Showing papers by "University of Bremen published in 2003"
TL;DR: It becomes clear that there exist multiple mechanisms which contribute to the carcinogenicity of cadmium, although the relative weights of these contributions are difficult to estimate.
1,407 citations
TL;DR: It is concluded that diatom frustules have evolved as mechanical protection for the cells because exceptional force is required to break them.
Abstract: Diatoms are the major contributors to phytoplankton blooms in lakes and in the sea and hence are central in aquatic ecosystems and the global carbon cycle1. All free-living diatoms differ from other phytoplankton groups in having silicified cell walls in the form of two ‘shells’ (the frustule) of manifold shape and intricate architecture2 whose function and role, if any, in contributing to the evolutionary success of diatoms is under debate3,4,5. We explored the defence potential of the frustules as armour against predators by measuring their strength. Real and virtual loading tests (using calibrated glass microneedles and finite element analysis) were performed on centric and pennate diatom cells. Here we show that the frustules are remarkably strong by virtue of their architecture and the material properties of the diatom silica. We conclude that diatom frustules have evolved as mechanical protection for the cells because exceptional force is required to break them. The evolutionary arms race between diatoms and their specialized predators will have had considerable influence in structuring pelagic food webs and biogeochemical cycles.
792 citations
TL;DR: In this paper, a review of the use of weighted site averages in indicator analysis is presented, showing that these have a high reliability and can complement or, in some cases, replace measurements to determine the values of environmental variables and monitor their change.
711 citations
TL;DR: In this paper, the authors used the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometers to measure the gas-phase absorption spectra of the most important atmospheric trace gases (O3, NO2, SO2, O2, H2O, CO, CO2, CH4, and N2O) in the 230-2380 nm range at medium spectral resolution and at several temperatures between 203 and 293
Abstract: Using the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometer, gas-phase absorption spectra of the most important atmospheric trace gases (O3, NO2, SO2, O2, OClO, H2CO, H2O, CO, CO2, CH4, and N2O) have been measured in the 230–2380 nm range at medium spectral resolution and at several temperatures between 203 and 293 K. The spectra show high signal-to-noise ratio (between 200 up to a few thousands), high baseline stability (better than 10−2) and an accurate wavelength calibration (better than 0.01 nm) and were scaled to absolute absorption cross-sections using previously published data. The results are important as reference data for atmospheric remote-sensing and physical chemistry. Amongst other results, the first measurements of the Wulf bands of O3 up to their origin above 1000 nm were made at five different temperatures between 203 and 293 K, the first UV-Vis absorption cross-sections of NO2 in gas-phase equilibrium at 203 K were recorded, and the ultraviolet absorption cross-sections of SO2 were measured at five different temperatures between 203 and 296 K. In addition, the molecular absorption spectra were used to improve the wavelength calibration of the SCIAMACHY spectrometer and to characterize the instrumental line shape (ILS) and straylight properties of the instrument. It is demonstrated that laboratory measurements of molecular trace gas absorption spectra prior to launch are important for satellite instrument characterization and to validate and improve the spectroscopic database.
630 citations
TL;DR: It is found that macaques do have discrete face-selective patches, similar in relative size and number to face patches in humans, and these results suggest that humans and macaques share a similar brain architecture for visual object processing.
Abstract: How are different object categories organized by the visual system? Current evidence indicates that monkeys and humans process object categories in fundamentally different ways. Functional magnetic resonance imaging (fMRI) studies suggest that humans have a ventral temporal face area, but such evidence is lacking in macaques. Instead, face-responsive neurons in macaques seem to be scattered throughout temporal cortex, with some relative concentration in the superior temporal sulcus (STS). Here, using fMRI in alert fixating macaque monkeys and humans, we found that macaques do have discrete face-selective patches, similar in relative size and number to face patches in humans. The face patches were embedded within a large swath of object-selective cortex extending from V4 to rostral TE. This large region responded better to pictures of intact objects compared to scrambled objects, with different object categories eliciting different patterns of activity, as in the human. Overall, our results suggest that humans and macaques share a similar brain architecture for visual object processing.
601 citations
TL;DR: The ability of each individual steroid to contribute to the overall effect of a mixture, even at individual no-effect concentrations, combined with the high estrogenic potency of the steroids, particularly the synthetic steroid EE2, emphasizes the need to consider the total estrogenic load of these chemicals in the authors' waterways.
