| 1. |
- Berthelsen, A., et al.
(författare)
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Recording marine airgun shots at offsets between 300 and 700 km
- 1991
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 18:4, s. 645-648
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Tidskriftsartikel (refereegranskat)abstract
- This paper demonstrates that - under favorable conditions - by using multichannel recording and subsequent stacking of adjacent records marine airgun shots have been detected at offset distances up to 700 km, the maximum offset at which the authors attempted to record data.^Besides a powerful airgun array, a low noise environment at the recording site and the elimination of static shifts are the prerequisites to obtain refracted and reflected arrivals from the crust and upper mantle at such large offsets.^Primary arrivals detected at offsets between 400 and 700 km image the upper mantle from 70 to about 120 km depth.^Stacking of neighboring shots and/or receivers successfully increases the signal-to-noise ratio, if the traces have been corrected for offset differences, which requires knowledge of the apparent phase velocities.^The data presented here were collected in autumn 1989 during the BABEL Project on the Baltic Shield.
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| 2. |
- Hobbs, R. W., et al.
(författare)
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Integrated seismic studies of the Baltic shield using data in the Gulf of Bothnia region
- 1993
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 112:3, s. 305-324
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Tidskriftsartikel (refereegranskat)abstract
- In the autumn of 1989 a co-operative experiment involving 12 research institutions in northwestern Europe collected 2268 km of deep seismic reflection profiles in the Gulf of Bothnia and the Baltic Sea. the 121 litre airgun array used for this profiling was also recorded by 62 muiticomponent land stations to provide coincident refraction surveys, fan-spreads, and 3-D seismic coverage of much of the Gulf of Bothnia. We thus have potentially both high-resolution impedance contrast images as well as more regional 3-D velocity models in both P- and S-waves. In the Bothnian Bay a south-dipping, non-reflective zone coincides with the conductive Archaean-Proterozoic boundary onshore in Finland. Between the Bothnian Bay and Bothnian Sea observed reflectivity geometries and velocity models at Moho depths suggest structures inherited from a 1.9Ga subduction zone; the upper crust here appears to have anomalously low velocity. Within the Bothnian Sea, reflectivity varies considerably beneath the metasedimentary/granitoid rocks of the Central Svecofennian Province (CSP) and the surrounding metavolcanic-arc rocks. Numerous dipping reflectors appear throughout the metavolcanic crust, whereas the CSP has little reflectivity. Wide-angle reflections indicate that the metasedimentary crust of the Bothnian Basin is 10 km thicker than the neighbouring Svecofennian subprovinces. Near the Åland archipelago Rapakivi granite plutons exhibit bright reflections, a contrast to the usual non-reflective plutons elsewhere in western Europe. Additional dipping reflections deep in the crust of this area may support models of rifting and crustal thinning during emplacement of the 1.70-1.54 Ga Rapakivi granites. Coeval gabbroic/anorthositic magmatism may explain the high reflectivity and high velocity of these plutons. the c. 1.25 Ga mafic sills and feeder dykes of the Central Scandinavian Dolerite Group also produce clear reflections on both near- and far-offset seismic sections. Continued modelling will produce better velocity models of the crust and better constrained contour maps of crustal thickness in this part of the Baltic shield.
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| 3. |
- Öhlander, Björn, et al.
(författare)
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Delineation and character of the Archaean-Proterozoic boundary in northern Sweden
- 1993
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Ingår i: Precambrian Research. - 0301-9268 .- 1872-7433. ; 64:1-4, s. 67-84
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Tidskriftsartikel (refereegranskat)abstract
- Before the deposition of a Proterozoic cover and the repeated Proterozoic reworking of the older rocks, the presently exposed Archaean areas in northern Sweden formed part of a coherent craton. In the present study, we have used Sm---Nd isotopic analyses of Proterozoic granitoids and metavolcanics to delineate the Archaean palaeoboundary. In a regional context, the transition from strongly negative εNd(t) values in the northeast to positive values in the southwest is distinct, and approximately defines the border of the old craton. The Archaean palaeoboundary extends in a WNW direction, and is subparallel to the longitudinal axis of the Skellefte sulphide ore district but it is situated ≈ 100 km farther to the north. The ≈ 1.9 Ga old granitoids on the two sides of the palaeoboundary were all formed in compressional environments, but those situated to the north have higher contents of LILE and LREE at similar contents of Si. This indicates that they were generated in an area with thicker crust and supports the location of the Archaean-Proterozoic palaeoboundary. There is no simple correlation between the Archaean palaeoboundary, as defined by the isotopic results, and any of the major fracture systems as interpreted from regional geophysical measurements. Reflection seismic work indicates that juvenile volcanic-arc terrains to the south have been thrust onto the Archaean craton. Possible thrust faults have been identified from aeromagnetic measurements. Rifting of the Archaean craton created a passive margin ≈ 2.0 Ga ago. Spreading shifted to convergence with subduction beneath the Archaean continent ≈ 1.9 Ga ago. Subsequently, the resulting juvenile volcanic arc collided with the old continent, and the Archaean palaeoboundary as existing today was formed by a collision characterized by overthrusting. The boundary then was disturbed by later deformation predominantly along NNE-trending fracture systems.
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| 4. |
- Lund, P E, et al.
(författare)
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Intracellular ATP mimics GTP-gamma-S in generating Ca2+ oscillations in pancreatic beta-cells.
