Showing papers by "University of Bremen published in 1993"

Gradient selection in inverse heteronuclear correlation spectroscopy

Abstract: After a brief theoretical description, new gradient-selected, proton-detected heteronuclear correlation sequences are introduced. The gs-HMBC and gs-Relayed-HMQC are closely related to the original gs-HMQC proposed by Hurd and John. A new approach to obtain pure absorption line shapes in gradient selected spectroscopy is used to measure phase-sensitive gs-HMQC spectra, to carry out multiplicity editing in HSQC spectra and to distinguish direct and long-range correlations in HMQC/HSQC–TOCSY spectra.

Multinuclear NMR studies on the energy metabolism of glial and neuronal cells.

Abstract: In this multinuclear NMR study myo-inositol is identified as a glia-specific marker for in vivo NMR studies. The unusually high inositol concentration may participate in the osmoregulatory system in astrocytes. Primary astrocytes also synthesize and export high amounts of hypotaurine, an intermediate of taurine synthesis. Taurine--another osmolyte--is synthesized from cysteine by astrocytes but not by primary neurons. Taurine as well as hypotaurine is accumulated by neurons from the extracellular medium. 13C NMR labelling results with 2-13C pyruvate indicate a considerable contribution of the anaplerotic pathway in primary neurons from rat. The activity is only half of the activity in primary astrocytes. The ratio of pyruvate carboxylase/malic enzyme activity versus pyruvate dehydrogenase activity reflects the degree of maturation. The 13C isotopomer ratio of glutamate and glutamine is different for pure astrocyte cultures. Therefore, the different isotopomer ratios of glutamate to glutamine obtained from intact brain studies alone do not prove TCA cycle compartimentation in the brain. Finally, the PCr/ATP ratio in primary astrocytes is 3 times higher than in primary neurons. This has to be considered in case of recovery from ischemic insults.

An automated leaching method for the determination of opal in sediments and particulate matter

Abstract: An automated leaching method for the analysis of biogenic silica (opal) in sediments and particulate matter is described. The opaline material is extracted with 1 M NaOH at 85°C in a stainless steel vessel under constant stirring, and the increase in dissolved silica is continuously monitored. For this purpose, a minor portion of the leaching solution is cycled to an autoanalyzer and analyzed for dissolved silicon by molybdate-blue spectrophotometry. The resulting absorbance versus time plot is then evaluated according to the extrapolation procedure of DeMaster (1981). The method has been tested on sponge spicules, radiolarian tests. Recent and Pliocene diatomaceous ooze samples, clay minerals and quartz, artificial sediment mixtures, and on various plankton, sediment trap and sediment samples. The results show that the relevant forms of biogenic opal in Quaternary sediments are quantitatively recovered. The time required for an analysis is dependent on the sample type, ranging from 10 to 20 min for plankton and sediment trap material and up to 40–60 min for Quaternary sediments. The silica co-extracted from silicate minerals is largely compensated for by the applied extrapolation technique. The remaining degree of uncertainty is on the order of 0.4 wt% SiO2 or less, depending on the clay mineral composition and content.

Reconstructing sea surface temperature and salinity using δ 18 O and alkenone records

Abstract: THE oxygen isotope (δ18O) composition of foraminiferal tests from deep-sea sediments is widely used as a palaeoclimate proxy, but it includes contributions from sea surface temperature, global ice volume and local salinity, which are difficult to separate. Recently a new technique for deriving palaeotemperatures has been developed which is based on the abundance ratios of unsaturated alkenones in phytoplankton algae1,2. Here we use a combination of oxygen isotope and alkenone records in a deep-sea core from the juncture of the Arabian Sea and the Bay of Bengal to extract the salinity signal from the former record. Variations in salinity are related to the balance between evaporation and precipitation3, and are thus a sensitive indicator of climate change. Our 170-kyr salinity record enables us to reconstruct changes in the Indian monsoon over this period, considerably extending earlier studies (which reached back to 18 kyr ago)4–8. Like these previous studies, we find that large variations in the monsoon occurred during the transition from the last glacial period to the present interglacial, but our results also provide a view of the monsoon throughout the last glacial and demonstrate the potential of this approach for reconstructing palaeosalinity.

