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Träfflista för sökning "LAR1:miun ;lar1:(kth);srt2:(1990-1994)"

Sökning: LAR1:miun > Kungliga Tekniska Högskolan > (1990-1994)

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2.
  • Brunnström, Kjell, et al. (författare)
  • Scale and Resolution in Active Analysis of Local Image Structure
  • 1990
  • Ingår i: Image and Vision Computing. - : Elsevier. ; 8:4, s. 289-296
  • Tidskriftsartikel (refereegranskat)abstract
    • Focus-of-attention is extremely important in human visual perception. If computer vision systems are to perform tasks in a complex, dynamic world they will have to be able to control processing in a way that is analogous to visual attention in humans. Problems connected to foveation (examination of selected regions of the world at high resolution) are examined. In particular, the problem of finding and classifying junctions from this aspect is considered. It is shown that foveation as simulated by controlled, active zooming in conjunction with scale-space techniques allows for robust detection and classification of junctions.
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3.
  • Holmberg, Erland, et al. (författare)
  • Reaction conditions for the resolution of 2-methylalkanoic acids in esterification and hydrolysis with lipase from Candida cylindracea
  • 1991
  • Ingår i: Applied Microbiology and Biotechnology. - 0175-7598. ; 35:5, s. 572-578
  • Tidskriftsartikel (refereegranskat)abstract
    • We have demonstrated resolution of 2-methylalkanoic acids using lipase from Candida cylindracea as a catalyst. The resolution of 2-methyldecanoic acid was more successful than that of 2-methylbutyric acid both by esterification and hydrolysis. This indicates that the resolution of the acid is dependent on the chain length of the acid moiety. The chain length of the alcohol moiety of the ester affected the resolution of the long-chain acid only. Using esterification, (R)-2-methyldecanoic acid was produced in an enantiomeric excess (e.e.) of 95% (E = 40). If the enantiomeric ratio is low (E = 3.6), as in the resolution of 2-methylbutyric acid, esterification combined with a high equilibrium conversion could be used to yield the remaining acid in a high e.e. In the hydrolytic reactions, the e.e. and the equilibrium conversion were dependent on the pH and the presence of CaCl2. When octyl 2-methyldecanoate was hydrolysed at pH 8.0 in the presence of CaCl2, the (S)-acid was formed with an e.e. of 80% (E = 9), but when the hydrolysis was carried out at pH 7.5 without CaCl2, a very low e.e. and a low equilibrium conversion were observed. The latter conditions allowed the esterification of 2-methyldecanoic acid with 1-octanol even in aqueous medium.
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4.
  • Högberg, Hans-Erik, et al. (författare)
  • Biocatalysis as a useful tool in pheromone synthesis. Enantiomerically pure building blocks from baker's yeast reductions and enzyme catalysed resoluti
  • 1994
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 22:3, s. 591-606
  • Tidskriftsartikel (refereegranskat)abstract
    • Biocatalytical methods are presented which provide useful building blocks for pheromone synthesis. Examples of the utility of this approach are the preparation of building blocks for the synthesis of stereochemically pure isomers of pine sawfly pheromones and some other pheromones. Enantiom- erically pure ( 98% ee) 2-methyl-1-alkanols 2 were obtained via baker's yeast reduction of suitable α,β-unsaturated aldehydes, and by using lipases from Pseudomonas to effect resolution by transesterification of suitable racemic precursors to 2-methyl-1-alkanols 2 which gave high enantiomeric ratios E > 100. The resolution by esterification mediated by lipase from Candida rugosa of racemic 2-methylalkanoic acids also gave high enantiomeric ratios E> 100 after having improved the reaction conditions by regulating water activity, by choice of the appropriate complimentary substrate alcohol and by adjusting the initial equivalents of the latter present at the start. Also discussed is the separation of diastereomers of diprionol 1, which is naturally occurring in the pine sawfly Neodiprion sertifer, where it is the direct precursor of its pheromone.
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