2,876 research outputs found
The ocean carbon sink – impacts, vulnerabilities and challenges
Carbon dioxide (CO2) is, next to water vapour, considered to be the most important natural greenhouse gas on Earth. Rapidly rising atmospheric CO2 concentrations caused by human actions such as fossil fuel burning, land-use change or cement production over the past 250 years have given cause for concern that changes in Earth’s climate system may progress at a much faster pace and larger extent than during the past 20 000 years. Investigating global carbon cycle pathways and finding suitable adaptation and mitigation strategies has, therefore, become of major concern in many research fields. The oceans have a key role in regulating atmospheric CO2 concentrations and currently take up about 25% of annual anthropogenic carbon emissions to the atmosphere. Questions that yet need to be answered are what the carbon uptake kinetics of the oceans will be in the future and how the increase in oceanic carbon inventory will affect its ecosystems and their services. This requires comprehensive investigations, including high-quality ocean carbon measurements on different spatial and temporal scales, the management of data in sophisticated databases, the application of Earth system models to provide future projections for given emission scenarios as well as a global synthesis and outreach to policy makers. In this paper, the current understanding of the ocean as an important carbon sink is reviewed with respect to these topics. Emphasis is placed on the complex interplay of different physical, chemical and biological processes that yield both positive and negative air–sea flux values for natural and anthropogenic CO2 as well as on increased CO2 (uptake) as the regulating force of the radiative warming of the atmosphere and the gradual acidification of the oceans. Major future ocean carbon challenges in the fields of ocean observations, modelling and process research as well as the relevance of other biogeochemical cycles and greenhouse gases are discussed
Editorial : Advances in the spatial and temporal evolution of oceanic arc-backarc systems
Non peer reviewe
Tu quoque arguments, subjunctive inconsistency, and questions of relevance
Tu quoque arguments regard inconsistencies in some speaker‘s performance. Most tu quoque arguments depend on actual inconsistencies. However, there are forms of tu quoque arguments that key, instead, on the conflicts a speaker would have, were some crucial contingent fact different. These, we call subjunctive tu quoque arguments. Finally, there are cases wherein the counterfactual inconsistencies of a speaker are relevant to the issue
A Graphene-based Hot Electron Transistor
We experimentally demonstrate DC functionality of graphene-based hot electron
transistors, which we call Graphene Base Transistors (GBT). The fabrication
scheme is potentially compatible with silicon technology and can be carried out
at the wafer scale with standard silicon technology. The state of the GBTs can
be switched by a potential applied to the transistor base, which is made of
graphene. Transfer characteristics of the GBTs show ON/OFF current ratios
exceeding 50.000.Comment: 18 pages, 6 figure
Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters
We investigate the circumstellar disc fraction as determined from L-band
excess observations of the young, massive Arches and Quintuplet clusters
residing in the central molecular zone of the Milky Way. The Quintuplet cluster
was searched for L-band excess sources for the first time. We find a total of
26 excess sources in the Quintuplet cluster and 21 in the Arches cluster, of
which 13 are new detections. With the aid of proper motion membership samples,
the disc fraction of the Quintuplet cluster was derived for the first time to
be 4.0 +/- 0.7%. There is no evidence for a radially varying disc fraction in
this cluster. In the case of the Arches cluster, a disc fraction of 9.2 +/-
1.2% approximately out to the cluster's predicted tidal radius, r < 1.5 pc, is
observed. This excess fraction is consistent with our previously found disc
fraction in the cluster in the radial range 0.3 < r < 0.8 pc. In both clusters,
the host star mass range covers late A- to early B-type stars, 2 < M < 15 Msun,
as derived from J-band photospheric magnitudes. We discuss the unexpected
finding of dusty circumstellar discs in these UV intense environments in the
context of primordial disc survival and formation scenarios of secondary discs.
We consider the possibility that the L-band excess sources in the Arches and
Quintuplet clusters could be the high-mass counterparts to T Tauri
pre-transitional discs. As such a scenario requires a long pre-transitional
disc lifetime in a UV intense environment, we suggest that mass transfer discs
in binary systems are a likely formation mechanism for the B-star discs
observed in these starburst clusters.Comment: 47 pages, 22 figures, accepted by A&
Nearly free electrons in the layered oxide superconductor Ag5Pb2O6
We present first measurements of quantum oscillations in the layered oxide
superconductor
Ag5Pb2O6. From a detailed angular and temperature dependent study of the dHvA
effect we determine the electronic structure and demonstrate that the electron
masses are very light, m^* is approximately equalt to 1.2 m_e. The Fermi
surface we observe is essentially that expected of nearly-free electrons -
establishing
Ag5Pb2O6 as the first known example of a monovalent, nearly-free electron
superconductor at ambient pressure.Comment: 4 pages, 3 figure
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