Seasonal patterns of vertical particle flux in equatorial and coastal upwelling areas of the eastern Atlantic

Abstract: Eight time-series sediment traps were deployed on moored arrays off Mauritania (Cap Blanc), in the northern and southern Guinea Basin, and off Namibia (Walvis Ridge). The highest total fluxes (66.8 and 59.1 g m−2y−1), as well as carbonate (28.7 and 32.9 g m−2y−1) and biogenic opal fluxes (5.4 and 8.2 g m−2y−1) were recorded at the two coastal sites, off Mauritania and off Namibia, respectively. Intermediate rates were recorded north and low rates south of the equator. Surprisingly, carbonate-producing organisms dominated total fluxes at all sites, whereas biogenic opal was only a minor contributor. The most distinct flux maxima were in July–August both at the Cap Blanc and the northern Guinea Basin site (2°N). Carbonate fluxes also peaked during that period. In contrast, highest opal fluxes were measured there in late winter/early spring. At the Cap Blanc site, high lithogenic fluxes correlate well with fluxes of biogenic components. At both equatorial sites, prominent flux maxima were observed in boreal spring, attributed to the southermost penetration of the ITCZ. These fluxes were characterized by a relatively high lithogenic contribution. South of the equator (2°S), sedimentation decreased rapidly to almost zero after May when the ITCZ started to migrate northwards. Seasonality was most expressed at the Walvis Ridge site, where a distinct bi-modal flux pattern occurred (June–July and October–November). In austral spring, elevated fluxes were determined for a relatively long period when wind-driven upwelling is strongest and the Namibia upwelling cell shows the greatest extension to the west approaching the trap position. Contribution of lithogenic material to total fluxes was very low at this site.

Hydrodynamic instabilities in cylindrical thermocapillary liquid bridges

Abstract: The hydrodynamic stability of steady axisymmetric thermocapillary flow in a cylindrical liquid bridge is investigated by linear stability theory. The basic state and the three-dimensional disturbance equations are solved by various spectral methods for aspect ratios close to unity. The critical modes have azimuthal wavenumber one and the most dangerous disturbance is either a pure hydrodynamic steady mode or an oscillatory hydrothermal wave, depending on the Prandtl number. The influence of heat transfer through the free surface, additional buoyancy forces, and variations of the aspect ratio on the stability boundaries and the neutral mode are discussed.

Application of scattering chaos to particle transport in a hydrodynamical flow.

Abstract: The dynamics of a passive particle in a hydrodynamical flow behind a cylinder is investigated. The velocity field has been determined both by a numerical simulation of the Navier–Stokes flow and by an analytically defined model flow. To analyze the Lagrangian dynamics, we apply methods coming from chaotic scattering: periodic orbits, time delay function, decay statistics. The asymptotic delay time statistics are dominated by the influence of the boundary conditions on the wall and exhibit algebraic decay. The short time behavior is exponential and represents hyperbolic effects.

Paedomorphosis and simplification in the nervous system of salamanders.

Abstract: Comparative neuroanatomists since Herrick [1914] have been aware of the paradox that the brain of amphibians, especially salamanders, is less complex than one would expect based on their phylogenetic position among the Tetrapoda. Many features of the brain are less differentiated in salamanders than in tetrapod outgroups, including chondrichthyans and bony fishes, and for some brain characters, the salamander brain is even more simple than that of the agnathans. Here, we perform a cladistic analysis on 23 characters of four sensory systems (visual, auditory, lateral line and olfactory) and the brain. Our taxa include myxinoids, lampreys, chondrichthyans, actinopterygians, Latimeria, Neoceratodus and the lepidosirenid lungfishes, amniotes, frogs, caecilians, salamanders and bolitoglossine salamanders. Of the 23 characters we examined, 19 are most parsimoniously interpreted as secondarily simplified in salamanders from a more complex ancestral state, two characters are equally parsimonious under both hypotheses, one character (well developed ipsilateral retinotectal projections) is more complex in bolitoglossine salamanders than in vertebrates generally, and only one character (migration of neurons in the medial pallium) is most parsimoniously interpreted as retention of the plesiomorphically simple condition. Secondary simplification of the salamander brain appears to result from paedomorphosis, or retention of juvenile or embryonic morphology into adulthood. Paedomorphosis is correlated with an increase in genome size, which in turn is positively correlated with cell size, but negatively correlated with cell proliferation and differentiation rates. Available data suggest that, although increasing genome size and paedomorphosis tend to compromise the function of the salamander brain, compensating mechanisms have evolved that may restore or even enhance brain function.