- 1991
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - 0006-291X .- 1090-2104. ; 177:2, s. 777-83
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular free calcium ([Ca2+]i) was measured in individual pancreatic beta-cells from mice using dual emission microfluorometry and the indicator Indo-1 applied by a patch clamp pipette. GTP-gamma-S (100 microM) injected together with 0.3 or 3 mM ATP evoked repetitive [Ca2+]i transients with a frequency of about 1 per min in beta-cells kept at a membrane potential of -70 mV. The oscillatory pattern was unaffected by the Ca2+ channel blocker verapamil (50 microM). When omitting GTP-gamma-S from the pipette medium it became evident that 3 mM ATP alone can induce oscillations. The results provide additional evidence for an important role of ATP in the ionic control of insulin release, indicating that such regulation may also involve activation of G-proteins.
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| 5. |
- Lund, P E, et al.
(författare)
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Caffeine inhibits cytoplasmic Ca2+ oscillations induced by carbachol and guanosine 5'-O-(3-thiotriphosphate) in hyperpolarized pancreatic beta-cells.
- 1994
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Ingår i: Naunyn-Schmiedeberg's Archives of Pharmacology. - 0028-1298 .- 1432-1912. ; 349:5, s. 503-9
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Tidskriftsartikel (refereegranskat)abstract
- The effects of caffeine on cytoplasmic Ca2+ oscillations induced by carbachol and guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S) were studied in individual mouse pancreatic beta-cells clamped at a hyperpolarized potential. Addition of 10 mM caffeine did not affect the cytoplasmic Ca2+ concentration ([Ca2+]i) in beta-cells exposed to 20 mM glucose and hyperpolarized with diazoxide. Under similar conditions 100 microM carbachol induced a typical response with a marked [Ca2+]i peak followed by a lower sustained elevation. Irrespective of whether 10 mM caffeine was present, there were [Ca2+]i transients with frequencies of 1-5/min superimposed on the sustained phase in 50-60% of the cells. In previously non-exposed cells the introduction of 10 mM caffeine caused temporary lowering of the sustained phase with disappearance of the transients. Subsequent omission of caffeine in the continued presence of carbachol caused a marked [Ca2+]i peak followed by reappearance of the [Ca2+]i transients. However, in cells oscillating in the presence of caffeine its omission caused disappearance of the transients. In this case reintroduction of caffeine restored the transients. In cells kept at -70 mV by a patch pipette containing 100 microM GTP-gamma-S and 3 mM Mg-ATP there were [Ca2+]i transients with frequencies of 0.5-2.5/min. These transients were sufficiently pronounced to activate repetitively a K+ current. Addition of 10 mM caffeine caused disappearance of the [Ca2+]i transients or reduction of their amplitudes and frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)
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| 6. |
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| 7. |
- Lund, P E, et al.
(författare)
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Activation of G-proteins induces Ca2+ oscillations with hyperpolarizing K+ currents in pancreatic beta-cells.
- 1991
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Ingår i: Second messengers and phosphoproteins. - 0895-7479. ; 14:3, s. 173-83
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Tidskriftsartikel (refereegranskat)abstract
- Activation of G-proteins by internal perfusion with GTP-gamma-S or external application of carbachol resulted in oscillations of cytoplasmic Ca2+ in isolated mouse pancreatic beta-cells. The Ca2+ transients were associated with the generation of K+ currents sufficiently pronounced to induce marked pulses of hyperpolarization. The oscillatory G-protein response remained largely unaffected when altering the membrane potential. The oscillations became less frequent in the presence of 1 mM neomycin and disappeared when the cells were internally perfused with 100 micrograms/ml heparin. The frequency of the oscillations was positively correlated with the basal level of cytoplasmic Ca2+. Addition of Ca2+ to the internal perfusion medium increased the oscillatory rate and buffering of the ion with Indo-1 or EGTA had the opposite effect. It is concluded that G-protein activation results in cyclic mobilisation of intracellular calcium mediated by inositol-1,4,5-triphosphate and that the basal concentration of cytoplasmic Ca2+ is an important determinant for the frequency of the oscillations.
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| 8. |
- Lund, P E, et al.
(författare)
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Stimulation of insulin release by isosmolar addition of permeant molecules.
- 1992
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Ingår i: Molecular and Cellular Biochemistry. - 0300-8177 .- 1573-4919. ; 109:1, s. 77-81
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatic beta-cells are known to respond to hyposmolar stress by releasing insulin. It was evident from perifusion studies using islet cells from ob/ob-mice mixed with polyacrylamide beads that a similar type of secretory response can be obtained by isosmolar addition of 10-25 mM of the rapidly penetrating urea molecule. There was no effect with hyperosmolar addition of urea. The urea-induced insulin release differed from the ordinary stimulation of secretion in not disappearing but being more pronounced after previous heating to 45 degrees C or removal of extracellular Ca2+. Isosmolar urea was exceptional as an insulin secretagogue in being effective also in the presence of the alpha 2-adrenergic agonist clonidine or when lowering the temperature to 24 degrees C. Further support for the idea that isosmolar addition of rapidly penetrating molecules induces insulin release was obtained by testing non-metabolizable glucose analogues. Whereas 25 mM 3-O-methyl-D-glucose doubled the secretory rate within 4 min, the non-permeant L-glucose had only a slight initial action. When not compensating for the alterations of the medium osmolarity 3-O-methyl-D-glucose was without effect. Although expansion of beta-cells cannot explain the existence of a pronounced initial secretory response to D-glucose it may under certain conditions contribute to the stimulatory effects of the sugar.
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