| 1. |
- Viscasillas Vázquez, C., et al.
(författare)
-
The Gaia -ESO survey : Age-chemical-clock relations spatially resolved in the Galactic disc
- 2022
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 660
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The last decade has seen a revolution in our knowledge of the Galaxy thanks to the Gaia and asteroseismic space missions and the ground-based spectroscopic surveys. Aims. To complete this picture, it is necessary to map the ages of its stellar populations. During recent years, the dependence on time of abundance ratios involving slow (s) neutron-capture and α elements (called chemical-clocks) has been used to provide estimates of stellar ages, usually in a limited volume close to the Sun. We aim to analyse the relations of chemical clocks in the Galactic disc extending the range to RGC∼ 6- 20 kpc. Methods. Using the sixth internal data release of the Gaia-ESO survey, we calibrated several relations between stellar ages and abundance ratios [s/α] using a sample of open clusters, the largest one so far used with this aim (62 clusters). Thanks to their wide galactocentric coverage, we investigated the radial variations of the shape of these relations, confirming their non-universality. Results. The multi-variate relations allowed us to infer stellar ages for field stars. We estimated our accuracy (ranging from 0.0 to -0.9 Gyr) and precision (from 0.4 to 2.3 Gyr) in recovering the global ages of open clusters, and the ages of their individual members. We applied the relations with the highest correlation coefficients to the field star population, finding an older population at lower metallicity and higher [α/Fe] in the thin disc, and a younger one at higher [Fe/H] and low [α/Fe], as expected. Conclusion. We confirm that there is no single age-chemical clock relationship valid for the whole disc, but that there is a dependence on the galactocentric position, which is related to the radial variation of the star formation history combined with the non-monotonic dependence on metallicity of the yields of the s-process elements from low- and intermediate-mass stars. Finally, the abundance ratios [Ba/α] are more sensitive to age than those with [Y/α] for young disc stars, and their slopes vary less with galactocentric distance. We remind the reader that the application of such relationships to field stars is only of statistical value.
|
|
| 2. |
- Duong, T. C., et al.
(författare)
-
A hierarchical computational thermodynamic and kinetic approach to discontinuous precipitation in the U-Nb system
- 2015
-
Ingår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015. - : International Conference on Solid-Solid Phase Transformations in Inorganic Materials. - 9780692437360 ; , s. 887-894
-
Konferensbidrag (refereegranskat)abstract
- U-Nb alloys decompose via discontinuous precipitation (DP) over a broad range of aging conditions, adversely affecting their properties. The growth kinetics, lamellar spacing, and Nb partitioning have been measured, but the thermodynamic and kinetic factors underlying these specific transformation characteristics and reaction paths, vis-a-vis the monotectoid reaction, are not fully resolved. In this work, a hierarchical computational thermodynamic and kinetic approach was carried out to investigate DP. The hierarchical approach started with density-functional theory (DFT) investigations of ground-state formation energies of bcc-based U-Nb alloys. The estimated energetic data was then utilized as an imposed first-principles-based constraint to improve the consistency of the CALPHAD thermodynamic and, subsequently, kinetic assessments of U-Nb. Phasefield simulations were then carried out to study DP's microstructure evolution using the assessed CALPHAD thermodynamic and kinetic representations. Good agreement with experiments on different physical/length scales was achieved, which validates the present theoretical contributions to a better understanding of DP in U-Nb alloys.
|
|
| 3. |
- Ades, A. E., et al.
(författare)
-
Zika virus infection in pregnancy : a protocol for the joint analysis of the prospective cohort studies of the ZIKAlliance, ZikaPLAN and ZIKAction consortia
- 2020
-
Ingår i: BMJ Open. - : BMJ PUBLISHING GROUP. - 2044-6055. ; 10:12
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Zika virus (ZIKV) infection in pregnancy has been associated with microcephaly and severe neurological damage to the fetus. Our aim is to document the risks of adverse pregnancy and birth outcomes and the prevalence of laboratory markers of congenital infection in deliveries to women experiencing ZIKV infection during pregnancy, using data from European Commission-funded prospective cohort studies in 20 centres in 11 countries across Latin America and the Caribbean.Methods and analysis: We will carry out a centre-by-centre analysis of the risks of adverse pregnancy and birth outcomes, comparing women with confirmed and suspected ZIKV infection in pregnancy to those with no evidence of infection in pregnancy. We will document the proportion of deliveries in which laboratory markers of congenital infection were present. Finally, we will investigate the associations of trimester of maternal infection in pregnancy, presence or absence of maternal symptoms of acute ZIKV infection and previous flavivirus infections with adverse outcomes and with markers of congenital infection. Centre-specific estimates will be pooled using a two-stage approach.Ethics and dissemination: Ethical approval was obtained at each centre. Findings will be presented at international conferences and published in peer-reviewed open access journals and discussed with local public health officials and representatives of the national Ministries of Health, Pan American Health Organization and WHO involved with ZIKV prevention and control activities.
|
|
| 4. |
- Palumbo, M., et al.