Abstract: The natural steroids estradiol-17beta (E2) and estrone (E1) and the synthetic steroid ethynylestradiol-17alpha (EE2) have frequently been measured in waters receiving domestic effluents. All of these steroids bind to the estrogen receptor(s) and have been shown to elicit a range of estrogenic responses in fish at environmentally relevant concentrations. At present, however, no relative potency estimates have been derived for either the individual steroidal estrogens or their mixtures in vivo. In this study the estrogenic activity of E2, E1, and EE2, and the combination effects of a mixture of E2 and EE2 (equi-potent fixed-ratio mixture), were assessed using vitellogenin induction in a 14-day in vivo juvenile rainbow trout screening assay. Median effective concentrations, relative to E2, for induction of vitellogenin were determined from the concentration-response curves and the relative estrogenic potencies of each of the test chemicals calculated. Median effective concentrations were between 19 and 26 ng L(-1) for E2, 60 ng L(-1) for E1, and between 0.95 and 1.8 ng L(-1) for EE2, implying that EE2 was approximately 11 to 27 times more potent than E2, while E2 was 2.3 to 3.2 times more potent than E1. The median effective concentration, relative to E2, for the binary mixture of E2 and EE2 was 15 ng L(-1) (comprising 14.4 ng L(-1) E2 and 0.6 ng L(-1) EE2). Using the model of concentration addition it was shown that this activity of the binary mixture could be predicted from the activity of the individual chemicals. The ability of each individual steroid to contribute to the overall effect of a mixture, even at individual no-effect concentrations, combined with the high estrogenic potency of the steroids, particularly the synthetic steroid EE2, emphasizes the need to consider the total estrogenic load of these chemicals in our waterways.
539 citations
01 Jan 2003
TL;DR: A novel, computationally efficient algorithm for detecting V-BLAST architectures with respect to the MMSE criterion is presented, which utilizes a sorted QR decomposition of the channel matrix and leads to a simple successive detection structure.
Abstract: In rich-scattering environments, layered space-time architectures like the BLAST system may exploit the capacity advantage of multiple antenna systems. We present a novel, computationally efficient algorithm for detecting V-BLAST architectures with respect to the MMSE criterion. It utilizes a sorted QR decomposition of the channel matrix and leads to a simple successive detection structure. The new algorithm needs only a fraction of computational effort compared to the standard V-BLAST algorithm and achieves the same error performance.
533 citations
TL;DR: In this article, the authors show that the late Holocene drought cycles following the 4.2 ka BP event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14C production rates, suggesting that solar variability is one fundamental cause behind Holocene rainfall changes over south Asia.
Abstract: [1] Planktonic oxygen isotope ratios off the Indus delta reveal climate changes with a multi-centennial pacing during the last 6 ka, with the most prominent change recorded at 4.2 ka BP. Opposing isotopic trends across the northern Arabian Sea surface at that time indicate a reduction in Indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south Asia. The 4.2 ka event is coherent with the termination of urban Harappan civilization in the Indus valley. Thus, drought may have initiated southeastward habitat tracking within the Harappan cultural domain. The late Holocene drought cycles following the 4.2 ka BP event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14C production rates. This suggests that solar variability is one fundamental cause behind Holocene rainfall changes over south Asia.
522 citations
TL;DR: The effect of flow rate on ion signals was studied systematically using mixtures of compounds with different physicochemical properties to find the functional dependence of certain analyte-ion ratios upon the flow rate can be correlated to changes in analyte partition during droplet fission prior to ion release.
472 citations
TL;DR: In this paper, the global distribution of organic-walled dinoflagellate cysts in the form of 61 maps illustrated by the relative abundance of individual cyst taxa in recent marine sediments from the Atlantic Ocean and adjacent basins, the Antarctic region (South Atlantic, southwestern Pacific and southern Indian Ocean sections), the Arabian Sea and the northwestern Pacific.
469 citations
TL;DR: Results even demonstrate that dissimilarly acting chemicals can show significant joint effects, predictable by independent action, when combined in concentrations below individual NOEC values, statistically estimated to elicit insignificant individual effects of only 1%.
TL;DR: It is concluded that puberty in rats is a vulnerable period with respect to the adverse effects of cannabinoid treatment, and chronic cannabinoid administration during pubertal development is proposed as an animal model for some aspects of the etiology of schizophrenia.
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TL;DR: In this article, a review of geochemical settings on the Continental Margins of the world's oceans is presented, along with an overview of the state-of-the-art and future prospect of scientific coring and drilling of Marine Sediments.
