Showing papers by "University of Bremen published in 1997"
TL;DR: In considering the available evidence, the carcinogenic properties of cadmium are interpreted using a multifactorial approach involving indirect genotoxicity (interference with DNA repair) and the upregulation of mitogenic signalling pathways.
540 citations
TL;DR: In this article, the authors argue that the rise of Comitology is an institutional response to the deep-seated tensions between the dual supranational and intergovernmentalist structure of the Community on the one hand, and its problem-solving tasks on the other.
Abstract: This article argues that the irresistible rise of Comitology is an institutional response to the deep‐seated tensions between the dual supranational and intergovernmentalist structure of the Community on the one hand, and its problem‐solving tasks on the other. Comitology has accordingly provided a forum in which problems are addressed through evolving and novel processes of interest formation and decision‐making. However, neither legal nor political science have been able properly to evaluate the workings of the committee system, both disciplines remaining trapped within normative structures and traditional methodologies ill‐suited to the analysis of these institutional innovations. As a consequence, this article advocates the trans‐disciplinary study of Comitology, and furthermore argues that the two disciplines might be drawn together by the concept of ‘deliberative supranationalism’: being on the one hand a normative approach which seeks both to preserve the legitimacy of national democracies and to set limits upon the traditional Nation State within a supranational community; and on the other, a theoretical tool which is nonetheless responsive to and accomodating of ‘real‐world’ phenomena.
539 citations
TL;DR: It is shown that this reaction deters protozoan herbivores, presumably through the production of highly concentrated acrylate, which has antimicrobial activity, which is believed to be the first report of grazing-activated chemical defence in unicellular microorganisms.
Abstract: Marine plankton use a variety of defences against predators, some of which affect trophic structure and biogeochemistry1. We have previously shown2 that, during grazing by the protozoan Oxyrrhis marina on the alga Emiliania huxleyi, dimethylsulphoniopropionate (DMSP) from the prey is converted to dimethyl sulphide (DMS) when lysis of ingested prey cells initiates mixing of algal DMSP and the enzyme DMSP lyase. Such a mechanism is similar to macrophyte defence reactions3,4. Here we show that this reaction deters protozoan herbivores, presumably through the production of highly concentrated acrylate, which has antimicrobial activity5. Protozoan predators differ in their ability to ingest and survive on prey with high-activity DMSP lyase, but all grazers preferentially select strains with low enzyme activity when offered prey mixtures. This defence system involves investment in a chemical precursor, DMSP, which is not self-toxic and has other useful metabolic functions. We believe this is the first report of grazing-activated chemical defence in unicellular microorganisms.
428 citations
TL;DR: In this paper, a novel method to measure the refractive index n in the near-infrared by simple extensions to a standard Abbe refractometer is described, and experimental results of refractive-index measurements at are compared with published data.
Abstract: A novel method to measure the refractive index n in the near-infrared by simple extensions to a standard Abbe refractometer is described. A technique is derived to correct for the dispersion of the glass prism and experimental results of refractive-index measurements at are compared with published data. These results prove the suitability of the described method, the accuracy being comparable to that of an Abbe refractometer used in the visible range; that is, the refractive index n can be measured to an accuracy of . Finally, new refractive-index data at 830 nm are given for methanol, water, acetone, ethanol, cyclohexane, glycol, di-2-ethyl hexyl-sabacate (DEHS), carbon tetrachloride, glycerol, toluene, ethyl salicylate, methyl salicylate and cinnamaldehyde at 20 and .
381 citations
TL;DR: The old concept stating that EEG alpha (10-Hz) activity reflects passive or idling states of the brain is giving way to modern views of 10-Hz oscillations in relation to diverse brain functions comprising sensory, motor, and memory processes.
369 citations
TL;DR: In this article, surface sediment samples from the eastern South Atlantic Ocean including the Walvis Ridge, the Angola and Cape basins, and the Southwest African continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences.
349 citations
TL;DR: Using axonal tracers, neurons projecting from the brain to the spinal cord as well as the terminal fields of ascending spinal projections in the brain of adult zebrafish with unlesioned or transected spinal cords are characterized.
