Determination of the short-range order structure of Au-25 At. Pct Fe using wide-angle diffuse synchrotron X-Ray scattering

The short-range order (SRO) structure of a Au-25 at. pct Fe single crystal was studied using wide-angle diffuse synchrotron X-radiation scattering at room temperature. Two heat treatments were investigated: a 400 °C aging treatment for 2 days and a 440 °C treatment for 5 days, both preceded by solution treatment in the single-phase field and water-quenched to room temperature. Evolution of the SRO structure with aging was determined by fitting the two sets of Cowley-Warren (C-W) SRO parameters to a pair of 140,608-atom models. The microstructures, although quite disordered, showed a trend with aging for an increasing volume fraction of an Fe-enriched and an Fe-depleted environment. The Fe-enriched environment displayed a preference for Fe segregation to the {110} and {100} face-centered cubic (fcc) matrix planes. A major portion of the Fe-depleted environment was found to contain elements (and variations of these elements) of the Dl_a ordered superstructure. The SRO contained in the Fe-depleted environment may be best described in terms of the standing concentration wave packet (SCWP) model. This study provides, for the first time, a quantitative real-space view of the atomic arrangements, which make up both environments in the SRO structure of Au-25 at. pct Fe. Formerly Graduate Research Assistant, University of Illinois, Urbana, IL.     

Density functional theory and machine learning guided search for RE2Si2O7 with targeted coefficient of thermal expansion

Density functional theory (DFT) calculations and machine learning (ML) methods are used to establish a relationship between the crystal structures of rare-earth (RE) disilicates (RE₂Si₂O₇) and their coefficient of thermal expansion (CTE). The DFT total energy data predict the presence of several energetically competing crystal structures, which is rationalized as one of the reasons for observing polymorphism. An ensemble of support vector regression models is trained to rapidly predict the CTE as a function of RE₂Si₂O₇ crystal chemistry. Experiments subsequently validated the structure and CTE predictions for Sm₂Si₂O₇.     

Effects of CaTiO3 addition on microstructures and electrical properties of Na0.52K0.48NbO3 lead-free piezoelectric ceramics

In this article, various amounts of CaTiO₃ (CT) were added into (Na_0.52K_0.48)NbO₃ (NKN) ceramics using conventional oxide-mixing method for improving NKN's properties. The experimental results show that the (1?x)(Na_0.52K_0.48)NbO₃–xCaTiO₃ (x=0～0.07) solid solution system can be successfully synthesized. Addition of CaTiO₃ not only effectively prevents materials from deliquescence, but also improves the density and the electrical properties of the ceramics. The dielectric constant–temperature (ε_r?T) curves exhibit that the temperatures of the Curie point (T_c) and the phase transition from tetragonal to orthorhombic (T_O?T) are decreasing monotonously as the amount of CT addition is increased. A morphotropic phase boundary (MPB) can be found in the (1?x)NKN?xCT solid solution system as the doping amount of x=0.03, and the 0.97NKN–0.03CT ceramics, with a high bulk density, 98% theoretical density, and an appropriate grain size of about 1～2 μm, present a superior domain switching ability and the optimum properties: d₃₃=117 pC/N, k_p=0.39, P_r=21 μC/cm², and T_c=333 °C.     

Common needs and different agendas: How trainee teachers make progress in their ability to use ICT in subject teaching. Some lessons from the UK

The paper reports on the outcomes of a British Educational Communications and Technology Agency (BECTa) funded study which explored the views of teacher trainees and their mentors in two different school subjects on what strategies, interventions and resources had a positive impact on their ability to use ICT effectively in their subject teaching.The research aimed to explore both commonalities in trainees’ views of which strategies and interventions had a positive influence on their ability to use ICT effectively in subject teaching, and subject discipline dimensions of ICT use, i.e. the ways in which training needs might vary between trainees in different school subjects.The study focused on the views of two successive cohorts of science and history trainees (133 trainees in all), and 21 of their supervising mentors. The outcomes showed that some important determinants of progression in the ability to deploy ICT confidently and effectively in subject teaching were common to both subject groups, but that there were differing views on which ICT applications offered most potential for enhancing teaching and learning in their subject and differences in their preferred priorities for investment in ICT. The study also revealed that trainees felt that many of the experiences and resources which they had encountered in the course of their training had not been helpful.A follow up survey was undertaken of 114 trainees across six subject areas to further explore some of the findings from the initial survey. The concluding section of the paper suggests ways in which trainee teachers might be prepared more effectively for using ICT in their subject teaching.     

Visualization and debugging of distributed multiagent systems

Visualizing the behavior of systems with distributed data, control, and process is a notoriously difficult task. Each component in the distributed system has only a local view of the whole setup, and the onus is on the user to integrate, into a coherent whole, the large amounts of limited information they provide. In this article, we describe an architecture and an implemented system for visualizing and controlling distributed multiagent applications. The system comprises a suite of tools, with each tool providing a different perspective of the application being visualized . Each tool interrogates the components of the distributed application, collates the returned information, and presents this information to users in an appropriate manner. This in essence, shifts the burden ofinference from the user to the visualizer. Our visualizer has been evaluated on four distributed multiagent systems: a travel management application, a telecommunications network management application, a business process management demonstrator, and an electronic commerce application. Lastly, we briefly show how the suite of tools can be used together for debugging multiagent applications - a process we refer to as debugging via corroboration.     