Abstract: Introductory Paper.- Sedimentary Settings on Continental Margins - an Overview.- Continental Margins - Review of Geochemical Settings.- Imaging the Subsurface with 2-D and 3-D Seismic Data.- State of the Art and Future Prospect of Scientific Coring and Drilling of Marine Sediments.- New Technologies for Ocean Margin Studies - Autonomous Instrument Carrier Systems.- Autonomous Underwater Vehicles: Are they the Ideal Sensor Platforms for Ocean Margin Science?.- Margin Building - Regulating Processes.- Physical Processes and Modelling at Ocean Margins.- Seabed Classification at Ocean Margins.- The Benthic Boundary Layer.- Ocean Margin Early Diagenetic Processes and Models.- Slope Instability of Continental Margins.- Margin Building - Regulating Processes.- Fluid Flow and Subsurface Material Transport.- Fluid Flow in Continental Margin Sediments.- Macrobenthic Activity and its Effects on Biogeochemical Reactions and Fluxes.- Cold Seep Communities on Continental Margins: Structure and Quantitative Distribution Relative to Geological and Fluid Venting Patterns.- The Importance of Mineralization Processes in Surface Sediments of Continental Margins.- Numerical Modelling of Transport Processes in the Subsurface.- Subsurface Fluid Flow and Material Transport.- Benthic Population Dynamics and Relationship to Sedimentary Settings.- Benthic Biodiversity Across and Along the Continental Margin: Patterns, Ecological and Historical Determinants, and Anthropogenic Threats.- Molecular Ecology and Evolution of Slope Species.- Larval and Reproductive Strategies on European Continental Margins.- Factors Controlling Soft Bottom Macrofauna Along and Across European Continental Margins.- Reef-Forming Cold-Water Corals.- Life at the Edge: Achieving Prediction from Environmental Variability and Biological Variety.- Microbial Systems in Sedimentary Environments.- Processes driven by the Small Sized Organisms at the Water-Sediment Interface.- Nucleic Acid-Based Techniques for Analyzing the Diversity, Structure, and Function of Microbial Communities in Marine Waters and Sediments.- Carbonate Mounds as a Possible Example for Microbial Activity in Geological Processes.- S. Guidard and the ODP "Proposal 573" Team.- The Anaerobic Oxidation of Methane: New Insights in Microbial Ecology and Biogeochemistry.- Microbial Systems in Sedimentary Environments of Continental Margins.
TL;DR: Centennial-scale paleoceanographic records from the southwest Pacific suggest close coupling of mid-southern latitudes with Antarctic climate during deglacial and interglacial periods and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations.
Abstract: In order to investigate rapid climatic changes at mid-southern latitudes, we have developed centennial-scale paleoceanographic records from the southwest Pacific that enable detailed comparison with Antarctic ice core records. These records suggest close coupling of mid-southern latitudes with Antarctic climate during deglacial and interglacial periods. Glacial sections display higher variability than is seen in Antarctic ice cores, which implies climatic decoupling between mid- and high southern latitudes due to enhanced circum-Antarctic circulation. Structural and temporal similarity with the Greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations.
TL;DR: In this paper, the authors present a discourse approach to the study of legitimacy of governance beyond the democratic state, starting from the empirical question of how international organizations legitimate themselves beyond the traditional democratic state.
Abstract: This article presents a discourse approach to the study of legitimacy of governance beyond the democratic state. It starts from the empirical question of how international organizations legitimate ...
TL;DR: It is concluded that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene and is best explained by enhancement and southward extension of rainfall from Mediterranean sources.
Abstract: Paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost Red Sea were used to infer hydrological changes at the southern margin of the Mediterranean climate zone during the Holocene. Between approximately 9.25 and 7.25 thousand years ago, about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff, which thereafter decreased to modern values. The northern Red Sea humid interval is best explained by enhancement and southward extension of rainfall from Mediterranean sources, possibly involving strengthened early-Holocene Arctic Oscillation patterns and a regional monsoon-type circulation induced by increased land-sea temperature contrasts. We conclude that Afro-Asian monsoonal rains did not cross the subtropical desert zone during the early to mid-Holocene.
TL;DR: The module Monitoring of User State [especially of] Emotion (MOUSE) is proposed in which a prosodic classifier is combined with other knowledge sources, such as conversationally peculiar linguistic behavior, for example, the use of repetitions.