Abstract: Using axonal tracers, we characterized the neurons projecting from the brain to the spinal cord as well as the terminal fields of ascending spinal projections in the brain of adult zebrafish with unlesioned or transected spinal cords. Twenty distinct brain nuclei were found to project to the spinal cord. These nuclei were similar to those found in the closely related goldfish, except that additionally the parvocellular preoptic nucleus, the medial octavolateralis nucleus, and the nucleus tangentialis, but not the facial lobe, projected to the spinal cord in zebrafish. Terminal fields of axons, visualized by anterograde tracing, were seen in the telencephalon, the diencephalon, the torus semicircularis, the optic tectum, the eminentia granularis, and throughout the ventral brainstem in unlesioned animals. Following spinal cord transection at a level approximately 3.5 mm caudal to the brainstem/spinal cord transition zone, neurons in most brain nuclei grew axons beyond the transection site into the distal spinal cord to the level of retrograde tracer application within 6 weeks. However, the individually identifiable Mauthner cells were never seen to do so up to 15 weeks after spinal cord transection. Nearly all neurons survived axotomy, and the vast majority of axons that had grown beyond the transection site belonged to previously axotomized neurons as shown by double tracing. Terminal fields were not re-established in the torus semicircularis and the eminentia granularis following spinal cord transection.
348 citations
TL;DR: In this article, the authors focus on the opportunities and strengths of a multi-method approach, widely called methodological triangulation, in which different investigative methods are applied to one research object.
Abstract: The essay focuses on the opportunities and strengths of a multi-method approach, widely called methodological triangulation, in which different investigative methods are applied to one research object. In practice, this can be realized with the coupling of quantitative structural data concerning the life course and the interpretation and evaluation of life course data collected with qualitative methods. This approach is examined in order to shed light on the problem that research findings often show different phenomena and not the different aspects of one phenomenon. The discussion of the relationships of the findings to one another (congruent, complementary or divergent) shows that in this context a multi-method approach can nevertheless be used to increase validity and to test hypotheses. Further, its particular strengths are the empirically induced modification of existing models and theories, as well as the development of new explanations.
254 citations
TL;DR: Since oxidative DNA damage is continuously induced during aerobic metabolism, an impaired repair of these lesions might well explain the carcinogenic action of nickel(II) and cadmium(II).
Abstract: Compounds of nickel(II) and cadmium(II) are carcinogenic to humans and to experimental animals. One frequently discussed mechanism involved in tumor formation is an increase in reactive oxygen species by both metals with the subsequent generation of oxidative DNA damage. In the present study we used human HeLa cells to investigate the potential of nickel(II) and cadmium(II) to induce DNA lesions typical for oxygen free radicals in intact cells and the effect on their repair. As indicators of oxidative DNA damage, we determined the frequencies of DNA strand breaks and of lesions recognized by the bacterial formamidopyrimidine-DNA glycosylase (Fpg protein), including 7,8-dihydro-8-oxoguanine (8-hydroxyguanine), a pre-mutagenic DNA base modification. Nickel(II) caused a slight increase in DNA strand breaks at 250 microM and higher, while the frequency of Fpg-sensitive sites was enhanced only at the cytotoxic concentration of 750 microM. The repair of oxidative DNA lesions induced by visible light was reduced at 50 microM and at 100 microM nickel(II) for Fpg-sensitive sites and DNA strand breaks, respectively; the removal of both types of lesions was blocked nearly completely at 250 microM nickel(II). In the case of cadmium(II), DNA strand breaks occurred at 10 microM and no Fpg-sensitive sites were detected. However, the repair of Fpg-sensitive DNA lesions induced by visible light was reduced at 0.5 microM cadmium(II) and higher, while the closure of DNA strand breaks was not affected. Since oxidative DNA damage is continuously induced during aerobic metabolism, an impaired repair of these lesions might well explain the carcinogenic action of nickel(II) and cadmium(II).
252 citations
TL;DR: A detailed dated sequence of turbidite sedimentation based on a core transect perpendicular to the active channel-levee system in the upper mid-fan area is presented in this paper.
Abstract: New stratigraphic and high-resolution seismic data from the Bengal Fan indicate that the world9s largest fan shows active growth during the most recent sea-level rise and the recent highstand. This unique phenomenon contradicts common sequence-stratigraphic models, and the sediment preserved provides new insight into the sedimentological response of a fan system to sea-level rise, climatic terminations, and monsoon intensity during the past climatic cycle. We present a detailed dated sequence of turbidite sedimentation based on a core transect perpendicular to the active channel-levee system in the upper mid-fan area. Between the two major terminations 1a (12 800 14 C yr B.P.) and 1b (9700 14 C yr B.P.), and especially at the end of the Younger Dryas, a 13-km-wide channel built up levees 50 m high. With decreasing sediment supply, continued sea-level rise, and increasing monsoon intensity during the early Holocene, turbidity currents were confined to the channel and gradually filled it. The canyon “Swatch of No Ground,” a shelf depocenter that serves as the source for frequent turbidity currents, and the channel-levee system provide the unique opportunity for studying an active highstand system. Many fans showed this behavior only during lowered sea-level.
