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- Johlander, Andreas, 1990-, et al.
(author)
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Electron Heating Scales in Collisionless Shocks Measured by MMS
- 2023
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In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 50:5
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Journal article (peer-reviewed)abstract
- Electron heating at collisionless shocks in space is a combination of adiabatic heating due to large-scale electric and magnetic fields and non-adiabatic scattering by high-frequency fluctuations. The scales at which heating happens hints to what physical processes are taking place. In this letter, we study electron heating scales with data from the Magnetospheric Multiscale (MMS) spacecraft at Earth's quasi-perpendicular bow shock. We utilize the tight tetrahedron formation and high-resolution plasma measurements of MMS to directly measure the electron temperature gradient. From this, we reconstruct the electron temperature profile inside the shock ramp and find that the electron temperature increase takes place on ion or sub-ion scales. Further, we use Liouville mapping to investigate the electron distributions through the ramp to estimate the deHoffmann-Teller potential and electric field. We find that electron heating is highly non-adiabatic at the high-Mach number shocks studied here.Plain Language SummaryShock waves appear whenever a supersonic medium, such as a plasma, encounters an obstacle. The plasma, which consists of charged ions and free electrons, is heated by the shock wave through interactions with the electromagnetic fields. In this work, we investigate how electrons are heated at plasma shocks. A key parameter to electron heating is the thickness of the layer where the heating takes place. Here, we use observations from the four Magnetospheric Multiscale spacecraft that regularly cross the standing bow shock that forms when the supersonic plasma, known as the solar wind, encounters Earth's magnetic field. We find that the thickness of the shock is larger than previously reported and is on the scales where ion physics dominate. We also find that the electron heating deviates significantly from simple adiabatic heating.
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- Lucas, Carlos, et al.
(author)
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High-temperature air and steam gasification of densified biofuels
- 2004
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In: BIOMASS BIOENERG. - : Elsevier BV. ; , s. 563-575
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Conference paper (peer-reviewed)abstract
- An experimental study was carried out to investigate gasification of densified biofuels using highly preheated air and steam as a gasifying agent. Preheat of air and steam is realised by means of the newly developed high-cycle regenerative air/steam preheater. Use of highly preheated feed gas provides additional energy into the gasification process, which enhances the thermal decomposition of the gasified solids. For the same type of feedstock the operating parameters, temperature, composition and amount of gasifying agent, were varied over a wide range. Results of experiments conducted in. a high-temperature air/steam fixed bed updraft gasifier show the capability of this technology of maximising the gaseous product yield as a result of the high heating rates involved, and the efficient tar reduction. Increase of the feed gas temperature reduces production of tars, soot and char residue as well as increases heating value of the dry fuel gas produced. Overall, it has been seen that the yield and the lower heating value of the dry fuel gas increase with increasing temperature.
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- Napp, Margus, et al.
(author)
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Adaptive ventilation for climate control in a medieval church in cold climate
- 2016
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In: The International Journal of Ventilation. - : Informa UK Limited. - 1473-3315 .- 2044-4044. ; 15:1, s. 1-14
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Journal article (peer-reviewed)abstract
- Old medieval churches hold objects of great historical and cultural value: organs, altars, paintings. But they have no systems for indoor climate control or the church may be heated only at services. These conditions are inadequate for the preservation of cultural heritage. The objective of this paper is to assess an adaptive ventilation (AV) solution in a church for reduction of the relative humidity (RH) in an unheated church to prevent mould growth and disintegration of wooden parts. The operation principle of the system is to ensure ventilation in the church when water vapour content in the outdoor air is lower than that indoors, to lower the RH in the church. A case study in Hangvar Church in Gotland, Sweden, was conducted to test the performance of AV to reduce the RH in the church. Field measurements showed that AV has a positive impact on the indoor RH of the church. During the measurement period without climate control, the RH in the church was higher than 70% of 98% of the time; with AV, the indoor RH was higher than 70% only 78% of the time. Building simulation was carried out to test the performance and energy consumption of AV under different conditions. The simulations showed that auxiliary heating and airflow rate both have high impact on the system performance. The higher the heating power, the more effective the system is; thus, lower airflow rates are needed. Infiltration has also high impact on the system performance: the lower the infiltration rate, the better the AV performance is.
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