| 1. |
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- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:1
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Forskningsöversikt (refereegranskat)
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| 2. |
- Bombarda, F., et al.
(författare)
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Runaway electron beam control
- 2019
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:1
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Krasilnikov, A., et al.
(författare)
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Evidence of 9 Be + p nuclear reactions during 2ω CH and hydrogen minority ICRH in JET-ILW hydrogen and deuterium plasmas
- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:2
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Tidskriftsartikel (refereegranskat)abstract
- The intensity of 9Be + p nuclear fusion reactions was experimentally studied during second harmonic (2ω CH) ion-cyclotron resonance heating (ICRH) and further analyzed during fundamental hydrogen minority ICRH of JET-ILW hydrogen and deuterium plasmas. In relatively low-density plasmas with a high ICRH power, a population of fast H+ ions was created and measured by neutral particle analyzers. Primary and secondary nuclear reaction products, due to 9Be + p interaction, were observed with fast ion loss detectors, γ-ray spectrometers and neutron flux monitors and spectrometers. The possibility of using 9Be(p, d)2α and 9Be(p, α)6Li nuclear reactions to create a population of fast alpha particles and study their behaviour in non-active stage of ITER operation is discussed in the paper.
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| 24. |
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- 2018
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 58:9
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Tidskriftsartikel (refereegranskat)
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| 25. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 26. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 27. |
- Kulmala, M., et al.
(författare)
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General overview: European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) - integrating aerosol research from nano to global scales
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:24, s. 13061-13143
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we describe and summarize the main achievements of the European Aerosol Cloud Climate and Air Quality Interactions project (EUCAARI). EUCAARI started on 1 January 2007 and ended on 31 December 2010 leaving a rich legacy including: (a) a comprehensive database with a year of observations of the physical, chemical and optical properties of aerosol particles over Europe, (b) comprehensive aerosol measurements in four developing countries, (c) a database of airborne measurements of aerosols and clouds over Europe during May 2008, (d) comprehensive modeling tools to study aerosol processes fron nano to global scale and their effects on climate and air quality. In addition a new Pan-European aerosol emissions inventory was developed and evaluated, a new cluster spectrometer was built and tested in the field and several new aerosol parameterizations and computations modules for chemical transport and global climate models were developed and evaluated. These achievements and related studies have substantially improved our understanding and reduced the uncertainties of aerosol radiative forcing and air quality-climate interactions. The EUCAARI results can be utilized in European and global environmental policy to assess the aerosol impacts and the corresponding abatement strategies.
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| 28. |
- Lappalainen, H. K., et al.
(författare)
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Overview: Recent advances in the understanding of the northern Eurasian environments and of the urban air quality in China - a Pan-Eurasian Experiment (PEEX) programme perspective
- 2022
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 22:7, s. 4413-4469
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Tidskriftsartikel (refereegranskat)abstract
- The Pan-Eurasian Experiment (PEEX) Science Plan, released in 2015, addressed a need for a holistic system understanding and outlined the most urgent research needs for the rapidly changing Arctic-boreal region. Air quality in China, together with the long-range transport of atmospheric pollutants, was also indicated as one of the most crucial topics of the research agenda. These two geographical regions, the northern Eurasian Arctic-boreal region and China, especially the megacities in China, were identified as a "PEEX region". It is also important to recognize that the PEEX geographical region is an area where science-based policy actions would have significant impacts on the global climate. This paper summarizes results obtained during the last 5 years in the northern Eurasian region, together with recent observations of the air quality in the urban environments in China, in the context of the PEEX programme. The main regions of interest are the Russian Arctic, northern Eurasian boreal forests (Siberia) and peatlands, and the megacities in China. We frame our analysis against research themes introduced in the PEEX Science Plan in 2015. We summarize recent progress towards an enhanced holistic understanding of the land-atmosphere-ocean systems feedbacks. We conclude that although the scientific knowledge in these regions has increased, the new results are in many cases insufficient, and there are still gaps in our understanding of large-scale climate-Earth surface interactions and feedbacks. This arises from limitations in research infrastructures, especially the lack of coordinated, continuous and comprehensive in situ observations of the study region as well as integrative data analyses, hindering a comprehensive system analysis. The fast-changing environment and ecosystem changes driven by climate change, socio-economic activities like the China Silk Road Initiative, and the global trends like urbanization further complicate such analyses. We recognize new topics with an increasing importance in the near future, especially "the enhancing biological sequestration capacity of greenhouse gases into forests and soils to mitigate climate change" and the "socio-economic development to tackle air quality issues".
