8,409 research outputs found
Episode of unusual high solar ultraviolet radiation over central Europe due to dynamical reduced total ozone in May 2005
In late May 2005 unusual high levels of solar ultraviolet radiation were observed over central Europe. In Northern Germany the measured irradiance of erythemally effective radiation exceeded the climatological mean by more than about 20%. An extreme low ozone event for the season coincided with high solar elevation angles and high pressure induced clear sky conditions leading to the highest value of erythemal UV-radiation ever observed over this location in May since 1994. This hereafter called "ozone mini-hole" was caused by an elevation of tropopause height accompanied with a poleward advection of ozone-poor air from the tropics. The resultant increase in UV-radiation is of particular significance for human health. Dynamically induced low ozone episodes that happen in late spring can considerably enhance the solar UV-radiation in mid latitudes and therefore contribute to the UV-burden of people living in these regions
Neutron matter from chiral effective field theory interactions
The neutron-matter equation of state constrains the properties of many
physical systems over a wide density range and can be studied systematically
using chiral effective field theory (EFT). In chiral EFT, all many-body forces
among neutrons are predicted to next-to-next-to-next-to-leading order (N3LO).
We present details and additional results of the first complete N3LO
calculation of the neutron-matter energy, which includes the subleading
three-nucleon as well as the leading four-nucleon forces, and provides
theoretical uncertainties. In addition, we discuss the impact of our results
for astrophysics: for the supernova equation of state, the symmetry energy and
its density derivative, and for the structure of neutron stars. Finally, we
give a first estimate for the size of the N3LO many-body contributions to the
energy of symmetric nuclear matter, which shows that their inclusion will be
important in nuclear structure calculations.Comment: published version; 21 pages, 11 figures, 5 table
Pairing in neutron matter: New uncertainty estimates and three-body forces
We present solutions of the BCS gap equation in the channels and
in neutron matter based on nuclear interactions derived
within chiral effective field theory (EFT). Our studies are based on a
representative set of nonlocal nucleon-nucleon (NN) plus three-nucleon (3N)
interactions up to next-to-next-to-next-to-leading order (NLO) as well as
local and semilocal chiral NN interactions up to NLO and NLO,
respectively. In particular, we investigate for the first time the impact of
subleading 3N forces at NLO on pairing gaps and also derive uncertainty
estimates by taking into account results for pairing gaps at different orders
in the chiral expansion. Finally, we discuss different methods for obtaining
self-consistent solutions of the gap equation. Besides the widely-used
quasi-linear method by Khodel et al. we demonstrate that the modified Broyden
method is well applicable and exhibits a robust convergence behavior. In
contrast to Khodel's method it is based on a direct iteration of the gap
equation without imposing an auxiliary potential and is straightforward to
implement
Climatological features of stratospheric streamers in the FUB-CMAM with increased horizontal resolution
International audienceThe purpose of this study is to investigate horizontal transport processes in the winter stratosphere using data with a resolution relevant for chemistry and climate modeling. For this reason the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) with its model top at 83 km altitude, increased horizontal resolution T42 and the semi-Lagrangian transport scheme for advecting passive tracers is used. A new approach of this paper is the classification of specific transport phenomena within the stratosphere into tropical-subtropical streamers (e.g. Offermann et al., 1999) and polar vortex extrusions hereafter called polar vortex streamers. To investigate the role played by these large-scale structures on the inter-annual and seasonal variability of transport processes in northern mid-latitudes, the global occurrence of such streamers was calculated based on a 10-year model climatology, concentrating on the existence of the Arctic polar vortex. For the identification and counting of streamers, the new method of zonal anomaly was chosen. The analysis of the months October-May yielded a maximum occurrence of tropical-subtropical streamers during Arctic winter and spring in the middle and upper stratosphere. Synoptic maps revealed highest intensities in the subtropics over East Asia with a secondary maximum over the Atlantic in the northern hemisphere. Furthermore, tropical-subtropical streamers exhibited a higher occurrence than polar vortex streamers, indicating that the subtropical barrier is more permeable than the polar vortex barrier (edge) in the model, which is in good correspondence with observations (e.g. Plumb, 2002; Neu et al., 2003). Interesting for the total ozone decrease in mid-latitudes is the consideration of the lower stratosphere for tropical-subtropical streamers and the stratosphere above ~20 km altitude for polar vortex streamers, where strongest ozone depletion is observed at polar latitudes (WMO, 2003). In the lower stratosphere the FUB-CMAM simulated a climatological maximum of 10% occurrence of tropical-subtropical streamers over East-Asia/West Pacific and the Atlantic during early- and mid-winter. The results of this paper demonstrate that stratospheric streamers e.g. large-scale, tongue-like structures transporting tropical-subtropical and polar vortex air masses into mid-latitudes occur frequently during Arctic winter. They can therefore play a significant role on the strength and variability of the observed total ozone decrease at mid-latitudes and should not be neglected in future climate change studies
The chiral condensate in neutron matter
We calculate the chiral condensate in neutron matter at zero temperature
based on nuclear forces derived within chiral effective field theory. Two-,
three- and four-nucleon interactions are included consistently to
next-to-next-to-next-to-leading order (N3LO) of the chiral expansion. We find
that the interaction contributions lead to a modest increase of the condensate,
thus impeding the restoration of chiral symmetry in dense matter and making a
chiral phase transition in neutron-rich matter unlikely for densities that are
not significantly higher than nuclear saturation density.Comment: published version, 6 pages, 4 figure
Quantification 2.0? Bibliometric Infrastructures in Academic Evaluation
Due to developments recently termed as ‘audit,’ ‘evaluation,’ or ‘metric society,’ universities have become subject to ratings and rankings and researchers are evaluated according to standardized quantitative indicators such as their publication output and their personal citation scores. Yet, this development is not only based on the rise of new public management and ideas on ‘the return on public or private investment.’ It has also profited from ongoing technological developments. Due to a massive increase in digital publishing corresponding with the growing availability of related data bibliometric infrastructures for evaluating science are continuously becoming more differentiated and elaborate. They allow for new ways of using bibliometric data through various easily applicable tools. Furthermore, they also produce new quantities of data due to new possibilities in following the digital traces of scientific publications. In this article, I discuss this development as quantification 2.0. The rise of digital infrastructures for publishing, indexing, and managing scientific publications has not only made bibliometric data become a valuable source for performance assessment. It has triggered an unprecedented growth in bibliometric data production turning freely accessible data about scientific work into edited databases and producing competition for its users. The production of bibliometric data has thus become decoupled from their application. Bibliometric data have turned into a self-serving end while their providers are constantly seeking for new tools to make use of them.Peer Reviewe
Theoretical Contributions to a sociology of (e)valuation
Valuation and evaluation processes are currently a much discussed topic, in particular, in the sociology of science, in science and technology studies and in economic sociology. Phenomena such as university rankings or credit ratings are addressed in research on classification, categorization, commensuration, standardization, and quantification. However, beyond such discussions about ratings and rankings, the paper argues that valuation and evaluation processes should be furthermore understood as a substantial feature of the social. Valuation as the construction of classificatory systems through the attribution of value to objects, people and practices and evaluation as the enactment of such value-charged classificatory systems fundamentally contribute to the institutionalization of a commonly shared understanding of social reality. Focusing on conflicts about the attribution of value and the appropriateness of evaluation frameworks within everyday situations of decision-making might then help to address questions such as on institutional change
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