-free transformers, superconducting magnetic-energy storage units, fault-current limiters, high-efficiency motors, and compact generators.Wires of 10–100 m in length can now be made, but material and processing issues must be solved before an optimized production scheme can be achieved.This issue covers a range of processing techniques using energetic beams, rolling, and laser and chemical methods to form wires with good superconducting properties.
MOCVD-Based YBCO-Coated Conductors
Authors: Selvamanickam V. , Xie Y. , Reeves J. , Chen Y.
Published: February 2011

Metalorganic chemical vapor deposition (MOCVD) is a well-developed deposition process that shows great promise for scaling up the production of high-temperature superconductors (HTSs) to quickly fabricate useful lengths of superconducting tapes and wires.The primary advantage of MOCVD is its potential for high tape throughput, a key factor in determining the cost of second-generation HTS tapes.This article details progress in long-length HTS tape fabrication, high-throughput processing, and techniques to improve critical current levels in high magnetic fields.
Flash Memory Scaling
Authors: Fazio Al
Published: February 2011

In order to meet technology scaling in the field of solid-state memory and data storage, the mainstream transistor-based flash technologies will start evolving to incorporate material and structural innovations. Dielectric scaling in nonvolatile memories is approaching the point where new approaches will be required to meet the scaling requirements while simultaneously meeting the reliability and performance requirements of future products. High-dielectric-constant materials are being explored as possible candidates to replace the traditional SiO2 and ONO (oxide/nitride/oxide) films used today in memory cells. Likewise, planar-based memory cell scaling is approaching the point where scaling constraints force exploration of new materials and nonplanar, three-dimensional scaling alternatives. This article will review the current status and discuss the approaches being explored to provide scaling solutions for future transistor floating-gate-based nonvolatile memory products. Based on the introduction of material innovations, it is expected that the planar transistor-based flash memory cells can scale through at least the end of the decade (2010) using techniques that are available today or projected to be available in the near future. More complex, structural innovations will be required to achieve further scaling.
Up Close: The Institute for Complex Adaptive Matter, An Emergent Institution
Authors: Boebinger Greg , Cox Daniel L. , Hurd Alan J. , Pines David
Published: February 2011

Many of the key challenges and opportunities in the study of matter involve complex and collective phenomena in which many parts exhibit organization without a central instruction set or clock. At the core of this enterprise in the study of matter is the search for an understanding of “emergent behavior”—that is, phenomena whose ultimate cause involves interactions between many simple units but which cannot be easily predicted from knowledge of the component parts alone. Examples of emergence are ordered convection cells in fluids, metabolic processes in cells, cognition, and stripes in superconductors. Our shorthand designation for soft, hard, and living matter exhibiting emergent behavior is “complex adaptive matter.”
Three-Dimensional X-Ray Diffraction Microscopy Using High-Energy X-Rays
Authors: Poulsen Henning F. , Jensen Dorte Juul , Vaughan Gavin B.M.
Published: February 2011

Three-dimensional x-ray diffraction (3DXRD) microscopy is a tool for fast and nondestructive characterization of the individual grains, subgrains, and domains inside bulk materials. The method is based on diffraction with very penetrating hard x-rays (E ≥ 50 keV), enabling 3D studies of millimeter-to-centimeter-thick specimens.The position, volume, orientation, and elastic and plastic strain can be derived for hundreds of grains simultaneously. Furthermore, by applying novel reconstruction methods, 3D maps of the grain boundaries can be generated. The 3DXRD microscope in use at the European Synchrotron Radiation Facility in Grenoble, France, has a spatial resolution of ∼5 μm and can detect grains as small as 150 nm. The technique enables, for the first time, dynamic studies of the individual grains within polycrystalline materials. In this article, some fundamental materials science applications of 3DXRD are reviewed: studies of nucleation and growth kinetics during recrystallization, recovery, and phase transformations, as well as studies of polycrystal deformation.
Recent Advances in Methods of Forming Carbon Nanotubes
Authors: Liu Jie , Fan Shoushan , Dai Hongjie
Published: February 2011

Since their discovery, carbon nanotubes, both single-walled and multiwalled, have been a focus in materials research. Fundamental research and application development hinge on high-quality nanotube materials and controlled routes to their organization and assembly. The aim of this article is to provide updated information on recent progress in the synthesis of carbon nanotubes.
Nanotubes and the Pursuit of Applications
Authors: de Heer Walt A.
Published: February 2011

A wide range of potential applications was suggested shortly after carbon nanotubes were discovered, including new super-strong materials, field-emission devices, hydrogen storage systems, novel electronic devices, and more. In this article, the actual advances in the technology of nanotubes over the last decade are examined. Particular attention is focused on current commercially viable applications and those with imminent commercial promise. The relatively large number of nanotube-related patents and nanotube-based startup companies stand in contrast to the relatively low output in commercial applications. The drive toward nanotube applications, in contrast to nanotube science, is investigated.
Photocatalysis of Cementitious Materials: Clean Buildings and Clean Air
Authors: Cassar Luigi
Published: February 2011

