Sputter deposited Mg₂Fe_xSi_1-x films of 250 nm thickness have been investigated by means of Mössbauer spectroscopy. While non-hydrogenated films are characterized by a quadrupole split doublet, hydrogenated regions show a singlet with reduced isomer shift. The relative areas of the spectra reflect the relation between loaded and unloaded regions prepared at the same loading conditions.

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The sub-surface, with its man-made and natural components, plays an important, if not crucial, role in the urban climate and global energy transition. On the one hand, the sub-surface is associated with a variety of challenges such as subsidence, pollution, damage to infrastructure and shortages of space for new urban systems. On the other hand, the sub-surface presents opportunities in terms of solutions for flooding, reduction in heat stress, and decentralized energy systems. Therefore, it is necessary to place sub-surface issues in their appropriate perspective, to enable a more resilient design that brings together ecosystem services, climate and urban systems, and which takes full account of the dynamics of the subsoil. To achieve this, the sub-surface must be an integral part of above ground planning and design. Organization of the sub-surface needs to be reflected visually in relation to - consideration of (surface) spatial morphology. The objective of this paper is to question the role of architectural representation of the subsurface. Discussion of architectural representation should include ‘design thinking’. An important element of design thinking is the concepts that are used to guide the design process. For this reason, this research tests the role of visualization in relation to a case from the Dutch context and more specifically to subsidence. The approach is built on a systematic processing of contextual information of the site under development, using the System Exploration Environment, Subsurface and results in a Technical Profile. Using input from subsurface specialists to rethink the urban landscape results in realisation of synergies between subsurface elements and the (re)design of vital urban infrastructure.@en

We study the adsorption of carbon dioxide at a graphite surface using the new Small System Method, and find that for the temperature range between 300 K and 550 K most relevant for CO₂ separation; adsorption takes place in two distinct thermodynamic layers defined according to Gibbs. We calculate the chemical potential and the activity coefficient of both layers directly from the simulations. Based on thermodynamic relations, the entropy and enthalpy of the CO₂ adsorbed layers are also obtained. Their values indicate that there is a trade-off between entropy and enthalpy when a molecule chooses for one of the two layers. The first layer is a densely packed monolayer of relatively constant excess density with relatively large repulsive interactions and negative enthalpy. The second layer has an excess density varying with the temperature, an activity coefficient, which also indicates repulsion, but to a much smaller degree than in the first layer. Results for activity coefficients, entropies and enthalpies can be used to model transport through and along graphitic membranes for carbon dioxide separation purposes.

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Thermodynamic equilibrium for adsorption means that the chemical potential of gas and adsorbed phase are equal. A precise knowledge of the chemical potential is, however, often lacking, because the activity coefficient of the adsorbate is not known. Adsorption isotherms are therefore commonly fitted to ideal models such as the Langmuir, Sips or Henry models. We propose here a new procedure to find the activity coefficient and the equilibrium constant for adsorption which uses the thermodynamic factor. Instead of fitting the data to a model, we calculate the thermodynamic factor and use this to find first the activity coefficient. We show, using published molecular simulation data, how this procedure gives the thermodynamic equilibrium constant and enthalpies of adsorption for CO2(g) on graphite. We also use published experimental data to find similar thermodynamic properties of CO2(g) and of CH4(g) adsorbed on activated carbon. The procedure gives a higher accuracy in the determination of enthalpies of adsorption than ideal models do. This journal is@en

The transport of gas molecules in hydrates is presently poorly understood. In sII structured hydrates with hydrogen guests there is, for instance, a mismatch between experimental and computed values for diffusion constants. We provide an explanation for the experimentally observed diffusion rates, using DFT-based molecular dynamics simulations at 100 K. By considering the effect of cage occupancy, as well as the flexibility of the water lattice, we show that barriers for hydrogen diffusing between cages, can approach values as low as 5 kJ mol-1, which is very close to experimental values.@en