219 citations
TL;DR: The authors used ocean temperature, salinity and chlorofluorocarbon concentration data to track the recent spreading of cold intermediate-depth water masses from the Labrador Sea across the northern North Atlantic Ocean.
Abstract: Ocean temperature, salinity and chlorofluorocarbon concentration data are used to track the recent spreading of cold intermediate-depth water masses from the Labrador Sea across the northern North Atlantic Ocean. These water masses, which are formed from surface waters by deep convection in the Labrador Sea, spread three to four times faster than previously estimated, with associated consequences for the North Atlantic thermohaline circulation.
TL;DR: In this paper, expanded sedimentary records of the late Paleocene thermal maximum, a dramatic global warming event that occurred at ca. 55 million years ago, were used to investigate the role of volcanic activity in ocean circulation.
Abstract: Two recently drilled Caribbean sites contain expanded sedimentary records of the late Paleocene thermal maximum, a dramatic global warming event that occurred at ca. 55 Ma. The records document significant environmental changes, including deep-water oxygen deficiency and a mass extinction of deep-sea fauna, intertwined with evidence for a major episode of explosive volcanism. We postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the Earth’s environment.
TL;DR: The isotopic difference between G. truncatulinoides and G. sacculifer from tropical gravity Core GeoB 1523-1 was significantly lower during isotope stage 2 as discussed by the authors, suggesting that the glacial temperature stratification of western equatorial Atlantic surface waters was significantly reduced relative to the Holocene.
Abstract: The δ 18 O difference between shallow- and deep-living planktonic foraminifera is a proxy for the stratification of surface waters. In Holocene sediments from the Atlantic this difference increases from about 0‰ in subpolar regions to ∼3‰ in the tropics. The δ 18 O values of the shallow dwellers Globigerinoides sacculifer and Neogloboquadrina pachyderma mainly reflect surface-water conditions. The calcification depth of the deep-living species Globorotalia truncatulinoides (right-coiling) is affected by the stratification of the water column. In the subtropics, shell formation of G. truncatulinoides (right-coiling) begins in weakly stratified surface waters. In the tropics, the initial shell is secreted below the mixed layer. This hydrographically induced difference in calcification depth allows the use of the isotopic difference between G. truncatulinoides and the shallow species as a proxy for the stratification of surface waters. The Δδ 18 O between G. truncatulinoides and G. sacculifer from tropical gravity Core GeoB 1523-1 was significantly lower during isotope stage 2. This suggests that the glacial temperature stratification of western equatorial Atlantic surface waters was significantly reduced relative to the Holocene.
TL;DR: Repairs inhibition may well explain the potentiation of genotoxic effects by arsenic in combination with other DNA damaging agents and may thus be of high relevance for the carcinogenic action of arsenic compounds.
Abstract: Even though epidemiological studies have identified arsenic compounds as carcinogenic to humans, they are not mutagenic in bacterial and mammalian test systems. However, they increase the mutagenicity and clastogenicity in combination with other DNA damaging agents and there are indications of inhibition of DNA repair processes. We investigated the effect of arsenic(III) on nucleotide excision repair (NER) after UV irradiation in human fibroblasts in detail by using two repair-proficient and one partly repair-deficient xeroderma pigmentosum group C human fibroblast cell lines. The results show that two steps of NER are affected by arsenite. Most severely, the incision frequency is reduced at concentrations as low as 2.5 microM arsenic(III); at higher, cytotoxic concentrations, the ligation of repair patches is also impaired. Furthermore, our results indicate that both the global genome repair pathway and the transcription-coupled repair pathway are affected by arsenite. Repair inhibition may well explain the potentiation of genotoxic effects by arsenic in combination with other DNA damaging agents and may thus be of high relevance for the carcinogenic action of arsenic compounds.
TL;DR: This minireview focuses mainly on more recent discoveries concerning the biosynthesis and turnover of DMSP, DMS, and related compounds in the biosphere and with respect to the role of DMS in the global sulfur cycle and climate.
Abstract: It has long been recognized that algae play a highly significant role in the global biogeochemical cycles of oxygen, carbon, nitrogen, phosphorus, and sulfw. The key chemical compounds driving these cycles are often low molecular weight and/or volatile species. In the case of sulfur, a dominant compound is dimethyl sulfide (DMS), which derives from dimethylsulfoniopropionate (DMSP) , an organic osmolyte that acts as a compatible solute in algal cells. High concentrations of DMS and DMSP can be found in areas of high algal productivity, such as marine phytoplankton blooms. In recent years research has unveiled greater detail concerning the biosynthesis and turnover of DMSP, DMS, and related compounds in the biosphere and with respect to the role of DMS in the global sulfur cycle and climate. In this minireview our aim is to concentrate mainly on these more recent discoveries.
