| 1. |
- Enkovaara, J., et al.
(författare)
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Electronic structure calculations with GPAW : a real-space implementation of the projector augmented-wave method
- 2010
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 22:25, s. 253202-
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Forskningsöversikt (refereegranskat)abstract
- Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.fysik.dtu.dk/gpaw) using a uniform real-space grid representation of the electronic wavefunctions. Compared to more traditional plane wave or localized basis set approaches, real-space grids offer several advantages, most notably good computational scalability and systematic convergence properties. However, as a unique feature GPAW also facilitates a localized atomic-orbital basis set in addition to the grid. The efficient atomic basis set is complementary to the more accurate grid, and the possibility to seamlessly switch between the two representations provides great flexibility. While DFT allows one to study ground state properties, time-dependent density-functional theory (TDDFT) provides access to the excited states. We have implemented the two common formulations of TDDFT, namely the linear-response and the time propagation schemes. Electron transport calculations under finite-bias conditions can be performed with GPAW using non-equilibrium Green functions and the localized basis set. In addition to the basic features of the real-space PAW method, we also describe the implementation of selected exchange-correlation functionals, parallelization schemes, Delta SCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals.
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| 2. |
- Ojanen, X, et al.
(författare)
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Relationships between tissue composition and viscoelastic properties in human trabecular bone.
- 2015
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 1873-2380 .- 0021-9290. ; 48:2, s. 269-275
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Tidskriftsartikel (refereegranskat)abstract
- Trabecular bone is a metabolically active tissue with a high surface to volume ratio. It exhibits viscoelastic properties that may change during aging. Changes in bone properties due to altered metabolism are sensitively revealed in trabecular bone. However, the relationships between material composition and viscoelastic properties of bone, and their changes during aging have not yet been elucidated. In this study, trabecular bone samples from the femoral neck of male cadavers (n=21) aged 17-82 years were collected and the tissue level composition and its associations with the tissue viscoelastic properties were evaluated by using Raman microspectroscopy and nanoindentation, respectively. For composition, collagen content, mineralization, carbonate substitution and mineral crystallinity were evaluated. The calculated mechanical properties included reduced modulus (Er), hardness (H) and the creep parameters (E1, E2, η1and η2), as obtained by fitting the experimental data to the Burgers model. The results indicated that the creep parameters, E1, E2, η1and η2, were linearly correlated with mineral crystallinity (r=0.769-0.924, p<0.001). Creep time constant (η2/E2) tended to increase with crystallinity (r=0.422, p=0.057). With age, the mineralization decreased (r=-0.587, p=0.005) while the carbonate substitution increased (r=0.728, p<0.001). Age showed no significant associations with nanoindentation parameters. The present findings suggest that, at the tissue-level, the viscoelastic properties of trabecular bone are related to the changes in characteristics of bone mineral. This association may be independent of human age.
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| 3. |
- Alisic, S., et al.
(författare)
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Final report on EURAMET comparison on 1 kg stainless steel mass standards
- 2020
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Ingår i: Metrologia. - : Institute of Physics Publishing. - 0026-1394 .- 1681-7575. ; 57:1 A
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Tidskriftsartikel (refereegranskat)abstract
- In order to demonstrate the equivalence in calibration of mass standards among National Metrology Institutes (NMIs) of EURAMET this key comparison (KC) on 1 kg stainless steel mass standards has been carried out under the auspices of EURAMET. The comparison was undertaken with reference to the International Prototype Kilogram (IPK) as the definition of the unit of mass. The overall result shows good consistency among the participants. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
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| 4. |
- Ojanen, X., et al.
