| 1. |
- Persson, Anders
(författare)
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Consumption patterns and excretion in aquatic food websenrichment
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis links biogeochemical cycling to classical ecology. Predictions derived from food chain theory, based on Lotka-Volterra type of interactions, were tested in aquatic environments with the main hypothesis that consumers affect lower levels of organization by both predation and excretion of limiting nutrients. From tank experiments it was concluded that predation may affect prey populations in agreement with food chain theory, but that species replacement within the prey community confounds predictions based on trophic level dynamics. By describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels. Results from experimental studies showed that the effects of fish on nutrient cycling could provide a complement to zooplanktivory in explaining algae dynamics. It was argued that the concept of carrying capacity, as used in food chain theory, prevents an adequate understanding of cascading trophic interactions. Hence, producer growth rate is determined by the availability of nutrients, which is partly set by the recycling by consumers, rather than the total amount of nutrients present in a system. Determination of the relative importance of phosphorus (P) excretion by fish in comparison to other P sources was performed for a hypertrophic lake. The results showed that excretion by fish may be of the same magnitude as the external load, but it did only explain a minor part of the internal load. In contrast, model simulations of the P dynamics of a hypertrophic lake showed that excretion of P by fish could be a significant part of the total P supply to phytoplankton growth, mostly due to translocation of P from the sediment to the water by benthic feeding fish. The simulations suggested that P was routed along the pelagic food chain to a larger extent if omnivorous fish biomass was reduced (biomanipulation), whereas the amount of phosphorus routed via the sediment and benthivorous fish decreased after biomanipulation. However, field studies in a hypertrophic lake showed that the overlap in resource utilization within the fish community was considerable, resulting in compensatory responses when the fish community was manipulated. Such responses may offset the anticipated effects of biomanipulation, a method proposed for the restoration of eutrophicated lakes.
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| 2. |
- Persson, Anders
(författare)
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"Försonarn vid sitt bröst, en stjernkrönt Qvinna" : jungfru- och moderstematiken hos C.J.L. Almqvist och P.D.A. Atterbom
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present Ph.D. dissertation proceeds from poetry on the theme of the Virgin Mary which blossomed for several decades during the Romantic era and is dedicated to the use of its virgin and maternal themes in the work of C.J.L. Almqvist and P.D.A. Atterbom.The first chapter discusses Almqvist's description of the perfect complementary unity of male and female - and divine and human - in his juvenile work Murnis (1819). In this sexually explicit work, theology and religious experience is eroticized while sexuality is sacralized. In Amorina (1822), a burgeoning transformation of Almqvist's "wholeness" vision can be observed. While wholeness can only be achieved through the perfect union of man and woman in Murnis, Amorina emerges as a perfect figure in and of herself.In the second chapter, the figure of Tintomara in Drottningens juvelsmycke (1835) is analyzed. In this novel, the dream of the merging of "twoness" into "oneness" seems to have been abandoned in favour of an experiment, wherein the unity of masculinity and femininity is realized in one single individual, the androgynous Tintomara. Despite the fact that the novel's androgynous idea is formulated with direct reference to Plato's Symposium, the significance of Jakob Böhme's speculations on androgyny are also emphasized here.The third chapter deals with the poetry about Mary written by Almqvist, especially Isidoros av Tadmor and Marjam (1839). Almqvist's image of Mary is characterized in terms of "perfection" and "complexity". In Marjam, this complexity is expressed both through the drama's upholding of the paradoxical content of the dogma of the Virgin Mary and the main theme of the double drama, the tension between the earthly and the eschatological family.The fourth and fifth chapters of this dissertation are dedicated to the maternal theme in the work of P.D.A. Atterbom. I proceed from the hypothesis that the transformations which the figure of Mary undergoes reflect a tension between Romantic syncretism and classic Christianity. I analyze four texts by Atterbom in which this conflict is particularly apparent.In Atterbom's prose draft for his fairy play Fågel blå (1818), as in his sonnets dedicated to Mary (1817-18), I discern a shift away from Romantic syncretism and toward more Biblical patterns. In the fairy play Lycksalighetens ö (1824-27), this tension emerges anew in the two Nyx epiphanies in the piece. The elegy "Ave Maria" (1831) comprises the clearest example of the shift in Atterbom's writing toward classical Mariology.In the conclusion, Almqvist's and Atterbom's respective thematic use of Mary - where she is portrayed as a complex, transgressive figure - is contrasted with an early example of Swedish Biedermeier poetry, Carl von Zeipel's "Jesus Christus. Evangeliska romanser" (1822), where Mary is placed in the context of the little, idyllic family.
