Direct Observation of Localized Radial Oxygen Migration in Functioning Tantalum Oxide Memristors

Oxygen migration in tantalum oxide, a promising next-generation storage material, is studied using in-operando x-ray absorption spectromicroscopy and is used to microphysically describe accelerated evolution of conduction channel and device failure. The resulting ring-like patterns of oxygen concentration are modeled using thermophoretic forces and Fick diffusion, establishing the critical role of temperature-activated oxygen migration that has been under question lately.Comment: 7 pages, Advanced Materials (2016); updated abstrac

Trial Advocacy - Final Trial Materials: 2016-17

Course Number 5270https://digitalcommons.osgoode.yorku.ca/casebooks/1062/thumbnail.jp

Special Education Law and Practice: Cases and Materials (2016)

Special Education Law and Practice is an experientially-focused casebook that also serves as a reference for attorneys who practice special education law and anyone interested in learning about the special education process. The casebook covers substantive special education rights, racial disparities in special education, discipline, procedural protections, federal court litigation, remedies, and attorneys\u27 fees. Each chapter begins with a problem, rich in facts and law, that places the student in the position of an attorney trying to resolve a problem for a client using that chapter\u27s materials. Comprehensive notes expand the areas covered by featured cases.https://digitalcommons.nyls.edu/fac_books/1077/thumbnail.jp

Measuring nonlinear stresses generated by defects in 3D colloidal crystals

The mechanical, structural and functional properties of crystals are determined by their defects and the distribution of stresses surrounding these defects has broad implications for the understanding of transport phenomena. When the defect density rises to levels routinely found in real-world materials, transport is governed by local stresses that are predominantly nonlinear. Such stress fields however, cannot be measured using conventional bulk and local measurement techniques. Here, we report direct and spatially resolved experimental measurements of the nonlinear stresses surrounding colloidal crystalline defect cores, and show that the stresses at vacancy cores generate attractive interactions between them. We also directly visualize the softening of crystalline regions surrounding dislocation cores, and find that stress fluctuations in quiescent polycrystals are uniformly distributed rather than localized at grain boundaries, as is the case in strained atomic polycrystals. Nonlinear stress measurements have important implications for strain hardening, yield, and fatigue.Comment: in Nature Materials (2016

Brittle or Quasi-Brittle Fracture of Engineering Materials 2016

1Department of Engineering Design and Materials, Norwegian University of Science and Technology (NTNU), 7491 Trondheim, Norway 2Faculty of Mechanical Engineering, Politehnica University of Timisoara, Blvd. M. Viteazu, Nr. 1, 300222 Timisoara, Romania 3Fatigue and Fracture Research Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics, School of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran 16846, Iran 4Institute of Strength Physics and Material Science, Department of Mechanical Engineering & Aeronautics, Russian Academy of Sciences, Siberian Branch, Tomsk 634021, Russia 5Laboratory of Technology & Strength of Materials (LTSM), Department of Mechanical Engineering & Aeronautics, University of Patras, 26500 Patras, Greec

Commercial Law: Secured Transactions Statutory and Supplementary Materials: 2016-17

Course Number 2030https://digitalcommons.osgoode.yorku.ca/casebooks/1060/thumbnail.jp

Top Selected Papers in the Physical Chemistry of Energy Materials 2016–2017

Research on energy materials continues to generate a huge amount of activity. The growth of the community in China is enormous, in terms of the creation of research facilities, endowing of major projects, and hiring of personnel, often rather young scientific experts who obtain starting grants after having spent a successful period of research in other laboratories. Energy materials research also continues to expand at a large rate of growth all over the world. Recently we observed the appearance of a serious number of new scientific journals across a variety of publishers that in many cases become rapidly successful. This is because the supply of papers on energy materials research appears to have no physical limits. We are very conscious that many investigators establish their choices of research strategy considering the demand of the topics in terms of facility of publication, impact, and funding. The attitudes and procedures of scientific journals form an essential piece in the machinery of the scientific system [...

Formation of Aluminum Particles with Shell Morphology during Pressureless Spark Plasma Sintering of Fe-Al Mixtures: Current-Related or Kirkendall Effect?

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects when electric current passes through the underdeveloped inter-particle contacts. Until now, inter-particle interactions during pressureless SPS have been studied mainly for particles of the same material. In this work, we focused on the interactions between particles of dissimilar materials in mixtures of micrometer-sized Fe and Al powders forming porous compacts during pressureless SPS at 500-650 °C. Due to the chemical interaction between Al and Fe, necks of conventional shape did not form between the dissimilar particles. At the early interaction stages, the Al particles acquired shell morphology. It was shown that this morphology change was not related to the influence of electric current but was due to the Kirkendall effect in the Fe-Al system and particle rearrangement in a porous compact. No experimental evidence of melting or melt ejection during pressureless SPS of the Fe-Al mixtures or Fe and Al powders sintered separately was observed. Porous FeAl-based compacts could be obtained from Fe-40at.%Al mixtures by pressureless SPS at 650 °C

A Scanning Transmission X-ray Microscopy Study of Cubic and Orthorhombic C₃A and Their Hydration Products in the Presence of Gypsum.

This paper shows the microstructural differences and phase characterization of pure phases and hydrated products of the cubic and orthorhombic (Na-doped) polymorphs of tricalcium aluminate (C₃A), which are commonly found in traditional Portland cements. Pure, anhydrous samples were characterized using scanning transmission X-ray microscopy (STXM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and demonstrated differences in the chemical and mineralogical composition as well as the morphology on a micro/nano-scale. C₃A/gypsum blends with mass ratios of 0.2 and 1.9 were hydrated using a water/C₃A ratio of 1.2, and the products obtained after three days were assessed using STXM. The hydration process and subsequent formation of calcium sulfate in the C₃A/gypsum systems were identified through the changes in the LIII edge fine structure for Calcium. The results also show greater Ca LII binding energies between hydrated samples with different gypsum contents. Conversely, the hydrated samples from the cubic and orthorhombic C₃A at the same amount of gypsum exhibited strong morphological differences but similar chemical environments

Neutron radiography based visualization and profiling of water uptake in (un)cracked and autonomously healed cementitious materials

Given their low tensile strength, cement-based materials are very susceptible to cracking. These cracks serve as preferential pathways for corrosion inducing substances. For large concrete infrastructure works, currently available time-consuming manual repair techniques are not always an option. Often, one simply cannot reach the damaged areas and when making those areas accessible anyway (e.g., by redirecting traffic), the economic impacts involved would be enormous. Under those circumstances, it might be useful to have concrete with an embedded autonomous healing mechanism. In this paper, the effectiveness of incorporating encapsulated high and low viscosity polyurethane-based healing agents to ensure (multiple) crack healing has been investigated by means of capillary absorption tests on mortar while monitoring the time-dependent water ingress with neutron radiography. Overall visual interpretation and water front/sample cross-section area ratios as well as water profiles representing the area around the crack and their integrals do not show a preference for the high or low viscosity healing agent. Another observation is that in presence of two cracks, only one is properly healed, especially when using the latter healing agent. Exposure to water immediately after release of the healing agent stimulates the foaming reaction of the polyurethane and ensures a better crack closure