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Träfflista för sökning "LAR1:umu srt2:(1980-1984)"

Sökning: LAR1:umu > (1980-1984)

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  • Agnemo, Roland, 1944- (författare)
  • Ligniners reaktioner med alkalisk väteperoxid
  • 1981
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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  • Allergren, Björn, et al. (författare)
  • Studiehandbok
  • 1981
  • Rapport (övrigt vetenskapligt/konstnärligt)
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  • Alm, Håkan, 1948- (författare)
  • Learning of probabilistic inference tasks : effects of uncertainty and function form
  • 1982
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • This thesis is concerned with the problem of how people learn to use uncer­tain information for making judgments. The general framework for the thesis is Social Judgment Theory (SJT). First the S3T paradigm, and some research conducted within the paradigm, is briefly described, and a series of four empirical studies is summarized. The studies are concerned with two factors that have been found to have great effect on subjects achievement in cue probability learning (CPL) tasks: task predictability, and the form of the function relating cue and criterion. The effects of these two factors were studied in experiments employing cue-probability learning tasks. The studies concerned with task predictability addressed the following questions (a) Do subjects understand the probabilistic nature of CPL-tasks? (b) Are subjects able to detect that a random task is, in fact, random, a study undertaken to test an aspect of Seligmans "theory of helplessness". This was also an attempt to bring emotional factors more in foeus.(c) Do subjects use data from the task only to test hypotheses, or do they use data also to construct hypotheses?The results showed that (a) subjects do not seem to be able to cope with probabilistic tasks in an optimal statistical manner. Instead they seem to use a deterministic approach to the tasks, because they do not understand the probabilistic nature of the task, (b) Task predictability affecs subjects mood, but not in the way predicted by Seligman, (c) Subjects seem to use data frorn the task only to test their hypotheses. The results thus supported the hypo­theses sampling model for the learning of CPL-tasks.As for the factor of function form, the following questions were addressed, (a) What hypotheses about relations between variables do subjects have? (b) Is the difficulties subjects have in learning complex rules in CPL-tasks due to a low availability of hypotheses about complex rules? The results showed that, (a) the hypothesis hierarchy as revealed in the present experiments was in general agreement with earlier results. However, few nonlinear hypotheses were observed, and other rules than functional rules were observed, (b) The difficulties subjects have to learn complex rules in CPL-tasks do not seem to be caused by low availability of rules.Finally, some suggestions are given for how the SJT-paradigm should be deve­loped. Specifically, it is suggested that the effects of emotional factors should be given more attention, and that the paradigm should be turned into a more general hypothesis testing model
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  • Andersson, Barbro, 1940- (författare)
  • Analysis of plant growth regulating substances
  • 1982
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Natural plant growth regulators (phytohormones) are a group of organic compounds which, in very small amounts, act as regulators of physiological processes in plants.Methods were developed for the analysis of phytohormones in samples from Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris (L.) Karst»). Identification of abscisic acid, 3-indoleacetic acid, gibbe-rellin Ag and the conjugate N-(3-indoleacetyl)aspartic acid was performed by GC-MS as their methyl esters. A quantitative determination of abscisic acid was made by GC-ECD and this method was also applied to anther samples of Anemone canadensis. 3-Indole-acetic acid and N-(3-indoleacetyl)aspartic acid were quantified by reversed-phase HPLC and spectrofluorimetric detection. Dichlorophene, used as a growth regulator in containerized seedlings of pine and spruce, was analysed by GC-MID in peat and paper.
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  • Andersson, Göran, et al. (författare)
  • Electrical resistivity measurements under hydrostatic conditions up to 10 GPa
  • 1984
  • Ingår i: Journal de Physique Colloques vol. 45. - : EDP Sciences. - 0449-1947. ; , s. 379-382
  • Konferensbidrag (refereegranskat)abstract
    • A large scale Bridgman anvil system has been designed. Steel gaskets permit compression of a methanol-ethanol medium over a volume of 500-250 mm3. Up to 12 wires have been used to contact specimens. The system has so far served up to 7.5 GPa, with anvils made of ASP tool steel. The transition Bi III-V was found to occur at a lower pressure than the recommended average. The electrical resistance of copper was measured up to 6 GPa under hydrostatic conditions.
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