| 1. |
- Bergqvist, Lars, 1976-, et al.
(författare)
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Magnetic and electronic structure of (Ga1-xMnx)As
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:20, s. 205201-
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Tidskriftsartikel (refereegranskat)abstract
- We present theoretical calculations of the magnetic and electronic structure of Mn-doped GaAs (in the zinc-blende structure). The magnetic properties are shown to be very sensitive to structural defects, in particular, As antisite defects and Mn at interstitial positions. Only when considering such defects can the experimental magnetic moments be reproduced by first-principles theory. We present a simple model for understanding the connection between the magnetic ordering and the As antisites, and the way in which the defects help to stabilize a partial disordered local-moment state. The connection between the energetics of the Mn substitution and the As antisite concentration is also analyzed. In addition, we compare the calculated magnetic properties and electronic structures of Mn situated on substitutional sites (Mn replacing a Ga atom) and on interstitial sites, where in agreement with observations the interstitial site is found to be less favorable. Finally, combining our first-principles calculations of the spin-wave excitation energies with a classical Heisenberg Hamiltonian we have calculated interatomic exchange interactions, and using Monte Carlo simulations we present theoretical values of the critical temperature as a function of Mn concentration.
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| 2. |
- Eriksson, Susanne P., 1964
(författare)
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Temporal variations of manganese in the haemolymph and tissues of the Norway lobster, Nephrops norvegicus (L.)
- 2000
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Ingår i: Aquatic Toxicology. - 0166-445X. ; 48:2-3, s. 297-307
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Tidskriftsartikel (refereegranskat)abstract
- The Norway lobster, Nephrops norvegicus, lives on sediments rich in manganese (Mn) and any dissolved Mn2+ can readily be taken up by the animal. To investigate temporal fluctuations of bioavailable Mn, a N. norvegicus fishing ground on the Swedish west coast was repeatedly sampled every 2 months from September 1992 to November 1994. The lobsters collected contained on average 91.7 mu g Mn g(-1) dry wt. (S.E. 4.2, n = 156). The oxygen saturation of the bottom water proved to be negatively correlated with both the temperature of the water and the Mn (concentration and total content) of the animal's haemolymph. The temporal fluctuations in animal Mn load were however, small compared to spatial differences found in an earlier study. There was an increase in the Mn concentration of the lobster exoskeleton (from 56 to 340 mu g Mn g(-1) dry wt, exoskeleton) and gills (from 34 to 160 mu g Mn g(-1) dry wt. gill) in postmoult animals compared to premoult. The Mn concentrations of the lobsters' hepatopancreas and muscle tissue remained relatively constant throughout the moult cycle and appear to be more conservative in their Mn concentration and less affected by exposure to Mn. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 3. |
- Eriksson, Susanne P., 1964
(författare)
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Variations of manganese in the eggs of the Norway lobster, Nephrops norvegicus (L.)
- 2000
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Ingår i: Aquatic Toxicology. - 0166-445X. ; 48:2-3, s. 291-295
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Tidskriftsartikel (refereegranskat)abstract
- The Norway lobster, Nephrops norvegicus, lives on sediments rich in manganese (Mn). Temporal fluctuations of Mn in the eggs of N. norvegicus was investigated, both in the field and in laboratory experiments. Female gonads and external eggs of different developmental stages were measured for Mn. The Mn concentration during oocyte maturation and throughout most of the embryogenesis (after fertilisation) remained stable around 5 mu g Mn g(-1) dry wt. egg. At the end of the embryonic development (about 6 months after fertilisation) the Mn concentration of the egg started to increase and had at the time of hatching reached concentrations of 120 mu g Mn g(-1) dry wt. egg. The egg shell was at this stage highly permeable and Mn was taken up by the embryo and egg shell in equal amounts. (C) 2000 Elsevier Science B.V. All rights reserved.
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| 4. |
- Spicer, J. I., et al.
(författare)
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Does the development of respiratory regulation always accompany the transition from pelagic larvae to benthic fossorial postlarvae in the Norway lobster Nephrops norvegicus (L.)?
- 2003
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Ingår i: Journal of Experimental Marine Biology and Ecology. - 0022-0981. ; 295:2, s. 219-243
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Tidskriftsartikel (refereegranskat)abstract
- The ability to regulate O-2 uptake during exposure to acutely declining PO2S co-occurred with metamorphosis from a planktonic to a benthic existence in the Norway lobster Nephrops norvegicus when cultured under normoxic conditions in the laboratory. The onset of this regulation appears to be related to the presence of a hypoxia-related hyperventilation of extrabranchial exchange surfaces (telson/uropods) by the pleopods and a shift from a low to a high He O-2 affinity. This co-occured with a dramatic calcification of the exoskeleton at metamorphosis, which will restrict gas exchange over the general body surface. Evidence marshalled here points to a shift from a pleopod-based, hypoxia-related, hyperventilation of the uropods/telson as gas exchange surfaces to, in later postlarval stages, a scaphognathitc-based response, where the gills are the main areas for gas exchange. This is the first time that experimental evidence has been put forward for the use of uropods/telson by larval lobsters as extrabranchial gas exchange surfaces. Pre-exposure of larval and postlarval N. norvegicus to reduced P-O2, both in the laboratory and in the field, resulted in the "adult" pattern of M-O2, regulation present during exposure to declining P-O2 being established before metamorphosis. Bringing the ontogeny of this regulation forward in the development itinerary was to some extent a result of a shift from a low to a high He O-2 affinity well before metamorphosis and an increase in the magnitude of the hypoxia-related hyperventilatory response in the planktonic larval stages. Thus, the development of respiratory regulation does not always accompany the transition from pelagic larvae to benthic fossorial larvae in N. norvegicus as its onset can be influenced prevailing O-2 conditions, both in the laboratory and the field. (C) 2003 Elsevier B.V. All rights reserved.
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