Phase-field modeling of void evolution and swelling in materials under irradiation

Void swelling is an important phenomenon observed in both nuclear fuels and cladding materials in operating nuclear reactors. In this work we develop a phase-field model to simulate void evolution and void volume change in irradiated materials. Important material processes, including the generation of defects such as vacancies and self-interstitials, their diffusion and annihilation, and void nucleation and evolution, have been taken into account in this model. The thermodynamic and kinetic properties, such...     

Miniature Wet-Bulb Technique for Measuring Gas Concentrations in Condensing or Evaporating Systems

Abstract

An analysis is presented to show that a miniature wet-bulb/dry-bulb probe can provide easy, rapid, and accurate point measurements of noncondensable gas concentrations in condensing or evaporating systems. The probe consists of a liquid-soaked porous sphere as small as 0.5 mm in diameter with a fine-gauge thermocouple embedded at its center. Performance of the probe is shown to improve with decreasing wet-bulb size. Measurements of only the total pressure and point wet-bulb temperature are needed to determine the local gas concentration for most gas-vapor systems. The use of the technique in systems with steep concentration gradients is demonstrated by application to the well-studied problem of the gas-loaded two-phase thermosyphon. 195pt     

Highly Stereoselective Synthesis of a C2-Symmetric 2,2′-Bipyridine Derived from Glucose

2-Bromo-6-lithiopyridine adds stereoselectively to the β-face of 1,2;5,6-di-O-isopropylidene-α-D-glucofuranos-3-ulose (2) to provide compound 5 in 50% yield as a single diastereomer. Compound 5 can be coupled to form novel C₂-symmetric 2,2′-bipyridine 7, the first example of a C₂-symmetric bipyridine that derives chirality from glucose.     

Efficacious Entry Into Substituted 5,6-Dihydro-4-Hydroxy-2H-Pyran-2-Ones and 2,3-Dihydro-4H-Pyran-4-Ones Utilizing Ketonic Dianions

Methyl acetoacetate and 2,4-pentanedione dianions were condensed with aldehydes and ketones to afford a 1,3,5-trioxygenated carboskeleton. Intramolecular cyclization of the aldol adducts delivered the title compounds in good yield.     

Kinetic Isotope Effect as a Tool To Investigate the Oxygen Reduction Reaction on Pt-based Electrocatalysts – Part II: Effect of Platinum Dispersion

We investigated the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) dispersed on several carbon blacks with various physicochemical properties (i. e. specific surface ranging from 80 to 900 m² g⁻¹, different graphitization degree, etc.). Using the kinetic isotope effect (KIE) along with various electrochemical characterizations, we determined that the rate determining step (RDS) of the ORR is a proton-independent step when the density of Pt NPs on the surface of the carbon support is high. Upon decrease of the density of Pt NPs on the surface, the RDS of the ORR starts involving a proton, as denoted by an increase of the KIE >1. This underlined the critical role played by the carbon support in the oxygen reduction reaction electrocatalysis by Pt supported on high surface area carbon.