While the primary function of concrete is structural, its pervasiveness in our society lends it to other functions and creates the need for it to maintain its integrity and aesthetic quality. Therefore, concrete with added functionality–for example, self-cleaning characteristics and the ability to remove pollutants–is desirable. Heterogeneous photocatalysis (e.g., gas–solid or liquid–solid catalytic processes caused by light irradiation) by semiconductor particles or coatings has now reached a high level of development and is a promising technology for the reduction of global environmental pollutants. Among the various semiconductor materials, TiO2 in the form of anatase has attracted wide interest, due to its strong oxidizing power under near-UV radiation, its chemical stability when exposed to acidic and basic compounds, its chemical inertness in the absence of UV light, and the absence of toxicity. TiO2 has proved very effective in the reduction of pollutants such as NOx, aromatics, ammonia, and aldehydes. Surprisingly, the use of TiO2 in combination with cementitious materials has shown a favorable synergistic effect in the reduction of pollutants. These new materials have already found relevant applications in self-cleaning building walls and in the reduction of urban pollutants.
Stacked, Folded, and Bent Lipid Membranes
Authors: Sasaki Darryl Y. , Stevens Mark J.
Published: February 2011

Lipid membranes are generally thought of as flat or spherical structures, much as we would view the plasma membrane of a cell. Within the cell, however, there exists a wide variety of stacked, folded, and other forms of bent structures that support and enable such functions as photosynthesis, light-sensing, protein synthesis, molecular shuttling, chemical uptake and release, and cell division. These functions benefit from the high asymmetry of the membrane. Stacked or folded structures provide a highly concentrated and ordered assembly for facile energy and molecular transport, while bent structures facilitate budding, division, and fusion events. In this article, we survey the progress made in understanding the formation of these membrane architectures, the development of synthetic forms of stacked and folded assemblies, and the unique materials issues they present.
Designing New Structural Materials Using Density Functional Theory: The Example of Gum MetalTM
Authors: Ikehata H. , Nagasako N. , Kuramoto S. , Saito T.
Published: February 2011

As an example of the application of density functional theory (DFT) to materials design, we describe our use of ab initio calculations based on DFT to develop a new structural material: Gum MetalTM, a novel, multifunctional titanium alloy with a low Young's modulus and high strength. We first carried out calculations on elastic constants in several Ti-X binary alloys to obtain the basic principles on which to determine the compositional limitations of an alloy with a low modulus. The elastic properties in the Ti-based binary alloys were successfully estimated by ab initio calculations, with the result implying absolute elastic softening at the valence electron number per atom, e/a, of 4.24. We also studied the effects of additional elements experimentally and, by comparison with electronic-structure calculations, found two more key parameters (approximately representing bond strength and electronegativity), critical for the design of practical elastic properties. We discuss dislocation-free plastic deformation of Gum Metal and its relation to the absolute elastic softening at an e/a value of 4.24, and finally we discuss the prospects for future applications of DFT in structural materials.
Membranes for Hydrogen Purification: An Important Step toward a Hydrogen-Based Economy
Authors: Nenoff Tina M. , Spontak Richard J. , Aberg Christopher M.
Published: February 2011

Production of pure molecular hydrogen is essential to the realization of the proposed “hydrogen economy” that could ultimately provide hydrogen as a clean, renewable source of energy; eliminate the industrialized world's dependence on petroleum; and reduce the generation of greenhouse gases linked to global warming. A crucial step in obtaining pure hydrogen is separating it from other gaseous compounds—mainly CO2—that often accompany hydrogen in industrial chemical reactions. Advanced membrane technology may prove to be the key to the successful, economical production of molecular hydrogen.

Size-sieving glassy polymer membranes can separate H2 on the basis of its small size. Alternatively, reverse-selective rubbery polymers can expedite the passage and, hence, removal of CO2 due to its relatively high solubility in such membranes alone or in conjunction with dissociative chemical reactions. Transition-metal membranes and their alloys can adsorb H2 molecules, dissociate the molecules into H atoms for transport through interstitial sites, and subsequently recombine the H atoms to form molecular H2 again on the opposite membrane side. Microporous amorphous silica and zeolite membranes comprising thin films on a multilayer porous support exhibit good sorption selectivity and high diffusion mobilities for H2, leading to high H2 fluxes. Finally, carbon-based membranes, including carbon nanotubes, may be viable for H2 separation on the basis of selective surface flow and molecular sieving. A wide variety of materials challenges exist in hydrogen purification, and the objective of this issue of MRS Bulletin is to address those challenges and their potential solutions from basic principles.
Pharmaceutical Materials Science: An Active New Frontier in Materials Research
Authors: Elliott James , Hancock Bruno
Published: February 2011

