Magnetic susceptibility in sediment records of Lake Ådran,eastern Sweden: correlation among cores and interpretation     

Per Sandgren  Jan Risberg  Roy Thompson 《Journal of Paleolimnology》1990,3(2):129-141

Magnetic susceptibility was used to test the representativity of the lithostratigraphy of a master sediment sequence from Lake Ådran, eastern Sweden. Five further sediment cores from the same lake were correlated and compared with the master sequence using magnetic susceptibility records. Mineral magnetic correlations are generally based on matching prominent susceptibility features but may be significantly improved by using slot sequence analyses. The result of these analyses show that the sediment in the Lake Ådran master sequence can be considered representative for the basin. The variations in the magnetic susceptibility in relation to pollen and diatom analyses also seem to reflect water level changes and shore displacement in the Baltic between 9900 ¹⁴C years B.P. and the isolation at 5900 ¹⁴C years B.P. The first emergence of scattered non-vegetated islands is characterised by high susceptibility values. Along with a continuous water lowering and the development of the vegetation during the Ancylus fresh water stage, susceptibility values gradually decrease. A rapid phase of the Ancylus regression between 9200 and 9000 ¹⁴C years B.P. is seen as an increase in magnetic susceptibility. During the following Baltic brackish water stage, the Litorina stage, susceptibility values are at their lowest, followed by higher values at the isolation from the Baltic with a maximum around 5000 ¹⁴C years B.P.Shore displacement between 9900 and 5900 ¹⁴C years B.P. is discussed based on the magnetic susceptibility measurements and their relationship to the pollen and diatom analyses.  相似文献   

The radio–optical correlation in steep-spectrum quasars     

Stephen Serjeant  Steve Rawlings  Stephen J. Maddox  Joanne C. Baker  Dave Clements  Mark Lacy  & Per B. Lilje 《Monthly notices of the Royal Astronomical Society》1998,294(3):494-504

Using complete samples of steep-spectrum quasars, we present evidence for a correlation between radio and optical luminosity which is not caused by selection effects, nor caused by an orientation dependence (such as relativistic beaming), nor a by-product of cosmic evolution. We argue that this rules out models of jet formation in which there are no parameters in common with the production of the optical continuum. This is arguably the most direct evidence to date for a close link between accretion on to a black hole and the fuelling of relativistic jets. The correlation also provides a natural explanation for the presence of aligned optical/radio structures in only the most radio-luminous high-redshift galaxies.  相似文献   

Estimation of sea surface topography in the Norwegian sea using gravimetry and Geosat altimetry     

Per Knudsen 《Journal of Geodesy》1992,66(1):27-40

An analysis of the quasi-stationary sea surface topography (QSST) is carried out in the Norwegian Sea region (54°<ø<72°, -25°<<20°) using marine gravimetry and one year of Geosat ERM altimetry. As reference models the geopotential model OSU91A and the QSST model OSU89D were used. Two procedures to extract the QSST from mean sea surface heights and gravity anomalies were tested. Spherical FFT techniques were applied in both procedures. The results show that QSST associated with wavelength shorter than 4000 km exists. Relative to the OSU89D model the QSST was found to have a variance of (0.219 m)² and a correlation length of 1.105°. The circulation pattern recovered in this paper agree with results of oceanographic analysis.  相似文献   

The production of relaid blue mussels (Mytilus edulis L.) in a Danish fjord     

Kristensen  Per Sand; Lassen  Hans 《ICES Journal of Marine Science》1997,54(5):854-865

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The stabilisation of wet sediment cores by means of a polyethylene glycol/freeze-drying treatment for display and permanent storage     