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| 29. |
- Yli-Juuti, T., et al.
(författare)
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Model for acid-base chemistry in nanoparticle growth (MABNAG)
- 2013
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 13:24, s. 12507-12524
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Tidskriftsartikel (refereegranskat)abstract
- Climatic effects of newly-formed atmospheric secondary aerosol particles are to a large extent determined by their condensational growth rates. However, all the vapours condensing on atmospheric nanoparticles and growing them to climatically relevant sizes are not identified yet and the effects of particle phase processes on particle growth rates are poorly known. Besides sulfuric acid, organic compounds are known to contribute significantly to atmospheric nanoparticle growth. In this study a particle growth model MABNAG (Model for Acid-Base chemistry in NAnoparticle Growth) was developed to study the effect of salt formation on nanoparticle growth, which has been proposed as a potential mechanism lowering the equilibrium vapour pressures of organic compounds through dissociation in the particle phase and thus preventing their evaporation. MABNAG is a model for monodisperse aqueous particles and it couples dynamics of condensation to particle phase chemistry. Non-zero equilibrium vapour pressures, with both size and composition dependence, are considered for condensation. The model was applied for atmospherically relevant systems with sulfuric acid, one organic acid, ammonia, one amine and water in the gas phase allowed to condense on 3-20 nm particles. The effect of dissociation of the organic acid was found to be small under ambient conditions typical for a boreal forest site, but considerable for base-rich environments (gas phase concentrations of about 10(10) cm(-3) for the sum of the bases). The contribution of the bases to particle mass decreased as particle size increased, except at very high gas phase concentra-tions of the bases. The relative importance of amine versus ammonia did not change significantly as a function of particle size. While our results give a reasonable first estimate on the maximum contribution of salt formation to nanoparticle growth, further studies on, e. g. the thermodynamic properties of the atmospheric organics, concentrations of low-volatility organics and amines, along with studies investigating the applicability of thermodynamics for the smallest nanoparticles are needed to truly understand the acid-base chemistry of atmospheric nanoparticles.
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| 30. |
- Boy, M., et al.
(författare)
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Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:3, s. 2015-2061
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Tidskriftsartikel (refereegranskat)abstract
- The Nordic Centre of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change-cryosphere interactions that affect Arctic amplification.
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| 31. |
- Hakola, A., et al.
(författare)
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Global migration of impurities in tokamaks
- 2013
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 55:12
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Tidskriftsartikel (refereegranskat)abstract
- The migration of impurities in tokamaks has been studied with the help of tracer-injection (C-13 and N-15) experiments in JET and ASDEX Upgrade since 2001. We have identified a common pattern for the migrating particles: scrape-off layer flows drive impurities from the low-field side towards the high-field side of the vessel. Migration is also sensitive to the density and magnetic configuration of the plasma, and strong local variations in the resulting deposition patterns require 3D treatment of the migration process. Moreover, re-erosion of the deposited particles has to be taken into account to properly describe the migration process during steady-state operation of the tokamak.
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| 32. |
- Mohr, C., et al.
(författare)
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Ambient observations of dimers from terpene oxidation in the gas phase: Implications for new particle formation and growth
- 2017
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Ingår i: Geophysical Research Letters. - 0094-8276. ; 44:6, s. 2958-2966
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Tidskriftsartikel (refereegranskat)abstract
- We present ambient observations of dimeric monoterpene oxidation products (C16-20HyO6-9) in gas and particle phases in the boreal forest in Finland in spring 2013 and 2014, detected with a chemical ionization mass spectrometer with a filter inlet for gases and aerosols employing acetate and iodide as reagent ions. These are among the first online dual-phase observations of such dimers in the atmosphere. Estimated saturation concentrations of 10(-15) to 10(-6)mu gm(-3) (based on observed thermal desorptions and group-contribution methods) and measured gas-phase concentrations of 10(-3) to 10(-2)mu gm(-3) (similar to 10(6)-10(7)moleculescm(-3)) corroborate a gas-phase formation mechanism. Regular new particle formation (NPF) events allowed insights into the potential role dimers may play for atmospheric NPF and growth. The observationally constrained Model for Acid-Base chemistry in NAnoparticle Growth indicates a contribution of similar to 5% to early stage particle growth from the similar to 60 gaseous dimer compounds. Plain Language Summary Atmospheric aerosol particles influence climate and air quality. We present new insights into how emissions of volatile organic compounds from trees are transformed in the atmosphere to contribute to the formation and growth of aerosol particles. We detected for the first time over a forest, a group of organic molecules, known to grow particles, in the gas phase at levels far higher than expected. Previous measurements had only measured them in the particles. This finding provides guidance on how models of aerosol formation and growth should describe their appearance and fate in the atmosphere.
