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- Bejhed, Johan, 1973-
(författare)
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Fluidic Microsystems for Micropropulsion Applications in Space
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spacecraft on interplanetary missions or advanced satellites orbiting the Earth all require propulsion systems to complete their missions. Introducing microelectromechanical systems technology to the space industry will not only reduce size and weight of the propulsion system, but can also increase the performance of the mission.Fluid handling systems are used in chemical and electric propulsion. Some components incorporated in a fluidic handling system are presented and evaluated in this work.Microsystems are very sensitive to contamination. Reliable, robust, and easily integrated filters were modeled, manufactured, and experimentally verified.A fluid connector, designed to withstand large temperature variations and aggressive propellants was manufactured and characterized. Similar designs was also be used as a thermally activated minute valve.The feasibility of a cold gas system for precise attitude control has been demonstrated. Steps towards improving the performance (from specific im-pulse 45 s) have been taken, by the integration of suspended heater elements.For electric propulsion, two thermally regulated flow restrictors have been characterized. These devices can fine-tune the propellant flow to e.g. an ion engine.A single-use valve using a soldered seal has also been successfully dem-onstrated within a pressure range of 5 to 100 bar.The microsystem-based propulsion systems of tomorrow’s spacecraft need to be demonstrated in space, in order to gain necessary credibility.
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- Dahlgren, Johan Petter, 1978-
(författare)
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Linking plant population dynamics to the local environment and forest succession
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Linking environmental variation to population dynamics is necessary to understand and predict how the environment influences species abundances and distributions. I used demographic, environmental and trait data of forest herbs to study effects of spatial variation in environmental factors on populations as well as environmental change in terms of effects of forest succession on field layer plants. The results show that abundances of field layer species during forest succession are correlated with their functional traits; species with high specific leaf area increased more in abundance. I also found that soil nutrients affect vegetative and flowering phenology of the forest herb Actaea spicata. The effect of nutrients shows that a wider range of environmental factors than usually assumed can influence plant phenology. Moreover, local environmental factors affected also the demography of A. spicata through effects on vital rates. An abiotic factor, soil potassium affecting individual growth rate, was more important for population growth rate than seed predation, the most conspicuous biotic interaction in this system. Density independent changes in soil potassium during forest succession, and to a lesser extent plant population size dependent seed predation, were predicted to alter population growth rate, and thereby the abundance, of A. spicata over time. Because these environmental factors had effects on population projections, they can potentially influence the occupancy pattern of this species along successional gradients. I conclude that including deterministic, as opposed to stochastic, environmental change in demographic models enables assessments of the effects of processes such as succession, altered land-use, and climate change on population dynamics. Models explicitly incorporating environmental factors are useful for studying population dynamics in a realistic context, and to guide management of threatened species in changing environments.
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- Degerstedt, Oliver, et al.
(författare)
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Quantitative imaging of doxorubicin diffusion and cellular uptake in biomimetic gels with human liver tumor cells
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Novel tumor-on-a-chip approaches are increasingly used to investigate tumor progression and potential treatment options. To improve the effect of any cancer treatment it is important to have an in-depth understanding of drug diffusion, penetration across the tumor extracellular matrix and cellular uptake. In this study, we have developed a miniaturized chip where drug diffusion and cellular uptake in different hydrogel environments can be quantified at high resolution using live imaging. Diffusion of doxorubicin was reduced in a biomimetic hydrogel mimicking tissue properties of cirrhotic liver and early stage hepatocellular carcinoma (362 ± 109 µm2/s) as compared to an agarose gel (571 ± 145 µm2/s, p = 0.0085). The diffusion was further lowered to 164 ± 33 µm2/s (p = 0.0023) by preparing the biomimetic gel in cell media instead of phosphate buffered saline. The addition of liver tumor cells (Huh7 or HepG2) to the gel, at two different densities, did not significantly influence drug diffusion. Clinically relevant and quantifiable doxorubicin concentration gradients (1-20 µM) were established in the chip within one hour. Intracellular increases in doxorubicin fluorescence correlated with decreasing fluorescence of the DNA-binding stain Hoechst 33342, and based on the quantified intracellular uptake of doxorubicin an apparent cell permeability (9.00 ± 0.74 x 10-4 µm/s for HepG2) was determined.