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| 3. |
- Persson, Anders L., 1963
(författare)
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Filler Controlled Morphology in Polymer Blends
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The morphology of a polymer blend can be altered very dramatically when a filler is added. Depending on the mutual interactions of the polymers and their individual interactions with the filler, many different filler distributions are possible. Inverse gas chromatography was the key tool to quantify the polymer-solid interaction potentials in terms of Lewis acid-base properties. These forecasted interaction strengths at the whisker-polymer interface coincided with the observed preferential adsorption. Selective adsorption of the minority polymer component made it form three-dimensional web structures with the whiskers in the matrix of the majority component. This ability to form co-continuous structures was quantified as electrical conductivity of blends containing the intrinsically conducting polymer poly(3-octyl thiophene). For a properly selected majority polymer the conductivity of the three-component composite increased several orders of magnitude. Interactions between polyamide-6 and the whisker surface are strong enough to perturb crystallization in a zone by the interface. Selective adsorption was exploited to create virtually highly filled composites as a non-interacting polymer was added as a processing aid. That polymer was extracted and left extreme composites comprising only whiskers and polamide-6 interphase. In order to collect data for derivation of a crystallinity gradient by the filler surface, the ratio of polyamide-6 to processing aid was varied. Once a beneficial phase morphology has been achieved, successive processing can easily rupture it unless its rheological limitations are considered. For example, the high shear rates created during injection molding ruined the co-continuous structure created during compounding of poly(styrene-co-acrylonitrile)/polyamide-6/whiskers. However, the ruptured morphology could have been restored by annealing at the processing temperature. In blends with components of comparable polymer-whisker interaction strength and substantial viscosity difference the whiskers are absorbed by the phase that minimizes the viscosity of the three-component system. Accordingly the whiskers were absorbed by the high viscosity phase unless supporting transformation of the minority low viscosity phase from dispersed to continuous. Such transformations and other shear induced morphological changes were followed as viscoelastic changes during steady and/or harmonic shear. This methodology has the prospects to become a valid instrument to optimize the processing route of blends and multicomponent systems.
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| 4. |
- Persson, Anders
(författare)
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Stereo- and enantioselective synthesis using palladium, ruthenium and enzyme catalysis
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis the use of palladium and ruthenium, with the latter in combination with enzymes, as selective catalysts in the transformation of organic substrates is discussed. The thesis is divided into two parts.The first part concerns the use of palladium(II) as a catalyst for the 1,4-oxidation of conjugated dienes using allylsilanes and carboxylic acids as internal nucleophiles. The reaction employing allylsilanes has been studied with two different reoxidation systems, p- benzoquinone and copper(II) chloride. By using the former oxidant highly stereoselective reactions took place, whereas the use of copper(II) chloride gave mixtures of isomeric products. It was demonstrated,by isolation and characterization of (p- allyl)palladium intermediates, that the allylsilane reacted as a nucleophile on the diene. The reactions using carboxylic acids as nucleophiles were conducted with the internal nucleophile connected to the side chain in the 2-position of the diene, giving six-membered lactones in good yields. High stereoselectivities across the diene were obtained, but in some cases the regioselectivity was lower and the 1,2-addition product wasformed.In the second part, studies of the combination of a ruthenium-catalyzed racemization with an enantioselective enzymatic acylation, in order to achieve a dynamic kinetic resolution ofsecondary alcohols, are described. It was found that the combination of a lipase from Candida antarctica, a stable ruthenium(II)-catalyst and a specifically designed acyl donor gave enantiomerically pure secondary acetates in good yields. Application of the reaction to symmetric diols gave enantiomerically pure diacetates in good yields and with high diastereoselectivities.
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