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| 33. |
- Aas, W., et al.
(författare)
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Lessons learnt from the first EMEP intensive measurement periods
- 2012
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:17, s. 8073-8094
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Tidskriftsartikel (refereegranskat)abstract
- The first EMEP intensive measurement periods were held in June 2006 and January 2007. The measurements aimed to characterize the aerosol chemical compositions, including the gas/aerosol partitioning of inorganic compounds. The measurement program during these periods included daily or hourly measurements of the secondary inorganic components, with additional measurements of elemental- and organic carbon (EC and OC) and mineral dust in PM1, PM2.5 and PM10. These measurements have provided extended knowledge regarding the composition of particulate matter and the temporal and spatial variability of PM, as well as an extended database for the assessment of chemical transport models. This paper summarise the first experiences of making use of measurements from the first EMEP intensive measurement periods along with EMEP model results from the updated model version to characterise aerosol composition. We investigated how the PM chemical composition varies between the summer and the winter month and geographically. The observation and model data are in general agreement regarding the main features of PM10 and PM2.5 composition and the relative contribution of different components, though the EMEP model tends to give slightly lower estimates of PM10 and PM2.5 compared to measurements. The intensive measurement data has identified areas where improvements are needed. Hourly concurrent measurements of gaseous and particulate components for the first time facilitated testing of modelled diurnal variability of the gas/aerosol partitioning of nitrogen species. In general, the modelled diurnal cycles of nitrate and ammonium aerosols are in fair agreement with the measurements, but the diurnal variability of ammonia is not well captured. The largest differences between model and observations of aerosol mass are seen in Italy during winter, which to a large extent may be explained by an underestimation of residential wood burning sources. It should be noted that both primary and secondary OC has been included in the calculations for the first time, showing promising results. Mineral dust is important, especially in southern Europe, and the model seems to capture the dust episodes well. The lack of measurements of mineral dust hampers the possibility for model evaluation for this highly uncertain PM component. There are also lessons learnt regarding improved measurements for future intensive periods. There is a need for increased comparability between the measurements at different sites. For the nitrogen compounds it is clear that more measurements using artefact free methods based on continuous measurement methods and/or denuders are needed. For EC/OC, a reference methodology (both in field and laboratory) was lacking during these periods giving problems with comparability, though measurement protocols have recently been established and these should be followed by the Parties to the EMEP Protocol. For measurements with no defined protocols, it might be a good solution to use centralised laboratories to ensure comparability across the network. To cope with the introduction of these new measurements, new reporting guidelines have been developed to ensure that all proper information about the methodologies and data quality is given.
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| 34. |
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| 35. |
- Bergman, Tommi, et al.
(författare)
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Description and evaluation of a secondary organic aerosol and new particle formation scheme within TM5-MP v1.2
- 2022
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:2, s. 683-713
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Tidskriftsartikel (refereegranskat)abstract
- We have implemented and evaluated a secondary organic aerosol scheme within the chemistry transport model TM5-MP in this work. In earlier versions of TM5-MP the secondary organic aerosol (SOA) was emitted as Aitken-sized particle mass emulating the condensation. In the current scheme we simulate the formation of secondary organic aerosol from oxidation of isoprene and monoterpenes by ozone and hydroxyl radicals, which produce semi-volatile organic compounds (SVOCs) and extremely low-volatility compounds (EVOCs). Subsequently, SVOCs and ELVOCs can condense on particles. Furthermore, we have introduced a new particle formation mechanism depending on the concentration of ELVOCs. For evaluation purposes, we have simulated the year 2010 with the old and new scheme; we see an increase in simulated production of SOA from 39.9ĝ€¯Tgĝ€¯yr-1 with the old scheme to 52.5ĝ€¯Tgĝ€¯yr-1 with the new scheme. For more detailed analysis, the particle mass and number concentrations and their influence on the simulated aerosol optical depth are compared to observations. Phenomenologically, the new particle formation scheme implemented here is able to reproduce the occurrence of observed particle formation events. However, the modelled concentrations of formed particles are clearly lower than in observations, as is the subsequent growth to larger sizes. Compared to the old scheme, the new scheme increases the number concentrations across the observation stations while still underestimating the observations. The organic aerosol mass concentrations in the US show a much better seasonal cycle and no clear overestimation of mass concentrations anymore. In Europe the mass concentrations are lowered, leading to a larger underestimation of observations. Aerosol optical depth (AOD) is generally slightly increased except in the northern high latitudes. This brings the simulated annual global mean AOD closer to the observational estimate. However, as the increase is rather uniform, biases tend to be reduced only in regions where the model underestimates the AOD. Furthermore, the correlations with satellite retrievals and ground-based sun-photometer observations of AOD are improved. Although the process-based approach to SOA formation causes a reduction in model performance in some areas, overall the new scheme improves the simulated aerosol fields.