The discipline of materials science has most commonly been associated with the study of structural or functional materials for engineering applications, such as metals, ceramics, and composites, but there are now, increasingly, great opportunities involving applications to soft matter, including polymers, powders, and biomaterials. The emerging discipline of pharmaceutical materials science attempts to apply physical principles common in materials science to challenges in such areas as drug delivery, control of drug form, manufacture and processing of nanoscopic and microscopic particle systems, and the structure and properties of bulk powders and their assemblies (e.g., tablets) for use in pharmaceutical applications. In this issue of MRS Bulletin, we have attempted to capture a snapshot of this rapidly developing new area of materials research, in order to bring it to the attention of the wider materials science community.
Particle Engineering: Fundamentals of Particle Formation and Crystal Growth
Authors: Lee Alfred Y. , Myerson Allan S.
Published: February 2011

The engineering of particles with customized properties optimized for dosage form manufacture (tablet, capsule, ointment, etc.) has long been a goal of the pharmaceutical industry. Particles can be designed through modification in the size, morphology, and packing arrangement of the solids. The most common approach in achieving this is through crystallization. In this bottom-up process, the two main steps, nucleation and crystal growth, both play a decisive role in shaping the quality of the final crystalline product. In this review, the role of nucleation and crystal growth in controlling particle properties is discussed, and examples are provided that demonstrate the variation in solid-state properties as a function of size, habit (morphology), and internal structure of the particles. In addition, the role of particle properties in product performance and dosage form development of pharmaceuticals is also discussed.
Materials Advances through Aberration-Corrected Electron Microscopy
Authors: Pennycook S.J. , Varela M. , Hetherington C.J.D. , Kirkland A.I.
Published: February 2011

Over the last few years, the performance of electron microscopes has undergone a dramatic improvement, with achievable resolution having more than doubled. It is now possible to probe individual atomic sites in many materials and to determine atomic and electronic structure with single-atom sensitivity. This revolution has been enabled by the successful correction of the dominant aberrations present in electron lenses. In this review, the authors present a brief overview of these instrumental advances, emphasizing the new insights they provide to several areas of materials research.
Formation of Bulk Metallic Glasses and Their Composites
Authors: Li Y. , Poon S. J. , Shiflet G. J. , Xu J. , Kim D. H. , Löffler J. F.
Published: February 2011

A great expansion in the number of alloy compositions known to give bulk metallic glasses (BMGs) has occurred in recent years. This progress is reviewed, and factors contributing to glass-forming ability are discussed. Practical strategies for pinpointing compositions with optimum glass-forming ability are presented, with examples of their use. Consideration is also given to the wide range of possibilities for BMG-based composites.
Mechanical Properties of Bulk Metallic Glasses
Authors: Yavari A. R. , Lewandowski J. J. , Eckert J.
Published: February 2011

In the absence of dislocation-mediated crystallographic slip, room-temperature deformation in metallic glasses occurs in thin shear bands initially only ∼10 nm thick. A sharp drop in viscosity (shear softening) occurs in deformed glassy matter and facilitates additional flow in existing shear bands. This further localization of plastic flow leads to shearing-off failure without any significant macroscopic plasticity.

However, whereas most bulk metallic glasses fail in this manner, some undergo surprisingly extensive plastic deformation (in some cases, up to 50% or more) in compression or bending. When this occurs, the flow is “jerky,” as indicated by serrated stress–strain curves. Each serration may correspond to the emission of a shear band that then ceases to operate, at least temporarily, despite the predicted shear softening. As elastic energy is converted to heat during shear, temperatures rise sharply at or near shear bands. This heating may lead to the growth of nanocrystals that then block propagation of shear bands and cracks. The understanding of the dependence of mechanical response of metallic glasses on intrinsic (elastic constants, chemistry) and extrinsic factors (shapes, flaws) is the subject of intense current interest.
Focused Ion Beam Microscopy and Micromachining
Authors: Volkert C. A. , Minor A. M.
Published: February 2011

The fairly recent availability of commercial focused ion beam (FIB) microscopes has led to rapid development of their applications for materials science. FIB instruments have both imaging and micromachining capabilities at the nanometer–micrometer scale; thus, a broad range of fundamental studies and technological applications have been enhanced or made possible with FIB technology. This introductory article covers the basic FIB instrument and the fundamentals of ion–solid interactions that lead to the many unique FIB capabilities as well as some of the unwanted artifacts associated with FIB instruments. The four topical articles following this introduction give overviews of specific applications of the FIB in materials science, focusing on its particular strengths as a tool for characterization and transmission electron microscopy sample preparation, as well as its potential for ion beam fabrication and prototyping.