TL;DR: In this paper, a transect off the West African coast has been investigated for their lipid content and compound-specific stable carbon isotope compositions, and the results show that only regions with a predominant C4 type vegetation, i.e., the Sahara, the Sahel, and Gabon, supply C4 plant-derived lipids to dust organic matter.
TL;DR: In this paper, a three-dimensional ocean circulation model was used to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation.
Abstract: During the two most recent deglaciations, the Southern Hemisphere warmed before Greenland. At the same time, the northern Atlantic Ocean was exposed to meltwater discharge, which is generally assumed to reduce the formation of North Atlantic Deep Water. Yet during deglaciation, the Atlantic thermohaline circulation became more vigorous, in the transition from a weak glacial to a strong interglacial mode. Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation. We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation, triggered by increased mass transport into the Atlantic Ocean via the warm (Indian Ocean) and cold (Pacific Ocean) water route. This effect prevails over the influence of meltwater discharge, which would oppose a strengthening of the thermohaline circulation. A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation, in agreement with the available proxy records.
TL;DR: In this paper, the magnetic properties of magnetic nanoparticles have been studied and the possibility of controlling the properties and the flow of these fluids with moderate magnetic fields has been shown to enable the design of various applications as well as basic experiments in hydrodynamics.
TL;DR: Metal workers, machinists, transport equipment operators and miners are among the major occupations contributing to occupational bladder cancer in men in Western Europe, with an increased risk for exposure to PAHs.
Abstract: Objectives: We examined which occupations and industries are currently at high risk for bladder cancer in men. Methods: We combined data from 11 case–control studies conducted between 1976–1996 in six European countries. The study comprised 3346 incident cases and 6840 controls, aged 30–79 years. Lifetime occupational and smoking histories were examined using common coding. Results: Odds ratios for eight a priori defined high-risk occupations were low, and with the exception of metal workers and machinists (OR = 1.16, 95% CI = 1.02–1.32), were not statistically significant. Higher risks were observed for specific categories of painters, metal, textile and electrical workers, for miners, transport operators, excavating-machine operators, and also for non-industrial workers such as concierges and janitors. Industries entailing a high risk included salt mining, manufacture of carpets, paints, plastics and industrial chemicals. An increased risk was found for exposure to PAHs (OR for highest exposure tertile = 1.23, 95% CI = 1.07–1.4). The risk attributable to occupation ranged from 4.2 to 7.4%, with an estimated 4.3% for exposure to PAHs. Conclusions: Metal workers, machinists, transport equipment operators and miners are among the major occupations contributing to occupational bladder cancer in men in Western Europe. In this population one in 10 to one in 20 cancers of the bladder can be attributed to occupation.
TL;DR: In this article, the authors present geochemical data from a total of 23 gravity cores and present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day.
01 Dec 2003
TL;DR: A new efficient algorithm for detecting layered space-time architectures with respect to the MMSE criterion is presented, which utilizes a sorted QR decomposition of the channel matrix and leads to a simple successive detection structure.
Abstract: Theoretical and experimental studies have shown that layered space-time architectures like the BLAST system can exploit the capacity advantage of multiple antenna systems in rich-scattering environments. We present a new efficient algorithm for detecting such architectures with respect to the MMSE criterion. This algorithm utilizes a sorted QR decomposition of the channel matrix and leads to a simple successive detection structure. The algorithm needs only a fraction of the computational effort compared to the standard V-BLAST algorithm and achieves the same bit error performance.
TL;DR: The isotope composition of atmospheric moisture over the Mediterranean Sea, collected during the cruise of the research vessel meteor in January 1995, confirmed that the intensive air-sea interaction near the coast under conditions of a large humidity deficit labels the resultant atmospheric waters with a large deuterium-excess parameter.
Abstract: The isotope composition of atmospheric moisture over the Mediterranean Sea, collected during the cruise of the research vessel meteor in January 1995, confirmed that the intensive air–sea interaction near the coast under conditions of a large humidity deficit labels the resultant atmospheric waters with a large deuterium-excess parameter. The present data set shows this effect to result both when cold air from the European continent moves over the sea as well as when warm and dry air from North Africa is involved. The situation in the eastern and western Mediterranean differ in the vertical structure of the isotope composition further away from the coast, as expressed by the gradients of the d excess values with altitude over the sea surface, i.e. increasing with altitude in the eastern Mediterranean, whereas the opposite effect is noted in the western section and near the coast. A comparison of the isotopic composition of the samples with the expected buildup of moisture over the sea, based on the Craig–Gordon model, suggests that up to one half of the added moisture may have resulted at times from the evaporation of sea-spray droplets, without any significant isotope fractionation, in addition to the vapour-mediated transport from the sea surface, which favors the lighter isotopic species. DOI: 10.1034/j.1600-0889.2003.00081.x
TL;DR: Results of swath mapping, heat flow, geochemistry and seismic surveys from the young eastern flank of the Juan de Fuca ridge show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km.