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| 36. |
- Handa, I. Tanya, et al.
(författare)
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Consequences of biodiversity loss for litter decomposition across biomes
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 509:7499, s. 218-221
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Tidskriftsartikel (refereegranskat)abstract
- The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems, and of carbon fluxes between the biosphere and the atmosphere(1-3). Decomposition is driven by a vast diversity of organisms that are structured in complex food webs(2,4). Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical(4-6) given the rapid loss of species worldwide and the effects of this loss on human well-being(7-9). Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition(4-6,10), key questions remain, including when, where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism(4,9-12). Here, in field experiments across five terrestrial and aquatic locations, ranging from the subarctic to the tropics, we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen. Moreover, we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants, but not between other plant functional types, highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition. The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales.
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| 37. |
- Jabiol, Jeremy, et al.
(författare)
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Diversity patterns of leaf-associated aquatic hyphomycetes along a broad latitudinal gradient
- 2013
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Ingår i: Fungal ecology. - : Elsevier. - 1754-5048 .- 1878-0083. ; 6:5, s. 439-448
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Tidskriftsartikel (refereegranskat)abstract
- Information about the global distribution of aquatic hyphomycetes is scarce, despite the primary importance of these fungi in stream ecosystem functioning. In particular, the relationship between their diversity and latitude remains unclear, due to a lack of coordinated surveys across broad latitudinal ranges. This study is a first report on latitudinal patterns of aquatic hyphomycete diversity associated with native leaf-litter species in five streams located along a gradient extending from the subarctic to the tropics. Exposure of leaf litter in mesh bags of three different mesh sizes facilitated assessing the effects of including or excluding different size-classes of litter-consuming invertebrates. Aquatic hyphomycete evenness was notably constant across all sites, whereas species richness and diversity, expressed as the Hill number, reached a maximum at mid-latitudes (Mediterranean and temperate streams). These latitudinal patterns were consistent across litter species, despite a notable influence of litter identity on fungal communities at the local scale. As a result, the bell-shaped distribution of species richness and Hill diversity deviated markedly from the latitudinal patterns of most other groups of organisms. Differences in the body-size distribution of invertebrate communities colonizing the leaves had no effect on aquatic hyphomycete species richness, Hill diversity or evenness, but invertebrates could still influence fungal communities by depleting litter, an effect that was not captured by the design of our experiment. (C) 2013 Elsevier Ltd and The British Mycological Society. All rights reserved.
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| 38. |
- Likonen, J., et al.
(författare)
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Deposition of (13)C tracer in the JET MkII-HD divertor
- 2011
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Ingår i: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0031-8949 .- 1402-4896. ; T145, s. 014004-
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Tidskriftsartikel (refereegranskat)abstract
- Migration of (13)C has been investigated at JET by injecting (13)C-labelled methane at the outer divertor base at the end of the 2009 campaign. The (13)C deposition profiles on carbon fibre composite divertor tiles were measured by secondary ion mass spectrometry and Rutherford backscattering techniques. (13)C was mainly deposited near the puffing location on the outer divertor base tiles. High amounts of (13)C were also found at the outer vertical target: at the bottom of the lower and at the top of the upper plates. Thirty-three percent of puffed (13)CH(4) was instantly pumped out by the divertor cryopump, which is close to the pump duct entrance. Global (13)C transport in the torus was modelled by the EDGE2D/EIRENE and DIVIMP codes, and local (13)C migration in the vicinity of the injection location by the ERO code. The DIVIMP and EDGE2D simulations show strong prompt deposition of (13)C directly adjacent to the injection point as well as in the far scrape-off layer (SOL) along both the inner and outer divertor targets. In addition, the measured (13)C deposition along the outer divertor wall tiles is qualitatively reproduced. However, EDGE2D and DIVIMP do not predict any deposition along the divertor surfaces facing the private plasma on the inner floor tile and inboard of the outer strike point on tile 5. The ERO calculations also indicate that most of the deposition occurs close to the injection location on the vertical face of the LBSRP tile and the horizontal part of tile 6.
