Showing papers by "University of Bremen published in 1992"
TL;DR: In this article, the authors presented a novel description of the phenomenology of the Eastern Mediterranean based upon a comprehensive pooled hydrographic data base collected during 1985-1987 and analyzed by cooperating scientists from several institutions and nations (the POEM project).
338 citations
TL;DR: In this article, the dissolution rates of various natural calcite samples, e.g. marbles, limestones and marine pelagic sediments, were measured in CO2-H2O solutions of fixed PCO2 and temperature during their approach to equilibrium with respect to calcite.
215 citations
TL;DR: The ultra‐fast application of the RARE experiment is described in detail, with special emphasis on its multifarious applications with preparation experiments that produce transverse magnetization.
Abstract: The ultra-fast application of the RARE experiment is described in detail, with special emphasis on its multifarious applications with preparation experiments that produce transverse magnetization. The factors affecting the temporal evolution of the magnetization during the experiment are described, and the implications for the slice profile when using a Gaussian refocusing pulse are experimentally examined. The choice of phase-encoding scheme for use with preparation experiments is discussed, as is the use of various phase-encoding schemes to reduce line broadening in the phase-encoding direction if a number of averages are acquired. An explanation for the decomposition of the echo are into two components if the read gradient is imbalanced is given, and the experimental conditions necessary for the coherent addition of these two echo groups are described. An alternative sequence that removes one of these groups from the acquisition window is proposed. The sensitivity of the sequence to flow and motion is investigated, and the drastic loss of signal in this situation explained. The in vivo and in vitro application of preparation experiments leading to the accurate measurement of T1, T2, diffusion constant, and magnetization transfer characteristics is presented. The implementation of zoom-imaging using spin- and stimulated-echo preparation is described, and 3D in vivo spin-echo zoom images are presented. Simple phantom experiments demonstrating the feasibility of chemical-shift selective and spectroscopic imaging are also given.
190 citations
TL;DR: 8-pCPT-cGMP is a very potent and selective activator of cGMP-PK in cell extracts and in intact human platelets and, in this respect, is superior to 8-Br-c GMP and other cG MP analogs used for intact cell studies.
138 citations
TL;DR: A new approach for triangulating trimmed surfaces that is particularly suitable for the generation of a valid triangulation model for many engineering applications, for example stereolothography.
Abstract: The paper presents a new approach for triangulating trimmed surfaces. The basic idea is to perform the triangulation completely in parametric space. The trimmed regions of the surfaces are first mapped into parametric space and approximated by 2D polygonal regions, which are then pretriangulated by a restricted Delaunay triangulation algorithm. The generated triangles are subdivided further until each edge of the triangles is smaller than the allowed length that results from the surface definition and the specified tolerance. All the triangles are finally mapped back into Euclidean space so that the coordinate triples for the triangle vertices can be calculated. This approach makes the triangulation more reliable and faster, and it is also easy to avoid cracks between patches and surfaces. Thus, the algorithm is particularly suitable for the generation of a valid triangulation model for many engineering applications, for example stereolothography.
132 citations
TL;DR: The data support the idea of a light-dependent DMSP biosynthesis, and demonstrate the stimulating effect of low water temperatures on the DMSP content of Antarctic green macroalgae.
Abstract: The effect of photon fluence rate on the s-dimethylsulphoniopropionate (DMSP) content of salt-stressed eulittoral green macroalgae from different geographic regions was determined. At 55 μmol photons m−2s−1 DMSP increased continuously with increasing salinities up to 68‰ in Ulothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa and Acrosiphonia arcta from Antarctica, while the Subantarctic/cold-temperate Ulva rigida and the temperate Blidingia minima showed a large rise in intracellular DMSP concentration only under gentle hypersaline treatment (51‰). At the highest salinity tested the DMSP content of the latter species declined. In contrast, the capacity to form DMSP in the dark under hypersaline conditions was very low in all species. In addition, the DMSP content of the Antarctic species was determined after one year cultivation at 0°C under photon fluence rates of 2, 30 and 55 μmol m−2s−1. All isolates increased their DMSP concentration with increasing irradiance. In contrast to previous experiments done at 10°C, these species exhibited up to 5 fold higher DMSP values at 0°C under most photon fluence rates. The data support the idea of a light-dependent DMSP biosynthesis, and also demonstrate the stimulating effect of low water temperatures on the DMSP content of Antarctic green macroalgae. Apparently, in these plants DMSP may function as a cryoprotectant.
