Communication: Improving the density functional theoryU description of CeO 2 by including the contribution of the O 2p electrons

Density functional theory (DFT) based approaches within the local-density approximation or generalized gradient approximation frameworks fail to predict the correct electron localization in strongly correlated systems due to the lack of cancellation of the Coulomb self-interaction. This problem might be circumvented either by using hybrid functionals or by introducing a Hubbard-like term to account for the on site interactions. This latter DFTU approach is less expensive and therefore more practical for extensive calculations in solid-state computational simulations. By and large, the U term only affects the metal electrons, in our case the Ce 4f ones. In the present work, we report a systematic analysis of the effect of adding such a U term also to the oxygen 2p electrons. We find that using a set of U f 5 eV and U p 5eV effective terms leads to improved description of the lattice parameters, band gaps, and formation and reduction energies of CeO

Theoretical investigation of the lattice thermal conductivities of II-IV-V2 pnictide semiconductors

Ternary pnictides semiconductors with II-IV-V2 stoichiometry hold potential as cost effective thermoelectric materials with suitable electronic transport properties, but their lattice thermal conductivities ($\kappa$) are typically too high. Gaining insight into their vibrational properties is therefore crucial to finding strategies to reduce $\kappa$ and achieve improved thermoelectric performance. We present a theoretical exploration of the lattice thermal conductivities for a set of pnictide semiconductors with ABX2 composition (A = Zn, Cd; B = Si, Ge, Sn; and X = P, As), using machine-learning based regression algorithms to extract force constants from a reduced number of density functional theory simulations, and then solving the Boltzmann transport equation for phonons. Our results align well available experimental data, decreasing the mean absolute error by ~3 Wm-1K-1 with respect to the best previous set of theoretical predictions. Zn-based ternary pnictides have, on average, more than double the thermal conductivity of the Cd-based compounds. Anisotropic behaviour increases with the mass difference between A and B cations, but while the nature of the anion does not affect the structural anisotropy, the thermal conductivity anisotropy is typically higher for arsenides than for phosphides. We identify compounds, like CdGeAs2, for which nanostructuring to an affordable range of particle sizes could lead to values low enough for thermoelectric applications.Comment: 24 pages, 8 figure

Spanish Dentists’ Awareness, Knowledge, and Practice Regarding COVID-19: A Multiple Regression Analysis

The authors thank the Spanish Society of Epidemiology and Oral Public Health (SESPO) for expert supervision of the questionnaire; the Spanish General Council of Dentists (GCD) and the Spanish societies of dental hygienists for their rapid dissemination of the survey to their members.Introduction: During the first months of the coronavirus disease 2019 (COVID-19) pandemic, Spain had the highest mortality rate and the second-highest infection rate in the world. Objective: To analyze the occupational situation of dentists, hygienists, and dental auxiliary staff during the peak of the pandemic, after the state of alarm was declared in Spain, and when the state of alarm was declared. In addition, a possible relationship between the geographical distribution of infected people and the availability of individual protection systems was investigated. Material and Methods: A cross-sectional questionnaire was answered by 6470 dentists and dental staff via WhatsApp and social media. Results: A total of 1 in 4 dental professionals ceased working completely. Of those that kept working, 25.28% of dentists and 19.61% of hygienist-auxiliary were equipped with filtering face piece (FFP) 2 masks (P < .05), and 61.8% complied with the official protection recommendations set by the General Council of Dentists of Spain. Nearly 59.4% of respondents had symptoms, but only 1.5% of dentists were tested, with 14% of dentists in isolation at the time of response. Overall, it is suggested that 10% of dental professionals may have been in direct contact with the coronavirus. Conclusions: Direct contact of Spanish dental health professionals with severe acute respiratory syndrome coronavirus disease 2 (SARS CoV-2) has been high during the most active phase of the pandemic. Dental professionals did not have personal protective equipment (PPE) necessary to care for patients, a situation that justified the reduction in scheduled dental care and only emergencies being treated. The Spanish geographical regions with the highest number of contagions had the least amount of individual protective resources (FFP2 and FFP3masks)

3-Phase Rectifier System with very demanding dynamic load

This paper present a distributed power architecture for aerospace application with very restrictive specifications. Additionally, the rectifier switching frequency has to be synchronized with an external frequency clock to minimize the interference of the converter harmonics with the load. In order to protect the 3 phase generator against high load steps, an intermediate bus (based in a high capacitance) to provide energy to the loads during the high load steps is included. Prototypes of the rectifier and EMI filter are built and the energy control is validated

The Constructionist Theory of Learning in Teacher Education. Perspectives from students and teachers through quantitative and qualitative research

Se presenta una investigación sobre la teoría Construccionista del Aprendizaje en formación del profesorado. Se utilizaron dos técnicas de recogida de información: cuantitativa (encuesta) y cualitativa (entrevista) para intentar entender mejor su complejidad. 41 universitarios portugueses que cursaban la misma asignatura de Grado y el profesor que la impartía accedieron a participar. El análisis de los resultados mostró que los participantes valoran positivamente la construcción y el uso de materiales para el desarrollo de su formación académica y para su labor profesional futura. Estos resultados son similares a los encontrados en muestras de universitarios españoles, lo que refuerza la bondad de la Teoría Construccionista del Aprendizaje en formación docente.The article presents a study on the usage of the Constructionist Theory of learning in Teacher Education. Two different assessment procedures were used: quantitative (questionnaire) and qualitative (interview) to try to understand the complexity of the problem. 41 Portuguese university students enrolled in the same curricular subject and their teacher agreed to participate. Results showed that the participants positively valued the construction and usage of materials for their academic development and for their professional career. These results are similar to previous results obtained in Spanish university students, which reinforces the positive effects of the Construccionist Theory of Learning in Teacher Education.Grupo FORCE (HUM-386). Departamento de Didáctica y Organización Escolar de la Universidad de Granad

High-throughput screening of the thermoelastic properties of ultrahigh-temperature ceramics

Ultrahigh-temperature ceramics (UHTCs) are a group of materials with high technological interest because of their applications in extreme environments. However, their characterization at high temperatures represents the main obstacle for their fast development. Obstacles are found from an experimental point of view, where only few laboratories around the world have the resources to test these materials under extreme conditions, and also from a theoretical point of view, where actual methods are expensive and difficult to apply to large sets of materials. Here, a new theoretical high-throughput framework for the prediction of the thermoelastic properties of materials is introduced. This approach can be systematically applied to any kind of crystalline material, drastically reducing the computational cost of previous methodologies up to 80% approximately. This new approach combines Taylor expansion and density functional theory calculations to predict the vibrational free energy of any arbitrary strained configuration, which represents the bottleneck in other methods. Using this framework, elastic constants for UHTCs have been calculated in a wide range of temperatures with excellent agreement with experimental values, when available. Using the elastic constants as the starting point, other mechanical properties such a bulk modulus, shear modulus, or Poisson ratio have been also explored, including upper and lower limits for polycrystalline materials. Finally, this work goes beyond the isotropic mechanical properties and represents one of the most comprehensive and exhaustive studies of some of the most important UHTCs, charting their anisotropy and thermal and thermodynamical properties.Ministerio de Ciencia e Innovación PID2019-106871GB-I00European Union 752608Red Española de Supercomputación QS-2019-2-0006, QS-2019-3-0021, QS-2020-2-003