A study of the UV—visible absorption spectrum of molecular chlorine

Abstract: The UV—visible absorption spectrum of molecular chlorine at 298 K was investigated in the wavelength range 200–550 nm with a spectral resolution of 0.2 nm. Except for minor discrepancies, the absorption cross-sections are in agreement with those found in the literature. In the region 250⩽λ⩽-550 nm, the Cl 2 spectrum can be adequately described by a semi-empirical function of the wavelength A (in vacuum) and temperature T where tanh=tanh( hc x559.751 cm −1 /2 kT ). The absorption of solar radiation by the weak continuum around λ max =406.5 nm contributes 9% or more of the photodissociation of molecular chlorine in the atmosphere, but the banded Cl 2 features (λ ⩾ 479 nm) are of negligible atmospheric significance.

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

Abstract: The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. IK values were between 18 and 53 μmol m−2 s−1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher IK values between 70 and 74 μmol m−2 s−1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m−2 s−1. Values of α were high: between 0.4 and 1.1 μmol O2 g−1 FW h−1 (μmol m−2 s−1)−1 in the brown and red algae and between 2.1 and 4.9 μmol O2 g−1 FW h−1 (μmol m−2 s−1)−1 in the green algal species. At 0°C Pmax values of the brown and red algae ranged from 6.8 to 19.1 μmol O2 g−1 FW h−1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q10 values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.

The locomotion, shape and pseudopodial dynamics of unstimulated Dictyostelium cells are not random

Abstract: The dynamic periphery of unstimulated, preaggregation, hunger-stage Dictyostelium discoideum amoebae was investigated by time-lapse videomicroscopy and digital image processing. Circular maps (i.e. of each of 360 radii around the cell transformed upon Cartesian coordinates) were constructed around the centroid of individual cell images and analysed in time series. This novel technique generated spatiotemporal structures of various degrees of order in the maps, which resemble classical wave interference patterns. The patterns thus demonstrate that cell movement is not random and that cells are intrinsically vibrating bodies, transited by self-organized, superpositioned, harmonic modes of rotating oscillatory waves (ROWS). These waves appear to depend upon spatiotemporal oscillations in the physicochemical reactions associated with actin polymerization, and they govern pseudopodial movements, cell shape and locomotion generally. ROWS in this case are unrelated to the cyclic-AMP-regulated oscillations, which characterize later, aggregative populations of Dictyostelium. However, the exposure of aggregation-stage cells to a pulse of the chemoattractant cyclic-AMP induces a characteristic sequence of changes in the global cellular concentration and spatiotemporal distribution of fibrillar (F-)actin. This reaction begins with what appears to be a phase resetting of ROWS and it may, therefore, underlie the cellular perception of and response to chemotactic signals. We also develop here an analytical mathematical description of ROWS, and use it to simulate cell movements accurately.

Modernisation, Culture and Part-Time Employment: The Example of Finland and West Germany:

Abstract: The paper discusses how differences between European countries in the rate of part-time employment among women can be explained. In contrast to the usual explanations, the paper emphasises the importance of cultural specificities in the respective countries with respect to the gender contract on the main family and integration model to which individuals as well as institutions refer in their orientations and behaviour. The differences are explained socio-historically by the specificities in the process of modernisation when transforming from an agrarian to an industrial society, showing why in each country a different family and integration model developed. Questions as to the form in which industrialisation occurred, which societal class dominated the transformation process culturally, and whether there was a cultural continuity or discontinuity, are important for cross-national differences in the family model and for the labour market behaviour of women today.