125 citations
01 Sep 1992
TL;DR: The planktonic foraminifera can be divided into two distinct provinces having a latitudinal boundary at 83°N, and the proportions of right-coiling individuals and subpolar species are decreasing going northward, caused by the input of Atlantic water masses transported into the Arctic Ocean.
Abstract: Planktonic foraminifera were collected in the Arctic Ocean with net tows (>63 μin) along a S-N transect from 81 to 86°N. Five depth intervals were sampled vertically between 500 m water depth and the sea surface. The most common species are Neogloboquadrina pachyderma and Globigerina quinqueloba. Based on the depth habitat, the faunal composition and the population structure, the planktonic foraminifera can be divided into two distinct provinces having a latitudinal boundary at 83°N. In the southern area, the concentrations of planktonic foraminifera are highest as well as the per cent of subpolar species and right-coiling individuals. Both species prefer the water below the pycnocline at about 100 m. North of 83°N, the two species display maximum abundance in the upper 50 m, where the water is colder and fresher than below the pycnocline. The proportions of right-coiling individuals and subpolar species are decreasing going northward. The observed changes are caused by the input of Atlantic water masses transported into the Arctic Ocean.
112 citations
TL;DR: Given the magnitude of the potential bias from nondifferential exposure misclassification and other sources, quantitative estimates of individual-level rate ratios from ecologic data should be interpreted with extreme caution.
Abstract: Although many authors have argued against inferring individual-level exposure-disease relations from ecologic data because of the potential "ecological fallacy." the availability of data from diverse populations promotes the continued use of this rapid and inexpensive study design. In ecologic studies, the exposure status of groups is often defined by the proportion of individuals exposed. In these studies, nondifferential exposure misclassification of individuals is shown to produce overestimation of exposure-disease associations that may be extreme when the ecologically derived rate ratios are applied to individuals. This overestimation contrasts with the bias toward the null resulting from nondifferential misclassification of a binary exposure in epidemiologic studies conducted at the individual level. Given the magnitude of the potential bias from nondifferential exposure misclassification and other sources, quantitative estimates of individual-level rate ratios from ecologic data should be interpreted with extreme caution.
106 citations
TL;DR: In this paper, unsubstituted and substituted aromatic 1,2-dinitriles were converted in the presence of strong bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1,5-Diazabicycleclo [4.3] non-5-ene(DBN) in bulk reactions or an n-pentanol in high yields to metal-free phthalocyanines and related macrocyclic compounds.
105 citations
TL;DR: DMSP accumulation after hyperosmotic shock was significantly delayed when methionine liberation from proteins was inhibited by a set of protease inhibitors and it is proposed that methamphetamineionine availability in T. subcordiformis determines the rate of DMSP synthesis.
Abstract: The unicellular alga Tetraselmis (Platymonas) subcordiformis (Prasinophyceae) displayed a two-phase increase in DMSP (dimethylsulfoniopropionate) contents in response to nitrogen deficiency. In the first phase, DMSP pools increased by 75% within 24 h. The second increase in DMSP was observed after 14 d and was accompanied by cyst formation. Methionine metabolism was involved in DMSP accumulation. A 2.6-fold increase of the DMSP pool could be induced by supplementing a complete ASP (artifical seawater Provasoli) medium with 100 μM L-methionine. Inhibition of methionine utilization by T. subcordiformis caused by the addition of S-adenosylhomocystein, a competitive inhibitor of S-adenosylmethionine-dependent transmethylases, resulted in a 24% increase of DMSP contents after 7 h. DMSP accumulation after hyperosmotic shock was significantly delayed when methionine liberation from proteins was inhibited by a set of protease inhibitors. A model for the mechanism of DMSP accumulation is presented on the basis of these data and additional information from the literature. It is proposed that methionine availability in T. subcordiformis determines the rate of DMSP synthesis.