Per Hoffmann  Jürgen P?tzold 《Geo-Marine Letters》2002,21(4):245-252

A reversible method is presented to transform waterlogged sediment cores into dry and stable specimens which can go on exhibition or into permanent storage, needing no special precautions. Wet sediment core segments are bath-impregnated with polyethylene glycol of molecular weight 3,350 (PEG 3,350) dissolved in water. The samples are then subjected to a freeze-drying process, during which the PEG forms a stabilising and bonding porous network structure in the capillary system of the sediment. Standard sediment cores at least 1 m long become strong enough to stand upright. Sediment types ranging from muddy deep-sea sediments to very coarse littoral Halimeda sand were successfully stabilised. For standard cores of 10-cm diameters split length-wise, impregnation times vary from 2 weeks for coarse sand to 6–10 weeks for more compacted sediments. With regard to the stability of the samples and the visual clarity of detail, best results were obtained by impregnation with 25 to 60% solutions of PEG 3,350, coarse sediments needing more PEG than finer ones. Colour changes are systematic – the processed samples are lighter in appearance and the contrasts are enhanced, but there is no serious shift in colour tones. The PEG can easily be re-dissolved and washed out of the sediments. Display specimens can thus be made available for research again.  相似文献   

TEMAS: fleet-based bio-economic simulation software to evaluate management strategies accounting for fleet behaviour   总被引：1，自引：0，他引：1  

Ulrich  Clara; Andersen  Bo Solgaard; Sparre  Per J.; Nielsen  J. Rasmus 《ICES Journal of Marine Science》2007,64(4):647-651

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Multi-satellite ocean tide modelling—the K₁ constituent     

Ole Baltazar Andersen  Per Knudsen 《Progress in Oceanography》1997,40(1-4)

All major ocean tide constituents are aliased into signals with periods less than 90 days from TOPEX/POSEIDON altimetry, except the K₁ constituent. The aliased K₁ has a period of 173 days. Consequently, it might be confounded with height variations caused by the semiannual cycle having a period of 183 days.The correlation between K₁ and the semiannual signal has been investigated both locally and globally using combinations of T/P, ERS-1 and GEOSAT observations. Subsequently, two empirical methods have been investigated to improve the mapping of K₁ from multiple satellites.At high latitudes, where the presence of crossing tracks cannot separate K₁ from the semiannual signal from TOPEX/POSEIDON, the importance of including ERS-1 and GEOSAT observations was demonstrated. A comparison with 29 pelagic and coastal tide gauges in the Southern Ocean south of 50°S gave 5.59 (M₂), 2.27 (S₂) and 5.04 (K₁) cm RMS agreement for FES95.1 ocean tide model. The same comparison for the best empirical estimated constituents based on TOPEX/POSEIDON + ERS-1 + GEOSAT gave 4.32, 2.21, and 4.29 cm for M₂, S₂ and K₁, respectively.  相似文献   

A Boussinesq model for waves breaking in shallow water   总被引：2，自引：0，他引：2  

Hemming A. Schffer  Per A. Madsen  Rolf Deigaard 《Coastal Engineering》1993,20(3-4)

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Investigating the Waterfront: The Entangled Sociomaterial Transformations of Coastal Space in Karnataka,India     

Alin Kadfak  Per Knutsson 《社会与自然资源》2017,30(6):707-722

Triggered by urbanization and changing land use, coastal transformation is a rapidly increasing phenomenon in the global south, driving dramatic livelihoods impacts. However, the existing literature on small-scale fisheries (SSF) has paid little attention to the way coastal transformations shape conditions for SSF livelihoods communities. This study proposes a new orientation in SSF studies by exploring the assemblage of entangled sociomaterial processes that account for coastal transformations by investigating waterfront transformation in a fishing community in Karnataka, India. Drawing on ethnographic fieldwork, we conclude that an entanglement of sociomaterial processes produces unequal outcomes among stakeholders that subsequently reinforce the political and economic marginalization of certain groups of waterfront users. Moreover, the investigated context-specific waterfront assemblage intimately connects to the broader context of national fishery policy, urbanization, and tourism, directing the way coastal space can and should be transformed. Such an analysis contributes to the understanding of changing livelihoods in SSF communities.  相似文献   

Nitrate vulnerability assessment of aquifers     

Birgitte Hansen  Torben O. Sonnenborg  Ingelise Møller  Jens Demant Bernth  Anne-Sophie Høyer  Per Rasmussen  Peter B.E. Sandersen  Flemming Jørgensen 《Environmental Earth Sciences》2016,75(12):999

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