49 research outputs found
Collisionless hydrodynamics for 1D motion of inhomogeneous degenerate electron gases: equivalence of two recent descriptions
Recently I. Tokatly and O. Pankratov (''TP'', Phys. Rev. B 60, 15550 (1999))
used velocity moments of a semiclassical kinetic equation to derive a
hydrodynamic description of electron motion in a degenerate electron gas.
Independently, the present authors (Theochem 501-502, 327 (2000)) used
considerations arising from the Harmonic Potential Theorem (Phys. Rev. Lett.
73, 2244 (1994)) to generate a new form of high-frequency hydrodynamics for
inhomogeneous degenerate electron gases (HPT-N3 hydrodynamics). We show here
that TP hydrodynamics yields HPT-N3 hydrodynamics when linearized about a
Thomas-Fermi groundstate with one-dimensional spatial inhomnogeneity.Comment: 17p
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Bridging the research-implementation gap in IUCN Red List assessments
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is central in biodiversity conservation, but insufficient resources hamper its long-term growth, updating, and consistency. Models or automated calculations can alleviate those challenges by providing standardised estimates required for assessments, or prioritising species for (re-)assessments. However, while numerous scientific papers have proposed such methods, few have been integrated into assessment practice, highlighting a critical research-implementation gap. We believe this gap can be bridged by fostering communication and collaboration between academic researchers and Red List practitioners, and by developing and maintaining user-friendly platforms to automate application of the methods. We propose that developing methods better encompassing Red List criteria, systems, and drivers is the next priority to support the Red List.Peer reviewe
Framing the concept of satellite remote sensing essential biodiversity variables: challenges and future directions
Although satellite-based variables have for long been expected to be key components to a unified and global biodiversity monitoring strategy, a definitive and agreed list of these variables still remains elusive. The growth of interest in biodiversity variables observable from space has been partly underpinned by the development of the essential biodiversity variable (EBV) framework by the Group on Earth Observations – Biodiversity Observation Network, which itself was guided by the process of identifying essential climate variables. This contribution aims to advance the development of a global biodiversity monitoring strategy by updating the previously published definition of EBV, providing a definition of satellite remote sensing (SRS) EBVs and introducing a set of principles that are believed to be necessary if ecologists and space agencies are to agree on a list of EBVs that can be routinely monitored from space. Progress toward the identification of SRS-EBVs will require a clear understanding of what makes a biodiversity variable essential, as well as agreement on who the users of the SRS-EBVs are. Technological and algorithmic developments are rapidly expanding the set of opportunities for SRS in monitoring biodiversity, and so the list of SRS-EBVs is likely to evolve over time. This means that a clear and common platform for data providers, ecologists, environmental managers, policy makers and remote sensing experts to interact and share ideas needs to be identified to support long-term coordinated actions
Helioseismology and Solar Abundances
Helioseismology has allowed us to study the structure of the Sun in
unprecedented detail. One of the triumphs of the theory of stellar evolution
was that helioseismic studies had shown that the structure of solar models is
very similar to that of the Sun. However, this agreement has been spoiled by
recent revisions of the solar heavy-element abundances. Heavy element
abundances determine the opacity of the stellar material and hence, are an
important input to stellar model calculations. The models with the new, low
abundances do not satisfy helioseismic constraints. We review here how
heavy-element abundances affect solar models, how these models are tested with
helioseismology, and the impact of the new abundances on standard solar models.
We also discuss the attempts made to improve the agreement of the low-abundance
models with the Sun and discuss how helioseismology is being used to determine
the solar heavy-element abundance. A review of current literature shows that
attempts to improve agreement between solar models with low heavy-element
abundances and seismic inference have been unsuccessful so far. The
low-metallicity models that have the least disagreement with seismic data
require changing all input physics to stellar models beyond their acceptable
ranges. Seismic determinations of the solar heavy-element abundance yield
results that are consistent with the older, higher values of the solar
abundance, and hence, no major changes to the inputs to solar models are
required to make higher-metallicity solar models consistent with helioseismic
data.Comment: To appear in Physics Reports. Large file (1.6M PDF, 3.4M PS), 27
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