888 research outputs found
Supertubes versus superconducting tubes
In this paper we show the relationship between cylindrical D2-branes and
cylindrical superconducting membranes described by a generic effective action
at the bosonic level. In the first case the extended objects considered, arose
as blown up type IIA superstrings to D2-branes, named supertubes. In the second
one, the cosmological objects arose from some sort of field theories. The
Dirac-Born-Infeld action describing supertubes is shown to be equivalent to the
generic effective action describing superconducting membranes via a special
transformation.Comment: Version with minor text changes with respect to the already publishe
Probing supernovae and kicks in post-supernova binaries
Knowledge of the formation of neutron stars (NSs) in supernova (SN)
explosions is of fundamental importance in wide areas of contemporary
astrophysics: X-ray binaries, magnetars, radio pulsars, and, not least, double
NS systems which merge and become gravitational wave sources. A recent study by
Richardson et al. reported that the NS in the Be-star/X-ray binary SGR
0755-2933 (CPD -29 2176) descended from an ultra-stripped SN. Using the same
observational data as Richardson et al., however, we find that the majority of
progenitor solutions for SGR 0755-2933 are of normal Type Ib/c SNe, which
allows for up to several solar masses of material to be ejected in the SN
event. To correctly probe the SN explosion physics and inferring pre-SN
conditions in a binary system, a full kinematic analysis based on post-SN data
is always needed.Comment: Nature, accepted for publication (10 pages, 5 figures, incl. Extended
Data), Matters Arising, Authors' versio
Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea Loch: An Integrative In Situ Study
© 2016, The Author(s). Based on in situ microprofiles, chamber incubations and eddy covariance measurements, we investigated the benthic carbon mineralization and nutrient regeneration in a ~65-m-deep sedimentation basin of Loch Etive, UK. The sediment hosted a considerable amount of infauna that was dominated by the brittle star A. filiformis. The numerous burrows were intensively irrigated enhancing the benthic in situ O2 uptake by ~50 %, and inducing highly variable redox conditions and O2 distribution in the surface sediment as also documented by complementary laboratory-based planar optode measurements. The average benthic O2 exchange as derived by chamber incubations and the eddy covariance approach were similar (14.9 ± 2.5 and 13.1 ± 9.0 mmol m−2 day−1) providing confidence in the two measuring approaches. Moreover, the non-invasive eddy approach revealed a flow-dependent benthic O2 flux that was partly ascribed to enhanced ventilation of infauna burrows during periods of elevated flow rates. The ratio in exchange rates of ΣCO2 and O2 was close to unity, confirming that the O2 uptake was a good proxy for the benthic carbon mineralization in this setting. The infauna activity resulted in highly dynamic redox conditions that presumably facilitated an efficient degradation of both terrestrial and marine-derived organic material. The complex O2 dynamics of the burrow environment also concurrently stimulated nitrification and coupled denitrification rates making the sediment an efficient sink for bioavailable nitrogen. Furthermore, bioturbation mediated a high efflux of dissolved phosphorus and silicate. The study documents a high spatial and temporal variation in benthic solute exchange with important implications for benthic turnover of organic carbon and nutrients. However, more long-term in situ investigations with like approaches are required to fully understand how environmental events and spatio-temporal variations interrelate to the overall biogeochemical functioning of coastal sediments
Benthic Carbon Mineralization and Nutrient Turnover in a Scottish Sea Loch: An Integrative In Situ Study
© 2016, The Author(s). Based on in situ microprofiles, chamber incubations and eddy covariance measurements, we investigated the benthic carbon mineralization and nutrient regeneration in a ~65-m-deep sedimentation basin of Loch Etive, UK. The sediment hosted a considerable amount of infauna that was dominated by the brittle star A. filiformis. The numerous burrows were intensively irrigated enhancing the benthic in situ O2 uptake by ~50 %, and inducing highly variable redox conditions and O2 distribution in the surface sediment as also documented by complementary laboratory-based planar optode measurements. The average benthic O2 exchange as derived by chamber incubations and the eddy covariance approach were similar (14.9 ± 2.5 and 13.1 ± 9.0 mmol m−2 day−1) providing confidence in the two measuring approaches. Moreover, the non-invasive eddy approach revealed a flow-dependent benthic O2 flux that was partly ascribed to enhanced ventilation of infauna burrows during periods of elevated flow rates. The ratio in exchange rates of ΣCO2 and O2 was close to unity, confirming that the O2 uptake was a good proxy for the benthic carbon mineralization in this setting. The infauna activity resulted in highly dynamic redox conditions that presumably facilitated an efficient degradation of both terrestrial and marine-derived organic material. The complex O2 dynamics of the burrow environment also concurrently stimulated nitrification and coupled denitrification rates making the sediment an efficient sink for bioavailable nitrogen. Furthermore, bioturbation mediated a high efflux of dissolved phosphorus and silicate. The study documents a high spatial and temporal variation in benthic solute exchange with important implications for benthic turnover of organic carbon and nutrients. However, more long-term in situ investigations with like approaches are required to fully understand how environmental events and spatio-temporal variations interrelate to the overall biogeochemical functioning of coastal sediments
Un-screened forces in Quark-Gluon Plasma?
We study the correlator of temporal Wilson lines at non-zero temperature in
2+1 flavor lattice QCD with the aim to define the heavy quark-antiquark
potential at non-zero temperature. For temperatures the spectral representation of this correlator is consistent
with a broadened peak in the spectral function, position or width of which then
defines the real or imaginary parts of the heavy quark-antiquark potential at
non-zero temperature, respectively. We find that the real part of the potential
is not screened contrary to the widely-held expectations. We comment on how
this fact may modify the picture of quarkonium melting in the quark-gluon
plasma
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