TL;DR: In this paper, the photo-oxidation of phenol and 2-, 3- and 4-monochlorophenols by irradiation with visible light in aqueous alkaline solution in the presence of photosensitizers and oxygen is described.
Abstract: The photo-oxidation of phenol and 2-, 3- and 4-monochlorophenols by irradiation with visible light in aqueous alkaline solution in the presence of photosensitizers and oxygen is described. The reactions were carried out in the absence or presence of detergents. The photosensitizers used were Al(III), Zn(II) and Ga(III) complexes of 2,9,16,23-tetrasulphophthalocyanine (1a–1c), 5,10,15,20-tetrakis(4-carboxy-phenyl)porphyrin (2), a cationically charged perylene tetracarboxylic acid diimide (3), rose bengal (4) and methylene blue (5). The photosensitizers exhibit different activities and photo-oxidative stabilities which are strongly dependent on the pH, hydrolysis sensitivity and aggregation tendency. Singlet oxygen, obtained by photoinduced energy transfer from the excited photosensitizers, dominates the initial steps of photo-oxidation. A reaction sequence is proposed on the basis of the identification of carbon dioxide and maleic or fumaric acid as the products of photo-oxidation in the absence of detergent and the evaluated mass balances.
TL;DR: In this paper, a rotating disk technique was used to investigate the effect of the DBL on the dissolution rates of CaCO 3, which allowed an exact adjustment of the thickness of the diffusion boundary layer by controlling the rotation speed of a circular sample of Ca CO 3.
TL;DR: In this article, the authors collected in net tows (>63 μm) along two east-west transects at 78 ° and 80 °N in the Fram Strait (northern Nordic Seas) at five concurrent depth intervals in the upper 200 m of the water column.
TL;DR: In this article, the carbon and oxygen isotope ratios of brachiopod shells from the Silurian of Gotland, Sweden, have been analyzed and interpreted as changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations.
TL;DR: The explosive force inferred for this event places it at the threshold of impacts believed to have global consequences, and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events, which are common on geological timescales.
Abstract: In 1995, an expedition on board the research vessel FS Polarstern explored the impact site of the Eltanin asteroid in the Southern Ocean, the only known asteroidimpact into a deep ocean basin. Analyses of the geological record of the impact region place the event in the late Pliocene (∼2.15 Myr) and constrain thesize of the asteroid to be >1 km. The explosive force inferred for this event places it at the threshold of impacts believed to have global consequences, and its studyshould therefore provide a baseline for the reconstruction and modelling of similar events, which are common on geological timescales.
21 Apr 1997
TL;DR: A multichannel-algorithm for speech enhancement for hands-free telephone systems in cars that yields better results in noise reduction with significantly less distortions and artificial noise than spectral subtraction or Wiener filtering alone.
Abstract: This paper presents a multichannel-algorithm for speech enhancement for hands-free telephone systems in cars. This new algorithm takes advantage of the special noise characteristics in fast driving cars. The incoherence of the noise allows to use adaptive Wiener filtering in the frequencies above a theoretically determined frequency. Below this frequency a smoothed spectral subtraction (SSS) is used to get an improved noise suppression. The algorithm yields better results in noise reduction with significantly less distortions and artificial noise than spectral subtraction or Wiener filtering alone.
TL;DR: In this article, the steady flow in rectangular cavities is investigated both numerically and experimentally, and it is found that the basic two-dimensional flow is not always unique.
Abstract: The steady flow in rectangular cavities is investigated both numerically and experimentally. The flow is driven by moving two facing walls tangentially in opposite directions. It is found that the basic two-dimensional flow is not always unique. For low Reynolds numbers it consists of two separate co-rotating vortices adjacent to the moving walls. If the difference in the sidewall Reynolds numbers is large this flow becomes unstable to a stationary three-dimensional mode with a long wavelength. When the aspect ratio is larger than two and both Reynolds numbers are large, but comparable in magnitude, a second two-dimensional flow exists. It takes the form of a single vortex occupying the whole cavity. This flow is the preferred state in the present experiment. It becomes unstable to a three-dimensional mode that subdivides the basic streched vortex flow into rectangular convective cells. The instability is supercritical when both sidewall Reynolds numbers are the same. When they differ the instability is subcritical. From an energy analysis and from the salient features of the three-dimensional flow it is concluded that the mechanism of destabilization is identical to the destabilization mechanism operative in the elliptical instability of highly strained vortices.
