Ultrasonic characterization of shrinkage microporosity in aluminum castings

Shrinkage microporosity in cast aluminum was characterized utilizing the frequency dependence of ultrasonic attenuation caused by scattering from the pores. Measurements were made with the plate specimen immersed in water, and, by using a focused transducer, spatial resolution of about 2 mm was obtained. An accurate measure of attenuation was obtained by comparing the specimen’s ultrasonic signal with that from a pore-free reference specimen. Although the attenuation could be fitted using a single spherical pore size, better fits were obtained by assuming a lognormal distribution of spheres. Pore volume fraction inferred from the lognormal fits overestimates the actual volume fraction, determined from density measurements, by the same factor for all volume fractions. The actual volume fraction is overestimated by more than 100%, due to the complicated, nonspherical pore shapes, and must be taken into account to obtain accurate values of porosity. The strong correlation (r²=0.97) between ultrasonic and density-derived volume fractions permits reliable, nondestructive laboratory measurements of porosity.     

The interaction of O2 with the surface of polycrystalline gadolinium at the temperature range 300–670 K

Auger-Electron-Spectroscopy (AES) and Direct-Recoils-Spectrometry (DRS) were applied to study the interaction of O₂ with a polycrystalline gadolinium surface, in the temperature range 300–670 K and oxygen pressure up to 2 × 10^? 6 Torr. It has been found that initial uptake of oxygen, at coverage measurable by the techniques used here, results in rapid oxide island formation. The subsurface is believed to be a mixture of oxide particles and oxygen dissolved in the Gd metal, the latter being the mobile species, even at relatively low temperatures.Enhanced inward diffusion of oxygen starts as early as 420 K and dictates the surface oxygen concentration and effective thickness of the forming oxide. The oxygen accumulation rate at the near-surface region, as measured by the O(KLL) AES signal intensity, goes through a maximum as a function of temperature at 420 K. This is a result of the combination of still efficient oxygen chemisorption that increases surface occupation and slow inward diffusion. The thickest oxide, ~ 1.7 nm, is formed at 300 K and its effective thickness was found to decrease with increasing temperature (due to oxygen dissolution into the metal bulk).Diffusion coefficients of the oxygen dissolution into the bulk were evaluated for various temperatures utilizing models for infinitely thin oxide layer and thick oxide layer, respectively. The best fit under our experimental procedure was obtained by the thick layer model, and the coefficients that were calculated are D₀ = 2.2 × 10^? 16m²s^? 1 and E_a = 46kJ/mol.     

Mean-field versus microconvection effects in nanofluid thermal conduction

Transient hot-wire data on thermal conductivity of suspensions of silica and perfluorinated particles show agreement with the mean-field theory of Maxwell but not with the recently postulated microconvection mechanism. The influence of interfacial thermal resistance, convective effects at microscales, and the possibility of thermal conductivity enhancements beyond the Maxwell limit are discussed.     

Coherent optical measurement techniques in profilometric determination of local mass transfer coefficients

Some measurement techniques using a coherent light source in profilometric determination of local mass transfer coefficients are described in this paper. Different optical setups for holographic interferometry coupled with the two basic profilometric techniques: the swollen polymer technique and the sublimation technique, are described in detail. Finally, the application of electronic speckle pattern interferometry to profilometric measurements is also discussed.     

Black Holes Are One-Dimensional

The holographic principle has revealed that phyical systems in 3-D space, black holes included, are basically two-dimensional as far as their information content is concerned. This conclusion is complemented by one sketched here: as far as entropy or information flow is concerned, a black hole behaves as a one-dimensional channel. We define a channel in flat spacetime in thermodynamic terms, and contrast it with common entropy emitting systems. A black hole is more like the former: its entropy output is related to the emitted power as it would be for a one-dimensional channel, and disposal of an information stream down a black hole is limited by the power invested in the same way as for a one-dimensional channel.     

Letter to the Editor: Radon isotope assessment of Submarine Groundwater Discharge (SGD) in Coleroon River Estuary,Tamil Nadu,India

Journal of Radioanalytical and Nuclear Chemistry -     

Event-shape-engineering study of charge separation in heavy-ion collisions

Recent measurements of charge-dependent azimuthal correlations in high-energy heavy-ion collisions have indicated charge-separation signals perpendicular to the reaction plane, and have been related to the chiral magnetic effect(CME). However, the correlation signal is contaminated with the background caused by the collective motion(flow) of the collision system, and an effective approach is needed to remove the flow background from the correlation. We present a method study with simplified Monte Carlo simulations and a multi-phase transport model,and develop a scheme to reveal the true CME signal via event-shape engineering with the flow vector of the particles of interest.     

Evaluating the impact of functional groups on membrane-mediated CO2/N2 gas separations using a common polymer backbone

Polymeric membranes have shown tremendous promise for the separation of CO₂ from flue gas streams. However, few systematic studies have been conducted to better understand the impact that chemical functionalities have on membrane-based gas separation performance. To address this gap, we herein describe the synthesis and gas separation performance of a series of vinyl-addition polynorbornenes bearing various CO₂-philic functional groups. To facilitate direct comparison between functional groups, each material was designed to maintain a common polymer backbone. Though the incorporation of CO₂-philic moieties within a dense polymeric membrane is frequently hypothesized to enhance CO₂ solubility, and thereby increase CO₂/N₂ selectivity, our results demonstrate that the incorporation of CO₂-philic groups onto a common polymer backbone do not necessarily result in increased gas separation performance. Experimental and computational results demonstrate that the incorporation of amidoxime groups onto a polynorbornene backbone increase CO₂/N₂ selectivity, whereas commonly employed ethereal side chains only increased permeability.     

Concise Synthesis of (+)-[13C4]-Anatoxin-a by Dynamic Kinetic Resolution of a Cyclic Iminium Ion

An asymmetric total synthesis of [¹³C₄]-anatoxin-a ([¹³C₄]- 1 ) has been developed from commercially available ethyl [¹³C₄]-acetoacetate ([¹³C₄]- 15 ). The unique requirements associated with isotope incorporation inspired a new, robust, and highly scalable route, providing access to 0.110 g of this internal standard for use in the detection and precise quantification of anatoxin-a in freshwater. A highlight of the synthesis is a method that leverages a cyclic iminium ion racemization to achieve dynamic kinetic resolution in an enantioselective Morita–Baylis–Hillman (MBH) cyclization.