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- Martens, C.S., et al.
(författare)
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Radon fluxes in tropical forest ecosystems of Brazilian Amazonia: night-time CO2 net ecosystem exchange derived from radon and eddy covariance methods.
- 2004
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 10:5, s. 618-629
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Tidskriftsartikel (refereegranskat)abstract
- Radon-222 (Rn-222) is used as a transport tracer of forest canopy–atmosphere CO2 exchange in an old-growth, tropical rain forest site near km 67 of the Tapajós National Forest, Pará, Brazil. Initial results, from month-long periods at the end of the wet season (June–July) and the end of the dry season (November–December) in 2001, demonstrate the potential of new Rn measurement instruments and methods to quantify mass transport processes between forest canopies and the atmosphere. Gas exchange rates yield mean canopy air residence times ranging from minutes during turbulent daytime hours to greater than 12 h during calm nights. Rn is an effective tracer for net ecosystem exchange of CO2 (CO2 NEE) during calm, night-time hours when eddy covariance-based NEE measurements are less certain because of low atmospheric turbulence. Rn-derived night-time CO2 NEE (9.00±0.99 μmol m−2 s−1 in the wet season, 6.39±0.59 in the dry season) was significantly higher than raw uncorrected, eddy covariance-derived CO2 NEE (5.96±0.51 wet season, 5.57±0.53 dry season), but agrees with corrected eddy covariance results (8.65±1.07 wet season, 6.56±0.73 dry season) derived by filtering out lower NEE values obtained during calm periods using independent meteorological criteria. The Rn CO2 results suggest that uncorrected eddy covariance values underestimate night-time CO2 loss at this site. If generalizable to other sites, these observations indicate that previous reports of strong net CO2 uptake in Amazonian terra firme forest may be overestimated.
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| 3. |
- Forsman, Jan, et al.
(författare)
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Density functional studies of solvation forces in hard sphere polymer solutions confined between adsorbing walls. I. Solvent effects and dependence on surface potential range.
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606. ; 118:16, s. 7672-7681
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Tidskriftsartikel (refereegranskat)abstract
- Solvation forces between large surfaces in athermal polymer solutions, in which both solvent particles and polymers are adsorbed at the surfaces, are studied with density functional theory. We investigate how the range of the surface potential affects the net interaction between the surfaces. Predictions from treatments in which the solvent is explicitly induced are compared with those obtained with more approximate models, where the solvent is either neglected, or enters the description implicitly. The results are interpreted via comparisons with simpler model systems. It is shown that a long-ranged surface potential, acting equally on monomers and solvent, leads to a solvent dominated repulsive solvation force, while polymer specific contributions dominate the net interactions when the adsorption potential has a short range. Effects of preferential polymer adsorption are also investigated. ©2003 American Institute of Physics.
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| 6. |
- Alekseev, A, et al.
(författare)
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Group-valued equivariant localization
- 2000
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Ingår i: INVENTIONES MATHEMATICAE. - : SPRINGER VERLAG. - 0020-9910. ; 140:2, s. 327-350
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Tidskriftsartikel (refereegranskat)abstract
- We prove a localization formula for group-valued equivariant de Rham cohomology of a compact G-manifold. This formula is a non-trivial generalization of the localization formula of Berline-Vergne and Atiyah-Bott for the usual equivariant de Rham cohomolog
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| 10. |
- Forsman, Jan, et al.
(författare)
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An improved density functional description of hard sphere polymer fluids at low density.
- 2003
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 119:4, s. 1889-1892
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Tidskriftsartikel (refereegranskat)abstract
- A refined formulation of an existing polymer density functional theory is presented, wherein an intrachain stiffness is introduced via a bending potential. Comparisons with Metropolis Monte Carlo simulations in a slit geometry shows that this leads to a considerable improvement of the predicted density profile for a hard sphere polymer melt, at low density. We also show how the corresponding surface interactions are affected by the inclusion of this intramolecular correlation. We expect that the improvement obtained will be even more important in the description of, for example, polyelectrolytes, although such comparisons are not made in this preliminary study. ©2003 American Institute of Physics.
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