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- Agnemo, Roland, 1944-
(author)
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Ligniners reaktioner med alkalisk väteperoxid
- 1981
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Doctoral thesis (other academic/artistic)abstract
- Under alkaline conditions hydrogen peroxide can be used either as a 1ignin-degrading or a 1ignin-preserving bleaching agent. If heavy metal ions are present and/or silicate is absent in the reaction medium, hydrogen peroxide decomposes via hydroxyl radicals and superoxide ions to oxygen and water. These decomposition products are able to react for example with phenolic lignin structures and thereby cause a partial degradation of lignin. In such a system peroxide could act as a bleaching and delignifying agent at the same time and these properties can be utilized for the bleaching of chemical pulps.In order to elucidate the factors which influence the degradation of phenolic structures by oxidation with alkaline hydrogen peroxide the lignin model compounds-methylsyringyl alcohol was studied.By determining the first order reaction rate constants for the oxidation, the main results which were obtained indicate that phenolic lignin structures can be efficiently degraded especially if:A. The pH in the bleaching liquor is close to the pK -valueàfor hydrogen peroxide.B. The ionic strength in the bleaching medium is as high as possible.C. A fixed amount of heavy metal ions (manganese) is added to the bleaching liquor.In the presence of silicate and diethylentriaminepenta-acetic acid (DTPA) hydrogen peroxide is stabilized against decomposition. Under these conditions alkaline hydrogen peroxide is able to react only with lignin units containing conjugated carbonyl groups such as quinone, aryl-oe-carbonyl and cinnamaldehyd structures, leading to an elimination of the chromophoric structures without any substantial dissolution of lignin. In this part of work we have elucidated the kinetic behavior and the reaction products from lignin model compounds of the aryl-of- carbonyl and cinnamaldehyde types.1,2-Diarylpropan-1,3,-diol structures constitute an important building unit in native lignins. We have demonstrated that under hydrogen peroxide bleaching conditions the model compound 2,3--bis(4-hydroxy-3-methoxyphenyl)-3-ethoxy-propanol was converted to stilbenes, ûe. structures which when present in pulps may contribute to a rapid yellowing. The results obtained with model compounds under simulated lignin retaining bleaching conditions demonstrate that there are possibilities to improve the bleaching of mechanical pulps with hydrogen peroxide if:A. The remaining heavy metal ions complexed with DTPA are present in their lowest valence states.B. The concentration of hydroperoxy ions can be maintained at a high level at the lowest possible pH-value.
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| 3. |
- Alfvén, Hannes
(author)
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The Voyager-1 - Saturn encounter and the cosmogonic shadow effect
- 1981
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In: Astrophysics and Space Science. - : Kluwer Academic Publishers. - 0004-640X .- 1572-946X. ; 79:2, s. 491-505
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Journal article (peer-reviewed)abstract
- If an electrically conducting medium (e.g. a dusty plasma) rotates around a gravitating central body, which possesses an axisymmetric dipole field, the medium is supported to two-thirds by the centrifugal force and to one-third by electromagnetic forces under the condition that the magnetic field is strong enough to controll the motion. If the electromagnetic forces disappear — e.g. by a de-ionisation of the dusty plasma — the medium will fall down to two-thirds of its original central distance. The result of this process will be a ‘cosmogonic shadow effect’ which is described in some detail.The Voyager 1/Saturn results demonstrate that the macro-structure of the Saturnian ring system can be explained as a result of this effect working at the formation of the system. The agreement between the theoretical results and the observations is better than a few percent.A similar analysis of the asteroidal belt shows that its macro-structure can also be explained by the cosmogonic shadow effect. The agreement between theory and observations is perhaps even better than in the Saturnian ring system.The observational results demonstrate that during their formation both the Saturnian ring and the asteroidal belt passed a plasma state dominated by electromagnetic effects.
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| 4. |
- Allard, Bert, et al.
(author)
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Actinide Sorption on Rock Minerals
- 1981
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In: Proceedings of the International Seminar on Chemistry and Process Engineering for High Level Liquid Waste. ; Jül Conf 42
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Conference paper (other academic/artistic)
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| 7. |
- Almbladh, Carl-Olof, et al.
(author)
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Statistical mechanics of band states and impurity states in semiconductors
- 1981
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In: Journal of Physics C: Solid State Physics. - 0022-3719. ; 14:31, s. 4575-4601
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Journal article (peer-reviewed)abstract
- Thermodynamic analogies have previously been invoked to interpret the temperature- and pressure-dependent electronic levels in a semiconductor as standard Gibbs free energies. In this paper it is shown by means of statistical mechanical arguments using the pressure ensemble that standard Gibbs free energies are the quantities determining equilibrium occupations of electronic levels and hence are the thermodynamic quantities that enter detailed balance relationships. Optical band gaps are identified with the 'nophonon line' gap for a transition in which the occupation numbers for the phonons and remaining electrons are unchanged. An exact expression for no phonon optical transition energies is given. It is shown rigorously that the optical no-phonon-line energy is identical to the corresponding free-energy change for any transition between band states and also for transitions involving localised states provided: (i) the effects of electronic degeneracy changes are excluded from the free energy definition; (ii) the localised state is not associated with a local lattice mode.
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| 8. |
- Andersson, Anders, et al.
(author)
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The epidermal indeterminate cell- a special cell type?
- 1981
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In: Acta dermato-venereologica. Supplementum. - 0365-8341. ; 99, s. 41-48
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Journal article (peer-reviewed)abstract
- Electron microscopy of normal human epidermiscomprising very large series of sections in combination withtilting of the sections has revealed that all "indeterminatecells" carry the specific markers of either melanocytes orLangerhans cells. The term "indeterminate cells" can thusbe abandoned. In addition, it is suggested that an epidermaldendritic cell lacking specific markers in the section underobservation can be characterized by the amount and distributionpattern of its microfilaments, an additional criterionbeing that the melanocytes carry a ciliunu
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| 9. |
- Andersson, Bo, et al.
(author)
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ON HIGH-ENERGY LEPTOPRODUCTION
- 1981
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In: Zeitschrift für Physik C Particles and Fields. - 0170-9739. ; C9, s. 233-233
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Journal article (peer-reviewed)
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| 10. |
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