Hydrogen generation and separation using Gd0.2Ce0.8O1.9−δ–Gd0.08Sr0.88Ti0.95Al0.05O3±δ mixed ionic and electronic conducting membranes

Decomposition of steam under a chemical driving force at moderate temperatures offers a simple and economical way to generate hydrogen. A significant amount of hydrogen can be generated and separated by splitting steam and removing the oxygen using Gd_0.2Ce_0.8O_1.9−δ (GDC)–Gd_0.08Sr_0.88Ti_0.95Al_0.05O_3±δ (GSTA) mixed oxygen ionic and electronic conducting membranes. Hydrogen generation experiments for the self-supported thick membranes and porous supported thin membranes were conducted at different oxygen partial pressure gradients across the membrane established using H₂–H₂O mixture gas. Experimental results indicate that the hydrogen generation from steam using GDC–GSTA MIEC membranes at elevated temperatures is mainly controlled by the bulk diffusion of oxygen for the self-supported thick membranes, while the permeation process for the porous supported thin membranes is mixed controlled, i.e. the hydrogen generation/oxygen permeation process is controlled by the surface exchange reactions and bulk diffusion of oxygen through the MIEC membrane. A mathematical model for the calculation of the area specific hydrogen generation rate is proposed in this paper based on the measured oxygen partial pressures, gas compositions, and gas flow rates of the inlet and outlet gases on feed side of the membrane, as well as the permeation area of the membrane.     

Three-dimensional filtering of engineering surfaces using envelope system

With the advent of cheap and powerful computers, three-dimensional evaluation of surfaces is possible. This article deals with the development of a computational method for three-dimensional filtering of surface using the envelope system (E-System, a dialation using a sphere) concept. The shape of the envelope surface is dependent only on the prominent peak points on the surface. The computational method developed uses this set of prominent points to facilitate fast evaluation of the envelope surface. Roughness values obtained by two, two-and-a-half, and three-dimensional evaluation of typical surfaces are also given. This procedure of waviness filtering gives a strong base for an integrated approach for surface and form measurements.     

An analysis of intermetallics formation of gold and copper ball bonding on thermal aging

In IC packages, thermosonic wire bonding is the preferred method for making electrical connections between the die pad and lead frame. These interconnect are made using fine metal wires. On thermal aging (under 175 °C for 5 h) gold aluminide easily forms in gold ball bonds while formation of intermetallic compound is absent in case of copper ball bonds. An analysis of the atomic property of the elements bonded explains that atomic radii and electronegativity factors favor gold aluminide formation.     

Die attach failures related to wafer back metal processing—an AES study

Die attach failures on Cr/Ni/Au back-metallised silicon wafers have been studied under different process conditions. The Auger studies on the failed devices show that the formation of nickel oxide causes poor die attachment even for an Au film thickness of ∼ 500 Å. The failures simulated experimentally revealed that nickel oxide formation depends on the film sintering conditions.     

Phase Constitution During Sintering of Red Mud and Red Mud–Fly Ash Mixtures

The phase constitution during the sintering of pure red mud and red mud–fly ash mixtures was studied in the temperature range of 900°–1250°C. The phases formed at different sintering temperatures were analyzed by X-ray powder diffraction. The phases that are likely to form at equilibrium at any isotherm were predicted using the Gibbs free energy minimization technique and the databases provided in the FactSage software. Although the thermodynamic prediction is in reasonable agreement with the experimental results for the major phases, there is some disagreement regarding the minor phases, especially the more complex phases. The major limitation of the thermodynamic approach presently is the non-availability of thermodynamic data for several complex and multi-component solution phases.     

In Vitro Selection of a Single-Stranded DNA Molecular Recognition Element against Atrazine

Widespread use of the chlorotriazine herbicide, atrazine, has led to serious environmental and human health consequences. Current methods of detecting atrazine contamination are neither rapid nor cost-effective. In this work, atrazine-specific single-stranded DNA (ssDNA) molecular recognition elements (MRE) were isolated. We utilized a stringent Systematic Evolution of Ligands by Exponential Enrichment (SELEX) methodology that placed the greatest emphasis on what the MRE should not bind to. After twelve rounds of SELEX, an atrazine-specific MRE with high affinity was obtained. The equilibrium dissociation constant (K_d) of the ssDNA sequence is 0.62 ± 0.21 nM. It also has significant selectivity for atrazine over atrazine metabolites and other pesticides found in environmentally similar locations and concentrations. Furthermore, we have detected environmentally relevant atrazine concentrations in river water using this MRE. The strong affinity and selectivity of the selected atrazine-specific ssDNA validated the stringent SELEX methodology and identified a MRE that will be useful for rapid atrazine detection in environmental samples.     

Asymmetric Contribution of Aromatic Interactions Stems from Spatial Positioning of the Interacting Aryl Pairs in β‐Hairpins

Isolated aromatic interactions in designed octapeptide β‐hairpin scaffolds display a near‐universal T‐shaped face‐to‐edge geometry in all positional permutations, with the exception of aryl‐Trp interactions. The heterogeneous asymmetric indole ring of Trp competes for a “shielding” face geometry, which lowers the scaffold stability in FtE aryl‐Trp pairs. Assessment of the contributions of aryl pairs (in the absence of solvent‐driven interactions) to the overall β‐hairpin structure reveals the superiority of Trp‐Phe and Trp‐Tyr contributions over the well‐established scaffold stabilization by Trp‐Trp.