(författare)
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Tissue viscoelasticity is related to tissue composition but may not fully predict the apparent-level viscoelasticity in human trabecular bone – An experimental and finite element study
- 2017
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 0021-9290. ; 65, s. 96-105
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Tidskriftsartikel (refereegranskat)abstract
- Trabecular bone is viscoelastic under dynamic loading. However, it is unclear how tissue viscoelasticity controls viscoelasticity at the apparent-level. In this study, viscoelasticity of cylindrical human trabecular bone samples (n = 11, male, age 18–78 years) from 11 proximal femurs were characterized using dynamic and stress-relaxation testing at the apparent-level and with creep nanoindentation at the tissue-level. In addition, bone tissue elasticity was determined using scanning acoustic microscope (SAM). Tissue composition and collagen crosslinks were assessed using Raman micro-spectroscopy and high performance liquid chromatography (HPLC), respectively. Values of material parameters were obtained from finite element (FE) models by optimizing tissue-level creep and apparent-level stress-relaxation to experimental nanoindentation and unconfined compression testing values, respectively, utilizing the second order Prony series to depict viscoelasticity. FE simulations showed that tissue-level equilibrium elastic modulus (Eeq) increased with increasing crystallinity (r = 0.730, p =.011) while at the apparent-level it increased with increasing hydroxylysyl pyridinoline content (r = 0.718, p =.019). In addition, the normalized shear modulus g1 (r = −0.780, p =.005) decreased with increasing collagen ratio (amide III/CH2) at the tissue-level, but increased (r = 0.696, p =.025) with increasing collagen ratio at the apparent-level. No significant relations were found between the measured or simulated viscoelastic parameters at the tissue- and apparent-levels nor were the parameters related to tissue elasticity determined with SAM. However, only Eeq, g2 and relaxation time τ1 from simulated viscoelastic values were statistically different between tissue- and apparent-levels (p <.01). These findings indicate that bone tissue viscoelasticity is affected by tissue composition but may not fully predict the macroscale viscoelasticity in human trabecular bone.
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| 5. |
- Ahola, Virpi, et al.
(författare)
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The Glanville fritillary genome retains an ancient karyotype and reveals selective chromosomal fusions in Lepidoptera
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4737-
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Tidskriftsartikel (refereegranskat)abstract
- Previous studies have reported that chromosome synteny in Lepidoptera has been well conserved, yet the number of haploid chromosomes varies widely from 5 to 223. Here we report the genome (393 Mb) of the Glanville fritillary butterfly (Melitaea cinxia; Nymphalidae), a widely recognized model species in metapopulation biology and eco-evolutionary research, which has the putative ancestral karyotype of n = 31. Using a phylogenetic analyses of Nymphalidae and of other Lepidoptera, combined with orthologue-level comparisons of chromosomes, we conclude that the ancestral lepidopteran karyotype has been n = 31 for at least 140 My. We show that fusion chromosomes have retained the ancestral chromosome segments and very few rearrangements have occurred across the fusion sites. The same, shortest ancestral chromosomes have independently participated in fusion events in species with smaller karyotypes. The short chromosomes have higher rearrangement rate than long ones. These characteristics highlight distinctive features of the evolutionary dynamics of butterflies and moths.
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| 6. |
- Bell, S., et al.
(författare)
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METefnet : Developments in metrology for moisture in materials
- 2015
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Ingår i: 17th International Congress of Metrology, CIM 2015. - Les Ulis, France : EDP Sciences.
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Konferensbidrag (refereegranskat)abstract
- Bien que les mesures de teneur en eau soient largement utilisées dans l'industrie, les considérations métrologiques quant à cette mesure ne sont pas complètement abouties de sorte à fournir des mesures fiables et traçables au SI. Afin de remédier à ceci, le projet de recherche conjoint, Joint Research Project SIB64 “METefnet – Metrology for moisture in materials”, est actuellement en cours, et contribue au programme européen de recherche en métrologie European Metrology Research Programme. Le projet METefnet a pour objectifs de développer et d'améliorer l'approche métrologique de ce sujet. Ceci inclus notamment: le travail sur de nouvelles méthodes de référence pour évaluer la fraction massique en eau, l'amélioration des mesures mettant en œuvre la méthode primaire de type titration Karl Fischer, le développement de nouveaux matériaux de référence certifiés présentant une très bonne stabilité et permettant une traçabilité au SI, le développement de nouveaux étalons de transfert, la réalisation d'études visant à quantifier et réduire les effets liés à la prise d'échantillon, son transport et sa manipulation, le développement d'une nouvelle méthode pour étalonner les instruments mesurant l'humidité de surface, et l'amélioration des méthodes d'estimation d'incertitudes de ces mesures. Ce travail, réalisé dans le domaine de la métrologie de l'humidité au sein des matériaux, couvre à la fois le mesurande décrit comme étant spécifiquement la teneur en eau, seule, dans les matériaux, mais également un mesurande plus large pouvant inclure l'eau ainsi que d'autres liquides ou composés organiques volatiles; ceci afin de bien mettre en exergue la différence qui peut être observée entre ces deux mesurandes. Le projet global a pour objectif de soutenir une action de dissémination et de traçabilité au système SI des mesures de teneur en eau dans les matériaux avec une exactitude optimale et de développer une infrastructure métrologique cohérente pour ce type de mesures. Le travail technique ainsi que les dernières avancées vous sont ainsi présentées.
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