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- Gustavsson, M. T., et al.
(författare)
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Modification of cellulose fiber surfaces by use of a lipase and a xyloglucan endotransglycosylase
- 2005
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 6:1, s. 196-203
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Tidskriftsartikel (refereegranskat)abstract
- A strategy for the modification of cellulose fiber surfaces was developed that used the ability of Candida antarctica lipase B (CALB) to acylate carbohydrates with high regioselectivity, combined with the transglycosylating activity of the Populus tremula x P. tremuloides xyloglucan endotransglycosylase 16A (PttXET16A). Xyloglucan oligosaccharides (XGOs) prepared from tamarind xyloglucan were acylated with CALB as a catalyst and vinyl stearate or gamma-thiobutyrolactone as acyl donors to produce carbohydrate molecules with hydrophobic alkyl chains or reactive sulfhydryl groups, respectively. The modified XGOs were shown to act as glycosyl acceptors in the transglycosylation reaction catalyzed by PttXET16A and could therefore be incorporated into high M-r xyloglucan chains. The resulting xyloglucan molecules exhibited a high affinity for cellulose surfaces, which enabled the essentially irreversible introduction of fatty acid esters or thiol groups to cellulose fibers.
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- Gustavsson, B., et al.
(författare)
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Electron gyroharmonic effects in ionization and electron acceleration during high-frequency pumping in the ionosphere
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:19, s. 195002-
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Tidskriftsartikel (refereegranskat)abstract
- Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 angstrom from N-2(+) that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of the thermosphere. The intensity at 4278 angstrom is asymmetric around the ionospheric electron gyroharmonic, being stronger above the gyroresonance. This contrasts with emissions at 6300 angstrom from O(D-1) and of electron temperature enhancements, which have minima at the gyroharmonic but have no apparent asymmetry. This direct evidence of pump-induced ionization contradicts previous indirect evidence, which indicated that ionization is most efficiently produced when the pump frequency was below the gyroharmonic.
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| 5. |
- Gustavsson, B, et al.
(författare)
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First observations of X-mode suppression of O-mode HF enhancements at 6300 angstrom
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36, s. L20102-
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of radio induced optical emissions from a HAARP experiment with simultaneous transmission in X and O-mode. The additional transmission of X-mode with a frequency 700 kHz higher than the O-mode, reduces the enhancement of the 6300 A emission. This suggests that the wave-plasma process that energizes the electrons, which excites oxygen to the O(D-1) state, is closely connected to the excitation of upper-hybrid waves, whose onset and initial growth are reduced by additional X-mode pumping. Citation: Gustavsson, B., R. Newsome, T. B. Leyser, M. J. Kosch, L. Norin, M. McCarrick, T. Pedersen, and B. J. Watkins (2009), First observations of X-mode suppression of O-mode HF enhancements at 6300 angstrom, Geophys. Res. Lett., 36, L20102, doi:10.1029/2009GL039421.
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- Löfås, Henrik, et al.
(författare)
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F-region electron heating by X-mode radiowaves in underdense conditions
- 2009
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 27:6, s. 2585-2592
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Tidskriftsartikel (refereegranskat)abstract
- Observations of modifications of the electron temperature in the F-region produced by powerful high frequency radiowaves at 4.04 MHz transmitted in X-mode are presented. The experiments were performed during quiet nighttime conditions with low ionospheric densities so no reflections occurred. Electron temperature enhancements of the order of 300-400K were obtained. Numerical simulation of ohmic heating by the pump wave reproduces both altitude profiles and temporal dependence of the temperature modifications in the experiments.
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