Artifacts in the Determination of Trace Metal Binding Forms in Anoxic Sediments by Sequential Extraction

Abstract: The binding forms of Co, Cd, Cu, Pb, and Zn in an anoxic, sulfide-bearing sediment were investigated by performing both thermodynamic equilibrium calculations and sequential extractions. Care was taken to maintain oxygen-free conditions during the whole experiment. The calculations suggested that trace metals were bound to sulfidic minerals. Sequential extraction results, however, showed increased importance of exchangeable and reducible fractions in the order Cu < Cd < Pb < Zn < Co. Thermodynamic equilibrium calculations of the chemical reactions during extraction showed that Cd, Co, Pb, and Zn sulfides are to a significant extent soluble in the acetate-exchangeable (step 1 + 2) and oxalate-reducible (step 3) fractions. Neglecting the dissolution of sulfide minerals would lead to a misinterpretation of the experimental results.

Permanent magnet micromotors on silicon substrates

Abstract: Different types of sliding, rolling, or rotating micromotors with rare-earth-based permanent magnet rotors are presented. The magnets move synchronously with rotating or traveling magnetic fields generated by 25- mu m-thick gold current lines on silicon substrates. The magnets are guided in channels or openings in the silicon itself or in additional glass layers. For magnets with a typical dimension of 1 mm, forces and torques of 150 mu N and 100 nNm could be achieved. Maximum velocities of 24 cm/s and a rotation frequency of 2000 r.p.m. have been measured. Magnetic clamping to the bottom confines the rotor to the system and allows a motor operation at any tilt angle. Noncontact magnetic transmission of forces to drive a ferromagnetic fluid has been demonstrated. >

Field theoretical computer-aided design of rectangular and circular iris coupled rectangular or circular waveguide cavity filters

Abstract: The rigorous CAD of a class of rectangular and circular waveguide cavity filters which are coupled by rectangular and/or circular irises is described. The design theory is based on the full-wave mode-matching method for three key building block elements (asymmetric rectangular double-step, asymmetric rectangular-to-circular and circular-to-circular waveguide junctions) associated with the generalized S-matrix technique for composite structures. The waveguide filters may be arbitrarily composed of the key building block elements and the rectangular or circular waveguide sections between them. Finite iris thicknesses, higher-order mode interactions, and asymmetric structures are rigorously taken into account. The theory is verified by measurements. >

Liposome-delivered Zn(II)-2,3-naphthalocyanines as potential sensitizers for PDT: synthesis, photochemical, pharmacokinetic and phototherapeutic studies.

Abstract: The aim of this investigation is to report the synthesis and fundamental photochemical properties of naphthalocyanines with potential interest for photodynamic therapy (PDT), as well as their pharmacokinetics and phototherapeutic effects in a tumor model. Four zinc naphthalocyanines (ZnNc), unsubstituted ZnNc 1 , tetraacetylamido-substituted ZnNc 2 , tetraamino-substituted ZnNc 3 and tetramethoxy-substituted ZnNc 4 absorbing around 760–770 nm, were synthesized. The dye-sensitized photo-oxidation of 1,3-diphenylisobenzofuran via 1 O 2 was studied in dimethylsulfoxide (DMSO). Quantum yields for this photoreaction are 0.135–0.164 and are relatively independent of the kind of substituent. In addition, the photoinduced electron transfer studied in N, N -dimethylformamide—water in the presence of methylviologen and mercaptoethanol is only slightly influenced by the kind of substituent. The pharmacokinetic properties of ZnNc 1 in hamsters bearing a transplanted rhabdomyosarcoma were studied using dipalmitoylphosphatidylcholine liposomes. Experimental PDT of rhabdomyosarcoma was carried out using liposome-delivered ZnNc 1–4 . The phototherapeutic effect was evaluated by tumor photonecrosis, the mean tumor diameter during the observation period and the percentage of cured animals. The best effect was found after PDT with ZnNc 2 (50% of the treated animals were cured). A slightly lower effect was observed after application of ZnNc 4 (40% cured animals). No effect at all was noted after PDT with ZnNc 3 and a very low efficiency was found after treatment with ZnNc 1 as photosensitizer. Obviously, the photodynamic effect depends on the biological characteristics as well as on the nature of the substituents.

