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- Hoel, Anders, 1969-
(författare)
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Electrical Properties of Nanocrystalline WO3 for Gas Sensing Applications
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tungsten trioxide is a material with a variety of application areas. For example, the material is used within thin film technologies as electrochromic material in smart windows, as electrochemically functional material in thermal control applications or as active layer in gas sensing application. Metal-oxide semiconductor gas sensors are of significant interest to detect toxic and hazardous gases. The use of small and cheep sensors is preferable since a large number of sensors easily can be placed at different sites to monitor the concentration of different species without involving huge investments.In this work, WO3 nanoparticle films were produced using an advanced gas deposition unit for gas sensing applications. The structure of the WO3 nanoparticle films was determined using X-ray diffraction, neutron scattering, X-ray photoelectron spectroscopy, elastic recoil detection analysis and electron microscopy. The as deposited films consist of sub-stoichiometric WO3 and exhibit a large degree of porosity, which together with the small particle size of about 5 nm results in a large surface area and therefore excellent prospects for gas sensor applications. Investigations on the optical properties and temperature dependence of the resistance indicate hopping conduction in the WO3 films. The bandgaps for tetragonal and monoclinic WO3 were found to be direct, which is in accordance with band structure calculations.Sensor properties were investigated using resistance measurements upon test gas exposures. The experiments were performed at fixed operating temperatures as well as on temperature modulated sensors. The films of WO3 showed excellent sensitivity to H2S gas and selectivity to other gases. The responses of temperature modulated sensors were further analyzed using mathematical transformations and pattern recognition methods whereby different gases could be distinguished.We also present a sensing technique using conduction noise as a tool for detection of alcohol vapor. The relative change of the noise, due to the inserted alcohol, can be as large as two orders of magnitude.
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- Solver, Torbjörn, et al.
(författare)
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Comparison of incentives for distribution system reliability in performance-based regulation
- 2004
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Ingår i: PROCEEDINGS OF THE 2004 IEEE INTERNATIONAL CONFERENCE ON ELECTRIC UTILITY DEREGULATION, RESTRUCTURING AND POWER TECHNOLOGIES, VOLS 1 AND 2. - NEW YORK : IEEE. - 0780382374 ; , s. 485-490
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Konferensbidrag (refereegranskat)abstract
- In recent years as many European electricity markets are deregulated, Network Utilities are liberalized and privatized. Consequently, the economic regulations of Distribution Utilities, which is applied due to the monopoly nature of network activities, have switched from cost-based regulation to Performance Based Regulation (PBR). PBR gives Distribution Utilities incentives to reduce costs. However, increased cost efficiency may lead to decrements in distribution quality, therefore is quality regulation necessary. In this paper the basic outlines of Distribution Utility regulation in Sweden, Norway, Spain and the Netherlands are compared. Focus in the comparison lie on the quality regulation framework and the incentives brought upon the Distribution Utilities based on the PBR-models' framework.
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- Torppa, Kaisa
(författare)
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Earthworm and arbuscular mycorrhizal communities in agricultural soils : management of key soil organisms for sustainable agriculture
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intensive agriculture is detrimental to soil biodiversity and functioning. Promoting communities of key soil organisms, such as earthworms and arbuscular mycorrhizal (AM) fungi, may help improve agricultural sustainability by replacing inputs with ecosystem services. In this thesis, I explore ways to manage earthworm communities for improved soil functioning via adjusted agricultural practices, promotion of source habitats in the landscape, and inoculation. I also explore the effects of soil compaction on AM fungal symbiosis in wheat varieties, and test application of grassland soil as a method to increase AM fungal diversity in agricultural soils. I show that diverse earthworm communities and bioturbation can be promoted by reducing tillage intensity and total earthworm densities can be increased via diversifying crop rotations. Moist and fertile semi-natural grasslands with high small-scale habitat heterogeneity may serve to sustain earthworm diversity in agricultural landscapes. Inoculation with commercially obtained Lumbricus terrestris earthworms may help restore populations of this tillage sensitive species and improve wheat growth but the long-term establishment of these worms is uncertain. Application of grassland soil may increase AM fungal diversity in agricultural soils but this may not be reflected in AM fungal taxa colonizing wheat roots. I also show that soil compaction differently affects AM colonization in wheat varieties. Further research needs to identify which earthworm and AM fungal community properties best result in functional benefits under different conditions. Nevertheless, I show that earthworm and AM fungal communities can be promoted in various ways, individually or in combination, suggesting potential to enhance functional effects of these key organisms in agricultural soils.
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