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Institution

University of Bremen

EducationBremen, Germany
About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Glacial period. The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.


Papers
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Journal ArticleDOI
TL;DR: Investigation of hydrothermally influenced sediment from the Guaymas Basin indicates that AOM and ANME archaea could be of biogeochemical relevance not only in cold to moderate but also in hot marine habitats.
Abstract: The anaerobic oxidation of methane (AOM) with sulfate controls the emission of the greenhouse gas methane from the ocean floor. AOM is performed by microbial consortia of archaea (ANME) associated with partners related to sulfate-reducing bacteria. In vitro enrichments of AOM were so far only successful at temperatures ⩽25 °C; however, energy gain for growth by AOM with sulfate is in principle also possible at higher temperatures. Sequences of 16S rRNA genes and core lipids characteristic for ANME as well as hints of in situ AOM activity were indeed reported for geothermally heated marine environments, yet no direct evidence for thermophilic growth of marine ANME consortia was obtained to date. To study possible thermophilic AOM, we investigated hydrothermally influenced sediment from the Guaymas Basin. In vitro incubations showed activity of sulfate-dependent methane oxidation between 5 and 70 °C with an apparent optimum between 45 and 60 °C. AOM was absent at temperatures ⩾75 °C. Long-term enrichment of AOM was fastest at 50 °C, yielding a 13-fold increase of methane-dependent sulfate reduction within 250 days, equivalent to an apparent doubling time of 68 days. The enrichments were dominated by novel ANME-1 consortia, mostly associated with bacterial partners of the deltaproteobacterial HotSeep-1 cluster, a deeply branching phylogenetic group previously found in a butane-amended 60 °C-enrichment culture of Guaymas sediments. The closest relatives (Desulfurella spp.; Hippea maritima) are moderately thermophilic sulfur reducers. Results indicate that AOM and ANME archaea could be of biogeochemical relevance not only in cold to moderate but also in hot marine habitats.

170 citations

Journal ArticleDOI
TL;DR: In this paper, the retention behavior of phenylureas, s-triazines and phenoxycarbonic acid derivatives in a reversed-phase high-performance liquid chromatographic (RPLC) system has been examined.

170 citations

Journal ArticleDOI
TL;DR: The present review discusses how hemin gets into brain cells, and examines the multiple routes through which hemin can be toxic, including the release of redox-active iron, the depletion of cellular stores of NADPH and glutathione, the production of superoxide and hydroxyl radicals, and the peroxidation of membrane lipids.
Abstract: Hemorrhagic stroke is a common cause of permanent brain damage, with a significant amount of the damage occurring in the weeks following a stroke. This secondary damage is partly due to the toxic effects of hemin, a breakdown product of hemoglobin. The serum proteins hemopexin and albumin can bind hemin, but these natural defenses are insufficient to cope with the extremely high amounts of hemin (10 mM) that can potentially be liberated from hemoglobin in a hematoma. The present review discusses how hemin gets into brain cells, and examines the multiple routes through which hemin can be toxic. These include the release of redox-active iron, the depletion of cellular stores of NADPH and glutathione, the production of superoxide and hydroxyl radicals, and the peroxidation of membrane lipids. Important gaps are revealed in contemporary knowledge about the metabolism of hemin by brain cells, particularly regarding how hemin interacts with hydrogen peroxide. Strategies currently being developed for the reduction of hemin toxicity after hemorrhagic stroke include chelation therapy, antioxidant therapy and the modulation of heme oxygenase activity. Future strategies may be directed at preventing the uptake of hemin into brain cells to limit the opportunity for toxic interactions.

169 citations

Journal ArticleDOI
TL;DR: A discretization of the scattering-states continuum ensures the correct boundary condition for an open quantum system and introduces two degenerate Wilson chains for current carrying left- and right-moving electrons reflecting time-reversal symmetry.
Abstract: We propose a numerical renormalization group (NRG) approach to steady-state currents through nanodevices. A discretization of the scattering-states continuum ensures the correct boundary condition for an open quantum system. We introduce two degenerate Wilson chains for current carrying left- and right-moving electrons reflecting time-reversal symmetry in the absence of a finite bias V. We employ the time-dependent NRG to evolve the known steady-state density operator for a noninteracting junction into the density operator of the fully interacting nanodevice at finite bias. We calculate the differential conductance as function of V, T, and the external magnetic field.

169 citations

Journal ArticleDOI
01 Aug 2008-Geology
TL;DR: In this article, the authors present data from the first hydrothermal system in which the sampled fluids fall on and above the critical point (CP) of seawater at 298 bar and 407 °C, which represents the threshold between subcritical and supercritical conditions.
Abstract: Hydrothermal circulation within oceanic crust depends on pressure ( P ) and temperature ( T ); the critical point (CP) of seawater at 298 bar and 407 °C represents the threshold between subcritical and supercritical conditions. Here we present data from the first hydrothermal system in which the sampled fluids fall on and above the CP. The vent system discovered at 5°S on the Mid-Atlantic Ridge is characterized by multiple fluid emanations at variable temperatures in water depths of ~3000 m. Vigorous vapor phase bubbling, stable emanation of superhot fluid at 407 °C, and decreased salinity indicate phase separation at conditions above the CP at one site. At another site the measured maximum T of 464 °C during a 20 s interval is by far the hottest fluid ever measured at the seafloor and falls into the vapor-phase supercritical region of seawater. Besides these two separate fields with ongoing phase separation and extremely hot fluids, a third vent field emanates non-phase-separated fluids at 349 °C and is used as a reference site. Fluid chemistry shows that supercritical fluids evolve differently than subcritical fluids, making this vent system a unique natural laboratory to investigate processes at high P - T conditions. The stability of the high temperature and fluid geochemistry measured in 2005 and 2006 after the assumed seismic trigger event in 2002 supports this as an exceptional site along the Mid-Atlantic Ridge.

169 citations


Authors

Showing all 14961 results

NameH-indexPapersCitations
Roger Y. Tsien163441138267
Klaus-Robert Müller12976479391
Ron Kikinis12668463398
Ulrich S. Schubert122222985604
Andreas Richter11076948262
Michael Böhm10875566103
Juan Bisquert10745046267
John P. Sumpter10126646184
Jos Lelieveld10057037657
Michael Schulz10075950719
Peter Singer9470237128
Charles R. Tyler9232531724
John P. Burrows9081536169
Hans-Peter Kriegel8944473932
Harald Haas8575034927
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
2023343
2022709
20212,106
20202,309
20192,191
20181,965