TL;DR: In this paper, the combination of fluorescence labelling of reduced inorganic sulfur compounds such as sulfide (S2−), sulfite(SO32−) with monobromobimane followed by an extraction of elemental sulfur (S°) by chloroform treatment enables the detection of all mentioned sulfur compounds as well as sulfate (remaining aqueous phase) in the same sample.
University of California, Santa Barbara1, Laval University2, University of Perugia3, University of Paris4, University of Paris-Sud5, University of North Carolina at Chapel Hill6, University of Miami7, Université catholique de Louvain8, University of Hamburg9, Goethe University Frankfurt10, Cardiff University11, University of Queensland12, University of Bremen13, Utkal University14, Technical University of Berlin15
TL;DR: In this paper, the first step of the very rapid and large scale lowest Triassic transgression was noted in different areas (S Alps, Taurus, Turkey, S Armenia, E Elburz, Iran, Central Iran and CentralAfghanistan) during the first phase of the Triassic transition.
Abstract: During the first step of the very rapid and large scale lowest Triassic transgression , we note in
different areas (S Alps, Taurus,Turkey, S Armenia, E Elburz, Iran, Central Iran and Central
Afghanistan) the growth of domal stromatolites, thrombolites and other microbial structures. At the
dawn of Triassic time, the carbonate factory was dominated by non-skeletal species and by
microrganisms able to precipitate carbonate.
TL;DR: The cocycle description of a nonaut autonomous system and the concept of a cocycle attractor are reviewed in the context of nonautonomous ordinary differential equations and variable time-step numerical schemes for autonomous ordinary differential equation.
Abstract: The concept of an attractor for autonomous systems is generally too restrictive in the nonautonomous context An appropriate generalization is the cocycle attractor which consists of a family of equivariant sets Here the cocycle description of a nonautonomous system and the concept of a cocycle attractor are reviewed in the context of nonautonomous ordinary differential equations and variable time-step numerical schemes for autonomous ordinary differential equations In the latter case, theorems are stated for the existence and convergence of numerical cocycle attractors to an assumed attractor of an autonomous ordinary differential equations
TL;DR: In this paper, the vertical distribution of δ18O values of net-sampled speciments, together with their abundances and proportion of calcification, are compared with water samples and foraminiferal tests from core-top sediments.
TL;DR: In this article, Buhmann and Dreybrodt proposed a theoretical model that predicts that precipitation rates of CaC03 minerals depend critically on the ratio V/A of the volume V of the solution to the surface area A of the mineral in contact with it, for both laminar and turbulent flow.
01 Sep 1997
TL;DR: An overview of the interdisciplinary DFG priority program on spatial cognition is given and one specific theme which was the topic of a recent workshop in Gottingen is presented in some more detail.
Abstract: The paper gives a brief overview of the interdisciplinary DFG priority program on spatial cognition and presents one specific theme which was the topic of a recent workshop in Gottingen in some more detail. A taxonomy of landmark, route, and survey knowledge for navigation tasks proposed at the workshop is presented. Different ways of acquiring route knowledge are discussed. The importance of employing different spatial reference systems for carrying out navigation tasks is emphasized. Basic mechanisms of spatial memory in human and animal navigation are presented. After outlining the fundamental representational issues, methodological issues in robot and human navigation are discussed. Three applications of spatial cognition research in navigation tasks are given to exemplify both technological relevance and human impact of basic research in cognition.
TL;DR: In this article, the melting of small particles and in particular, embedded small particles which have been studied less extensively is discussed. And the observed asymmetry in the solidification and melting behavior of metals and alloys is investigated.
TL;DR: Fast hybrid mode-matching/boundary-contour (MM/BC) and mode- matching/finite-element ( MM/FE) waveguide building blocks are described for the optimization-oriented use in powerful circuit computer-aided design (CAD) tools and the automated design of waveguide components.
Abstract: Fast hybrid mode-matching/boundary-contour (MM/BC) and mode-matching/finite-element (MM/FE) waveguide building blocks are described for the optimization-oriented use in powerful circuit computer-aided design (CAD) tools and the automated design of waveguide components. The efficient electromagnetic (EM) CAD technique allows the accurate design of a comprehensive class of rectangular and circular waveguide components including realistic structures of higher complexity. The efficiency and flexibility of the hybrid CAD method is demonstrated at advanced EM design examples, such as broad-band circular-to-rectangular waveguide transitions including octagonal cross sections, waveguide resonator filters with rounded corners, optimum-shaped bends, dual-mode filters with coupling sections without tuning screws, ridged waveguide filters with rounded corners, and multiplexers. The designed components are directly amenable to cost-efficient fabrication techniques like computer-controlled milling methods. The theory is verified by available measurements.