| 1. |
- Berthomier, M., et al.
(författare)
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Alfven : magnetosphere-ionosphere connection explorers
- 2012
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Ingår i: Experimental astronomy. - Dordrecht : Springer. - 0922-6435 .- 1572-9508. ; 33:2-3, s. 445-489
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Tidskriftsartikel (refereegranskat)abstract
- The aurorae are dynamic, luminous displays that grace the night skies of Earth's high latitude regions. The solar wind emanating from the Sun is their ultimate energy source, but the chain of plasma physical processes leading to auroral displays is complex. The special conditions at the interface between the solar wind-driven magnetosphere and the ionospheric environment at the top of Earth's atmosphere play a central role. In this Auroral Acceleration Region (AAR) persistent electric fields directed along the magnetic field accelerate magnetospheric electrons to the high energies needed to excite luminosity when they hit the atmosphere. The "ideal magnetohydrodynamics" description of space plasmas which is useful in much of the magnetosphere cannot be used to understand the AAR. The AAR has been studied by a small number of single spacecraft missions which revealed an environment rich in wave-particle interactions, plasma turbulence, and nonlinear acceleration processes, acting on a variety of spatio-temporal scales. The pioneering 4-spacecraft Cluster magnetospheric research mission is now fortuitously visiting the AAR, but its particle instruments are too slow to allow resolve many of the key plasma physics phenomena. The Alfv,n concept is designed specifically to take the next step in studying the aurora, by making the crucial high-time resolution, multi-scale measurements in the AAR, needed to address the key science questions of auroral plasma physics. The new knowledge that the mission will produce will find application in studies of the Sun, the processes that accelerate the solar wind and that produce aurora on other planets.
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| 2. |
- Dahlgren, Hanna, et al.
(författare)
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Energy and flux variations across thin auroral arcs
- 2011
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 29:10, s. 1699-1712
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Tidskriftsartikel (refereegranskat)abstract
- Two discrete auroral arc filaments, with widths of less than 1 km, have been analysed using multi-station, multi-monochromatic optical observations from small and medium field-of-view imagers and the EISCAT radar. The energy and flux of the precipitating electrons, volume emission rates and local electric fields in the ionosphere have been determined at high temporal (up to 30 Hz) and spatial (down to tens of metres) resolution. A new time-dependent inversion model is used to derive energy spectra from EISCAT electron density profiles. The energy and flux are also derived independently from optical emissions combined with ion-chemistry modelling, and a good agreement is found. A robust method to obtain detailed 2-D maps of the average energy and number flux of small scale aurora is presented. The arcs are stretched in the north-south direction, and the lowest energies are found on the western, leading edges of the arcs. The large ionospheric electric fields (250 mV m(-1)) found from tristatic radar measurements are evidence of strong currents associated with the region close to the optical arcs. The different data sets indicate that the arcs appear on the boundaries between regions with different average energy of diffuse precipitation, caused by pitch-angle scattering. The two thin arcs on these boundaries are found to be related to an increase in number flux (and thus increased energy flux) without an increase in energy.
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| 3. |
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| 4. |
- Lindblom, Erik, et al.
(författare)
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Dynamic modelling of nitrous oxide emissions from three Swedish sludge liquor treatment systems
- 2016
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 73:4, s. 798-806
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to model the dynamics and validate the results of nitrous oxide (N2O) emissions from three Swedish nitrifying/denitrifying, nitritation and anammox systems treating real anaerobic digester sludge liquor. The Activated Sludge Model No. 1 is extended to describe N2O production by both heterotrophic and autotrophic denitrification. In addition, mass transfer equations are implemented to characterize the dynamics of N2O in the water and the gas phases. The biochemical model is simulated and validated for two hydraulic patterns: (1) a sequencing batch reactor; and (2) a moving-bed biofilm reactor. Results show that the calibrated model is partly capable of reproducing the behaviour of N2O as well as the nitritation/nitrification/denitrification dynamics. However, the results emphasize that additional work is required before N2O emissions from sludge liquor treatment plants can be generally predicted with high certainty by simulations. Continued efforts should focus on determining the switching conditions for different N2O formation pathways and, if full-scale data are used, more detailed modelling of the measurement devices might improve the conclusions that can be drawn.
