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- Leu, E., et al.
(författare)
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Fatty acid dynamics during the spring bloom in a High Arctic fjord: importance of abiotic factors versus community changes
- 2006
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - 0706-652X. ; 63:12, s. 2760-2779
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Tidskriftsartikel (refereegranskat)abstract
- We followed the fatty acid composition of particulate organic matter (POM) in a High Arctic fjord (79 degrees N; Svalbard, Norway) during and after the spring bloom. The content of essential polyunsaturated fatty acids (PUFAs) was highest (45% of total fatty acids) at the beginning of the bloom, well before the biomass maximum, and decreased linearly towards the end (30%). During the postbloom period, the concentrations of PUFAs remained stable, between 25% and 30%. Redundancy analysis was used to identify the environmental factors that explained the observed variability in the fatty acid composition of phytoplankton. A particular emphasis was put on the potential influence of high irradiances. During the spring bloom, nutrient availability (Si and N), as well as shifts in phytoplankton community composition and chlorophyll a, were shown to account for much of the pattern in fatty acid composition. During the postbloom period, particularly during periods of stratification, light had a pronounced effect on the fatty acid composition. In general, we found a decrease in the relative amount of PUFAs under high light intensities and nutrient limitation.
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| 4. |
- Howe, P. S., et al.
(författare)
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Kappa-symmetry for coincident D-branes
- 2007
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media LLC. - 1126-6708 .- 1029-8479. ; 09
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Tidskriftsartikel (refereegranskat)abstract
- A kappa-symmetric action for coincident D-branes is presented. It is valid in the approximation that the additional fermionic variables, used to incorporate the non-abelian degrees of freedom, are treated classically. The action is written as a Bernstein-Leites integral on the supermanifold obtained from the bosonic worldvolume by adjoining the extra fermions. The integrand is a very simple extension of the usual Green-Schwarz action for a single brane; all symmetries, except for kappa, are manifest, and the proof of kappa-symmetry is very similar to the abelian case.
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| 7. |
- Leu, E., et al.
(författare)
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Effects of changes in ambient PAR and UV radiation on the nutritional quality of an Arctic diatom (Thalassiosira antaretica var. borealis)
- 2006
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Ingår i: Journal of Experimental Marine Biology and Ecology. - : Elsevier BV. - 0022-0981. ; 337:1, s. 65-81
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Tidskriftsartikel (refereegranskat)abstract
- Polyunsaturated fatty acids (PUFAs) are essential macromolecules that are synthesized by phytoplankton during spring bloom, and they play a key role in the Arctic food web. They are, however, considered to be sensitive to oxidation by UV radiation (280-400 nm). Changes in the food quality of primary producers may affect the transport of biomass and energy in the whole ecosystem. Using a common Arctic diatom, we looked at the effect of ambient and increased UV radiation on its nutritional quality, specifically, the fatty acid composition and elemental ratios. In May 2004, in the archipelago of Svalbard (79 degrees N), a unialgal culture of Thalassiosira antarctica var. borealis was subjected to a 17-day experiment in outdoor aquaria. The diatoms were kept in semi-continuous culture (40 1) and exposed to three treatments with different levels of UV radiation: none (UV-shielded), ambient, and enhanced. Fatty acid composition, C:N:P ratios, photosynthetic pigment composition, optimum quantum yield of PSII, and cell numbers were analysed over the experimental period. An initial increase in PAR (photosynthetically active radiation, 400-700 nm) intensities profoundly affected the fatty acid composition and substantially inhibited the synthesis of PUFAs, but the relative amounts of PUFAs were not reduced by UV radiation. Enhanced UV radiation did, however, cause a significant reduction in optimum quantum yield of PSII and affected some fatty acids, mainly 18:0 and 16:1 n-7, during the first week of the experiment. Both ambient and enhanced UV radiation caused significantly lower C:P and N:P ratios. At the same time, these treatments elicited a higher relative content of the photoprotective pigments diadinoxanthin and diatoxanthin. After acclimation to the new light levels these effects faded off. Thus, brief periods with high light exposure may cause significant changes in photosynthetic activity and food quality, but the capacity for photo-acclimation seems high. The impact of UV radiation seems to be less important for food quality than that of PAR during a sudden rise in total light intensity. (c) 2006 Elsevier B.V. All rights reserved.
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| 9. |
- Sondhauss, Peter, et al.
(författare)
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Picosecond X-ray studies of coherent folded phonons in a multiple quantum well
- 2005
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Ingår i: Physical Review Letters. - Lund Univ, Dept Phys, SE-22100 Lund, Sweden. European Synchrotron Radiat Facil, F-38043 Grenoble, France. Malmo Univ, Sch Technol & Soc, S-20506 Malmo, Sweden. Univ Oxford, Dept Phys, Clarendon Lab, Oxford OX1 3PU, England. : AMERICAN PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 94
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Tidskriftsartikel (refereegranskat)abstract
- Coherent folded acoustic phonons in a multilayered GaSb/InAs epitaxial heterostructure were generated by femtosecond laser pulses and studied by means of ultrafast x-ray diffraction. Coherent phonons excited simultaneously in the fundamental acoustic branch and the first back-folded branch were detected. This represents the first clear evidence for phonon branch folding based directly on the atomic motion to which x-ray diffraction is sensitive. From a comparison of the measured phonon-modulated x-ray reflectivity with simulations, evidence was found for a reduction of the laser penetration depth. This reduction can be explained by the self-modulation of the refractive index due to photogenerated free carriers.
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| 10. |
- Wulff, Angela, 1963, et al.
(författare)
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Depth distribution of photosynthetic pigments and diatoms in the sediments of a microtidal fjord
- 2005
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 534:1-3, s. 117-130
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Tidskriftsartikel (refereegranskat)abstract
- The depth distribution of photosynthetic pigments and benthic marine diatoms was investigated in late spring at three different sites on the Swedish west coast. At each site, sediment cores were taken at six depths (7-35 m) by scuba divers. It was hypothesized that (1) living benthic diatoms constitute a substantial part of the benthic micro. ora even at depths where the light levels are <1% of the surface irradiance, and (2) the changing light environment along the depth gradient will be reflected in ( a) the composition of diatom assemblages, and (b) different pigment ratios. Sediment microalgal communities were analysed using epifluorescence microscopy ( to study live cells), light microscopy and scanning electron microscopy ( diatom preparations), and HPLC ( photosynthetic pigments). Pigments were calculated as concentrations (mg m(-2)) and as ratios relative to chlorophyll a. Hypothesis (1) was accepted. At 20 m, the irradiance was 0.2% of surface irradiance and at 7 m, 1%. Living (epifluorescent) benthic diatoms were found down to 20 m at all sites. The cell counts corroborated the diatom pigment concentrations, decreasing with depth from 7 to 25 m, levelling out between 25 and 35 m. There were significant positive correlations between chlorophyll a and living (epifluorescent) benthic diatoms and between the diatom pigment fucoxanthin and chlorophyll a. Hypothesis (2) was only partly accepted because it could not be shown that light was the main environmental factor. A principal component analysis on diatom species showed that pelagic forms characterized the deeper locations (25-35 m), and epipelic-epipsammic taxa the shallower sites (7-20 m). Redundancy analyses showed a significant relationship between diatom taxa and environmental factors temperature, salinity, and light intensities explained 57% of diatom taxa variations.
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