102 citations
TL;DR: In this article, a small spring-fed stream precipitates calcite by outgassing of CO 2 due to chemically controlled inorganic processes and water analyses were carried out at the same time.
TL;DR: In a hospital-based case-control study 194 lung cancer cases, 194 hospital controls, and 194 population controls were interviewed for their smoking, occupational, and residential history by trained interviewers, using a standardized questionnaire to quantify occupational exposure to known carcinogens of the lung.
Abstract: In a hospital-based case-control study 194 lung cancer cases, 194 hospital controls, and 194 population controls were interviewed for their smoking, occupational, and residential history by trained interviewers, using a standardized questionnaire. In order to include many different environmental exposures, case ascertainment took place in seven different hospitals with catchment areas ranging from rural to highly industrialized. Lung cancer risk strongly increases with cumulative cigarette dose, reaching an odds ratio (OR) of 16.19 (95% confidence limits (CL): 5.10, 51.33) for male smokers of more than 40 pack-years and an OR of 19.99 (95% CL: 4.98, 80.24) for female smokers of more than 20 pack-years. For the quantification of occupational exposure to known carcinogens of the lung a novel approach was developed which accumulates exposure information obtained by supplemental questionnaires through an automatic procedure. The OR for the highest exposure group in males was 2.7 (95% CL: 1.23, 5.78). Significantly increased risks were observed in the metal industry, particularly in smelter and foundry workers (OR 4.8, 95% CL: 1.15, 20.16) and in turners (OR 2.2, 95% CL: 1.05, 4.75). In the construction industry the risks were particularly high in road construction workers (OR 3.7, 95% CL: 1.06, 13.20) and in unskilled construction workers (OR 2.7, 95% CL: 1.24, 5.76). The risks in these occupational groups increased with duration and with latency. Quantification of air pollution was done on a county basis by time period. An index based on emission data for sulphur dioxide was compared to a semiquantitative index, which included additional information on ambient air pollution. After adjustment for smoking and occupational exposures an OR of 1.01 (95% CL: 0.53, 1.91) for an emission index and of 1.16 (95% CL: 0.64, 2.13) for a semiquantitative index was obtained.
TL;DR: In this article, a rigorous computer-aided design of rectangular waveguide structures coupled by open or rectangular iris loaded E- or H-plane T-junctions is described, based on the full wave mode-matching method for the key-building block T-junction element associated with the generalized S-matrix technique for composite structures.
Abstract: The rigorous computer-aided design of rectangular waveguide structures coupled by open or rectangular iris loaded E- or H-plane T-junctions is described. The design theory is based on the full wave mode-matching method for the key-building-block T-junction element associated with the generalized S-matrix technique for composite structures. The waveguide structures may be arbitrarily composed of the T-junction and already known key-building-block elements (such as the double step and the septum discontinuity) combined with homogeneous waveguide sections between them. The E- or H-plane T-junction effect, large apertures, finite iris or septum thicknesses, and higher-order mode interactions at all step discontinuities are rigorously taken into account. Typical design examples, like rectangular iris coupled T-junctions, narrow-stopband waveguide filters, high return loss E-plane T-junction diplexers, an elliptic function E-plane integrated metal insert filter and a simple ortho-mode transducer demonstrate the efficiency of the method. The theory is verified by measurements. >
TL;DR: Evidence for the interference of Co(II) with DNA repair processes is discussed, regarded as relevant for the risk assessment of human exposure to cobalt in combination with other agents.
01 Sep 1992
TL;DR: In this article, a detailed study of long sediment cores taken during the 1987 ARK IV/3 expedition of R.V. Polarstern in the eastern Arctic Ocean was carried out.