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| 5. |
- Roseborough, Diana, et al.
(författare)
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Surface composition of industrial metal samples with potential for atmospheric mercury deposition
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Laser Ablation Inductively Coupled Plasma Time of Flight Mass Spectrometry, Auger electron spectroscopy and X-ray photoelectron spectroscopy were used to study atmospherically exposed metal samples for surface mercury concentration at room temperature. The metals were collected from industrial and pre-conditioned sources. In most cases, mercury detection was impossible because the samples were found to be highly contaminated from sources such as oxygen, carbon, chlorine and sulfur. However, the methods were effective at determining surface atoms and bulk substrate atoms that may be surface diffusive. Depth profiling was conducted on the samples that were found to contain mercury.
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| 6. |
- Simpson, N. E., et al.
(författare)
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Biochemical consequences of alginate encapsulation : A NMR study of insulin-secreting cells
- 2006
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Ingår i: Biomaterials. - : Elsevier BV. - 0142-9612 .- 1878-5905. ; 27:12, s. 2577-2586
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Tidskriftsartikel (refereegranskat)abstract
- In this study we explore the biochemical consequences of alginate encapsulation on beta TC3 cells. C-13 NMR spectroscopy and isotopomer analysis were used to investigate the effects of encapsulation on several enzymatic processes associated with the TCA cycle. Our data show statistically significant differences in various enzymatic fluxes related to the TCA cycle and insulin secretion between monolayer and algainate-encapsulated cultures. The principal cause for these effects was the process of trypsinization. Embedding the trypsinized cells in alginate beads did not have a compounded effect on the enzymatic fluxes of entrapped cells. However, an additional small but statistically significant decrease in insulin secretion was measured in encapsulated cells. Finally, differences in either enzymatic fluxes or Qlucose consumption as a function of bead diameter were not observed. However, differences in T-2, assessed by H-1 NMR microimaging, were observed as a function of bead diameter, suggesting that smaller beads became more organized with time in culture, while larger beads displayed a looser organization.
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| 7. |
- Whiter, D. K., et al.
(författare)
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Relative brightness of the O+(2D-2P) doublets in low-energy aurorae
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 797:1, s. 64-
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Tidskriftsartikel (refereegranskat)abstract
- The ratio of the emission line doublets from O+ at 732.0 nm (I-732) and 733.0 nm (I-733) has been measured in auroral conditions of low-energy electron precipitation from Svalbard (78.degrees 20 north, 15.degrees 83 east). Accurate determination of R = I-732/I-733 provides a powerful method for separating the density of the O+ P-2(1/2,3/2)o levels in modeling of the emissions from the doublets. A total of 383 spectra were included from the winter of 2003-2004. The value obtained is R = I-732/I-733 = 1.38 +/- 0.02, which is higher than theoretical values for thermal equilibrium in fully ionized plasma, but is lower than reported measurements by other authors in similar auroral conditions. The continuity equations for the densities of the two levels are solved for different conditions, in order to estimate the possible variations of R. The results suggest that the production of ions in the two levels from O(P-3(1)) and O(P-3(2)) does not follow the statistical weights, unlike astrophysical calculations for plasmas in nebulae. The physics of auroral impact ionization may account for this difference, and therefore for the raised value of R. In addition, the auroral solution of the densities of the ions, and thus of the value of R, is sensitive to the temperature of the neutral atmosphere. Although the present work is a statistical study, it shows that it is necessary to determine whether there are significant variations in the ratio resulting from non-equilibrium conditions, from auroral energy deposition, large electric fields, and changes in temperature and composition.
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