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- Bergquist, Bjarne
(författare)
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Statistical approaches to PM steel process improvements
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased performance:cost ratios for PM steel components is vital if current growth rate of market shares of such components versus competing technology is to be sustained. Both performance and cost of components are affected by variation of component properties. This work focuses on variation; where major variation sources lie and measures to circumvent problems that could be taken.A design-of-experiments approach was used to identify the most important green compact variations and interactions of a Fe-P alloy. The results show that the highest impact energies are obtained for high green densities, and without graphite addition. It is concluded that sintered density is the reason for the observed impact energies. Variation sources controlling phosphorus content and added graphite content are of concern since they affect the dimensional stability. Prospects for a robust sintering operation of same alloy is investigated. The objective is to find a setting of the variables investigated to maintain high tensile strength and proof stress without loss of dimensional stability, tensile elongation or impact energy. In the study, an endothermic sintering atmosphere was better for the robustness of the tested properties. A mechanism for the occasionally brittle behavior of the system is concluded to be loss of grain boundary cohesion due to decarburization.Possibilities for improved particle size distribution of water atomized powder are studied experimentally and by simulations. The most important variable for all studied responses is water pressure. Higher melt temperatures reduce particle size due to decreased viscosity. Large sulfur additions reduce particle size and this is an effect of reduced surface tension. Narrower size distributions were obtained for powder atomized with aluminum additions and for increased melt temperatures. A model for particle size for water atomization is presented and used in simulations.
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| 2. |
- Lindahl, Olof
(författare)
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The impression technique for assessment of tissue oedema : instrumentation, evaluation and applications
- 1993
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An instrument for clinical noninvasive assessment of tissue oedema based on an impression method was developed. The method measures and evaluates the decaying force, due to translocation of tissue fluid, during mechanical compression of any site of tissue. We applied the impression method on physical models, animal models, and patients. Significant parameters for the assessment of tissue oedema that estimated tissue fluid translocation and tissue pressure could be derived from the registered impression force curves.Accuracy was determined theoretically and reproducibility was estimated on plastic foam. We described the clinical procedure for the instrument, and preliminary results from patients with chronic pitting oedema showed that the instrument detected larger fluid translocation on oedematous sites than on non-oedematous sites. We concluded that the instrument was acceptable for accurate measurements on biological tissue.Evaluation was performed in a rat testis model in which testicular interstitial fluid volume could be changed both artificially by 30-min infusions of different fluids with different fluid resistance properties, and pharmacologically by administration of hormones. We found that tissue pressure increased with infused fluid volume, and changes as small as 16 μl (7 % of total testis interstitial fluid volume) could be detected. Fluid translocation changed depending upon the infused fluid's resistance properties. Hormone-induced changes in rat-testis oedema altered both fluid translocation and tissue pressure. Discrete changes in vascular permeability were monitored.Investigation of generalised oedema in patients suffering from burn injury showed that tissue fluid translocation increased up to a maximum value after 6 days postburn and declined thereafter. We found tissue pressure to be relatively high during the first 7 days postburn as compared with 3-week postburn values. Force curve analysis suggested a flux of water-like fluid from the vasculature to the interstitial space during the first 6 days postburn. The course of postburn tissue swelling could be followed and estimated with the impression technique.Comparison with a new tactile sensor that measured physical properties of soft tissue showed that both methods detected changes in silicone hardness/softness and in hormone-induced changes of rat-testis interstitial fluid. We concluded that impression force estimated hardness of soft tissue, which can be helpful when investigating hardness of oedematous tissue.
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| 5. |
- Wetterlund, Elisabeth, 1978-
(författare)
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System studies of forest-based biomass gasification
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bioenergy will play an important role in reaching the EU targets for renewable energy. Sweden, with abundant forest resources and a well-established forest industry, has a key position regarding modern biomass use. Biomass gasification (BMG) offers several advantages compared to biomass combustion-based processes, the most prominent being the possibility for downstream conversion to motor fuels (biofuels), and the potential for higher electrical efficiency if used for electricity generation in a biomass integrated gasification combined cycle (BIGCC). BMG-based processes in general have a considerable surplus of heat, which facilitates integration with district heating or industrial processes.In this thesis integration of large-scale BMG, for biofuel or electricity production, with other parts of the energy system is analysed. Focus is on forest-based biomass, with the analysis including techno-economic aspects as well as considerations regarding effects on global fossil CO2 emissions. The analysis has been done using two approaches – bottom-up with detailed case studies of BMG integrated with local systems, and top-down with BMG studied on a European scale.The results show that BMG-based biofuel or electricity production can constitute economically interesting alternatives for integration with district heating or pulp and paper production. However, due to uncertainties concerning future energy market conditions and due to the large capital commitment of investment in BMG technology, forceful economic support policies will be needed if BMG is a desired route for the future energy system, unless oil and electricity prices are high enough to provide sufficient incentives for BMG-based biofuel or electricity production. While BMG-based biofuel production could make integration with either district heating or pulp and paper production economically attractive, BIGCC shows considerably more promise if integrated with pulp and paper production than with district heating.Bioenergy use is often considered CO2-neutral, because uptake in growing plants is assumed to fully balance the CO2 released when the biomass is combusted. As one of the alternatives in this thesis, biomass is viewed as limited. This means that increased use of bioenergy in one part of the energy system limits the amount of biomass available for other applications, thus increasing the CO2 emissions for those applications. The results show that when such marginal effects of increased biomass use are acknowledged, the CO2 mitigation potential for BMG-based biofuel production becomes highly uncertain. In fact, most of the BMG-based biofuel cases studied in this thesis would lead to an increase rather than the desired decrease of global CO2 emissions, when considering biomass as limited.
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