| 1. |
- Tupitsyn, Igor S., et al.
(författare)
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Coulomb and electron-phonon interactions in metals
- 2016
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 94:15
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Tidskriftsartikel (refereegranskat)abstract
- An accurate and consistent theory of phonons in metals requires that all long-range Coulomb interactions between charged particles (electrons and ions) be treated on equal footing. So far, all attempts to deal with this nonperturbative system were relying on uncontrolled approximations in the absence of small parameters. In this paper, we develop the diagrammatic Monte Carlo approach for a two-component Coulomb system that obtains the solution to this fundamental problem in an approximation-free way by computing vertex corrections from higher-order skeleton graphs. The feasibility of the method is demonstrated by calculating the spectrum of longitudinal acoustic phonons in a simple cubic lattice, determining their sound velocity, and obtaining the phonon spectral densities by analytic continuation of the Matsubara-Green's functions. Final results are checked against the lowest-order fully self-consistent GW approximation in both adiabatic and nonadiabatic regimes.
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| 2. |
- Van Houcke, Kris, et al.
(författare)
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Dielectric function and thermodynamic properties of jellium in the GW approximation
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:19
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Tidskriftsartikel (refereegranskat)abstract
- The fully self-consistent GW approximation is an established method for electronic structure calculations. Its most serious deficiency is known to be an incorrect prediction of the dielectric response. In this work, we examine the GW approximation for the homogeneous electron gas and find that problems with the dielectric response are drastically improved by enforcing the particle-number conservation law in the polarization function. We also find that previously reported data for the ground-state energy contradict each other well outside of reported error bounds. Some of these results created a false impression of how accurate the fully self-consistent GW approximation is. Our two independent implementations of the GW method agree with the data plotted in X.-Z. Yan [Phys. Rev. E 84, 016706 (2011)], thus confirming only that data set. We also present values for other key Fermi-liquid properties.
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| 3. |
- van Swaay, Chris A.M., et al.
(författare)
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The European Butterfly Indicator for Grassland species: 1990-2015
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents the sixth version of the European Grassland Butterfly Indicator, one of the EU biodiversity indicators of the European Environment Agency.The indicator is based on more than 9200 transects in national Butterfly Monitoring Schemes covering 22 countries across Europe, most of them active in the European Union. In 2015, counts were made in more than 4500 transects.Butterflies represent the largest animal group (insects), highly included in food webs, having a high impact on ecosystem services and stability. This report does not represent only the patrimonial conservation of some species, but indicates the changes in biodiversity on grasslands and discusses underlying causes.Fluctuations in numbers between years are typical features of butterfly populations. The assessment of change istherefore made on an analysis of the underlying trend.Indicators were produced on EU, European (EU plus Norway and Switzerland) and pan-European level (including Ukraine, Russia and Armenia).The underlying analysis of the indicator shows that since 1990, grassland butterfly abundance has declined by 30%.The rate of loss has slowed in the last 5-10 years. Part of this slowing down might be caused by climate warming, as this favours cold-blooded animals like butterflies, thus masking the effects of intensification. In parts of Western Europe butterfly numbers outside nature reserves have come to an absolute minimum, meaning it is unlikely for the indicator to further drop.The priority now is to halt further losses and support recovery. This can only come about with greater protection and more sustainable management of semi-natural grassland.
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| 4. |
- van Swaay, Chris, et al.
(författare)
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The European Grassland Butterfly Indicator: 1990–2011
- 2013
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents the European Grassland Butterfly Indicator, based on national Butterfly Monitoring Schemes (BMS) in 19 countries across Europe, most of them in the European Union. The indicator shows that since 1990 till 2011 butterfly populations have declined by almost 50 %, indicating a dramatic loss of grassland biodiversity. This also means the situation has not improved since the first version of the indicator published in 2005. Of the 17 species, 8 have declined in Europe, 2 have remained stable and 1 increased. For six species the trend is uncertain. The main driver behind the decline of grassland butterflies is the change in rural land use: agricultural intensification where the land is relatively flat and easy to cultivate, and abandonment in mountains and wet areas, mainly in eastern and southern Europe. Agricultural intensification leads to uniform, almost sterile grasslands for biodiversity. Grassland butterflies thus mainly survive in traditionally farmed low‑input systems (High Nature Value (HNV) Farmland) as well as nature reserves, and on marginal land such as road verges and amenity areas.
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