(författare)
-
Thermodynamic modelling of crystalline unary phases
- 2014
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 251:1, s. 14-32
-
Tidskriftsartikel (refereegranskat)abstract
- Progress in materials science through thermodynamic modelling may rest crucially on access to a database, such as that developed by Scientific Group Thermodata Europe (SGTE) around 1990. It gives the Gibbs energy G(T) of the elements in the form of series as a function of temperature, i.e. essentially a curve fitting to experimental data. In the light of progress in theoretical understanding and first-principles calculation methods, the possibility for an improved database description of the thermodynamics of the elements has become evident. It is the purpose of this paper to provide a framework for such work. Lattice vibrations, which usually give the major contribution to G(T), are treated in some detail with a discussion of neutron scattering studies of anharmonicity in aluminium, first-principles calculations including ab initio molecular dynamics (AIMD), and the strength and weakness of analytic model representations of data. Similarly, electronic contributions to G(T) are treated on the basis of the density of states N(E) for metals, with emphasis on effects at high T. Further, we consider G(T) below 300K, which is not covered by SGTE. Other parts in the paper discuss metastable and dynamically unstable lattices, G(T) in the region of superheated solids and the requirement on a database in the calculation of phase diagrams.
|
|
| 5. |
- Landa, A., et al.
(författare)
-
Ab initio study of advanced metallic nuclear fuels for fast breeder reactors
- 2012
-
Ingår i: Actinides And Nuclear Energy Materials. - : Materials Research Society. - 9781605114217 ; , s. 67-78
-
Konferensbidrag (refereegranskat)abstract
- Density-functional formalism is applied to study the ground state properties of γ-U-Zr and γ-U-Mo solid solutions. Calculated heats of formation are compared with CALPHAD assessments. We discuss how the heat of formation in both alloys correlates with the charge transfer between the alloy components. The decomposition curves for γ-based U-Zr and U-Mo solid solutions are derived from Ising-type Monte Carlo simulations. We explore the idea of stabilization of the γ-UZr2 compound against the α-Zr (hcp) structure due to increase of Zr d-band occupancy by the addition of U to Zr. We discuss how the specific behavior of the electronic density of states in the vicinity of the Fermi level promotes the stabilization of the U2Mo compound. The mechanism of possible Am redistribution in the U-Zr and U-Mo fuels is also discussed.
|
|
| 6. |
- Landa, A., et al.
(författare)
-
Density-functional study of bcc Pu-U, Pu-Np, Pu-Am, and Pu-Cm alloys
- 2011
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 408:1, s. 61-66
-
Tidskriftsartikel (refereegranskat)abstract
- Density-functional theory previously used to describe phase equilibria in the gamma-Pu-U-Zr alloys [A. Landa, P. Soderlind, PEA. Turchi, L. Vitos, A. Ruban, J. Nucl. Mater. 385 (2009) 68; A. Landa, P. Soderlind, PEA. Turchi, L. Vitos, A. Ruban, J. Nucl. Mater. 393 (2009) 141], is extended to study ground-state properties of the gamma-Pu-Np, gamma-Pu-Am, and gamma-Pu-Cm solid solutions. Calculated heats of formation are compared with CALPHAD assessments where possible. We discuss how the heat of formation correlates with the charge transfer between the alloy components.
|
|
| 7. |
- Landa, A., et al.
(författare)
-
Density-functional study of Zr-based actinide alloys
- 2009
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 385:1, s. 68-71
-
Tidskriftsartikel (refereegranskat)abstract
- Density-functional formalism is applied to study the phase equilibria in the U-Zr system. The obtained ground-state properties of the gamma (bcc) and delta (02) phases are in good agreement with experimental data. The decomposition curve for the gamma-based U-Zr solutions is calculated. We argue that stabilization of the delta-UZr2 phase relative to the alpha-Zr (hcp) structure is due to an increase of the Zr d-band occupancy that occurs when U is alloyed with Zr.
|
|
| 8. |
- Landa, A., et al.
(författare)
-
Density-functional study of Zr-based actinide alloys : 2. U-Pu-Zr system
- 2009
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 393:1, s. 141-145
-
Tidskriftsartikel (refereegranskat)abstract
- Density-functional theory, previously used to describe phase equilibria in the U-Zr alloys [A. Landa, P. Soderlind, P.E.A. Turchi, L. Vitos, A. Ruban, J. Nucl. Mater. 385 (2009) 68[, is applied to study ground-state properties of the bcc U-Pu-Zr solid solutions. Calculated heats of formation of the Pu-U and Pu-Zr alloys are in a good agreement with CALPHAD assessments. We found that account for spin-orbit coupling is important for successful description of Pu-containing alloys.
|
|
| 9. |
- Söderlind, P., et al.
