Stability and electronic structure of the (1×1)(1\times 1) SrTiO3_3(110) polar surfaces by first principles calculations

The electronic and atomic structure of several $(1\times 1)$ terminations of the (110) polar orientation of SrTiO$_3$ surface are systematically studied by first-principles calculations. The electronic structure of the two stoichiometric SrTiO- and O$_2$-terminations are characterized by marked differences with respect to the bulk, as a consequence of the polarity compensation. In the former, the Fermi level is located at the bottom of the conduction band, while in the latter the formation of a peroxo bond between the two surface oxygens results in a small-gap insulating surface with states in the gap of the bulk projected band structure. We also consider three non stoichiometric terminations with TiO, Sr and O compositions, respectively, in the outermost atomic layer, which automatically allows the surface to be free from any macroscopic polarization. They are all insulating. The cleavage and surface energies of the five terminations are computed and compared, taking into account the influence of the chemical environment as a function of the relative richness in O and Sr. From our calculations it appears that some (110) faces can even compete with the TiO$_2$ and SrO terminations of the (100) cleavage surface: in particular, the (110)-TiO termination is stable in Sr-poor conditions, the (110)-Sr one in simultaneously O- and Sr-rich environments. The available experimental data are compared to the outcomes of our calculations and discussed.Comment: accepted for publication in Phys. Rev.

Extracorporeal life support for primary graft dysfunction after heart transplantation

OBJECTIVES Survival after heart transplantation is steadily improving but primary graft dysfunction (PGD) is still a leading cause of death. Medical management seems useful in mild or moderate PGD, whereas extracorporeal life support (ECLS) could be suggested for severe PGD refractory to conventional treatment. Our aim is to present the results of ECLS for PGD after heart transplantation at a single-centre experience. METHODS We performed an observational analysis of our local database. According to the International Society for Heart and Lung Transplantation classification, patients were divided into a left and biventricular failure (PGD-LV) or isolated right ventricular failure (PGD-RV) group. The primary end point was survival to hospital discharge. RESULTS Between January 2010 and December 2016, 38 patients presented with PGD (PGD-LV n = 22, 58%; PGD-RV n = 16, 42%) requiring ECLS support. The mean age was 50.8 ± 12.4 years and 79% were males. Baseline characteristics were comparable between the 2 groups. PGD-LV patients displayed a significantly higher mortality rate on ECLS support as opposed to PGD-RV patients (46% vs 13%, P = 0.033). The rate of complications during ECLS support was comparable between the 2 groups. Twenty-three (61%) patients were successfully weaned from ECLS (PGD-LV = 50% vs PGD-RV = 75%, P = 0.111) after a mean support of 9.0 ± 6.4 days. Seventeen (45%) patients survived to hospital discharge (PGD-LV = 41% vs PGD-RV = 50%, P = 0.410). CONCLUSIONS In case of severe PGD with various manifestations of ventricular failure refractory to conventional treatment, ECLS can be considered as a feasible option with satisfactory survival in this critically ill population

Calculations of thermodynamical properties of U3Si2

International audienceUranium silicide compounds, especially U3Si2, have been studied as a potential replacement for uranium dioxide fuel in pressurized water reactors. These compounds offer several superior properties as a larger thermal conductivity and a higher uranium density. The thermodynamical quantities (specific heat, thermal expansion and conductivity…) are crucial to drive the fuel design. They are directly related to the atomic vibrations and more specifically, they can be extracted from the phonon spectra and the crystal structure.In this work we calculate the phonon spectra of different structures of the U3Si2 compound, up to the meltin curve, by taking into account the anharmonic effects and by using the TDEP method[1]. The thermodynamical properties extracted from these phonon spectra will then be compared to the previous calculations and the available experimental data. We show that the unique features of the crystallographic structure of this compound drive its behaviour in temperature

Sound velocities and thermodynamical properties of hcp iron at high pressure and temperature