Compressive response of multilayered pyramidal lattices during underwater shock loading

The quasi-static and dynamic compressive mechanical response of a multilayered pyramidal lattice structure constructed from stainless-steel was investigated. The lattices were fabricated by folding perforated 304 stainless steel sheets and bonding them to thin intervening sheets using a transient liquid-phase bonding technique. The resulting structure was attached to thick face sheets and the through thickness mechanical response was investigated quasi-statically and dynamically, in the latter case using a planar explosive loading technique. The lattice is found to crush in a progressive manner by the sequential (cooperative) buckling of truss layers. This results in a quasi-static stress strain response that exhibits a significant “metal foam” like stress plateau to strains of about 60% before rapid hardening due to truss impingement with the intermediate face sheets. During dynamic loading, sequential buckling of the truss layers was manifested as a series of transmitted pressure pulses measured at the back face of the test samples. The sequential buckling extended the duration of the back face pressure–time waveform and significantly reduced the transmitted pressure measured at the back face. The impulse transmitted to the structure is found to be about 28% less than that predicted by analytic treatments of the fluid-structure interaction for fully supported structures. This transmitted impulse reduction appears to be a consequence of the wet side face sheet movement away from the blast wave and is facilitated by the low crush resistance of the lattice structure.     

Engineered clay products for the paper industry

The need for kaolin pigments by the paper industry with controlled optical and physical properties have significantly changed the type of filler and coating clays available to the paper industry. Processing equipment now used in the production of kaolin products is much more sophisticated and controllable than in the past. Better understanding of the mineralogy and the physical and chemical properties of kaolins, in addition to improved processing techniques, has allowed the kaolin processors to produce engineered or tailored grades that meet particular needs of the user. Particle size and shape, brightness, gloss, opacity, and viscosity can be altered and controlled to meet specific requirements of the paper coater. Examples of several types of engineered products available for use by the paper industry are discussed.     

Titanium Alloy Lattice Structures with Millimeter Scale Cell Sizes

Titanium sandwich panels with cellular cores of a uniform 1–5 mm diameter open cell size are well suited for impact energy absorption and cross flow heat exchange applications. Periodic cellular structures (lattices) made from high specific strength, high temperature alloys are preferred for these multifunctional uses. A diffusion bonding method has been applied here to make cellular lattice structures from a Ti–6A1–4V alloy. To illustrate the approach, lattice structures with both square and diamond collinear topologies, a 2 mm open cell size, and a relative density of 15% were made from 254 µm diameter titanium alloy wires. These structures were found to have a compressive strength of 40 ± 5 MPa that was controlled by plastic yield followed by buckling of the struts. The cellular structures have been brazed to titanium alloy face sheets to create sandwich panel structures that appear well suited for multifunctional applications up to 420 °C.     

Residual strain gradient determination in metal matrix composites by synchrotron X-ray energy dispersive diffraction

An X-ray technique for the measurement of internal residual strain gradients near the continuous reinforcements of metal matrix composites has been investigated. The technique utilizes high intensity white X-ray radiation from a synchrotron radiation source to obtain energy spectra from small (10^-3 mm³) volumes deep within composite samples. The energy peak positions satisfy Bragg’s law and allow determination of the lattice parameter. As the probe volume is translated, the peaks of the spectra shift and are used to infer lattice spacing changes and thus strains with a precision of 10^-3 to 10^-4 (depending on the sample grain size/probe volume ratio). The viability of the technique has first been tested using a model system with 800 μm A1₂O₃ fibers and a commercial purity titanium matrix. For this system (which remained elastic on cooling), good agreement was observed between the measured residual radial and hoop strain gradients and those estimated from a simple elastic concentric cylinders model. The technique was then used to assess the strains near (SCS-6) silicon carbide fibers in a Ti-14Al-21Nb matrix after consolidation processing. Reasonable agreement between measured and calculated strains was seen provided the probe volume was located 50 μm or more from the fiber/matrix interface. Close to the interface, the measured elastic strains were smaller than anticipated, due to relaxation of the residual stress by plasticity and radial cracking during sample cooling. Formerly Graduate Student, Department of Materials Science, University of Virginia, Charlottesville     

Decomposition and dissolution kinetics ofδ′ precipitation in Al-Li binary alloys

Aside from its technological importance, the Al-Li alloy system also exhibits interesting phase transformations involving both equilibrium and metastable states. Recent theoretical studies have shown that a supersaturated solid solution could take different transformation paths when it is quenched into theα +γ′ field. Suggestions were made that a rapidly quenched solution phase should first undergo a congruent ordering transformation before it decomposes into a two-phase mixture by either a secondary spinodal decomposition or the classical nucleation and growth process. Moreover, a metastable miscibility gap was predicted at lower temperatures. The objective of this research is to study the transformation paths and dynamics in Al-Li binary alloys of three compositions (5.2, 7.0, and 12.0 at. pct Li). This investigation emphasizes thein situ small-angle X-ray scattering (SAXS) observations on specimens subjected to various aging conditions. Special attention is paid to the early stages of the transformation in an attempt to characterize the various possible modes of phase separation on one hand and to study the dynamics of the precipitation process on the other. The following results are obtained: the congruent ordering precedes decomposition at low temperatures; the metastableγ′ solvus curve is reconfirmed; but the predicted metastable miscibility gap is not found. Guinier radii measurements of the particles showed Ostwald ripening is quickly reached upon heating to the aging temperatures. Slowing down behavior is seen at aging temperatures close to the solvus boundary. Activation energies for Li diffusion were obtained using the modified Lifshitz, Slyozov, and Wagner (MLSW) model. A test of dynamical scaling behavior is carried out for the Al-12.0 at. pct Li alloy. Formerly Visiting Scientists at the University of Illinois