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| 2. |
- Persson, Anders, 1956-, et al.
(författare)
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Effects of benthivorous fish on biogeochemical processes in lake sediments
- 2006
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Ingår i: Freshwater Biology. - West Sussex, UK : Wiley-Blackwell. - 0046-5070 .- 1365-2427. ; 51:7, s. 1298-1309
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Tidskriftsartikel (refereegranskat)abstract
- 1. Studies of aquatic environments have shown that community organisation may strongly affect ecosystem functioning. One common phenomenon is a change in nutrient level following a shift in the fish community composition. Although several hypotheses have been suggested, there is no consensus on which mechanisms are involved. Our study evaluated indirect effects of benthivorous fish on the biogeochemical processes at the sediment-water interface separately from direct effects caused by nutrient excretion or sediment resuspension.2. We assigned field enclosures to three treatments representing typical pond communities; without fish, addition of approximately 10 small tench or addition of one large bream. After one summer, we monitored the water chemistry, benthic invertebrates and periphyton in the enclosures and sampled sediment cores for laboratory analysis of biochemical process rates (oxygen, phosphorus and nitrogen exchange between sediment and water, and denitrification rate).3. Fish had strong negative effects on benthic invertebrates, but weaker effects on periphyton, organic content and porosity of the sediment. Moreover, there were significant positive fish effects on both phosphorus and nitrogen concentrations in the water. However, there were no general treatment effects on sediment processes that could explain the treatment effects on water chemistry in the enclosures.4. Hence, overall treatment effects attenuated along the chain of interactions. We conclude that the observed effect of benthic fish on water chemistry was probably because of direct effects on nutrient excretion or resuspension of sediment. The similarity between bream and tench treatments suggests large niche complementarity despite their different habitat preferences.
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| 5. |
- Persson, Anders, et al.
(författare)
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Reverse conversion architectures for signed-digit residue number systems
- 2006
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Ingår i: Proceedings - IEEE International Symposium on Circuits and Systems 2006. - New York : IEEE Press. - 0780393899 - 9780780393905 ; , s. 2701-2704
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Konferensbidrag (refereegranskat)abstract
- This paper presents circuits for conversion from radix-2 signed-digit residue numbers to binary form. Four reverse converters for combined RNS/SD number systems based on different moduli sets are presented. Implementations are compared with respect to timing, area and area-delay products. Finite impulse response (FIR) filters are used as reference designs in order to evaluate the performance of RNS/SD processing in a typical DSP block using the suggested moduli sets.
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| 6. |
- Persson, Anders, et al.
(författare)
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Successful Swedish headmasters in tension fields and alliances
- 2005
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Ingår i: International Journal of Leadership in Education. - London : Informa UK Limited. - 1360-3124 .- 1464-5092. ; 8:1 (January-March 2005), s. 53-72
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Tidskriftsartikel (refereegranskat)abstract
- What makes a headmaster successful? And what does a successful headmaster do? This article presents some results from a research project – Successful school leadership in different school cultures – that aims to provide answers to these questions. The results derive from interviews, questionnaires, observations and pupils’ essays, and comprise the criteria by which different parties involved in schools assess the success of headmasters. As with other research in this field, this article establishes that headmasters find themselves in tension fields that are constituted by the varied interests of the different parties involved in schools. These relationships are analysed with regard to three tension fields that affect Swedish schools today: between employer and employees; between pupils and adults; and between change and continuity.However, the work lives of headmasters isn’t characterised by tensions only, but by Alliances as well. Hence, headmasters’ alliances with various other parties within the school are also analysed. These alliances are both a way of dealing with the tensions that headmasters meet on a daily basis, and a way of creating both success and a leadership based on the school culture. However, the general development trend that we find in Swedish schools, which lift the headmaster out of the school to become the last among superiors rather than the firstamong equals, constricts the latitude for more culture-specific school leadership.
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| 7. |
- Persson, Anders, 1956-, et al.
(författare)
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Vertical distribution of benthic community responses to fish predators, and effects on algae and suspended material
- 2006
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Ingår i: Aquatic Ecology. - Dordrecht, Netherlands : Springer Netherlands. - 1386-2588 .- 1573-5125. ; 40:1, s. 85-95
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Tidskriftsartikel (refereegranskat)abstract
- The vertical positioning of benthic invertebrates should be a trade-off between the risky, but productive, sediment surface and the safer, but physiologically harsher, conditions deeper down in the sediment. This is because the foraging efficiency of benthic fish decreases with sediment depth, whereas the sediment surface is generally better oxygenated and has a higher resource quality than lower layers. We studied how two benthic fish predators, bream (Abramis brama) and ruffe (Gymnocephalus cernuus), affected the community composition and vertical distribution of benthos, and their indirect effects on algae and suspended material, in field enclosures. Whereas bream had significant effects on the density, composition and distribution of the benthos, ruffe had no such effects. The total benthos biomass in bream treatments was an-order of magnitude lower in the upper sediment layer (0-1 cm) and three times lower in the middle layer (1-3 cm) than in the controls, whereas there were no significant effects in the deepest layer (3-10 cm). Bivalves persisted in the deepest layer although their density was reduced in shallow sediment, whereas gastropods faced the risk of local extinction in the presence of bream. As indirect effects, small-bodied cladocerans, phytoplankton, periphyton and both organic and inorganic suspended material were higher in the bream treatments. We conclude that the impact of bream diminished substantially with increasing sediment depth, enabling invertebrates to survive in the sediment and to persist in the presence of bream. However, there were no indications of any group adjusting their vertical position behaviourally as a response to predation threat.
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