Abstract: A detailed paleomagnetic and calcareous nannofossil study has been carried out on long sediment cores taken during the 1987 ARK IV/3 expedition of R.V. Polarstern in the eastern Arctic Ocean. The Brunhes-Matuyama boundary was not recovered in any of the cores. The magnetostratigraphies reflect the complex behaviour of the geomagnetic field during the Brunhes Chron of predominent normal polarity. Several short excursions and polarity events of the earth's magnetic field are documented in the cores. Their regional correlation was possible on the basis of the characteristic downcore magnetic susceptibility patterns and other physical properties of the sediments. Using the calcareous nannofossil chronostratigraphic framework, seven geomagnetic events of short duration were identified for the last 200 ky.
Sedimentation rates derived from the stratigraphic data are highly variable for the Nansen-Gakkel Ridge area, ranging from a few mm ky-1 to several cm ky-1 . More uniform rates of 2-3 cm ky-1 were obtained for the central Fram Strait, the eastern Yermak Plateau, and the southern Nansen Basin and up to 9 cm ky-1 at the Svalbard continental slope and the northern edge of the Yermak Plateau.
The chronostratigraphic scheme of geomagnetic events and coccolith abundance patterns developed for the Fram Strait area was applied to the sites of the ARK IV/3 expedition further north. It was then possible to relate the occurrence of coccoliths in the sediments to time. Towards the north, coccoliths occur later in the interglacial cycle, reflecting the influx of southerly currents carrying coccolith stocks to the Arctic Ocean.
TL;DR: Glial cells synthesized more amino acids, ie, their TCA cycle was used to a larger extent for biosynthesis than is the case of neurons, where it is preferentially used for the energy metabolism.
TL;DR: The eclogite-facies metasedimentary rocks in the Munchberg gneiss complex (T=630±30° C/P≥17-24 kbar) locally contain CO2−N2-rich fluid inclusions of extremely low molar volumes (32 cm3/mol) in quartz as mentioned in this paper.
Abstract: The eclogite-facies metasedimentary rocks in the Munchberg gneiss complex (T=630±30° C/P≥17–24 kbar) locally contain CO2−N2-rich fluid inclusions of extremely low molar volumes (32 cm3/mol) in quartz. These fluid compositions are mainly found in rocks intercalated with calcsilicate bands. Densities were determined from low-temperature phase transitions like stable or metastable homogenization (L+V→L), partial homogenization (S+L+V→S+L) and the transition S+L→L (L = liquid, V = vapour, S = solid). The high fluid densities are in agreement with eclogite-facies pressure and temperature and subsequent amphibolite facies. CO2−N2 inclusions were not observed in adjacent eclogites nor in non-calcareous metasediments. These rock types contain predominantly H2O-rich inclusions correlating with amphibolite-facies conditions. The variation of fluid composition with lithological differences indicates local fluid gradients and speaks against a pervasive fluid flow during eclogite-facies metamorphism.
TL;DR: In this paper, the soil fauna of eco-farmed and conventionally farmed fields and grasslands was investigated in various regions of Austria and the results obtained from the evaluation of a total of 13 paired sites are reviewed in this contribution.
TL;DR: Results indicate that radiation-induced DNA fragmentation can be prevented by adding the protein kinase C inhibitor H-7 or staurosporine to the thymocytes during incubation time, and suggest that the role of protein Kinase C plays an important role in this process.
Abstract: The role of protein kinase C in radiation-induced death of thymocytes was studied. For this purpose murine thymocytes were irradiated and incubated for 6 h at 37°C and afterwards the fraction of fragmented DNA was measured. Results indicate that radiation-induced DNA fragmentation can be prevented by adding the protein kinase C inhibitor H-7 or staurosporine to the thymocytes during incubation time. Incubation of irradiated cells with HA-1004, an inhibitor of cAMP-dependent protein kinase, with a minor effect on protein kinase C did not affect the DNA fragmentation induced by irradiation. Incubation of cells with phorboldibutyrate gave a dose-dependent induction of DNA fragmentation. This effect can be inhibited by staurosporine. These results suggest that radiation-induced DNA fragmentation is an active cellular process in which protein kinase C plays an important role.
