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- Hammarlund, Dan, et al.
(författare)
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Rapid hydrological changes during the Holocene revealed by stable isotope records of lacustrine carbonates from Lake Igelsjon, southern Sweden
- 2003
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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 22:2-4, s. 353-370
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Tidskriftsartikel (refereegranskat)abstract
- A Holocene sediment sequence from Lake Igelsjon, south central Sweden, was studied by stable oxygen- and carbon-isotope analyses of different carbonate components. The deposit, which covers the time-span from ca 11,500 cal BP to the present, was laid down in a small, kettle-hole lake, the hydrological balance of which is presently dominated by groundwater flow. Isotopic records obtained on bulk carbonates originating mainly from summer-produced, calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand, likely reflecting pronounced hydrological variations. Corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts, probably related to an extended calcification season. The isotopic records were complemented by studies of modern isotope hydrology, and our interpretations are based on a simplistic climate-hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface/volume ratio of the basin during the ice-free season. Assumed periods of decreased lake volume in a relatively dry climate (low lake level) are characterised by enrichment in O-18 and C-13 resulting from increased evaporation/inflow ratio and atmospheric equilibration, respectively. In clear contrast to this situation, intervals of more humid climatic conditions give rise to increased lake volume (high lake level), possibly surface over flow, and relatively depleted isotopic ratios. Relatively humid conditions, which may correlate to a wide-spread cooling event recorded by various proxies across the North Atlantic region, are indicated by distinct isotopic shifts at ca 8300 and 8000 cal BP, bracketing a period of O-18-depletion. The period between ca 8000 and 4000 cal BP was characterised by relatively dry and stable climatic conditions, whereas the subsequent part of the Holocene experienced a more humid and variable climate following marked and coherent depletions in O-18 and C-13 at ca 4000 cal BP. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 3. |
- Brockstedt, Sara, et al.
(författare)
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High-resolution diffusion imaging using phase-corrected segmented echo-planar imaging
- 2000
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Ingår i: Magnetic Resonance Imaging. - 1873-5894. ; 18:6, s. 649-657
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion magnetic resonance imaging (MRI) was performed with a high-resolution segmented echo-planar imaging technique, which provided images with substantially less susceptibility artifacts than images obtained with single-shot echo-planar imaging (EPI). Diffusion imaging performed with any multishot pulse sequence is inherently sensitive to motion artifacts and in order to reduce motion artifacts, the presented method utilizes navigator echo phase corrections, performed after a one-dimensional Fourier transform along the frequency-encoding direction. Navigator echo phases were fitted to a straight line prior to phase correction to avoid errors from internal motion. In vivo imaging was performed using electro cardiographic (ECG) triggering. Apparent diffusion coefficient (ADC) maps were calculated on a pixel-by-pixel basis using up to seven diffusion sensitivities, ranging from b = 0 to 1129 x 10(6) s/m(2).
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| 10. |
- Linnet, K.M., Dalsgaard, S., Obel, C., Wisborg, K., Henriksen, T.B., Rodriguez, Alina, Kotimaa, A., Moilanen, I., Thomsen, P.H., Olsen, J., Järvelin, M.R.
(författare)
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Maternal lifestyle factors in pregnancy and risk of Attention-Deficit Hyperactivity Disorders: A review of current evidence.
- 2003
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Ingår i: American Journal of Psychiatry. ; 160:6, s. 1028-1040
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Tidskriftsartikel (refereegranskat)
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