Cellular damage by ferric nitrilotriacetate and ferric citrate in V79 cells: interrelationship between lipid peroxidation, DNA strand breaks and sister chromatid exchanges.

Abstract: Ferric nitrilotriacetate (Fe-NTA) and ferric citrate (Fe-citrate) were used to study the cellular damage mediated by iron overload with respect to cytotoxicity, lipid peroxidation, DNA strand breaks and sister chromatid exchanges (SCE) At non-toxic concentrations, Fe-NTA induced lipid peroxidation, DNA strand breaks and SCE in a dose- and time-dependent manner Comparing the time courses of the different events, the increase in lipid peroxidation seems to be associated with the generation of DNA strand breaks, since both types of cellular damage were observed after 1-3 h of incubation In contrast, the induction of SCE was low after 24 h and increased after 48 and 72 h treatment, indicating the requirement of other types of DNA damage Fe-citrate was inactive in the induction of lipid peroxidation and SCE, and no significant number of DNA strand breaks were generated, as determined by the alkaline unwinding method Our results suggest that the induction of lipid peroxidation and DNA strand breaks by iron overload depend on special features of the iron complex applied, while the chromosomal and genetic effects require site specific DNA damage dependent on intracellular iron metabolism It is concluded that iron overload is able to induce genetic damage in intact cells provided that iron is present in a bioavailable form

A limit set trichotomy for self-mappings of normal cones in banach spaces

Abstract: (Here, we use the notation x > y and x 2 y to mean, respectively, x y E k” and x y E K”.) This result extends an earlier theorem of Smith [2] concerning “discrete dynamics of monotone, concave maps”; some interesting applications to differential equations can be found in [l, 21. Another extension of Smith’s theorem has been given by TakaE in [3]. In this paper we shall extend the above trichotomy in two directions. First, we shall allow general normal cones K with nonempty interior in a Banach space. Second, we shall allow a class of maps which is considerably more general than classes allowed in earlier results, even for K, the positive orthant in I?“. The key observation which we shall exploit centers about a metric p, called the part metric or Thompson’s metric (see [l, 4-61 and the references given there; and Section 2 below) which is defined on the interior I? of a cone. The proper class of maps to study seems to be those maps T: I? + k such that T”‘, the mth iterate of T, satisfies

Multistable Visual Perception Induces a Slow Positive EEG Wave

Abstract: Seven subjects observed a multistable pattern (stroboscopic alternative motion: SAM), and were instructed to press the button immediately after perceptual switching with the aim of detecting some neu-rophysiological parameters of EEG activity. Our results indicate that the EEG changes observed during multistable perception are similar to the family of event related potentials which we called perceptual switching related positivity. Furthermore, the frequency component of this potential has a similarity to the frequency content of stimulus locked P300.

Inflectional rules in children’s grammars: evidence from German participles

Abstract: In recent studies on the acquisition of inflectional morphology in English much debate has centred around the question whether children’s overregularization errors, such as goed instead of went result from a morphological rule or from a connectionist network such as the one suggested by Rumelhart and McClelland (1986). Pinker and Prince (1992) and Marcus et al. (1992) have argued that the -ed affix has the status of a symbolic rule in the children’s grammars which is qualitatively distinct from an associative memory for irregulars. However, researchers such as Marchman and Bates (1991) and MacWhinney and Leinbach (1992) have disputed the existence of such symbolic rules and suggested that overregularizations are effects of associative networks: In English, the -ed affix has much higher type frequencies than the irregular past tense forms, and is therefore preferred in children’s inflectional errors.