International audienceSound velocities and thermodynamical properties of hcp iron have been computed using ab initio calculations over an extended density and temperature range, encompassing the conditions directly relevant for the Earth's inner core. At room temperature, and up to 350 GPa, an excellent agreement is obtained between present results and experimental data for many thermodynamical quantities: phonon density of states, vibrational entropy, heat capacity, Grüneisen parameter and thermal expansion. With increasing temperature, along an isochore, we observe a strong decrease of the phonon frequencies, demonstrating that intrinsic anharmonic effects cannot be neglected. We also carefully compare previous theoretical data for the sound velocities and try to explain the discrepancies observed with experiments. Finally, we propose a temperature dependant Birch's law that we compare with previous experimental wor

Calculations of thermodynamical properties of U3Si2

International audienceUranium silicide compounds, especially U3Si2, have been studied as a potential replacement for uranium dioxide fuel in pressurized water reactors. These compounds offer several superior properties as a larger thermal conductivity and a higher uranium density. The thermodynamical quantities (specific heat, thermal expansion and conductivity…) are crucial to drive the fuel design. They are directly related to the atomic vibrations and more specifically, they can be extracted from the phonon spectra and the crystal structure.In this work we calculate the phonon spectra of different structures of the U3Si2 compound, up to the meltin curve, by taking into account the anharmonic effects and by using the TDEP method[1]. The thermodynamical properties extracted from these phonon spectra will then be compared to the previous calculations and the available experimental data. We show that the unique features of the crystallographic structure of this compound drive its behaviour in temperature

Implementation of the projector augmented-wave method in the ABINIT code: Application to the study of iron under pressure

The projector augmented wave method (PAW), introduced for the first time by Blochl [P. Blochl, Phys. Rev. B 50 (1994) 17953], has been implemented in the ABINIT code [X. Gonze, J.-M. Beuken, R. Caracas, F. Detraux, M. Fuchs, G.-M. Rignanese, L. Sindic, M. Verstaete, G. Zerah, F. Jollet, et al., Comput. Mater. Sci. 25 (2002) 478]. This implementation allows self-consistent calculations of the electronic structure of a periodic solid within the density functional theory (DFT), including the analytic calculation of forces and stresses. Geometry optimization and molecular dynamics are also available. We present here I he details of the implementation, including the analytic formula for forces and stresses. Results concerning the study of iron under pressure are presented to validate the implementation. (C) 2007 Elsevier B.V. All rights reserved

Analytical study of the impact of thickness over thermal transfer in a plate with boilingflow.

International audienc

Ab initio Canonical Sampling based on Variational Inference

International audienceFinite temperature calculations, based on ab initio molecular dynamics (AIMD) simulations, are a powerful tool able to predict material properties that cannot be deduced from ground state calculations. However, the high computational cost of AIMD limits its applicability for large or complex systems. To circumvent this limitation we introduce a new method named Machine Learning Assisted Canonical Sampling (MLACS), which accelerates the sampling of the Born--Oppenheimer potential surface in the canonical ensemble. Based on a self-consistent variational procedure, the method iteratively trains a Machine Learning Interatomic Potential to generate configurations that approximate the canonical distribution of positions associated with the ab initio potential energy. By proving the reliability of the method on anharmonic systems, we show that the method is able to reproduce the results of AIMD with an ab initio accuracy at a fraction of its computational cost

Analytical study of the impact of thickness over thermal transfer in a plate with boilingflow.

International audienc

CoCoNet: Towards coast to coast networks of marine protected areas (From the shore to the high and deep sea), coupled with sea-based wind energy potential

This volume contains the main results of the EC FP7 "The Ocean of Tomorrow" Project CoCoNet, divided in two sections: 1) a set of guidelines to design networks of Marine Protected Areas in the Mediterranean and the Black Seas; 2) a smart wind chart that will allow evaluating the possibility of installing Offshore Wind Farms in both seas. The concept of Cells of Ecosystem Functioning, based on connectivity, is introduced to define natural units of management and conservation. The definition of Good Environmental Status, as defined in the Marine Strategy Framework Directive, is fully embraced to set the objectives of the project, by adopting a holistic approach that integrates a full set of disciplines, ranging from physics to bio-ecology, economics, engineering and many sub-disciplines. The CoCoNet Consortium involved scientist sfrom 22 states, based in Africa, Asia, and Europe, contributing to build a coherent scientific community