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  • 2000-2004  (42)
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  • 1
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    Magnetic resonance imaging of sea-ice pore fluids: methods and thermal evolution of pore microstructure (2000)
    In:  EPIC3Cold Regions Science and Technology, 31, pp. 207-225
    Details
    Publikationsdatum: 2019-07-16
    Beschreibung: Microstructure and thermal evolution of sea-ice brine inclusions were investigated with magnetic resonance imaging (MRI) techniques. Ice samples were kept at temperatures between -2°C and -25°C during 1H imaging in a 4.7-T magnet at 200 MHz. Measurements were completed in a 20-cm diameter cylindrical probe and actively shielded gradient coils (max. 50 mT m-1, pixel dimensions 〉0.2 mm, slice thicknesses 〉1 mm), and for higher resolution in a mini-imaging unit with a 9-cm diameter probe with gradient coils of 200 mT m-1 (pixel dimensions 〈0.1 mm, slicethickness 〈0.4 mm). Absorption of radio-frequency (RF) signals in the dielectrically lossy brine resulted in degraded signals and was alleviated by use of a contrast agent (decane). MRI data and sea-ice thin section images agree very well (〈5% deviation for pore microstructural parameters). Analysis of ice grown under different current speeds indicates that pores are smaller and pore number densities larger at higher current speeds. The thermal evolution of fluid inclusions was studied on cold first-year ice samples, maintained at close to in-situ temperatures prior to experiments. Warming from -21°C to -10°C to -6°C is associated with a distinct increase in pore size (from 1.5 to 1.7 to 2.6 mm forthe upper 10-percentile in the vertical) and elongation (4.0 to 4.2 to 6.2 for ratio of major to minor pore axes in the vertical) and a decrease in number densities (0.75 to 0.62 to 0.58 mm-3 in the vertical). Aspect ratios increased from 4:2:1 to 6:2:1 (upper 10-percentile), indicating expansion and merging of pores in the vertical, possibly promoted by microscopic residual brine inclusions.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 2
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    Simultaneous observations of haemolymph flow and ventilation in marine spider crabs at different temperatures: a flow weighted MRI study (2001)
    In:  EPIC3Magnetic resonance imaging, 19, pp. 1113-1124
    Details
    Publikationsdatum: 2019-07-16
    Beschreibung: In vivo magnetic resonance imaging (MRI) and angiography were applied to the marine spider crab Maja squinado for a study of temperature effects and thermal tolerance. Ventilation and haemolymph circulation were investigated during progressive cooling from 12°C to 2°C. The anatomical resolution of MR images from Maja squinado obtained with a standard spin echo sequence were suitable to resolve the structures of various internal organs. The heart of the animal could be depicted without movement artifacts. The use of a flow compensated gradient echo sequence allowed simultaneous observations of ventilation, reflected by water flow through the gill chambers as well as of haemolymph flow. Simultaneous investigation of various arteries was possible by use of flow weighted MRI. In addition to those accessible by standard invasive flow sensitive doppler sensors, flow changes in gill, leg arteries and the venous return could be observed. Both ventilation and haemolymph flow decreased during progressive cooling and changes in haemolymph flow varied between arteries. Haemolymph flow through the Arteria sternalis, some gill and leg arteries was maintained at low temperatures indicating a reduced thermal sensitivity of flow in selected vessels. In support of previous invasive studies of haemolymph flow as well as heart and ventilation rates, the results demonstrate that the operation of gills and the maintenance of locomotor activity are critical for cold tolerance. A shift in haemolymph flow between arteries likely occurs to ensure the functioning of locomotion and ventilation in the cold.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 3
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    In vivo MR spectroscopy and MR imaging on non-anaesthetized marine fish: techniques and first results (2002)
    In:  EPIC3Magnetic resonance imaging, 20, pp. 165-172, ISSN: 0730-725X
    Details
    Publikationsdatum: 2019-07-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
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  • 4
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    Resistance to freshwater exposure in White Sea Littorina spp II. Acid-base regulation (2000)
    In:  EPIC3Journal of comparative physiology b-biochemical systemic and environmental physiology, 170, pp. 105-115
    Details
    Publikationsdatum: 2019-07-16