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- Eriksson, Daniel, et al.
(författare)
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Tic-Tac-Textiles: A waiting game
- 2010. - 11
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Ingår i: IT+Textiles. - (2010 reprint) Borås, Sweden: Centre for Textile Research. (2005 first edition) Helsinki: IT Press/Edita : .. - 9518267936 ; , s. 66-75
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- In light of the imminent arrival of ambient intelligence and smart textiles, the design of computational and textile things are rapidly converging. Substantial attention is directed towards the new technical possibilities of these new materials, but less effort seems to be put into the challenging task of re-thinking the use of textiles and computational technology as design materials on the basis of the complex mixture of traditions, perspectives, concepts and methods that result from such convergence. These challenges and opportunities inspired the IT+Textiles design research program. Trying to dissolve the distinction between technologies and design materials, we have combined textile and interaction design, textile and electrical engineering, philosophy and the behavioural sciences to find new approaches to issues of use and context, form and aesthetics, practice and theory. In this book, we describe the collection of materials, examples, methods and concepts we have developed in our investigation of this emerging design space.
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- Eriksson, Johan, 1956-
(författare)
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Polybrominated diphenyl ethers and Tetrabromobisphenol A : Chemical synthesis, X-ray crystallography and Photochemical degradation
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the 1960s’ several manmade chemicals were detected in the environment, far from their sources. The most well known, and most likely those with the largest impact on the society, were DDT and its related compounds, and PCBs. These anthropogenic compounds were characterised as persistent organic pollutants (POPs). Following these POPs, several other chemicals have found their way to the environment. Over the last two decades, brominated flame retardants (BFRs) have become a matter of concern. Among all BFRs being commercially produced, tetrabromobisphenol A (TBBPA) and polybrominated diphenyl ethers (PBDEs) are the ones with the largest annual production. TBBPA is a very well defined compound while PBDEs consist of a large number of isomers and homologues (congeners). TBBPA does not seem to accumulate in biota as the PBDEs do, but is still of concern since it is found in e.g. sediments. The PBDEs can reach accumulation levels up in the ppm range. Still there is a lack of basic data for both TBBPA and PBDEs. Hence the present thesis is aimed to fill some of the data gaps by pursuing work on 1) photochemical degradation of TBBPA, some related compounds, and PBDEs; 2) synthesis of PBDE congeners and of TBBPA degradation products and 3) structural identifications of a selected set of BFRs by X-ray crystallography.An apparatus was designed for carrying out photochemical degradation test of chemicals in general but in particular for BFRs. Quantum yield, rate of degradation and to some extent, identification of degradation products were performed on TBBPA, the corresponding chlorinated compound and a number of TBBPA degradation products and on 15 single PBDE congeners. In order to make this work possible all three nonaBDE isomers were synthesised via a reductive pathway applying sodium borohydride as a reducing agent. The three nona-BDEs were all characterised by X-ray crystallography. The results of the photochemical degradation of TBBPA in water show a rapidly degradable compound also at pH’s that are environmentally relevant. Hence it is likely that TBBPA is not transported long distances, when exposed to sunlight, without undergoing photochemical degradation. It is notable that the TBBPA is degraded through cleavage between the two phenol rings. When the method was applied to study quantum yields and rate constants for the reaction of PBDE congeners it is evident that the decabromodiphenyl ether (BDE-209) is rapidly transformed. The reaction rate differ drastically from PBDEs with four or five bromine substituents that have very long half-lives when subjected to UV-light under the same conditions as for BDE-209. Lower brominated diphenyl ethers and polybrominated dibenzofurans were identified as PBDE degradation products. The synthesis of PBDEs and of TBBPA degradation products expanded the study as did the X-ray structure identifications.
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