AFLOW-QHA3P: Robust and automated method to compute thermodynamic properties of solids

Accelerating the calculations of finite-temperature thermodynamic properties is a major challenge for rational materials design. Reliable methods can be quite expensive, limiting their applicability in autonomous high-throughput workflows. Here, the three-phonon quasiharmonic approximation (QHA) method is introduced, requiring only three phonon calculations to obtain a thorough characterization of the material. Leveraging a Taylor expansion of the phonon frequencies around the equilibrium volume, the method efficiently resolves the volumetric thermal expansion coefficient, specific heat at constant pressure, the enthalpy, and bulk modulus. Results from the standard QHA and experiments corroborate the procedure, and additional comparisons are made with the recently developed self-consistent QHA. The three approaches—three-phonon, standard, and self-consistent QHAs—are all included within the open-source ab initio framework aflow, allowing the automated determination of properties with various implementations within the same framework

European Use of Space Shuttle

Europe\u27s association with the Space Shuttle started in 1973 when the European Space Agency (ESA) signed a Memorandum of Understanding with NASA for the development in Europe with European funds of Spacelab. In addition, it was agreed that ESA would provide approximately one half of the first Spacelab payload which will be carried on the SL-1 mission in September 1983. Further usage of Spacelab is foreseen either in missions dedicated to European countries or in missions shared with NASA. Also, it is anticipated that European space projects will make use of the launch and recovery capability of the Space Shuttle when these services are considered to be cost attractive. Finally, augmentation of the Shuttle\u27s capabilities is another likely area of participation through the provision of a European-built upper stage. This paper summarises these activities both from an ESA-NASA point of view and from the outlook of bilateral (i.e. NASA-ESA Member State) co-operation

Optical spectroscopy for biotechnology students

Spectroscopy is a fundamental and a professionalizing content for biotechnology students. In particular, optical spectroscopy represents an important link between physical optics, its main applications and its atomic-molecular interpretations. After a teaching intervention concerning physical optics, a laboratorybased activity, carried out with optical goniometer, was conducted with freshmen in biotechnology in the context of their physics course at Udine University (IT). The study aims to monitor students’ reasoning and learning difficulties about the interpretation of discrete atomic spectra, so the activity was accompanied by a IBL tutorial and by a post-test inspired by the existing Physics Education Research literature. 56 students completed the tutorial, 45 of them competed the post-test. Here we report and discuss the results emerged from data analysis of the students’ written answers

Answering to physics teachers' needs in professional development

The IDIFO project conducted at the University of Udine, in collaboration with 18 Italian universities, is an example of integration and collaboration between schools and universities proposals on innovation in physics education. The aspects of the project relating to the professional development of teachers are discussed, presenting the various implementation methods designed and activated, also answering to the formative needs of schools relating to laboratory-based scientific teaching/learning

From one slit to diffraction grating: Optical physics lab by means of computer on-line sensors

Diffraction is a crucial phenomenon and its interpretation bridges from geometrical to wave optics and from wave optics to Quantum mechanics. Becoming familiar with the characteristics of the diffraction in the cases of one, two, many slits is an important experience for students not only from the subject point of view, but also on the methodological plan. The exploration of the relative interpretation by means of simulation and modelling offers to the students the opportunity to experience the typical methodological work in physics. An educational proposal was developed for the study of optical diffraction: from the analysis of a single slit diffraction, to a double slit and to a diffraction grating. It is based on a USB acquisition system designed and developed for experimental data acquisition in an educational lab, correlating position and light intensity measurements in one direction. Data can be exported in text format and data fitting can be done by means of an electronic sheet. The phenomenon laws obtained by data are interpreted under the wave nature of light by students and these laws are used for spectroscopic analysis of different light sources. Simulation software allows to build models of interpretation of phenomenology based on the first principles

DNS and LES of turbulent flow in a closed channel featuring a pattern of hemispherical roughness elements

Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES) were performed for fully-developed turbulent flow in channels with smooth walls and walls featuring hemispherical roughness elements at shear Reynolds numbers Reτ = 180 and 400, with the goal of studying the effect of these roughness elements on the wall-layer structure and on the friction factor. The LES and DNS approaches were verified first by comparison with existing DNS databases for smooth walls. Then, a parametric study for the hemispherical roughness elements was conducted, including the effects of shear Reynolds number, normalized roughness height (k⁺ = 10–20) and relative roughness spacing (s⁺/k⁺ = 2–6). The sensitivity study also included the effect of distribution pattern (regular square lattice vs. random pattern) of the roughness elements on the walls. The hemispherical roughness elements generate turbulence, thus increasing the friction factor with respect to the smooth-wall case, and causing a downward shift in the mean velocity profiles. The simulations revealed that the friction factor decreases with increasing Reynolds number and roughness spacing, and increases strongly with increasing roughness height. The effect of random element distribution on friction factor and mean velocities is however weak. In all cases, there is a clear cut between the inner layer near the wall, which is affected by the presence of the roughness elements, and the outer layer, which remains relatively unaffected. The study reveals that the presence of roughness elements of this shape promotes locally the instantaneous flow motion in the lateral direction in the wall layer, causing a transfer of energy from the streamwise Reynolds stress to the lateral component. The study indicates also that the coherent structures developing in the wall layer are rather similar to the smooth case but are lifted up by almost a constant wall-unit shift y⁺(∼10–15), which, interestingly, corresponds to the relative roughness k⁺ = 10

Macroscopic polarization and band offsets at nitride heterojunctions

Ab initio electronic structure studies of prototypical polar interfaces of wurtzite III-V nitrides show that large uniform electric fields exist in epitaxial nitride overlayers, due to the discontinuity across the interface of the macroscopic polarization of the constituent materials. Polarization fields forbid a standard evaluation of band offsets and formation energies: using new techniques, we find a large forward-backward asymmetry of the offset (0.2 eV for AlN/GaN (0001), 0.85 eV for GaN/AlN (0001)), and tiny interface formation energies.Comment: RevTeX 4 pages, 2 figure