TL;DR: The stable carbon and oxygen isotopic compositions of the massive coralPorites lobata collected from the Gulf of Eilat, Red Sea, in May 1987 were measured along the vertical growth axis and indicate that the high-density bands are enriched in18O and deposited during the season of lowest water temperature (winter).
Abstract: The stable carbon and oxygen isotopic compositions of the massive coralPorites lobata collected from the Gulf of Eilat, Red Sea, in May 1987 were measured along the vertical growth axis. The isotopic compositions show annual periodicity. The variations along the isotopic profile, compared with the X-radiography, indicate that the high-density bands are enriched in18O and deposited during the season of lowest water temperature (winter). In contrast, the low-density bands are depleted in18O and deposited during the warmest seawater temperatures (summer). The stable carbon and the oxygen isotopic ratios are negatively correlated with a shift in phase. During the season of higher water temperatures and light intensity values (summer), the skeleton is depleted in18O and enriched in13C and vice versa for the winter time. The shift between the carbon and the oxygen isotopic curves reflects the shift between the seasonal light intensities and seasonal temperature variations in the shallow water. The oxygen isotope ratio was used to detect the seasonal variations in seawater temperatures. The coral aragonitic skeleton is depleted in18O compared to apparent equilibrium with ambient seawater. The disequilibria range from (ca.) -3.10‰ to -3.50‰ with an average value of 3.40‰. The isotope fractionation behavior during skeleton precipitation is discussed in light of the environmental variables.
TL;DR: Isotopic studies on sediment trap samples from the King George Basin revealed that benthic macroalgae contributed strongly to the total organic carbon pool of the deeper basin waters during austral spring and summer.
Abstract: Stable carbon isotope composition of macroalgae collected at King George Island (Antarctica) ranged from about -8‰ to -34‰. We hypothesize that the δ13C values are related to the depth distribution: species inhabiting greater depth had much lower values (around-30‰) compared to species from shallower waters (around -17‰). Isotopic studies on sediment trap samples from the King George Basin (2,000 m deep) revealed that benthic macroalgae contributed strongly to the total organic carbon pool of the deeper basin waters during austral spring and summer. Fragments of brown macroalgae (Desmarestiales) were detected in microscopical analyses of semi-thin sections of sediment samples from the Bransfield Strait. Possible mechanisms regarding the erosion of benthic macroalgae and their transport to the deeper waters and to the sediment are summarized.
01 Nov 1992
TL;DR: In this paper, the relative proportions of trace metals in the dissolved and solid phases were interpreted in terms of conditional distribution coefficients, whose magnitude depends critically on which fraction of particulate metal is selected (i.e. available or total).
Abstract: Trace metals in the dissolved phase, and in operationally defined available and total particulate associations, have been determined along an axial transect of the Weser Estuary, together with measurements of salinity, temperature, pH, dissolved oxygen, suspended particulate matter (SPM), chlorophyll a, free and attached bacteria, particulate carbon and particle specific surface area.
Throughout the estuary the dissolved metals exhibited non-conservative behaviour due to sorption reactions with particle surfaces and sediment-water exchange processes. This reactivity was enhanced at the fresh water-brackish water interface where changes in the master variables were most pronounced. The influence of sorptive processes on total particulate metal distributions was not evident and major compositional variability was ascribed to physical mixing of different particle populations.
The relative proportions of trace metals in the dissolved and solid phases were interpreted in terms of conditional distribution coefficients, KDs, whose magnitude depends critically on which fraction of particulate metal is selected (i.e. available or total). The KDs for Fe and Mn increased with increased SPM concentration, whereas those for Cu, Ni, Zn and possibly Pb decreased with SPM; such observations are related to whether particle-water exchange processes at any locality in the system are far from or at (quasi-) equilibrium, and to differences in the sorptive characteristics of suspended particle populations.
