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Grain boundary (GB) segregation of Al in ZnO plays an important role in lowering its thermal conductivity for thermoelectric applications. However, the effect of Al concentration on the GB complexions and their transition is not well understood. Herein, a genetic algorithm assisted multiscale modelling framework was used to study the role of GB concentration on the GB segregation of Al on five special twin GBs of ZnO. A critical concentration of 5–6 atoms/nm2 was determined for the complexion transition from single layer to multilayer. Calculated segregation energies were used in a phenomenological model to link GB concentration with the nominal concentration of dopants. The model was used to calculate the nominal solubility of Al in ZnO as a function of grain size, which was validated with the experimental data from the literature. The proposed framework provides a path for establishing GB-structure – property correlation and thereby, predictive dopant engineering of ceramics. [ABSTRACT FROM AUTHOR]

Understanding the atomistic structure of Calcium silicate hydrate (C-S-H), the main product of cement hydration, is of paramount importance to better formulate sustainable cement. The existing atomistic models are not in total agreement with experimental results and fail to explain the nanosized nature of C-S-H. Here, we present a new approach for describing the complexity of these structures at the molecular level, enabling a detailed comparison of C-S-H models. The new methodology encodes a full, large scale atomistic C-S-H structure by a simple, readable string of characters, similar to the way the base sequence in DNA encodes a vast range of different proteins. We then use the methodology to assess 14 Å tobermorite-defect structures and their stabilities using DFT and classical molecular dynamics. Finally we highlight how the model may be extended to develop reliable atomistic C-S-H models for a range of Ca/Si ratios and conditions. [ABSTRACT FROM AUTHOR]

Doping is the most common strategy employed in the development of new and improved materials. However, predicting the effects of doping on the atomic-scale structure of a material is often difficult or limited to high-end experimental techniques. Doping can induce phase separation in a material, undermining the material's stability. A further complication is that dopant atoms can segregate to interfaces in a material such as grain boundaries (GBs), with consequences for key macroscopic properties of the material such as its conductivity. Here, we demonstrate a computational methodology based on semi-grand canonical Monte Carlo which can be used to probe these phenomena at the atomic scale for metal oxide solid solutions. The methodology can provide precise predictions of the thermodynamic conditions at which phase separation occurs. It can also provide the segregation patterns exhibited by GBs at given conditions. We apply the methodology to one of the most important catalytic materials, ceria–zirconia. Our calculations reveal an interesting richness in the GB segregation in this system. Most GBs we examined exhibited continuous increases in Zr segregation upon Zr doping, with a concomitant reduction in the formation enthalpies of the GBs. However, a few GBs exhibited no segregation at low temperatures. We also observed evidence of first-order complexion transitions in some GBs. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper reviews atomistic force field parameterizations for molecular simulations of cementitious minerals, such as tricalcium silicate (C 3 S), portlandite (CH), tobermorites (model C-S-H). Computational techniques applied to these materials include classical molecular simulations, density functional theory and energy minimization. Such simulations hold promise to capture the nanoscale mechanisms operating in cementitious materials and guide in performance optimization. Many force fields have been developed, such as Born–Mayer–Huggins, InterfaceFF (IFF), ClayFF, CSH-FF, CementFF, GULP, ReaxFF, and UFF. The benefits and limitations of these approaches are discussed and a database is introduced, accessible via a web-link ( http://cemff.epfl.ch ). The database provides information on the different force fields, energy expressions, and model validations using systematic comparisons of computed data with benchmarks from experiment and from ab-initio calculations. The cemff database aims at helping researchers to evaluate and choose suitable potentials for specific systems. New force fields can be added to the database. [ABSTRACT FROM AUTHOR]

Patients with advanced metastatic melanoma have poor prognosis and the genetics underlying its pathogenesis are poorly understood. High-throughput sequencing has allowed comprehensive discovery of somatic mutations in cancer samples. Here, on analysis of our whole-genome and whole-exome sequencing data of 29 melanoma samples, we identified several genes that harbor recurrent nonsynonymous mutations. These included MAP3K5 (mitogen-activated protein kinase kinase kinase-5), which in a prevalence screen of 288 melanomas was found to harbor a R256C substitution in 5 cases. All MAP3K5-mutated samples were wild type for BRAF, suggesting a mutual exclusivity for these mutations. Functional analysis of the MAP3K5 R256C mutation revealed attenuation of MKK4 (mitogen-activated protein kinase kinase 4) activation through increased binding of the inhibitory protein thioredoxin (TXN/TRX-1/Trx), resulting in increased proliferation and anchorage-independent growth of melanoma cells. This mutation represents a potential target for the design of new therapies to treat melanoma. [ABSTRACT FROM AUTHOR]

Oxides are critical materials for energy devices like solid oxide cells, catalysts, and membranes. Their performance is often limited by their catalytic activity at reduced temperatures. In this work, a simple etching process with acetic acid at room temperature was used to investigate how oxygen exchange is influenced by surface chemistry and mesoporous structuring in single-crystalline epitaxial (La 0.60 Sr 0.40) 0.95 (Co 0.20 Fe 0.80)O 3. Using low energy ion scattering and electrical measurements, it is shown that increasing the B-site transition metal cation surface exposure (most notably with Fe) leads to strongly reduced activation energy from E a ≈ 1 eV to E a ≈ 0.4 eV for oxygen exchange and an order of magnitude increased oxygen exchange kinetics below 400 °C. Increasing the active area by ∼200% via mesoporous structuring leads to increased oxygen reduction rates by the same percentage. Density functional calculations indicate that a B-site exposed surface with high oxygen vacancy concentration can explain the experimental results. The work opens a pathway to tune surfaces and optimize oxygen exchange for energy devices. • LSCF and LSCF-MgO are etched to study oxygen exchange kinetics. • The roles of surface topography and chemistry on oxygen exchange are investigated. • Etching removes Sr-excess, exposes B-site cations & increases 200% LSCF-MgO surface. • Etching results in reduced activation energy from 1 eV to 0.4 eV. • Etching enhances oxygen exchange kinetics by an order of magnitude. [ABSTRACT FROM AUTHOR]