Random phase approximation up to the melting point: Impact of anharmonicity and nonlocal many-body effects on the thermodynamics of Au

Application of the generalized gradient corrected functional within standard density-functional theory results in a dramatic failure for Au, leading to divergent thermodynamic properties well below the melting point. By combining the upsampled thermodynamic integration using Langevin dynamics technique with the random phase approximation, we show that inclusion of nonlocal many-body effects leads to a stabilization and to an excellent agreement with experiment. © Published by the American Physical Society

2-Sulfoethylammonium trifluoromethanesulfonate as an Ionic Liquid for High Temperature PEM Fuel Cells

2-Sulfoethylammonium trifluoromethanesulfonate ([2-Sea+][TfO−]) represents a novel class of proton-conducting ionic liquids (PILs) based on aminoalkylsulfonic acids. The fundamental suitability of [2-Sea+][TfO−] for application as a protic electrolyte in high temperature PEM fuel cells (HT-PEFCs) was investigated up to a temperature of 130°C. A comparison was made against a state-of-the-art electrolyte, phosphoric acid. [2-Sea+][TfO−] is electrochemically and thermally stable up to 140°C. The specific conductivity of 95 wt% [2-Sea+][TfO−] aqueous solution at 130°C is ≈20 times lower compared to 95 wt% H3PO4. The strong coupling of ion transport and viscous flow suggests a vehicular ion (proton) transport in [2-Sea+][TfO−]. 95 wt% [2-Sea+][TfO−] shows superior kinetics in terms of oxygen reduction reaction (ORR) on polycrystalline Pt compared to 95 wt% H3PO4 at temperatures greater than 90°C in a fuel cell-applicable potential range. Double layer capacitances suggest a complex double layer structure, including adsorbed [2-Sea+][TfO−] and water, as well as intermediates of oxygen reduction and Pt oxidation. Potential and temperature-dependent ORR kinetics in the presence of 95 wt% [2-Sea+][TfO−] yield different Tafel slopes (b = 82–139 mV) and symmetry factors (β = 0.46–0.96), indicating changes in surface coverages of the adsorbed species and possibly also a change in the reaction mechanism

A Continuum Saltation Model for Sand Dunes

We derive a phenomenological continuum saltation model for aeolian sand transport that can serve as an efficient tool for geomorphological applications. The coupled differential equations for the average density and velocity of sand in the saltation layer reproduce both known equilibrium relations for the sand flux and the time evolution of the sand flux as predicted by microscopic saltation models. The three phenomenological parameters of the model are a reference height for the grain-air interaction, an effective restitution coefficient for the grain-bed interaction, and a multiplication factor characterizing the chain reaction caused by the impacts leading to a typical time or length scale of the saturation transients. We determine the values of these parameters by comparing our model with wind tunnel measurements. Our main interest are out of equilibrium situations where saturation transients are important, for instance at phase boundaries (ground/sand) or under unsteady wind conditions. We point out that saturation transients are indispensable for a proper description of sand flux over structured terrain, by applying the model to the windward side of an isolated dune, thereby resolving recently reported discrepancies between field measurements and theoretical predictions.Comment: 11 pages, 7 figure

Corridors of barchan dunes: stability and size selection

Barchans are crescentic dunes propagating on a solid ground. They form dune fields in the shape of elongated corridors in which the size and spacing between dunes are rather well selected. We show that even very realistic models for solitary dunes do not reproduce these corridors. Instead, two instabilities take place. First, barchans receive a sand flux at their back proportional to their width while the sand escapes only from their horns. Large dunes proportionally capture more than they loose sand, while the situation is reversed for small ones: therefore, solitary dunes cannot remain in a steady state. Second, the propagation speed of dunes decreases with the size of the dune: this leads -- through the collision process -- to a coarsening of barchan fields. We show that these phenomena are not specific to the model, but result from general and robust mechanisms. The length scales needed for these instabilities to develop are derived and discussed. They turn out to be much smaller than the dune field length. As a conclusion, there should exist further - yet unknown - mechanisms regulating and selecting the size of dunes.Comment: 13 pages, 13 figures. New version resubmitted to Phys. Rev. E. Pictures of better quality available on reques

The InSight HP^3 mole on Mars: Lessons learned from attempts to penetrate to depth in the Martian soil

The NASA InSight mission payload includes the Heat Flow and Physical Properties Package HP^3 to measure the surface heat flow. The package was designed to use a small penetrator - nicknamed the mole - to implement a string of temperature sensors in the soil to a depth of 5m. The mole itself is equipped with sensors to measure a thermal conductivity as it proceeds to depth. The heat flow would be calculated from the product of the temperature gradient and the thermal conductivity. To avoid the perturbation caused by annual surface temperature variations, the measurements would be taken at a depth between 3 m and 5 m. The mole was designed to penetrate cohesionless soil similar to Quartz sand which was expected to provide a good analogue material for Martian sand. The sand would provide friction to the buried mole hull to balance the remaining recoil of the mole hammer mechanism that drives the mole forward. Unfortunately, the mole did not penetrate more than a mole length of 40 cm. The failure to penetrate deeper was largely due to a few tens of centimeter thick cohesive duricrust that failed to provide the required friction. Although a suppressor mass and spring in the hammer mechanism absorbed much of the recoil, the available mass did not allow a system that would have eliminated the recoil. The mole penetrated to 40 cm depth benefiting from friction provided by springs in the support structure from which it was deployed. It was found in addition that the Martian soil provided unexpected levels of penetration resistance that would have motivated to designing a more powerful mole. It is concluded that more mass would have allowed to design a more robust system with little or no recoil, more energy of the mole hammer mechanism and a more massive support structure.Comment: 34 pages, 15 figures, submitted to Adnaves in Space Researc

Collision dynamics of two barchan dunes simulated by a simple model

The collision processes of two crescentic dunes called barchans are systematically studied using a simple computer simulation model. The simulated processes, coalescence, ejection and reorganization, qualitatively correspond to those observed in a water tank experiment. Moreover we found the realized types of collision depend both on the mass ratio and on the lateral distance between barchans under initial conditions. A simple set of differential equations to describe the collision of one-dimensional (1D) dunes is introduced.Comment: 4 pages, 5 figures : To be published in Journal of the Physical Society of Japa

Double-plating of ovine critical sized defects of the tibia: a low morbidity model enabling continuous in vivo monitoring of bone healing

<p>Abstract</p> <p>Background</p> <p>Recent studies using sheep critical sized defect models to test tissue engineered products report high morbidity and complications rates. This study evaluates a large bone defect model in the sheep tibia, stabilized with two, a novel Carbon fibre Poly-ether-ether-ketone (CF-PEEK) and a locking compression plate (LCP) which could sustain duration for up to 6 month with an acceptable low complication rate.</p> <p>Methods</p> <p>A large bone defect of 3 cm was performed in the mid diaphysis of the right tibia in 33 sheep. The defect was stabilised with the CF - PEEK plate and an LCP. All sheep were supported with slings for 8 weeks after surgery. The study was carried out for 3 months in 6 and for 6 months in 27 animals.</p> <p>Results</p> <p>The surgical procedure could easily be performed in all sheep and continuous in vivo radiographic evaluation of the defect was possible. This long bone critical sized defect model shows with 6.1% a low rate of complications compared with numbers mentioned in the literature.</p> <p>Conclusions</p> <p>This experimental animal model could serve as a standard model in comparative research. A well defined standard model would reduce the number of experimental animals needed in future studies and would therefore add to ethical considerations.</p