These results have implications for the behaviour of trace metals in the Weser Estuary and are also discussed in the context of the value of the KD concept for quantitative modelling of dissolved trace metal distribution in estuaries.
TL;DR: The hypothesis that pathological gambling can lead to delinquent behavior is supported and a multiple regression within the framework of path analysis was computed to explore causal links between pathological gambling and delinquency.
Abstract: In a comprehensive research project on gamblers in self-help groups in West Germany one object of investigation was the question of whether or not pathological gambling has a criminogenic effect. 54.5% of the 437 members of Gamblers Anonymous interviewed stated that they had committed illegal actions in order to obtain money for gambling. Comparisons of this sub-group with those interviewees who did not admit having committed criminal offences show distinct differences: Those who admitted illegal action were more excessive in their gambling behavior and experienced a higher degree of subjective satisfaction through gambling. They also showed a more pronounced problem behavior and more psychosocial problems because of gambling. A multiple regression within the framework of path analysis was computed in order to explore causal links between pathological gambling and delinquency. The results support the hypothesis that pathological gambling can lead to delinquent behavior. Forensic implications are discussed.
TL;DR: In this article, large liquid bridges of constant volume (initial length L0 = 50 mm and radius R0 = 25 mm) placed between two equal plane circular disks have been stretched in Plateau simulations (neutral buoyancy tank) by moving one disk with a constant velocity.
Abstract: Large liquid bridges of constant volume (initial length L0 = 50 mm and radius R0 = 25 mm) placed between two equal plane circular disks have been stretched in Plateau simulations (neutral buoyancy tank) by moving one disk with a constant velocity. While interfacial tension forces minimize the surface area, leading to contraction and break-up of the liquid bridge, inertia and friction forces act against it. Increasing inertia, friction and flow resistance, due to elongational viscosity, tend to stabilize the liquid bridge and thus form more cylindrical bridges. It has been found that none of the forces, especially inertia and interfacial tension forces, can be neglected even at elongation rates as low as 0.1 s−1.
TL;DR: In this paper, an analysis of the optical spectra indicates that dye monomers are encapsulated in the cages of SAPO-34 and that monomers as well as dimers are hosted simultaneously in the parallel, cylindrical unidimensional channels of AIPO4-5 and SAPO5.
01 Jan 1992
TL;DR: In this paper, a random dynamical system of affine mappings of d whose linear part is hyperbolic has been shown to have a unique invariant measure using multiplicative ergodic theory, which generalizes and sheds new light on results of Barnsley and Elton on iterated function systems.
Abstract: Given a random dynamical system of affine mappings of ℝ d whose linear part is hyperbolic, we prove that it has a unique invariant measure. The proof uses multiplicative ergodic theory. The result generalizes and sheds new light on results of Barnsley and Elton on Iterated Function Systems.
TL;DR: In amphibians, there is a close correspondence between the degree of secondary simplification on the one hand and genome size (DNA content) and cell size on the other, and it is hypothesize that this process is the major cause of the observedsecondary simplification.
Abstract: The evolutionary success of extant amphibians is accompanied by secondary simplification of sense organs and of the nervous system. Strong morphological reduction is found in the lateral line system and in the auditory and visual systems. Canal neuromasts are absent; additional loss of epidermal neuromasts and ampullary organs generally corresponds to terrestrial life. Reduction of the auditory system of some anurans and of many salamanders and caecilians affects middle and inner ear structures as well as central auditory structures. The visual system of caecilians and salamanders is strongly reduced with respect to the number and morphology of retinal ganglion cells and the morphological differentiation of central visual areas, particularly the tectum opticum. The extremes of secondary simplification are found in the salamanders of the plethodontid tribe Bolitoglossini. At the same time, these salamanders are one of the most successful groups of amphibians, and they possess the most derived feeding syste...
TL;DR: Analytical data on the occurrence of the polyhydric alcohol mannitol in the red algal genus Caloglossa (Ceramiales, Delesseriaceae) were obtained by 13 C NMR and HPLC techniques and the possible function ofMannitol as a compatible solute in Calog Lossa is discussed.