Review of computational approaches to predict the thermodynamic stability of inorganic solids

Journal of Materials Science - Improvements in the efficiency and availability of quantum chemistry codes, supercomputing centers, and open materials databases have transformed the accessibility of...     

High-efficiency binary phase-transmission-grating using e-beam lithography

Abstract

Rigorous coupled-wave analysis indicates that diffraction efficiencies greater than 99% are feasible for dielectric phase-gratings with a rectangular profile. The use of rectangular rather than blazed profiles implies simplified fabrication techniques, since deep-etch submicrometre structuring techniques can be utilized. We identify several parameter combinations with high diffraction efficiencies using rigorous coupled wave analysis, demonstrate experimentally diffraction efficiencies of 94% in a Bragg mount configuration at a wavelength of 543 nm and discuss the influence of substrate thickness on the transmitted light intensities. A direct writing electron-beam lithography fabrication process gives wide flexibility in design realization.     

Transport and Metabolism of the Endogenous Auxin Precursor lndole-3-Butyric Acid

T Plant growth and morphogenesis depend on the levels and distribution of the plant hormone auxin. Plants tightly regulate cellular levels of the active auxin indole-3-acetic acid (IAA) through synthesis, inactivation, and transport. Although the transporters that move IAA into and out of cells are well characterized and play important roles in development, little is known about the transport of IAA precursors. In this review, we discuss the accumulating evidence suggesting that the IAA precursor indole-3-butyric acid (IBA) is transported independently of the characterized IAA transport machinery along with the recent identification of specific IBA efflux carriers and enzymes suggested to metabolize IBA. These studies have revealed important roles for IBA in maintaining IAA levels and distribution within the plant to support normal development.     

Particle atomic layer deposition of alumina for sintering yttria-stabilized cubic zirconia

The addition of aluminum oxide (Al₂O₃) as a sintering aid to yttria-stabilized zirconia (YSZ) reduces the required densification temperature. Sintering aids are incorporated using a number of processes which can lead to ambiguity when determining the effect of the sintering aid on the densification mechanism. In this study, a novel method for sintering aid addition, Particle Atomic Layer Deposition (ALD), was used to deposit an amorphous Al₂O₃ thin film on YSZ particles. Transmission electron microscopy confirmed the deposition of conformal Al₂O₃ thin films on the surface of the YSZ particles. The addition of Al₂O₃ to YSZ reduced the temperature at which densification began by ~75°C, and 2.2 wt% Al₂O₃ addition resulted in a minimum activation energy for the intermediate stage of densification. This concentration is well in excess of the solubility limit of Al₂O₃ in YSZ, showing that Al₂O₃ does not enhance the densification of YSZ solely by dissolving into the YSZ lattice and activating volume diffusion. The addition of 0.7 wt% Al₂O₃ with one Particle ALD cycle enhanced the ionic conductivity of YSZ by 23% after sintering at 1350°C for 2 hours, demonstrating that dense parts with high oxygen ion conductivities can be produced after sintering at reduced temperatures. One Particle ALD cycle is a fast, easily scaled-up process that eliminates the use of solvents and has substantial cost/performance advantages over conventional processing.     

Bücherschau

Ohne Zusammenfassung VDI     

Uncertainty in NIST Force Measurements

This paper focuses upon the uncertainty of force calibration measurements at the National Institute of Standards and Technology (NIST). The uncertainty of the realization of force for the national deadweight force standards at NIST is discussed, as well as the uncertainties associated with NIST’s voltage-ratio measuring instruments and with the characteristics of transducers being calibrated. The combined uncertainty is related to the uncertainty of dissemination for force transfer standards sent to NIST for calibration.     

High temperature low cycle fatigue in beta processed Ti-5Al-5Sn-2Zr-2Mo-0.25Si

The effects ofβ heat treatment andβ-work on microstructure and high temperature low cycle fatigue properties of Ti-5Al-5Sn-2Zr-2Mo-0.25Si were investigated. Strain control tests at total strains ranging from 1.2 to 2.5 pct were conducted at 427, 482, and 538 °C with frequencies of 10 and 0.4 cpm. The results showed shorter fatigue life at the higher temperature and lower frequency for all microstructural conditions.β-worked material with shorterα-platelet structure showed the highest fatigue strength for all test conditions. At these high temperatures, fatigue cracks initiate along theα/β interfaces with longer initial cracks in theβ-annealed condition which had longer interfaces. It is suggested that oxygen diffusion along theα/β interfaces is responsible for surface connected interfacial cracking leading to the observed temperature and frequency dependence. The better HTLCF life of theβ-worked material is related to the shorter initial interface cracks. Formerly with the Metals and Ceramics Division, AFML, W-PAFB, OH 45433     

Bioactive and nuclease-resistant L-DNA ligand of vasopressin

In vitro selection experiments have produced nucleic acid ligands (aptamers) that bind tightly and specifically to a great variety of target biomolecules. The utility of aptamers is often limited by their vulnerability to nucleases present in biological materials. One way to circumvent this problem is to select an aptamer that binds the enantiomer of the target, then synthesize the enantiomer of the aptamer as a nuclease-insensitive ligand of the normal target. We have so identified a mirror-image single-stranded DNA that binds the peptide hormone vasopressin and have demonstrated its stability to nucleases and its bioactivity as a vasopressin antagonist in cell culture.