(författare)
-
Prediction of the new efficient permanent magnet SmCoNiFe3
- 2017
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:10
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a new efficient permanent magnet, SmCoNiFe3, which is a development of the well-known SmCo5 prototype. More modern neodymium magnets of the Nd-Fe-B type have an advantage over SmCo5 because of their greater maximum energy products due to their iron-rich stoichiometry. Our new magnet, however, removes most of this disadvantage of SmCo5 while preserving its superior high-temperature efficiency over the neodymium magnets. We show by means of first-principles electronic-structure calculations that SmCoNiFe3 has very favorable magnetic properties and could therefore potentially replace SmCo5 or Nd-Fe-B types in various applications.
|
|
| 10. |
- Duong, Thien C., et al.
(författare)
-
Revisiting thermodynamics and kinetic diffusivities of uranium-niobium with Bayesian uncertainty analysis
- 2016
-
Ingår i: CALPHAD-COMPUTER COUPLING OF PHASE DIAGRAMS AND THERMOCHEMISTRY. - : Elsevier. - 0364-5916. ; 55, s. 219-230
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, thermodynamic and kinetic diffusivities of uranium-niobium (U-Nb) are re-assessed by means of the CALPHAD (CALculation of PHAse Diagram) methodology. In order to improve the consistency and reliability of the assessments, first-principles calculations are coupled with CALPHAD. In particular, heats of formation of gamma-U-Nb are estimated and verified using various density-functional theory (DFT) approaches. These thermochemistry data are then used as constraints to guide the thermodynamic optimization process in such a way that the mutual-consistency between first-principles calculations and CALPHAD assessment is satisfactory. In addition, long-term aging experiments are conducted in order to generate new phase equilibria data at the gamma(2)/alpha + gamma(2) boundary. These data are meant to verify the thermodynamic model. Assessment results are generally in good agreement with experiments and previous calculations, without showing the artifacts that were observed in previous modeling. The mutual-consistent thermodynamic description is then used to evaluate atomic mobility and diffusivity of gamma-U-Nb. Finally, Bayesian analysis is conducted to evaluate the uncertainty of the thermodynamic model and its impact on the system's phase stability.
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
- Turchi, Patrice E. A., et al.
(författare)
-
Interface between quantum-mechanical-based approaches, experiments, and CALPHAD methodology
- 2007
-
Ingår i: Calphad. - : Elsevier BV. - 0364-5916 .- 1873-2984. ; 31:1, s. 4-27
-
Tidskriftsartikel (refereegranskat)abstract
- The increased application of quantum-mechanical-based methodologies to the study of alloy stability has required a re-assessment of the field. The focus is mainly on inorganic materials in the solid state. In a first part, after a brief overview of the so-called ab initio methods with their approximations, constraints, and limitations, recommendations are made for a good usage of first-principles codes with a set of qualifiers. Examples are given to illustrate the power and the limitations of ab initio codes. However, despite the "success" of these methodologies, thermodynamics of complex multi-component alloys, as used in engineering applications, requires a more versatile approach presently afforded within CALPHAD. Hence, in a second part, the links that presently exist between ab initio methodologies, experiments, and the CALPHAD approach are examined with illustrations. Finally, the issues of dynamical instability and of the role of lattice vibrations that still constitute the subject of ample discussions within the CALPHAD community are revisited in the light of our current knowledge with a set of recommendations.
|
|
| 14. |
- Wilder-Smith, Annelies, et al.
(författare)
-
The legacy of ZikaPLAN: a transnational research consortium addressing Zika
- 2021
-
Ingår i: Global Health Action. - : Taylor & Francis. - 1654-9716 .- 1654-9880. ; 14
-
Forskningsöversikt (refereegranskat)abstract
- Global health research partnerships with institutions from high-income countries and low- and middle-income countries are one of the European Commission's flagship programmes. Here, we report on the ZikaPLAN research consortium funded by the European Commission with the primary goal of addressing the urgent knowledge gaps related to the Zika epidemic and the secondary goal of building up research capacity and establishing a Latin American-European research network for emerging vector-borne diseases. Five years of collaborative research effort have led to a better understanding of the full clinical spectrum of congenital Zika syndrome in children and the neurological complications of Zika virus infections in adults and helped explore the origins and trajectory of Zika virus transmission. Individual-level data from ZikaPLAN`s cohort studies were shared for joint analyses as part of the Zika Brazilian Cohorts Consortium, the European Commission-funded Zika Cohorts Vertical Transmission Study Group, and the World Health Organization-led Zika Virus Individual Participant Data Consortium. Furthermore, the legacy of ZikaPLAN includes new tools for birth defect surveillance and a Latin American birth defect surveillance network, an enhanced Guillain-Barre Syndrome research collaboration, a de-centralized evaluation platform for diagnostic assays, a global vector control hub, and the REDe network with freely available training resources to enhance global research capacity in vector-borne diseases.
|
|