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| 39. |
- Petersson, Per, et al.
(författare)
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Overview of nitrogen-15 application as a tracer gas for material migration and retention studies in tokamaks
- 2014
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; T159, s. 014042-
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Tidskriftsartikel (refereegranskat)abstract
- Experimental and analytical procedures related to the application of nitrogen-15 isotope for material migration studies have been developed and used for tracer experiments in the TEXTOR and ASDEX-Upgrade tokamaks in order to assess the retention of nitrogen in plasma-facing components made of graphite and tungsten. The surface study was performed by time-of-flight heavy ion elastic recoil detection analysis and by means of nuclear reaction analysis based on the N-15(p, gamma alpha)C-12 process. In both tokamaks nitrogen retention has exceeded 10% of the injected gas. In ASDEX-Upgrade the largest fraction of N-15 has been detected on protruding parts near the injection port, while around 4% has been found in the divertor. The ASDEX-Upgrade results have also been modeled. Helium trapping has been measured in deposits containing tungsten and nitrogen.
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| 40. |
- Raisanen, P., et al.
(författare)
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Impact of dust particle non-sphericity on climate simulations
- 2013
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Ingår i: Quarterly Journal of the Royal Meteorological Society. - : Wiley. - 0035-9009 .- 1477-870X. ; 139:677, s. 2222-2232
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Tidskriftsartikel (refereegranskat)abstract
- Although mineral aerosol (dust) particles are irregular in shape, they are treated as homogeneous spheres in climate model radiative transfer calculations. Here, we test the effect of dust particle non-sphericity in the ECHAM5.5-HAM2 global aerosol-climate model. The short-wave optical properties of the two insoluble dust modes in HAM2 are modelled using an ensemble of spheroids that has been optimized to reproduce the optical properties of dust-like aerosols, thereby providing a significant improvement over spheres. First, the direct radiative effects (DRE) of dust non-sphericity were evaluated diagnostically, by comparing spheroids with both volume-equivalent and volume-to-area (V/A) equivalent spheres. In the volume-equivalent case, the short-wave DRE of insoluble dust at the surface and at the top of the atmosphere (TOA) was slightly smaller (typically by 3-4%) for spheroidal than for spherical dust particles. This rather small difference stems from compensating non-sphericity effects on the dust optical thickness and asymmetry parameter. In the V/A-equivalent case, the difference in optical thickness was virtually eliminated and the DRE at the TOA (surface) was approximate to 20% (approximate to 13%) smaller for spheroids than for spheres, due to a larger asymmetry parameter. Even then, however, the global-mean DRE of non-sphericity was only 0.055 W m(-2) at the TOA and 0.070 W m(-2) at the surface. Subsequently, the effects of dust non-sphericity were tested interactively in simulations in which ECHAM5.5-HAM2 was coupled to a mixed-layer ocean model. Consistent with the rather small radiative effects noted above, the climatic differences from simulations with spherical dust optics were generally negligible.
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| 41. |
- Tuomisto, F, et al.
(författare)
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Dissociation of V-Ga-O-N complexes in HVPE GaN by high pressure and high temperature annealing
- 2006
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1436-1440
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Tidskriftsartikel (refereegranskat)abstract
- We have used positron annihilation spectroscopy to study the high-pressure annealing induced thermal recovery of vacancy defects in free-standing GaN grown by hydride vapor phase epitaxy (HYPE). The results show that the in-grown Ga vacancy complexes recover after annealing at 1500-1700 K. Comparison of the experimental positron data with ab-initio calculations indicates that the Doppler broadening measurement of the electron momentum distribution is sensitive enough to distinguish between the N and O atoms surrounding the Ga vacancy. We show that the difference between the isolated V-Ga in electron irradiated GaN and the V-Ga-O-N complexes in highly O-doped GaN is clear, and the Ga vacancy related defect complexes that start dissociating at 1500 K can be identified as V-Ga-O-N pairs.
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| 42. |
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