    Beschreibung: Parameters of acid-base and energy status were studied in three White Sea Littorina spp. (L. littorea, L. saxatilis and L. obtusata) during prolonged anaerobiosis in freshwater by in vivo 31P-NMR spectroscopy. Intracellular pH (pHi) decreased significantly, especially during the early period. Later on the pHi decrease slowed down considerably suggesting a good ability of pHi regulation in all three studied species. There was a trend for pHi to fall most rapidly in the least freshwater resistant species L. obtusata as compared to the most resistant L. littorea. Non-bicarbonate, non-phosphate buffer values estimated by the homogenate technique were similar in the three studied species (28 - 37 mmol pH-1 kg-1 wet weight) and did not change during freshwater exposure. The CaCO3 buffer value of the foot tissues was considerably higher (171-218 mmol pH-1 kg-1 wet weight) and decreased significantly during freshwater exposure. The contribution of the multiple tissue buffering systems to pHi regulation in Littorina spp. shifts between different stages of freshwater exposure. Initially the non-bicarbonate, non-phosphate tissue buffering system seems to be of major importance for metabolic proton buffering at pHi between 7.5 and 7.0. During later stages of anaerobiosis and at lower pHi, the CaCO3 buffer is involved in proton buffering. Decrease in the CaCO3 buffer value during freshwater exposure was in quantitative agreement with the amount of metabolic protons buffered thus suggesting that CaCO3 tissue stores may serve as a major buffering system during prolonged anaerobiosis in Littorina spp.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 5
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    A contribution of acid-base regulation to metabolic depression in marine ectotherms (2000)
    In:  EPIC3Life in the cold / Eleventh International Hibernation Symposium. Gerhard Heldmaier ... (eds.); Berlin [u.a.] : Springer, pp. 443-458, ISBN: 3-540-67410-1
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    Publikationsdatum: 2019-07-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Inbook , peerRev
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  • 6
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    The cost of being a caring mother: the ignored factor in the reproduction of marine invertebrates. (2000)
    In:  EPIC3Ecology Letters, 3, pp. 487-494
    Details
    Publikationsdatum: 2019-07-16
    Beschreibung: Investment in reproduction ranges from gamete production to active parental care, and marine invertebrates span this range. However, the cost of parental care has not yet been systematically quantified, nor incorporated into life history studies of marine invertebrates, in contrast to most other animal taxa. Since oxygen is a limiting factor in egg masses of marine invertebrates, we studied patterns of oxygen partial pressure over time in embryo masses of Brachyuran crabs, and correlated these results with the cost of providing oxygen to the embryos. We found that: (1) oxygen is limiting in the embryo masses, (2) female crabs show an active brooding behaviour that we think helps to provide oxygen to the embryo mass, and (3) there is a substantial parental investment associated with brooding behaviours. Oxygen limitation and parental investment seem to be associated in many taxa of marine invertebrates, and we suggest that oxygen provision to the embryos may be a critical factor determining parental investment in this group.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 7
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    Brain metabolism parameters in torpor as measured with MRI (2002)
    In:  EPIC3Brain, behavior and torpor related damage in ground squirrels. Informal workshop on European ground squirrel hibernation research. Animal behavior. University of Groningen, Haren, The Netherlands.04-23.04.02., 22
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    Publikationsdatum: 2019-07-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
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  • 8
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    Hypoxia induced changes in the brain of hypoxic tolerant cuttlefish Sepia officinalis (2004)
    In:  EPIC3Proceedings of the International Society of Magnetic Resonance in Medicine, 12th Scientific meeting and exhibition, Kyoto, JapanMay, 15, 1455 p.
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    Publikationsdatum: 2019-07-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
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  • 9
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    23Na NMR spectroscopy and Diffusion weighted MRI studies on sea-ice at different temperatures. The influence of environmental effects on ice growth (2003)
    In:  EPIC3Proceedings of the International Society of Magnetic Resonance in Medicine. 11th scientific meeting and exhibition, Toronto, CanadaJuly, 10, 883 p.
    Details
    Publikationsdatum: 2019-07-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
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  • 10
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    In vivo 31P-NMR studies of speeding fish: Online monitoring of muscular energetics in Atlantic cod (Gadus morhua) (2002)
    In:  EPIC3Proceedings of the International Society of Magnetic Resonance in Medicine. 10th scientific meeting and exhibition, Honolulu, USAMay, 18, 1878 p.
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    Publikationsdatum: 2019-07-16
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Conference , notRev
    Format: application/pdf
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