Abstract: Hydrothermal circulation within the sea floor, through lithosphere older than one million years (Myr), is responsible for 30% of the energy released from plate cooling, and for 70% of the global heat flow anomaly (the difference between observed thermal output and that predicted by conductive cooling models)1,2. Hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 Myr old3,4. But in view of the relatively impermeable sediments that cover most ridge flanks5, it has been difficult to explain how these fluids transport heat from the crust to the ocean. Here we present results of swath mapping, heat flow, geochemistry and seismic surveys from the young eastern flank of the Juan de Fuca ridge, which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km. Our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops. We find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies.
TL;DR: It is concluded that, in the mid-Pleistocene, changes in atmospheric moisture content—driven by tropical sea surface temperature changes and the strength of the African monsoon—controlled aridity on the African continent, and hence large-scale vegetation changes.
Abstract: The dominant forcing factors for past large-scale changes in vegetation are widely debated. Changes in the distribution of C4 plants—adapted to warm, dry conditions and low atmospheric CO2 concentrations1—have been attributed to marked changes in environmental conditions, but the relative impacts of changes in aridity, temperature2,3 and CO2 concentration4,5 are not well understood. Here, we present a record of African C4 plant abundance between 1.2 and 0.45 million years ago, derived from compound-specific carbon isotope analyses of wind-transported terrigenous plant waxes. We find that large-scale changes in African vegetation are linked closely to sea surface temperatures in the tropical Atlantic Ocean. We conclude that, in the mid-Pleistocene, changes in atmospheric moisture content—driven by tropical sea surface temperature changes and the strength of the African monsoon—controlled aridity on the African continent, and hence large-scale vegetation changes.
TL;DR: In this paper, a study of colluvial, fluvial and lacustrine sediment archives from 12 sites in Germany for the last ca 5000 years demonstrates that there is no synchronous development of the cultural landscape.
TL;DR: A survey and latest developments on the material, processing technologies, and fields of composite materials can be found in this paper, where the authors present a survey of the latest developments in composite materials.
Abstract: Composite materials with thermoplastic matrices and a reinforcement of natural fibers are increasingly regarded as an alternative to glass fiber-reinforced composites. The substitution of the traditionally used reinforcing glass fibers by natural fibers such as flax, kenaf, or cotton can lead to a reduction of the component's weight and furthermore to a significant improvement of specific properties like impact strength, crash behaviour, or sound absorption. One of the major fields of application for such materials can be found in structural components for the automotive industry. Product examples are door trim panels, headliners, or back panels. At present the processing of such materials into structural parts usually takes place by thermal compression molding. Semiproducts (so-called hybrid fleeces) are employed, which are generated by carding or air-laid processes and subsequent mechanical bonding. This paper presents a survey and latest developments on the material, processing technologies, and fields...
TL;DR: In this article, the meridional transport within the Ekman layer is intense enough to export at least 25% of the iron input away from the Antarctic Zone before it can be used by phytoplankton.
Abstract: [1] After 1 decade of research it is a well-established fact that iron limits photosynthetic CO2 fixation and phytoplankton growth in the Southern Ocean; intense blooms are scarce However, the input of iron to the Southern Ocean is considerable An important factor for diminished phytoplankton production refers to the meridional circulation of the Southern Ocean Intense, spatially relatively homogeneous upwelling of Upper Circumpolar Deep Water (UCDW) causes a large iron flux into the surface layer However, the main entrainment of upwelled UCDW into the surface layer occurs in autumn and winter, which strongly restricts the usefullness of iron supply for phytoplankton due to unfavorable light conditions Moreover, the meridional transport within the Ekman layer is intense enough to export at least 25% of the iron input away from the Antarctic Zone before it can be used by phytoplankton This also depresses the potential phytoplankton primary production by at least 25% Most iron that crosses the Polar Front unused probably leaves the surface ocean north of the Polar Front because the surface water participates in Antarctic Intermediate Water/Mode Water formation
TL;DR: Jeppsson et al. as discussed by the authors used isotope data from nine sections at the NW coast of Gotland to study the Ireviken Event and showed that first extinctions precede the isotope excursion.